Water Regulation & Acid-Base Balance

Renal System continued

Drugs to lower blood pressure

• Beta blockers (lower HR)

• Loop diuretic (lower SV)

How do loop diuretics work?

inhibits NKCC transporter in the thick ascending limb, which decreases the ability to reabsorb Na+, K+, Cl-. If you don’t reabsorb the solutes you don’t absorb the water, urinate more, decreasing blood volume > decreasing SV, decreasing BP

What is prescribed with loop diuretics?

K+ supplement prescribed because if the body loses 6% K+ it could cause heart failure

Why is the proximal tubule avoided?

because you want to keep absorption of glucose and amino acids

Why do the kidneys care about BP?

it’s the driving force of GFR

What if BP is too low?

• increase water retention

• increase blood volume > increase SV > increase BP

What is stimulated when BP is too low?

• stimulate cardiovascular system to increase HR and SV

• stimulate brain, thirst

• stimulate kidneys

What is the response to chronically low BP?

Renin-Angiotensin System

retain more water (lose less water, put more in)

Renin-Angiotensin System cascade of events

Liver releases angiotensinogen > angiotensin I > angiotensin II (hormone)

What converts angiotensin I to II

ACE (angiotensin converting enzyme), endothelial cells

What stimulates the conversion of angiotensinogen to angiotensin I?

renin (kidneys release enzyme renin, granular cells)

What are the main effects of angiotensin II?

• causes release of vasopressin/ADH from the posterior pituitary (produced in hypothalamus, stored in post. pit.)

• causes release of aldosterone (steroid hormone) from the adrenal gland (cortex)

• vasoconstriction of afferent arterioles (decrease GFR, less water into Bowman’s capsule)

• creates thirst sensation

What is the effect of aldosterone?

• creates more Na/KATPase pumps on the basal lateral side

• more Na+ channels on the tubular lumen side

• reabsorb more Na+, retain more water

What is the effect of ADH?

• move aquaporins to the tubular lumen side instead of inside the cell since water is being absorbed transcellularly (distal tubular cells tightly packed)

• absorb more water

What if BP is chronically high?

lower blood volume > lower SV > lower BP (more water loss)

stimulate atria

What happens when the atria is stimulated in response to high BP?

atrial natriuretic peptide/factor/hormone released by atria

What is the effect of ANP?

inhibits NKCC > inhibiting the reabsorption of water (excreting more, if less solutes absorbed, less water absorbed)

vasodilation of the afferent arterioles (increase GFR, pushing more water from the blood into the Bowman’s capsule, pushing more water that won’t be reabsorbed)

What is the cause of most hypertension?

idiopathic “cause unknown”

for some reason the body is allowing for it to happen

Henderson-Hasselbalch Equation

pH = pKa + log [HCO3] / [CO2]

What is the normal pH range?

7.35-7.45 (average 7.40)

What controls [HCO3]

HCO3 concentration dictated by the kidneys

if increases, pH increases

What controls [CO2]

CO2 concentration dictated by the lungs

if increase, pH decreases