Renal System Flashcards
What are the functions of the kidney?
excretory function
- to protect the internal environment. excretion of metabolic wastes, urea, creatinine, toxins,
drugs, excess minerals… water.
homeostatic function
- regulation of the water balance, electrolyte balance and acid-base balance.
endocrine secretory function
- secretion of renin, erythropoietin and prostaglandins
endocrine metabolic function
- conversion of Vitamin D3 in active 1,25- dihydroxycholecalciferol
What is the structure of the nephron?
has the glomerulus (produces ultra filtrate from the plasma), bowman’s capsule, proximal convoluted tubule, loop of henle (descending and ascending), distal convoluted tubule and the collecting duct
What is the structure of the kidney? How does blood enter?
has the
- pelvis, ureter, renal artery and vein (enter via the hilus), medulla, cortex and renal capsule
blood enters via the real artery
nephrons located in the kidney, filter the blood
- toxins and waste are removed and collected as urine
urine drains into the calyx which leads to the pelvis and leaves via the ureter
- urine is propelled through the ureter via peristalsis
What is the flow of blood in the nephron/kidneys?
renal artery = route of blood entry into the kidney hilum interlobar arteries arcuate arteries interlobular arteries afferent arteries glomerulus capillaries = site of filtration efferent arteriol peritubular capillaries venues interlobular veins arcuate veins interlobar veins renal vein
What is glomerular filtration rate? What is
- glomerular hydrostatic or capillary pressure (GHP or GCP)
- glomerular colloid osmotic pressure (COP)
- capsular hydrostatic pressure (CP)
glomerular filtration rate = volume of filtrate/min
glomerular hydrostatic or capillary pressure
= fluid pressure exerted by the fluid on the blood vessel - pushes filtrate out
glomerular colloid osmotic pressure
= opposing force to filtration = osmotic pressure of proteins, albumin to keep water in
capsular hydrostatic pressure
= fluid in the glomerular capsule creates pressure pushing the fluid out into the glomerulus
= fluid trying to go back in
What are the different mechanisms of tubular transport?
diffusion
- through tight junctions and intercellular spaces
- driven by concentration, osmosis, or electrical gradients.
facilitated diffusion
- iion channels and uniporters
active transport
- carrier mediated through epithelial cells
= primary active transport - ATP consumption
= secondary active transport - concentration gradient created by primary active transport.
= co-transport/symporters = 2 solutes, depending on gradient of one
= counter transport/antiporters
What are the processes in urine formation/tubular transport?
glomerulus
- filters small molecules from the blood and produces ultra filtrate from the plasma = pushed into the capsul
= glomerular capillary endothelium has fenestrations that make it more permeable to allow passage of solute
= podocytes have pedicles that create gaps in the filtration slits
proximal convoluted tubule
- reabsorbs ion, water, glucose and removes toxins
= water is not actively reabsorbed, increase in osmolality due to ion movement facilitates water reabsorption
= glucose is reabsorbed with sodium via SGUT
= reabsorption of water increases tubular contraction of ion which facilitates movement down the conc gradient
loop of henle = counter current multiplier
- reabsorbs sodium and chlorine from the filtrate into the interstitial fluid
- descending tubule permeable to water but not urea
= water is reabsorbed
- ascending tubule is permeable to urea not water
= solutes (sodium and chlorine) are actively transported via the co-transporter
collecting duct
- urine concentration is achieved by continuing to secrete the solutes while increasing the water reabsorption
- is impermeable to urea and water except when anti-diuretic hormone/vasopressin is present
What is renal clearance?
Volume of plasma cleared of a substance in a unit time and excreted in urine.
Measured as a test of kidney function
Clearance (Cl) = (U x V) / P
ml/min
When is renal clearance the same as glomerular filtration rate?
How does GFR show kidney failure?
If a substance is filtered, and not reabsorbed or secreted, the clearance of that substance will representative of the GFR
GFR 15 – 90 is chronic kidney disease (CKD) in 5 stages
What is creatinine?
Creatinine is a natural waste product released from skeletal muscle
The clearance of creatinine is taken as a measure of the glomerular filtration rate (GFR)
Is glucose ever filtered? When?
Glucose is not usually cleared from the blood into the urine – so renal clearance is zero
= uncontrolled diabetes mellitus when so much glucose is filtered that some escapes reabsorption and ends up in the urine
How can osmolality be controlled?
anti-diuretic hormone or vasopressin
action on KIDNEY
- collecting duct
= insertion of aquaporins (pores) increases water reabsorption
hypothalamus is stimulated to release vasopressin from the posterior pituitary gland or stimulates feeling of thirst
How is vasopressin made and released?
hypothalamus is stimulated by increased plasma osmolality = wants water reabsorption
the supraoptic nucleus and paraventricular nucleus in the hypothalamus synthesise vasopressin which is then transported to the posterior pituitary gland and stored as secretory granules
What is anti-diuretic hormone/vasopressin mechanism of action?
ADH acts on cells in the collecting duct of the nephron
- binds to V2 receptors stimulating the insertion of water channels (aquaporins) in their apical membrane via the cAMP pathway
= ADH binds to V2 receptor on the GPCR. heterotrimeric subunits disassociate and alpha subunit binds to adenylate cyclase. catalyses conversion of ATP to cAMP. cAMP activates PKA which phosphorylates proteins and increases synthesis of insertion of aquaporins
= increases the permeability of the collecting duct to water, promoting water reabsorption
How does the renin angiotensin aldosterone system control blood pressure and blood volume?
blood pressure falls
renin is released from the granular cells of renal juxtaglomerular apparatus (cells of the kidney)
renin acts on angiotensinogen released/produced from the liver
- cleaved into angiotensin 1
angiotensin 1 is converted into angiotensin 2 by angiotensin converting enzyme (ACE)
- produced by endothelial cells in the lungs and kidneys
