Human Physiology

• make urine
• regulate osmotic pressure of plasma and other extracellular fluids
• regulate the excretion of sodium and water
• regulate the individual concentration of numerous electrolytes
• regulate plasma bicarbonate concentration
• eliminate metabolic waste products
• produce hormones, proteolytic enzymes, paracrines, active D, and glucose

cortex

medulla

nephron

• A - Proximal Convoluted Tubule
• B - Loop of Henle
• C - Distal Convoluted Tubule
• D - Collecting Duct

• cortical
• juxtamedullary

loop of Henle is short

long loop of henle

• 85% cortical
• 15% juxtamedullary

• microvilli
• brush border
• tight junction
• basolateral cell membrane
• basement membrane

• ^artery
• afferent arterioles
• glomerulus
• efferent arteriole
• peritubular capillaries
• vein

^{capillaries that descend into and ascend from the medulla in parallel with the tubular structrures}

glomerulus b/c filtration happens there

• peritubular capillaries for uptake of fluid reabsorbed by the tubules
• maintain higher osmotic pressure

innervation by SNS releases NE that binds to alpha receptors causing vasoconstriction of the afferent arterioles

intrinsic mechanisms/renal auto regulation

• if BP/flow increases, the afferent arterioles constrict
• if BP/flow decreases, the afferent arterioles dilate

changes in BP/flow = changes in filtration = big changes in excretion

permanent constriction of afferent arterioles leads to kidney failure

structure in the kidneys consisting of macula densa, extraglomerular mesangial cells, and granular cells, located in the region where the distal tubule touches afferent and efferent arterioles of its parent glomerulus

cells embedded in the smooth muscle walls of afferent arterioles responsible for synthesizing and releasing renin

by the granular cells of the juxtaglomerular apparatus

if BP/flow decreases to the kidneys then renin released end result is angiotensin II is formed that stims adrenal cortex to secrete aldosterone

stims Na reabsorption by the collecting ducts

epithelial cells in the DCT

messenger cells b/t the granular and macula densa cells

NaCl composition of tubule fluid in DCT is relayed bact to afferent arterioles, changes in blood flow changes filtration

form urine

• glomerular filtration
• tubular reabsorption
• tubular secretion

• the first step in the formation of urine that is non-selective filtration of plasma
• allows passage of anything w/ mw <10,000 out of blood into lumen of Bowman's capsule

the # of ozs. filtered out of blood at given amt. of time

process whereby substances are transferred out of the tubular fluid and returned to the peritubular capillaries; much more selective

PCT

mvmt of substances across tubule epithelium in a direction opposite to reabsorption

• excrete 1.5 -2L/day
• filter 180 L/day
• reabsorb 178L/day

always takes out of blood into lumen of tubule

three layers capillary endothelium, glomerular basement membrane, podocyte cell layer

fenestrae pores of about 50 -100 nm

meshwork of fine fibrils embedded in a gel-like matrix

has slit pores

contain glycoproteins that are negatively charged, which repel negative charged plasma proteins

valuable indication of renal fuxn

a cmpd that is not secreted or reabsorbed, allows the amt filtered to = amt excreted

inulin

cmpd form onion/artichoke

C = (U * V)/ P

the rate of excretion of a substance divided by its plasma concentration

• u - urine concentration
• p - plasma concentration
• v - urine flow rate

2ml/ min

120ml/min

• active
• passive

2L/day

the amt of we need to excrete a day which is 400ml/day

• glucose
• Na
• uric acid
• phosphate

• in PCT
• coupled transport tw/ Na out of lumen
• into PCT cell out basolateral membrane by facilitated diffusion

• in PCT
• coupled to glucose, some amino acids, phosphate, Cl, and water

in PCT

high plasma levels of uric acid

big toe pain b/c crystal build up in the vessels of that region

uricosuric agent to lower uric acid levels in plasma by blocking reabsorption of uric acid

Probenecid

• water
• Cl
• urea

out of peritubular capillaries into tubule fluid

supplements filtration process

• organic ion
• penecillin

probenecid

• probenecid
• to help patients that don't come back for next shot
• inhibits peniciliin secretion

H and K secretion by antiport transport

in PCT

H in urine

early in collecting ducts

assoc. w/ Na/K ATPase pump

PAH

almost completely cleared from the blood in 1 pass thru

625 ml/min

• Na reabsorption causes water reabsorption
• Na reabsorption coupled to reabsorption of organic and inorganic ions
• Na reabsorption related to secretion of H and K
• 80% of energy supports Na reabsorption

PCT

• enters lumen by Na/solute cotransporters
• exits by basolateral Na/K ATPase pumps

peritubular capillary Starling forces

tubules pressure is low do to the blood passing thru other vessels, favors the uptake of Na

20% of Na and 10% of water

the ascending loop is impermeable to water

• reabsorption occurs through coupled transport of Na/K/Cl
• exits by Na/K ATPase pump from the basolateral membrane

b/c of tight epithelial

9% of Na and 19% of water

hormones

aldosterone

Na/K exchanger

increase collecting duct permeability, causes more water reabsorption

• less water reabsorbed causing freguent urination
• 15-20L/day = polyuria

glomerulus

BP/flow increases

renal plasma clearances

PCT

reabsorption of Na and water

K is controlled by this process

dependent upon Na/K ATPase pump

requires both ascending and descending limbs

is decreased with low MAP

urea show this

responds to ADH

has microvilli

has fenestrae

releases renin

has foot processes

• ECF - 1/3 of body water
• ICF - 2/3 of body water

osmotic pressure

electrolytes

osmolality

total solute conc.

the amt of solute in that compartment

osmolality increases

• water moves from lower osmolality to higher osmolality
• water moves from lower osmotic pressure to higher OP

the OP of ECF and ICF

Na and its accompanying anions accounts for 90%

K

balancing water, electrolytes, protons, and some organic cmpds.

hormonal and thirst

ADH controls renal excretion of water

• osmoreceptors in the hypothalamus detect cellular hydration
• signal cerebral cortex
• you feel thirsty

• blood vol receptors in CV system and kidneys
• causes hypovolemia and
• you fell thirsty

urine

ECF

negative feedback system

• GFR
• plasma aldosterone levels
• renal SNS activity
• Plasma ANP
• peritubular capillary starling forces
• intrarenal blood flow distribution

increase of ECF <increase of GFR < increase in sodium excretion

decrease ECF vol <renin release<leads to angiotensin II< aldosterone< Na reabsorption

decrease of renal sodium excretion

increase Na excretion

increase Na excretion with increase in hydrostatic pressure or decrease of colloid osmotic pressure