Kidneys

What are the main points to know about the kidneys (5)

Regulating water and electrolyte balance

Maintains acid-base balance/homeostasis

Helps retain protein and glucose in the body

Excretes wastes and toxins

Has endocrine function of secreting hormones

What does renin do

Secreted by the kidney - mediates extracellular volume and arterial vasoconstriction (aka regulates blood pressure) via renin-angiotensin system

What does aldosterone do

Stimulates active sodium resorption - so water will stay

What does ADH do

Stimulates passive water resorption (antidiuretic hormone) - doesn’t let water leave

Nephrons are

Functional unit of the kidney and the kidney is made up of these

What is the nephron made up of

Glomerulus (surrounded by Bowman’s capsule) and its tubule

What are the parts of the tubule

Proximal tubule

Medullary loop of Henle

Distal tubule - empties into collecting duct

Where does filtration occur

Glomerular capillaries - filtration is driven by hydrostatic pressure as a direct result of arterial pressure

What does GFR stand for and what does it mean

Glomerular filtration rate - the rate of filtration that is driven by hydrostatic pressure

Where are sodium and chloride resorbed back into the body

Loop of Henle - also responsible for concentrating the urine

What is the final urine concentration dependent on

Amount of ADH secreted by pituitary gland

What does the proximal tubule do

Resorts all glucose, amino acids, and most bicarbonate, phosphate and water

When does renin, which increases angiotensin II production, get released

When intravascular volume drops either by dehydration, blood loss, etc.

What is the renin-angiotensin-aldosterone-system (RAAS)

Renin is released → increases angiotensin II production → aldosterone is released from adrenal cortex → ADH is released from posterior pituitary → leads to increased thirst, constriction of efferent arteriole to maintain GFR

Leads to conservation of water and increase in intravascular volume/BP

Where is aldosterone released from

Adrenal cortex

Where is ADH released from

Posterior pituitary

What does aldosterone do

Causes sodium and water resorption in distal tubule and collecting duct

Where sodium is exchanged for potassium and hydrogen

When does aldosterone get released other than when intravascular volume drops

When sodium is low in blood - either via vomit or loss of gastric acids

This leads to alkalosis

What does ADH do

Makes distal tubule and collecting tubule more permeable to water → increases urine concentration

If ADH is present, what does that do to urine

Urine is more concentrated - keep water inside

If ADH is not present, what does that do to the urine

Tubule is not very permeable to water so urine is diluted

What causes the hypothalamus to stimulate the pituitary to make ADH which would make urine more concentrated

When osmotic blood pressure rises (?)

What else do the kidneys produce

Vitamin D - Calcitriol → helps promote calcium absorption from intestine

Erythropoietin - stimulates production of RBC

What are kidney values on a blood panel

BUN

Creatinine

What is another way to check if renal failure is impaired on blood work

Amylase - b/c it is excreted through kidneys, if it is increased, that means renal function may be impaired

What is the best indicator of kidney function

GFR