Glomerulus Filtration

What is the main organ in the body that filters blood?

kidney

What is the primary functional unit of the kidney?

nephron

What is the glomerulus?

the capillary bed that the bowman’s capsule contains

What supplies the rest of the nephron, after the Bowman’s capsule?

efferent arteriole

What supplies many nephrons?

arcuate artery

What supplies one nephron only?

efferent/afferent arterioles

What is the renal corpuscle?

contains both the glomerulus and bowman’s capsule

How does plasma enter the nephron?

20% of blood leaves the glomerulus and enters the bowman’s capsule at the renal corpuscle, the rest of the blood leaves glomerulus via the efferent arteriole

How does the glomerulus act as a net to keep important components of blood in the vessel?

the three layers allow things to either be filtered out the blood vessel into the bowman’s capsule OR avoid it from leaving

What are things that are filtered out the glomerulus?

water, electrolytes, glucose, uremic toxins

What are things that do not leave the glomerulus, therefore staying in the vasculature?

cells (RBC), large proteins, protein bound molecules (calcium)

What are the three layers of the glomerulus?

capillary endothelium, basement membrane, and podocytes (epithelium)

What is the glomerular endothelium?

a negatively charged single layer of endothelial cells with fenestrations and tight junctions between them that line the capillary

What is the glomerular endothelium a barrier to?

cells and large molecules due to being too big to pass through fenestrations and negatively charged molecules are repelled

What is the glomerular basement membrane?

fusion of two membranes - endothelial and epithelial membranes, with the function to restrict flow of water thanks to glycoproteins

What are podocytes?

layer of foot like epithelial cells that wrap around capillaries, gaps between foot processes allow filtrate to pass through but NOT negative items due to negative charge

What are the gaps between the foot processes in podocytes called?

slit diaphragms

What are hydrostatic forces?

physical pressure the fluid is under

What are oncotic forces?

proteins change solution osmolarity, water wants to follow the higher osmolarity the proteins provide to achieve an equilibrium

What is the hydrostatic pressure in the glomerulus capillary vs the bowmans capsule?

60 mmHg vs 18 mmHg; wants to move out of the capillary into the nephron

What is the oncontic pressure in the glomerulus capillary vs the bowmans capsule?

32 mmHg vs 0 mmHg; proteins in capillary oppose the fluid leaving

Why is the oncotic pressure in the bowman’s capsule close to zero?

the three layers of the glomerulus are doing their job as a barrier, keeping proteins in blood

What pushes fluid out of glomerular capillaries?

capillary hydrostatic pressure

What pulls fluid into the bowman’s capsule?

oncotic pressure of Bowman’s space

What pushes fluid away from the Bowman’s capsule?

hydrostatic pressure of Bowman’s space

What keeps fluid in the glomerular capillaries?

capillary oncotic pressure

What is the strongest force acting on filtration?

capillary hydrostatic pressure

What is used as a measure of kidney function?

glomerular filtration rate

GFR = ______ x _________

filtration coefficient, net filtration pressure

Net filtration pressure = (________) - (________)

(glomerular hydrostatic + bowman’s oncotic) - (glomerular oncotic + bowman’s hydrostatic)

What is the usual net filtration pressure?

10 mmHg; (60+0) - (32-18)

As fluid leaves the glomerulus, glomerular hydrostatic pressure ________.

decreases

As fluid leaves the glomerulus, glomerular oncotic pressure ________.

increases

What is the filtration coefficient based on?

how easy it is to pass the three layers and a combination of membrane thickness and surface area

What is the normal GFR for dogs?

3.5-4.5 ml/kg/min

What is the normal GFR for cats?

2.5-3.5 ml/kg/min

What is the normal GFR for horses?

2.2-2.5 ml/kg/min

What is the filtration fraction?

GFR/Renal plasma flow

How do you calculate renal plasma flow?

GFR x 5

What can cause an increase in bowman’s hydrostatic pressure?

urinary obstruction which decreases GFR

How do we usually measure GFR in veterinary medicine?

calculate the clearance of a molecule

What is the ideal substance to calculate GFR defined as?

a substance that is equal to the GFR, a substance that 20% leaves and 80% stays with no changes in nephron; uncharged small unbound molecule

What is the ideal substance to calculate GFR?

inulin

Since inulin is hard to calculate in reality, what do we use clinically?

creatinine

How is GFR maintained constant?

altering blood pressure and speed of blood flow