Excretory - eliminate toxins/harmful substances, metabolic waste and excess substances
Regulatory - maintain a constant volume and composition of the body fluids by varying the excretion of solutes and water (regulate water; ion, osmotic and pH balance; blood pressure)
Endocrine - synthesize and secrete (i) Renin (ii) Erythropoietin (iii) 1,25-dihydroxycholecalciferol
The renal artery and vein, lymphatics, nerves and the ureter pass through a single indentation or hilus
Sympathetic nervous system input
Triggers vasoconstriction of the arterioles reduce renal blood flow into the glomerulus and decrease urine production
Parasympathetic nervous system input
Via the renal branches of the vagus nerve, causes vasodilation and increased blood flow of the arterioles; increase urine production
Glomeruli located in the outer and middle cortices
Associated with the loop of Henle that extend to the junction of the cortex and medulla or into the outer zone of the medulla, e.g. marine aquatic mammals
Juxtamedullary nephrons
Glomeruli in the cortex close to the medulla
Associated with loops of Henle that extend more deep into the medulla, e.g. mammals in arid region, such as the Kangaroo rat
Avian kidneys contain both mammalian-type and reptilian-type nephrons
Glomerulus
Filters blood, Solutes, water, urea, creatinine
Tuft of capillaries enclosed within the glomerular/Bowman's capsule
Layers of the capillary wall
Capillary endothelium
Basement membrane
Visceral epithelium
Capillary endothelium
Single layer of thin cells
Endothelial fenestrae - transcellular pores that conduct water and other components into the blood
Basement membrane
Thick, acellular
Composed of various glycoproteins, primarily laminins, type IV collagens and heparin sulfate (proteoglycan)
Visceral epithelium
Layer of interlocking cells called podocytes
Interdigitation of podocyte appendages creates filtration slits between the cells
The size of these filtration slits is the primary determinant of which particles can filter out of the blood
Proximal tubule
Reabsorbs most filtered water and solutes (Na+, K+, Cl-, HCO-3, H2O, glucose, amino acids)
Descending/thin limb of the loop of Henle
Maintains medullary hypertonicity
Reabsorbs H2O, *NaCl, *urea
Ascending/thick limb of the loop of Henle
Reabsorbs Na+, K+ and Cl-
Dilutes tubule fluid
Generates medullary hypertonicity
Distal convoluted tubule
Reabsorbs Na+, Ca2+, Mg2+, Cl-
Dilutes tubule fluid
Connecting segment
Regulates acid, HCO-3, ammonia, Na+, Ca2+, K+ and water excretion
Cortical collecting duct
Regulates acid, HCO-3, ammonia, Na+, K+ and water excretion
Medullary collecting duct
Regulates acid, ammonia, urea, Na+, K+ and water excretion
Volume of plasma delivered to the kidneys per unit time
Effective renal plasma flow
A measure used in renal physiology to calculate renal plasma flow and hence estimate renal function
Describes a fraction of plasma flow through a nephron; the level in renal venous plasma is not measured
Glomerular filtrate/ultra-filtrate
The fluid formed via filtration of the blood by the glomerulus, which is nearly identical to plasma in its electrolyte and water
Glomerular filtration rate
The quantity of glomerular filtrate formed each minute in all the nephrons of both the kidneys/kg body weight
A 10 kg dog, with a typical GFR of 3.7 mL/min/kg would produce approximately 37 mL of glomerular filtrate per min
Three factors that determine the filtration pressure
Glomerular pressure
Plasma colloidal osmotic pressure (COP)
Bowman's capsular pressure
Greater the glomerular pressure
Greater the filtration
Greater the plasma COP and Bowman's capsular pressure
Less filtration
Main force favoring filtration
Hydrostatic pressure of the blood within the capillary
Forces opposing filtration
Plasma oncotic pressure within the glomerular capillary and the hydrostatic pressure in Bowman's space
Greater the blood flow
Greater the filtration rate
Afferent arteriolar constriction
Decreases the rate of blood flow into the glomerulus and decreases GFR = decreased filtration rate
Efferent arteriolar constriction
Increases the resistance and outflow from the glomeruli increases the glomerular pressure and GFR initially but when blood remains in the glomerulus for a prolonged period, increase in plasma COP occurs which causes a fall in GFR = net effect is slight increase in GFR
Mild to moderate sympathetic stimulation
Causes afferent arteriolar constriction and decreases GFR
Strong sympathetic stimulation
Causes great reduction in the glomerular blood flow and glomerular pressure resulting in decrease of GFR
Myogenic response
Immediate afferent arteriolar constriction after an increase in arteriolar wall tension = increase resistance to blood flow in response to increased perfusion pressure
Arteriolar dilation occurs almost immediately after a decrease in arteriolar wall tension = reduce resistance to flow when vascular perfusion pressure decreases
Tubuloglomerular feedback
Mediated by the macula densa cells of the JG apparatus
These cells sense changes in the Na+ and CL-
If GFR is increased, due to increased glomerular HP there will be increase in macula densa flow and Na+ and CL- delivery initiates a response that returns GFR and macula densa flow towards the normal due to afferent arteriole constriction (which lowers glomerular HP)
If renal blood flow falls too low it decreases the GFR decreases Na+ and CL- delivery to the distal tubule which initiate a signal from macula densa and dilates the afferent arterioles and it increases glomerular blood flow and glomerular pressure = GFR increase to normal