File Name: anatomy and physiology of human digestive system .zip
- Gastrointestinal tract
- Quick Anatomy Lesson: Human Digestive System
- 22.1A: Anatomy of the Digestive System
The gastrointestinal tract GIT consists of a hollow muscular tube starting from the oral cavity, where food enters the mouth, continuing through the pharynx, oesophagus, stomach and intestines to the rectum and anus, where food is expelled. There are various accessory organs that assist the tract by secreting enzymes to help break down food into its component nutrients.
The human gastrointestinal tract refers to the stomach and intestine, and sometimes to all the structures from the mouth to the anus. Upper and lower gastrointestinal tract : The major organs of the human gastrointestinal system. The upper gastrointestinal tract consists of the esophagus, stomach, and duodenum.
The gastrointestinal tract , GI tract , GIT , digestive tract , digestion tract , alimentary canal is the tract from the mouth to the anus which includes all the organs of the digestive system in humans and other animals. Food taken in through the mouth is digested to extract nutrients and absorb energy, and the waste expelled as feces. The mouth , esophagus , stomach and intestines are all part of the gastrointestinal tract. Gastrointestinal is an adjective meaning of or pertaining to the stomach and intestines.
A tract is a collection of related anatomic structures or a series of connected body organs. All vertebrates and most invertebrates have a digestive tract. The sponges , cnidarians , and ctenophores are the early invertebrates with an incomplete digestive tract having just one opening instead of two, where food is taken in and waste expelled. The human gastrointestinal tract consists of the esophagus , stomach , and intestines, and is divided into the upper and lower gastrointestinal tracts.
However, the complete human digestive system is made up of the gastrointestinal tract plus the accessory organs of digestion the tongue , salivary glands , pancreas , liver and gallbladder. The whole human GI tract is about nine metres 30 feet long at autopsy. It is considerably shorter in the living body because the intestines, which are tubes of smooth muscle tissue , maintain constant muscle tone in a halfway-tense state but can relax in spots to allow for local distention and peristalsis.
The gastrointestinal tract contains trillions of microbes , with some 4, different strains of bacteria having diverse roles in maintenance of immune health and metabolism. These digestive hormones , including gastrin , secretin , cholecystokinin , and ghrelin , are mediated through either intracrine or autocrine mechanisms, indicating that the cells releasing these hormones are conserved structures throughout evolution.
The structure and function can be described both as gross anatomy and as microscopic anatomy or histology. The tract itself is divided into upper and lower tracts, and the intestines small and large parts. The upper gastrointestinal tract consists of the mouth , pharynx , esophagus , stomach , and duodenum.
This differentiates the embryonic borders between the foregut and midgut, and is also the division commonly used by clinicians to describe gastrointestinal bleeding as being of either "upper" or "lower" origin. Upon dissection , the duodenum may appear to be a unified organ, but it is divided into four segments based upon function, location, and internal anatomy. The four segments of the duodenum are as follows starting at the stomach, and moving toward the jejunum : bulb , descending, horizontal, and ascending.
The suspensory muscle attaches the superior border of the ascending duodenum to the diaphragm. The suspensory muscle is an important anatomical landmark which shows the formal division between the duodenum and the jejunum, the first and second parts of the small intestine, respectively.
The lower gastrointestinal tract includes most of the small intestine and all of the large intestine. In humans, the small intestine is further subdivided into the duodenum , jejunum and ileum while the large intestine is subdivided into the cecum , ascending, transverse, descending and sigmoid colon , rectum , and anal canal.
The small intestine begins at the duodenum and is a tubular structure, usually between 6 and 7 m long.
There are three major divisions:. The large intestine also called the colon, consists of the cecum , rectum , and anal canal. It also includes the appendix , which is attached to the cecum. The colon is further divided into:. The main function of the large intestine is to absorb water. The gut is an endoderm -derived structure. At approximately the sixteenth day of human development, the embryo begins to fold ventrally with the embryo's ventral surface becoming concave in two directions: the sides of the embryo fold in on each other and the head and tail fold toward one another.
The result is that a piece of the yolk sac , an endoderm -lined structure in contact with the ventral aspect of the embryo, begins to be pinched off to become the primitive gut. The yolk sac remains connected to the gut tube via the vitelline duct. Usually, this structure regresses during development; in cases where it does not, it is known as Meckel's diverticulum.
During fetal life, the primitive gut is gradually patterned into three segments: foregut , midgut , and hindgut. Although these terms are often used in reference to segments of the primitive gut, they are also used regularly to describe regions of the definitive gut as well. Each segment of the gut is further specified and gives rise to specific gut and gut-related structures in later development.
Components derived from the gut proper, including the stomach and colon , develop as swellings or dilatations in the cells of the primitive gut. In contrast, gut-related derivatives — that is, those structures that derive from the primitive gut but are not part of the gut proper, in general, develop as out-pouchings of the primitive gut.
The blood vessels supplying these structures remain constant throughout development. The gastrointestinal tract has a form of general histology with some differences that reflect the specialization in functional anatomy. The mucosa is the innermost layer of the gastrointestinal tract. The mucosa surrounds the lumen , or open space within the tube.
This layer comes in direct contact with digested food chyme. The mucosa is made up of:. The mucosae are highly specialized in each organ of the gastrointestinal tract to deal with the different conditions.
The most variation is seen in the epithelium. The submucosa consists of a dense irregular layer of connective tissue with large blood vessels, lymphatics, and nerves branching into the mucosa and muscularis externa. It contains the submucosal plexus , an enteric nervous plexus , situated on the inner surface of the muscularis externa. The muscular layer consists of an inner circular layer and a longitudinal outer layer. The circular layer prevents food from traveling backward and the longitudinal layer shortens the tract.
The layers are not truly longitudinal or circular, rather the layers of muscle are helical with different pitches. The inner circular is helical with a steep pitch and the outer longitudinal is helical with a much shallower pitch. The muscularis externa of the stomach is composed of the inner oblique layer, middle circular layer, and outer longitudinal layer. Between the circular and longitudinal muscle layers is the myenteric plexus.
This controls peristalsis. Activity is initiated by the pacemaker cells, myenteric interstitial cells of Cajal. The gut has intrinsic peristaltic activity basal electrical rhythm due to its self-contained enteric nervous system.
The rate can be modulated by the rest of the autonomic nervous system. The coordinated contractions of these layers is called peristalsis and propels the food through the tract. Food in the GI tract is called a bolus ball of food from the mouth down to the stomach. After the stomach, the food is partially digested and semi-liquid, and is referred to as chyme.
In the large intestine the remaining semi-solid substance is referred to as faeces. The outermost layer of the gastrointestinal tract consists of several layers of connective tissue.
Intraperitoneal parts of the GI tract are covered with serosa. These include most of the stomach , first part of the duodenum , all of the small intestine , caecum and appendix , transverse colon , sigmoid colon and rectum.
In these sections of the gut there is clear boundary between the gut and the surrounding tissue. These parts of the tract have a mesentery. Retroperitoneal parts are covered with adventitia. They blend into the surrounding tissue and are fixed in position.
For example, the retroperitoneal section of the duodenum usually passes through the transpyloric plane. These include the esophagus , pylorus of the stomach, distal duodenum , ascending colon , descending colon and anal canal.
In addition, the oral cavity has adventitia. Specific proteins expressed in the stomach and duodenum involved in defence include mucin proteins, such as mucin 6 and intelectin The time taken for food to transit through the gastrointestinal tract varies on multiple factors, including age, ethnicity, and gender. The gastrointestinal tract forms an important part of the immune system.
There are additional factors contributing to protection from pathogen invasion. For example, low pH ranging from 1 to 4 of the stomach is fatal for many microorganisms that enter it. Beneficial bacteria also can contribute to the homeostasis of the gastrointestinal immune system. For example, Clostridia , one of the most predominant bacterial groups in the GI tract, play an important role in influencing the dynamics of the gut's immune system.
This is due to the production of short-chain fatty acids during the fermentation of plant-derived nutrients such as butyrate and propionate. Basically, the butyrate induces the differentiation of Treg cells by enhancing histone H3 acetylation in the promoter and conserved non-coding sequence regions of the FOXP3 locus, thus regulating the T cells , resulting in the reduction of the inflammatory response and allergies. The large intestine hosts several kinds of bacteria that can deal with molecules that the human body cannot otherwise break down.
These bacteria also account for the production of gases at host-pathogen interface , inside our intestine this gas is released as flatulence when eliminated through the anus. However the large intestine is mainly concerned with the absorption of water from digested material which is regulated by the hypothalamus and the re absorption of sodium , as well as any nutrients that may have escaped primary digestion in the ileum.
Health-enhancing intestinal bacteria of the gut flora serve to prevent the overgrowth of potentially harmful bacteria in the gut. These two types of bacteria compete for space and "food", as there are limited resources within the intestinal tract.
Enzymes such as CYP3A4 , along with the antiporter activities, are also instrumental in the intestine's role of drug metabolism in the detoxification of antigens and xenobiotics. There are many diseases and conditions that can affect the gastrointestinal system, including infections , inflammation and cancer.
Various pathogens , such as bacteria that cause foodborne illnesses , can induce gastroenteritis which results from inflammation of the stomach and small intestine. Antibiotics to treat such bacterial infections can decrease the microbiome diversity of the gastrointestinal tract, and further enable inflammatory mediators. Diverticular disease is a condition that is very common in older people in industrialized countries. It usually affects the large intestine but has been known to affect the small intestine as well.
Diverticulosis occurs when pouches form on the intestinal wall. Once the pouches become inflamed it is known as diverticulitis. Inflammatory bowel disease is an inflammatory condition affecting the bowel walls, and includes the subtypes Crohn's disease and ulcerative colitis.
While Crohn's can affect the entire gastrointestinal tract, ulcerative colitis is limited to the large intestine. Crohn's disease is widely regarded as an autoimmune disease.
Although ulcerative colitis is often treated as though it were an autoimmune disease, there is no consensus that it actually is such.
Quick Anatomy Lesson: Human Digestive System
This book offers one of the most comprehensive reviews in the field of gastrointestinal GI physiology, guiding readers on a journey through the complete digestive tract, while also highlighting related organs and glandular systems. It is not solely limited to organ system physiology, and related disciplines like anatomy and histology, but also examines the molecular and cellular processes that keep the digestive system running. As such, the book provides extensive information on the molecular, cellular, tissue, organ, and system levels of functions in the GI system. Covering both traditional and contemporary topics, it is a valuable resource for biomedical students, as well as healthcare and scientific professionals. Skip to main content Skip to table of contents.
22.1A: Anatomy of the Digestive System
The human digestive system, also known as the digestive tract, the GI tract, the alimentary canal is a series of connected organs leading from the mouth to the anus. The digestive system allows us to break down the food we eat to obtain energy and nourishment. The digestive system -- which can be up to 30 feet in length in adults -- is usually divided into eight parts: the mouth, the esophagus, the stomach, the small intestine or "small bowel" and the large intestine also called "large bowel" or "colon" with the liver, pancreas, and gallbladder adding secretions to help digestion. These organs combine to perform six tasks: ingestion, secretion, propulsion, digestion, absorption, and defecation.
The function of the digestive system is to break down the foods you eat, release their nutrients, and absorb those nutrients into the body. Although the small intestine is the workhorse of the system, where the majority of digestion occurs, and where most of the released nutrients are absorbed into the blood or lymph, each of the digestive system organs makes a vital contribution to this process [link]. As is the case with all body systems, the digestive system does not work in isolation; it functions cooperatively with the other systems of the body. Consider for example, the interrelationship between the digestive and cardiovascular systems.
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