kidney function 1 Flashcards
what is the function of the kidneys ?
to excrete metabolites or ingested substances
what are some examples of the substances that kidneys excrete ?
where do these substances come from ?
- urea from protein
- uric acid from nucleic acids
- creatinine from creatine
- hormone metabolites
- end products of haemoglobin breakdown
- foreign chemicals
what are the 3 ways the kidneys control plasma ?
- volume regulation
- osmoregulation
- pH regulation
what are some examples of hormones that act on the kidney ?
- anti-diuretic hormone (ADH)
- aldosterone
- natriuretic peptides
- parathyroid
- fibroblast growth factor 23
what are some hormones produced by the kidney ?
renin
vitamin D3
erythropoietin
prostaglandins
where are the kidneys found ?
- found behind the peritoneum
- one kidney on either side of vertabarl coloumn
- between T12 and L3 vertbrea
what is each nephron made up of ?
- renal corpuscle
- tubule
what arteriole supplies the kidneys ?
afferent arteriole
where is the ultrafiltration found ?
in bowmans capsule
where is the filtration barrier ?
between bowmans spaces + glomerulus
what make up the 3 layers of the filtration barrier ?
- fenestrated capillary endothelium
- basement membrane
- tubular epithelium ( podocytes )
what is a feature of the fenestrated capillary endothelium ?
has large pore sizes
up to 15 nm
what is a feature of the basement membrane ?
has fixed polyanions ( negative charges )
what is a feature of the tubular epithelium ?
has filtration silts
8nm
what are the podocyte foot process?
refers to large extensions of the podocyte
how are podocytes connected ?
they digilate with each other
do not touch
what are the 2 types of nephrons ?
where are the types found ?
- cortical (85%)
outer 2/3 of cortex - juxtamedullary (15%)
inner 1/3 of cortex
what is a feature of the cortical nephron ?
has short loop of Henle
doesn’t penetrate into medullla
what is a feature of juxtamedullary nephrons ?
has a long loop of Henle
plunges deep into medulla
what is the juxtaglomerular apparatus ?
macula densa + juxtaglomerular cells
can sometimes include extraglomerular mesangial cells
what is interesting about the nephron blood supply ?
has 2 sets of arteiroles ( afferent + efferent )
has 2 sets of capillary beds (glomeruli + peritubular )
work in series
what are the 3 basic renal processes ?
- glomerular filtration
- tubular reabsorption
- tubular secretion
what is glomerular filtration ?
what does it rely on ?
refers to the 20% of plasma that enters the Bowman’s capsule
relies on hydrostatic + osmotic gradients
what is the tubular secretion ?
secretion of solutes from peritubular capillaries into the tubules
also refers to movement of solute from tubule epithelium to tubule lumen
what is tubular reabsorption ?
where is it greatest ?
movement of materials from the filtrate in the tubules into the peritubular capillaries
greatest in proximal tubules
what does the amount of substance excreted into urine depend on ?
amount excreted = amount filtered + amount secreted - amount reabsorbed
what is another renal process ?
metabolism - removes substances from blood / glomeular filtrate + metabolise them
what does glomerular filtration depend on ?
- molecular size
- charge
- shape of substance
what is not found in ultrafiltrate ?
- cells + large proteins
- drugs + certain ions because they bind to proteins
what can effect the glomerulus ?
- infection
- damage
- high blood pressure
what is the result of a damaged glomerulus ?
- protein in urine ( proteinuria)
- haemoglobin in urine ( haemoglobinuria)
- red cells in urine (haematuria)
what is the glomerular filtration rate (GFR)?
volume of fluid filtered from the glomeruli per minute ml/min
what does GFR depend on ?
- net filtration pressure
- permeability characterisitc
- surface area
also regulated by hormonal + neural control
what is GFR a good determinate of ?
what does a high GFR mean ?
- renal functiton
- higher GFR = greater excretion of salt + water
what are the 2 starling forces involved in filtrations ?
hydrostatic pressure difference
colloid osmotic pressure difference
what determines the hydrostatic pressure difference ?
pressure of fluid against glomeularus wall
what determins colloid osmotic pressure ?
pressure exerted by large molecules
how does plasma flow across the capillary wall with reference to pressure ?
- high to low hydrostatic pressure
- low to high colloid osmotic pressure
what is the net glomerular filtration pressure ?
16 mmHG
how can you decrease GFR ?
- constriction of afferent arteriole = decreased glomerular capillary hydrostatic pressure = decreased GFR
- dilation of efferent arteriole = decreased glomerular capillary hydrostatic pressure = decreased GFR
how to increase GFR ?
- dilation of afferent arteriole = increased glomerular capillary hydrostatic pressure = increased GFR
- constriction of efferent arteriole = increased glomerular capillary hydrostatic pressure = increased GFR
how does sympathetic influence effect the SA of filtration ?
increase sympathetic activity = contraction of mesangial cells = decreased SA for filtration = decreased GFR
why is urine output much less than GFR ?
because reabsorption occurs
describe the structure of the cells found in the proximal tubule :
- walls are a single layer of columnar cells
- have lots of microvilli
- lots of mitochondria
how are organic nutrients reabsorbed ?
Na coupled co-transporter in the luminal membrane
a tubular maximum system
specific transporters for specific molecules
how is glucose reabsorbed ?
SGLT-Na dependent glucose co-transporter on the luminal membrane
glucose enters the proximal tubules + leaves via a GLUT faciliated transporter on the basolateral membrane
how are amino acids reabsorbed ?
- reabsorbed in proximal tubule
- different transporters for different groups of amino acids e.g ones for neutral AA, basic AA + acidic AA
how is protein reabsorbed ?
- mostly reabsorbed in the proximal convulated tubule
- absorbed by endocytosis + degraded into amino acids
- amino acids are later reabsorbed by transporters on basolateral membrane
how does secretion take place in the proximal tubule ?
- 2 stage process
- involves basolateral + luminal membrane transporters
what are examples of some organic acids secreted in the proximal tubules ?
- bile salts
- fatty acids
- drugs e.g penicillin
- para-aminohippuric acid ( PAH)
how are organic anions secreted ?
- anion enters epithelial cells via transporters
- enters tubule lumen via ATP dependent transporter
what are some examples of organic cations
- choline
- creatinine
- morphine
- atropine
how are cation secreted ?
enter cell via transporters
enter tubule via countertransporters
