Part 4.6: Digestion Flashcards
Hepatic portal vein containing blood from the gut flows across the sinusoids and then the ___ __
central vein.
hepatocytes dump bile into the ___ ___
bile canalculi
components of bile
bile salts, cholesterol, lecithin
purpose of bile
assists in fat digestion by emulsifying larger fat droplets in aqueous environment of duodenum. emulsifying larger fat droplets into smaller micells increases surface area for lipase.
bile salts have a ____ soluble end and a ____ soluble head. Outline the general structure of a bile salt.
bile salts have a LIPID soluble end and a WATER soluble head.
_____ breaks up triglycerides into monoglycrerides and hydrophobic fatty acids, but they still need to be absorbed. Normally, they would float on top of aqueous chyme. How does bile prevent this?
bile helps to form MICELLES, which are a milion times smaller than emulsified fat droplets that have a water solbule surface but a LIPID SOLUBLE CORE. allows the fat to be absorbed. also allows some fat soluble vitamins to be absorbed too.
opening of the bile duct into the duodenum is controlled by the ___ ___ ___, and is stored in the ____ until this opens.
controlled by SPHINCTER OF ODDI, and is stored in the gall bladder.
___ released by duodenum stimulates contraction of ___ ___ and relaxation of the sphincter of ____ for bile release
CCK released by duodenum stimulates contraction of GALL BLADDER and relaxation of the sphincter of ODDI for bile release
how are bile salts retained in the body?
via enterohepatic circulation that starts in the terminal ileum. we have special transporters of bile salts back into blood in the terminal ileum, then back into hepatic portal system. Only about 5% is lost in feces.
bilirubin is derived from:
Purpose of bilirubin?
the breakdown of old red blood cells. aids in the ultimate produce of heme removal pathway. bilirubin is created by old heme by KUPFER cells.
liver necrosis or blockage of liver ducts resulting in the inability to get rid of bilirubin leads to
Jaundice. production of bilirubin is faster than it can be removed. Causes yellow color of skin and white of the eyes. normally, bilirubin moves through the sinusoids of the liver gest excreted in the urine.
4 layers to the wall of the digestive tract
1) mucosa (epithelial lining, lamina propria, muscularis mucosa) 2) submucosa 3) muscularis externa 4) serosa. + the mesentary holding things together
3 layers of the mucosa and what are their purposes?
1) mucous membrane. protective layer with sites for secretion and absorption. endocrine cells and epithelial cells. - endocrine: signalling cells -epithelial cells: typically used for absorption
2) lamina propria - connective tissue with blood vessels, lymph vessels, nerve fibers. - GALT to protect against bacteria (immune system)
3) muscularis mucosa. outer layer of smooth muscle. helps to move fat a little bit, but isn’t respondible for peristalsis.
the submucosa is made of ___ ___. Purpose of the submucosa
connective tissue. allows the intestine to be distensible and elastic.
how many layers in the muscularis externa?
2 layers of smooth muscle. - inner circular, outer longitudinal.
purpose of the serosa
connective tissue covering the digestive tract. secretes watery fluid which lubricates organs and surrounding viscera.
mesentery purpose
holds up the digestive tract like a sling. Attaches it to the peritoneum
adaptations for increasing surface area (3) for absorption
1) folding of the mucosal surface (plicae circulares)
2) microscopic villi project into the lumen
3) microvilli that project from the villi. also called the brush boarder.
how are villi dynamic in a python?
villi are dynamic because their epithelial cells can increase rate of digestion. the dynamic villi allows the intestine to increase in size. energy cost to the python= 1/2 of the energetic value of the meal just to maintain the cells.
the brushborder purpose
1) houses carriers for specific nutrients and electrolytes
2)digestive enzymes are associated ON the brushborder to complete last minute protein and carbohydrate digestion.
components of villi structure. purpose of the central lacteal?
1) capillary network 2) lymphatic vessel called CENTRAL LACTEAL, which occupies the center of the villus core. It’s important for dealing with intestinal bacteria
purpose of central lacteal in villi
important for dealing with intestinal bacteria.
after nutients get absorbed by the villi, they flow into the ____ fluid
interstitial
T/F small intestine undergoes peristalsis.
false, they undergo segmentation contraction that is much slower than peristalsis. one segment contracts while adjacent segments relax. digesta moves in both directions out of the area of contraction. improves mixing of bile and food.
how is segmentation contraction controlled?
pacesetter cells.
if segmentation contraction moves digesta back and forth, how can it move to the end of the intestine?
because segments don’t all contract at the same rate. duodenum muscularis contracts more frequently because duodenal pacesetter cells depolarize ore easily. 12 per minute in duodenum vs 9 in the ileum. ensures slow motility, thorough mixing etc.
3 factors that influence segmentation contractions
1) distention or stretching
2) gastrin
3) extrinsic autonomic input.
duodenum motility is initiated by digesta in the gut after feeding.
after digestion, segmentation contraction turns into peristalsis. why?
in order to “clean out” your intestines.
ileocecal valve. function
junction between small and large intestine. ensures one way flow of digesta. a one way valve that can be pushed open from the ileum but not from the colon. remains mildly constricted most of the time to prevent colonic bacteria from entering small intestine
gastrin ____ the ileocecal valve, and ____ the stomach
relaxes, and causes the stomach be more active
there is some digestion occuring in the small intestine. where do these enzymes come from
pancreas
what non-digestive secretion gets put out by the small intestine? Purpose of this secretion?
succus entericus. no digestive enzymes, but watery portion helps with hydrolysis.
there are some digestive enzymes produed by he small intestine itself but the enzymes remain bound in the wall, so techincally all the digestive enzymes in the lumen of the small intestine are from the pancreas
crypt of lieberkuhn function
pits where cell division is going on to make new villi epithelial cells. cells migrate up the villi and push cells off the tips. 100 million cells are shed. 3-day turnover of entire epithelium in the small intestine.
also secretes succus entericus (mucousy salt water to aid in hydrolysis)
functional unit of the liver.
lobule: a hexagonal sub unit with many hepatocytes arranged around a central vein.
components of the hepatic portal system
1) branch of hepatic artery
2) branch of hepatic PORTAL vein
3) bile duct.
____ are expanded capillary spaces around hepatocytes
SINUSOIDS.
blood from the central vein flows into the ___ ___, which moves to the inferior vena cava
HEPATIC VEIN
cells found in the capillaries (sinusoids) of the liver
1) kupfer cells
2) ito cells
what is enterohepatic circulation
most bile salts are reabsorbed back into the blood by special active-transport mechanisms located in the mammalian terminal ileum. From here the bile salts are returned via the hepatic portal system to the liver, which resecretes them into the bile. This recycling of bile salts (and some of the other biliary constituents) between the small intestine and liver is referred to as the en- terohepatic circulation.
absorption of nutrients in the small intestines occurs across the ___ ___
epithelial cells
