ANHB2214 Lecture Notes - Lecture 1: Gastrin, Osmotic Concentration, Red Pulp
29 May 2018
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ANHB4 TEST TWO NOTES
The Urinary System:
• General structure of the kidney
o Bean shaped organ in abdominal cavity
o Covered by a connective tissue capsule
o Medial border → concave → contains a hilus through which renal
vessels/nerves pass and origin of ureter leaves
o Divided into outer cortex and inner medulla
o Medulla
▪ 8-12 conical structures → pyramids
▪ Bases of pyramid face capsule, apices face hilus
▪ Pyramids consist of numerous tubules and vessels which
converge from the base to apex
▪ Tissue between pyramids → renal column → continuous
with cortex
o Cortex
▪ Multiple straight and convoluted tubules, blood vessels and
renal corpuscles
▪ Pyramid with is overlying cortical tissue and neighboring
tissue in renal columns → lobe of kidney
▪ Lobes of kidney further subdivided into lobules → consists
of cortical material between 2 interlobular arteries
o Renal pelvis
▪ Expanded origin of the ureter
▪ Divides into major calyces
▪ Major calyces further subdivide into minor calyces →
collect urine from the apex of a pyramid
▪ Portion of the pyramidal apex that projects into minor calyx
→ papilla
• Nephron
o Functional unit of the kidney
o Consists of
▪ Nephron → renal corpuscle + convoluted and straight
tubules
▪ Renal corpuscle → Bowmans capsule + glomerulus
▪ Glomerulus → tuft of capillaries contained in Bowmans
capsule
• Renal Corpuscle
o Filtration apparatus of kidney
o Produces ~180L of plasma filtrate per day
o Consists of a tuft of capillaries (glomerulus) sitting inside a double
walled epithelial capsule Bowmans capsule
o Blood enters via afferent arterioles and leaves via efferent
arterioles
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o )nner layer of Bowmans capsule envelops capillaries of
glomerulus → visceral epithelium
o Outer layer forms wall of capsule → parietal epithelium
o Both layers are made of simple squamous epithelium
o Between 2 layers → urinary space → receives plasma filtrate
o Point at which capillaries enter Bowmans capsule → vascular pole
o Point at which capillaries leave Bowmans capsule → urinary pole
o Complex filtration barrier prevents cells/large molecules entering
urinary space
o Visceral layer contains modified epithelial cells → podocytes →
wrap around capillaries with hundreds of foot processes
o Narrow filtration slits between foot processes covered by a thin
membrane → filtration slit membrane
o Pressure in glomerular capillaries > pressure in urinary space →
fluid leaks out of glomerular capillaries
• Kidney tubules
o As glomerular filtrate passes through kidney tubules it undergoes
a number of changes
▪ Many substances within filtrate are reabsorbed
▪ Certain substances are added to the filtrate
▪ Volume of filtrate reduced significantly
▪ Urine is hypertonic → concentrated through loop of Henle
o Proximal thick segment
▪ Consists of proximal convoluted tubule and descending
thick tubule
▪ Made up of large simple cuboidal cells
▪ Apical surfaces contain microvilli → form brush border
▪ Also contains pinocytic vesicles → endocytose proteins
from urine
▪ Na+/K+ ATPase localized by basolateral membranes →
transport Na+ out of cell
▪ Numerous mitochondria located at base of cell → provide
ATP
▪ Urinary volume reduced by 80% by removal of Na+, Cl- and
water
o Loop of Henle
▪ Characteristic feature → thin limb
▪ Epithelium of thin limb → simple squamous
▪ Proximal and distal ends → sudden transition to thicker
epithelium of proximal and distal tubules
▪ Thin loop plays an important role in concentration of urine
and conservation of water
o Distal tubule
▪ Comprises ascending straight portion and distal convoluted
tubule
▪ Cells of distal tubule → cuboidal to columnar
▪ Contain fewer mitochondria
▪ Less eosinophilic than cells of proximal tubule
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▪ Ascending straight portion specialized for active transport
of Na+ but is impermeable to water
▪ Removal of NaCl and retention of water makes interstitial
fluid hypertonic and contents of tubule hypotonic
▪ Several distal tubules join to a collecting tubule/duct
o Collecting tubule
▪ Lined with cuboidal to columnar cells with pale cytoplasms
and demarcated borders
▪ Darkly staining nuclei and round apices that bulge into
lumen
▪ Numerous tubules open into a minor calyx → epithelium
becomes transitional
▪ Normally impermeable to water → permeability influenced
by ADH
• Juxtaglomerular apparatus
o Wall of afferent arteriole contains modified smooth muscle cells
that contain granules → juxtaglomerular cells
o Closely apposed to these cells → specialized region of distal
convoluted tubule → macula densa
o Cells of macula densa are taller, narrower and closer than other
cells in tubule
o Granules of juxtaglomerular cells contain renin → released in
response to a decrease in ECF volume
o Macula densa plays an important role in transmitting information
about the flow of urine and its osmolarity to juxtaglomerular cells
o Controls reabsorption of water from collecting ducts
• Blood supply
o Each kidney receives the renal artery → enters at hilus
o Renal artery divides and each branch sends interlobular branches
that travel between pyramids to junction between cortex and
medulla
o At this point → run long base of pyramids → arcuate arteries
o Small interlobular arteries branch off arcuate arteries and travel
through cortex towards capsule
o Interlobular arteries form boundaries of renal lobules -> cortical
tissue between 2 interlobular arteries
o Afferent arteriole arises from interlobular arteries → supplies
blood to glomerulus → joins to efferent arteriole
o Peritubular capillaries arise from efferent arteriole → supply
blood to tubules in cortex
o Other efferent arterioles descend into medulla with Loop of Henle
→ forms vasa recta → supplies tubules of medulla
o These vessels loop back into cortex and empty into arcuate veins
o Blood from arcuate veins drains into interlobular veins →
converge to form renal vein that leaves kidney at hilus
• Bladder and urinary passages
o Urine from collecting ducts enter through a papilla to a minor
calyx → combine to form major calyx
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