Reabsorption Flashcards
(18 cards)
What is tubule reabsorption
process where water and solutes are reabsorbed from the tubular fluid and returned to the blood
Where does most of the reabsorption happen?
proximal convoluted tubule
Which parts of the nephron allow for reabsorption and why?
- proximal convoluted tubule: reabsorbs ~65% due to its length, microvilli, and abundant mitochondria
- nephron loop: reabsorbs ~25% Na+, K+, and Cl-, and 15% of water to maintain osmotic gradient
Function of the distal convoluted tubules (DCT)
- reabsorption
- hormonal regulation: aldosterone, ADH, PTH, natriuetic peptides
- secretes potassium and hydrogen ions
- maintains acid-base balance
Function of collecting ducts
conserve water and concentrate urine
What materials are transported in the collecting duct and where are they transported?
- water is reabsorbed from the tubular fluid back into the bloodstream
- uea is reabsorbed into the medulla
- sodium chlroide (NaCl) is reabsorbed from the tubular fluid into the interstital fluid of the renal medulla
Role of ADH on the DCT and collecting duct
DCT: minor role
Collecting duct: increases water reabsorption
Role of aldosterone on the DCT and collecting duct
stimulates sodium reabsorption and potassium secretion for both
Role of angiotensin II on the DCT and collecting duct
stimulates aldosterone secretion, indirectly promoting sodium and water absorption for both
Role of parathyroid hormone on the DCT and collecting duct
DCT: increases calcium reabsorption
Collecting duct: weaker effect
Role of natriuretic peptides on the DCT and collecting duct
DCT: dilates afferent arterioles and constrict efferent arterioles, which increases GFR
Collecting duct: inhibit sodium reabsorption leading to increased urine volume and decreased BP
What is the transport maximum?
maximum rate of reabsorption that can occur for a given solute
Describe the different ways that materials can be transported in and out of the tubules
- transcellular route: substances pass through the cytoplasm and out the base of the epithelial cells
- paracellular route: substances pass through gaps between the cells
- active transport: requires ATP to move substances against their concentration gradient
- passive transport: doesn’t require energy and moves substances down their concentration gradient
- osmosis: water moves across the membrane from an area of low solute concentration to an area of high solute concentration
Describe important dynamics of carrier proteins
- saturation: once all carrier proteins are occupied, the system can no longer be more saturated; transport maximum
- specificity: each carrier protein is designed to bind and transport a specific substance
- competition: transport rate may be reduced if two substances are fighting for the same carrier protein
- regulation: activity can be regulated by hormones and other factors
What are the peritubular capillaries and vasa recta?
peritubular capillaries:
- surrounds the proximal and distal convoluted
tubules
- reabsorbs water and solutes from the tubular fluid and secrete substances into the tubular fluid
vasa recta:
- long, straight capillaries that dip down into the medulla alongside the nephron loops
- helps maintain the osmotic gradient in the medulla
Function of the proximal convoluted tubule (PCT)
reabsorbs 65% of the filtrate
What materials are transported in the PCT and where are they transported?
reabsorbs water, sodium, chloride, glucose, amino acids, and urea and transports them into the peritubular capillaries
Pathway of reabsorbed materials
- materials in the tubular fluid are reabsorbed in the PCT, nephron loop, DCT, or collecting duct
- passes through the apical membrane of the tubule cells
- enters the interstitial fluid surrounding the tubules
- taken up by the peritubular capillaries in the cortex OR the vasa recta in the medulla
- peritubular capillaries and vasa recta drain into the venous system eventually leading to the renal vein and inferior vena cava
