Terms in this set (76)
What structural modification underlies the stomach's ability to mechanically digest food?
the stomach has an extra group of muscles called the oblique muscles that are responsible for the churning and mechanical digestion of food
What is the role of intrinsic factor?
intrinsic factor acts as a mediator that allows vitamin B12 to be absorbed since it doesn't have a receptor
What are the components of gastric juice?
gastric juice is made up of mucus, hydrochloric acid, and pepsinogen
Where is mucus secreted from?
mucous neck cells as mucin
Where is hydrochloric acid secreted from?
Where is pepsinogen secreted from?
How does the medulla oblongata respond to sensory input of food?
vagus nerve fibers from the medulla stimulate the enteric nervous system, which in turn stimulates gastric activity
How does ingested food stimulate gastric activity?
by stretching the stomach and by raising the pH of its contents
What chemical signals activate HCl secretion?
acetylcholine from the vagus nerves, histamine and gastrin from the enteroendocrine cells of the gastric glands.
What signals the chief cells to secrete pepsinogen?
acetylcholine and gastrin
What happens when chyme enters the duodenum?
- acid and semi-digested fats in the duodenum trigger inhibitory signals, sent to the stomach by way of the enteric nervous system
- signals from the duodenum to the medulla oblongata inhibit vagal nerve stimulation of the stomach and activate sympathetic neurons, which inhibit gastric activity
- duodenal enteroendocrine cells release the hormones secretin and CCK, which suppress gastric activity
What is the cumulative effect of the intestinal phase?
telling the stomach to slow down and give the duodenum time to process the chyme it already contains before sending more
What are the major functions of the liver?
bile production, nutrient conversion of amino acids for storage, synthesis of mainly plasma proteins, and defense and detoxification
What are the major exocrine products of the pancreas?
pancreatic juice- bicarbonate, proteolytic enzymes, lipases, nucleases, amylases
What hormones regulate secretion of bile?
CCK and secretin
What happens to bile salts after they assist in digestion and absorption?
transporters in the ileum bring them from lumen of digestive tract to intestinal capillaries, where they are transported to the liver via hepatic portal duct to be secreted again. ~ 5% lost in the feces
How is acidic chyme neutralized in the small intestine?
pancreatic juice neutralizes chyme due to its aqueous component, which is largely bicarbonate. the sodium bicarbonate in the juice gives it a slightly alkaline (basic) pH that buffers acidic juice in chyme, stops the action of pepsin from the stomach, and creates the proper pH for the action of digestive enzymes in the small intestine
What digests protein in the stomach?
pepsin and HCl
How are the monosaccharides absorbed?
glucose and galactose are absorbed via cotransport with sodium ions; fructose passes via facilitated diffusion
How are lipids absorbed?
enter intestinal cells via diffusion, then packed into chylomicrons to enter lacteals of the villi and are transported to systemic circulation via the lymph in the thoracic duct
What are 3 lines of defense against microorganisms that come with food?
- enzymes in saliva and bile help detoxify antigens and xenobiotics
- the low pH of the stomach is fatal for many microorganisms that enter it
- immunoglobulin A prevents attachment of microbes so they cannot penetrate the epithelium, and lysozyme kills bacteria
Why is the sodium/potassium pump required during nutrient absorption?
to produce energy that creates a gradient for amino acids and monosaccharides to enter the intestinal lumen
Does the enteric nervous system require input from the central nervous system?
How are cells in the stomach wall protected from proteolytic activity?
proteolytic pepsin enzyme is active only after being secreted to the lumen
Where does digestion start?
mouth- teeth break down food
What prevents stomach from tearing when it expands?
rugae- lots of folds means the folds just smooth out when the stomach stretches and nothing tears
Which type of tissue faces the lumen?
What causes peristalsis?
contraction and relaxation of longitudinal and circular muscles
What causes churning of food in stomach?
Why are epithelial cells not damaged by acidity?
What occurs in vomiting?
release of esophageal sphincter- soft palate closes connection between oropharynx and nasopharynx but that doesn't always work
Where is bile secreted from?
What is the benefit of the structure of the mucosal layer in the small intestine?
adds surface area so there is more effective digestion/absorption
What is the role of circular folds in the mucosa?
slows chyme down through the duodenum assuring complete digestion and absorption
What do villi do?
further increase surface area within circular folds
What is the epithelium of the mucosa made up of?
- absorptive cells
- goblet cells secreting mucus
- enteroendocrine cells secreting hormones
Why do you need tight connections between absorptive cells?
due to fenestrated capillaries there is almost no filtration, tight connections make sure no bad substances get into the blood
What is celiac's disease?
gluten not properly digested by pepsin, and since epithelial cells are leaky, some gluten peptides make it between cells. develop an autoimmune response to glucose- damage to intestines causing GI pain
What is the largest internal organ?
What is bile?
alkaline solution neutralizing acidic chyme in the duodenum
What is the role of bile salts?
assist in emulsifying fats in duodenum and in digestion and absorption of fat and cholesterol
What does the gall bladder do?
stores and concentrates bile by absorbing its water and ions
What could cause gall stones?
too much cholesterol or too few bile salts (both causing cholesterol crystallization)
What are the functions of the liver?
- bile production
- nutrient conversion
- defense and detoxification
What is hepatitis mainly caused by?
What is cirrhosis?
progressive chronic inflammation of the liver caused mainly by alcoholism and chronic hepatitis, replacement of hepatocytes by connective tissue
What is the function of secretin other than secreting more bile?
increases output of bicarbonate ions in pancreas
What is the function of CCK other than secreting more bile?
increases output of pancreatic juice
What is the stimulus for secretin release?
What is the stimulus for CCK release?
What is the duodenum structurally adapted for?
a role in absorption
What is mostly secreted in the duodenum?
What are the major sites of absorption?
duodenum and jejunum
What is the role the ileum?
recycling of bile salts
What breaks down proteins into large polypeptides?
pepsin in presence of HCl in the stomach
What breaks down large polypeptides into small polypeptides/peptides?
pancreatic enzymes in the small intestine
What breaks down peptides into amino acids?
brush border enzymes
How are amino acids stored?
converted to fat/glucose and stored as glycogen
What breaks down starch and disaccharides?
salivary amylase in the mouth and pancreatic amylase in the small intestine
What breaks down disaccharides into monosaccharides?
brush border enzymes
How do monosaccharides exit the epithelia?
What happens when we have too much fructose?
our liver fails, leads to diabetes because of too much simple sugar
What happens to unemulsified fats?
emulsified by the detergent action of bile salts in small intestine, further broken down by pancreatic lipase in small intestine
Is lipid/fatty acid absorption passive or active?
How are lipids transported in the blood?
What is the main component of chylomicrons?
How does the make up of VLDLs compare to that of chylomicrons?
still most triglycerides, but much more phospholipids and cholesterol
What is the main component of LDLs?
What is the main component HDLs?
If we eat more than our allotted food intake of cholesterol, what happens?
the body just makes less cholesterol to balance it out
How is cholesterol transported?
liver packs it into LDL and goes to cells that have receptors for LDLs
What happens with too much LDL?
stays on the blood vessel and causes inflammation
What do HDLs do?
collect extra cholesterol and bring it back to the liver to get broken down
Does digestion occur in the large intestine?
other than digestion of enteric bacteria, no
What occurs in the large intestine?
reabsorption of water, vitamins, electrolytes
What is the major function of the large intestine?
propulsion of fecal material toward anus?
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