expository essay on digestive system

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Human digestive system interactive

The lips and cheeks, the roof of the mouth, the floor of the mouth.

• Salivary glands
• Blood and nerve supply
• Stomach contractions
• Gastric mucosa
• Gastric secretion
• Absorption and emptying
• Contractions and motility
• Rectum and anus
• Gross anatomy
• Microscopic anatomy
• Acinar cells
• Islet cells
• General features of digestion and absorption
• Carbohydrates
• Fat-soluble vitamins
• Vitamin B 12
• Intestinal gas
• Production and secretion of peptides
• Somatostatin
• Cholecystokinin
• Gastric inhibitory peptide
• Intestinal glucagon
• Neurotensin
• Pancreatic polypeptide
• Vasoactive intestinal peptide
• Substance P
• Endorphins and enkephalins
• Prostaglandins
• The gastrointestinal tract as an organ of immunity
• Embryonic development
• Evolutionary development

human digestive system

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• Mayo Clinic - See How Your Digestive System Works
• Healthline - Digestive Health Basics
• LiveScience - Digestive System: Facts, Function and Diseases
• Patient - The digestive system
• Cleveland Cliinic - Digestive System
• National Institute of Diabetes and Digestive and Kidney Diseases - Your Digestive System & How it Works
• WebMD - The Digestive System: How It Works
• University of Minnesota Libraries - Human Biology - The Digestive System
• digestive system - Children's Encyclopedia (Ages 8-11)
• digestive system - Student Encyclopedia (Ages 11 and up)
• Table Of Contents

human digestive system , system used in the human body for the process of digestion . The human digestive system consists primarily of the digestive tract , or the series of structures and organs through which food and liquids pass during their processing into forms that can be absorbed into the bloodstream. The system also consists of the structures through which wastes pass in the process of elimination and of organs that contribute juices necessary for the digestive process.

In order to function properly, the human body requires nutrients. Some such nutrients serve as raw materials for the synthesis of cellular materials, while others help regulate chemical reactions or, upon oxidation, yield energy. Many nutrients, however, are in a form that is unsuitable for immediate use by the body; to be useful, they must undergo physical and chemical changes, which are facilitated by digestion.

Structures and functions of the human digestive system

The digestive tract begins at the lips and ends at the anus . It consists of the mouth , or oral cavity, with its teeth , for grinding the food, and its tongue , which serves to knead food and mix it with saliva ; the throat, or pharynx ; the esophagus ; the stomach ; the small intestine , consisting of the duodenum , the jejunum, and the ileum ; and the large intestine , consisting of the cecum , a closed-end sac connecting with the ileum, the ascending colon, the transverse colon, the descending colon, and the sigmoid colon , which terminates in the rectum . Glands contributing digestive juices include the salivary glands , the gastric glands in the stomach lining, the pancreas , and the liver and its adjuncts—the gallbladder and bile ducts. All of these organs and glands contribute to the physical and chemical breaking down of ingested food and to the eventual elimination of nondigestible wastes. Their structures and functions are described step by step in this section.

Mouth and oral structures

Little digestion of food actually takes place in the mouth. However, through the process of mastication , or chewing, food is prepared in the mouth for transport through the upper digestive tract into the stomach and small intestine, where the principal digestive processes take place. Chewing is the first mechanical process to which food is subjected. Movements of the lower jaw in chewing are brought about by the muscles of mastication (the masseter, the temporal , the medial and lateral pterygoids, and the buccinator). The sensitivity of the periodontal membrane that surrounds and supports the teeth, rather than the power of the muscles of mastication, determines the force of the bite.

Mastication is not essential for adequate digestion. Chewing does aid digestion, however, by reducing food to small particles and mixing it with the saliva secreted by the salivary glands. The saliva lubricates and moistens dry food, while chewing distributes the saliva throughout the food mass. The movement of the tongue against the hard palate and the cheeks helps to form a rounded mass, or bolus , of food.

The lips, two fleshy folds that surround the mouth, are composed externally of skin and internally of mucous membrane , or mucosa. The mucosa is rich in mucus-secreting glands, which together with saliva ensure adequate lubrication for the purposes of speech and mastication.

The cheeks, the sides of the mouth, are continuous with the lips and have a similar structure. A distinct fat pad is found in the subcutaneous tissue (the tissue beneath the skin) of the cheek; this pad is especially large in infants and is known as the sucking pad. On the inner surface of each cheek, opposite the second upper molar tooth, is a slight elevation that marks the opening of the parotid duct, leading from the parotid salivary gland, which is located in front of the ear. Just behind this gland are four to five mucus-secreting glands, the ducts of which open opposite the last molar tooth.

The roof of the mouth is concave and is formed by the hard and soft palate . The hard palate is formed by the horizontal portions of the two palatine bones and the palatine portions of the maxillae, or upper jaws. The hard palate is covered by a thick, somewhat pale mucous membrane that is continuous with that of the gums and is bound to the upper jaw and palate bones by firm fibrous tissue. The soft palate is continuous with the hard palate in front. Posteriorly it is continuous with the mucous membrane covering the floor of the nasal cavity. The soft palate is composed of a strong, thin, fibrous sheet, the palatine aponeurosis, and the glossopalatine and pharyngopalatine muscles. A small projection called the uvula hangs free from the posterior of the soft palate.

The floor of the mouth can be seen only when the tongue is raised. In the midline is a prominent, elevated fold of mucous membrane ( frenulum linguae ) that binds each lip to the gums, and on each side of this is a slight fold called a sublingual papilla , from which the ducts of the submandibular salivary glands open. Running outward and backward from each sublingual papilla is a ridge (the plica sublingualis) that marks the upper edge of the sublingual (under the tongue) salivary gland and onto which most of the ducts of that gland open.

The gums consist of mucous membranes connected by thick fibrous tissue to the membrane surrounding the bones of the jaw. The gum membrane rises to form a collar around the base of the crown (exposed portion) of each tooth. Rich in blood vessels, the gum tissues receive branches from the alveolar arteries; these vessels, called alveolar because of their relationship to the alveoli dentales, or tooth sockets, also supply the teeth and the spongy bone of the upper and lower jaws, in which the teeth are lodged.

The Digestive System in the Human Body Essay

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Introduction

The stomach, large intestines, small intestines, works cited.

Human biology is a field in biology that deals with nutrition, anthropology, and medicine. The body of a human being contains a digestive system that deals with the digestion and absorption of food nutrients into the body. The stomach, small intestines, and large intestines are part of the digestive system. All of them are located at different positions in the body and have different functions and structures.

The stomach is an organ of digestion located between the esophagus and the duodenum on the left upper part of the abdominal cavity. It is a muscular, elastic pear-shaped bag lying just below the diaphragm. It is made up of five layers. The innermost layer is referred to as mucosa. The four sections of the stomach are the fundus, cardia, body, and pylorus. It is involved in the second phase of digestion after chewing. It secretes enzymes that help in the digestion of proteins. It also secretes some acids that help in the digestion of food. The major secretions are hydrochloric acid and protease enzymes. The work of hydrochloric acid is to kill any bacteria that may be in the food and provide an acidic pH that allows proteases to work effectively (Chiras 95).

The large intestines of the human body are located between the ileocecal junction and the rectum. They are about one and a half meters long and two and a half centimeters wide. The major parts of the large intestines are the caecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, and anal canal (Tortora and Grabowski 46). The large intestines receive food contents and fluids from the small intestines. The large intestines help in the re-absorption of water into the body system. The water absorbed is used to maintain the fluid balance of the body. Some vitamins that are created by the bacteria in the large intestines are also absorbed. They also help in the transport of waste products in form of stool out of the body.

The small intestines are located between the stomach and the large intestines. Specifically, they start at the pyloric sphincter and end at the ileocaecal valve. They are narrow and long to allow digestion and absorption of food. The standard length of the small intestines in an adult human being is five meters but they may be shorter or longer. The three parts of the small intestines are the duodenum, jejunum, and ileum (Tortora and Grabowski 49). The majority of digestion and absorption of food takes place in the small intestines. Chemical digestion takes place in the small intestines where many enzymes that facilitate digestion are secreted. In the small intestines, proteins and peptides are digested into amino acids. Lipase enzymes are used to degrade fats into glycerol and fatty acids. Some carbohydrates are also digested in the stomach to form simple sugars. The process of absorption takes place where food nutrients are diffused into the bloodstream. The small intestines have many villi that have networks of capillaries to help indigestion. Monosaccharides, amino acids, water, iron, and many others are absorbed here.

The digestive system in the human body mainly deals with digestion and absorption of food nutrients and fluids. The stomach is located between the esophagus and the duodenum and helps in the digestion of partially chewed food. The large intestines are located between the ileocecal junction and the rectum. They help in the absorption of water, some nutrients, and the excretion of wastes out of the body. The small intestines are located between the pyloric sphincter and the ileocaecal valve. They help in the digestion of food and absorption of food nutrients into the bloodstream.

Chiras, Daniel. Human Biology. Sixth Edition. London: Jones and Bartlett Punishers, 2009. Print.

Tortora, Gerald and Grabowski, Sandra. Introduction to the human body: the essentials of anatomy and physiology. Volume 1. New York: John Wiley & Sons, 2004. Print.

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IvyPanda. (2022, March 13). The Digestive System in the Human Body. https://ivypanda.com/essays/the-digestive-system-in-the-human-body/

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High school biology

Course: high school biology   >   unit 2.

• Meet the heart!
• The circulatory system review
• Meet the lungs!
• The respiratory system review
• Meet the gastrointestinal tract!

The digestive and excretory systems review

• The nervous and endocrine systems review
• The musculoskeletal system review
• Welcome to the reproductive system
• The reproductive system review
• The immune system review
• Apply: organ system interactions

The digestive system

Accessory organs.

• Salivary glands : moisten food and begin chemical digestion of starches.
• Liver : creates bile for fat digestion, detoxifies blood, processes absorbed vitamins
• Gallbladder : stores bile produced by the liver
• Pancreas : secretes pancreatic juices to help digestion of proteins and carbohydrates

The excretory system

• the skin , which removes excess water and salt via sweat,
• the lungs , which exhale carbon dioxide, and
• the liver , which breaks down toxic substances in the blood and convert nitrogenous waste into urea

Urinary tract

• Filtration : Blood enters a nephron, which filters out impurities.
• Reabsorption : The impurities move through tubules, while the rest of the blood is reabsorbed through capillary walls into the blood.
• Excretion : Urine is transported from the kidneys through the ureters and into the urinary bladder . It remains stored in the bladder until it is released through the urethra.

Common mistakes and misconceptions

• Incorrect : Digestion begins in the stomach.
• Correct : While some digestion occurs in the stomach, the process actually begins in the mouth, where chewing and salivary amylase act on the food.
• Incorrect : The digestive system produces urine.
• Correct : Some people think that the digestive system has two outlets—one for feces and one for urine. However, urine is a product of the excretory system, not the digestive system.
• Incorrect : The small intestine is shorter than the large intestine.
• Correct : The small intestine is actually longer than the large intestine. In fact, at approximately 20 feet in length, the small intestine is nearly four times as long as the large intestine (5 feet long)! However, the intestines are named for their diameters , not their lengths. The large intestine has a diameter of about 3 inches compared to the small intestine, with a diameter of about 1 inch.

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How to Write an Expository Essay | Structure, Tips & Examples

Published on July 14, 2020 by Jack Caulfield . Revised on July 23, 2023.

“Expository” means “intended to explain or describe something.” An expository essay provides a clear, focused explanation of a particular topic, process, or set of ideas. It doesn’t set out to prove a point, just to give a balanced view of its subject matter.

Expository essays are usually short assignments intended to test your composition skills or your understanding of a subject. They tend to involve less research and original arguments than argumentative essays .

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When should you write an expository essay, how to approach an expository essay, introducing your essay, writing the body paragraphs, concluding your essay, other interesting articles, frequently asked questions about expository essays.

In school and university, you might have to write expository essays as in-class exercises, exam questions, or coursework assignments.

Sometimes it won’t be directly stated that the assignment is an expository essay, but there are certain keywords that imply expository writing is required. Consider the prompts below.

The word “explain” here is the clue: An essay responding to this prompt should provide an explanation of this historical process—not necessarily an original argument about it.

Sometimes you’ll be asked to define a particular term or concept. This means more than just copying down the dictionary definition; you’ll be expected to explore different ideas surrounding the term, as this prompt emphasizes.

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An expository essay should take an objective approach: It isn’t about your personal opinions or experiences. Instead, your goal is to provide an informative and balanced explanation of your topic. Avoid using the first or second person (“I” or “you”).

The structure of your expository essay will vary according to the scope of your assignment and the demands of your topic. It’s worthwhile to plan out your structure before you start, using an essay outline .

A common structure for a short expository essay consists of five paragraphs: An introduction, three body paragraphs, and a conclusion.

Like all essays, an expository essay begins with an introduction . This serves to hook the reader’s interest, briefly introduce your topic, and provide a thesis statement summarizing what you’re going to say about it.

Hover over different parts of the example below to see how a typical introduction works.

In many ways, the invention of the printing press marked the end of the Middle Ages. The medieval period in Europe is often remembered as a time of intellectual and political stagnation. Prior to the Renaissance, the average person had very limited access to books and was unlikely to be literate. The invention of the printing press in the 15th century allowed for much less restricted circulation of information in Europe, paving the way for the Reformation.

The body of your essay is where you cover your topic in depth. It often consists of three paragraphs, but may be more for a longer essay. This is where you present the details of the process, idea or topic you’re explaining.

It’s important to make sure each paragraph covers its own clearly defined topic, introduced with a topic sentence . Different topics (all related to the overall subject matter of the essay) should be presented in a logical order, with clear transitions between paragraphs.

Hover over different parts of the example paragraph below to see how a body paragraph is constructed.

The invention of the printing press in 1440 changed this situation dramatically. Johannes Gutenberg, who had worked as a goldsmith, used his knowledge of metals in the design of the press. He made his type from an alloy of lead, tin, and antimony, whose durability allowed for the reliable production of high-quality books. This new technology allowed texts to be reproduced and disseminated on a much larger scale than was previously possible. The Gutenberg Bible appeared in the 1450s, and a large number of printing presses sprang up across the continent in the following decades. Gutenberg’s invention rapidly transformed cultural production in Europe; among other things, it would lead to the Protestant Reformation.

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The conclusion of an expository essay serves to summarize the topic under discussion. It should not present any new information or evidence, but should instead focus on reinforcing the points made so far. Essentially, your conclusion is there to round off the essay in an engaging way.

Hover over different parts of the example below to see how a conclusion works.

The invention of the printing press was important not only in terms of its immediate cultural and economic effects, but also in terms of its major impact on politics and religion across Europe. In the century following the invention of the printing press, the relatively stationary intellectual atmosphere of the Middle Ages gave way to the social upheavals of the Reformation and the Renaissance. A single technological innovation had contributed to the total reshaping of the continent.

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An expository essay is a broad form that varies in length according to the scope of the assignment.

Expository essays are often assigned as a writing exercise or as part of an exam, in which case a five-paragraph essay of around 800 words may be appropriate.

You’ll usually be given guidelines regarding length; if you’re not sure, ask.

An expository essay is a common assignment in high-school and university composition classes. It might be assigned as coursework, in class, or as part of an exam.

Sometimes you might not be told explicitly to write an expository essay. Look out for prompts containing keywords like “explain” and “define.” An expository essay is usually the right response to these prompts.

An argumentative essay tends to be a longer essay involving independent research, and aims to make an original argument about a topic. Its thesis statement makes a contentious claim that must be supported in an objective, evidence-based way.

An expository essay also aims to be objective, but it doesn’t have to make an original argument. Rather, it aims to explain something (e.g., a process or idea) in a clear, concise way. Expository essays are often shorter assignments and rely less on research.

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Digestive system

Author: Lorenzo Crumbie, MBBS, BSc • Reviewer: Francesca Salvador, MSc Last reviewed: November 02, 2023 Reading time: 30 minutes

Extending from the mouth to the anus , the digestive tract is one of the largest systems in the human body. It contains organs that regulate food intake, its digestion and absorbtion of the useful materia that it contains. In addition to this, the digestive system also eliminates the waste products from food and products from various endogenous metabolic processes.

In a nutshell, the digestive tract has the tumultuous responsibility of converting large chunks of food into their constituent micro-molecules that will subsequently be used to build and repair the body.

This article will discuss the anatomy of the digestive system.

To improve your understanding of digestive system terminology, take a closer look at some commonly used roots, prefixes and suffixes in the digestive system in this video:

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Mastication, swallowing and physical digestion, chemical digestion, buccal cavity, bowel mnemonic, salivary glands, gallbladder, arterial supply, innervation, venous drainage, examination of the digestive system.

The digestive system can be broken down into two major components:

• There is the primary digestive tract , which functions mainly as a conduit and storage pathway. This portion is needed in order to move food contents along the tract (peristalsis) so that absorption of nutrients and excretion of undigested substances can occur. The tract also allows for segmentation of food at different stages of digestion. This is important because some enzymes produced in one part of the tract (e.g. pepsin in the stomach) will not function optimally in another part of the tract (e.g. the jejunum).
• The other component is the accessory digestive tract . This group of organs are responsible for the synthesis and secretion enzymes to facilitate chemical digestion.

This article aims to give an overview of the anatomy and function of the digestive tract. Details regarding neurovascular supply, histology , and clinically significant points regarding each segment of the digestive tract can be found in the respective articles. It will also briefly mention a few elements of the abdominal examination.

Give it a shot and test yourself on the main organs of the digestive system!

Functions of the digestive system

The function of the digestive system truly begins within the brain . Whenever the body’s energy stores (i.e. blood glucose, protein, or fat stores) fall below a set point, the hunger centres of the hypothalamus are activated. These centres regulate satiety (fullness) and appetite in order to maintain energy homeostasis. This signals to the brain that there is a need to obtain food. Keep in mind, however, that this is not the only source of hunger stimulation, as there are elements of pleasure and comfort that can be derived from ingesting food.

Monogastric organisms like humans have two kinds of digestive processes occurring in the digestive tract – mechanical and chemical digestion. Once the desired food is obtained, the digestive process begins in the mouth with mechanical digestion . Here the teeth are used to cut, tear, and grind chunks of food into smaller particles. This process of mastication involves the alternating action of the muscles of mastication (namely, the superficial and deep masseter , the pterygoids , and the temporalis muscles ).

Mastication is actually a reflex action that is stimulated once food is present in the mouth. At that point, there is inhibition of the muscles of mastication which results in a fall of the mandible. This causes distention of the muscles of mastication, resulting in reflex contraction of the muscle fibres; thus raising the mandible. That action causes apposition of the upper and lower rows of teeth, crushing the food that is between them. The cycle is repeated until the food particles can be rolled into a bolus .

As the tongue rolls the chewed food into a bolus, the salivary glands secrete saliva to moisten the bolus in order for it to pass smoothly to the stomach. Also note that some amount of chemical digestion also occurs in the mouth, as saliva contains the enzyme amylase , which breaks down some carbohydrates in the mouth.

Once the bolus is prepared, then swallowing will be initiated. This is another intricate reflex arc that involves the action of afferent and efferent tracts of several cranial nerves being relayed to and from the nucleus tractus solitarius and nucleus ambiguus of the brainstem .

The end result is that these nerves send motor signals to the tongue, which moves the bolus against the hard and soft palate, then into the oropharynx (which is also under brainstem regulation). The bolus then continues inferiorly towards the laryngopharynx and the swallowing reflex is initiated at the esophagus . All the actions of swallowing up to this point were under voluntary control ; however, the rest of the action is carried out by involuntary peristaltic contractions that travel in a craniocaudal fashion. At the level of the pharynx:

• Superiorly, the bolus is prevented from entering the nasopharynx by the actions of Passavant’s ridge . This structure is formed by the joint actions of the palatopharyngeal sphincters, the superior constrictor muscles, salpingopharyngeus and the muscles of the soft palate.
• The epiglottis closes off the larynx to prevent food from entering the airway. The vocal cords are also adducted as an additional protective measure.

At the level of the esophagus :

• There is relaxation of the cricopharyngeal sphincter and the bolus enters the proximal esophagus. The presence of the bolus causes distention of the myenteric plexus within the walls of the esophagus, initiating the primary esophageal peristaltic wave.
• The continued presence of the food stimulates the secondary peristaltic waves in a craniocaudal direction.

These waves, along with the action of gravity, move the bolus toward the lower esophageal sphincter at a rate of 4 cm/s. At rest, the sphincter has a high tone. However, the presence of the bolus aids relaxation of the lower esophageal sphincter, and food is able to enter the stomach. Here, the majority of the chemical digestion will take place.

Once the bolus enters the stomach , there is regulated release of a variety of enzymes that facilitate chemical digestion. Some of these enzymes also stimulate the accessory digestive organs to release their enzymes to aid in digestion. In addition to chemical digestion (particularly of proteins), the stomach also functions as:

• A storage point , which gradually releases its contents into the small intestines , to allow adequate time for further digestion and absorption.
• A mixer : the mode of contraction and arrangement of the stomach mucosa results in further mixing of the food contents to form chyme.
• A conduit : essentially passing food from the esophagus to the small intestines.
• Immunological defence : the acidic pH of the stomach aids in dissolving invading pathogens before they are able to cause an infection.
• Other micronutrients : iron (Fe), vitamin B12 ,and folate absorption are heavily regulated by the stomach.

The stomach can be functionally divided into proximal and distal motor pumps, which stores food content and pumps chyme along the conduit, respectively. Portions of chyme are passed into the pylorus and into the small intestines .

Once chyme has entered the first part of the duodenum, it activates the neurohormonal axis which promotes the release of bile (from the liver and gallbladder ) and other enzymes from the pancreas. The peristaltic waves continue to move the chyme along the intestinal tract. The intricate folding of the intestines facilitates absorption of nutrients from the chyme. Majority of the nutrients are absorbed within the small intestines. The remnants are passed through the unidirectional ileocecal valve into the cecum.

As the peristaltic waves continue into the colon, the chyme continues to move along the tract. Further absorption of electrolytes and water from the remaining chyme occurs and the chyme is then converted into stool, which is stored in the rectum. As the rectum becomes distended, the stretch receptors signal to the brain that promotes defecation . While the internal anal sphincters are under autonomic regulation, the external anal sphincters are under voluntary control. Therefore the individual may resist the urge to defecate until an appropriate time and place is identified.

Organs of the digestive system

The digestive tract is also referred to as the alimentary canal. It is a tubular continuum that is segmented into dilated regions. These dilated regions are often separated by thickened regions of the wall that form sphincters . This prevents unintended mixing of the contents in the respective segments.

The buccal cavity marks the opening of the digestive tract. It is made up by the oral vestibule (space between the inner cheeks and the teeth) and the oral cavity proper (behind the teeth). The buccal cavity also contains the teeth and tongue. It is limited anteriorly by the lips and teeth and posterolaterally by the palatopharyngeal arches. Posteriorly the buccal cavity opens into the oropharynx. The roof is formed by the hard palate (at the anterior two-thirds) and the soft palate (at the posterior third), and the floor of the oral cavity also contains the tongue.

The teeth can be subdivided into incisors (designed for cutting), canines (designed for tearing), premolars , and molars  (designed for grinding). The molars and premolars have complementary surfaces that also aid in grinding. The tongue consists of intrinsic and extrinsic muscles. It is also populated  with taste buds that facilitate gustatory sensation.

Posterior to the oral cavity proper is the oropharynx . This is the middle part of the pharynx that communicates superiorly with the nasopharynx and inferiorly with the laryngopharynx. The walls of the oropharynx are formed by the superior and middle pharyngeal constrictor muscles . Anterolaterally, the palatopharyngeal folds form a demarcation between the oral cavity proper and the oropharynx.

The base of the tongue also serves as another landmark in the anteroinferior aspect of the oropharynx. The mucosa of the walls also contains numerous mucosa associated lymphatic tissue (MALT) . It can be separated from the nasopharynx by the muscles of Passavant’s ridge and the supporting structures of the soft palate during deglutition.  

The tubular conduit responsible for transferring food from the oropharynx to the stomach is the esophagus. It can be divided into three parts:

• abdominal components

The total length of the muscular tube is 25 cm, commencing at the cricopharyngeus at the lower border of the cricoid cartilage at the sixth cervical vertebrae (C6) . It journeys posteriorly to the trachea in the neck along its caudal course. It then travels through the superior, then posterior mediastinum alongside the thoracic vertebrae. It pierces the diaphragm at the tenth thoracic vertebra (T10). The remaining 2.5 cm of the esophagus is the abdominal part. It transitions into the stomach at the gastroesophageal junction, where the physiological lower esophageal sphincter exists.

Within the abdominal cavity, the esophagus enters the stomach. This is a dilated area of the alimentary canal that participates in both mechanical and chemical digestion. It is divided into four main parts, namely the:

Laterally, there is a greater curvature , and medially there is a lesser curvature . There are two distinct notches on the stomach. The first is the cardiac incisura formed at the lateral border of the cardioesophageal junction. The other is the less pronounced incisura angularis found distally at the caudal end of the lesser curvature (at the pyloric antrum). The pylorus is the distal aspect of the stomach that is thickened. It acts as a physiological sphincter that regulates the passage of chyme from the stomach to the beginning of the small intestines.

The duodenum marks the beginning of the small intestines. It is roughly 20 – 25 cm long, extending from the pylorus to the ligament of Treitz . Not only is the duodenum the shortest part of the small intestines, but it is also the widest. It can be subdivided into four parts based on its geometrical orientation. The first part is known as pars superioris (the superior part); it is roughly 2 – 3 cm long and travels above the head of the pancreas. The second part is pars descendens which commences behind the neck of the gallbladder. It travels about 8 – 10 cm lateral to the head to the pancreas.

The inferior duodenal flexure (where pars descendens begins to turn) marks the transition of the second part of the duodenum to the third part – pars horizontalis . It travels for roughly 10 cm before it begins to curve upwards into the final segment of the duodenum, the pars ascendens (which is only 2.5 cm long).

The transition from the duodenum to jejunum occurs at the ligament of Treitz . The difference in the luminal diameter of the jejunum and duodenum is an important distinguishing feature. The duodenum is significantly wider than the jejunum.

However, it may be more challenging to distinguish between the jejunum and ileum as there are no external anatomical landmarks to guide. The key distinguishing features are as follows:

• The external diameter of the jejunum (4 cm) is greater than that of the ileum (3.5 cm).
• The internal diameter of the ileum (2 cm) is also smaller than that of the jejunum (2.5 cm).
• The walls of the jejunum appear thicker than that of the ileum.
• Additionally, the jejunum appears more hyperaemic than the ileum because it has a more extensive vascular supply.
• The luminal surface of the jejunum is significantly folded into plicae circulares that are more numerous and appear deeper than anywhere else within the digestive tract. Furthermore, the plicae circulares become less abundant distally within the ileum.
• Finally, the luminal mucosa of the ileum has more prominent mucosa-associated lymphoid tissue (MALT) than the jejunum.

The ileum terminates at the ileocecal valve ; which marks the transition from the small intestines to the large intestines . The ileocecal valve is a one way structure that prevents reflux of the bolus from the large intestines to the small intestines.

The proximal end of the large intestines – also known as the colon – is formed by a dilated cul-de-sac known as the cecum . There is also a vermiform appendix attached at variable parts of the cecum. The colon is divided into:

• sigmoid parts

Externally, the colon has a segmented appearance due to the haustrations that are present on the luminal surface of the conduit. The muscular layers of the colon are concentrated into three muscular bands known as taenia coli ; which travel along the length of the colon. The three taenia are:

• Taenia libera is the free taenia that is found at the antimesenteric surface of the colon; which is located on the anterior surface of the colon.
• Taenia omentalis is located posterolaterally and is attached to the omentum of the large intestines.
• Taenia mesocolic is found at the midpoint between the taenia libera and the mesenteric attachment on the colon.

Importantly, the cecum does not have the prominent haustrations seen on the rest of the colon. As the ascending colon travels from the right iliac fossa superiorly, it transitions to the transverse colon at the hepatic (right colic) flexure. The transverse colon travels across from the left to the right hypochondriac regions . It turns caudally at the splenic (left colic) flexure to form the descending colon . As the descending colon travels from the left hypochondrium to the left iliac fossa, it transitions into the sigmoid colon . This distal segment enters the pelvic inlet and terminates at the rectosigmoid junction at the level of the third sacral vertebra (S3).

Unlike the preceding colon, the rectum is circumferentially walled by smooth muscles . It does not have haustrations and is devoid of taenia coli. This distal continuation of the large intestines functions of a reservoir for stool, prior to excretion. It terminates at the level of the sacrococcygeal curvature . It passes over the pelvic diaphragm to form the anorectal junction .

The portion of the alimentary tract between the stomach and the anal canal is known as  bowel  and is formed of the following components:

You can remember this easily if you use the mnemonic  D ow J ones I ndustrial A verage C losing S tock R eport, where the first letter of each word corresponds to the first letter of a bowel component!

The final passageway through which undigested food and exfoliated mucosa will exit the body is called the anal canal. It continues from the anorectal junction and passes through the loop formed by the puborectalis muscle, which swings the anal canal anteriorly. Distally, the mucosa of the anal canal transitions from the columnar epithelium with goblet cells found throughout the colon, to the squamous epithelium of the perianal skin. This point is referred to as the anal verge .  

Organs of the accessory digestive system

The organs of the accessory digestive system have the principal role of synthesizing and secreting digestive enzymes to further break down food into nutrients. The salivary glands are paired structures in the oral cavity that secrete saliva and other enzymes that mix with the masticated food to form the bolus. There are three major salivary glands in the oral cavity:

• Parotid glands
• Submandibular glands
• Sublingual glands

Another important accessory digestive organ is the liver. It is located in the right upper quadrant of the abdomen , beneath the right hemidiaphragm. The liver has two anatomical lobes, but eight functional segments. In addition to producing bile to digest fats, all of the nutrients absorbed from the small intestines enter the liver via the hepatic portal venous system .

From the liver, the nutrients are integrated into various catabolic processes and sent throughout the body. Most of the bile made by the liver is stored in the gallbladder . This muscular, sac-like organ that resides on the posterior surface of the liver drains its contents into the extrahepatic biliary tree following a fatty meal.

Finally, the pancreas is a retroabdominal organ that also provides enzymes for digestion. The head of the pancreas is found within the  C-shaped loop of the duodenum. The body extends superolaterally, behind the gastric antrum. The tail of the pancreas terminates at the hilum of the spleen .

Neurovascular supply and venous drainage

The vast majority of the digestive system is supplied by the abdominal aorta . In the abdominal cavity, the aorta gives off three major branches that, in succession, supply the derivatives of the foregut, midgut and hindgut:

• Celiac trunk , which after a short course further splits three into major branches; left gastric , common hepatic and splenic arteries . Via these branches, the celiac trunk supplies the foregut, including the abdominal part of the esophagus, stomach, upper 1/3 of the duodenum, liver, spleen, and pancreas.
• Superior mesenteric artery , which gives off the inferior pancreaticoduodenal , middle colic , right colic , ileocolic arteries , jejunal and ileal branches, and the marginal artery of Drummond . These branches supply the midgut, which includes the distal 2/3 of the duodenum, jejunum, ileum, cecum, appendix, ascending colon and proximal 1/3 of the transverse colon.
• Inferior mesenteric artery , which gives off the left colic , sigmoid, and superior rectal arteries . These branches provide blood to the hindgut, supplying the distal 1/3 of the transverse colon, descending colon, sigmoid colon, rectum and anus.

The digestive system receives both sympathetic and parasympathetic innervation. Sympathetic innervation stems from the abdominopelvic splanchnic nerves . These nerves arise from the sympathetic trunk and include the thoracic and lumbar splanchnic nerves . The splanchnic nerves synapse with prevertebral ganglia (celiac, aorticorenal, superior mesenteric, and inferior mesenteric ganglia) which project postganglionic fibers to innervate the organs of the digestive system. Sympathetic innervation inhibits peristalsis, constricts blood vessels and redirects blood from the digestive system to the skeletal muscles and contracts the anal sphincters.

The parasympathetic supply to the digestive system stems from the vagus nerve (CN X) and pelvic splanchnic nerves . The vagus nerve supplies the digestive tract from the esophagus to the transverse colon, while the pelvic splanchnic nerves supply the descending colon, sigmoid colon and rectum. Parasympathetic innervation increases peristalsis, promotes secretion of digestive juices, relaxes the internal anal sphincter and contracts the rectum.

There are two venous systems that drain the organs of the digestive tract; portal venous system and the systemic venous system .

In the portal venous system, the nutrient-rich blood from the digestive tract is drained by the hepatic portal vein into the liver to be filtered and detoxified. The hepatic portal vein is formed by the merger of the  superior mesenteric vein and the splenic vein .

After being processed by the liver, the blood is carried into the systemic venous system by the hepatic veins , which drain into the inferior vena cava .

Gastrointestinal pathology ranks high among the chief presenting complaints of patients presenting to both outpatient and emergency settings. Obtaining adequate historical details will aid the clinician in narrowing down the pathology to a particular part of the digestive system. Once the history is complete, the clinical examination is conducted to confirm, rule-in or rule-out any diagnosis. The examination follows the rules of inspection, palpation, percussion, and auscultation.

Adequate exposure of the patient for an abdominal exam should allow visibility from the nipple line to mid thigh. Inspect the abdomen for:

• distention (either symmetrical or asymmetrical)
• distended superficial veins (caput medusae)
• cutaneous discoloration
• visible peristalsis

On inspection, also ask the patient to cover their mouth and cough while the examiner observes the abdominal wall. A visible cough impulse (localized distention of the abdominal wall due to raised intra-abdominal pressure from coughing) suggests that there is a hernia at that site.

Palpation should be performed to assess for any masses as well as to determine the surface texture of the liver. The examiner may also determine if there is an enlargement of the kidneys or spleen at this time as well. The abdominal cavity has the potential to store a large volume of interstitial fluid. Large volumes of fluid can be detected during palpation by eliciting a fluid thrill. Smaller volumes can be picked up during percussion with the shifting dullness technique. Percussion also helps the examiner to confirm the size and location (if enlarged) of the liver and spleen. Be sure to auscultate the abdomen for bowel sounds and bruits. The abdominal exam is concluded with a digital rectal and genital examination.

References:

• Ahima, Rexford S., and Daniel A. Antwi:  "Brain Regulation Of Appetite And Satiety." Endocrinology And Metabolism Clinics Of North America, vol 37, no. 4, 2008, pp. 811-823. Elsevier BV, doi:10.1016/j.ecl.2008.08.005.
• Burnand, Kevin G, and Norman L Browse:  Browse's Introduction To The Symptoms & Signs Of Surgical Disease. 5th ed., Boca Raton, FL, CRC Press, Taylor & Francis Group, 2015,.
• Guyton, Arthur C, and John E Hall:  Textbook Of Medical Physiology. 11th ed., Philadelphia, PA, Elsevier Saunders, 2007,.
• Standring, S., Borley, N. and Gray, H.:  (2008). Gray's Anatomy. 42nd ed. [Edinburgh]: Churchill Livingstone/Elsevier, pp.1191-1195.

Illustrators:

• Digestive system (Small intestine) - Begoña Rodriguez
• Hypothalamus (Ventromedial nucleus - lateral-left view) - Paul Kim
• Masseter muscle - Paul Kim
• Nucleus ambiguus (lateral-left view) - Paul Kim
• Esophagus (lateral-left view) - Yousun Koh
• Circular layer of muscular coat of stomach (ventral view) - Rebecca Betts
• Duodenum (ventral view) - Samantha Zimmerman
• Oral cavity proper (ventral view) - Paul Kim
• Palatopharyngeal muscle (dorsal view) - Yousun Koh
• Greater curvature of the stomach (ventral view) - Irina Münstermann
• Descending part of duodenum (ventral view) - Begoña Rodriguez
• Jejunum (ventral view) - Irina Münstermann
• Taenia mesocolica (ventral view) - Begoña Rodriguez
• Rectum (ventral view) - Samantha Zimmerman
• Sublingual gland - Paul Kim
• Liver (ventral view) - Begoña Rodriguez
• Duodenum and jejunum during a surgical intervention - Prof. Carlos Suárez-Quian
• Cecum, appendix and ascending colon in a cadaver - Prof. Carlos Suárez-Quian
• Pharynx (cadaveric dissection) - Prof. Carlos Suárez-Quian

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Home — Essay Samples — Nursing & Health — Digestive System — Organs of Digestive system

Organs of Digestive System

• Categories: Digestive System Human Anatomy

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Published: Dec 18, 2018

Words: 1435 | Pages: 3 | 8 min read

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Small intestine.

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Human Digestive System - Free Essay Examples and Topic Ideas

The human digestive system is responsible for breaking down ingested food into its constituent molecules, which can then be absorbed into the bloodstream for use by the body. It consists of organs such as the mouth, esophagus, stomach, small intestine, large intestine, rectum and anus, each of which serves a specific purpose in the process of digestion. Various enzymes and acids are involved in breaking down food as it moves through the digestive tract, while muscles throughout the system help move food along and mix it with digestive secretions. Finally, waste products are eliminated from the body through the rectum and anus as solid feces.

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How to write an expository essay

Published September 27, 2020. Updated June 5, 2022.

Expository essay definition

An expository essay is a type of academic or research essay. An expository essay exposes information.

Overview of an expository essay

An expository essay is the traditional academic essay: you give information and analyze what it means. To write an effective expository essay, research needs to be conducted on the topic to find credible sources. Then, the findings should be presented along with their own analysis to explain the research and the connections between the sources. Every essay will have three parts: an introduction, a body, and a conclusion. The introduction part consists of a hook, background information, and a thesis statement. A typical expository essay should have at least three body paragraphs. The essay should be concluded by tying back to the thesis statement (in the introduction). Then, the main parts of the essay should be summarized. Since the body paragraphs of an expository essay need to include analysis as well as information, the MEAL plan is one way to organize them. MEAL stands for M ain idea, E vidence, A nalysis, and L ink/ L ead out.

This page will cover the following points:

Key takeaways

What is an expository essay, parts of an essay, the meal plan.

• Essay outline
• Expository essay templates and examples
• An expository essay is also known as an academic essay or a research essay.
• It will take time to write an expository essay because you need to do research, see how the evidence from various sources fits together, and analyze your evidence.
• Outlines are helpful for seeing quickly and easily if you have enough information, how your ideas relate to each other, if your argument is logical, and if there are any gaps or irrelevant ideas.
• Use the MEAL plan to write the body paragraphs.
• Cite your sources!

Look at the word “expository.” Doesn’t it look like the word “expose”? Expository essays expose information. An expository essay is the traditional academic essay: you give information and analyze what it means. You may be asked to write an expository essay for many different types of classes, not just writing classes, and it is a valuable skill for many careers as well. To write an effective expository essay, you will need to conduct research on your topic to find credible sources, and then present your findings along with your own analysis to explain the research and the connections between sources.

Worried about your writing? Submit your paper for a Chegg Writing essay check , or for an Expert Check proofreading . Both can help you find and fix potential writing issues.

Before you begin writing, make sure to conduct thorough research on your topic and identify a variety of credible sources. Since the goal of an expository essay is to present and analyze the information you found, the tone of your essay should be objective and you should avoid the use of humor or emotion. Every essay you write will have three parts: an introduction, a body, and a conclusion.

Think of the organization of an essay like this:

• Intro – Tell your reader what you’re going to write about.
• Body – Write about it (using the MEAL plan).
• Conclusion – Tell them what you wrote about.

Let’s go through each of those parts for an expository essay. Each part will include a sample. The complete sample essay is available here .

Note: All sources for the evidence were linked in the sample essay. This is how online articles cite sources. However, this is not a proper academic citation method. When you write your own expository essay, make sure you know which citation method you are required to use.

Introduction

You want to begin your essay with a hook. A hook is an interesting opening that “catches” your reader’s attention and makes them want to read more. Your hook is usually the first sentence (or the first few sentences). You will begin your introduction with a general idea that is connected to your topic.

After you’ve hooked the reader, you want to give some context or background information. Your background information can include information from other sources. Make sure you cite them!

Think of each sentence in your intro as a stepping point. Each sentence brings you closer to your thesis statement.

Once you’ve given some context, write a thesis statement, which in an expository essay is called a claim.

Your claim must be arguable. In order to be arguable, your claim should not be a statement of fact, since you cannot argue with facts. It should also not just be your personal bias since everyone is entitled to their opinion. Rather, it should be an idea you came to after researching your topic.

Your claim tells the reader exactly what they’re going to read about. Think of it like a map to the rest of your essay.

Sample introduction

• In this sample, look at how the hook is written. Did the first several sentences get your attention?
• In which sentence is the main topic of the essay introduced?
• Are there sources in the introduction paragraph? How do you know?
• Can you see how each sentence in the introduction brings you closer to the thesis statement?
• Can you identify the thesis statement? What is the claim?

Do you believe you’re creative? Do you consider yourself athletic? What about musically inclined?  If not, do you think you could become those things? What if you worked really hard at them? Carol Dweck , an American psychologist who studied motivation in children, came up with the theory of fixed versus growth mindset. As this article explains, the concept is rather simple: there are children who believe that their abilities are innate. They are either smart or not, athletic or not, creative or not. That is fixed mindset. Then, there are children that believe that their abilities can be developed through hard work. That is growth mindset. In this article , Dweck states that children with a growth mindset tend to be more successful since they believe that hard work leads to mastery. Furthermore, Dweck claims that growth mindset can be taught, which leads to academic improvement. As logical and intuitive as this theory is, it is not without controversy. There are several criticisms directed at the theory and the studies that led to it, and this paper will examine some of them.

A typical expository essay should have at least three body paragraphs—fewer than three wouldn’t give you the space needed to put forth evidence for your claim and analyze it.  However, you can write as many paragraphs as you need (or as many as your teacher assigns you). Regardless of how many body paragraphs you have, they will all be organized in a similar manner. Make sure to cite any evidence you use from your sources, and either paraphrase information in your own words or include direct quotations to avoid plagiarizing. Once you have presented your evidence and appropriately cited it, it is important that you then explain your analysis of the evidence and connect it to the claim of your essay.

For more information on body paragraphs in expository essays, go to the MEAL plan section.

Sample body paragraph

Note: Due to length, only one sample body paragraph is included. The complete sample essay is available here.

• Can you identify the main idea (topic sentence)? Does it link to the claim? Is it in the writer’s own words?
• Can you identify which sentences are evidence and which are analysis?
• Can you identify a link or lead out?

The main criticism of Dweck’s research with mindset is that her findings are not replicable. According to this article and this article , Dweck’s main study showed drastic results when students were praised in a way that encouraged growth mindset. These drastic results raised red flags since psychological experiments tend to show very small results. Clearly, when a study claims significant results, the scientific community tries to replicate those results to further validate the findings. So far, this has not happened. This article describes another experiment that was conducted on growth mindset with a group of students from a low socioeconomic status school. The results actually showed that teaching growth mindset only benefitted students who were already academically advanced. In fact, for one of the other groups, teaching about growth mindset disadvantaged the highest performing students. The results from this particular experiment seem to directly contradict the results claimed by Dweck. With inconsistent results like these, the findings from Dweck’s studies are put into question.

This is how your essay ends and is the last impression your reader takes away.

Conclude your essay by tying back to your thesis statement (in the introduction). Then, summarize main points from your essay.

Since you are re-stating your claim and summarizing your findings, you are not including any new evidence. You do not need any citations in your conclusion. However, if you do introduce new evidence or include a quote taken from a source already mentioned, make sure you cite it.

If you want, end with a closing statement: an idea that you want your reader to walk away with.

Sample conclusion

• Can you identify the sentence that ties back to the thesis statement?
• Can you identify the summary of the main points?
• Can you identify a closing statement?

This essay explored some of the criticisms of a theory that caused quite a sensation when it was first published. Like any scientific discovery, experiments need to be replicated with similar results in order to confirm their validity. The more the study is replicated, the more the results are trusted. However, that has not happened with Dweck’s research. In addition, the techniques for developing growth mindset in students have been found to be problematic, with some teachers misunderstanding the steps needed. In some cases, this has resulted in unintended, negative consequences. Some students have performed worse when taught about growth mindset. This might be caused by students feeling less “special” by realizing that what made them successful was hard work. Regardless of how clear and apparent a theory seems to be, due diligence must be done in order to confirm its validity.

Since the body paragraphs of an expository essay need to include analysis as well as information, the MEAL plan is one way to organize them. MEAL stands for:

• L ink/ L ead out

The Main idea of each body paragraph will be the topic sentence. This sentence is written in your own words (that is, it’s not information that comes from other sources). It should have a connection to the thesis statement (your claim) and give the reader a general idea of what the paragraph is about.

The Evidence is the information you gather from other sources to support your claim. Since it comes from other sources, evidence must be cited.

The Analysis is where you interpret the evidence and give it meaning, supporting your claim. Analysis should be in your own words and not from other sources. You don’t cite analysis.

Note: Your body paragraph should have several sentences of evidence followed by analysis. How you organize that is up to you. For example, you could have:

E, E, A, E, E, A.

Or: E, A, A, E, A, E, A, A.

Or: E, A, E, A, E, A, E, A.

That is up to you and will depend on what information you find.

However, you should NOT have: E, E, E, E, A, A, A, A. Every piece of evidence should be followed by its analysis.

The Link , or Lead out , will either link back to the main claim (the thesis statement) or summarize and lead out to the next paragraph. Whether you link back or lead out, your paragraph should have a feeling of conclusion.

Complete expository essay outline example

I. There are several criticisms directed at Dweck’s Growth Mindset theory and the studies that led to it

II. Findings are not replicable

A. Dweck’s studies showed drastic results https://www.spectator.co.uk/article/a-myth-that-keeps-growing-and-growing https://www.buzzfeed.com/tomchivers/what-is-your-mindset

• Red flags – psych studies tend to show small results
• Significant results, try to replicate results to validate

B. Low socioeconomic students https://www.psychologytoday.com/us/blog/ulterior-motives/201710/the-growth-mindset-works-not-everyone

C. Only benefitted academically advanced students

D. Other group: Disadvantaged highest performing students

• This experiment contradicts Dweck

With inconsistent results like these, the findings from  Dweck’s studies are put into question.

III. Difficulty in applying the principles in a classroom setting

A. “Educators have applied principles with tremendously gratifying results” https://www.edweek.org/leadership/opinion-caorl-dweck-revisits-the-growth-mindset/2015/00

B. However: “Teachers misunderstand how to develop mindset”

C. Teachers need to be taught principles and steps

• Dweck seems to try to justify herself and her results

D. “If scientists trying to replicate have a hard time teaching, how can we expect teachers to do it right?” https://www.spectator.co.uk/article/a-myth-that-keeps-growing-and-growing

• Teaching initiative should come with training, or could backfire

IV. Learning about growth mindset might negatively impact high-performing students

A. High-performing students feel special = feedback loop https://www.psychologytoday.com/us/blog/ulterior-motives/201710/the-growth-mindset-works-not-everyone

B. Perhaps learning they performed well because they worked hard = demotivating https://www.happyasannie.com/adopt-growth-mindset/

• Being “gifted” more important than being “hardworking”

C. Society glorifies geniuses & natural talents – we’ve adopted “collective fixed mindset”

D. “Anyone can try hard and succeed. Nothing special. But try and fail? Pathetic”

• Society rewarding “special” not hardworking.
• Geniuses: How often do we see them on social media working hard?
• We usually see end result, not process.

V. Regardless of how clear and apparent a theory seems to be, due diligence must be done in order to confirm its validity

Templates and examples

Expository essay template in mla, expository essay template in apa, example expository essay.

Before you turn in that paper, don’t forget to cite your sources in APA format , MLA format , or a style of your choice.

By Halina Stolar. Halina has a master’s degree in teaching and taught English as a Second Language and writing for almost 15 years overseas. She now works as a freelance writer and geeks out over grammar for fun.

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