Digestive System Anatomy
In either event, pregnancy complicates their problems because the gastrointestinal disturbances that often…. Look no further than our Inside-Out Anatomy series, which lets you see your body in a whole new light. Learn about them by visiting our section on digestive diseases and conditions. Digestive enzymes area unit found within the organic process tracts of animals and humans and within the traps of carnivorous plants, wherever they aid within the digestion of food, similarly as within cells, particularly in their lysosomes, wherever they perform to keep up cellular survival. A number of alterations, often causing more or less distress, occur in the physical condition and functions of the gastrointestinal tract during pregnancy. Thank you for your feedback. In addition, it has exocrine functions of secreting digestive enzymes and sodium bicarbonate.
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The system also consists of the structures through which wastes pass in the process of elimination and other organs that contribute juices necessary for the digestive process. A number of alterations, often causing more or less distress, occur in the physical condition and functions of the gastrointestinal tract during pregnancy. 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. 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. Th muscularis externa, also called the muscularis surrounds the submucosa. The muscularis is responsible for segmentation and peristalsis. It typically has an inner circular layer and an outer longitudal layer of smooth muscle cells.
In several places along the tract, the circular layer thickens and forms sphincters that act as valves that control food passage from one organ to the next, they also prevent backflow. In most alimentary canal organs, its made up of areolar connective tissue covered with mesothelium , a single layer of squamous epithelial cells.
In the esophagus, which is located in the thoracic instead of the abdominopelvic cavity, the serosa is replaced by an adventitia , ordinary fibrous connective tissue that binds the esophagus to surrounding structures. Retroperitoneal organs have both a serosa facing the peritoneal cavity and an adventia on the side abutting the dorsal body wall.
Your email address will not be published. If you study biology or medicine, having a solid understanding of homeostasis is extremely important. All living systems are based. One of the basic concepts in anatomy and physiology is the idea of organization. Levels of structural organization in the. The heart is an extremely interesting and powerful pump. The large intestine primarily serves as a site for fermentation of indigestible matter by gut bacteria and for resorption of water from digests before excretion.
In mammals , preparation for digestion begins with the cephalic phase in which saliva is produced in the mouth and digestive enzymes are produced in the stomach. Mechanical and chemical digestion begin in the mouth where food is chewed , and mixed with saliva to begin enzymatic processing of starches. The stomach continues to break food down mechanically and chemically through churning and mixing with both acids and enzymes. Absorption occurs in the stomach and gastrointestinal tract , and the process finishes with defecation.
The human gastrointestinal tract is around 9 meters long. Food digestion physiology varies between individuals and upon other factors such as the characteristics of the food and size of the meal, and the process of digestion normally takes between 24 and 72 hours.
Digestion begins in the mouth with the secretion of saliva and its digestive enzymes. Food is formed into a bolus by the mechanical mastication and swallowed into the esophagus from where it enters the stomach through the action of peristalsis. Gastric juice contains hydrochloric acid and pepsin which would damage the walls of the stomach and mucus is secreted for protection.
In the stomach further release of enzymes break down the food further and this is combined with the churning action of the stomach.
The partially digested food enters the duodenum as a thick semi-liquid chyme. In the small intestine, the larger part of digestion takes place and this is helped by the secretions of bile , pancreatic juice and intestinal juice.
The intestinal walls are lined with villi , and their epithelial cells is covered with numerous microvilli to improve the absorption of nutrients by increasing the surface area of the intestine. In the large intestine the passage of food is slower to enable fermentation by the gut flora to take place. Here water is absorbed and waste material stored as feces to be removed by defecation via the anal canal and anus.
Different phases of digestion take place including: The cephalic phase occurs at the sight, thought and smell of food, which stimulate the cerebral cortex. Taste and smell stimuli are sent to the hypothalamus and medulla oblongata. After this it is routed through the vagus nerve and release of acetylcholine. Acidity in the stomach is not buffered by food at this point and thus acts to inhibit parietal secretes acid and G cell secretes gastrin activity via D cell secretion of somatostatin.
The gastric phase takes 3 to 4 hours. It is stimulated by distension of the stomach, presence of food in stomach and decrease in pH. Distention activates long and myenteric reflexes.
This activates the release of acetylcholine , which stimulates the release of more gastric juices. As protein enters the stomach, it binds to hydrogen ions, which raises the pH of the stomach. Inhibition of gastrin and gastric acid secretion is lifted. This triggers G cells to release gastrin , which in turn stimulates parietal cells to secrete gastric acid. Gastric acid is about 0. Acid release is also triggered by acetylcholine and histamine.
The intestinal phase has two parts, the excitatory and the inhibitory. Partially digested food fills the duodenum. This triggers intestinal gastrin to be released. Enterogastric reflex inhibits vagal nuclei, activating sympathetic fibers causing the pyloric sphincter to tighten to prevent more food from entering, and inhibits local reflexes.
Protein digestion occurs in the stomach and duodenum in which 3 main enzymes, pepsin secreted by the stomach and trypsin and chymotrypsin secreted by the pancreas, break down food proteins into polypeptides that are then broken down by various exopeptidases and dipeptidases into amino acids. The digestive enzymes however are mostly secreted as their inactive precursors, the zymogens. For example, trypsin is secreted by pancreas in the form of trypsinogen , which is activated in the duodenum by enterokinase to form trypsin.
Trypsin then cleaves proteins to smaller polypeptides. Digestion of some fats can begin in the mouth where lingual lipase breaks down some short chain lipids into diglycerides.
However fats are mainly digested in the small intestine. In humans, dietary starches are composed of glucose units arranged in long chains called amylose, a polysaccharide.
During digestion, bonds between glucose molecules are broken by salivary and pancreatic amylase , resulting in progressively smaller chains of glucose. This results in simple sugars glucose and maltose 2 glucose molecules that can be absorbed by the small intestine.
Lactase is an enzyme that breaks down the disaccharide lactose to its component parts, glucose and galactose. Glucose and galactose can be absorbed by the small intestine. Approximately 65 percent of the adult population produce only small amounts of lactase and are unable to eat unfermented milk-based foods. This is commonly known as lactose intolerance. Lactose intolerance varies widely by ethnic heritage; more than 90 percent of peoples of east Asian descent are lactose intolerant, in contrast to about 5 percent of people of northern European descent.
Sucrase is an enzyme that breaks down the disaccharide sucrose , commonly known as table sugar, cane sugar, or beet sugar. Sucrose digestion yields the sugars fructose and glucose which are readily absorbed by the small intestine.
Some nutrients are complex molecules for example vitamin B 12 which would be destroyed if they were broken down into their functional groups. To digest vitamin B 12 non-destructively, haptocorrin in saliva strongly binds and protects the B 12 molecules from stomach acid as they enter the stomach and are cleaved from their protein complexes. After the B 12 -haptocorrin complexes pass from the stomach via the pylorus to the duodenum, pancreatic proteases cleave haptocorrin from the B 12 molecules which rebind to intrinsic factor IF.
These B 12 -IF complexes travel to the ileum portion of the small intestine where cubilin receptors enable assimilation and circulation of B 12 -IF complexes in the blood. There are at least five hormones that aid and regulate the digestive system in mammals.
There are variations across the vertebrates, as for instance in birds. Arrangements are complex and additional details are regularly discovered. For instance, more connections to metabolic control largely the glucose-insulin system have been uncovered in recent years. Digestion is a complex process controlled by several factors. In the mouth, pharynx and esophagus, pH is typically about 6. Saliva controls pH in this region of the digestive tract. Salivary amylase is contained in saliva and starts the breakdown of carbohydrates into monosaccharides.
Most digestive enzymes are sensitive to pH and will denature in a high or low pH environment. The stomach's high acidity inhibits the breakdown of carbohydrates within it. This acidity confers two benefits: In the small intestines, the duodenum provides critical pH balancing to activate digestive enzymes. The liver secretes bile into the duodenum to neutralize the acidic conditions from the stomach, and the pancreatic duct empties into the duodenum, adding bicarbonate to neutralize the acidic chyme , thus creating a neutral environment.
The mucosal tissue of the small intestines is alkaline with a pH of about 8. From Wikipedia, the free encyclopedia. For the industrial process, see anaerobic digestion.
For the journal, see Digestion journal. A Catalina Macaw 's seed-shearing beak. This section needs expansion with: You can help by adding to it.