Renal system Flashcards
Functions of the kidney
Waste removal and to regulate blood pressure
Filtration in the glomerulus
Substances in the blood filter from the glomerulus into the Bowman’s capsule because the hydrostatic pressure in the glomerulus is higher than the glomerular oncotic pressure and capusular hydrostatic pressure
Oncotic pressure
Pressure keeping things in the blood vessel because of proteins (e.g. albumin) which draw water
Hydrostatic pressure
Pressure exerted by blood pushing against the walls of the capillaries, pushing things out
Filtrate contains (9):
Water Sodium Chloride Potassium Bicarbonate Glucose Amino acids Creatinine Urea
Reabsorption in the proximal convoluted tubule
Active reabsorption of glucose, sodium, potassium, phosphate, and sulphate
Passive reabsorption of urea, water, and chloride
Secretion in the proximal convoluted tubule
Uric acid
Creatinine
Drugs
Function of the loop of Henle
To create a hyperosmolar medulla (a counter current multiplier) - lots of water lost by bottom of loop - to help with fluid reabsorption
Reabsorption in the descending loop of Henle
Passive removal of water, sodium and chloride
Reabsorption in the ascending loop of Henle
Active removal of chloride
Urine formation process
- ADH released from posterior pituitary
- Creates aquaporins (water channels) in collecting duct wall
- Medulla is hyperosmolar so water is pulled out of filtrate back into blood vessels
Osmolarity
The number of solute particles dissolved in one litre of water, measured using specific gravity.
High osmolarity = high pull of water
Renin-Angiotensin-Aldosterone System
- Low fluid volume in nephron causes kidney to produce enzyme renin
- Renin acts on angiotensinogen from liver to create angiotensin I
- Angiotensin I converted to angiotensin II by ACE in the lungs
- Angiotensin II causes adrenal gland to secrete aldosterone (steroid hormone)
- Aldosterone creates more sodium channels in the distal convoluted tubule and increases activity of the sodium-potassium pump in the blood vessel, thus increasing sodium reabsorption
- Change in osmolarity increases water reabsorption
The Juxtaglomerular Apparatus consists of…
Justaglomerular (granular) cells in the afferent arteriole and macula densa cells in the distal convoluted tubule
In response to high sodium chloride levels, macula densa cells…
Cause the afferent arteriole to constrict, leading to a lower glomerular filtration rate and less sodium chloride entering the filtrate
In response to low sodium chloride levels, macula densa cells…
Cause the afferent arteriole to dilate, and stimulates renin release to increase blood pressure
Juxtaglomerular cells release renin in response to (3):
- Stimulation of the beta-1 adrenergic receptor
- Stretch receptors detecting a decreased blood pressure
- Signal from the macula densa due to low sodium chloride levels
Positive feedback loop of urination
Urine into bladder ->
Bladder increases in size ->
Stretch causes increased nerve impulse to brain ->
Cholinergic nerves fire on detrusor muscle via M3 receptors ->
Detrusor muscle contracts, urethral smooth muscle relaxes
2 sphincters of the bladder
Inner - involuntary
Outer - voluntary, nicotinic
Young and old people urinate more frequently because…
Parasympathetic nerve tone is increased at the extremities of age
Older people can faint when they urinate because…
The parasympathetic system slows heart rate and drops BP
Larger prostate causes frequent urination because…
The prostate squeezes on the urethra, meaning more pressure is needed in the bladder for fluid to pass into the urethra, thus fluid is left in the bladder even after passing urine
The aim of diuretics is to…
Lose sodium
Loop of Henle diuretics
- Prevent passive transport pump from transporting sodium ions into the blood
- Sodium ions build up in ultrafiltrate
- Ultrafiltrate has a high osmolarity so retains water
