Homeostasis

Question 1

Definition of homeostasis?

Answer 1

the maintenance of an internal environment in an organism, within restricted limits

Question 2

What is negative feedback?

Answer 2

occurs when the stimulus causes the corrective measures to be turned off, returning the system to original levels

Question 3

Mechanism of the 2nd messenger model

Answer 3

adrenaline binds to a transmembrane protein receptor in liver cell membrane, causing the protein to change shape on the inside of the membrane
change in shape activates adenyl cyclase which converts ATP to cyclic AMP
cAMP is a 2nd messenger that binds to protein kinase, activating it.
protein kinase converts glycogen to glucose

Question 4

What is glycogenesis

Answer 4

conversion of glucose into glycogen

Question 5

what is glycogenolysis?

Answer 5

breakdown of glycogen to glucose

Question 6

What is gluconeogenesis

Answer 6

production of glucose from sources other than carbohydrates

Question 7

How does insulin decrease blood glucose?

Answer 7

b-cells of the pancreas detect the rise in blood gluc.
insulin is secreted and binds with glycoprotein receptors, causing:
-a change in the tertiary structure of glucose channels, and increasing the number of carrier proteins
- activating enzymes that convert glucose to glycogen

Question 8

How does glucagon increase blood glucose?

Answer 8

a-cells of the pancreas detect the fall in blood gluc.
Glucagon is secreted into blood plasma
glucagon attaches to protein receptors on membrane of liver cells
activates enzymes that convert glycogen to glucose
activates gluconeogenesis

Question 9

Formation of glomerular filtrate by ultrafiltration

Answer 9

there is a high hydrostatic pressure due to afferent arteriole being larger than the efferent arteriole
small molecules pass into the renal capsule as glomerular filtrate
large molecules remain in the blood

Question 10

Explain selective reabsorption of glucose and water by the proximal convulated tubule

Answer 10

the cells lining the PCT actively transport Na+ into the capillaries
Na+ moves into cells through carrier proteins (Fac dif)
carrier proteins also carry glucose into cells by co-transport

Question 11

Maintaining the gradient of Na+ in the medulla by the loop of henle

Answer 11

• Na+ actively transported out of ascending limb
• low water potential in interstitial space
• water passes out of descending limb as walls are permeable to water
• collecting duct is permeable to water so water passes out by osmosis

Question 12

How does the body respond to a fall in water potential?

Answer 12

• osmoreceptors in the hypothalamus detect the fall in water potential and shrink, causing the hypothalamus to produce ADH
• ADH passes into pituitary and then into the blood
• in the kidney, ADH increases permeability to water of the cell surface membranes
• ADH increases permeability of collecting duct to urea so it passes out, decreasing water potential of interstitial space so water also passes out.

Question 13

How does the body respond to a rise in water potential?

Answer 13

• osmoreceptors in the hypothalamus detect the rise in water potential and increase frequency of impulses to the pituitary gland to reduce release of ADH
• less ADH, via the blood leads to a decrease in permeability of collecting ducts to urea and water
  less water is reabsorbed and urine is more dilute