Renal physiology

Question 1

What is the functional unit of the kidney?

Answer 1

nephron

Question 2

What is the glomerulus?

Answer 2

tuft of glomerular capillaries

Question 3

What is the normal filtration rate of the kidneys?

Answer 3

~180L/day

Question 4

How much water is normally excreted via urine, and how much solute?

Answer 4

~1.5L water
600 milliosmoles of solute

Question 5

Kidney holistic functions

Answer 5

filtration - removal of metabolic products and toxins from the blood for excretion

regulation of fluid balance, electrolyte balance, and acid-base balance

produce or activate hormones involved in erythrogenesis, calcium metabolism and the regulation of blood pressure

(volume, concentration, pH, metabolic, excretory, endocrine)

Question 6

How can the kidneys produce glucose?

Answer 6

gluconeogenesis

Question 7

What metabolic waste products do the kidneys excrete?

Answer 7

creatinine
urea

Question 8

What endocrine actions does the kidney have?

Answer 8

renin production

RAAS system first of 4 pathways to correct low circulating volume

EPO - new red blood cell production

Vit D - controls calcium and phosphorus metabolism

Question 9

Why is renal blood flow tightly controlled?

Answer 9

blood flow is closely linked to rate of renal filtration and excretion

local renal blood flow must be autoregulated in response to changes in systemic BP to prevent damage

Question 10

Describe glomerular filtrate

Answer 10

essentially protein-free plasma
produced at rate of 125ml/min (GFR)
contains urea and creatinine

Question 11

What is GFR determined by?

Answer 11

net filtration pressure across the glomerular capillaries

Question 12

How is renal blood flow controlled?

Answer 12

vascular bed has 2 major sites of resistance control - afferent and efferent arterioles

selective constriction or relaxation of the afferent and efferent arterioles permit control of blood flow and hydrostatic pressure in the intervening glomerular capillary, and subsequently glomerular filtration

many physiological mediators control arteriolar resistances

Question 13

Effect of increased afferent arteriolar resistance on renal blood flow and net ultrafiltration pressure

Answer 13

decreased renal blood flow
decreased net ultrafiltration pressure

Question 14

Effect of decreased afferent arteriolar resistance on renal blood flow and net ultrafiltration pressure

Answer 14

increased renal blood flow
increased net ultrafiltration pressure

Question 15

Effect of increased efferent arteriolar resistance on renal blood flow and net ultrafiltration pressure

Answer 15

decreased renal blood flow
increased net ultrafiltration pressure

Question 16

Effect of decreased efferent arteriolar resistance on renal blood flow and net ultrafiltration pressure

Answer 16

increased renal blood flow
decreased net ultrafiltration pressure

Question 17

General action of sympathetic nerves on afferent and efferent arterioles?

Answer 17

vasoconstriction
both afferent and efferent arteriolar resistances rise
generally decreases both renal blood flow and GFR

Question 18

General action of prostaglandins on afferent and efferent arterioles?

Answer 18

vasodilation
dampens the renal vasoconstrictor effects of sympathetic nerves or angiotensin II

Question 19

General action of natriuretic peptides on afferent and efferent arterioles?

Answer 19

vasodilation
dominant action on afferent arterioles
net effect is increased renal blood flow and GFR

Question 20

Describe autoregulation of the kidneys

Answer 20

maintain renal blood flow and GFR within narrow limits, although MAP may vary

2 mechanisms for renal autoregulation:
- myogenic response of smooth muscle of the afferent arterioles
- tuboglomerular feedback mechanism

Question 21

Describe the myogenic response in renal autoregulation

Answer 21

afferent arterioles have the ability to respond to changes in vessel circumference by contracting or relaxing

constriction in response to pressure prevents the vessel from being overstretched and, by increasing vascular resistance, helps prevent excessive increases in renal blood flow and GFR when BP rises

Question 22

Describe the tubuloglomerular feedback in renal autoregulation

Answer 22

increase in arterial pressure increases filtration and ultimately sodium and chloride in proximal tubule

sensed by macula densa cells of the JGA

macula densa cell to release paracrine agents which triggers contraction of nearby vascular smooth muscle cells in afferent arteriole

increased afferent arteriolar resistance decreases GFR, counteracting the initial increase in GFR

Question 23

Define hydrostatic pressure

Answer 23

force a fluid exerts on walls of compartment (eg. walls of capillaries or Bowman’s capsule)

Question 24

Define oncotic pressure

Answer 24

pressure exerted by plasma proteins on walls of compartment (encourages fluid to be drawn in)

Question 25

Define GFR

Answer 25

glomerular filtration rate
total amount of filtrate formed in corpuscles in both kidneys per minute

Question 26

What factors does GFR take into account?

Answer 26

surface area available for filtration
permeability of glomeruli

Question 27

What increases the kidneys contribution to whole-body glucose production?

Answer 27

prolonged fasting

Question 28

Which mediator acts to selectively modulate the sympathetic vasoconstrictive effects on the afferent arterioles to prevent sustained damage?

Answer 28

prostaglandin

Question 29

How do the kidneys help regulate acid-base balance?

Answer 29

reabsorbing HCO3- into the bloodstream in proximal convoluted tubule

excreting H+ into the urine

Question 30

What is the enzyme involved in dissolving carbonic acid into bicarb and hydrogen?

Answer 30

carbonic anhydrase type 2

Question 31

How do the kidneys stop the urine becoming too acidic (pH<4.5)?

Answer 31

ammonia buffer system
phosphate buffer system