10/11 - Renal system I & II Flashcards
where is water absorption most active?
jejunum followed by ileum
where does Na+ absorption occur?
all along intestine
where does K+ net absorption occur?
jejunum and ileum
colon absorption (2)
- can absorb water against osmotic gradient
- very active in Na+ absorption
what can result in excessive los of K+?
severe diarrhoea
what does blood plasma contain? (5)
- water
- ions
- organic molecules
- trace elements and vitamins
- gases
cellular elements of blood plasma (3)
- RBC
- WBC
- platelets
which type of molecules flow into bowman’s capsule? (5)
- molecules in plasma
1. amino acids
2. glucose
3. nitrogenous waste
4. CO2
5. O2 - no proteins/lipids
the nephron (2)
- filtration unit
- single cell layer
4 major processes of nephron (4)
- filtration
- reabsorption
- secretion
- excretion
where does 100% plasma filtration occur?
bowman’s capsule
70% filtrate reabsorbed
proximal tubule (next to bowman’s capsule)
20% filtrate reabsorbed
loop of Henle
9% filtrate reabsorbed
distal tubule and collecting duct
how much of total filtrate is excreted?
1%
proximal tubule secretions
H+ secreted to acidify urine, drugs and ureic acid also secreted
distal tubule and collecting duct secretions
urea and hormones
filtration
transfer of soluble components (water and waste)
reabsorption
absorption of ions and water
secretion
transfer of H+, creatinine, drugs, K+ and urea
excretion
urine containing water, wastes, ions, H+, creatinine, urea and drugs etc
why does amount of urine change?
reabsorption changes depending on temperature, exercise, water and salt intake
myogenic autoregulation when mean arterial pressure is low (4)
- renal flow into afferent arteriole reduces
- hydrostatic pressure reduces and blood pressure at efferent arteriole temporarily increases resulting in stretch on walls
- triggers myogenic autoregulation in efferent arteriole
- vasoconstriction at efferent arteriole increases blood pressure in glomerulus keeping pressure constant
myogenic autoregulation when mean arterial pressure is high (4)
- renal blood flow into afferent arterioles increased
- afferent arteriole temporarily have stretch on walls
- triggers myogenic autoregulation in afferent arteriole
- vasoconstriction at afferent arteriole reduces blood pressure in glomerulus, keeping pressure constant
mechanism keeping glomerulus filtration rate constant
myogenic autoregulation
3 main functions of proximal tubule (3)
- water reabsorption (70%)
- sodium ion (Na+) absorption
- glucose absorption (only tissue with glucose transporters)
interstitial fluid (3)
- type of body fluid between cells
- component very similar to plasma
- ion concentration in interstitial fluid helps transfer of ions from nephron cells back to peritubular capillary cells (tiny blood vessels)
pathway of filtrate (5)
- lumen of nephron
- proximal tubule cells
- interstitial fluid
- peritubular capillary cells
- lumen of capillary
reabsorption of Na+ and H2O (5)
- Na+ enters proximal tubule cells via epithelial Na+ channel down electrochemical gradient
- Na+ moved out of lumen of nephron down electrochemical gradient
- H2O enters proximal tubule via aquaporin (H2O channel), down osmotic gradient across nephron lumen side of proximal tubule
- Na+ actively pumped out to interstitial fluid via Na+ K+ ATPase pump in proximal tubule cell membrane facing towards peritubular capillary
- H2O leaves proximal tubule cell via aquaporin down osmotic gradient across cell membrane facing interstitial side
active transport of Na+ (4)
- Na+ actively pumped out from proximal tubule to interstitial fluid via Na+/K+ exchange ATPase pump
- ATP used to pump out Na+ while K+ brought in
- K+ let out via leak channel
- ATPase pump/leak channel ensures low Na+ potential inside proximal tubule cell compared to lumen of nephron (electrochemical gradient across nephron lumen side of proximal tubule cell membrane)
reabsorption of glucose (4)
- Na+ moving down electrochemical gradient uses sodium-glucose transporter protein to pull glucose into cell against concentration gradient
- glucose diffuses out of basolateral side of cell using glucose transporter proteins
- Na+ pumped out by Na+ K+ ATPase pump
- K+ let out by potassium leak channel
what does a longer loop of Henle result in?
more concentrated urine produced
what uptake occurs in the ascending loop of Henle?
absorption of ions via primary active, secondary active and passive transport
what uptake occurs in the descending loop of Henle?
absorption of water via aquaporin
peritubular capillaries (3)
- capillary blood vessel in the renal system
- run right next to nephrons (surround proximal and distal tubules)
- made of one layer of cells, have channels and transporters
what are peritubular capillaries surrounding the loop of Henle called?
vasa recta
loop of Henle counter-current multiplier (3)
- filtrate entering descending limb becomes progressively more concentrated as it loses water
- blood in vasa recta removes water leaving loop of Henle
- ascending limb pumps out Na+, K+ and Cl-, filtrate becomes hypotonic
explain counter-current role in vasa recta in reabsorption of H2O from loop of Henle (3)
- create strong osmotic gradient across fluid in nephron and blood in peritubular capillary (flow in opposite directions)
- ion conc highest in loop of Henle, ions transported from ascending loop to interstitial space via respective channels, co-transporters and ATPase pumps. ions then move to peritubular capillaries (flowing opposite direction to fluid in loop of Henle)
- ion conc at loop of peritubular capillaries highest. aquaporins only present in descending loop of Henle, water molecules move from inside nephron to peritubular capillaries following osmotic gradient
what does vasa recta mean?
vasa (vessel) recta (straight)
(2 straight vessels that are loop of Henle and peritubular capillary run parallel to eachother)
role of distal tubule
removes remaining 9% of water from nephron
what is aldosterone? (3)
- steroid hormone synthesised in adrenal cortex (outer portion of adrenal gland sits atop each hormone)
- hydrophobic (remains in capillary)
- acts on distal tubule and collecting duct cells
how does aldosterone affect nephrons (4)
- aldosterone molecules arrive at distal tubule - secreted into interstitial fluid and distal nephron cell (combines with cytoplasmic receptor)
- hormone-receptor complex initiates transcription in nucleus
- translation/protein synthesis makes new protein channels and pumps
- aldosterone-induced proteins modulate and enhance activity of existing channels and pumps (blood absorbs more Na+)
role of aldosterone
induces Na+ reabsorption to the blood
kidney response to ingesting too much Na+ (4)
- cardiac hormone (atrial natriuretic peptide) secreted from atria
- causes decrease in number of aldosterone molecules in blood
- decreasing number of Na+ channels in nephron cells
- majority of Na+ remains inside nephron and excreted
vasopressin (3)
- 9 amino acid peptide protein hormone
- protein that isn’t filtrated at glomerulus
- causes insertion of water channel (aquaporin) into apical membrane
vasopressin effect on nephron (5)
- vasopressin in blood arrives next to collecting duct, binds to vasopressin receptor on collecting duct cell
- binding induces signalling leading to exocytosis of storage vesicles, leads to vesicles with aquaporins moved and fused to cell membrane facing collecting duct
- more aquaporins moved to cell membrane - allows H2O molecules to enter collecting duct cells
- storage vesicles with aquaporin also moved to medullary interstitial fluid side of membrane
- H2O molecules let out to medullary interstitial space, loaded into peritubular capillary by osmosis
role of vasopressin
increases H2O absorption in nephrons - diluting plasma - less urine produced
erythropoietin (2)
- peptide hormone
- produced in kidneys
role of erythropoietin (2)
- produced when kidneys sense low oxygen level (concentration of O2 gas pressure (PO2) in the arterial blood should be just below 100 mmHg)
- stimulates production of red blood cells
