Glomerular Filtration

Question 1

What are the functions of the kidneys?

Answer 1

• regulation of ECF volume and BP
• regulation of osmolality of plasma and ECF
• maintain ion balance
• regulate pH
• excretion of waste
• production of hormones

Question 2

What are the main nephron processes?

Answer 2

• filtration in glomerulus
• obligatory absorption and secretion by PCT
• generation of osmotic gradient by loop of Henle
• regulated absorption and secretion by DCT
• regulation of water uptake by collecting ducts

Question 3

What is glomerular filtration?

Answer 3

passive process that forces fluid and solutes out of the blood due to hydrostatic pressure

Question 4

How does the glomerulus produce a large volume of filtrate?

Answer 4

• filtration membrane very permeable to water and solutes

- glomerular BP is much higher than other capillary beds in the body

Question 5

Describe the triple barrier of the glomerulus

Answer 5

• epithelial lining of capillaries
• basement membrane of capillaries
• foot processes of epithelial cells (podocytes)

Question 6

What are the functions of the triple barrier of the glomerulus?

Answer 6

• allows for opposition movement of cells and large proteins
• allows negatively charged molecules to be filtered less easily than positively charged ones

Question 7

What are the barriers in the glomerulus to filtration?

Answer 7

• endothelial fenestrations
• basement membrane repels proteins
• filtration slit diaphragms

Question 8

What is RBF and RPF?

Answer 8

• RBF: total amount of blood that moves through renal artery/vein per unit time
• RPF: total amount of plasma that moves through renal artery/vein per unit time

Question 9

What is the net filtration pressure? What values make up this value?

Answer 9

• net filtration = +10 mmHg

from:

• blood hydrostatic pressure = +55 mmHg
• hydrostatic pressure of tubule = -15 mmHg
• oncotic pressure of blood = -30 mmHg

Question 10

What are the regulation mechanisms of glomerular filtration?

Answer 10

Autoregulation mechanisms:

• myogenic
• tubuloglomerular feedback

Question 11

How does myogenic autoregulation work?

Answer 11

• in afferent arteriole when constriction occurs, filtration pressure and glomerular filtration decreases
• in dilation there is an increase in pressure driving ultrafiltration so GFR increases
• in efferent arterioles constriction causes pressure to back up in capillary so GFR increases
• dilation allows blood to escape easily so pressure and GFR decreases

Question 12

How does the tubuloglomerular feedback mechanism work in low filtrate flow rate?

Answer 12

• when macula densa cells are exposed to low filtration flow there is low concentration of NaCl entry
• causes release of prostaglandins E1 activating endothelial NO synthase
• increased cell cAMP and muscle relaxation, vasodilation and increased GFR

Question 13

How does the tubuloglomerular feedback mechanism work in high filtrate flow rate?

Answer 13

• increased NaCl entry into macula densa cells
• causes cells to swell, depolarise and release ATP
• adenosine binds to A1 receptors causing constriction of afferent arterioles reducing GFR

Question 14

What are the extrinsic factors that cause afferent vasoconstriction?

Answer 14

• noradrenaline
• circulating epinephrine
• endothelins
• leukotrienes

Question 15

What are the extrinsic factors that causes afferent and efferent vasoconstriction?

Answer 15

• renal prostaglandins
• NO
• ANP
• dopamine

Question 16

What are the extrinsic factors that cause efferent vasoconstriction?

Answer 16

angiotensin II