Flashcards in Urinary System Deck (23)
What are the opposing forces, in the glomerulus, to hydrostatic pressure
Colloid Oncotic Pressure - By the plasma proteins
Fluid Pressure - From the liquid in the ultrafiltrate
What is the difference between paracellular and transcellular reabsorption?
Paracellular - solutes pass through the gaps between cells
Transcellular - solutes move directly through the cell
What is the difference between the ascending and descending limb in the nephron?
The descending limb is permeable to water and not solutes...
Where as the ascending limb is permeable to solutes. but not water
What is the difference between primary and secondary active transport?
Primary = only one molecule moves
Secondary = Two molecules are moved
Explain how Na+ and HCO3- are reabsorbed, whilst H+ is secreted into the tubule in the PCT?
Metabolic reactions cause H2O and CO2 to form carbonic acid
This carbonic acid then dissocaites to H+ and HCO3-
The HCO- is reabsorbed into the capillary via facilitated diffusion on the basal-lateral membrane
The H+ ions are secreted into the tubule via an antiporter with Na+ (secondary active transport)
The Na+ is then actively transported into the capillary
How is glucose reabsorbed in the PCT?
It enters the cell via a symport with Na+
It is then taken into the capillary via facilitated diffusion
What does the term 'Obligatory' mean when coupled with the concept of water?
The movement of ions into the capillary from the tubule causes water to follow
This is because the movement of ions causes the WP of the cell/capillary to decrease --> leading to water moving in via osmosis
What reaborption occurs in the ascending limb of the loop of henle?
Na+ is actively transported
K+ and Cl- are co-transported
Water is not reabsorbed!!
Explain how the renin-angiotensin-aldosterone system works
An increase in K+ or decrease in Na+ causes the adrenal cortex to secrete aldosterone
The kidneys detect a decrease in blood pressure, resulting in renin being secreted, which converts angiotensin (from the liver) to Angiotensin 1, and then into 2 (by ACE enzymes)
Angiotensin 2 casues blood vessels constrict to increase blood pressure, as well as increasing the synthesis of aldosterone
The more aldosterone that is present, the less water is lost, due to the increase retnesion of Na+, and loss of more K+
Explain how ADH/Vasopressin works
ADH is released from the posterior pituitary due to stimulation from the baroreceptors and osmoreceptors in the hypothalamus
The ADH then causes vasoconstriction, as well as causing an increase in water reabsorption from the kidneys. It does this by stimulating cAMP which causes aquaporins to bind to the apical membrane, allowing more water to be reabsorbed
What is ANP?
And what is its function?
Atrial Natriuretic Peptide
It is secreted from the heart when a increase in blood volume is sensed in the right atrium. It causes the kidney to excrete more Na+, and so more water is lost also
It also inhibits aldosterone and ADH secretion
What is the short term, and long term, effect of the body to maintain acid-base balance?
Short term = Ventilation to remove CO2 quicker
Long term = The kidneys change H+ concentrations
Explain the role of the kidneys in acidosis
The pH is too low, and so H+ needs to be removed
Type A intercalated cells pump H+ out whilst K+ is moved in via coupled transport. This transporter is on the apical surface
HCO3- is moved into the intersitial space in order to buffer the loss of H+
Explain the role of the kidneys in alkalosis
The pH is too high, so H+ need to be reabsorbed
Type B intercalated cells are used to move H+ into the intersitial space, with K+ going the other way. This transporter is on the basal surface
HCO3- is also excreted along with H+
Explain how, using GFR, the mechanism of renal clearance can be found
GFR = Insulin clearance, which is 100ml/min
Reabsorption = GFR < 100
Secretion = GFR > 100
What causes the movement of urine into the ureter/bladder?
What is the purpose of the 'slight kink' in the ureter?
To prevent the backflow of urine, and so prevent infections
What is the main muscle of the bladder wall?
Of the two sphincters that control the urethral opening, which is under volunatary control?
The external sphincter
The internal sphincter is under involuntary control
Both are closed in the normal state
What is the trigone muscle?
This muscle is the stretch receptor for the bladder, which also contains openings to the urethra
Outline the involuntrary reflex for micturition
The urine fills the bladder, causing the stetch receptors to send signals via afferent neurone to the spinal cord
Parasympathetic efferent fibres then stimulate the detrusor muscle to contract, and force the internal sphincter to relax --> allowing micturition to occur
Outline the only difference between involuntrary and voluntrary micturition
Once at the spinal cord, the signals are sent to the pons in the brain
If we then want to, the cerebral cortex causes the external sphincter to relax, allowing urine to pass