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Urinary SystemAlap Shah (ashah36@uiuc.edu)(pictures are straight from lecture and lab, but they are all very high yield)

Overview

PurposeFiltration, reabsorption, excretion of metabolic waste from the blood

Conserve body fluid and electrolytes, regulate blood pressure

Structures involved

Kidneys Ureters Bladder Urethra

KidneysFunction

Filter blood to produce urine removing toxic byproducts of metabolism, keepingsome salts, glucose, proteins

Concentrate urine to conserve body fluid levelsProduce erythropoietin, renin, prostaglandins, activate vitamin D

Structure

Each kidney comprised of 1.3 million uriniferous tubules, made of nephron +collecting duct

Renal corpuscle blood is filtered to make ultrafiltrate

Fenestrated capillaries surrounded by Bowmans capsule

Renal corpuscle Proximal convoluted tubule Thick descending limb Thin limb

Thick ascending limb Distal convoluted tubule Collecting duct

Filtration

Filtered blood - 1.25 L/min

Filtrate - 125 mL/min

Filtration in first capillary network because of high capillary pressure (can behave changed by constriction or dilation of afferent or efferent arteriole)

Reabsorption in second capillary network because of low capillary pressure

mailto:ashah36@uiuc.edumailto:ashah36@uiuc.edumailto:ashah36@uiuc.edu

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Blood supply to kidney

Interlobar artery (vertical) Arcuate artery (horizontal) Interlobular artery (vertical)

Afferent glomerular arteriole Glomerular capillary network Efferent glomerular

arteriole

Cortical nephrons (85% of nephrons) and Juxtamedullary nephrons (15% of nephrons)

Cortical nephron short loops of Henle, extend into outer medulla

Juxtamedullary nephron long loops of Henle, extend into pyramid, essentialfor countercurrent mechanism

Countercurrent multiplier mechanismThin descending limb freely permeable to water and salts

Thin ascending limb impermeable to water

Cl pump used to pull Na ions out of tube into interstitium

Vasa recta freely permeable to water and salts

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Countercurrent multiplier mechanism

Functions of each section of uriniferous tubule

renal corpuscle filtration (creation of ultrafiltrate)proximal tubule - resorption of 67% of water and salt and all protein,

amino acids, glucose, and bicarbonate

henle's loop remove water, remove salts; from isotonic to hypertonic tohypotonic in juxtamedullary nephrons

macula densa - monitor Na level and volume of urine in lumen of distal

tubuledistal tubule - responds to aldosterone by resorbing Na, Cl

collecting tubule - responds to ADH / water leaves lumen, enters interstitium

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Podocytecell surrounding glomerular capillaries

foot processes of cell hug capillary wall, creating 25 nm slits that filter fluid

from blood

negative charge on processes restrict cation movement

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Juxtaglomerular apparatus

macula densa between distal convoluted tubule and juxtaglomerular cells

juxtaglomerular cells modified smooth muscle cells, play role in renin systemmacula densa senses [Na] in distal convoluted tubule, sends signals to

juxtalgomerular cells to release / not release renin

renin ACE

angiotensinogen angiotensin I angiotensin II

Effects of angiotensin II

stimulates aldosterone release resorption of NaCl by distal convoluted

vasoconstriction raise blood pressure

stimulate ADH release resorption of NaCl by collecting duct

Tubal epithelia

proximal convoluted cuboidal w/ brush border

thin Henle limb squamousdistal convoluted cuboidal w/ basolateral foldings (no brush border)

collecting duct cuboidal w/ good boundaries, (no brush border)

Ureter

Epithelia

transitional epithelium 5 cells thick when relaxed, 3 when distended

made of special thick plaques + interplaque regions

empty bladder plaques folded irregularly, at angular contours

when stretched contours disappear

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Clinical correlation

diabetes insipidus - central (ADH) or nephrogenic (ADH receptor or waterchannel), polyuria, polydypsia - absence of ADH effects on collecting duct

proteinuria - loss of the net negative charge on the glomerular basal lamina and/or

structural defects in the filtration barriernephronal bleeding- red blood cell casts or dysmorphic RBCs in the urine

decreased glomerular filtration rate - salt retention, edema, volume overload,

congestive heart failure, and hypertension

Structures to findKidney

capsule outer layer of kidneycortex contains corpuscles

medulla no lymphatics, no corpuscles

medullary rays - straight portions of thick descending proximal, thick ascending

distal, collecting ductslong and short nephrons short extend into outer medulla, long to pyramid

uriniferous tubules tube from glomerulus to ureter

renal corpsucle found in cortex, contains Bowmans things

glomerulus capillary network within Bowmans capsule

Bowman'scapsule (parietal and visceral layers)

Bowmans capsule + glomerulus = corpusclevisceral layer made of podocytes

parietal layer layer that opens into proximal convoluted

Bowman'sspace area where ultrafiltrate collects before proximal convolutedendothelialcells visible in glomerular capillaries

podocytes cells hugging glomerular capillaries, creating filtration slits

mesangial cells (intra- and extraglomerular)contractile cells sandwiched between macula densa and glomerulus

also remove trapped residues from glomerular basement membrane

also secrete signals

vascular pole pole opposite urinary polemacula densa layer of cells between distal convoluted and glomerulus, in

communication with mesangial cells

urinary pole area where ultrafiltrate enters proximal convolutedproximal tubule direct continuation of Bowmans space, brush border

thick limb of Henle thicker epithelium

thin limb of Henle sparse squamous epitheliumdistal tubule cuboidal epithelium, many infoldings

collecting duct where urine collects, relatively wider than other structures

vasa recta extremely sparse squamous epithelium

juxtaglomerular complex macula densa + juxtaglomerular cells (secretory) +

mesangial cells

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Ureter

transitional epithelium 5 cell layers thick when relaxed

smooth muscle arranged as inner longitudinal layer, outer circular layer