Goodwin Renal

What happens to GFR if there is significant loss of blood volume?

A large loss of blood volume decreases GFR significantly because:

              Decreases in blood volume or pressure can shut down renal filtration:

§  Blood volume decreases and renal perfusion pressure decreases

§  Glomerular hydrostatic pressure decreases

§  These both cause GFR to decrease

What portion of the nephron has the highest osmolarity?

The deep medullar region (bottom of loop of Henle and collecting duct)

o   Countercurrent multiplier creates hyperosmotic medulla

o   Osmolarity can reach ~1200 mOsM

-          High osmolarity allows water to be reabsorbed later

What portion of the nephron has the lowest osmolarity?

The thick ascending limb/ early distal tubule

o   AKA diluting segment

o   Mechanism:

§  Na+, K+, Cl- are actively pumped out

§  Not permeable to water

o   Results in very dilute filtrate

Urine osmolarities can vary between 50-1200mOsM. Why?

The kidney can adjust water reabsorption based on body needs

o   Controlled mainly by ADH (vasopressin)

o   Two extremes:

§  Low ADH – dilute urine

§  High ADH – concentrated urine

o   Kidney tunes this balance to maintain osmolarity and homeostasis

What hormone regulates the rate of water reabsorption in the distal tubule and collecting ducts?

ADH – vasopressin

o   Inserts Aquaporin-2 channels into cells

o   Water moves:

§  From tubule into blood

o   No ADH = no water reabsorption causing diluted urine

How are cells of the distal nephron able to respond so quickly to hormonal stimulation?

They use pre-made proteins (Aquaporins).

o   ADH causes rapid insertion of AQP2 channels

o   No need for new protein synthesis

o   Leads to FAST response

What hormone plays a critical role in sodium reabsorption and how is it regulated?

Aldosterone:

o   Increases Na+ reabsorption and K+ secretion

Regulation

o   Controlled by RAAS (Renin-Angiotensin-Aldosterone System)

§  Triggered by:

·       Low bp

·       Low blood volume

·       High potassium

-          Helps restore volume and BP

What are the side effects of Angiotensin II on blood pressure?

Angiotensin II raises blood pressure through multiple mechanisms:

a.      Vasoconstriction

b.      Increased aldosterone causing increased sodium and water retention/absorption

c.      Increased Vasopressin causing increased water retention/absorption

d.      Increased thirst

e.      Increased sympathetic activity

-          Strong increase in BP and volume

What are the effects of ANP on the renal system?

ANP (Atrial Natriuretic Peptide) does the opposite of RAAS:

a.      Increases GFR (more filtration)

b.      Decreases Na+ reabsorption

c.      Decreases water reabsorption

d.      Inhibits renin, aldosterone, and ADH

Net effect: Decreased blood volume and bp

What hormone helps to regulate potassium concentration in plasma?

Aldosterone

o   Increases K+ secretion into urine

o   Can excrete up to 150% of filtered load

Keeps plasma K+ in a tight range

What are some key differences between Aldosterone and ADH/AVP/Vasopressin?

Aldosterone = salt

ADH = Water

Can you die from drinking too much water?

Yes

o   Excess water causes decreased plasma osmolarity

o   Leads to:

§  Hyponatremia

§  Cell swelling (especially in the brain)