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The Urinary system Cheat Sheet by

year one exams cts module


- two kidneys, two ureters, one urinary bladder & one urethra
- urine excreted from each kidney through its ureter & is stored in bladder until expulsion from body through urethra
- nephrology = specia­lised branch of medicine dealing with structure, function & diseases of the male & female urinary systems & the male reprod­uctive system
- urology = branch of surgery related to male & female urinary systems & the male reprod­uctive system

internal anatomy of kidney

renal cortex = superf­icial layer
renal medulla = inner portion consisting of 8-18 cone-s­haped renal pyramids separated by renal columns, renal papilla point toward centre of kidney
drainage system fills renal sinus cavity
cuplike structure (mino calyces) collect urine from papillary ducts of papilla
minor & major calyces empty into renal pelvis which empties into ureter
if asked the difference between hilus & sinus - outline a major calyx & the border between cortex & medulla.

cortical nephron

- 80-85% nephrons
- renal corpuscles are in outer cortex & loops of Henle lie main in cortex
blood flow:
Bowman's capsule - PCT - descending limb - thin ascending limb - thick ascending limb - DCT

juxtam­edu­llary nephron

- 15 -20% of nephrons are juxtam­edu­llary nephrons
- renal corpuscles close to medulla & long loops of Henle extend into deepest medulla enabling excretion of dilute­/co­nce­ntrated urine.
blood flow:
Bowman's capsule - PCT - descending limb - thin ascending limb - thick ascending limb - DCT

renal corpuscle structure

Bowman's capsule surrounds capsular space
podocytes cover capill­aries to form visceral layer
simple squamous cells form parietal layer of capsule
glomerular capill­aries arise from afferent arteriole & form a ball before emptying into efferent arteriole

renal physiology

nephrons & CDs perform:
- glomerular filtra­tion: a portion of the blood plasma is filtered into kidney
- tubular reabso­rption: water & useful substances are reabsorbed into the blood
- tubular secretion: wastes are removed from the blood & secreted into urine
rate of excretion of any substance is its rate of filtration + rate of secretion - rate of reabso­rption.

kidney functions

regulation of blood ionic compos­ition - Na+, K+, Ca2+, Cl- & phosphate ions
regulation of blood pH, osmolarity & glucose
regulation of blood volume - conserving or elimin­ating water
regulation of BP - secreting renin enzyme, adjusting renal resistance
release of erythr­opo­ieitin & calcitriol
excretion of wastes & foreign substances

blood & nerve supply of kidney

abundantly supplies with blood vessels - receive approx 20% of resting cardiac output via renal arteries

functions of different capillary beds:
- glomerular capill­aries where filtration of blood occurs: vasoco­nst­riction & vasodi­lation of afferent & efferent arterioles produce large changes in renal filtration
- peritu­bular capill­aries carry away reabsorbed substances from filtrate
- vasa recta supplies nutrients to medulla without disrupting its osmolarity form
- the nerve supply to the kidney is derived from renal plexus (sympa­thetic division of ANS), sympat­hetic vasomotor nerves regulate blood flow & renal resistance by altering arteri­oles.
renal artery - segmental arteries - interlobar arteries - arcuate arteries - interl­obular arteries - afferent arterioles - glomerular capill­aries - efferent arterioles - peritu­bular capill­aries &/or vasa recta - interl­obular veins - arcuate veins - interlobar veins - segmental veins - renal vein

nephro­n/c­oll­ecting duct histology

glomerular capsule consists of visceral & parietal layers, visceral layer has modified simple squamous epithelial cells (podoc­ytes), parietal layer has simple squamous epithelium & forms outer wall of capsule
fluid filtered from glomerular capill­aries enters capsular space
single layer of epithelial cells forms walls of entire tube
- microv­illi, cuboidal vs simple epithe­lium, hormone receptors are distin­ctive features due to function of each region

CD & Renal tubule histology

PCT - simple cuboidal with brush border of microvilli to increase SA
descending limb - simple squamous
ascending limb - simple cuboidal to low columnar, forms juxtag­lom­erular apparatus where makes contact with afferent arteriole, macula densa is a special part of ascending limb
DCT & CDs - simple cuboidal composed of principal & interc­alated cells which have microvilli
the juxtag­lom­erular apparatus is a structure where afferent arteriole makes contact with ascending limb of loop of Henle - macula densa is thickened part of ascending limb, juxtag­lom­erular cells are modified muscle cells in arteriole

external anatomy of kidney

- near centre of concave medial border is a vertical fissue called the hilus through which the ureter leaves & blood vessels, lymphatic vessels, & nerves enter & exit
- three layers of tissue surround each kidney; renal capsule, adipose capsule & renal fascia
- nephro­ptosis is an inferior displa­cement of the kidneys, most often occurs in thin people - ureters may kink & block urine flow
- paired kidney­-bean shaped organ
- 4-5 in long, 2-3 in wide, 1 in thick
- found just above waist between peritoneum & posterior wall of abdomen
- retrop­eri­toneal (along with adrenal glands & ureters)
- protected by 11th & 12th ribs, with right kidney lower


consists of a renal corpuscle where fluid is filtered & a renal tubule into which the filtered fluid passes
three basic functions - glomerular filtra­tion, tubular reabso­rption & tubular secretion
renal tubule consists of PCT, loop of Henle, DCT
DCTs of several nephrons drain into a single collecting duct & many collecting ducts drain into a small number of papillary ducts
glomerular capill­aries are formed between afferent & efferent arterioles
efferent arterioles give rise to the peritu­bular capill­aries & vasa reccta
loop of Henle has a descending limb, thin ascending limb & thick ascending limb
cortical nephron has glomerulus in outer portion of cortex & short loop of Henle penetr­ating only into outer portion of medulla
juxtam­edu­llary nephron has glomerus deep in cortex close to medulla, long loop of Henle stretches through medulla & almost reaches renal papilla.
corpuscle = site of plasma filtra­tion, glomerulus is capill­aries where filtration occurs & Bowman's capsule is double­-walled epithelial cup that collects filtrate
tubule = PCT, loop of Henle dips down into medulla, DCT
collecting ducts & papillary ducts drain urine to renal pelvis & ureter
- number of nephrons remains constant from birth - any increase in kidney size is size increase of individual nephrons & if injured, no replac­ement occurs. Dysfun­ction is not evident until function declined by 25% of normal. Removal of one kidney causes enlarg­ement of remaining until it can filter at 80% of normal rate of 2 kidneys.

glomerular filtration

- BP produces glomerular filtrate
- filtration fraction is 20% of plasma
- 48 gallon­s/day filtrate reabsorbed to 1-2 qt. urine
- filtering capacity is enhanced by: thinness of membrane & large SA of glomerular capill­aries, glomerular capillary BP is high due to small size of efferent arteriole
GFR = amount of filtrate formed in all renal corpuscles of both kidney­s/m­inute.
average adult male = 125mL/min
Homeos­tasis requires GFR that is constant as if it is too high, useful substances are lost due to speed of fluid passage through nephron & if it is too low, sufficient waste products may not be removed from the body.
Changes in net filtration pressure affect GFR - filtration stops if GBHP drops to 44mm Hg, functions normally with mean arterial pressure 80 - 180 mm Hg


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