Lecture 25: Renal Structure, Function And Filtration Flashcards
Look at slide 7 and learn it
Yeh
What are the functions of the kidneys
- Excretion of metabolic wastes and foreign chemicals
Homeostatic functions - Regulation of water in the body (regulates osmolality of body fluids)
- Regulation of Na+ (regulates ECF volume, plasma volume and blood pressure)
- Regulation of K+ (maintains membrane potentials)
- Regulates Ca2+ (affects bone density and other functions)
- Regulates H+ and HCO3- (regulated pH)
- Endocrine roles: erythropoietin secretion, activation of renin-angiotensin-aldosterone system, activation of vitamin D3
- Gluconeogenesis
Renal blood flow
Artery➡ afferent arteriole ➡ glomerular capillaries➡ efferent arteriole➡ perk tubular capillaries ➡vein
Juxtaglomerular apparatus. Describe what it is and what it does
- functionally important area of the nephron
- located where the start of the distal tubule passes between afferent and efferent arterioles
2 specialised cell types:
A) macula densa cells - in wall of the DT (detect flow rate) and secrete paracrines to communicate with afferent and efferent anteriole.
B) juxtaglomerular (or granular) cells in wall of afferent arteriole. Specialised smooth muscle cells that can secret renin
Paracrines (local) communication between these two cell types
How urine formed? Simply
- Glomerular filtration- flow from the glomerular capillaries into the bowmans capsule- slide 10
- Reabsorption: from tubules to perk tubular capillaries
- Secretion: from peri tubular capillaries to tubules
- Excretion: elimination from tubules out of the body as urine
Glomerular filtration
Filtrate must cross 3 barriers to enter bowmans capsule, what are they
Filtrate must cross 3 barriers to enter bowmans capsule
A) capillary endothelial layer
B) basement membrane
C) epithelial cell layer
Water and solutes pass between cells not through cells
Side 11
-net filtration occurs because of pressure gradient
-filtration mainly based on size
-no blood cells are filtered into bowmans capsule normally
-virtually no protein filtered normally
-water and other small solutes in plasma are freely filtered
-not very selective
-concentration of each solute in filtrate= concentration in plasma
-note that small molecules that are protein-bound will not be freely filtered eg Ca2+
-normally about 20% of plasma is filtered
Glomerular filtration rate (GFR)
“Volume of plasma filtered through both kidneys per unit time”
- GFR is a critical indicator of kidney function
- GFR is an average young adult is 125ml/mi or 180L a day
- > 99% filtrate is reabsorb end by renal tubules
- ursine production about 1ml/min (or 1.5L/day)
Filtration Fraction (FF)
Fraction of the plasma entering the glomerulus that is filtered per unit time
- 20% of plasma entering glomerulus is filtered into bowmans capsule
- remaining 80% continues to efferent arteriole.
FF= GFR/ renal plasma flow
GFR and FilTration pressure
GFR is determined by?
- Net glomerular filtration pressure
- Permeability of filtration barrier
- Surface area available for filtration
As permeability and SA don’t change much normally, GFR is largely determined by the filtration pressure
-filtration pressure is a balance between hydrostatic pressures and colloid osmotic pressures (starling forces)
Glomerular filtration pressures:
1. Hydrostatic pressure
-pressure exerted by a fluid in a container
-the more fluid, the greater the hydrostatic pressure
-fluid moves across a semi-permeable membrane from regions of high to low hydrostatic pressure
Slide 16
Glomerular filtration pressure
Colloid osmotic pressure:
-the pressure of non-permeating solutes exert an osmotic pressure
-the pressure generated by non-permeating solutes is call the colloid osmotic pressure
-in blood vessels, colloid osmotic pressure is created predominantly by proteins
-draws water from areas if low protein concentration to areas of high protein concentration
Slide 17 and take a look at slide 18 also
Filtration pressure in kidneys
-Net filtration pressure: the balance between hydrostatic and colloid osmotic pressures acting across the filtration membrane.
-colloid osmotic pressure of the filtrate in bowmans capsule is very close to O mmHg (virtually no proteins) so can be ignored
-it is always a positive value otherwise the kidneys would stop forming urine (renal failure)
Side 19
How is GFR autoregulated?
Kidneys maintain a stable GFR whilst MAP varies between 80-180mm Hg via renal auto regulation
-local response achieved through changes in vascular resistance of the affect arteriole.
Autoregulation mechanisms:
1. Myogenic regulation
2. Tubuloglomerular feedback
How does auto regulation affect GFR?
Check out slide 21
How does changing resistance in afferent arteriole affect GFR?
-if MAP increases, it will drive more blood through afferent arteriole into glomerular capillaries. This will increase hydrostatic pressure in glomerular capillaries and increase GFR
-auto regulation: the afferent arteriole constricts and this limits the amount of blood coming into the glomerular capillaries and limits the increase in glomerular hydrostatic pressure and GFR ie. it
prevents GFR from increasing under influence of increased MAP
-similarly a decrease in MAP will cause glomerular hydrostatic pressure and GFR to fall
Autoregulation: the afferent arteriole dilates and lets more blood into glomerulus so the glomerulus hydrostatic pressure will not fall as much. So it prevents GFR from falling.
