Lec 17- Intro to Renal Sys + Glomerular Filtration

Chp 14, Sections 14.1-14.3 ; somewhat incomplete, go back and add more

main functions of the renal system

• regulation of water, ions(Na+,K+,Ca²⁺), and acid-base balance

• removal of metabolic wastes(urea, uric acid, creatine from normal muscle metabolism)

• production of hormones(EPO, renin)

hormones produces by the renal system

EPO and renin

what is considered metabolic waste in the renal system

urea, uric acid, creatine from normal muscle metabolism

importance of acid-base balance

metabolic acidosis or metabolic alkalosis could occur otherwise

what is the nephron

structural and functional units that forms urine

two main parts of the nephron

• renal corpuscle

• renal tubule

parts of the renal corpuscle

• glomerulus

• bowman’s capsule

renal blood vessels receives how much of cardiac output

25%

SEQ blood vessels in kidney(in order)

afferent arteriole(“dirty blood”) → glomerulus → efferent arteriole(“clean blood”) → peritubular capillary → venules

SEQ blood vessel in normal system

artery → arteriole → capillaries → venules → veins

glomerulus function

allows for efficient filtrate formation

filtrate is very rich (contains lots of glucose, water, nutrients, ions)

cells located bowman’s capsule

podocytes

podocytes function

act as filtration slits, allow filtrate to pass into capsular space

juxtaglomerular complex (JGC) cells

• macula densa

• granular cells(aka juxtaglomerular cells)

significance of the juxtaglomerular complex(JGC)

blood pressure and Na+ content

how is urine produced

from filtrate

urine characteristics

• metabolic wastes and unneeded substances

• <1% of original filtrate

processes involved in urine formation + adjustment of blood composition

1. glomerular filtration

2. tubular reabsorption

3. tubular secretion

glomerular filtration

hydrostatic pressure forces fluids and solutes through filtration membrane into glomerular capsule

cell and protein-free filtrate

what is the filtration membrane and its layers

• allows water and solutes smaller than plasma proteins to pass

• contains 3 layers

1. fenestrated endothelium of glomerular capillaries

2. basement membrane

3. foot processes of podocytes

basement membrane

selective filter(mesh)

foot processes of podocytes

contains filter slits, slit diaphragms repel macromolecules

<3 nm only should pass(glucose, nitrogenous waste, ions, etc)

why do plasma proteins need to remain in blood

in order to maintain colloid(think protein) osmotic pressure → no loss of water to capsular space

what are pressures that affect filtration

• outward pressures

• inward pressures

• net filtration pressure(NFP)

outward pressures

forces that promote filtrate formation, like:

• hydrostatic pressure in glomerular capillaries

hydrostatic pressure in glomerular capillaries(HP_gc)

= glomerular BP

• chief forces pushing water, solutes out of blood

• 55 mmHg(average is 26 mmHg)

inward pressures

forces inhibiting filtrate formation like:

• hydrostatic pressure in capsular space (HP_cs) : 15mmHg

• colloid osmotic pressure in capillaries(OP_gc) : 30mmHg (protein pull)

net filtration pressure(NFP)

• pressure responsible for filtrate formation

• determines GFR

• primary pressure is glomerular hydrostatic pressure

how to calculate net filtration pressure(NFP)

outward pressure - inward pressures

(HP_gc)-(HP_cs+OP_cs)

ex. 55-(15+30)= 10mmHg

what is glomerular filtration rate(GFR) + directly proportionate to what?

• amount of volume(filtrate) the kidney filters per minute (120-125mL/min)

• directly proportional to

  • net filtration pressure (NFP)

  • total surface area available for filtration

  • filtration membrane permeability

total surface area available for filtration

larger surface area → more filtration

filtration membrane permeability

eg. glucose blocking membrane is a problem → hardening of pores

regulation of glomerular filtration

• constant GFR allows kidneys to make filtrate and maintain extracellular homeostasis(maintains BP)

• GFR affects systemic BP

what does increased GFR cause

increase urine output, which lowers blood pressure

what does decreased GFR cause

renal failure

decreased urine output, which increases blood pressure

diabetic nephropathy symptoms

• retaining water(no urination)

• chronic kidney disease; GFR of 60mL/min

why do high proteins in the urine indicate kidney failure

macromolecules should not be able to get through BM

how does hemodialysis replace the function of the failing kidneys

acts as the glomerulus and filters out waste from blood

what is normal GFR

120-125 mL/min