3.6 Homeostasis + control of water potential

Question 1

define homeostasis

Answer 1

physiological control systems that maintain the internal environment within restricted limits.

Question 2

what is the importance of a stable core temp

Answer 2

• enzymes work at optimum temp
• too low-> not enough Ek->fewer successful collisions
• too high->enzymes denature, H bonds in tertiary break->active site changes shape, no longer complementary to substrate->fewer successful collisions

Question 3

what is the importance of a stable blood pH

Answer 3

enzymes work at optimum pH
-too low/high-> enzymes denature, ionic bonds in tertiary structure break->active site changes shape->no longer complementary to substrate->fewer successful collisions

Question 4

too low blood conc

Answer 4

• not enough glucose for respiratio
• less ATP produced
• active transport cant happen

Question 5

too high blood conc

Answer 5

blood has low wp
water lost from tissue to blood via osmosis
kidney cant absorb all glucose->more water lost in urine ->dehydration

Question 6

describe the action of insulin

Answer 6

• secreted by B cells in islet of langerhans in pancreas when blood glucose conc too high
• binds to specific receptors on cell surface membrane of liver/muscle cells(target cells)
  1. increases permeability of muscle cell membrane to glucose->increasing no. of channel proteins->more uptake of glucose from blood by facillitated diffusion
  2. activation of enzymes in liver/muscle cells that convert glucose to glyocogen
  3. rate of respiration increases
• decreases blood glucose conc

Question 7

what is glycogenesis

Answer 7

glucose–>glycogen

Question 8

describe the action of glucagon

Answer 8

• secreted by A cells in iselt of langerhans in pancreas when blood glucoe conc too low
• binds to specific receptors on liver cell surface membrane
  1. activates enzymes involved to convert glycogen to glucose
  2. activates enzymes involved to convert glycerol/amino acids to glucose
  3. rate of respiration decreases
• increases blood glucose conc

Question 9

describe the role of adrenaline

Answer 9

• secreted by adrenal glands when blood glucose conc low
• binds to specific receptors on cell surface membrane of liver cells
  1. activates enzymes to convert glycogen to glucose
  2. inhibits glycogenesis
• activates secretion of glucagon
• increases blood glucose conc

Question 10

what is glycogenolysis

Answer 10

glycogen->glucose

Question 11

describe the secondary messenger model

Answer 11

• adrenaline + glucagon do this
  1. adrenaline/glucgon binds to specific complementary receptors on cell membrane
  2. activates adenylate cyclase
  3. converts ATP to cyclic AMP(secondary messenger)
  4. cAMP activates protein kinase A enzyme
  5. protein kinase A breaks down glycogen to glucose

Question 12

what causes type 1 diabetes

Answer 12

gene mutation->autoimmune response on B cells of iselts of langerhans-> body cells cant produce insulin

Question 13

how is type 1 controlled

Answer 13

• injections of insulin

- dose of insulin matched to glucose intake

Question 14

how is type 1 controlled diet

Answer 14

• eating reguarly, control carb intake

- avoid sudden rise in glucose

Question 15

what causes type 11 diabetes

Answer 15

poor diet/lack of exercise/obsesity->glycoprotein/receptor loses responsiveness to insulin->cells less responsive to insulin/dont take up enough glucose

Question 16

how is type 11 controlled

Answer 16

• use of drugs which target insulin receptors

- more glucose uptake by cells

Question 17

how is type 11 controlled diet

Answer 17

-reduce sugar intake 
less sugar absorbed into blood
-reduced fat intake
less fat converted to glucose
-more regular exercise  
uses glucose 
-lose weight 
increased sensitivity of cells to insulin

Question 18

how does the body respond to a decrease in water ptotential

Answer 18

• detected by osmoreceptors in hypothalamus, water moves out of them via osmosis into blood
• hypothalamus produces more ADH->posterior pituitary gland secretes more ADH into blood
• ADH travels in blood to kidney +attaches to receptors on CD
• more aquaporins fuse with cell membrane->more water absorbed via osmosis
• less vol of water, more conc

Question 19

formation of glomerular filterate

Answer 19

• diameter of efferent arteriole smalller than afferent
• increase in hydrostatic pressure
• forces out small molecules, ie water, glucose, mineral ions out capillary into bowman’s capsule to form glomeular filterate
• larger molecules ie proteins unable to leave as too large so stay in capillary
• glomerular filterate goes through pores in capillary endothelium, basement membrane (acts as filter), podocytes

Question 20

reabsorption of glucose + water by PCT

Answer 20

1. Na+ actively transported out epithelial cell to capillary
   - lowers conc of Na+ in epithelial cell
2. Na+ moves via facilliated diffusion from PCT into epithelial cell down conc gradient
   - co transporits glucose
   - increasing conc of glucose in epithelial cell
3. glucose moves into capillary via facilliated diffusion down conc gradient
   - lowers wp in capillary
4. water moves via osmosis down wp gradient into capillary = reabsorbed