Filtration and Reabsorption
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Filtration and Reabsorption - Details
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15 questions
| 🇬🇧 | 🇬🇧 |
| Definition of Filtration | Passive process where the water and other small molecules are driven through a selective filter by the gradient of hydrostatic pressure |
| Damage to what can lead to proteinuria | Basement membrane so protein leak pass and is present in urine |
| Why does constant pressure need to be maintained and how | Why --> To allow maintain filtration and efficient reabsorption How --> By changing arteriole resistance --> done by the number of contractions of smooth muscles in the walls |
| What happens to the arterioles if the GFR is too low | Afferent arterioles respond by dilating and efferent arterioles constrict This leads to pressure drop from renal artery to glomerular capillary therefore results in increase in glomerular capillary hydrostatic pressure, hence there is increased filtrate |
| What happens if the GFR is too high | Afferent arterioles constrict while efferent arterioles dilate Leads to decrease in glomerular capillary hydrostatic pressure, and therefore decrease GFR, while dilation makes it easier for blood to leave the glomerular capillary, therefore ↓glomerular capillary hydrostatic pressure |
| What are the different factors affecting GFR | Myogenic response → reflex and autoregulation ( FAST ) Macula Densa Tubuloglomerular feedback ( type of autoregulation and is slow ) Sympathetic Nervous System ( relatively fast ) Hormones → Angiotensin II , ANP, Aldosterone ( Slow ) |
| What is the maximum rate at which glucose can be reabsorbed | Renal threshold above this glucose will be found in urine ( glucosuria ) |
| How can you measure GFR | Clinically creatinine is used since it is made at a constant rate and is not reabsorbed as a result the creatinine clearance gives a good estimate of GFR however some is secreted in the nephron so it is a little above the actual value |
| Renal clearance formula | X = conc of x in urine * urine flow rate / conc of x in plasma |
| What can be used to measure the GFR rate and why | Creatinine clearance is used Creatinine produced naturally at a relatively constant rate by the breakdown of muscles and Creatinine is not reabsorbed, but a small amount is secreted in the nephron Hence the GFR rate it gives is slightly higher but can still be used ( eGFR ) |
| What is the site of major reabsorption in the kidneys | The PCT Around 67% of filtrate is reabsorbed from the PCT into the peritubular capillaries |
| What channels are located in the PCT | Na+ K+ ATPase SGLT2 transporter - glucose and sodium co-transporter ( glucose is completely reabsorbed ) , important in type 2 diabetes management SLC transporter - Absorption of amino acids with Na+ |
| In the descending loop of henle , what channels does it contain | Permenant aquaporins 1 channels to allow unrestricted movement of water from the descending loop leading to the filtrate becoming hypertonic Descending loop of henle reabsorbs 15% of water ( over 80% of water is reabsorbed at this point ) |
| What channels does the ascending loop of henle contain | The TAL consists of simple cuboidal epithelial cells that lack aquaporin-1 channels therefore the TAL is relatively impermeable to water Na+/K+ ATPase pumps in the basolasteral membrane create an electrochemical gradient that allows reabsorption of Cl– by Na+ /Cl– symporters in the apical membrane Leads to the formation of hypotonic fluid |
| What channels contained in the DCT | Approx. 5% of the filtered Na+ is reabsorbed in the DCT. Mainly via the thiazide-sensitive Na+ -Cl-cotransporter (NCCT) Calcium ions are reabsorbed via a specific epithelial Ca2+ channel under the influence of PTH and calcitriol |