Lecture 17

Question 1

What is the space in between the cells?

Answer 1

Lateral intercellular (paracellular) space, only permeable via tight junctions for small uncharged molecules

Question 2

What are the two types of cell transport?

Answer 2

Transcellular and paracellular transport

Question 3

How can you calculate electrical resistance of an epithelial tissue?

Answer 3

Ohms law

Question 4

What does it mean for the number of tight junctions when theres a high electrical resistance?

Answer 4

Theres a high number of tight junction strands

Question 5

What are the classifications of epithelium?

Answer 5

Leaky epithelium, paracellular transport dominates AND tight epithelium, transcellular transport dominates

Question 6

What are the features the transport which occurs at the proximal end?

Answer 6

More leaky epithelium, this means lower electrical resistance and number of strands, more bulk transport, duodenum/proximal tubule

Question 7

What are the features of transport that occur at the distal end?

Answer 7

More tight epithelium, which means higher number of electrical resistance, higher number of strands and more hormonally controlled (transcellular), colon/collect duct

Question 8

What is special about the transport in the distal section of GI tract and kidney?

Answer 8

This last section is what your body can up or down regulate depending on what your body needs

Question 9

What is absorption

Answer 9

From lumen to blood, first entry step via the apical membrane

Question 10

what is secretion?

Answer 10

Blood to lumen, first entry step via the basolateral membrane

Question 11

What is needed in terms of the electrochemical gradient in transepithelial transport?

Answer 11

A gradient is needed, and this can be either passive or established actively

Question 12

What is needed in terms of electroneutrality for transepithelial transport?

Answer 12

A movement of an ion will cause an ion of the opposite charge to move along with it so that charge of the cell is maintained.

Question 13

What happens in terms of osmolarity in transepithelial transport?

Answer 13

the movement of ions will cause differences in osmolarity that causes water to move by osmosis

Question 14

What can be said about the speed of water transport?

Answer 14

Very fast, so fast that you can not measure an osmotic gradient

Question 15

What does the sodium glucose symporter do?

Answer 15

It uses energy of a Na gradient to actively accumulate glucose above its concentration gradient

Question 16

What is the function of GLUT

Answer 16

Mediates glucose exit across the basolateral membrane via passive diffusion

Question 17

What happens in glucose-galactose malabsorption syndrome?

Answer 17

A mutation to the glucose symporter in the small intestine means that sugar is retained in the intestine lumen, increasing the osmolarity , inducing water reflux and causing diarrhea.

Question 18

What is a treatment for glucose galactose malabsorption?

Answer 18

Removing glucose and galactose from the diet. Using fructose as a source of carbohydrates. (GLUT5 and GLUT2)

Question 19

What happens in the kidney?

Answer 19

It filters glucose in the plasma, needs to be reabsorbed.

Question 20

What does the NaK2Cl symporter do?

Answer 20

It uses the energy of the Na gradient to actively accumulate chloride above its electrochemical gradient

Question 21

What is the rate determining step of chloride secretion?

Answer 21

The Cl- channel (CFTR) which is strictly regulated

Question 22

What is secretory diarrhoea?

Answer 22

When there is excessive stimulation of secretory cells in the crypts of the small intestine and colon

Question 23

What causes this stimulation?

Answer 23

Abnormally high concentration of endogenous secretagogues produced by tumours or inflammation, or secretion of eneterotoxins from bacteria such as cholerae

Question 24

What is the function of enterotoxins?

Answer 24

They irreversibly activate adenylate cyclase causing maximal stimulation of the CFTR leading to a secretion that overwhelms the absorptive capacity of the colon.

Question 25

What is the life cycle of the small intestine cells

Answer 25

crypt cells (secretion of chloride ) are always undergoing renewal, then they get pushed to the villus (absorption of glucose ) then get lost into the lumen.

Question 26

How can secretory diarrhoea be treated?

Answer 26

Upregulate absorption by oral rehydration therapy, this will eventually cause patients to cure themselves as the lifecycle of infection takes 5 days.

Question 27

What organs do cystic fibrosis affect

Answer 27

Airways (clogging of bronchial passages), liver (clogs bile ducts), pancreas (damage to ducts, no secretion of pancreatic enzymes), small intestine (blocked colon), male reproductive tract (no ejaculation fluid) skin (salty sweat)

Question 28

What is a common theme in cystic fibrosis?

Answer 28

Involvement of epithelial tissues, usually die due to respiratory disease

Question 29

What are clinical managements of cystic fibrosis

Answer 29

Chest percussion to improve clearance, antibiotics, pancreatic enzyme replacement, attention to nutritional status, median survival is 38 years

Question 30

What is interesting about the chloride ion channel?

Answer 30

Secretagogue activates cAMP which activates protein kinase A which phosphorylates the R domain which sits in the pore of the channel. Only when phosphorylated, the channel can bind ATP which is used to open the channel.

Question 31

What is the pathology of cystic fibrosis for lungs?

Answer 31

The lung surface is dry due to enhanced Na+ absorption, isotonic fluid secretion is prevented

Question 32

Describe cystic fibrosis and sweat formation

Answer 32

Epithelial cells in the ducts of sweat glands don’t reabsorb NaCl causing salty sweat

Question 33

What is the pathology behind salty sweat in cystic fibrosis

Answer 33

As the membrane potential is depolarized, Cl- wants to go down its electrochemical gradient but cannot so it accumulates in the duct lumen