Lecture 42 11/28/23

Question 1

What are the characteristics of absorption?

Answer 1

-process of moving digested nutrients/water/ions across intestinal mucosa and into bloodstream
-requires transporters for most substances

Question 2

Which molecules are transported via co-transport with sodium?

Answer 2

-glucose
-amino acids
-vitamins
-bile acids

Question 3

What allows for basal-lateral facilitated diffusion of glucose?

Answer 3

high glucose conc. within the cell

Question 4

What are the two types of passive transport?

Answer 4

-transcellular through ion channels
-paracellular through tight junctions

Question 5

What are the major ions absorbed?

Answer 5

-sodium
-bicarbonate
-potassium
-chloride

Question 6

What are the mechanisms of sodium absorption?

Answer 6

-co-transport with proteins via secondary active transport
-Na+/H+ exchanger
-simple diffusion through ion channels

Question 7

What are the characteristics of the Na+/H+ exchanger?

Answer 7

-high H+ drives Na+ exchange
-occurs at the same time as HCO3-/Cl- exchange
-occurs in ileum and colon

Question 8

What are the mechanisms of chloride absorption?

Answer 8

-HCO3-/Cl- exchange coupled with Na+ transport
-paracellular absorption coupled with sodium co-transport
-direct HCO3-/Cl- exchange without Na+ transport

Question 9

What are the products of the sodium bicarb. and HCl reaction?

Answer 9

-NaCl
-water
-CO2

Question 10

What are the steps of bicarbonate absorption?

Answer 10

-H+ and HCO3- are formed in the cell
-H+ is neutralized in the lumen with HCO3-
-Na+ charge balances HCO3- in cell
-Na+ and HCO3- absorbed into bloodstream

Question 11

What are the characteristics of potassium absorption?

Answer 11

-potassium conc. is often higher than sodium conc.
-as water and other solutes are absorbed, K+ conc. increases
-conc. gradient forms, favoring absorption
-paracellular
-coupled with water absorption
-some active reabsorption in distal colon

Question 12

Where does sodium co-transport primarily occur?

Answer 12

duodenum and upper jejunum

Question 13

Where does chloride-coupled sodium absorption primarily occur?

Answer 13

ileum and colon

Question 14

Where does HCO3-/Cl- exchange occur?

Answer 14

ileum and colon

Question 15

Where does bicarbonate absorption occur?

Answer 15

ileum and colon

Question 16

Where does potassium absorption occur?

Answer 16

ileum and colon

Question 17

What are the characteristics of water absorption?

Answer 17

-passive through osmosis
-can be transcellular through aquaporins
-can be paracellular through tight junctions

Question 18

What are the basic characteristics of cobalamin?

Answer 18

-central cobalt atom
-synthesized by microbes
-meat-containing diets provide sufficient amounts

Question 19

What are the characteristics of R-protein/Haptacorrin?

Answer 19

-produced in saliva or gastric juice
-binds to cobalamin in stomach to prevent degradation
-released from B12 in duodenum by pancreatic enzymes

Question 20

What are the characteristics of vitamin B12 absorption?

Answer 20

-R-protein transfers cobalamin to intrinsic factor in duodenum
-ileum is major site of absorption
-transported systemically with transcobalamin

Question 21

What is the main function of cobalamin?

Answer 21

function in coenzymes

Question 22

What are the characteristics of cobalamin deficiency?

Answer 22

-bacterial overgrowth leads to decreases in absorption
-main symptoms are megaloblastic anemia, weight loss, diarrhea, and vomiting