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Functions of the digestive system

Ingestion, digestion, propulsion, secretion, absorption, & elimination of wastes



Introduction of solid & liquid materials into the oral cavity. The first step in the process of digesting & absorbing nutrients



Breakdown of large foods into smaller structures & molecules. Two aspects: mechanical digestion & chemical digestion


Mechanical digestion

Physically breaks down ingested materials into smaller pieces. First part is mastication, the chewing of ingested material by the teeth in the oral cavity


Chemical digestion

Breaks down ingested material into smaller molecules by using enzymes



Process of moving swallowed materials through the GI tract. Two ways of movement involved: Peristalsis & segmentation


Peristalsis is

The process of muscular contraction that forms ripples along part of the GI tract & forces material to move further along the tract


Segmentation is

Churning & mixing movements in the small intestine. Help disperse the material being ingested & combine it with digestive organ secretions


Secretion is

The process of producing & releasing mucin or fluids such as acid, bile, & digestive enzymes. When these products are secreted into the lumen of the GI tract, they facilitate chemical digestion & the passage of material through the GI tract.


Mucin secretions serve a protective function. How?

Mucin mixes with water to form mucus, which coats the GI wall to protect & lubricate it against acidic secretions & abrasions by passing materials


Absorption involves

Either passive movement or active transport of electrolytes, digestion products, vitamins, & water across the GI tract epithelium & into GI tract blood & lymph vessels


Elimination of wastes

All undigestable materials as well as the waste products secreted by the accessory organs into the GI tract are compacted into feces, or fecal material, & the eliminated from the GI tract by the process of defecation


Hard Palate is

Anterior two thirds of the palate. Formed by the palatine processes of the maxillae & the horizontal plates of the palatine bones. Covered w/dense connective tissue & nonkeratinized stratified squamous epithelium & exhibits transverse palatine folds that assist the tongue in manipulating ingested materials prior to swallowing


Soft palate is

Composed of skeletal muscle & covered w/keratinized stratified squamous epithelium. Posterior part is a projection called uvula. When swallowing, the soft palate & uvula elevate to close off the posterior entrance into the nasopharynx & prevent ingested materials from entering the nasal region


Palatine tonsils are

Housed between the palatoglossal arch & the palatopharyngeal arch. Serve as an "early line of defense" as they monitor ingested food & drink for antigens, & initiate an immune response when necessary


Papillae are

Numerous small projections that cover the superior (dorsal) surface of the tongue.


Lingual tonsils are

Located posteriorinferior surface of the tongue. A collection of lymphoid follicles on the posterior portion of the dorsum of the tongue


Bolus is

The chewed food mixed with saliva. The stomach processes the bolus and turns it into a paste-like substance called chyme.


What is the function of the stomach?

It continues the mechanical & chemical digestion of the bolus. After the bolus has been completely processed in the stomach, the product is called chyme. Facilitates the mechanical digestion by the contractions of its thick muscularis layer, which churns & mixes the bolus & the gastric secretions. Facilitates chemical digestion through its gastric secretions of acid & enzymes


Deciduous teeth are

Also called milk teeth, 20 erupt between 6 months & 30 months after birth in an infant. Eventually lost and replaced by 32 permanent teeth


Lamina propria is

One of three components of mucosa. An underlying areolar connective tissue


What supplies the abdominal GI tract?

Branches of the celiac trunk, superior mesenteric artery, & inferior mesenteric artery


How do the different branches of blood vessels supply the abdominal GI tract?

Branches travel w/in the tunics, & the mucosa contains capillaries that have fenestrated endothelial cells to promote absorption. The veins arising in the mucosa form anastomoses in the submucosa before exiting the wall of the GI tract adjacent to their companion arteries . The veins merge to form the hepatic portal system of veins


Peyer patches are?

Lymphatic structures, aggregate nodules. They appear as oval bodies the size of a pea.



(Mucosa-associated lymphatic tissue) Lymphatic structures found in the small intestine & appendix. In the small intestine they are called peyers patches.


Gastric pits

Distinguishes the stomach mucosa from the default pattern. Numerous depressions that indent the stomach.


Gastric glands are?

Several branched tubular glands at the base of each gastric pit. Extend through the length of the mucosa to its base


Gastric juices are produced by?

Cells in the gastric glands, & their secretions are released into gastric pits, which funnel them to the lumen of the stomach


Parietal cells are

located primarily in the proximal & middle parts of the gastric gland. Their features are small intracellular channels called canaliculi, which are lined by microvilli. Hydrochloric acid secreted across the cells surface helps denature proteins to facilitate chemical digestion. They produce intrinsic factor.


Intrinsic factor is

A molecule that binds vitamin B12 in the stomach to lumen & assists in B12 absorption in the ileum of the small intestine


Chief cells are

Housed primarily in the distal part of the gastric gland. Synthesize & secrete enzymes, primarily inactive pepsinogen, into the lumen of the stomach. The acid content of the stomach then converts inactive pepsinogen into the active enzyme pepsin


Pepsinogen is

An enzyme synthesized & secreted by chief cells. It is inactive until the acid of the stomach converts it to the active enzyme pepsin, which chemically digests denature proteins in the stomach into smaller fragments


Gastrin is

A hormone that enters the blood and stimulates the secretory activities of the chief & parietal cells & the contractile activity of gastric muscle


Enteroendocrine cells are

Endocrine cells widely distributed in the gastric glands of the stomach. Secrete gastrin & produce other hormones, like somatostatin, that modulate the function of nearby enteroendocrine & exocrine cells


Function of the small intestine is

Finishes the chemical digestion process & is responsible for absorbing up to 90% of the nutrients & water. Ingested nutrients spend at least 12 hours in the small intestine as chemical digestion & absorption are completed


Villi is

Small fingerlike projections of mucosa in the circular fold in the small intestine. They further increase the surface area for absorption & secretion


Microvilli in the small intestine are

Increasing the absorptive surface area even further. Along the free surface of the simple columnar cells. Individual microvilli are not clearly visible in light micrographs of the small intestine; they collectively appear as a brush border.


Brush border are

Microvilli that resembles a brightly staining surface on the apical end of the simple columnar cells


Lacteals in the small intestine are

Responsible for absorbing lipids & lipid soluble vitamines, which are too large to be absorbed by the capillaries


Intestinal glands are

Invaginations of mucosa. Also known as intestinal crypts or crypts of lieberkuhn. Extend to the base of the mucosa & slightly resemble the gastric glands of the stomach. They are lined w/simple columnar epithelial cells (w/goblet cells) & enteroendocrine cells


Function of intestinal glands in the small intestines

Increase surface area for both absorption & chemical digestion; enteroendocrine cells lining intestinal glands secrete digestive hormones


Brunner glands are

Also called submucosal glands. Produce a viscous alkaline mucus that protects the duodenum from the acidic chyme


Function of goblet cells in the small intestine

Produce mucin to lubricate & protect the intestinal lining as materials being digested pass through


What role do the plicae circulares play in the small intestine?

Also called circular folds, they slow down PG 799


Digestive enzymes of the small intestine

Enteroendocrine cells release hormones such as secretin, cholecystokinin, & gastric inhibitory peptide. Some of these hormones temp. slow down digested activities as material from the stomach begins to enter the small intestine, prolonging the time for the stomach emptying into the small intestine


Surface area in the small intestine

The circular folds; on the folds the villi & microvilli increase surface area


Peritoneum of the large intestine

Anterior surface of the ascending colon is covered w/peritoneum


Mesenteries are

Folds of peritoneum that support & stabilize the intraperitoneal GI tract organs. Blood vessels, lymph vessels, & nerves are sandwiched between the two folds & supply the digestive organs


Greater omentum

Extends inferiorly like an apron from the greater curvature of the stomach & covers most of the abdominal organs. Often accumulates large amounts of adipose connective tissue


Lesser omentum

Connects the lesser curvature of the stomach & the proximal end of the duodenum to the liver. May be subdivided into a hepatogastric ligament, which runs from the liver to the stomach, & the hepatoduodenal ligament, which runs from the liver to the duodenum


Peritoneum is

The portion of the serous membrane that lines the inside surface of the body wall, is called the parietal peritoneum. The portion that folds back (reflects) to cover the surface of internal organs is called the visceral peritoneum. Between these two layers is the peritoneal cavity


Peritoneal cavity is

Potential space where the peritoneal layers that face each other secrete a lubricating serous fluid. This thin layer of fluid lubricates both the wall & the internal organ surfaces, allowing the abdominal organs to move freely, & reducing any friction resulting from this movement


Intraperitoneal organs

W/in the abdomen, organs that are completely surrounded by visceral peritoneum. Stomach, part of duodenum, jejunum, ileum, cecum, appendix, & transverse & sigmoid colon


Retroperitonial organs

Lie directly against the posterior abdominal wall, only their anterolateral portions are covered w/peritoneum. Include most of the duodenum, pancreas, ascending/descending colon & the rectum


Functions of the liver

Producing bile, hepatocytes detoxify drugs, metabolizes, & poisons


Falciform ligament is

A peritoneal fold that secures the liver to the anterior abdominal wall


Round ligament of the liver is

Ligamentum teres, represents the remnant of the fetal umbilical vein


The hepatic triad of the liver is

Composed of branches of the hepatic portal vein, the hepatic artery, & the bile duct. At the periphery of each lobule, also called portal triads


Hepatic sinusoids are

Bordered by cords of hepatocytes. Thin walled, porous or "leaky" capillaries where venous & arterial blood are mixed & then flow slowly through the hepatic lobule toward the central vein. Lined w/ stellate cells called reticuloendothelial cells (Kupffer cells)


Kupffer (reticuloendothelial) cells are

Phagocytic cells that have an immune function. They line the sinusoids


Bile production

Hepatocytes absorb nutrients from the sinusoids, & they also produce bile. Between each cord of hepatocytes is a small bile canaliculus which conduct bile from the hepatocytes to the bile duct in the portal triad


Gallbladder is

Attached to the inferior surface of the liver. Concentrates bile produced by the liver & stores this concentrate until it is needed for digestion


What is the pancreas head?

It is adjacent to the curvature of the duodenum


What is the body of the pancreas?

Central elongated body projecting towards the left lateral abdominal wall


Function of the large intestine

Absorbs most of the water & ions from the remaining digested material. In so doing, the watery material the first enters the large intestine soon solidifies & becomes feces. The large intestine stores the feces until the body is ready to defecate (expel the feces). Also absorbs a small percentage of nutrients still remaining in the digested material


Function of circular folds of the small intestine

Slow down the passage of materials undergoing digestion; increase surface area for both absorption & chemical digestion


Function of Villi of the small intestine

Increase surface area for both absorption & chemical digestion


Function of microvilli of small intestine

Increase surface area for both absorption & chemical digestion


Function of intestinal glands of the small intestine

Increase surface area for both absorption & chemical digestion; enteroendocrine cells lining intestinal glands secrete digestive hormones


Chyme is

When the stomach processes the bolus & turns it into a paste-like substance called chyme


HCL of the stomach is

Hydrochloric acid secreted by parietal cells. Helps denature proteins to facilitate chemical digestion.


Permanent teeth

Replace deciduous teeth. There are 32 permanent teeth.


Reverse peristalsis is

Antiperistalsis A wave of contraction of GI tract smooth muscle which moves contents orally.


Masticate is

Chewing, this involves mixing food with saliva, which contains an enzyme called salivary amylase which partially digests the food


Adventitia is

One of the four concentric layers (tunics) of the GI tract. Composed of areolar connective tissue with dispersed collagen & elastic fibers.


What is the difference between adventitia and serosa?

Serosa has the same components as the adventitia, but is covered by a visceral peritoneum.


What are the circular muscles of the gut wall in the muscularis layer?

Fibers of the inner layer of smooth muscle are oriented circumferentially around the GI tract, and are called the inner circular layer


What are the longitudinal muscles in the muscularis layer of the gut wall?

The fibers of the outer layer are oriented lengthwise along the GI tract, and are called outer longitudinal layers


Lymphatics of the gut wall

Lymphatic capillaries arise as blind tubes in the mucosa of the GI tract. In the small intestine, each villus usually contains a single, blind-ended, central lymphatic capillary called a lacteal.


Responsible for absorbing dietary lipids & lipid soluble vitamins



Outside the organ walls, lymphatic capillaries merge to form

Lymphatic vessels. These vessels enter & exit the many lymph nodes scattered near the organs & w/in the mesentery. This lymph will be transported to the cisterna chili, which drains into the thoracic duct


The lymphatic structures within the GI tract lie primarily in the

Lamina propria of the mucosa.


Goblet cells

Produce mucin to lubricate & protect the intestinal lining as materials being digested pass through


Glandular epithelial cells found in the lining of the digestive and respiratory tracts. They are used to secret mucus. Mucus is a sticky, viscous substance composed of mucins, enzymes and electrolytes.

Goblet cells


Plicae circulares are

Numerous permanent crescentic folds of mucous membrane found in the small intestine especially in the lower part of the duodenum and the jejunum


What provides most of ATP?



Circular folds, which can be seen with the naked eye, help increase the surface area through which nutrients can be absorbed. Act like speed bumps to slow down the movement of chyme & ensure that it remains w/in the small intestine for maximal nutrient absorption. More numerous in the duodenum & jejunum, and least numerous in the ileum

Plicae circulares


Why is the pancreas referred to as a mixed gland?

Because it exhibits both endocrine & exocrine functions.


Endocrine functions of the pancreas

Performed by the cells of the pancreatic islets


Exocrine functions of the pancreas

Results in the secretion of digestive enzymes & bicarbonate, collectively called pancreatic juice, into the duodenum


Acinar cells in the pancreas

The pancreas contains modified simple cuboidal epithelial cells called acinar cells. These cells which are organized into clusters termed acini, or lobules, secrete the mucin & digestive enzymes of the pancreatic juice.


Anatomy of the pancreas

Has a wide head adjacent to the curvature of the duodenum, a central elongated body projecting toward the left lateral abdominal wall, and a tail that tapers as it approaches the spleen


Pancreatic islets are

Also called islets of Langerhans, are tiny clusters of cells scattered throughout the pancreas. Pancreatic islets contain several types of cells, including beta cells, that produce the hormone insulin.


Egestion is

The process of removing undigested food that is stored in the rectum and its eventual passing through the anus as faeces. When we eat, water is absorbed back into the body in the large intestine and the undigested food goes to the lower part of the large intestine


Compaction is

Progressive dehydration of indigestible materials and organic wastes prior to elimination from the body


Histology of Digestive Tract (Deep to Superficial)



Lowers PH of gastric juice, kills microorganisms, breaks down food, activates chief cells



Lobes of liver

Right, left, quadrate, caudate


Between liver and diaphragm

Coronary ligament


Liver lobules are

The basic functional units of liver