Kidneys lecture notes for BIOL2521 Integrated Physiological Systems (previously Applied Physiology) at Durham University. Covers functions, organisation, structure and processes (filtration, reabsorption and secretion). Received a 1:1 on this module.
Excretion of metabolic waste products and foreign chemical
Regulation of water/electrolyte balance
Regulation of body fluid osmolality and electrolyte concentrations
Regulation of acid-base balance
Organisation of the Kidneys
Two kidneys (left kidney slightly higher in humans)
Hilum containing...
o Ureter
o Renal artery and vein, dividing into...
Interlobular arteries and veins
Glomerular and peritubular capillaries (separated by efferent arterioles)
o Lymphatics
o Nerves
Tough fibrous capsule around outside for protection
Outer cortex
Inner medulla
o Renal pyramids tipped with papillas
o Cortex-medulla border (where renal artery divides into many arterioles)
o Renal pelvis
Major and minor calyces collect urine from the tubules of each papilla
Nephron
Functional unit of the kidneys
Made up of...
o Glomerelus (glomerular capillaries)
o Long tubule (segments)
o Cortex
Proximal tubule
Distal tubule
Macula densa (specialised epithelial cells)
Involved in sensing GFR via the concentration of NaCl in the
filtrate
Bowman's capsule (surrounds glomerelus)
Connecting tubule
Cortical collecting tubule
o Medulla
Loop of Henle (descending and ascending limbs)
Medullary collecting tubule
Collecting duct
Not regenerated so ageing causes loss of nephrons
Renal corpuscle: glomerelus + Bowman's capsule
, Cortical collecting ducts join to form medullary collecting ducts join to form
collecting duct
Cortical nephrons
o Short loops of Henle
o Short distance into medulla
o Peritubular capillaries
Juxtamedullary nephrons
o Long loops of Henle
o Deep into medulla
o Long efferent arterioles
o Specialised peritubular capillaries
Vasa recta
Concentrated urine
Processes
Glomerular filtration
o Movement of fluid from blood into lumen of nephron
o Pass through three layers
Glomerular capillary wall
Single layer of flattened endothelial cells
Fenestrations
Very permeable to water
Basement membrane
No cells
Collagen for strength
Glycoproteins negatively charged and repels plasma proteins
(negatively charged)
After vigorous exercise, proteins may enter urine due to high
blood pressure
Inner layer of Bowman's capsule
Podocytes: cells of the capsule in direct contact with the
capillaries
Filtration slits
Fluid leaving the glomerular capillaries enter lumen of
Bowman's capsule
o Layers function as fine molecular sieve
o Filtrate contains water, electrolytes, waste, nutrients, but NOT plasma proteins
or red blood cells
o Blood pressure in the glomerular capillary is the major force involved
Also involves plasma-colloid osmotic pressure and Bowman's capsule
hydrostatic pressure
These oppose filtration but blood pressure ensures net favoured
filtration
o Glomerular filtration rate = Kf * net filtration pressure
Relatively constant
Blood pressure fluctuates but autoregulation adjusts afferent arteriole
diameter
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