renal phys pt2

Question 1

what is autoregulation?

Answer 1

renal blood flow and GFR are maintained at relatively constant levels regardless of level of arterial pressure

Question 2

what is renal blood flow autoregulated by?
explain how the two mechanisms/feedback work when there is increased RBF

Answer 2

myogenic mechanism and tubuloglomerular feedback
1. myogenic mechanism
- increased RBF –> increased BP –> shear stress on arterial walls –> stretch receptors in vascular smooth muscle initiate vasoconstriction –> decreased RBF –> decreased glomerular pressure –> decreased GFR (back to normal)
2. tubuloglomerular feedback
- increased RBF –> macula densa cells release adenosine –> constriction of afferent arterioles –> increased resistance in afferent arteriole –> decreased RBF –> decreased glomerular pressure –> decreased GFR

Question 3

what are the effects on the osmolarity and volume of ECF and ICF upon ingesting NaCl tablets?

Answer 3

1. increased osmolarity of ECF
2. water enters ECF from ICF –> increased ECF volume
3. decreased ICF volume –> shrunken cells

Question 4

what is natriuresis?

Answer 4

the excretion of sodium in urine

Question 5

explain the pressure natriuresis mechanism when there is a decrease in mean arterial pressure (MAP)

Answer 5

decreased MAP –> decreased urinary excretion of Na+ and H2O –> increased plasma volume –> increased MAP

Question 6

how does the body sense changes in Na+ levels?

Answer 6

1. CVS stretch-sensitive and baroreceptors (atria, veins, arteries)
2. renal sensors (intrarenal baroreceptors, macula densa)

Question 7

how does aldosterone control Na+ reabsorption?

Answer 7

aldosterone released into bloodstream –> diffuses across interstitial fluid into tubular cells –> forms complex with mineralocorticoid receptor
- increased expression of proteins involved in Na+ reabsorption
- increased synthesis of Na+ channels on luminal membrane
- increased expression of Na+/K+ ATPase pumps on basolateral membrane

Question 8

what is the function of the renin-angiotensin system (RAS)?

Answer 8

control of blood pressure

Question 9

what is renin?

Answer 9

enzyme responsible for the formation of Angiotensin II

Question 10

where is renin synthesised?

Answer 10

granular cells of juxtaglomerular region of afferent renal arteriole

Question 11

what are the factors involved in regulation of renin secretion?

Answer 11

1. decreased renal arterial pressure –> decreased stretch of juxtaglomerular cells –> decreased [Ca2+] –> increased renin secretion (myogenic mechanism)
2. decreased luminal Na+ passing macula densa –> prostaglandin release –> vasodilate afferent arteriole –> increase renin secretion
3. increased renal sympathetic activity –> release NA that act on B receptors within juxtaglomerular cells –> increase renin secretion

Question 12

list the 5 effects of Angiotensin II

Answer 12

1. increased renal sympathetic activity
2. increased tubular Na+ reabsorption, K+ excretion and water retention
3. increased aldosterone secretion
4. increased vasoconstriction –> increased BP (increased TPR)
5. increased ADH secretion –> acts on posterior pituitary gland –> increased H2O reabsorption

overall water and salt retention, perfusion of juxtaglomerular apparatus increased –> inhibit release of renin

Question 13

where does our daily water intake come from?

Answer 13

beverages: 50%
food: 30%
cellular metabolism: 10%

Question 14

where does our daily water ouput go into?

Answer 14

urine: 60%
insensible loss through skin (perspiration, evaporation) and lungs (respiration): 28%
sweat: 8% (can increase with exercise)
faeces: 4% (can increase with diarrhoea)

Question 15

where is ADH/vasopressin produced and stored in?

Answer 15

supraoptic nuclei of hypothalamus
stored in herring bodies in posterior pituitary gland

Question 16

what is ADH secretion stimulated by?

Answer 16

1. increased plasma osmolarity
   - increased plasma osmolarity –> osmoreceptors lose water and shrink in size –> increased firing rate –> increased secretion of ADH from posterior pituitary nerve terminals
2. decreased arterial blood volume

osmoreceptors: specialised sensory cells primarily in hypothalamus

Question 17

how does ADH increase H2O permeability of late distal tubule and collecting duct cells?

Answer 17

ADH bind to v-type receptors on basolateral membrane –> activation of adenylate cyclase –> cAMP –> protein kinase –> insertion of aquaporins in luminal membrane –> increased permeability –> increased reabsorption of H2O

Question 18

what is the purpose of the renal counter current mechanism?

Answer 18

generate concentration gradient in renal medulla

Question 19

what are the types of buffers in ECF, cells and in urine?

Answer 19

ECF: HCO3-, phosphates
cells: proteins (eg. haemoglobin), phosphates
urine: phosphates, ammonia

Question 20

what is the normal plasma bicarbonate level?

Answer 20

24nM

Question 21

what are the main buffers in ECF?

Answer 21

HCO3-, proteins (albumin)

Question 22

what are the main buffers in ICF?

Answer 22

organic phosphates, proteins

Question 23

When the bladder is full, contraction of the detrusor muscle:

a .Is regulated by sympathetic nerve innervation (hypogastric plexus)
b. Opens the internal urethral sphincter
c. Is regulated by somatic motor innervation (pudendal nerve)
d. Opens the external urethral sphincter

Answer 23

b. Opens the internal urethral sphincter