Renal Flashcards
Major renal functions
Regulation of water and electrolyte balance.
Hydrogen ion regulation (long term regulation of pH)
Excretion of wastes (metabolic and bio active substances)
Regulation of arterial blood pressure
Regulation of RBC production due to release of EPO
Regulation of vit D production
Gluconeogenesis
Anatomy of kidneys and urinary system
Medulla (external surface)
Cortex (internal surface, houses nephrons, urine drains into renal pelvis and down into ureter)
Parietal fat is protective mechanism
Renal corpuscle:
- glomerulus- bed, tuff of capillaries
- Bowmans capsule- surround glomerulus for protection
Proximal tubule- high reabsorption
Descending limb/ ascending limb (loop of Henle)
Collecting duct- more towards bladder
Vascular elements of kidneys
Two sets of capillaries: glomerular capillaries, peri tubular capillaries
Unique blood vessel arrangement: renal artery- small arteries- afferent arterioles- glomerulus (capillaries) - efferent arterioles- peri tubular capillaries / vasa recta- veins
Nephron function
Glomerulus supplied blood by an afferent arteriole
Renal corpuscle forms a plasma derived fluid filtrate
Around 20% of plasma volume filters into capsule, remaining blood leaves the glomerulus by the efferent arteriole
Filtration barrier ensures filtrate is free of cells and most proteins
Filtrate leaves Bowmans capsule and enters the tubule
Fluid reaching end of nephron combines in the collecting ducts
Fluid drains from end of collecting duct into renal pelvis which is continuous with the ureter
Renal processes
Glomerular filtration
- filtration of fluid from plasma
- initial filtrate has same composition as plasma but does not contain cells and most plasma proteins
Once in nephron tubule, filtrate composition adjusted by:
- tubular reabsorption: movement of substances from tubule to peritubular capillary plasma
- tubular secretion: movement of substances from peritubular capillary plasma to tubule
Purpose of filtration
- clears body of wastes and foreign substances rapidly
- allows constant and rapid adjustments to maintain individual substance balance (eg. Maintain ion levels at set point)
- retain 100% glucose
- 50% urea
- more secretion than filtration of penicillin (try to get rid of drugs)
Nephron filtration
- osmolarity in glomerulus is the same as plasma, but decreases at the end of loop of Henle to ~100- higher the osmolarity, the higher the urine concentration
- bulk of reabsorption occurs in proximal tubule all the way up to Distal tubule
- collecting duct is where fine tune filtration occurs
Renal blood flow
Kidneys receive 1L/ min
All of this blood flows through glomeruli in cortex. The vast majority continues on via efferent arterioles to peritubular capillaries in cortex and then into renal venous system.
The vasculature of the cortex is unusual due ton2 sets of arterioles and 2 sets of capillaries
Renal blood flow
RBF = change in pressure / resistance
R varied by changing arteriolar radii. Normally afferent and efferent are equal, but not always.
If either afferent or efferent constrict- decreased RBF
If either afferent or efferent dilate- increased RBF
Glomerular filtration barriers
Filtration structures; renal corpuscles (glomerulus and Bowmans)
Filtrate composition = plasma, except filtration barrier prevents entry of RBC and proteins.
3 layers: fenestrated capillaries, basement membrane, podocytes- foot processed extensions
Each of these surfaces is neg charged so prevents entry of neg, LARGE charged proteins
Glomerular filtration rate
Favouring filtration:
-Pgc (glomerular capillary BP) chief force pushing fluid across filtration membrane. Varied to control GFR
~55mmHg
Opposing filtration:
- piegc- osmotic force due to protein in plasma ~30mmHg
- Pbs - fluid pressure in Bowmans space ~15mmHg
Therefore net filtration pressure is 15
Regulation of GFR: autoregulation
An intrinsic mechanism that constricts/ dilates afferent arterioles to offset and rise/ fall in BP and prevent change in Pgc
- important to maintain GFR and prevent damage to structures
When BP increases, GFR does not change from 80-180mmHg- kept constant in this range
Autoregulation: myogenic mechanism
- vascular smooth muscle tends to contract when stretched (stretch sensitive ion channels open- depolarisation- voltage gated Ca2+ channels open- Ca2+ contracts smooth muscle
- if BP increases, afferent arterioles constrict and restrict blood flow into glomerulus, restricting increases Pgc and increases GFR
- if BP decreases, afferent arterioles dilate and promote blood flow into glomerulus, restricting decreases Pgc, decreases GFR
Tubuloglomerular feedback mechanism
Local control pathway in which fluid flow through the nephron tubule influences GFR
Directed by macula densa cells (salt detectors)
- as filtration rate in an individual nephron increases, increased NaCl that escapes reabsorption (insufficient time). Increased filtrate (NaCl). Macula densa cells increase NaCl of filtrate and release a vasoconstrictor chemical. Vasoconstriction of afferent arteriole reduced Pgc and therefore GFR decreases
Extrinsic control of GFR
Local controls for GFR can be overridden my sympathetic nerve fibres of autonomic NS due to importance of kidneys in maintaining arterial blood pressure.