Filtering Blood Flashcards
ULTRAfiltration
- Filtration of small molecules from blood under high pressure
- Happens at the glomerulus and Bowman’s capsule
- High hydrostatic/ blood pressure at glomerulus
- Left ventricle contracts/ ventricular systole
- Afferent arteriole has wider diameter than efferent so efferent arteriole has a narrower lumen
- Bottleneck effect = increase in pressure of glomerulus
3 layers
- Glomerulus capillaries have endothelium cells with fenestrations/ small pores between them
- Basement membrane- has pores and acts as a molecular sieve or dialysing membrane through which large molecules can’t pass
- Made of collagen and glycoproteins - Podocytes (squamous epithelial cells)- podocyte feet wrap around capillary and have filtration slits
Process of ultrafiltration
- Systole and arterioles increase the blood pressure
- Forces small solutes/ components of plasma through fenestrae, basement membrane and slits between pedicels into the Bowman’s capsule
- Molecules <30000 RMM can pass through basement easily
- Molecules with RMM>68000 too large (proteins, blood cells, platelets)
What small molecules are present in glomerular filtrate
Forced from glomerulus into capsule and pass through the gaps:
- Glucose
- Water
- Amino acids
- Urea
- Fatty acids
- SMALL proteins
High arterial pressure effect
- Increased glomerular filtration
- Dehydration
- Increased volume urine
- Damaged kidney
Cause of protein in urine
- Greater glomerular pressure
- Damage to basement membrane
- Proteins forced through
Low protein diet effect on filtration rate
- Less protein in the plasma
- Osmotic pressure decreases / water potential higher
- Overall pressure forming filtrate increases = more filtrate produced
- Rate of filtration faster
Effect of blood loss
- Blood pressure decreased
- Less filtrate formed
- Lower filtration rate
How to increase glomerular pressure (arterioles)
1) Constrict efferent arteriole so that it gets narrower
2) Dilate the afferent arteriole so that it gets wider
Arterioles adjusting to pressure
Too high
- Circular muscles contract making the lumen smaller
- Less difference between diameter of afferent and efferent arteriole
- Pressure drops
Selective reabsorption
Uptake of specific useful molecules from filtrate back into bloodstream
Adaptations of PCT cells
- Microvilli to provide larger and increased SA for reabsorption
- Large no of mitochondria = ATP for active transport of Na+ ions and glucose
- Folded basement membrane
- Tight junctions between cells = molecules do not diffuse between adjacent cells
- Close association with capillaries = short diffusion pathway
Glucose selective reabsorption
ALL GLUCOSE REABSORBED
- Facilitated diffusion through protein channels or carriers
- Glucose + amino acids diffuse with Na+ ions via co-transport proteins
- Glucose and amino acids diffuse out of PCT into blood
- Glucose also actively transported from PCT cells into blood
Water selective reabsorption
90% OF WATER REABSORBED
- Absorbed by osmosis
- From an area of high w.p to an area of low w.p
- Across partially permeable membrane into PCT wall and into blood
- No energy required = no ATP
Na+ ions selective reabsorption
- Facilitated diffusion into cell from glomerular filtrate
- Active transport from cell into blood via the Na/K pump in basal membrane
- ATP used
- Higher [Na+] in filtrate so more moves into cell via f.d
Cl- ions selective reabsorption
- Facilitated diffusion through protein channels or carriers into PCT wall and into blood
- Down the concentration gradient
- No energy required
Why are proteins not reabsorbed into bloodstream?
- Too large to pass through and diffuse back into the blood
- No specific carrier or channel proteins for them to diffuse back in
Why does [urea] increases along PCT?
Water has been reabsorbed into the capillaries as it leaves the tubule by osmosis. Urea not reabsorbed (very little)
Respiratory inhibitor (PCT)
- Inhibits active transport
- Glucose reabsorption prevented
- Water reabsorption still occurs
- Ratio/ concentration of glucose increases
Glucose and NaCl to prevent dehydration
- More glucose and sodium absorbed from gut into blood
- More glucose and Na+ in glomerular filtrate
- More Na+ ions diffuse into PCT cells (higher conc grad)
- More glucose co-transported
- Lowers water potential so more water reabsorbed by osmosis
Function of loop of Henle
Creates osmotic (conc) gradient/ low water potential in the medulla so water can be reabsorbed
Loop of Henle
- Descending limb permeable to water
- Ascending limb impermeable to water
- Water leaves descending limb by osmosis
- Na+ ions are retained = going down conc increases
- At apex, Na+ very concentrated as filtrate rich in Na+
- Na+ and Cl- ions actively transported out of ascending limb
- Lower w.p in tissue fluid of medulla
- Countercurrent system
Longer loop
- Lower water potential in medulla
- As more ions actively transported
- More water leaves collecting duct by osmosis
