Gene models & nephron function Flashcards
What % of plasma is filtered into Bowman’s capsule?
20%
What is tubular secretion?
movement from peritubular capillary
What is the diameter of the glomerulus?
20um
How much plasma is filtered per day?
180 litres/day filtrate
Describe the level of energy needed for glomerular filtration to take place
High levels of energy
What arteriole carries blood into the glomerular capillaries?
afferent arteriole
What arteriole carries blood out of the glomerular capillaries?
efferent arteriole
What does the glomerulus permit across its membrane?
H20 & small molecules
What does the glomerulus restricts across its membrane?
blood cells & proteins
What is ultra-filtrate composed of?
- consists of protein free plasma
- 1% protein filtered (albumin) - usually reabsorbed by the proximal tubule
What can proteins in urine be a sign of?
UTI
What is movement from the lumen of the nephron into peritubular called?
transcellular reabsorption
What is movement from the peritubular capillary into the lumen of tubule called?
transcellular secretion
What is movement in both directions between the lumen of tubule & peritubular capillary called?
Paracellular secretion or reabsorption
What is transcellular reabsorption called?
transport using transport proteins, transpiring ion solutes + water into cell across membrane
What does paracellular movement move?
Between cell
How many genes does the human genome have?
33,000 genes
How many renal genes does a human have?
Several hundred
How much reabsorption takes place in the proximal tubule?
- 70% (H2O & Na+)
- approx 100% glucose & amino acids
- 90% HCO3 (bicarbonate)
- high levels of mitochondria to allow energy-requiring processes to occur
What ATPase is found on the proximal tubule basolateral membrane?
sodium-potassium ATPase
What membrane are potassium channels found on in the basolateral membrane?
basolateral
Describe the intracellular sodium concentration in the proximal tubule
low
What cotransporters are involved on the apical surface of the proximal tubule involved in the movement pf sodium & glucose into the cell?
SGL T1 & SGL T2
What is the sodium phosphate cotransporter (NaPiII) involved in?
The movement of phosphate into cell
What are the results of NaPiII knockout mouse phenotype?
- Less Pi reabsorption
- More lost in urine
- Issues renal mineralisation
(renal mineralisation - renal stone/crystal formation)
What is the importance of phosphate?
- bone formation
- used for ATP
What staining is used to see the NaPiIIa knockout in a mouse?
Von Kossa staining - lots of dark-stained sports indication of mineralisation
What occurs as a result of low intracellular sodium concentration?
creates an electrochemical gradient for cotransporter to move sodium into the cell & hydrogen out of the cell
What happens to the hydrogen once it has left the cell?
it binds to HCO3 (bicarbonate), forming H2CO3 (carbonic acid). Carbon anhydrase then moves CO2 & H20 into the cell. Intracellular anhydrase then moves bicarbonate out of the cell via the basolateral exit
Why is reabsorption of bicarbonate important?
regulates the pH of the body
What is the effect of knocking out the NHE3 gene?
struggle to reabsorb plasma bicarbonate (HCO3), and a lower pH due to lack of pH regulation
What is the relationship between plasma glucose concentration & plasma glucose reabsorption?
linear relationship
When does plasma glucose concentration not have a linear relationship with plasma glucose reabsorption?
when there is no more free carriers for reabsorption
What is the renal threshold?
concentration of a substance dissolved in the blood above which the kidneys begin to remove it into the urine
What is the inherited disease given to those whose sodium-glucose carriers don’t work?
diabetes
What 2 systems are used to remove substances from the proximal tubule?
organic cations & organic anions
What is the function of the Loop of Henle?
- concentration of the urine
- reabsorption of Na+, Cl-, H2O
- reabsorption of Ca2+ & Mg2+
- site of action of loop diuretics
What are the 3 parts of the loop of Henle?
- descending limb
- thin ascending limb
- thick ascending limb
What size diameter is the descending limb?
thin
What leaves in the thin descending limb?
water
what leaves in the ascending limb?
sodium & chloride
What is the purpose for water leaving in the descending limb & sodium & chloride leaving in the thin ascending limb?
creates osmotic gradient which allows for water reabsorption
What leaves the thick ascending limb?
1 sodium, 1 potassium, 2 chloride ions released into the intracellular compartment
How does sodium leave the body?
via a sodium ATPase
What is needed for the CLCK channel to reabsorb chloride?
Barttin (beta subunit)
What does ROMK allow?
potassium reabsorption
What does Bartter’s syndrome lead to?
problem with sodium & chloride reabsorption
- hypotension (due to reduced ECF)
- kypokalaemia
- metabolic alkalosis
- hypercalciuria (calcium in urine)
- nephrocalcinosis - kidney stones
What is the biological effect of inability to produce barttin?
faulty CLCK
What do diuretics do?
increase urine, therefore reducing high blood pressure
What are people with Barter’s syndrome unlikely to experience?
hypertension
What occurs in the early distal tubule?
- reabsorption of Na + Cl
- reabsorption of Mg2+
- sensitive to thiazine diuretics
What is Gitelman’s syndrome?
salt wasting & polyuria (lots of urine)
- hypotension
- hypokalaemia
- metabolic alkalosis
- hypocalciuria
What is the role of NCC?
transport of sodium & chloride into early distal tubule, no potassium
What occurs in the late distal tubule?
- increasing the concentration of the urine
- reabsorption of Na+ & H2O
- secretion K+ & H+
What 2 types of cell is the late distal tubule & cortical collecting duct?
principal & intercalated cells
What occurs in principal cells in the late distal tubule?
- Na & H2O reabsorption
- K+ & H+ secretion
What occurs in intercalated cells in the late distal tubule?
a (alpha) IC & b (beta) IC
IC = intercalated
- different levels of A&B cells lead to different levels of hydrogen & bicarbonate secretion & absorption
What is the ENaC channel in principal cells?
Epithelium sodium channel
What does ROMK do in principal cells?
secretion of potassium, which is driven by reabsorption of sodium
What does aquaporin 2 do?
reabsorb water
What is lost in the urine?
potassium
What is the role of the ATPase?
- maintain negative membrane potential
- maintain low intracellular concentration
What diseases can be caused by principal cell?
diabetes insipidus - AQP2
Liddle’s syndrome - ENaC
What is the effect of amiloride?
- to increase fluid loss - block Na+ channel = lower H2O = decrease blood pressure
What is lost in alpha intercalated cells?
Hydrogen cells (using ATP)
What does the AE1 (anion exchange protein 1) cotransporter do?
move chloride (that has been moved out) into cell, while bicarbonate is moved out
What happens in B intercalated cells?
AE1 cotransporter on apical membrane
- hydrogen removed via ATP in basolateral membrane
What is the difference between an alpha intercalated cells & beta intercalated cells?
alpha - hydrogen removed from apical & bicarbonate on basolateral
beta - hydrogen removed on basolateral & bicarbonate on apical membrane
What will more b cells being present lead to?
more hydrogen ion being retained
What will more a cells being present lead to?
more hydrogen excretion
What occurs in the medullary collecting duct?
- Low Na+ permeability
- High H20 & urea permeability in the presence of antidiuretic hormone
What is acute renal failure?
reversible impaired fluid & electrolyte homeostasis
- accumulation nitrogenous waste
- lasts 1 week
What are the general symptoms of renal failure?
- hypervolaemia
- hyperkalaemia
- acidosis
- high urea/creatinine
What is hypervolaemia?
lack of urine due to a fall in GFR
What is hyperkalaemia?
lack of K+ secretion
What is acidosis, and its consequence?
acidic bodily fluids - leads to depressed central nervous system - stops function of neurones
What can high urea/creatinine lead to?
impaired mental function, nausea, vomiting
What is oliguria?
Fall in GFR
What is a pre-renal cause of acute renal failure?
Rhabdomyolysis - release myoglobin from damaged muscle - toxic effects on kidney tubules
What is a renal cause of acute renal failure?
High K+ lack of defection & release from damaged cells - tachycardia
What can a lack of bicarbonate lead to?
acidosis
What is used to hyperkalaemia?
IV saline
What is used to treat acidosis?
increase in bicarbonate
What is antidiuretic hormone?
vasopressin
Where is ADH released from?
posterior pituitary gland
Where do axons move down?
pituitary stalk
What type of cells fire action potentials?
neuronal cells
What does ADH do?
regulates body fluid osmolality - conserves H2O
What happens if there is an increase in ADH?
there is an increase in body fluid
What happens if there is a decrease in ADH?
there is a decrease in body fluid
Other than water, what else does ADH regulate?
sodium concentration
What detects water levels?
hypothalamic osmoreceptors
What level of water change do hypothalamic osmoreceptors detect?
3 mosmol/kg H2O
What occurs if the supra-optic & paraventricular nuclei is stimulated?
- Release ADH from posterior pituitary
- feeling of thirst
What occurs following activation of osmoreceptors?
activation of neuronal cells. This leads to an increase in ADH released
What occurs if ADH levels is increased?
increase osmolality plasma
What does ecstasy promote?
water retention
What occurs if ADH levels is decreased?
decrease in osmolality plasma
Describe the effect of alcohol on ADH release
inhibits the release of ADH - high level of water released
What is the normal plasma ADH pg/ml?
4
What is the normal plasma osmolality mosm/kgH2O?
285
How is an osmotic force created on principal cells?
there are aquaporins present on both the apical & basolateral membrane
What is the V2 receptor?
receptor for ADH. This activates protein kinase A (PKA), which leads to high levels of aquaporin 2 being inserted into the membrane.
What happens if there are a high number of aquaporin 2 in the membrane?
high number of aquaporin 2 = high number of channels = high level of water absorption
Are aquaporins 3+4 regulated ADH?
aquaporin 2
What is the net effect of ADH?
- increase in H2O reabsorption
- fall in body fluid osmolality
How many litres of dilute urine do people with diabetes insipidus excrete a day?
23
What is diabetes insipidus caused by?
no ADH released - defect in secretory neurones of ADH
What can treat diabetes insipidus?
nasal spray - desmopressin
What is nephrogenic diabetes insipidus?
- defect in V2 receptor
- H2O channel defect
Where is aldosterone released from?
cortex of the adrenal gland -zona glomerulosa layer
What does mineralocirticoid do?
regulates plasma Na+, K+ & body fluid volume
When is aldosterone released?
released in response to:
- increase in plasma K+ - 01mM
- decrease plasma Na+ - minor concentration maintained by osmoregulation
- decrease volume - via renin-angiotensin
What structures does aldosterone act on?
- late distal tubule
- collecting duct
What are the causes of aldosterone release?
- increased reabsorption of Na+
- increased reabsorption of H2O
- increased secretion of K+ & H+
What is the result of aldosterone on ENaC?
aldosterone puts more channels in the membrane & makes the channels stay open for longer
What is a Pseudohypoaldosteronism?
- salt loss but high aldosterone
- loss response to aldosterone
- mineralocorticoid receptor problem
What does renin-angiotensin regulate?
body fluid volume, plasma Na & K
Where is Renin released from?
juxtaglomerular apparatus (JGA)
What type of cells within the juxtaglomerular apparatus (JGA)?
granular cells
What triggers the release of angiotensinogen?
renin
What is necessary to allow the conversion from angiotensin 1 to angiotensin 2?
ACE (angiotensin cascade enzyme)
What does angiotensin 2 release?
aldosterone
Describe what would occur if you ingested salt?
- increase in plasma Na+ & H2O moves out of ICF
- increase in extracellular fluid volume & an increase osmolality plasma
How does a decrease in ECFV occur?
- decrease aldosterone
- increase in loss of Na+
- increase in loss of H2O
- decrease in ECFV
How does an increase in ECFV occur?
- increase in ADH
- increase in absorption of H2O
- decrease in osmolality
- increase in extracellular fluid volume
Why is extracellular volume key in integration?
blood pressure is most important over water content