Renal System - Glomerular and Tubular Function Flashcards
What are the forces involved in glomerular filtration?
Hydrostatic pressure - pressure created by fluid against the walls of a structure
Colloid osmotic pressure - osmotic pressure created by presence of plasma proteins within a blood vessel
Filtration is favoured at the glomerulus because blood hydrostatic pressure in the glomerular capillaries is greater in comparison to most other capillaries
How is water reabsorbed ?
Water is reabsorbed by both paracellular and transcellular routes by osmosis
ADH controls permeability of water absorbing structures such as collecting duct and loop of Henle
Water reabsorption occurs because of the osmotic gradient which exists between the tubular and interstitial fluids of the kidney
The size of the gradient increases from the cortex to the medulla of the kidney
How are Na+ ions reabsorbed ?
Most Na+ ions are reabsorbed by active transport via the transcellular route
This pathway is facilitated by the concentration gradient for Na+ established between the tubular cell interior and the interstitial fluid by the Na+,K+ ATPase pump
Exhibits gradient time limited transport
Process is regulated by hormone aldosterone
What is the transport maximum ?
Maximum rate of glucose/ amino acid reabsorption
Units are mmol/ min
If plasma glucose/ amino acid levels exceed transport maximum = renal threshold ( mmol/L )
This causes glucose and amino acids to be observed in the urine
The limit is due to the saturation of transport systems involved
What is the reabsorption pathway ?
There are two pathways which substances can take to reach the interstitial fluid surrounding the peritubular capillaries
The paracellular path - this involves the diffusion of water and solutes through the junctional spaces between the tubular cells.
Transcellular path - this involves the movement of water and solutes across the tubular epithelial cell membrane and cytosol
How is glucose and amino acids reabsorbed ?
PCT reabsorbs 100% of filtered glucose and amino acids
To cross from the tubule lumen to the PCT cell interior, glucose and amino acids utilise a secondary active transport mechanism
Co-transporters are used as they move glucose/amino acids in the same direction as Na+
To cross the PCT cell membrane on the interstitial fluid side a facilitated diffusion transporter is utilised
What is tubular resorption ?
Tubular reabsorption is the process of reclaiming substances from the tubular fluid - ensures minimal fluid is lost through urine and useful substances like glucose are filtered and kept
Largest contribution to tubular reabsorption is made by proximal convoluted tubule - microvilli and basal invaginations to increase SA for reabsorption
What is tubular secretion ?
Tubular secretion - when substances are transported from the peri-tubular capillaries without passing through the glomerulus to the tubular fluid for excretion.
How is the glomerular filtration regulated ?
If glomerular filtration rate GFR is too high normal reabsorption doesn’t occur
If GFR is too slow waste is reabsorbed
Kidneys regulate glomerular hydrostatic pressure by myogenic auto regulation of afferent and efferent arterioles
Changing blood flow into glomerulus by adjusting diameter of afferent arteriole resulting in either vasoconstriction/ vasodilation
Adjusting diameter of efferent arteriole - narrowing of efferent lumen increases hydrostatic pressure
Angiotensin II narrows efferent arteriole maintaining hydrostatic pressure in glomerulus
What is glomerular filtration ?
Glomerular filtration - process by which water and some solutes pass from the plasma in the glomerular capillary into the Bowman’s capsule
What is the glomerular filtration membrane composed of ?
Glomerular capillary endothelium,
Basement membrane; negatively charged
Bowman’s capsule epithelium; consist of podocytes and pedicel extensions
Forms glomerular filtrate which is similar in composition to plasma
RBC, plasma proteins are too large to pass through filtration membrane
