Homeostasis

Question 1

negative feedback loop when you skip lunch:

Answer 1

• blood glucose concentration decreases
• detected by alpha cells of islets of langerhan (in pancreas)
• glucagon secreted into blood
• only binfs to complimentary receptors on target cells
• in liver cells (2nd msngr model) activates enzymes that convert glycogen to glucose
• and other enzymes convert fatty acids -> amino acids
• blood sugar increases back to normal

Question 2

negative feedback when you eat too many chocolates

Answer 2

• blood glucose conc. increases
• detected by bbeta cells of islets of langerhan (in pancreas)
• insulin secreted into blood
• binds to receptors on target cells
• vesicles w/ glucose channel proteins fuse w the CSM making them more permeable to glucose
• more glucose absorbed into cells by FD
• in all cells (esp. muscle) increased rate of resp
• IN LIVER CELLS insulin activates enzymes glucose -> glycogen
• IN ADIPOSE (fat) CELLS activates enzymes glycose -> 3G
• blood sugar conc. decreases

Question 3

gluconeogenesis meaning

Answer 3

production of glucose via fatty acids and amino acids
* activates enzymes
* producing glucose from fatty acids / amino acids

Question 4

how does conversion of glucose to glycogen lead to further reduction of blood glucose concentration? (4)

Answer 4

S: glucose converted to glycogen
* glucose conc. in cell falls
* conc. higher in blood
* creates glucose conc. gradient
* glucose enters cell from blood by FD

E: amount of glucose in blood decreases further

NOT +ve feedback loop; glucose conc is ALWAYS negative; not abt hormones

Question 5

explain how urea is concentrated in the filtrate (4)

Answer 5

S: low conc of urea in filtrate
* active transport of ions creates conc. gradient
so low WP in interstitial fluid so water moves down conc. gradient out of PCT
* water reabsorbed
* by osmosis at the PCT / descending LoH
* and the DCT / collecting duct

E: urea is at high conc.

Question 6

where are osmoreceptors found

Answer 6

hypothalamus

Question 7

what is ADH

Answer 7

hormone produced in the hypothalamus and stored in posterior pituitary gland
PPG releases ADH into blood when stimulated to do so by osmoreceptors in hypothalamus

Question 8

How does ADH reduce urine production

Answer 8

• makes cells more permeable to water
• by increasing number of aquaporins in CSM

Question 9

Process that occurs when you are dehydrated (blood WP low)

Answer 9

• water potential in blood is low
• detected by osmoreceptors in hypothalamus
• water moves out of osmoreceptors so they shrink
• so it sends a higher frequency of impulses to pituitary gland
• so PPG releases MORE ADH which travels in blood
• ADH binds to receptors on DCT and collecting duct
• causes vesicles containing aquaporins to fuse w CSM
• more aquaporins embedded increasing cell permeability to water
• more water reabsorbed from collecting duct to blood by osmosis
• thr4 LOWER volume of MORE conc urine produced

Question 10

what is homeostasis

Answer 10

maintaining a constant internal environment

Question 11

Describe how ultrafiltration produces glomerular filtrate (5)

Answer 11

• hydrostatic pressure created at glomerulus
• h2o and other small molecules forced out thru fenestrations
• pass thru basement layer; acts as filter
• proteins too large to go thru so stay behind
• go past podocytes on capillaries

Question 12

explain how a lack of insulin affects reabsorbtion of glucose in the kidneys of a person who does not secrete insulin (5)

Answer 12

• high concentration of glucose in blood
• high concentration in filtrate
• reabsorbed by FD
• requires proteins
• these are working at maximum rate
• not all glucose is reabsorbed