KIDNEY & URINARY SYSTEM

Where are your kidneys?

posterior abdominal wall

List the parts of the urinary system in order

Kidneys → ureters → urinary bladder → urethra

What are the main functions of the kidney?

Filter blood, regulate waste or electrocycle, acid balance, produce renin/erythropoietin, excrete waste

What causes UTI?

Bacteria colonize urethra → bladder → kidneys

Who is more at risk for UTI?

Females, they have a shorter urethra

What is a nephron?

The functional unit of the kidney | ~1 million per kidney

Where is the nephron located?

Cortex & medulla

What is the function of a nephron?

Filters blood at glomerulus → reabsorbs needed substances → secretes waste → produces urine via tubules

Which types of change in blood pressure activates the RAA pathway?

Low blood pressure or sodium levels

How does the RAA pathway correct its homeostatic issue?

Renin release → angiotensin I formation → angiotensin II activation (ACE - enzyme) → vasoconstriction → fluid retention (aldosterone) → thirst & brain signaling (ADH) → INCREASE blood pressure

What are the risk factors for kidney disease?

Diabetes, hypertension, obesity, smoking, old age, UTIs

What factors might influence racial differences in rates of preemptive kidney transplantation?

black patients receive preemptive transplants at far lower rates than white people despite higher ESRD burden

How is dialysis performed?

blood crosses semi-permeable membrane → wastes diffuse into dialysate down concentration gradient

Why would kidney disease lead to uremia (build-up of wastes in the blood)?

Can't excrete urea

Why would kidney disease lead to anemia?

No EPO

Why would kidney disease lead to hypertension?

Fluid retention

Why would kidney disease lead to acidosis?

Can't excrete hydrogen ions

Why would kidney disease lead to hypocalcemia?

Can't activate vitamin D

What are the 3 major actions with the nephron during filtration (glomerulus)?

Blood → tubule; water, salts, glucose, urea - NOT proteins or RBC

What are the 3 major actions with the nephron during reabsorption (tubules)?

Tubule → blood; recuses glucose, Na+, H2O, amino acids (~99% of filtrate)

What are the 3 major actions with the nephron during secretion (distal tubule)?

Blood → tubule; adds H+, K+, drugs, toxins

What are three major waste products that are included in urine?

Urea, creatinine, uric acid

What is the pathway of blood through the kidney?

Renal artery → afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries → renal vein

When and where does blood enter the nephron?

Glomerulus or bowman's capsule

How much filtrate is reabsorbed in the nephron?

180 L/day filtered, ~99% absorbed → 1.5 L urine

What does flux have to do with the process of hemodialysis?

Flux is the waste move by diffusion from high concentration (blood) → low concentration (dialysate)

What does the mass balance have to do with the process of hemodialysis?

Countercurrent flow that maximizes the gradient throughout; mass balance: waste lost from blood = waste gained by dialysate

What is the path of filtrate through a nephron & what are the names of all the parts?

Kidney → renal cortex → glomerulus (bowman's capsule) → proximal tubule → distal tubule → renal medulla → loop of henle → collecting duct → renal pelvis

Which segments of the nephron are usually in the renal medulla?

Loop of henle, collecting duct, renal pelvis, ureter

Which segments of the nephron are usually in the renal cortex?

Glomerulus, bowman's capsule, proximal tubule, distal tubule

Why are nephrons small & numerous?

More surface area for filtration/reabsorption per unit → volume → more efficient exchange

What types of substances can pass through the filtration membrane?

Water, ions, glucose, amino acids, urea, small drugs (<8nm)

What major disorders affect filtration?

Glomerulonephritis (inflamed, or leak of proteins/RBCs in urine); nephrotic syndrome (massive protein loss)

Which is wider: the afferent or effect arteriole?

Afferent, it creates high pressure in glomerulus to drive filtration

What does it mean that the filtration of plasma into the nephrons is said to be "size selective"

Acts as a tiny strainer, allows only small molecules to pass through the nephron

What is hydrostatic pressure (HP)?

Physical pressure of fluid pushing against a membrane.

What is osmotic pressure (OP)? What increases or decreases it?

Pressure from solutes pulling water across a membrane

If you have a HP gradient, in what direction does water move?

water moves from high HP to low HP

If you have an OP gradient, in what direction does water move?

water moves toward higher solute concentration (lower water concentration)

What may increase or decrease HP/OP?

↑ blood proteins = ↑ OP (pulls water back into blood); edema = ↓ OP (proteins lost → water stays in tissue)

What formula is used to calculate filtration pressure?

NFP = glomerular HP (55) - capsule HP (15) - blood OP (30) = 10 mmHg

What happens to filtration pressure if glomerular HP changes?

↑ NFP → more filtration

What happens if glomerular OP changes?

↓ NFP → less filtration

What happens if capsule HP increases?

↓ NFP → less filtration

What happens if the diameters of the afferent arteriole changes?

(dilation): ↑ glomerular HP → ↑ NFP

(constriction): ↑ vascular resistance → ↓ BP & NFP → reduction in urine production

What happens if the diameters of the efferent arterioles change?

(narrowing): ↑ glomerular HP → ↑ in NFP → more fluid out of the blood → ↑ urine output

(widening): blood flows out glomerulus → ↓ in NFP → less filtrate

Why are carrier proteins "rate-limiet" in their activity?

Finite number of transporters → can only reabsorb up to a maximum rate = Tmax

What is Tmax in relation to renal reabsorption?

Transport maximum, the rate of that renal tubules can reabsorb or secrete specific substances

How do you calculate the amount of solute that may be reabsorbed or lost in urine if you are given Tmax & the amount of solute that is filtered into a nephron?

Amount in urine = filtered load - Tmax

If filtered load > Tmax → excess spills into urine

Why does a diabetic with high blood glucose have glucose in their urine?

blood glucose → filtered glucose >> Tmax → glucose in urine (glucosuria)

What are the main regions of the nephron where reabsorption occurs?

Proximal tubule, loop of henle, distal tubule, collecting duct

What are the main regions of the nephron where secretion occurs?

Proximal tubule, distal tubule, collecting duct

What type of substances is reabsorbed & secreted in the proximal tubule?

Reabsorbed: ~65%: Na+, glucose, AA, HCO3-, H2O

Secreted: H+, drugs, toxins

What type of substances is reabsorbed & secreted in the loop of henle?

Reabsorbed: Nacl (ascending), H2O (descending)

Secreted: NONE

What type of substances is reabsorbed & secreted in the distal tubule?

Reabsorbed: Na+, Ca2+ (aldosterone/PTH control)

Secreted: H+, K+

What type of substances is reabsorbed & secreted in the collecting duct?

Reabsorbed: H20 (ADH), Na+ (aldosterone)

Secreted: H+, K+

What is the main purpose of countercurrent multiplication?

Create a highly concentrated, salty environment deep within the kidneys

What is a descending loop?

Permeable to water (water leaves)

What is an ascending loop?

Pumps NaCl OUT → builds up salt concentration in medulla → concentrated medulla pulls water from collecting duct when ADH is present