25A
Describe the two processes of movement of chyme through the digestive tract.
Peristalsis - back-and-forth movement, rhythmic, squeeze and pull down
Segmentation - only in small intestine. Forward-and-backward movement, multiple contractions at once, pushes chyme against wall for contact digestion.
What is the primary role of the large intestines?
Extra question for anyone: How much time is spent in the large intestine?
Water and electrolyte absorption to concentrate fecal matter.
12-24 hrs.
What is the vital function of the stomach?
Secretes intrinsic factor, which facilitates vitamin B12 absorption in the small intestine.
What anatomical feature of the liver allows the entry and exit of the hepatic artery, hepatic portal vein, and common hepatic duct?
Porta hepatis
Where does the majority of nutrient absorption occur?
Jejunum
Describe the long and short intrinsic controls of the GI tract.
What type of muscle makes up the esophagus?
Upper 1/3 - skeletal mm
Middle 1/3 - mix of skeletal and smooth mm
Lower 1/3 - smooth mm
What is the unique anatomical feature of the stomach in regard to the four layers of the alimentary canal?
Contains a 3rd layer of smooth mm -- the oblique layer!
Extra question: what type of tissue is the stomach made of?
What is the function of the gallbladder?
Store, release, and concentrate bile.
Microvilli in the small intestine make up the brush border. Why is this border significant?
Contains brush border enzymes which are vital to final breakdowns of lipids, proteins, and carbs. This is where the contact digestion of segmentation occurs!
What does the myenteric plexus do and where is it located?
Located between layers of the muscularis externa. Inneravates muscularis externa. Generally takes care of motility.
What role does the appendix have?
Has no role -- is a nonvital part of the immune system. If it bursts, it lets in pathogens found in the large intestine into the peritoneal cavity.
What gland cells do you find in the stomach and what do they do?
Mucous neck cells - secrete acidic mucous
Chief cells - Secrete pepsinogen and enzymes
Parietal cells - secrete HCl and intrinsic factor
Enteroendocrine cells - secrete chemical messengers (histamine, gastrin, etc)
Stem cells
What are hepatocytes? What are their functions?
Hepatocytes - major functional cell of the liver.
Functions: synthesize bile, detoxification, and store glycogen, amino acids, and fat soluble vitamins
What cells do you find in the intestinal crypts? What do they do?
Enteroendocrine cells - release chemical messengers (secretin, CCK, etc)
T cells - intraepithelial lymphocytes
Paneth cells - release antimicrobial proteins
Stem cells
What does the submucosal plexus do and where is it located?
Located in the submucosa. Innervates the muscularis mucosae. Mostly deals with secretions.
What are enzymes found in saliva? What do they do?
Lingual lipase - digests lipids starting in stomach (only works with pH of 2)
Salivary amylase - digests starches beginning in the mouth
What does gastrin do?
Stimulates chief cells and parietal cells, causing an increase in HCl production and enzyme release.
What does pancreatic juice do? What pH does it function at?
Contains enzymes needed for all major molecule breakdown. Functions at pH at 8 so also contains A LOT of bicarbonate.
What keeps lipids from clumping? What are fats packaged with in order to be reabsorbed into lacteals?
Bile keeps lipids from clumping.
Fats (lipids) are packaged with proteins, also known as chylomicrons, to be reabsorbed into lacteals (which carry lymph)
Identify and describe the four layers of the alimentary canals.
Mucosa - secretes mucus, enzymes, and hormones; absorb nutrients; protect; has 3 layers: epithelium (strat squam or simp columnar), lamina propria (loose areolar CT w/ blood supply and MALT), muscularis mucosae (causes wrinkling)
Submucosa - loose areolar CT w/ blood, nerves, and lymphatic
Muscularis externa - smooth mm with a longitudinal layer and circular layer
Serorsa - visceral peritoneum
What is the process of deglutition?
Food bolus is pushed to the back of the throat with the tongue. During swallowing, the uvula flips up to cover the nasal pathways. The tongue touches the top of the mouth so food does not pass back through. Epiglottis flips down and covers the trachea. Downstream signaling alerts the lower esophageal sphincter that food is coming. Peristalsis starts, pushing the food bolus down the esophagus. The lower esophageal sphincter opens to admit the food into the stomach and closes tightly after.
How is hydrochloric acid secreted in the stomach?
Uses the formula H20 + CO2 -> H2CO3 -> HCO3- + H+
CO2 from blood combines with H2O in parietal cell forming H2CO3. This divides into a H+ ion which enters the lumen of the gastric gland, and HCO3- which leaves the cell through the Chloride shift. The chloride gained combines with the H+ ion, forming HCl.
Extra question: what does this cause in the blood?
What hormones regulate bile and pancreatic juice?
Secretin causes the release of bicarb and pancreatic juice.
Cholecystokinin causes gallbladder contraction in the presence of fatty chyme (releases bile).
What does bile do?
What cells are found in intestinal crypts? What do they do?
Enteroendocrine cells - release chemical messengers (secretin, CCK, etc)
T cells - intraepithelial lymphocytes (immune)
Paneth cells - release antimicrobial proteins
Stem cells