Kidneys Notes - Applied Human Physiology

Functions:

 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