Kidneys and Urinary System Flashcards
List the functions of the urinary system
Excretion of metabolic products and toxic substances
Retain useful substances
Regulate body fluid osmolality and volume
Regulate electrolyte and acid base balance
Produce and secrete hormones
Modify and regulate plasma composition
Describe the basic structure of the kidneys
Cortex surrounds the medulla
Medulla is made up of renal pyramids
A the base of the pyramids is papilla which drain into the renal pelvis
Leaving the renal pelvis is renal artery, nerve and vain and the ureter
What is a nephron?
Building block and functional unit of the kidneys
What are the two different types of nephrons?
Cortical- majority, role in absorption and secretion
Juxtamedullary- create conditions to concentrate urine
What is the function of nephrons?
Generate ultrafiltrate from the blood
Control how much is reabsorbed and excess removed as urine
What is the glomerulus?
Capillary network within bowmans capsule of the nephron
Where is the site of filtration in the nephron?
Glomerulus
What happens in the proximal tubule?
Most fluid is reabsorbed
Where is urine concentration controlled in the nephron?
Juxtamedullary nephrons loop of henle
What is the role of the distal convoluted tubule?
Control electrolyte balance
What cell types form filtration barrier around the glomerulus?
Podocytes- wrap capillaries to allow fluid but not protein leakage, full coverage of capillary by primary and secondary processes
Pedicels- extra coverage of capillaries to only allow water and small molecules through
What is meant by the juxtaglomerular apparatus?
Point where distal tubule loops back and makes contact with the glomerulus
Specialised hormone secreting region
What is the arterial supply to the nephron?
Branch of renal artery forms afferent arteriole which enters glomerulus
Efferent arteriole leaves the glomerulus
What is the vasa recta
Formed from efferent arteriole, surrounds nephron to supply nutrients, gas exchange and collect water and solutes reabsorbed by nephron
Why is blood supply to the kidney autoregulated?
Keep glomerular filtration rate constant and keep it functioning despite arterial blood pressure changes
What is used to measure glomerular filtration rate and what is it?
Using creatinine which is waste product of natural breakdown of muscle, usually delivered into circulation at constant rate
Why can creatinine be used to measure GFR?
Is freely filtered from glomerulus and not reabsorbed from tubule or secreted into tubule so what appears in urine is directly from glomerular filtration
Describe the structure of the proximal tubule walls
Apical surface of epithelial cells have microvilli
Cells packed with mitochondria
What is the function of the proximal tubule?
Reabsorption of solutes and bulk of filtered fluid back into the blood
Helps regulate body fluid pH
Secretes some organic molecules, often end products of metabolism
What type of process is glucose transport in the proximal tubule?
Carrier mediated process
What are the normal levels of plasma and intracellular fluid pH?
Plasma- 7.35-7.45
Intracellular- 7-7.1
Why is plasma osmolality regulated?
Prevent cell swelling or shrinkage, one of the most tightly controlled homeostatic mechanisms
What hormone is responsible for controlling body water?
Antidiuretic hormone
How is antidiuretic hormone secreted?
Hypothalamus produces in paraventricular and supraoptic nuclei then is transported to axon terminals in posterior pituitary to be released into the blood
When is there increased release of ADH?
Increase in plasma osmolality
What are the physiological mechanisms to control water balance?
Drinking and urine output
What is the action of ADH?
Increases water permeability of collecting duct
Increases NaCl reabsorption in thick ascending limb
Increases urea permeability in inner medullar region of collecting duct
All help water reabsorption
What ion transporters are present in the ascending limb?
Na-K-Cl cotransporter in apical membrane and Na pump in basolateral membrane
Explain how ADH takes action
ADH from blood binds to V2 receptor on basolateral membrane of tubule cell
Stimulates adenylate cyclase to generate cAMP and activate protein kinases
Increases insertion of aquaporins into apical surface of cell increasing permeability
More water flows out of tubule into medullary interstitium
What happens when blood volume is decrease?
Na+ retention in blood increased in kidney
Water follows Na+ into blood
Blood volume restored
What are the high pressure sensors of blood volume?
Arterial baroreceptors- carotid sinus, aortic arch. Increases sympathetic activity to kidneys in response to hypovolaemia
Juxtaglomerular apparatus- renal blood flow decreases, hormonal response reduces Na+ and water loss in the kidneys
What are low pressure sensors of blood volume?
Cardiac atria
Pulmonary vasculature
Explain the importance of regulating blood volume
Plasma and cellular components are in fixed proportions so all compartments are regulated by regulating blood volume
Blood pressure is determined by blood volume so also controls arterial blood pressure
What response do juxtaglomerular apparatus have in response to low blood pressure?
Renin is secreted
How is Angiotensin I formed?
Renin binding with angiotensinogen
How is angiotensin I converted to angiotensin II?
In lung by angiotensin converting enzyme
What is angiotensin II and what is its role?
Active form of renin
Causes vasoconstrictor response, stimulates ADH release and stimulates aldosterone release
What is aldosterone and how does it work?
Na converting hormone
Increases Na+ reabsorption by nephron drawing in water
How does aldosterone work?
Acts on distal convoluted tubule
Binds to receptor which stimulates transcription of apical Na+ channels
Increased NaCl reabsorption in distal tubule and collecting duct and Na+ enters blood by ATPase
Water follows paracellularly
What is the response to increased blood volume?
Atria stretch causing release of ANP which causes excretion of Na+ and so water
What is ANP and where is it made and stored?
Atrial natriuretic peptise
Synthesised and stored in atrial myocytes
What happens in hypokalaemia and hyperkalaemia?
Hypo- cell less excitable
Hyper- cell more easily excitable
Explain how extracellular potassium is regulated
Increased plasma K+ enhances secretion and depolarises zona glomerulosa cells causing Ca2+ influx into cell to stimulate aldosterone release
Aldosterone helps enhance secretion of K+
Where is body calcium stored?
Most in bones and teeth
Only 1% accessible in ECF
What states is calcium found in the body?
Ionised- 50%, biologically active
Bound to plasma proteins- 40%
Rest is complexed to plasma anions
What affect does alkalaemia have on calcium binding?
Ca2+ is competitive with H+ to bind, the less H+ more Ca2+ binds so less is found in ionised state
What limits calcium intake?
Absorption in the gut
How is active vitamin D3 synthesised?
Cholecalciferol taken in by diet or sun is hydroxylated in liver and kidneys to the active form of vitamin D
What is the main role of vitamin D on calcium?
Regulates intestinal calcium absorption
Describe the pathway of urine from the collecting duct
Renal pelvis
Ureters
Bladder
Urethra
How does urine pass down the ureters?
Peristalsis originating form pacemaker in renal pelvis
What are the different regions of the bladder walls made of?
Dome- detrusor smooth muscle
Trigone- non-contractile
What is innervation of bladders detrusors smooth muscle?
Parasympathetic nerves that release acetyl choline to cause muscle contraction
Describe the lining of the bladder walls and its purpose
Mucosa, urothelium, suburothelium
Tight barrier to prevent urine leakage
What is the external urethral sphincter muscle type?
Skeletal
What is meant by the bladder being compliant?
Volume in the bladder can increase with a very small pressure rise
What are the nervous pathways of storing urine?
Sensory afferent nerves synapse from bladder to midbrain and signals are relayed, one to prefrontal cortex and makes choice to not void
What nerve is supressed in order to keep the bladder relaxed?
Pelvic nerve
What nerve contracts the internal urethral sphincter?
Hypogastric nerve
What nerve contracts the external urethral sphincter?
Pudendal nerve
What nerve causes the bladder to contract?
Active pelvic nerve
Why doe the urethra relax?
Inactivated hypogastric nerve
What is the response to increased blood volume?
ANP is released by atrial myocytes in response to atria overstretching
Causes inhibition of aldosterone and renin secretion, inhibition of ADH release causing increased water secretion in urine, vasodilates afferent arteriole increasing GFR and causes reduced sodium reabsorption in CT so reduced water reabsorption
