Digestive System
What layers are associated with the alimentary canal? What are they composed of?
(From the inside out) the innermost layer is mucosa, submucosa, muscularis, and serosa. The mucosa consists of epithelium, a underlying loose connective tissue layer, and a thin layer of smooth muscle. The submucosa consists of dense irregular layer of connective tissue with large blood vessels, lymphatics, and nerves that branch into the mucosa and muscularis externa. The muscularis consists of an inner circular muscular layer and a longitudinal outer muscular layer. The serosa consists of a secretory epithelial layer and a thin connective tissue layer.
What is the brush border composed of? What purpose does it serve?
3,000 microvilli, digestive enzymes produced and secreted by enterocytes catalyze reactions that break down disaccharides and peptides
What are the two categories of organs associated with the digestive system? Which organs belong to which category?
Alimentary Organs and Accessory Organs. The alimentary tract is composed of the mouth, pharynx, esophagus, stomach, small and large intestines, rectum and anus. The organs associated with accessory organs are salivary organs, liver, gallbladder, and pancreas
What role does bicarbonate play in digestion
Bicarbonate also serves much in the digestive system. It raises the internal pH of the stomach, after highly acidic digestive juices have finished in their digestion of food. Bicarbonate also acts to regulate pH in the small intestine.
Explain the function of chief cells
Chief cells are responsible for secreting pepsinogen. They have basally located nuclei and a basophilic cytoplasm with abundant rough endoplasmic reticulum and many secretory granules that contain pepsinogen. These are secreted into the lumen of the gastric gland.
Differentiate between gastrin inhibitory peptide and cholecystokinin
Cholecystokinin (CCK) is in the duodenum and stimulates the release of digestive enzymes in the pancreas and the emptying of bile from the gall bladder. Gastric inhibitory peptide (GIP) is in the duodenum and decreases the stomach churning in order to slow the emptying of the stomach.
Explain how the enteric nervous system regulates digestion
Control of the digestive system is also maintained by enteric nervous system (ENS), which can be thought of as a digestive brain that helps to regulate motility, secretion, and growth. The enteric nervous system can act as a fast, internal response to digestive stimuli. When this occurs, it is called a short reflex.
Describe the process of deglutition
Deglutition is a complex reflex mechanism by which food is pushed from the oral cavity into the esophagus and then pushed to the stomach. This movement of food from the oral cavity on to the esophagus and stomach by pushing is called propulsion, and it is an important part of the digestive process.
Describe how emesis is meant to be a protective feature of the stomach
Emesis is a medical term that means vomiting. Vomiting is when contents in your stomach come up and exit through your mouth. It is usually accompanied by nausea. Nausea is the feeling of having an upset stomach, and generally occurs before the actual vomiting.
Explain the function of enteroendocrine (g) cells
Enteroendocrine cells produce a range of gut hormones that have key roles in the coordination of food digestion and absorption, insulin secretion and appetite.
Describe the composition and function of gastric pits
Gastric pits open into a channel leading into a cluster of oxyntic glands, one of which is shown here. The surface mucus cells secrete mucus to line the stomach and protect it from its acid environment. The mucus contains mucin and HCO3− to neutralize stomach acid.
Describe how and when the most common electrolytes are absorbed
In the small intestine, regardless of need
Differentiate between incisors, canines, pre-molars, and molars
Incisors and canines help in cutting and tearing food into smaller bits. Once the food is broken down, it is then chewed before the food before it is swallowed. Premolars and molars play a vital role in the process of grinding and chewing.
Differentiate between the internal and external anal sphincters. How are these controlled?
Internal: simply thickened circularly layer of muscularis externa, supplied by parasympathetic motor neurons (involuntary) External: composed of skeletal muscle, supplied by somatic motor neurons controlled by cerebral cortex (voluntary)
Explain the importance of intrinsic factor and vitamin B12
Intrinsic factor is a glycoprotein secreted by parietal (humans) or chief (rodents) cells of the gastric mucosa. In humans, it has an important role in the absorption of vitamin B12 (cobalamin) in the intestine, and failure to produce or utilize intrinsic factor results in the condition pernicious anemia.
Describe the anatomical features of the pharynx (oro and laryngopharynx only)
It lies between the oral cavity, below the nasopharynx, and above the laryngopharynx, and has an opening to each of these other cavities. The anterior wall of the oropharynx consists of the base of the tongue and the superior wall consists of the bottom surface of the soft palate and the uvula. The laryngopharynx or hypopharynx is the caudal part of the pharynx; it is the part of the throat that connects to the esophagus and trachea. It lies inferior to the epiglottis and marks the division between the respiratory and digestive system pathways.
Explain the function of mucous neck cells
Mucous neck cells are found in the upper parts (isthmus and neck) of the gastric glands (SEM). They are smaller than surface mucous cells. They secrete an acidic fluid containing mucin proteins. ... The mucus protects the gland from gastric acid and proteolytic enzymes.
Explain the function of parietal cells
Parietal cells are the epithelial cells that secrete HCl and intrinsic factor. They are located in the gastric glands found in lining of fundus and stomach.
Describe the peritoneal cavity and explain the purpose of serous fluid
Peritoneal membranes secrete a serous fluid that lubricates the peritoneal surfaces, enabling the intraperitoneal organs to glide across one another with minimal friction. Peritoneal cavity. The peritoneal cavity is the fluid-filled space within the peritoneal sac. The peritoneal cavity is completely closed in males.
Describe the composition of saliva and explain its function
Saliva is 98% water, but it contains many important substances, including electrolytes, mucus, antibacterial compounds and various enzymes. Saliva contains the enzyme amylase that breaks some starches down into maltose and dextrin.
Describe the two components of the serosa of the alimentary canal
Serosa consists of a secretory epithelial layer and a thin connective tissue layer that reduces the friction from muscle movements
Differentiate between the buccal and pharyngeal-esophageal phases of deglutition. Which if under voluntary control? Which is under involuntary control?
The buccal phase involves the contraction of the tongue to push the bolus up against the soft palate and then posteriorly into the oropharynx by both the tongue and the soft palate. The pharyngeal phase is involuntary, it moves the bolus from the oropharynx into the esophagus. The esophageal phase is also involuntary, it moves the bolus through the esophagus and into the stomach.
Describe the cephalic reflex of gastric secretion in detail
The cephalic phase (reflex phase) of gastric secretion, which is relatively brief, takes place before food enters the stomach. The smell, taste, sight, or thought of food triggers this phase. ... This stimulates parasympathetic neurons to release acetylcholine, which then provokes increased secretion of gastric juice.
Describe the enterogastric reflex (intestinal phase) of gastric secretion in detail
The enterogastric reflex is stimulated by the senses. This reflex releases acid in the duodenum or in the stomach, and suppresses the release of digestive proteins. The gastrocolic reflex increases movement in the gastrointestinal tract, and reacts to stretches in the stomach walls as well as in the colon
Describe the anatomical composition of the esophagus including the location and function of sphincters
The esophagus is a muscular tube connecting the throat (pharynx) with the stomach. The esophagus is about 8 inches long, and is lined by moist pink tissue called mucosa. The esophagus runs behind the windpipe (trachea) and heart, and in front of the spine.
Describe the gastric phase of gastric secretion in detail
The gastric phase is a period in which swallowed food and semi-digested protein ( peptides and amino acids ) activate gastric activity. About two-thirds of gastric secretion occurs during this phase. Ingested food stimulates gastric activity in two ways: by stretching the stomach and by raising the pH of its contents.
Describe the functions of : hydrochloric acid, pepsin, rennin, ghrelin, and gastrin in stomach physiology
The hydrochloric acid in the gastric juice breaks down the food and the digestive enzymes split up the proteins. The acidic gastric juice also kills bacteria. The mucus covers the stomach wall with a protective coating. Pepsin is an endopeptidase that breaks down proteins into smaller peptides. It is produced in the chief cells of the stomach lining and is one of the main digestive enzymes in the digestive systems of humans and many other animals, where it helps digest the proteins in food. Chymosin, known also as rennin, is a proteolytic enzyme related to pepsin that synthesized by chief cells in the stomach of some animals. Its role in digestion is to curdle or coagulate milk in the stomach, a process of considerable importance in the very young animal. Ghrelin is a multifaceted gut hormone which activates its receptor, growth hormone secretagogue receptor (GHS-R). Ghrelin's hallmark functions are its stimulatory effects on food intake, fat deposition and growth hormone release. Ghrelin is famously known as the "hunger hormone". Gastrin is a peptide hormone primarily responsible for enhancing gastric mucosal growth, gastric motility, and secretion of hydrochloric acid (HCl) into the stomach. It is present in the G cells of the gastric antrum and duodenum
Explain the purpose of the mesenteries
The mesentery attaches the intestines to the abdominal wall, and also helps storing the fat and allows the blood and lymph vessels, as well as the nerves, to supply the intestines.
Describe the anatomical features of the mouth including the teeth
The mouth is an oval-shaped cavity inside the skull. The two main functions of the mouth are eating and speaking. Parts of the mouth include the lips, vestibule, mouth cavity, gums, teeth, hard and soft palate, tongue and salivary glands
Explain the three main functions of the mouth
The mouths three main functions are to bite, chew, and swallow.
Describe the three components of the mucosal layer of the alimentary canal
The mucosa is the innermost layer of the GI tract. It is made up of three layers: the epithelium, lamina propria, and muscularis mucosae. The mucosa surrounds the lumen, or open space within the digestive tube. This layer comes in direct contact with digested food (chyme).
Describe the composition of the muscularis externa. How is the smooth muscle regualted?
The muscularis externa consists of an inner circular layer and a longitudinal outer muscular layer. It should not be confused with a thin layer of muscle known as the muscularis mucosa, which lies within the submucosa, a layer of tissue adjacent to the muscularis externa.
Explain how the composition of a mean (high fat, high protein, high carb) affects stomach emptying
The rate of gastric emptying is known to have an influence in the feeling of fullness and satiety, and therefore it has been suggested to be linked with obesity. ... Their results suggest that faster gastric emptying and lower postprandial volume are typical of obese patients
Describe the location of the salivary glands
The salivary glands are found in and around the mouth and throat, and front and beneath the ear.
Describe the anatomical features of the stomach
The stomach has four major regions: the cardia, fundus, body, and pylorus. The addition of an inner oblique smooth muscle layer gives the muscularis the ability to vigorously churn and mix food. The convex lateral surface of the stomach is called the greater curvature; the concave medial border is the lesser curvature.
What are the three main functions of the stomach
The stomach's three main functions are: temporary storage for food, mixing and breaking down of food, and digestion of food.
Describe the components and the function of the submucosal layer of the alimentary canal
The submucosa consists of a dense irregular layer of connective tissue with large blood vessels, lymphatics, and nerves that branch into the mucosa and muscularis externa. It contains Meissner's plexus, an enteric nervous plexus, situated on the inner surface of the muscularis externa. The submucosa is a connective tissue layer deep to and supporting the mucosa. Examples: The substance of the submucosa is ordinary loose connective tissue. It allows the mucosa to move flexibly during peristalsis
Describe the role of the Vagus nerve in digestion
The vagus nerve is responsible for the regulation of internal organ functions, such as digestion, heart rate, and respiratory rate, as well as vasomotor activity, and certain reflex actions, such as coughing, sneezing, swallowing, and vomiting.
Differentiate between water soluble and fat soluble vitamins
Water soluble: polar molecules, most water soluble are absorbed in small intestine Fat soluble: lipid bases, nonpolar, packed into micells with fats and other lipids and are absorbed with them
What is the composition and function of bile
a yellow green liquid that contains multiple components, emulsifies fat in the small intestine, breaking it down into fatty acids and glycerols for absorption
What is the function of villi and plicae circulares (circular folds) in the jejunum
absorption
Describe how nucleic acid digestion occurs
acids are digested in the small intestine with help of pancreatic enzymes called nucleases
Explain how fat is digested and absorbed in the small intestine
are emulsified by bile
Describe the anatomy of the duodenum
begins at pyloric sphincter; shortest of 3 divisions, only 25 cm long
Describe how lipid digestion occurs
begins in mouth with small amounts of lipase then lipids are broken apart by stomach churning and broken down by gastric lipase, then lipids enter small intestine and are emulsified by bile salts
Describe how carbohydrate digestion occurs
begins in the mouth via salivary amylase then chemical digestion resumes in small intestine via pancreatic amylase
Describe how protein digestion occurs
begins in the stomach, encounter enzymes like pepsin and rennin then hydrolysis of proteins is completed in SI with enzymes from the pancreas and additional peptidases
How does blood move through the hepatic portal circulation
capillaries of villi, superior mesenteric vein, hepatic portal vein, sinusoids of lobules, central vein of lobules, hepatic vein, IVC, and right atrium
Explain the role of the portal triad in the liver function
carries bile
What are enterocytes? What are their function?
cells of the small intestine; produce multiple digestive enzymes, hormones, and mucus
Describe the composition of intestinal juices produced by the small intestine
clear to pale yellow, watery secretion composed of hormones
Explain why increasing surface area within the small intestine is beneficial? What 3 structural increase surface area?
folds increase surface area available for absorption about 400 to 600 times. Circular folds, villus, microvillus
Describe how blood and bile move through a portal triad
hepatic sinusoids; blood flows slowly through sinusoids as materials are exchanged between blood and hepatocytes. Bile flows through liver loves in opposite direction, from hepatocytes into tiny ducts
Describe the composition and function of an intestinal crypt
houses glands with both enteroendocrine cells and mucus secreting goblet cells
What is the function of the appendix
houses multiple lymphatic nodules and plays a role in immune system
Describe the anatomy of the liver
located in the right upper quadrant just inferior to diaphragm surface
Describe the anatomy of the jejunum
middle, begins at duodenojejunal flexure and sits within peritoneal cavity, about 7.5 ft in length
What is the function of a lacteal?
nutrient absorption
How do nutrients move from the lumen of the small intestine into the blood/lymph
nutrients travel across the mucosal layer into the villi then enter the capillaries and lacteals and are carried to the liver by the blood and lymph
Differentiate between enzyme rich pancreatic juice and bicarbonate rich pancreatic juice
pancreatic juice: aids in digestion of foods, triggered for release when fats and proteins hit duodenum due to secretion of CCK produced in response to secretin, pH 8.4, neutralizes acidic stomach chyme. raises pH close to neutral
Differentiate between peristalsis and segmentation
peristalsis: alternating contractions of longitudinal and circular layers of smooth muscle in muscularis externa. Segmentation: contraction of only circular layer of smooth muscle, produces a squeezing motion
What are the functions of Brunner's glands?
produce alkaline mucus to protect duodenum from acidic chyme
What is the function of Peyer's patches
protects SI from bacteria living in the LI
Describe the role of the bacteria within the large intestine
releases 500 mL of gases/day and metabolize some remaining nutrients into vitamins B12 and K
Describe the anatomy of the large intestine
runs along border of abdominal cavity, surrounding small intestine and other abdominal organs like a frame; 5 ft long, larger in diameter than small intestine, receives material from small intestine that was not digested or absorbed and is a passageway for feces to exit body, 3 unique features: teniae coli, haustra and epiploic appendages
Describe the roles of secretin and CCK in digestion
secretin: released by duodenum, delivered via blood stream to promote the pancreas to release bicarbonate rich pancreatic juice and the liver to release bile CCK: released by duodenum in response to fats and proteins coming from pylorus; delivered via blood stream to promote the pancreas to release enzyme rich pancreatic juice and the gallbladder to contract and release bile
What are the four main processes that occur in the small intestine
secretion, digestion, absorption, and propulsion
Differentiate between segmentation and mass movements
segmentation: circular muscle of each hastrum contracts repeatedly, aids in water and electrolyte absorption primarily controlled by local neurons of ENS mass movement: multiple haustra undergo peristalsis, movement occurs 3-4 times a day, appears to be triggered by food consumption
Describe the anatomy of the ileum
small intestines final segment, measures 10.8 ft in length, terminates at portions of large intestine called cecum
Describe the anatomy of the gallbladder
small sac that sits on posterior liver
What role does the gallbladder play in digestion
stores bile, concentrates it and releases it when stimulated
Describe the main functions of the liver
stores glycogen and fat soluble vitamins, uses amino acids to produce plasma proteins like albumin to maintain BOP, detoxification of substances like ammonia, alcohol, drugs and lactic acid, breaks down bilirubin as its a waste to produce heme created when RBC's are broken down
Describe the defection reflex
stretch receptors transmit sensation of rectal distention to spinal cord
Describe the anatomy of the pancreas
triangular gland with both endocrine and exocrine functions, posterior to stomach
How are most nutrients absorbed in the small intestine
via active transport
What are feces made of
water, mucus, bacteria, undigested food (cellulose) bile pigments, salts, and epithelial cells