Part 4.6: Digestion

Question 1

Hepatic portal vein containing blood from the gut flows across the sinusoids and then the ___ __

Answer 1

central vein.

Question 2

hepatocytes dump bile into the ___ ___

Answer 2

bile canalculi

Question 3

components of bile

Answer 3

bile salts, cholesterol, lecithin

Question 4

purpose of bile

Answer 4

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.

Question 5

bile salts have a ____ soluble end and a ____ soluble head. Outline the general structure of a bile salt.

Answer 5

bile salts have a LIPID soluble end and a WATER soluble head.

Question 6

_____ 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?

Answer 6

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.

Question 7

opening of the bile duct into the duodenum is controlled by the ___ ___ ___, and is stored in the ____ until this opens.

Answer 7

controlled by SPHINCTER OF ODDI, and is stored in the gall bladder.

Question 8

___ released by duodenum stimulates contraction of ___ ___ and relaxation of the sphincter of ____ for bile release

Answer 8

CCK released by duodenum stimulates contraction of GALL BLADDER and relaxation of the sphincter of ODDI for bile release

Question 9

how are bile salts retained in the body?

Answer 9

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.

Question 10

bilirubin is derived from:

Purpose of bilirubin?

Answer 10

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.

Question 11

liver necrosis or blockage of liver ducts resulting in the inability to get rid of bilirubin leads to

Answer 11

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.

Question 12

4 layers to the wall of the digestive tract

Answer 12

1) mucosa (epithelial lining, lamina propria, muscularis mucosa) 2) submucosa 3) muscularis externa 4) serosa. + the mesentary holding things together

Question 13

3 layers of the mucosa and what are their purposes?

Answer 13

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.

Question 14

the submucosa is made of ___ ___. Purpose of the submucosa

Answer 14

connective tissue. allows the intestine to be distensible and elastic.

Question 15

how many layers in the muscularis externa?

Answer 15

2 layers of smooth muscle. - inner circular, outer longitudinal.

Question 16

purpose of the serosa

Answer 16

connective tissue covering the digestive tract. secretes watery fluid which lubricates organs and surrounding viscera.

Question 17

mesentery purpose

Answer 17

holds up the digestive tract like a sling. Attaches it to the peritoneum

Question 18

adaptations for increasing surface area (3) for absorption

Answer 18

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.

Question 19

how are villi dynamic in a python?

Answer 19

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.

Question 20

the brushborder purpose

Answer 20

1) houses carriers for specific nutrients and electrolytes

2)digestive enzymes are associated ON the brushborder to complete last minute protein and carbohydrate digestion.

Question 21

components of villi structure. purpose of the central lacteal?

Answer 21

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

Question 22

purpose of central lacteal in villi

Answer 22

important for dealing with intestinal bacteria.

Question 23

after nutients get absorbed by the villi, they flow into the ____ fluid

Answer 23

interstitial

Question 24

T/F small intestine undergoes peristalsis.

Answer 24

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.

Question 25

how is segmentation contraction controlled?

Answer 25

pacesetter cells.

Question 26

if segmentation contraction moves digesta back and forth, how can it move to the end of the intestine?

Answer 26

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.

Question 27

3 factors that influence segmentation contractions

Answer 27

1) distention or stretching
2) gastrin
3) extrinsic autonomic input.

duodenum motility is initiated by digesta in the gut after feeding.

Question 28

after digestion, segmentation contraction turns into peristalsis. why?

Answer 28

in order to “clean out” your intestines.

Question 29

ileocecal valve. function

Answer 29

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

Question 30

gastrin ____ the ileocecal valve, and ____ the stomach

Answer 30

relaxes, and causes the stomach be more active

Question 31

there is some digestion occuring in the small intestine. where do these enzymes come from

Answer 31

pancreas

Question 32

what non-digestive secretion gets put out by the small intestine? Purpose of this secretion?

Answer 32

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

Question 33

crypt of lieberkuhn function

Answer 33

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)

Question 34

functional unit of the liver.

Answer 34

lobule: a hexagonal sub unit with many hepatocytes arranged around a central vein.

Question 35

components of the hepatic portal system

Answer 35

1) branch of hepatic artery
2) branch of hepatic PORTAL vein
3) bile duct.

Question 36

____ are expanded capillary spaces around hepatocytes

Answer 36

SINUSOIDS.

Question 37

blood from the central vein flows into the ___ ___, which moves to the inferior vena cava

Answer 37

HEPATIC VEIN

Question 38

cells found in the capillaries (sinusoids) of the liver

Answer 38

1) kupfer cells
2) ito cells

Question 40

what is enterohepatic circulation

Answer 40

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.

Question 41

absorption of nutrients in the small intestines occurs across the ___ ___

Answer 41

epithelial cells