Renal system

Question 1

RAAS

Answer 1

Receptors detect changes in renal perfusion (concentration of Na and Cl in renal filtrate)
Kidneys release renin (from the granular cells in the JGA)
Renin increases Na reabsorption from DCT and CT, also increasing water retention
Renin converts angiotensinogen to active state angiotensin I.
Angiotensin I is converted to angiotensin II by ACE (angiotensin converting enzyme)

Angiotensin II:
Is a potent vasoconstrictor
Increases SNS, HR and SV, CO and TPR
Triggers release of aldosterone from the adrenal gland, which increases Na reabsorption which increases water reabsorption too since salt follows water.

Triggers release of vasopressin/anti-diuretic hormone ADH from the posterior pituitary gland which increases water reabsorption
By increasing number of aquaporins in the walls of collecting ducts

Question 2

Juxtaglomerular apparatus

Answer 2

Mix of vascular and tubular component of kidneys
Produces substances involved in kidney function

1) Juxtaglomerular granular cells produces renal hormones: renin and erythropoietin. Specialised smooth muscle cells primarily found on the afferent arteriole
2) Macula densa cells: specialised epithelial cells on the DCT that detect sodium concentration of renal filtrate

Question 3

GFR
Glomerular filtration rate

• what is it influenced by
• how is it regulated

Answer 3

GFR is influenced by:
1) Glomerular capillary blood pressure is the main driving force that drives fluid through the membrane
2) Net filtration pressure helps a little ← influenced by vasodilation or constriction of afferent arteriole ← influenced by baroreflex
3) Opposing forces: plasma-colloid osmotic pressure and hydrostatic pressure of Bowman’s capsule
4) Filtration coefficient is influenced by permeability of the membrane.

Regulation of GFR:
1) Myogenic mechanism
Automatic contraction of muscles in response to high blood flow

2) Tubularglomerular feedback
Macula densa cells detect changes in renal perfusion of Na and Cl (affected by filtrate flow)
If flow rate high: higher salt delivery → release vasoactive mediators ATP and adenosine which induce vasoconstriction, reducing flow
If flow rate low: lower salt delivery → release vasoactive mediators nitric oxide which induce vasodilation, increasing flow rate.

Question 4

Sodium and water reabsorption process

Answer 4

Four steps of renal system
1) Glomerular filtration
Blood flows through glomerular capillaries
Basement membrane filters out large proteins and blood cells

2) Tubular reabsorption
Useful substances are all reabsorbed into the peritubular capillaries in the PCT

3) Tubular secretion
Selected substances are excreted back from the peritubular capillaries into the renal tubules in the loop of Henle, DCT and collecting tubules in order to regulate renal perfusion of various substances

4) Urine excretion
All remaining plasma substances are passed to renal pelvis for excretion