Glomerular Filteration and Reabsorbtion Flashcards
What are the 5 main functions of the kidney
what are the hormones of the kidney (released)
- elimination of waste (urea)
- maintenance of bodily fluids
- regulation of blood pressure (RAAS)
- acid-base balance
- synthesis and secretion of hormones
Hormones
- RAAS: renin -angiotension-aldosterone system
- erythropoietin (from glomerular epithelial and peritubular cells)
- Vit D activation
- ADH activity (acts on the DCT and collecting ducts)
Nephron basics
two types of nephrones
Juxtamedullary nephrons: deeper LOH and majority of urine is concentrated here
cortical nephrons: less deep; more involved in electrolye and soulte concentrations
so concentrated (1 million per kidney) –> wont see changes in the renal function until down to about < 500,000 (great at compensation)
Vasculature of the Nephron
explain blood flow precentage to the kidney
- the glomerulus: afferent and efferent arteriole (but no change in oxygenation here– just feeding the cells of the nephron so they can participate in the soulte exchange
remeber arterioles are muscualr, thus the afferrent and the efferent can constrict and dilate to adjust flow
afferent arteriole: into the glomerulus
glomerulus: responsibly for the exchagne of soultes (small) through the fenestrated capillary bed into the filtarte
efferent arteriole: continues on to feed oxygen to the nephron cells throughout the process
peritubular capillaries: NORMAL capillary beds –> responsible for delivering the oxygen to the cells
vasa recta: the network of arteries and veins which feed the LOH –> controls the concentration gradient and speed of flow (slow) therefore impacting the concentration of the urine
venules :carry deoxy. blood back
Blood Flow to Kidney
- approx. 20% (1200 mL/min) of cardiac output get to the renal system
- 1/5th of that is filtered out
- 99% of that filtered is reabsorbed
explain the pressure systems which exist within the nephron
high pressure system: the glomerulus and the proximal blood flow
- Renal Artery (approx. 100 mmhg)
- glomerulus (60 mmhg) – allows for the hydrostatic pressure to flow from high to low (blood to filtrate)
- efferent arteriole (18 mmhg) – allows for enough pressure to deliver the O2 to the cells after glomerulus
the low pressure system: the O2 flow (from the efferent) to the rest of the nephron
- peritubular capillaries (13 mmhg)
- vasa recta (8mmhg) least pressure
Waste Elimination of the Kidneys
- how much water is eliminated
- what metabolites
Water: a waste product (amount depends on the hydration status of each pt.)
- approx. 1000-15000 ml of urine in 24 hrs. is water
metabolites
- urea from protein metabolism
- uric acid frrom DNA/RNA breakdwon (purine metabolism)
- creatitine from creatine in muscle
- drug metabolites!!
What are the processes that the kidney uses to elimate these wastes
- Filteration
(cells associated and their respective function)
Filteration, Reabsorbtion, Secretion, Excretion
Filteration: happens at the level of the glomerulus –> dependent on specialized structures & relies on hydropstatic pressures from the vasculature to the filtrate (eventually urine)
Specifics of the Glomerulus
- endothielial fenistrations
the capillaries are 100x more pourous than other capillaries (but regulated by mesangial cells and podocyte charge)
- basement membrane allows for the passage of specific subsatnces
- epithelium and podocytes of the bowman’s capsule
- podocytes: maintain a negative charge to only allow specific substances to pass (damage to this creates nephrotic diseases)
- mesangial cells: immune and sturctural function
specifics of mesangial cells and their role in the glomerulus and filteration
mesangial cells are located between the afferent and efferent arterioles
(function as part of the JG apparatus)
- mesangial cells are contractile: can change the surface area avalible for filteration to occur: therefore changing the GFR
- (these are higly responsive to endothelins, AGII and NE, and ANF) to then change the SA accordingly
- also have phagocytic propoerties
- produce a substance that can fill the gaps within the basement membrane
what are some restricitions to the filteration process
- the size of the pores: this prevents large molecules from passing through from the vasculature to the urine
- the strong negative charge of the podocytes: repels any negative charged plasma protiens (like albumin!)
when damage to the size or the charge occurs there is a reduced ability to properly filter
What are the pressures which effect the filteration process
equation & chagnes with constrction of afferent and efferent
the net pressure must favor filteration
3 pressures involved in filteration
1. hydrostatic/hemodynamic pressure: FAVORS the filteration process (high pressure in the vessel pushes out to the low pressure in the urine)
2. plasma colloid/oncotic pressure: OPPOSES the filteration process– more protein within the vessel pulls the fuluid back towards it
3. pressure within the Bowman’s Capsule would OPPOSE the filteration process
Net Filteration
Net Filteration Pressure = GFP - (Plasma colloid pressure - bowman’s pressure)
= will result in a net postive NFP to favor filteration
Changes in the plasma colloid pressure, bowmans pressure or hydrostatic pressure can alter the filteration
with constriction of the Afferent Arteriole – you decrease the pressure getting to the golmerulus – thuse there is a rapid decrease in pressure and drop in NET filteration
with Efferent contrstion – you have a build up of pressure which backflows into the glomerulus leadng to a higher pressure within the Bowman’s capsule thus there is no longer a pressure change in the golmerulus to flow – and there is no filteration (from high –> higher pressure? no that wont happen)
clinical correlation between poor filteration of the glomerulus due to intergrity of the mebrane leads to what
what are some ways which the glomerular intergrity can be damaged
if there is poor intergrtiy of the membrane –> affects the size of the pores and/or the charge barrier of the Renal corspuscle
first to leave is albumin – because its small and if the charge barrier is gone – itll pass through
- if there is a loss of albumin to the urine –> this will imapct plasma oncotic (protein pull pressure) leading to edema and third-spacing of fluid
- evidence of albumin snkeaing through is seen as proteinuria
Ways the Glomerual Intergrity can be compromised
- increased thickness of the membrane : leads to inability for soultes to pass at all and theres a net decrease in filteration
- rention of waste productes (spcifically azotemia (nitogen) can be toxic –> uremia!!!
what is GFR
what is normal
GFR: glomerular filteration rate
normal GFR: 125mL/min
- daily basis: 180 liters are filter & 99% reabsorbed
changes in GFR depend on the fluid status of the pateinets (the volume)
< 125 mL/min = too little fluid passing
> 125 mL/min = too much fluid passing (overhydrated!)
where does Reabsorbtion occur within the nephron?
what is reabsorbed?
99% of things are reasborbed : priamry action of reabsorbtion is the proximal convoluted tubule
- of the reabsorbed: only a small percent is waste products
What is Reabsorbed?
- metabolites, inorganic nutrients are reabsorbed
examples
- all of excreted glucose is reabsorbed
- most bicarb is reabsorbed
- most sodium
- most chloride
- most potassium
- about 50% of urea (takes a lot of passes to get rid)
- NO creatinine is reabsorbed (hence why its used to estimate GFR)
where does this occur?
- PCT: the cells of the PCT have good permiability; with transport mechanims in the lateral and basal surfaces
- have a bursh border to increase surface area
Pressures within the PCT which allow for reabsorption to occur
what is absorbed
the net force of pressures favor the reabsorbtion process from the PCT back into the capillary
What is absorbed?
- approx. 60-80% of the filtered water
- essentailly all metabolites essentail for the body will be
- (the remained of water and Na+ and Cl- are reabsorbed later in the tubules)
Process of reabsorbtion
- water = passive diffusion of osmosis from filterate through cells and to blood
- small solutes (Na+ and glucose) = use passive or active diffusion
Processes of how Sodium is reabsorbed at the PCT
3 mechanisms of transport
names and specifics of glucose transporters
Sodium
- at the luminal surface (urine facing with brush border) main mechanism is diffusion based on the concentration gradeitn to pull Na+ into the cells
- at the baso-lateral surface (cell facing the capillary) main mechanism is Na+/K+/ATPase active transporter – but the swap of the positives doesnt mess with the charge
end goal of sodium is that its taken back into the peritubular capillaries or the remainer is within the lumen
co-transport of sodium
- while sodium is being passively diffused into the cell –> this triggers the co-transport of glucose, amino acids and other molecules to go from the urine into the cells
- the amino acids and the glucose then can diffuse from the cell into the blood
glucose transporters of co-transport
- SGLT (sodium dependent glucose transporters) are the speciifc name of those which transport glucose into the cell
- GLUt 1-7 work to faciliate diffusion
- glut-4 is affected by insulin– not within the kidney
SGLT 1&2: bring the glucose and sodium into the cell together
then the GLUT1-7 (except 4) trasnport the glucose via facilated diffusion into the capillary
counter-trasnport
- uptake of sodium inot the cell for the release of an H+ ion into the urine
what solutes are able to pass throught the PCT back to the blood via passive transport
- water: through the tight junctions
- chloride
- urea (its small, so it will be reabsored but more filteration slowly gets rid of it)
