Lecture 18 Renal Physiology Flashcards
angiotensin bruv
What are the various functions of the kidneys?
- Maintain purity and chemical consistency of plasma and interstitial fluid and in the process form urine
- Regulate volume of blood plasma, waste products in blood, concentration of electrolytes, and plasma pH
What are the 3 main metabolic wastes that are excreted by the urinary system?
Urea, uric acid, and creatinine
What microscopic structures does the renal cortex contain?
- many peritubular capillaries
- outer parts of nephrons: glomerular capsule, PCT, DCT
What does the renal medulla consist of?
Renal pyramids separated by renal columns
What microscopic structures do the renal pyramids contain?
Nephron loops (loops of henle),most of the length of the collecting ducts, and the vasa recta capillaries
All blood vessels that supply and drain the kidney are (in the correct path of blood flow through renal blood vessels):
Aorta –> Renal artery –> segmental artery –> interlobar artery –> arcuate artery –> cortical radiate artery –>
(nephron-associated blood vessels) afferent glomerular arteriole –> glomerulus (capillaries) –> efferent glomerular arteriole –> peritubular capillaries/ vasa recta –> cortical radiate vein –> arcuate vein –> interlobar vein –> renal vein –> inferior vena cava
What is the nephron and its function?
- The basic structural and functional (urine-producing) unit of the kidney
- To regulate the concentration of water and soluble substances by filtering the blood, reabsorbing what is needed back to blood, secreting what is not, and excreting the rest as urine
What are the 3 mechanisms/ processes that occur during urine production?
- Glomerular filtration
- Reabsorption
- Secretion
What is glomerular filtration and where does it occur?
A filtrate of the blood leaves glomerular capillaries (glomerulus) and enters the glomerular capsule of nephron.
Explain the process of reabsorption
Most of the nutrients, water and essential ions are recovered from the filtrate and returned to the blood of capillaries (peritubular capillaries or vasa recta) in the surrounding CT
Explain the process of secretion
Remaining wastes and unnecessary substances in blood are moved into renal tubules from surrounding peritubular capillaries.
What are the 3 layers of the filtration membrane in order (innermost to outermost)
- Fenestrated endothelium of glomerular capillaries
- Glomerular basement membrane
- Filtration slits and slit diaphragm of visceral layer of glomerular capsule (podocytes)
What is the main job of the fenestrated endothelium of glomerular capillaries?
Prevent passage of RBCs, WBCs, and platelets into the filtrate
The glomerular basement membrance (basal lamina) helps prevent the passage/ filtration of…
Larger proteins
Genetic defects in the proteins that compose the slit diaphragms result in massive leakage of plasma proteins into the filtrate leads to what?
Proteinuria
What is the name of the fluid that enters the glomerular capsule?
Filtrate or ultrafiltrate
True or False: Reabsorption happens only in the PCT and DCT
FALSE: Reabsorption happens at all 3 parts of the renal tubule
(PCT, Loop of Henle, DCT and collecting duct)
What is obligatory water loss?
Minimum of urine (400ml/ day) necessary to excrete metabolic wastes
At the PCT, the filtrate is isosmotic, which means the osmolality of the filtrate is essentially the same as that of plasma.
Can reabsorption of water by osmosis occur in this state? Why?
No it cannot because osmosis requires a concentration gradient. There is no concentration gradient if the filtrate is isosmotic.
What is the glomerular filtration rate (GFR)?
Volume of filtrate produced by BOTH kidneys
App. 125 ml/min or 180l/day
What is step 1 of reabsorption at the PCT?
- Na+ is actively transported from renal tubular fluid to peritubular fluid (aka interstitial fluid) surrounding the PCT
Occurs via sodium/ glucose cotransport. This creates a potential difference across the wall of the tubule, with the tubular lumen as the negative pole.
What is step 2 of reabsorption at the PCT?
Electrical gradient favors the passive transport of Cl- toward the higher Na+ concentration in the peritubular fluid
What is step 3 for reabsorption at the PCT?
- Accumulation of NaCl increases the osmolarity in the peritubular fluid above that of the tubular fluid. An osmotic gradient is then created that moves water from the tubular fluid into the peritubular fluid.
What is the final step of reabsorption at the PCT?
- The salt and water that were reabsorbed from tubular fluid can then move passively into plasma of the surrounding peritubular capillaries
Those who suffer from uncontrolled diabetes mellitus exhibit hyperglycemia and therefore….
Glycosuria
How does reabsorption at the Loop of Henle work?
Through an osmotic gradient generated via the countercurrent multiplier system
COUNTERCURRENT MULTIPLIER SYSTEM: What happens in the Descending loop of henle?
- Impermeable to passive diffusion of salt but permeable to water
- Water is drawn out of descending limb by osmosis and enters vasa recta blood capillaries (due to hypertonicity of interstitial fluid)
- Result is the tip of the loop of descending loop has same osmolality of surrounding interstitial fluid (1200-1400 mOsm)
- Therefore, there is a higher salt concentration at the start of the ascending limb
COUNTERCURRENT MULTIPLIER SYSTEM: What happens in the Ascending loop of henle?
- Divided into two regions: thin segment which receives filtrate from descending limb and thick segment which carries the filtrate into DCT
- NaCl ACTIVELY extruded from thick segment of ascending limb into surrounding interstitial fluid
- Walls of ascending limb NOT permeable to water
COUNTERCURRENT MULTIPLIER SYSTEM: Describe how the positive feedback loop works
- Ascending limb forces out NaCl into Interstitial Fluid and salt gets trapped. Increase in salt in IF causes H2O to diffuse from descending limb into IF thus concentrating filtrate as it moves closer to Ascending loop
- Increased concentration of filtrate in AL results in forcing out NaCl into interstitial fluid and salt gets trapped
In a nutshell, what does the countercurrent multiplier system accomplish?
Accomplishes the creation of concentrated urine by establishing a high osmotic gradient in the renal medulla, allowing for the reabsorption of water from the tubular fluid.
What is the vasa recta and what is its role in the Countercurrent Multiplier System?
- Long, thin-walled vessels that follow closely the Loop of Henles of the juxtamedullary nephrons.
- Most of the salt that is forced out from the ascending limbs must remain in interstitial fluid of medulla while most water that leaves descending limbs must be removed by the blood –> vasa recta takes care of this
What is the countercurrent exchange and how does it work?
- NaCl and other dissolved solutes like urea diffuse into descending vasa recta from interstitial fluid
- However, the same solutes passively diffuse out of the ascending vasa recta into the IF
- Solutes are recirculated and trapped in the renal medulla
The collecting ducts in the renal medulla are impermeable to ______ and permeable to ______
NaCl, Water
How are adjustments made in the collecting ducts?
- By regulating the number of aquaporins in the apical plasma membranes of the collecting duct epithelial cells, which allow water to travel faster across the cell membrane
- This regulation is under the control of antidiuretic hormone (ADH/ vasopressin)
When does plasma osmolality occur? What does it cause?
Occurs when plasma becomes more concentrated due to dehydration or excessive salt intake
Causes the release of of ADH from posterior pituitary
What is the effect of urine when ADH is high vs when it’s low?
High ADH: H2O is drawn out of collecting duct by high osmolarity of medullary interstitial fluid and is reabsorbed by peritubular capillaries resulting in LESS water excreted in urine
Low ADH: less H2O is drawn out of CD and more H2O is excreted as urine
What is aldosterone? How do you stimulate the release of aldosterone?
- A steroid hormone secreted by the adrenal cortex that stimulates the reabsorption of salt by the kidneys at the DCT and cortical portions of CD.
- Release of aldosterone is stimulated by salt deprivation, low blood volume or low blood pressure via Renin Angiotensin- Aldosterone System (RAAS)
What does the juxtaglomerular apparatus of the kidneys sense? What does it secrete?
- A decrease in the amount of Na+ and water in the renal filtrate or a decrease in blood volume/ blood pressure
- Secretes enzyme renin
What does renin convert? What does the product of that convert?
Renin converts angiotensinogen into angiotensin I.
Angiotensin passes through the body’s capillaries where angiotensin converting enzyme (ACE) converts angiotensin I to angiotensin II
What does angiotensin II do? (pt 1)
- Stimulates adrenal cortex to secrete ALDOSTERONE
- Stimulates vasoconstriction of arterioles
What does angiotensin II do in hypothalamus? (pt 2)
- stimulates plasma protein to secret ADH and tells CDS to insert more apical aquaporins leading to increased H2O reabsorption at CDS
- stimulates thirst center and increases H2O intake
What is Atrial Natriuretic Peptide?
- ANP is a hormone produced by atria due to stretching of walls when there is an increase in venous return
- Opposite of aldosterone and ADH and counteracts increased venous return and resulting increase in BP
- Stimulates salt and H2O excretion at the kidneys and acts as an endogenous diuretic to decrease BP
Where does secretion take place?
Mostly at the Distal convoluted tubules but sometimes at the Proximal convoluted tubules
What do multispecific transporters transport?
Endogenous molecules: Steroids, bile, salts
Xenobiotics: therapeutic or abused drugs
What is the normal blood pH?
What is the most important buffer in blood?
How do kidneys help regulate blood pH?
- 7.35 to 7.45
- Bicarbonate
- By secreting H+ ions or reabsorbing Bicarbonate (HCO3- ions)
What is volatile acid and nonvolatile acid?
Volatile acid is an acid that can be converted to a gas (eg. H2CO3- carbonic acid)
Nonvolatile acid cannot leave the blood and must be excreted via kidneys (eg. lactic acid, fatty acids, ketone bodies)
At what pH does acidosis and alkalosis occur?
Acidosis: pH < 7.35
Alkalosis: pH > 7.45
How is respiratory acidosis and respiratory alkalosis caused and what do they cause?
- Respiratory acidosis: caused by hypoventilation and causes increase in blood CO2, carbonic acid and lowers pH
- Respiratory alkalosis: caused by hyperventilation and causes decrease in blood CO2, carbonic acid and raises pH
How is metabolic acidosis and alkalosis caused?
- Metabolic acidosis: Excess of nonvolatile acids
- Metabolic alkalosis: too little nonvolatile acids or too much bicarbonate
