Lecture 8: Digestive Physiology #2 (small intestine - rectum) Flashcards
What are the main hormones of digestion?
Ghrelin, gastrin, secretin, and cholecystokinin (CCK)
Describe the function of the hormone “ghrelin”
It is made in the stomach and increases appetite by signaling the brain
Describe the function of the hormone “gastrin”
It is made in the stomach due to stretch and stimulates the stomach
Describe the function of the hormone “secretin”
It is made in the duodenum and stimulates the pancreas/gallbladder, it slows the stomach’s functions
Describe the function of the hormone “cholecystokinin” (CCK)
It is made in the duodenum and reduces the appetite, slows stomach, and stimulates the release of bile
What do the liver, gallbladder, and pancreas do?
They all release important secretions into the small intestine to continue digestion
What are some functions of the liver?
Bile production/secretion, secretion of bilirubin, cholesterol, and hormones, metabolism of fats, proteins, carbs, activate enzymes, store glycogen, vitamins, and minerals, synthesize plasma proteins (albumin, clotting factors), blood detoxification & purification
What is bile? Where is it stored?
Bile is yellow-green in color and alkaline (basic). It is secreted from the liver and stored in the gallbladder.
What does bile contain?
Bile salts, bilirubin, cholesterol, neutral fats, phospholipids & electrolytes
What are bile salts?
Bile salts are cholesterol derivatives that function in fat emulsification & absorption
What is bilirubin?
It is a pigment that is formed from heme
What is the gallbladder? What does it do?
The gallbladder is a thin walled, muscular sac on the ventral surface of the liver. It stores & concentrates bile (absorbs its water & ions).
Where does bile go from the gallbladder?
The bile is released via cystic duct, which flows into the bile duct which flows into the small intestine
What is the endrocrine function of the pancreas?
Pancreatic islets secrete insulin & glucagon to regulate blood glucose
What is the exocrine function of the pancreas?
Acini (clusters of secretory cells) secrete pancreatic juice. Zymogen granules of secretory cells contain zymogens and active digestive enzymes
What are pancreatic acini?
Digestive enzymes + bicarbonate rich fluid. Includes proteases (as zygomens), pancreatic amylase, lipases & nucleases
What are pancreatic acini stimulated by?
Cholecystokinin, VIP, secretin, and Ach
What are zygomens?
Inactive forms of enzymes
What are some examples of pancreatic proteases?
Trypsinogen, chymotrypsinogen, and procarboxypeptidase
What is trypsinogen activated by?
Enterokinase/enteropeptidase in the duodenum
What are the pancreatic enzymes secreted in active form?
a-amylase, lipases, nucleases
What does secretin released from the duodenum in response to acidic chyme do?
It stimulates all ducts to secrete bicarbonate
What does CCK released from the duodenum in response to arrival of acid & fat do?
It stimulates contraction of the gallbladder and secretion of pancreatic enzymes
What is the duodenum?
The duodenum curves around the pancreas. It receives stomach contents, pancreatic juice, and bile. It also neutralizes stomach acids, emulsifies fats, pepsin is inactivated by a pH increase and houses pancreatic enzymes
What are the parts of the small intestine?
The duodenum, jejunum, and ileum
What is the jejunum?
A portion of the small intestine with large tall circular folds and thick muscular walls. Most digestion and nutrient absorption happens here
What is the ileum?
Contains peyers patches which aid in immune function. It is the last part of the small intestine and ends at the ileocecal junction
What are plicae circulares?
Deep circular folds of mucosa and submucosa
What are villi?
They are fingerlike extensions of mucosa that are absorptive cells (enterocytes)
What are microvilli?
Microvilli are tiny projections of absorptive mucosal cells’ plasma membranes (“brush border”
What amylase completes digestion of polysaccharides?
Pancreatic amylase
What kind of proteins absorb glucose & galactose?
Sodium-glucose transport proteins (SGLT)
What are these SGLT proteins powered by?
Na/K-ATPase
How are carbohydrates absorbed?
They are pulled through the cell & diffused into interstitial space where they flow into blood and then into the liver
What pancreatic enzymes aid in digestion of proteins?
Trypsin, chymotrypsin, and carboxypeptidase
What brush border enzymes aid in digestion of proteins?
Aminopeptides, carboxy peptidases, and dipeptidases
What kind of digestion happens in the mouth?
Mechanical digestion (chewing)
What kind of digestion happens in the stomach?
Denaturation (HCl) and enzymatic digestion (pepsin)
What kind of digestion happens in the small intestine?
Enzymatic digestion (chymotrypsin, trypsin, and proteases) and absorption of amino acids, di-peptides, and tri-peptides
What are proteins absorbed by in protein absorption?
They are absorbed by transport proteins
What causes emulsifications of fats?
Bile
What breaks down triglycerides? What do they turn into?
Pancreatic lipase breaks down triglycerides into monoglyceride & fatty acids
What are monoglycerides?
They are micelles as well as bile salts, fatty acids, phospholipids, and cholesterol
How are fats absorbed?
Micelles are diffused through the plasma membrane and reformed into triglycerides. Then they are combined with proteins to cause chylomicrons and then they are exocytosed and enter lymphatic system.
What does the large intestine consist of?
The cecum, colon, rectum
Does digestion happen in the large intestine?
No, other than fermentation
Where is fecal matter created/stored?
In the large intestine
What parts of the large intestine create mucus?
Intestinal crypts or sunken glands
In most species, where is the largest concentration of microbes?
The large intestine
What are the two sphincters of the anus?
The internal anal sphincter (smooth muscle) and the external anal sphincter (skeletal muscle)
What do parasympathetic signals do in defecation?
They contract the colon & rectum and relax the internal anal sphincter to allow defecation
