Glomerular Filtration Flashcards
Glomerular Filtration
Filtration of blood at kidney’s nephron (movement from blood to tubular system). Step in producing urine
Peritubular Capillaries Secretion
Substances added directly from blood (peritubular capillaries) to urine (forming in renal tubule)
Where does blood enter nephron
Afferent arteriole to Boweman’s (glomelular) capsule via diffusion
What substance shouldn’t enter Boweman’s capsule
Large proteins. If protein is found in urine it indicates problems with glomerulus
Glomerulus Def
Dense capillary network in Boweman’s capsule. Plasma filters through this
Glomerulus (boweman’s) capsule
Collects glomuler filtrate (plasma only). Blood cells and protein don’t pass through this but move with other unfiltered plasma (80%) into efferent arteriole (smaller then afferent)
3 layers of globular filtration
capillaries, filtration membrane and Boweman’s capsule
Make up of capillary endothelium
Simple fenesetrated
Glomerular Capsule Make up
Basement membrane (negatively charged, lipid membrane (repels proteins)), podocytes (structures that filter by size, stops large molecules entering) and filtration slips (gaps betwwen podocytes)
Filtration Forces
Glomerular Capillary Blood Pressure (favours), plasma-colloid osmatic pressure (opposes) and boweman capsule hydrostatic pressure (opposes)
Greatest force in filtration
Glomerular capillary blood pressure. Significantly higher, results in net filtration pressure being positive (in favour, filtration occurs). Caused by afferent arterioles having a much larger lumen then efferent causing a build up of plasma
Osmotic Gradient Caused by
Large proteins in plasma forms osmatic gradient across membrane. Holds plasma in place
Hydrostatic Pressure Caused By
Filtrate already in capsule works against filtration
Glomerular Filtration Rate
ml of plasma filtered in both kidneys per minute. Clinically used to asses kidney function. When kidney’s aren’t working glomerular filtration rate decreases. Creatine levels in blood increases as GFR decreases
Tubular system function
Reabsorbs filtered plasma. Highly selective reabsorption (removes substances). Most is reabsorbed but some passes into urine. Exchange of substances caused by peritubular capillaries
Descending Limb of loop of Henlee
reabsorbed to blood: H20 excreted from blood: urea
Ascending Limb of loop of Henlee
Reabsorbs to blood: Na+, Cl- and K+
Where does most reabsorption to blood occur
Proximal Convoluted Tubule
Factor that effects how much sodium and water is absorbed
Blood Pressure
Transepithelial transport
Lumen of tubule, entering membrane of tubular cell, passing through cell’s cytosol, exiting through cell’s basolateral membrane, moves through interstitial fluid, moves throgh capillary cell into it’s lumen
Relationship between high blood pressure and Na+ levels
High Na+ levels = high water retention = high blood volume
How much energy does sodium reabsorption require in kidney
80% of total kidney energy expenditure. Active transport
Where Na pumps are located
Basolateral membrane. Moves ions across conc gradient
How does Na+ move into loop of Henlee
Down conc gradient. Passive
How does Na+ move into blood vessels
Up conc gradient. Active transport, ATPase pumps
Proximal Tubule Na+ absorption
Most (67%). Aids reabsorption of other substances (secondary active transport) eg glucose
Loop of Henlee Na+ absorption
25% absorbed. Helps produce urine in altering blood pressure
Distal Convoluted Tubule Na+ absorption
8% absorbed. Controlled by aldosterone
What hormone controls absorption of water
Anti-diuretic hormone
GLUT Transporter
Glucose facilitated diffusion across basolateral membrane
Regulation of Glucose Reabsorption
Not controlled by kidney. Controlled by capacity of glucose transporters. All glucose should be reabsorbed into plasma (needed in liver and endocrine). In diabetes glucose won’t be fully reabsorbed
Potassium secretion
Active via ATPase pumps. K+ is secreted from blood as Na+ is reabsorbed
Urea production
Breakdown of protein in liver. Filtered by kidneys (~50% filtered urea is reabsorbed). Blood urea nitrogen test (BUN) is an indication of kidney health
