Phys 335 UW Madison Exam 4

difference between urinary and renal system?

-renal means kidneys

-kidneys are one part of the urinary system

functions of the kidneys

1. regulation of water, ions, and acid balance

2. removal of metabolic waste products from blood into urine

3. removal of foreign chemicals from blood into urine

4. gluconeogenesis

5. production of hormones/enzymes: erythropoietin, renin, and activated vitamin D

where are kidneys located in the abdomen?

retroperitoneal (top/back)

what is the functional unit of the kidney?

nephron

tubular components of a nephron:

1. bowman's capsule

2. proximal convoluted tubule

3. descending loop of henle

4. ascending loop of henle

5. distal convoluted tubule

6. collecting duct (cortical and medullary)

vascular components associated with nephron:

1. renal artery

2. afferent arteriole

3. glomerular capillaries (glomerulus)

4. peritubular capillaries (vasa recta)

5. renal vein

renal corpuscle

glomerular capillaries and bowman's capsule

juxtamedullary nephron

-long loop of henle

-generate gradient in medulla that is important for H2O reabsorption

-15% of all nephrons

cortical nephron

-short loop of henle

-do not contribute to gradient in medulla

renal cortex

-outer layer of kidney

-contain renal corpuscles

-contain proximal and distal tubules

-contain cortical nephrons

renal medulla

-inner layer of kidney

-renal pyramids

-contain long loops of henle from juxtamedullary nephrons

-contain medullary portion of collecting ducts

juxtaglomerular cells

-also called granular cells

-surround afferent arteriole

-synthesize, store, and secrete renin

-respond to BP, norep, and macula densa

macula densa

-part of wall of distal tubule

-sense filtrate flow

-sends paracrine signals to afferent arteriole

sympathetic nerve fiber

-comes from VM center

-constricts afferent arteriole

-causes renin secretion from JG cells

excretion formula

excretion = filtration + secretion - reabsorption

____% of plasma is filtered?

20

drugs and toxins are:

1. freely filtered

2. 100% secreted

Na+, Cl-, and H2O are:

1. freely filtered

2. partially reabsorbed

glucose and amino acids are:

1. freely filtered

2. 100% reabsorbed

3 layers of glomerular filtration barrier

1. capillary endothelium (fenestrated = more exchange)

2. basement membrane (negatively charged matrix)

3. bowman's epithelium (podocytes and filtration slits)

filtrate

blood plasma except for RBCs and proteins

what can be passed through the glomerular filter?

water, electrolytes, glucose, amino acids, vitamins, urea, uric acid, creatinine

what cannot be passed through the glomerular filter?

blood cells, plasma proteins, large anions, protein-bound minerals/hormones, big molecules

glomerular filtration rate (GFR)

125 mL/min (180 L/day)

typical glomerular capillary blood pressure:

60 mmHg

effect on GFR of constriction of afferent arteriole:

decreased GFR

effect on GFR of dilation of efferent arteriole:

decreased GFR

effect on GFR of constriction of efferent arteriole:

increased GFR

effect on GFR of dilation of afferent arteriole:

increased GFR (caffeine does this!)

typical fluid pressure in bowman's space:

15 mmHg

typical osmotic force due to protein in plasma:

29 mmHg

typical net glomerular filtration pressure

16 mmHg

what change to starling forces do kidney stones cause?

increases the pressure in bowman's space

how do kidney stones affect net glomerular filtration pressure?

decreases

filtered load equation

filtered load = GFR * [P]s

excreted load equation

urine flow rate (V) * [U]s

filtered load > excreted load

reabsorption

filtered load < excreted load

secretion

% of water reabsorbed:

99%

% of sodium reabsorbed:

99.5%

% of glucose reabsorbed:

100%

% of urea reabsorbed:

44%

modes of tubular reabsorption

1. diffusion

2. mediated transport

what uses diffusion?

lipid soluble substances that don't need carriers

diffusion route:

1. tight junctions

2. renal interstitial fluid

3. peritubular capillaries

what uses mediated transport?

large/charged substances

mediated transport route:

1. apical membrane

2. basolateral membrane

3. renal interstitial fluid

4. peritubular capillaries

where does most secretion occur?

Proximal tubules (except K+ and H+ which are secreted into cortical collecting duct)

most secretion is done via _________________.

active transport

renal plasma clearance of a substance (RPCs)

volume of plasma cleared of substance S per unit of time

RPCs equation

RPCs = (Us * V) / Ps

-Us = urine concentration of S

-V = urine volume per unit of time

-Ps = plasma concentration of S

inulin

-substance that is freely filtered but NOT secreted or reabsorbed

-RPC of inulin = GFR (125 mL/min)

para-aminohippurate (PAH)

-substance that is freely filtered and 100% secreted but NOT reabsorbed

-RPC of PAH = RPF (625 mL/min)

creatinine

-freely filtered

-not reabsorbed

-slightly secreted (10%)

-RPC of creatinine is about the true GFR

detrusor

-smooth muscle

-parasympathetic

-inhibited during filling

-stimulated during urination

internal urethral sphincter

-smooth muscle

-sympathetic

-stimulated during filling

-inhibited during urination

external urethral sphincter

-skeletal muscle

-somatic motor

-stimulated during filling

-inhibited during urination

main points for body balance of water

1. for homeostasis, intake must equal output

2. urine is the main regulator for intake to match output

main points for body balance of sodium (and chloride)

1. for homeostasis, intake must equal output

2. urine is the main regulator for intake to match output

effect on cells when drinking water

-bulk flow from plasma to ISF

-creates hypotonic ECF solution

-H2O enters ICF

effect on cells when adding excess NaCl

1. increases plasma volume and MAP

-increases ISF volume

2. net diffusion of NaCl into ISF

-creates hypertonic ECF solution

-H2O exits ICF

majority of H2O goes _____________.

into cells

NaCl stays in ________.

ECF/

baroreceptors detect pressure changes in the ________ due to __________.

ECF, gain of NaCl

osmoreceptors detect ________________________ due to ________________.

ECF osmolarity changes, pure gains in H2O

mechanism of Na+ reabsorption in the proximal tubule

1. Na+/K+ ATPase pump (primary active) pumps Na+ into ISF and K+ into proximal tubule

2. Na+ is antiported with H+ into proximal tubule. Na+ is symported into proximal tubule with glucose, amino acids, etc. creating a concentration gradient (secondary active transport)

3. facilitated diffusion of glucose, amino acids, etc. into ISF

-65% of Na+ reabsorption occurs here

-unregulated

mechanism of Na+ reabsorption in the ascending limb of the loop of henle

1. Na+/K+ ATPase pump (primary active) pumps Na+ into ISF and K+ into loop of henle

2. NKCC transporter in apical membrane cotransports Na+, K+, and 2Cl- into loop of henle

3. Cl- channel moves Cl- into ISF

-25% of Na+ reabsorption occurs here

-unregulated

mechanism of Na+ reabsorption in the cortical collecting duct

1. Na+/K+ ATPase pump (primary active) pumps Na+ into ISF and K+ into collecting duct

2. diffusion of K+ into tubular lumen from collecting duct. diffusion of Na+ into collecting duct from tubular lumen.

-regulated

role of aldosterone in Na+ reabsorption

builds more Na+ and K+ channels and Na+/K+ ATPases

coupling H2O reabsorption to Na+ reabsorption by osmosis

1. Na+ decreases in tubular lumen (goes to tubular epithelial cells)

2. local osmolarity decreases

3. H2O follows Na+ into tubular epithelial cells

paracellular water transport

-main water route in proximal tubule

-65% of water reabsorption

-non-regulated

transcellular water transport

-main water route in collecting ducts

-requires aquaporins

-regulated by ADH

how does ADH regulate water reabsorption?

1. ADH binds ADH receptor

2. triggers cAMP formation

3. cAMP activates PKA

4. PKA causes protein phosphorylation

5. induces AQP2 insertion into collecting duct cell

AQP2

allows water to be reabsorbed out of filtrate and transcellularly reabsorbed into body via AQP4 and AQp3

renal medullary gradient

-osmolarity increases the deeper you go into the medulla

-created by countercurrent multiplier system and urea recycling

-maintained by vasa recta circulation

countercurrent multiplier system

-reabsorption of NaCl in ascending limb

-water cannot flow in ascending limb (tight junctions are too tight)

-reabsorption of water in descending limb makes filtrate more concentrated

urea recycling

-urea secreted in bottom of loop of henle

-55% of urea reabsorbed in inner medulla section of cortical collecting duct

-increases medullary osmotic gradient bc urea draws a lot of water to it

medullary circulation

-solutes keep getting exchanged between ascending and descending vasa recta and are trapped in the medulla

-small blood flow in medulla helps maintain the gradient

why can we still piss when we're dehydrated and ADH is present?

hyperosmotic medullary ISF

ADH also increases ________ absorption for a net result of even more H2O reabsorption

urea

Na+ excreted equation

Na+ excreted = Na+ filtered -Na+ reabsorbed

Na+ filtered equation

Na+ filtered = GFR * [plasma]Na+

2 ways to alter Na+ excretion

1. regulating filtered load by changing GFR

2. regulating rate of reabsorption

effect of Na+ and H2O loss on kidneys

1. decreased MAP

2. increased constriction of afferent renal arteries

3. decreased net glomerular filtration pressure

4. decreased GFR

5. decreased Na+ and H2O excreted

what 3 things happen after a decrease in plasma volume that cause an increase in plasma renin?

1. increased activity of renal sympathetic nerves

2. decreased arterial pressure

3. decreased GFR, causing decreased flow to macula densa

how does an increase in renin increase blood pressure?

-increases angiotensin I

-increased angiotensin II

-increased aldosterone from adrenal cortex to kidneys

-increased Na+ and H2O retention

-increased BP

ACE inhibitors

-inhibits angiotensin-converting enzymes

-cannot make angiotensin II

angiotensin II blockers

blocks receptors that angiotensin II binds to

aldosterone receptor blockers

blocks aldosterone binding on renal distal convoluted tubule

atrial natriuretic peptide (ANP)

anti-aldosterone

natriuresis

loss of Na+ via urine

diuresis

loss of H2O via urine

how does ANP increase Na+ excretion?

-afferent arteriole dilation

-decreased aldosterone

-increased GFR

-increased Na+ excretion

how does increased H2O ingestion cause increased H2O excretion?

1. decreases body fluid osmolarity

2. decreased firing by hypothalamic osmoreceptors

3. decreased ADH secretion

4. decreased plasma ADH

5. collecting duct tubules are less permeable to H2O

6. decreased H2O reabsorption

7. increased H2O excretion

diabetes mellitus (osmotic diuresis)

-failure to reabsorb glucose

-large amount of glucose in urine

-H2O retained in lumen

diabetes insipidus (water diuresis)

-failure of pituitary to release ADH or failure of kidney to respond to ADH

-H2O permeability is low

-increased H2O loss

what renal processes does K+ experience?

-filtration

-reabsorption

-secretion

there is net ____________________ of K+ in the proximal tubule and is __________________

reabsorption, non-regulated

How is K+ reabsorbed in the proximal tubule?

paracellularly by following H2O, which follows Na+

there is net __________________ of K+ in the ascending loop of henle

reabsorption