Part 4.7 Digestion

Question 1

hepatocytes aggregate into ___

Answer 1

lobules.

Question 2

functional unit of liver

Answer 2

hepatic lobules.

Question 3

T/F Digestion occurs in small intestine

Answer 3

true. tripsogen secretion from pancreas is responsible for short chain polypeptide breakdown

Question 4

the ____ of _____ secrete the succus entericus, and is the nusery site for new epithelial cells of the small intestine

Answer 4

crypts of lieberkuhn. they make cells via mitosis and they crawl up the villi pole

Question 5

enzymes from the ____ do most of the digestion in the lumen of the small intestine

Answer 5

enzymes from the pancreas. small intestine duodenum also secrete things but they are mainly alklaine solution (brunner glands) or secretion of water (for hydrolysis) and mucus. others include enterokinases that are locked within the small intestinal wall and are not secreted into the lumen

Question 6

fats need to be in the form of ____ in order to be absorbed

Answer 6

micelles

Question 7

purpose of brush border enzymes. examples?

Answer 7

enzymes of the small intestine that are secreted by the small intestine but do not leave the wall.

1) enterokinases: activates more pancreatic trypsinogen
2) disaccharidases: maltase, sucrase, lactase hydrolyse respective disaccharides 3) aminopeptidases. hydrolyse peptide fragments into aminoacids.

Question 8

T/F Brush border enzymes are species dependent

Answer 8

true. dependent on diet. ex/ birds do not have lactase disaccharidase because they do not drink milk. they do have an esterase which hydrolyse esters in ripening fruit.

Question 9

long term dietary changes can alter the length of intestines and density of transporter. and example of this is acclimatization response of omnivores to a high carb diet, what happens to the intestine?

Answer 9

there is an upregulation of glucose transporters in the brushboarder enzymes.

Question 10

T/F: types of transporters and size of intestine is closely matched to diets of species

Answer 10

true. for example, herbivores have a lot of carb transporters

Question 11

what is the small intestine reserve capacity?

Answer 11

small intestine portions can be lost and we can still absorb nutrients. Except for the ileum. if you remove the ileum, you need B12 supplementation.

Question 12

sodium is absorbed in the small intestine both ___ and ___

Answer 12

passively and actively.

Question 13

on the brushboarder of the lumen, there is a ____ for sodium, and drags along a product of digestion with it (is this passive or active). Outline the process of Na+ absorption

Answer 13

cotransporter for digesta and sodium. driven by chemical gradient. there are more nutrients and Na+ in the lumen, allowing the cotransporter to let Na+ into the cells. This portion is passive, because it follows the chemical gradient of the digesta

Question 14

once the epithelial cells contain sodium taken from the lumen, a ___-___ATPase pump sodium into the interstitial space and ultimately into the plasma.

Answer 14

once the epithelial cells contain sodium (via the brushboarder cotransporter), an Na+-K+ATPase pump sodium into the interstitial space and ultimately into the plasma.

Question 15

how is Na+ passively transportered? Actively?

Answer 15

Passively:

1) through leaky tight junctions 2) through Gi-Na+ cotransporter.

actively transported via Na+-K+ atpase.

Question 16

purpose for sodium active transport in the small intestine.

Answer 16

for water absorption. Na+ creates an OSMOTIC PRESSUE in the INTERSTITIAL FLUID so water is absorbed. 2) for cotransport of glucose and amino acids.

Question 17

ourline carb absorption in the small intestine

Answer 17

1) dissacharidases in brushborder break down disaccharides into monosaccharides
2) monosaccharides abssrobed via cotranport (with sodium)
3) Ms’s then enter the interstitial fluid and then the blood via CARRIER_MEDIATED DIFFUSION - or through leaky tight junctions.

Question 18

outline the process of protein absorption in the small intestine

Answer 18

1) exogenous and endogenous protein get broken down by pepsin (stomahc) and pancreatic enymes
2) aminopeptidases in brushborder of SI break things into AAs
3) AA and glc co transport process allow them to be aborbed into epithelium

**some intracellular peptidases break down any remaining peptides in the epithelial cell into AAs

4) carrier-mediated diffusion on basolateral membrane of the epithelial cell allows them to move into intersitium and capillaries.

Question 19

T/F endogenous proteins account for over 50% of daily protein absopriton

Answer 19

true. in addition to food, we digest ourselves. we have proteins from digestive enzymes that are reabsorbed, proteins from mucosal cells. and traces of plasma proteins that leak into the lumen. beneficial historically when we didn’t eat as much meat.

Question 20

purpose of intercellular peptidases

Answer 20

sometimes, larger polypeptide chains rather than single AAs enter the epithelial cell via the Na+-AA cotransporter. these intercellular peptidases break down any residual protein chains that were not broken down by the aminopeptidases on the brush border.

Question 21

oultine fat absorption in the small intestine

Answer 21

1) bile emulsifies fat into droplets for lipase
2) lipase forms micelles of monoglycerides and free fatty acids
3) micelles can enter brushborder cells via PASSIVE diffusion- they do not need cotransporters into epithelial cells because they are hydrophobic.
4) when in the epithelial cells, they are re-synthesized into triglycerides and packaged into CHYLOMICRONS.
5) chylomicrons leave the cell by exocytosis and enter the central lacteal (lymph vessels of mammals) or capillaries in birds

Question 22

when in the epithelial cells, FFA micelles are re-synthesized into triglycerides and packaged into ______

Answer 22

when in the epithelial cells, FFA micelles are re-synthesized into triglycerides and packaged into CHYLOMICRONS.

Question 23

what is a chylomicron

Answer 23

tryglyceride coated with water soluble lipoprotein

Question 24

chylomicrons leave the epithelial small intestine cell by exocytosis and enter the ____ ____ (of mammals) or capillaries in birds

Answer 24

CENTRAL LACTEAL. however, some free fatty acids sneak out of epithelial cell and end up in blood supply without being formed into a chylomicron or going into central lacteal

Question 25

where are bile salts reaborbed

Answer 25

in the ileum of the small intestine

Question 26

once the products of digestion (except for fat that is in the central lacteal) are in the plasma, where is this blood delivered? Why?

Answer 26

to the liver via the hepatic portal vein. digestive processing and detoxification before entering the vena cava and general circulation

Question 27

most fat (in the form of chylomicrons) do not go into the liver because they are part of the central lacteal of the villi and not in the blood vessels. What happens instead? Purpose of not going directly to the liver.

Answer 27

doesn’t go directly to the liver but enters the lymphatic system. some is taken by adipose cells before ever reaching the liver. eventually, some fat makes its way into the liver and are processed into LIPOPROTEINS. fat dilution via direct entry into adipocytes or by being retained in the lymphatic system avoids the liver from being overwhelmed with too much fat for it to process.

Question 28

3 purposes of large intestine

Answer 28

1) water reaborption
2) holding and propelling feces
3) symbiotic microbes for fermentation (in some species that rely on high-cellulose diets –> primarily done in the cecum)

Question 29

specialized portion of the cecum in humans for immune function

Answer 29

the veriform appendix.

Question 30

human colon is divided into three sections:

Answer 30

1) ascending 2) transverse 3) descending branch

Question 31

ileum connects to large intestine via _____ valve

Answer 31

ileocecal valve.

Question 32

omnivores and herbivores tend to have enlarged _____ for microbial digestion

Answer 32

enlarged colon/cecum for microbial digestion/fermentation because of their high-cellulose diets.

Question 33

Glucose and galactose are both absorbed by secondary active transport, in which symport carriers, such as the ___ –_____ cotransporter (SGLT) on the luminal membrane transport both of them from the lumen into the interior of the intestinal cell. Recall that the operation of these carriers, which do not directly use energy themselves, depends on the Na+ concen- tration gradient established by the energy-consuming baso- lateral Na+/K+ pump, which is pumping Na+ out of the cell, constantly keeping the ICF lower in Na+ than the lumen

Answer 33

Glucose and galactose are both absorbed by secondary active transport, in which symport carriers, such as the sodium–glucose cotransporter (SGLT; see Figure 14-25b) on the luminal membrane transport both the monosaccharide and Na+ from the lumen into the interior of the intestinal cell. Recall that the operation of these carriers, which do not directly use energy themselves, depends on the Na+ concen- tration gradient established by the energy-consuming baso- lateral Na+/K+ pump