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Introduction to nephron/kidney (Movement of fluid (Need a concentration…
Introduction to nephron/kidney
Urinary tract
Ureters
Convey urine from kidneys to bladder
Bladder
Storage of urine prior to evacuation
Kidneys
2 positioned either side of spine behind caudal rib
Urethra
Convey urine from bladder to outside world
Renal anatomy
Nephron
Function
Blood plasma filtrated through glomerular capillaries into glomerular capsule
Filtered fluid passes into renal tubule (3 sections, PCT, loop of Henle, DCT)
Structure
Glomerulus - Filtration
PCT - Bulk unregulated reabsorption of filtrate
Loop of Henle - Sets up osmotic gradient within renal medulla
DCT - Regulated reabsorption from filtrate and secretion into filtrate
Functional unit of kidney
Blood vessels and tubules
In renal pyramid
Outer cortex and inner medulla
Cortex
Filtration to form urine
Medulla
Collect and excrete urine
Blood supply
Renal artery -> Segmental artery -> Arcurate artery -> Interlobular artery -> Afferent arterioles -> Glomerular capillaries -> Efferent arterioles -> Interlobular vein -> Arcurate vein -> Interlobar vein -> Segmental vein -> Renal vein
Afferent A -> Glomerular C -> Efferent A
Capillary network between 2 arterioles. Afferent has wider diameter
Peritubular capillaries
Second capillary network minus glomerular filtrate
Wrapped around glomerular capillary bed
Urine formation
Glomerular filtration
Pressure forces filtration of blood in glomerulus.
GFR (glomerular filtration rate) is amount of filtrate formed in all the renal corpuscles of both kidneys each minute
Tubular reabsorption
Process of returning important substances from filtrate back to body
Tubular secretion
Movement of waste materials from body to filtrate
Functions of kidney
Excretion of waste
metabolic waste (e.g. creatinine, urea), foreign substances e.g. medicines
Production of hormones
Regulation of fluid and electrolyte balance
ECF and blood pressure, osmolarity, ion balance, pH
Filtrate within nephron
Urine when leaves
Movement of fluid
Filtered into Bowman's capsule
(membrane impermeable to cells and most proteins)
Peritubular capillaries have v high oncotic pressure so extremely high absorption from PCT (around 70% of filtrate reabsorbed)
Interstitial fluid in renal medulla gets increasingly hyperosmotic. Allows production of highly concentrated urine
Need a concentration gradient against which to concentrate the urine
Created by LOH
Descending limb
Permeable to water but not ions
Ascending limb
Permeable to ions but not water
Active transport of ions out of the ascending limb leads to osmotic transport of water out of the descending limb
When filtrate reaches DCT is hypoosmotic. 90% filtered Na has been reabsorbed, 80% filtered water reabsorbed, 100% filtered potassium and bicarbonate has been reabsorbed
Takes ~25 mins to filter entire plasma volume
Normal animal excretes 1ml/kg/hr of urine
Kidney linked closely to heart, can take ~20% of cardiac output