PHYL2001 Study Guide - Final Guide: Aquaporin, Membrane Potential, Vasodilation
Renal Physiology
Body Fluid Composition:
• Body is made up of 45-75% water
• % of body weight that is water depends on
amount of fat
• Male of average build ~60% water
• Female of average build ~50% water
• Extracellular water
o 1/3 of total body water
o Plasma → 1/5
o Interstitial fluid → 4/5
• Intracellular water
o 2/3 of total body water
Anatomy of the Urinary System:
• 2x kidneys → supplied by renal artery and vein
o Maintain composition of extracellular fluid within narrow limits
compatible to life
• 2x ureters
• Urinary bladder
• Urethra
Function of the Urinary System:
• Maintaining water balance
• Maintaining osmolarity of body fluids
• Regulating quantity and concentration of ECF ions
• Maintaining proper plasma volume
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• Helping maintain proper acid-base balance of the body
• Excreting the end products of body metabolism
• Excreting many foreign compounds
• Producing erythropoietin
• Producing renin
• Converting vitamin D into its active form
The Nephron:
• Functional unit of the kidney
• Arrangement of nephrons gives 2 distinct regions of the kidney
o Renal cortex → granular
o Renal medulla → renal pyramids
• Vascular component
o Afferent arteriole → carries blood to glomerulus
o Glomerulus → tuft of capillaries that filters a protein-free plasma
into tubular component
o Efferent arteriole → carries blood from glomerulus
o Peritubular capillaries → supply renal tissue, involved in
exchanges with fluid in tubular lumen
• Tubular component
o Bowmans capsule → cups glomerulus and collects filtered fluid
o Proximal tubule → where uncontrolled reabsorption and secretion
of selected substances occurs
o Loop of Henle → establishes osmotic gradient important in the
kidneys ability to produce urine of varying concentrations
o Distal tubule → where variable, controlled reabsorption and
secretion occur
o Collecting duct → fluid here is urine, enters renal pelvis
• Types of nephrons
o Juxtamedullary nephron
▪ 15-20% of total
▪ Glomeruli in inner cortex
▪ Loop of Henle descends fully into medulla
o Cortical nephrons
▪ 80% of total
▪ Glomeruli in outer cortex
▪ Loop of Henle dips slightly into medulla
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Glomerular Filtration:
• Extracellular phenomenon
• Filtered fluid passes through 3 layers that surround glomerular
capillaries
o Glomerular capillary wall
▪ Single layer of flattened endothelial cells
▪ Perforated by large pores more soluble to water and solutes
▪ Endothelial cells perforated by fenestrations
o Basement membrane
▪ Acellular gelatinous layer
▪ Composed of collagen and glycoproteins
▪ Collagen → structural strength
▪ Glycoproteins → discourage filtration of small plasma
proteins
o Podocytes
▪ Filtration slits between cellular foot processes
Forces Affecting Glomerular Filtration:
• Glomerular capillary blood pressure
o Fluid pressure exerted by blood within glomerular capillaries
o Depends on contraction of the heart and resistance to blood flow
offered by afferent and efferent arterioles
o Glomerular blood pressure → 55mmHg
o Higher pressure due to larger diameter of afferent arteriole
compared to efferent arteriole
o Favours filtration
• Plasma-colloid osmotic pressure
o Caused by unequal distribution of plasma proteins across
glomerular membrane
o Proteins present in glomerular capillaries but not Bowmans
capsule → higher osmolarity of glomerular blood
o Acts to draw water back to glomerulus
o Opposes filtration
• Bowmans capsule hydrostatic pressure
o Pressure exerted by fluid in Bowmans capsule
o Fluid dams in Bowmans capsule → causing backwards pressure
o Opposes filtration
o Tends to push fluid out of Bowmans capsule
Glomerular Filtration Rate:
• Rate of flow of filtrate (L/min)
• Depends on
o Net filtration pressure (NFP)
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Document Summary
Intracellular water: 2/3 of total body water. Anatomy of the urinary system: 2x kidneys supplied by renal artery and vein, maintain composition of extracellular fluid within narrow limits compatible to life, 2x ureters, urinary bladder, urethra. Juxtamedullary nephron: 15-20% of total, glomeruli in inner cortex, loop of henle descends fully into medulla, cortical nephrons, 80% of total, glomeruli in outer cortex, loop of henle dips slightly into medulla. Glucose, amino acid, and other nutrient reabsorption: the reabsorption of sodium. Water reabsorption: proximal tubules 65% reabsorbed obligatory, loop of henle 15% reabsorbed obligatory, distal tubule and collecting duct 20% reabsorbed hormonal control. Increased osmolarity of ecf due to ions and nutrients draws water from tubule to ecf. Increased water current creates a positive pressure in lateral spaces: high osmolarity of capillary blood due to protein concentration induces water movement into capillaries, passes primarily through aquaporins formed by specific plasma proteins in tubular cells.
