PH1124 - kidneys & urinary system Flashcards
why do we need a urinary system?
excretion of metabolic waste products
what do they kidneys do? (3)
- excrete waste products into urine
- homeostasis
- secrete hormones
what is the definition of excretion?
- removal of a variety of waste products produced by metabolism
what happens at the glomerulus?
- ultrafiltration via basement membrane and podocytes
what does the glomerulus filtrate contain? (5)
- water
- glucose
- amino acids
- ions
- urea
where do substances move from in the proximal convoluted tubule?
- move from proximal tubule to interstitual fluid via the apical to basolateral membrane
what happens at the loop of henle?
- descending limb is highly permeable to water but impermeable to solutes (and vice versa for the ascending limb)
- active transport of Na+ out of the lumen followed by Cl-
what is water reabsorption regulated by?
- ADH in the collecting duct
what does ADH do?
- increases urine osmolality (increases concentration) and decreases water excretion (more water reabsorbed)
how does ADH regulate water reabsorption? (3)
- increases water permeability of collecting duct for reabsorption
- (short term) insertion of aquaporin 2 into the apical membrane of the collecting duct by endocytosis
- (long term) ADH increases aquaporin 2 gene expression so more channels are synthesized
what is autoregulation?
- small fluctuations in blood pressure are returned to normal as filtration rate in the glomerulus needs to be kept constant
how does salt content change blood pressure?
- if blood pressure is low we can retain more sodium which means we retain more water therefore increase blood volume
what is renin?
- secreted by the kidney in response to decrease blood flow and promotes vasoconstriction and release of aldosterone from the adrenal cortex
how is renin released? (2)
- macular densa cells detect low blood volume/low sodium content
- triggers the granular cells (juxtaglomerular cells) to release renin
what is the renin-angiotensin-aldosterone system? (3)
- body’s response to low blood pressure
- renin (primarily release by kidneys) stimulates the formation of angiotensin in blood and tissues
- this in turn stimulates the release of aldosterone from the adrenal cortex causing the body to retain water and increase BP
what does aldosterone regulate? (3)
- blood volume
- blood pressure
- levels of Na+, K+, H+
what is the fate of angiotensin I? (2)
- travels in circulation system till it reaches the lungs which contain ACE (angiotension converting enzyme)
- CE converts angiotensin I to angiotensin II
what is angiotensin II effect on the adrenal cortex? (2)
- aldosterone is produced which increases the sodium and water reabsorption in the kidneys as well as increase secretion of potassium and protons into the urine
- this in turn increases blood volume thus blood pressure returns to normal
what is the ureter?
- tubes that carry urine from each kidney to the bladder
what is urine backflow prevented by?
- ureterovesical valves
how is urine passed from the kidneys to the bladder?
- peristaltic waves
what is the bladder mainly composed of?
- smooth muscle
what is important to remember about the control of the sphincter muscles in the bladder?
- they are made from striated muscle so can be controlled
what are the layers of the bladder wall? (5)
- peritoneum
- fat
- muscle
- lamina propina
- urothelium
what is the micturition reflex? (2)
- its activated when the urinary bladder wall is stretched and it results in urination
- this reflex occurs in the spinal cord (specifically in the sacral region) that is modified by the higher centers in the brain the pons and cerebrum
what are the phases of the micturition reflex? (2)
- storage phase
- voiding phase
what is the storage phase of the micturition reflex? (3)
- as the bladder fills pressure stays low
- when the bladder is full wall tension is detected
- messages sent to brain and locally
what is the voiding phase of the micturition reflex? (2)
- voluntary signals relax external sphincter (somatic)
- autonomic contraction of detrusor muscle
what makes sure the flow doesn’t stop still bladder is empty?
- urethra plays an excitatory role which maintains flow toll bladder is empty
which receptors detect the bladder is full?
- detrusor muscle stretch and viscerosensory nerves sense this
what will sympathetic innervation on bladder control do?
- stop urination
what will parasympathetic innervation on bladder control do?
- start reflex contractions to start urination
how does the sympathetic nervous system stop urination? (2)
- nerve from the micturition center sends signals via the lumbar section in the spinal cord to the hypogastric nerve
- the hypogastric nerve then causes the internal sphincter to contract
how does the parasympathetic nervous system allow urination? (2)
- the micturition centre in the brain sends a signal to the pelvic nerve via the sacral region of the spinal cord
- this causes relaxation of the internal sphincters allowing urination
how does somatic innervation stop urination?
- voluntary constriction of external sphincter to prevent micturition
how is the human able to control urination?
- external sphincter is formed from striated muscle so is under control
what type of receptors are present in the sympathetic control of the bladder?
- alpha and beta adrenoceptors that rely on noradrenaline
what type of receptors are present in the parasympathetic control of the bladder?
- nicotinic receptors and muscarinic receptors that rely on acetylcholine
