Overview of Kidney Function

What is the nephron?

functional unit of kidney where filtration and exchange occur

What is the order of fluid flow through the nephron?

glomerular capsule, pct, descending loop of henle, ascending loop of henle, dct, collecting duct

What is the role of the afferent arteriole?

carries blood into glomerulus

What is the role of the efferent arteriole?

carries blood away from glomerulus

What is the function of the glomerulus?

filters water and small solutes from blood

What is the function of the peritubular capillaries?

exchange between blood and nephron tubules

What are the vasa recta?

blood vessels associated with juxtamedullary nephrons

hat structures make up the renal corpuscle?

glomerulus, glomerular capsule

What is the function of the glomerular capsule?

collects filtrate produced by glomerular filtration

What is the capsular space?

space where filtrate collects before entering pct

What are podocytes?

cells of visceral layer of glomerular capsule that form filtration slits

What are the three layers of the filtration membrane?

endothelium, basement membrane, podocytes

What can pass through the filtration membrane?

water and small dissolved solutes

What is normally prevented from passing through the filtration membrane?

blood cells and large proteins

What is glomerular filtration?

movement of water and small solutes from glomerular blood into capsular space

What is the approximate glomerular filtration rate (GFR)?

125 ml/min, 180l /day

What percentage of renal plasma flow is filtered?

25%

How does the composition of filtrate compare with plasma?

similar concentration of small solutes, lacks blood cells and large proteins

What is net filtration pressure (NFP)?

net pressure which determines how much fluid and small solutes leave glomerular blood

What is the formula for net filtration pressure?

nfp = gbhp - chp - bcop

What is glomerular blood hydrostatic pressure (GBHP)?

pressure that pushes fluid out glomerular capillaries into capsular space, 55 mmhg

What is capsular hydrostatic pressure (CHP)?

pressure opposing filtration, 15 mmhg

What is blood colloid osmotic pressure (BCOP)?

osmotic pull of plasma proteins that draws water towards blood, 30 mmhg

What is the approximate net filtration pressure?

10 mmhg

Why are the afferent and efferent arterioles important for GFR?

changes in resistance changes glomerular blood pressure

What happens to GFR when the afferent arteriole constricts?

decreases because pressure decreases

What happens to GFR when the afferent arteriole dilates?

increases because pressure increases

How can the kidney buffer an increase in arterial pressure?

constricting afferent arteriole

How can the kidney buffer a decrease in arterial pressure?

constricting efferent arteriole

What are the three mechanisms that regulate GFR?

autoregulation, neural regulation, hormonal regulation

What is the effect of increased sympathetic nerve activity on the kidney?

causes vasoconstriction, affecting renal bood flow and filtration

How does angiotensin II regulate glomerular filtration?

constricts afferent and efferent arterioles, mostly efferent

How does atrial natriuretic peptide (ANP) affect filtration?

relaxes mesangial cells, increasing surface area for filtration

What is renal autoregulation?

kidneys ability to regulate blood flow so that gfr remains constant

What are the two mechanisms of autoregulation mentioned in the lecture?

myogenic autoregulation, tubuloglomerular feedback

What is tubuloglomerular feedback (TGF)?

negative feedback mechanism that maintains gfr

Which cells detect changes in the salt content of tubular fluid?

macula densa cells

What happens when GFR increases and more Na⁺ and Cl⁻ reach the macula densa?

nitric oxide release decreases, causes afferent arteriole to constrict and reduced gfr

Why is tubuloglomerular feedback protective?

high salt conc in filtrate triggers a decrease in filtration

Does tubuloglomerular feedback directly restore body sodium levels or regulate blood pressure?

no

Is urine output always constant during renal autoregulation?

no, increases as renal pressure increases

What is the difference between cortical and juxtamedullary nephrons?

cortical nephrons produce dilute urine, juxtamedullary nephrons extend into the medulla and produce concentrated urine

What are the three processes involved in urine formation?

filtration, reabsorption, secretion

What is filtration?

movement of water and small solutes from blood to nephron tubule

What is reabsorption?

movement of substances from nephron tubule back into blood

What is secretion?

movement of substances from blood into nephron tubule

What is the formula for excretion?

excretion = filtration - reabsorption + secretion

Approximately how much fluid is filtered and reabsorbed each day?

180L filtered, 178-179L reabsorbed

What happens to glucose in the renal handling example from the lecture?

180g/day filtered, all reabsorbed and none excreted

What happens to water in the renal handling example?

180L/day filtered, 178.6 reabsorbed and 1.4 excreted

What happens to sodium in the renal handling example?

25,560 mmold/day filtered, 25,410 reabsrobed, 150 excreted

What happens to creatinine in the renal handling example?

1.8 g/day filtered, none reabsorbed, all excreted