The Kidneys

  • Created by: Willow
  • Created on: 12-05-19 12:18

Kidney Function

  • Excretory organ
  •  Excrete waste products of metabolism
  •  Produces urine by filtering blood
  • Osmoregulation
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  • The regulation of water potential in the blood
  • too high = water enters cells and they burst
  • too low= water leaves cells and cell shrinks
  • reduces function of cells if not regulated
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  • Product of the breakdown of excess amino acids
  • toxic
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  • Long tubules which make up the main functional structures of the kidney
  • Site of blood filtration
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Structure and location of Kidneys

  • Located behind abdomen 
  • outer layer - Cortex (lighter colour observed) 
  • inner layer - medulla (darker colour observed) 
  • renal pelvis 
  • fibrous capsule - provides stability and protection, thin outer layer
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Blood moving through Kidneys

  • oxygenated blood enters through renal artery (blood from aorta)
  • deoxygenated blood leaves via renal vein 
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  • located in cortex
  • mesh of capillaries
  • surrounded by bowmans capsule 
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Journey of filtrate

  • filtered out of blood in glomerulus 
  • into bowmans capsule 
  • PCT (proximal convouted tubule)
  • Loop of henle
  • DCT (distal convoluted tubule)
  • collecting tube to renal pelvis
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Ultrafiltration definition

  • process of filtering blood
  • at molecular level
  • under high pressure 
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Ultrafiltration process

  • blood enters glomerulus via afferent artiriole
  • afferent artiriole has wide lumen
  • blood leaves glomerulus via efferent artiriole
  • efferent has small lumen
  • high hydrostatic pressure inside glomerulus
  • fluid pushed against walls of glomerulus and forced into bowmans capsule 
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Glomerulus to bowmans capsule

  • three layers between glomerulus and bowmans capsule 
  • glomerular endothelium 
  • basement membrane 
  • podocytes (epithilium cells of bowmans capsule)
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Glomerular endothelium

  • single sheet of cells
  • pores between cells allows movement of fluid 
  • also specialised to have holes called fenestrations 
  • allows everything but red blood cells and large proteins to move out 
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Basement membrane

  • mesh of collagen fibres and other glycoprotein fibres
  • doesnt allow RBC, large proteins, platelets 
  • does allow glucose, urea, amino acids, small proteins 
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Podocytes (epithelial of bowmans capsule)

  • specialised shape
  • finger like projections called major processes/ pedicels
  • allow gaps for filtrate to exit
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selective reabsorption definition

  • the reabsorbtion of only some molecules from the glomerular filtrate into the blood 
  • important substances reabsorbed 
  • glucose
  • amino acids
  • water 
  • mineral ions 
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reabsorption where and how

  • mostly in the PCT (85% fluid reabsorbed in PCT)
  • also small amount occours in the collecting duct
  • required active transport
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adaptations for reabsorption

  • epitihluim lining PCT has two sides 
  • apical side= side of tubules
  • basil side= side of blood
  • apical side has microvilli, increase SA, more transport pumps/proteins, more reabsorption
  • basil side slightly folded, increase SA
  • PCT is tangled, increase distance for reabsorbtion to occour over
  • many mitochondria, supply ATP for active transport
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Active transport of sodium

  • sodium important for membrane electrical gradient and protein function
  • needs to be reabsorbed into blood
  • sodium potassium pump on basil side actively pumps Na into blood
  • creates low conc of Na inside PCT cell and high conc in blood
  • transports against conc gradient 
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  • cotransport occours on apical side
  • secondary active transport
  • glucose and amino acids transported with Na on apical side
  • low conc generated inside PCT by basil side active transport
  • causes Na from tubules to diffuse in, carrying glucose or amino acids with it
  • amino acids and glucose then diffuse passively into blood due to constant supply of blood maintaining conc gradient 
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water reabsorption

  • reduce the loss of water from the body 
  • apical side
  • movement of glucose, amino acids and sodium out of the tubules into the PCT cells creates low water potential inside PCT cells and high water potential in tubules
  • water moves by osmosis down the gradient into the PCT cells
  • moves via osmosis into blood 
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loop of hence structure and function

  • reduces water potential of the medulla 
  • uses counter current multiplication
  • loop has a descending limb which desends into the medulla from the cortex
  • has an ascending limb which ascends from the medulla back to the cortex
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descending limb

  • thin
  • permeable to water 
  • permeable to ions 
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ascending limb

  • thick
  • permeable to ions 
  • also contains ion pumps to pump ions out
  • not permeable to water
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counter current multiplication

  • fluid flows in opposite directions to maximise diffusion 
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DCT structure and function

  • helps balance mineral concentrations
  • regulates pH
  • many mitochondria for active transport
  • microvilli increase SA for active transport 
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