overview
- 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
parenchyma |
renal cortex = superficial layer |
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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 |
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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.
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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
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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 |
nephron
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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