Renal Flashcards
What are the 6 main functions of the kidneys in the entire body?
- regulation of ECF volume and blood pressure
- regulation of osmolarity
- maintenance of ion balance
- homeostatic regulation of pH
- excretion of wastes
- production of hormones
What is the specific function of kidney parts? 4
- Filtration from blood into the lumen of the nephron
- reabsorption from the filtrate in the lumen of the tubule back into the blood
- secretion from blood into lumen of the body
- excretion from lumen to out of the body
What is capillary pressure verse hydrostatic pressure?
- capillary pressure causes filtration
- hydrostatic pressure is blood pressure
What is oncotic pressure?
- colloid osmotic pressure
The pressure from having things dissolved in the blood
How is fluid pressure created in the kidney?
By fluid in the Bowman’s capsule
How much plasma is filtered in the glomerulus?
Only 20%
Where does reabsorption occur in the kidney?
All tubules
Where does secretion occur in the kidney?
Proximal and distal convulated tubules, collecting duct
List the stages of filtration throughout the kidney
- Plasma volume entering afferent arterioles = 100%
- 20% volume filters in glomerulus
- > 19% of fluid is reabsorbed
- > 99% of plasma entering the kidney returns to systemic circulation
- > 1% is excreted
What is the amount excreted equal to?
Amount excreted = amount filtered - amount reabsorbed + amount secreted
What are the filtration barriers in the glomerulus?
Podocytes: foot-like processes which surround the capillary, leaving slits through which filtration takes place
What three structures form the three-layer filtration barrier in the glomerulus?
The glomerular capillary endothelium, basal lamina and Bowman’s capsule epithelium. Filtered substance pass through epithelial pores and filtration slits
How is net filtration calculated?
Hydrostatic pressure (blood pressure) (Ph) - colloid osmotic pressure gradient (pi) - fluid pressure (P fluid)
Describe factors of Glomerular Filtration Rate (GFR)
- rate is relatively constant (despite BP changes)
What are the two factors influenciing GFR?
- net filtration pressure: hydrostatic pressure - colloid osmotic pressure - fluid pressure
2. Filtration coefficient: SA of glomerular capillaries available for filtration; permeability of interface between the capillary ad Bowman’s capsule
How are the two ways GFR autoregulation?
- Myogenic response
2. Tubuloglomerular control
What is Myogenic response?
GFR regulation
- intrinsic ability of vascular smooth muscle to respond to pressure changes
What is tubuloglomerular feedback?
GFR autoregulation
What is the nervous control ways GFR is regulated?
Hormones and autonomic neurons
- by changing resistance in arterioles
- by altering the filtration coefficient
List the eight stages of tubuloglomerular feedback loop to help GFR autoregulation
- GFR increases
- Flow through tubule increases
- Flow past macula densa increases
- Paracrine from macula densa to afferent arteriole
- Afferent arteriole constricts
- resistance in afferent arteriole increases
- Hydrostatic pressure in glomerulus decreases
- GFR decreases
List the four steps of reabsorption in the kidney tubules
- Na+ is reabsorbed by active transport
- Electrochemical gradient drives anion reabsorption
- Water moves by osmosis, following solute reabsorption. Concentrations of other solutes increase as fluid volume in lumen decreases
- Permeable solutes are reabsorbed by diffusion through membrane transporters or by the paracellular pathway
How does sodium reabsorption occcur in the proximal tubules? ENaC
- Na+ enters cell through various membrane proteins, moving down its electrochemical gradient.
- Na+ is pumped out the basolateral side of cell by the Na+-K+-ATPase
What are the two ways sodium is reabsorbed in the proximal tubule?
- NHE: Sodium-Hydrogen exchange
- ENaC: Epithelium Sodium Channel
What is the central role of Na+?
The active transport of sodium allows for secondary active transport of other molecules which symport with sodium
e.g. Urea - passive reabsorption, plasma proteins - receptor-mediated endocytosis
What is secretion?
- transfer of molecules from ECF into lumen of the nephron: active process (indirect)
- important in homeostatic regulation: K+ and H+
- increasing secretion enhances nephron excretion
- a competitive process
Describe the three steps of organic anion secretion?
- Direct active transport. The Na+-K+-ATPase keeps intracellular Na+ low
- Secondary indirect active transport. Na+ dicarboxilate cotransporter concentrates a dicrabosylate inside the cell using energy stored in the (Na+) gradient
- Tertiary indirect active transport. The basolateral organic anion transporter concentrates organic anions (OA-) inside the cell, using the energy stored in the dicarboxylate gradient
- Organic anions enter the lumen by facilitated diffusion
Describe excretion
Excretion = filtration - reabsorption + secretion
Clearance:
- rate at which solute disappears from the body by excretio
How is change in volume and blood pressure com batted by the kidneys?
dec. volume and blood pressure -> volume receptors in atria and carotid and aortic baroreceptors -> trigger homeostatic reflexes -> kidneys -> conserve H2O to minimise further volume loss
Explain osmolarity changes as fluid flows through the nephron
- Ososmotic fluid leaving the proximal tubule becomes progressively more concentrated in the descending limb
- Removal of solute on the thick ascending limb creates hyposmotic fluid
- Permeability to water and solutes in the distal tubule and collecting duct is regulated by hormones
- Final urine osmolarity depends on reabsorption in the collecting duct
What does vasopression do?
increase water reabsorption
how does vasopressin effect the kidney?
- Vasopressin binds to membrane receptor
- Receptor activates cAMP second messenger system
- Cell inserts AQP2 water pores into apical membrane
- Water is absorbed by osmosis into the blood
What does the renal countercurrent exchange system consist of?
- closely associated tubules and capillaries of the vasa recta
What does the vasa recta do?
removes water and prevents dilution of the medulla interstitial fluid
Explain the four steps of the countercurrent mechanism
- 1200 mOsm enters ascending loop of Henle
- Salts are reabsorbed
- Watter cannot follow solute
- 100 mOsm leaving the loop
Explain the 5 steps of how aldosterone acts on principal cells?
- aldosterone combines with a cytoplasmic receptor
- Hormone-receptor complex initiates transcription in the nucleus
- Translation and protein synthesis makes new protein channels and pumps
- Alsdoterone-induced proteins modulate existing channels and pumps
- Results is increased Na+ reabsorption and K+ secretion
What are the two abnormal pH affects on the nervous system?
Acidosis: neurons become less excitable; CNS depression
Alkalosis: hyoerexcitable
What creates fluctuations in pH?
Hydrogen
What are the three buffers against plasma pH?
- HCO3- in ECF
- proteins, hemoglobin, phosphates in cells
- phosphates, ammonia in urine
What is the pH equation?
CO2 + H2O <> H2CO3 <> H+ + HCO3-
What are two ways you can regulate pH?
- ventilation
- renal system
Explain renal regulation of pH
- Directly by excreting or reabsorbing H+
- indirectly by changing in the rate at which HCO3- buffer is reabsorbed or excreted
What are the three ways the renal system compensates Acid-base disturbances in the proximal tubule?
- Apical Na+-H+ exchanger (NHE)
- Basolateral Na+-HCO3- symport
- Na+-NH4+ antiporter
What are the three ways the renal system compensates Acid-base disturbances in the distal tubule?
H+-ATPase
H+-K+-ATPase
