renal system Flashcards
describe the renal system
- in the kidney
- acts as an integrative system
- process plasma
what are the functions of kidneys?
- regulate water concentration, inorganic ion compositions, acid base balance and fluid volume
- excrete metabolic waste products into urine e.g. urea, creatine
- urinary excretion of some foreign chemicals e.g. drugs, pesticides and food additives
what process is the renal system involved in?
- gluconeogenesis during prolonged fasting
- kidneys synthesis glucose from amino acids and other precursors and release it to blood
what do kidneys act as? what hormones do they release?
- act as endocrine glands
- release erythropoietin and dihydroxy vitamin D, renin
- control blood pressure and sodium balance
what is the main functional unit of the kidney? what does it contain?
- nephron (1 million in kidney)
- renal corpuscle
- tubule that extends from renal corpuscle
what is the glomerulus?
- main plasma filtering unit
- formed by network of small blood vessels enclosed within Bowmans capsule
what gives an added layer of filtration?
- podocytes ; glomerulus very porous so elements such as sodium, glucose, aas further filtered
is efferent or afferent smaller?
- lumen of efferent is smaller therefore high pressure is maintained
what is the driving force of ultrafiltration across glomerulus?
- contraction of left ventricle creates arterial pressure
what is the proximal convoluted tubule?
- site of bulk reabsorption
- found in cortex
what takes place in proximal convoluted tubules?
- active transport of filtrate occurs and reabsorption of water, amino acids, glucose into bloodstream
what happens in descending and ascending loop?
- water diffuses out of descending loop
- ascending loop reabsorbs Na+, Cl- and K+
describe the descending limb
- generates hyperosmotic interstitial fluid in medulla; majority of water is removed
- fluid reaches an equilibrium with adjacent interstitial fluid
describe ascending limb
- where sodium, potassium and chloride is pumped out via net passive diffusion from tubule to interstitial fluid
what does solute removal from ascending limb cause?
- hyperosmolarity of medulla
what limb of loop of henle is permeable to water?
- descending limb is permeable so water diffuses out
what occurs in the distal convoluted tubule?
- more sodium reabsorption occurs
- increased by aldosterone
what happens in the collecting duct?
- ADH acts
- reabsorbs water as all remaining fluid enters collecting duct system which runs through hyperosmotic medulla to drain to pelvis
what state is the water in entering the collecting duct?
- hyposomotic
- due to sodium removal by active transport
what is the renal capsule?
- contains glomerulus and renal tubule
what is the juxtaglomerular apparatus?
- composed of macula densa and juxtaglomerular cells
what are juxtaglomerular cells?
- mechanoreceptors (detect BP change)
- found in afferent arteriole
what are macula densa cells?
- chemoreceptors responding to changes in NaCl
describe differential handling in the kidney
- substances can enter the tubule and be excreted by urine
- substances can be completely reabsorbed
how do you work out the amount excreted?
amount excreted = amount filtered + amount secreted - amount reabsorbed
what are the three main processes of the renal system
- glomerular filtration
- tubular reabsorption
- tubular secretion
what is GFR?
- glomerular filtration rate
- amount of blood filtered by glomeruli each minute
what is the normal GFR for a healthy adult?
-120ml/min
how do you work out the net filtration pressure?
net filtration pressure= change in hydrostatic pressure - change in osmotic force
what happens to colloid osmotic pressure along glomerular capillaries?
- it increases
how many times a day do the kidneys filter the entire plasma?
- 60 times
how is osmotic pressure maintained during filtration?
- through plasma proteins remaining in the plasma
what factors affect the GFR?
- capillary permeability
- surface area of capillary bed
- hydrostatic pressure that drives fluid out of capillaries
- osmotic forces within capillaries
what does low GFR show?
- signifies a lack of functioning nephrons
what law is GFR governed by?
- Starling’s law; hydrostatic pressure difference across capillary wall vs protein difference across capillary wall
what changes are GFR controlled by?
- vascular changes
why are glomeruli more efficient filters than other capillary beds?
- filtration membrane has a large surface area and is very permeable to water/ solutes
- glomerular pressure is higher so they produce 180L/day vs 3-4l/ day by others
what is it called when blood cells or protein are found in urine? what does this indicate?
- proteinuria
- indicates a problem with filtration membrane
- found in diabetes/ hypertension; signals kidney damage
why would filtrate become dilute?
- due to imbalance between sodium and water reabsorption in loop of Henle
- produces hypoosmotic filtrate and more dilute as it flows through distal tubules
when does urine have highest osmolarity?
- in the morning
- we secrete ADH during sleep
- urine concentrated
when does tubular reabsorption begin?
- as soon as filtrate enters tubule cells
what is paracellular transport?
- transfer of molecules between adjacent cells
what kind of process is tubular reabsorption ?
- can be active or passive
describe tubular secretion
- H,ion, potassium and organic anions move from patibula capillaries into tabular lumen
what is tubular secretion important for?
- removing excess K+, controlling blood pH, disposing of drugs, excreting undesired substances
where does reabsorption occur in tubules?
- mainly in proximal tubule and loop of Henle
- ensures masses of solutes and volume of water entering distal tubule are small
what segment does fine tuning and why?
- distal segments> determines amount of excreted in urine
what is renal clearance?
- amount of substance filtered per minute (mL/min)
how do you work out renal clearance?
RC= (conc of substance in urine x flow rate of urine formation) / conc of substance in plasma
what substances are used to determine renal clearance?
- insulin, creatine
- insulin more effective as creatine partly secreted/ reabsorbed
what must the substance be to be useful for GFR?
- not metabolised/ secreted by kidneys
- nontoxic
- small
- easily measured in blood/ urine
is clearance of a substance dependent of its plasma conc. ?
- a substance like insulin is independent of its plasma conc.
when can renal clearance ratio allow us to estimate GFR?
- if substance is freely filtered
what does it show if there is a net reabsorption of a substance?
- clearance is less than GFR
what is the filtration fraction?
- proportion of plasma entering the kidneys and is filtered at the glomerulus
how do you work out filtration fraction?
GFR/ renal plasma flow
what is the typical filtration fraction?
- 0.16 to 0.20 so 20 % of the blood entering the kidneys is filtered
what happens to RPF and GFR with age?
- declines with age
- but rate of declines are such that filtration fraction remains constant
