Flashcards in Session 4 - Changes in Plasma Volume (Cells of the tubules) Deck (62)
What is in predominant in the ECF?
What ion is predominant in the ICF?
What occurs at the glomerulus?
• Filters of 180l/d (bulk filter)
What occurs at the PCT?
• Freely permeable membrane
• Reabsorbs electrolytes, glucose (100%), urea (50%) and amino acids (100%)
• Reabsorbs large amount of fluid (66%)
Reduces water content
What occurs at the thin descending tube of the loop of henle?
• High conc of sodium
• Concentrates filtrate due to loss of water
What happens at the thin ascending tube of the loop of henle?
• Pulls Cl- and Na+ out of filtrate without H20
• Causes filtrate to become dilute
Why is the DCT special?
• Selective reabsorption
What happens at the DCT?
• Reabsorbs water and concentrates urine via action of ADH
• Reabsorbs Na and water as a result of aldosterone action
• Secretes K+ as a result of aldosterone
What occurs in the collecting duct?
• Permeability affected by ADH
• Absorbs or secretes K+, Na+, H+ and ammonia according to body's needs
What are the excretory ranges of sodium?
• Low salt diet 0.5g/d
Why can't we directly excrete water?
• No water pump
• Must follow solute
Why is important to control the volume of the ECF?
• Includes the vascular system (blood pressure), the volume of which needs to be controlled within very tight limits
What is sodium balance?
The kidneys must match input of sodium with output
Why does ECF expansion occur
• If Na+ excretion is less than intake, it is retained in the body in the ECF
• This causes water to be drawn into the ECF from the nephron, causing increase in volume
• Blood volume and arterial pressure increase
• Oedema may follow
Why does ECF contraction occur?
• If Na+ excretion is greater than intake (patient is in negative balance) the Na+ content decreases
• Less water drawn out of nephron, so ECF volume decreases along with blood volume and arterial pressure
Does an increase in Na+ mean you get an increase in ECF osmolarlity?
• If conc of Na+ in the ECF increases, then so does the volume
• Increased volume gives increased CO, so increase Na+ excretion
State the % of Sodium filtered at each point of the nephron
• PCT - 67%
• Descending thin limb of Henle's loop - 0%
• Ascending thin and thick limb of Henle's loop - 25%
• Distal convoluted tubule - 5%
• Collecting duct system - 3%
State the % of water filtered at each point
• PCT - 65%
• Descending thin limb of Henle's loop - 10-15%
• Ascending thin and thick limb of Henle's loop - 0
• Distal convoluted tubule - 0
• Collecting duct system - 5 (>24% during dehydration)
How much Na+ is filtered in glomerulus?
How much Na+ is reabsorbed in the PCT?
What is glomerular tubular balance?
• Reabsorption of sodium is always around 67%
• Blunts Na+ excretion response
What do all transporters depend on?
The action of Na+/K+ATPase
What are the two regions of the PCT?
• Section 1 (early)
Section 2 + 3(late)
Give one transporters found in the basolateral membrane of the S1 section of PCT
Give five transporters found in apical membrane of S1 of PCT
• Co-Transported with glucose
• Na-H exchange
• Co-transport with AA/Carboxylic Acids
• Co-transport with phosphate (increase with [PTH])
What happens to Urea and Cl- in S1 of the PCT?
• Remain in filtrate, to counterbalance loss of glucose/AA/phosphate/HCO3
• Gives conc grad for Cl-
What is found in basolateral membrane of S2-S3?
What drives reabsorption of Cl- in S2-S3?
• Conc gradient
How is Cl- primarily reabsorbed in S2-S3?
• Na-H exchanger
• Paracelluar Cl- reabsorption
• Transcellular Cl- reabsorption