Physiological Functions of the Kidneys Flashcards
roles of the kidneys
regulating fluid volume
regulating conc. of electrolytes
regulation of acid-base balance
excreting waste
conserving nutrients
hormone secretion
which hormones and enzymes are secreted by the kidneys
erythropoetin - hormone
calcitriol - hormone
renin - enxyme
when is erythropoeitin released and what is its function
in response to hypoxia in the renal circulation
it stimulates erythropoiesis (RBC production) in the bone marrow
what is the role of calcitriol
it is the activated form of vitamin D and it promotes intestinal absorption of calciu,
what is the role of calcitriol
it is the activated form of vitamin D and it promotes intestinal absorption of calcium
what is the role of renin and where and when is it released?
released from juxtaglomerular apparatus
released in response to reduction in tubular flow or sodium content
regulates angiotensin and aldosterone levels which control blood pressure
what functions of the kidney play a crucial role in blood pressure control?
renin release
regulation of fluid volume and plasma electrolytes
what muscle needs to relax to allow urine to drain through the urethra and is it voluntary or involuntary
sphincter muscle
voluntary
what two layers surround the kidneys
renal fascia - tough connective tissue
capsule of peri-renal fat
what structures are found in the renal hilum
first part the ureter
nerves
arteries and veins
what is the basic functional unit of the kidney
nephron
how many nephrons are in a kidney
~1 million
what is urea
the nitrogen containing end product of protein metabolism
what part of the body has the most control over the hydration status of the body
the kidneys
what is the glomerulus and what is it enclosed within
a bundle of specialised capillaries with a permeable membrane
enclosed within Bowman’s capsule
which type of arteriole supplies the glomerulus and which type returns contents to the systemic circulation
afferent supplies
efferent drains
what percentage of sodium and chloride are reabsorbed in proximal convoluted tubule
65%
what is recovered in the PCT
sodium, potassium, calcium, magnesium
phosphate and chloride ions
bicarbonate
glucose
amino acid
urea
water
how are sodium, potassium and chloride reabsorbed in the PCT
by passive transport
how is glucose reabsorbed in the PCT
cotransported with sodium
how are calcium and magnesium reabsorbed in the PCT
they compete for exchange with sodium ions
how is phosphate reabsorbed in the PCT
reabsorbed with sodium
how is water reabsorbed in the PCT
osmotically with solutes through aquaporin channels
water follows movement of solutes
what is actively excreted in the PCT
creatinine, uric acid and many drugs
where does the loop of henle descend into and what is a key characteristic of this region
the renal medulla
it is highly concentrated
what is reabsorbed in the descending limb of LoH
water
how is water reabsorbed in the DL or LoH
by osmosis as the extratubular concentration is high
how is the high concentration maintained in the renal medulla
by countercurrent exhange process where urea is recycled between the tubules and interstirium
what is reabsorbed in the ascending limb of LoH
sodium, potassium and chloride ions
calcium and magnisum ions
how is sodium, potassium and chloride reabsorbed in the LoH
by a specialised symporter protein which transports a sodium ion, two chloride ions and a potassium ion
how is calciuma and phosphate reabsorbed in the ascending limbd og LoH
passive transport
what percentage of sodium and chloride are reabsorbed in the DL of LoH
0%
what percentage of sodium and chloride are reabsorbed in the AL of LoH
25%
what percentage of sodium and chloride are reabsorbed in the DCT
10%
what is reabsorbed in the DCT
sodium and chloride ions
calcium
how are sodium and chloride ions reabsorbed in the DCT
in first part - by symporter protein
in second part - sodium reabsorbed in exchange for excretion of potassium or hydrogen
what stimulates the reabsorption of sodium in exchange for excretion of potassium or hydrogen in the distal part of the DCT
aldosterone
what is the function the reabsorption of sodium in exchange for excretion of potassium or hydrogen in the distal part of the DCT
regulation of pH of the urine and body
what stimulates calcium reabsorption in the body
parathyroid hormone
what is reabsorbed in the collecting duct
sodium
water
what is osmolality
the relative proportions of salt and water in the body
what structure detects significant rises in plasma osmolality
hypothalamus
how does the body respond to a significant rise in plasma osmolality
- hypothalamus detects it
- communicates with posterior pituitary gland
- vasopressin/ADH released
- vasopressin causes aquaporins to translocate to the membrane of the collecting duct cells
- this allows water to cross the normally impermeable membrane and be reabsorbed in the body by the vasa recta
- this increases the plasma volume of the body
what lies next to the afferent arteriole in each glomerulus and why
ascending limb of LoH
allows for specialised tubular cells called the macula densa to provide feedback regulartion in response to changes in the tubular content of water and electrolytes
when is the renin angiotensin system activated
hypotension
hypovolaemia
where is the macula densa found
between LoH and DCT
what type of cells make up the macula densa
juxtaglomerular cells
what are juxtaglomerular cells sensitive to
the concentration of sodium chloride in tubular fluid
the pressure in the afferent arteriole
signals from sympathetic nervous system
an increase/decrease of sodium chloride concentration stimulates release of renin
deccrease
what reaction does renin catalyse
angiotensinogen -> angiotensin I
what enzyme catalyses angiotensin I -> angiotensin II
angiotensin converting enzyme
what type of drug inhibits the formation of angiotensin II
ACEi (e.g. ramipril)
how does angiotensin increase blood pressure
constricts efferent arteriole to increase glomerular capillary pressure and filtration
systemic vasconstriction
stimulates thirst
stimulate release of vasopressin which conserves water
stimulates release of aldosterone which conserves sodium
what hormone is in charge of sodium conservation and where is it released from
aldosterone
adrenal cortex
what hormone is in charge of water conservation and where is it released from
vasopressin
posterior pituitary
what is the GFR a measure of
the performance of the kidneys
volume of plasma filtered at the kidneys every minute
what is a typical GFR of a healthy adult
120mL/minute
how much kidney function is lost with healthy ageing
can be up to 50% in 80 year old
what are the consequences of reduced kidney function due to disease
reduced clearance of waste products, ions, drugs, water and acid
uraemia and reduced erythropoietin formation -> anaemia
phosphate retention and failure to convert precursors to vitamin D -> renal bone disease
what are the three categories of acute renal impairment
pre-renal
renal
post renal
why does pre-renal renal impairment occur
failure of sufficient blood flow getting to the kidneys
common causes of pre renal renal impairment
systemic dehydration due to illness or diuretics
low arterial blood pressure due to drugs or haemorrhage
blockage of major renal arteries due to atherosclerosis or thrombosis
vasoconstriction of cortical vessels because of drugs (e.g. NSAIDs)
what are renal causes of renal impairment
intrinsic renal disease or damage due to drugs or other toxins
what are post renal causes of renal impairment
renal impairment due to obstruction of the urinary tract commonly due to
- compression of ureter between kidney and bladder as a result of tumour
- obstruction of bladder outflow (e.g. due to prostate disease)
is damage caused by AKI reversible
yes, usually
but may result in permanent reduction in baseline GFR
