Session 18 - Urinary system - Tubular Reabsorption and Secretion Flashcards
purpose of tubular reabsorption
return filtered water and solutes to blood stream
how is reabsorption achieved
Proximal convoluted tubule have microvilli - this is how most is reabsorbed.
- Solutes are reabsorbed by both active and passive transport
- Water follows by osmosis
- Small proteins by pinocytosis
tubular secretion definition
transfer of materials from blood and tubule cells into glomerular filtrate
- controls blood pH
- elimate certain substances
A - renal corpuscle
B - renal tubule and collecting duct
Two routes of reabsorption routes
- paracellular reabsorption
- movement between adjacent tubule cells
- via osmosis
- transcellular reabsorption
- movement through an individual tubule cells
- via active transport
transport mechanisms
- two main mechanisms
- active transport
- primary and secondary
- passive transport
- osmosis
- active transport
primary sctive transport
ATP used to pump across membrane
- sodium potassium ATPase pumps in basolateral membrane
secondary active transport
- ion electrochemical gradient drive substances across the membrane
- symporters: membrane proteins moving two or more substances in the same direction across a membrane
- antiporters: membrane proteins moving two or more substances in opposite directions across membrane
passive transport
- osmosis
-
obligatory water reabsorption
- water is obliged to follow the solutes which are being reabsorbed
- occurs in proximal convoluted tubule and descending limb of the loop of Henle
-
facultative water reabsorption
- adapted to specific needs
- occurs in the collecting duct
-
obligatory water reabsorption
facultative water reabosption controlled by
- antidiuretic hormone
- if more water is needed to be reabsorped by the body, ADH is released for insertion of aquaporins in the collecting duct
largest amount of solutes and water are reabsorped where
reabsorption in proximal convulted tubule
secretion from the proximal convoluted tubule
- deamination of the glutamine by PCT cells
- ammonia and urea in blood
- secreted into tubules
how and where is sodium reabsorbed
Achieved by several mechanisms in the proximal convoluted tubule:
- by sodium glucose symporters
-
sodium/hydrogen antiporters
- sodium reabsorp into blood and H secretion into tubular fluid
bicarbonate (HCO3-) reabsorption
- facilitated diffusion
- filtered through simulataneously with hydrogen
how are sodium, potassium, calcium, magnesium and urea reabsorped
passive diffusion into peritubular capillaries via both paracellular and transcellular routes
water reabsorption in proximal convoluted tubule
- osmosis followed by solute reabsorption
- via both paracellular and transcellular routes
- aquaporin-1
the loop of henle reabsorps a large proportion
of chloride, sodium, potassium and water
loop of henle controls..
regulation of volume and osmolarity of body fluids
sodium , chloride and postassium reabsorption occurs where in the loop of henle
- apical membrane by symporters, leakage channels or paracellular route
- blue square in image
- basolateral membrane by active sodium transport and leakage channels for chloride
- red square in image
what is
- I,
- II,
- VII and
- VIII
- afferent arteriole
- efferent arteriole
- glomerulus
- bowmans capsule
Glomerulus and bowmans capsule where filtration occurs
label
- III
- VI
- V
- IV
- proximal convoluted tubule
- descending loop of henle
- ascending loop of henle
- distal convoluted tubule
What two regions can the descending and ascending loop of henle be divided in to
- thick descending and thin descending
- thin descending freely permeable to water
- thick ascending and thin ascending
- ascending permeable to sodium chloride
water reabsorption in loop of henle
- descending limb = 15%
- ascending limb = little/no water reabsorbed
reabsorption in early distal convoluted tubule
- reabsorp of calcium under control of parathyroid hormone (PTH)
- reabsorp of very little/no water
late distal convoluted tubule and collecting duct reabsorp/secretions
- water and solute reabsorp depend on bodys needs
- eg ADH
What cells compose the distal convoluted tubule DCT and collecting duct
- principal cells
- sodium reabsorption
- sodium leakage channels or sodium potassium pump depending on side of cell
- secretion of potassium via leakage channels
- major source of potassium in urine
- sodium reabsorption
- intercalated cells
- Bicarbonate reabsorption which regulates body fluid pH
- H secretion (H+ATPase pump) which can make urine more acidic than blood
how is urine buffered
- hydrogen phosphate and ammonia
- this allows the body to excrete more hydrogen through the urine
what 5 hormones regulate tubular reabsorption and secretion
- angtiotensin 2
- aldosterone
- ADH (antidiuretic hormone)
- atrial natriuetic peptide
- parathyroid hormone
angiotensin 2
- increases reabsorption of sodium and water
- -> increses blood volume and BP
- Works on PCT (proximal convoluted tubule)
aldosterone
- increases secretion of potassium
- increses reabsorp of sodium and chloride
- this increases water reabsorp -> increasing blood volume and pressure
- Acts on DCT and collecting duct
atrial natriuretic peptide
- incresaes excretion of sodium in urine
- increases fluid loss and therefore urine output
- lowers blood volume and BP
parathyroid hormone
- increases calcium reabsorp
antidiuretic hormone (ADH)/ vasopressin
- increases facultative reabsorption of water, decreasing osmolarity of body fluids
- works on collecting duct
how does ADH act and how is it regulated
- ADH secretion leads to aquaporin-2 channels into the membrane allowing water molecules to move more rapidly
- increased osmolarity of plasma = ADH secretion
- principal cells more permeable to water increasing water reabsorption
tubular reabsorption brings how much renal filtrate back into use
99%
renin-angiotensin aldosterone system (RAS)
- renin from kidney
- converts angiotensinogen to angiotensin 1
- ACE is released from lungs which converts angiotensin 1 to angiotensin 2
- angiotensin 2 stimulates release of aldosterone (also causes vasoconstriction)
- = reabsorption of water and salt
