Kidney Lecture 1:Structure and Blood Filtration Flashcards
The Kidney : Functions
Regulation of Water, Salts, Acid-Base balance
Removal of metabolic waste
Removal of foreign chemicals
Gluconeogenesis (formation of glucose)
Production of hormones / enzymes
Erythropoietin (controls red blood cell production)
Renin (controls blood pressure and sodium balance)
Activates Vitamin D (regulates calcium)
Millions of nephrons feed into output from one kidney
Each kidney contains about 1 million nephrons
Each nephron feeds into collecting ducts
These feed into the ureter
Kidney branched tubular organ resembling a tree
Nephron : Key functions
Glomerular Filtration
Tubular Secretion
Tubular Reabsorption
Podocytes
surround blood vessels within the glomerulus
Foot-like process create a sieve-like structure
Allows free passage of small molecules from blood to kidney tubules
Glomerular Filtration Rate
Fluid filtered through glomeruli by pressure of flow through blood vessels
Glomerular Filtration Rate (GFR) - Volume of fluid filtered from glomeruli to bowman’s space per unit time
GFR regulated by adjusting blood pressure either side of glomerulus
One way kidneys maintain water and salt balance
Reducing pressure in the glomerulus reduces GFR
Constricting afferent vessels
Dilating efferent vessels
Reduces water and salt loss through excretion
Increasing pressure in the glomerulus increases GFR
Constricting efferent vessels
Dilating afferent vessels
Increases water and salt excretion
Identify key parts of the kidney functional unit: the nephron
Glomerulus, Proximal Convoluted Tubule, Loop of Henle, Distal Convoluted Tubule, Collecting duct
Describe process of glomerular filtration
Filtration of water and small molecules from blood to nephron through glomerulus
How glomerular filtration rate is regulated
Dilation and constriction of afferent and efferent blood vessels around the glomerulus
proximal tubule-salt reabsorbed
Tubule – Cell : Na/X (e.g Glucose cotransport), Na/H counter transport
Na+ moved from tubules into cells through two mechanisms:
Co-transport with other molecules. E.g. Glucose
Counter-transport of Hydrogen ions (Na+ in , H+ out)
Cell – Body : Na/K ATP Pump
Na+ moved from cells to interstitial space and then blood via active transport
Na+/K+ ATPase pump, requires ATP
K+ returns to interstitial fluid via ion channels
Down concentration gradient
Ascending Loop of Henle- salt reabsorbed
Tubule – Cell : Na – K – Cl cotransporter (NKCC)
Na+ moved from tubules into cells through cotransport with K+ and Cl-
Na-K-Cl cotransporter (NKCC)
K+ moves back into tubule via ion channels
Down concentration gradient
Cell – Body : Na/K ATP Pump
Na+/K+ ATPase moves Na+ out to interstitial space and K+ into cells
K+ returns to interstitial fluid via ion channels
Down concentration gradient
Collecting Ducts-salt reabsorbed
Tubule – Cell : Na Channel
Tube – Cell : Na+ moves into cell and K+ moves out through ion channel
Down concentration gradient
Cell – Body : Na/K ATP Pump
Cell – Body : Na+/K+ ATPase moves Na+ out to interstitial space and K+ into cells
Hormonal Control - salt reabsorbed
Aldosterone : Expression of extra ion channels / pumps in collecting duct
Aldosterone : steroid hormone
Regulates Na+ reabsorption and blood pressure
Acts in collecting duct tubule cells
Increases expression of ion channels and Na+/K+ ATPase
Descending Loop of Henle
- how water is reabsorbed
High salt content in interstitial fluid drives water diffusion from loop
Blood flow counter to tubule flow maintains gradients
Only descending loop permeant to water
Ascending loop reabsorbs salts – creates hypertonic solution in interstitial fluid around loop
This causes water to diffuse out of descending loop
Blood flow around loop of Henle is counter to flow through loop of Henle.
Freshly filtered blood (low in salt) first encounters ascending loop of Henle
Encourages salt absorption
This salt-rich blood then circulates around descending loop
Water from descending loop moves into blood
Maintains concentration gradients
