The Urinary System Physiology Flashcards
What do kidneys regulate ?
- plasma ionic composition
- plasma volume
- plasma pH and osmolarity
- removal of metabolic wastes
- the number of red blood cells
- vitamin D production
Which structures compose the nephron ?
- renal corpuscle
- renal tubule
What are the structures composing the renal corpuscle ?
- glomerulus
- Bowman’s capsule
Which structures compose the renal tubule ?
- proximal tubule
- loop of henle
- distal convoluted tubule
- collecting duct
In the kidney what structure regulates blood pressure ?
Juxtaglomerular apparatus composed of :
- macula dansa
- granular cells secreting renin
Which structures of the nephron are found in the renal cortex ?
Renal corpuscle
The proximal tubule
The distal convoluted tubule
Which structures of the nephron are found in the renal medulla
Descending and ascending limbs of henle loops
What are the 2 types of nephron ?
Cortical nephrons
Juxtamedullary nephrons
What is the blood supply of nephrons ?
The efferent arteriole forms a second capillary bed around the renal tubule
In cortical nephron : peritubular capillaries
In juxtamedullary nephron : vasa recta
What are the functions of the nephron allowing the regulation of the composition of plasma
- filtration
- reabsorption
- secretion
What is the role of bowman’s capsule in the nephron ?
It surrounds the glomerulus to form a lumen and captures and directs the filtrate to the proximal tubule. It is composed of a parietal layer and a visceral layer.
What is the proportion of plasma entering the Bowman’s capsule ?
10-20% of plasma enters
Explain how glomerular filtration takes place ?
Glomerular capillaries are fenestrated. The only thing separating the blood from the filtrate is the shared basement membrane. This system ensures a filtration based on size : blood cells and large proteins cannot pass but most other constituents go through.
Proteins associated with fenestration are negatively charged which allows positively charged proteins to pass through more readily. This leads to the creation of a filtrate with a composition very similar to plasma but with a slight predominance of positively charged substances.
What is the glomerular filtration rate ?
The volume of filtrate formed by both kidneys per minute
Which factors can affect the glomerular filtration rate ?
- hydrostatic pressure (pressure produced by a fluid against a surface)
- osmotic pressure
What means an osmotic pressure near to zero ?
Absence of proteins in the filtrate
In the glomerular filtration what are the pressures in favor of filtration ?
- glomerular capillary hydrostatic pressure (60 mmHg)
- Bowman’s capsule osmotic pressure (0 mmHg)
In the glomerular filtration what are the pressures opposing to filtration ?
Bowman’s hydrostatic pressure (15 mmHg)
Glomerular capillary osmotic pressure (30 mmHg)
What is the glomerular filtration rate ?
125 ml/min which equals to 180L of filtrate a date
What is the renal plasma flow ?
The volume of plasma flowing through the kidneys and which equals to 625 ml/min
What is the filtration fraction
The filtration rate divided by the plasma flow rate which equals to 20%
From the 625 ml of plasma arriving per minute to the kidney only 20% arrives to renal tubule
Which factor influences the glomerular capillary hydrostatic pressure ?
The mean arterial pressure
If it rises then the glomerular capillary hydrostatic pressure rises too and favors filtration
At which mean arterial pressure is the glomerular filtration rate kept constant ?
80 mmHg < MAP < 180 mmHg
How is glomerular filtration rate controlled ?
- myogenic regulation
- glomerulotubular feedback
Explain the myogenic regulation of GFR
Mean Arterial Pressure stretches smooth muscles in afferent arteriole Vasoconstriction Higher resistance Less blood flow Lesser pressure in glomerulus
And vice versa
Explain the tubuloglomerular feedback
Change in glomerular filtration rate affect the flow of tubular fluid
Cells of macula dansa sense this flow
Secretion of paracrine signals
Smooth muscle contraction / dilatation in afferent arteriole
If GFR rises : vasoconstriction takes place
If GFR drops : vasodilatation takes place
When does the extrinsic regulation of GFR take place ?
When the mean arterial pressure is < 80 mmHg
Describe the extrinsic regulation of GFR
Sympathetic activation through baroreceptor reflex
Vasoconstriction in afferent and efferent arteriole
Higher resistance
Less blood flow
Less urine output to minimize the diminution of blood volume
Where does tubular reabsorption take place ?
Distal and proximal convoluted tubules
When reabsorbed which barriers faces a substance ?
- Tubule epithelium
- Capillary endothelium
Renal tubules are the primary barriers because epithelial cells are connected through tight junctions.
Which types of molecules can come across the cell membrane freely ?
Small and uncharged molecules (O2, CO2, H20), as well as hydrophobic substances
Which type of zone polar / non polar does the phospholipid bilayer create ?
Non-polar zone
Which substances cannot pass through the cell’s membrane ?
Ions or large hydrophilic substances
What are the different types of passive transport through the cellular membrane ?
- diffusion
- osmosis
- facilitated diffusion
What are the different types of active transport through the cellular membrane ?
- protein pumps
- co transport
- endocytosis/ Exocytosis
What is diffusion ?
Passive transport which doesn’t require energy
Solute moves freely across the membrane
The molecules move down their concentration gradient
What is osmosis
Passive transport across the cellular membrane which doesn’t require energy
Solvent moves freely across the membrane
The molecules move down their concentration gradient
What is facilitated diffusion
A passive transport through the membrane which doesn’t require energy
The substance uses a protein gateway to move through
The molecules move down their concentration gradient
What is a concentration gradient ?
When there is an unequal repartition of solute across the membrane
What are protein pumps
Active transport through the membrane requiring ATP
Ions move against the concentration gradient
Protein pumps are membrane proteins that actively move specific molecules to where they are needed and ultimately create a concentration gradient
What is co-transport
An active transport through cellular membrane
From a region of low concentration to a region of high concentration
Using a pre established concentration gradient to move ions and large hydrophilic molecules
What are the specificities of tubular reabsorption ?
Various portions of the nephron differ in their capacity to reabsorb water and specific solute
Takes place in the proximal and distal convoluted tubules
Substances need to cross the apical membrane and the basolateral membrane to exit the tubular lumen
Water reabsorption follow the active reabsorption of the solute
Which substances are secreted by the renal tubule ?
Hydrogen ions Potassium ions Urea Drugs Creatinine Ammonia
Describe reabsorption taking place in the proximal microtubules
Mass absorption due to the presence of microvili, of many mitochondria available for active transport and the paracellular transport
- 70% of the water
- Na+
- K+
- 100% of glucose
- amino acids
- vitamins
- 50% of Cl-
- Ca2+
- Mg2+
- phosphates
- bicarbonate (blood pH homeostasis)
How is water recovery promoted through reabsorption
Formation of osmotic gradient promoting water recovery.
Acquaporin proteins are found in varying amounts and help regulate water movement
Describe the reabsorption process in the loop of Henle
- most of water and Na+ that were filtered by the glomerulus
- the descending loop of Henle has permanent aquaporin channel proteins allowing unrestricted movement of water
- 15% of water is reabsorbed here
- urea is secreted inside the tubular lumen
- thick portion of ascending loop is completely impermeable to water : active removal of sodium, Cl- follows Na+ because of the electrochemical gradient so the resulting filtrate is hypotonic
What happens to the tonicity of urine in the loop of Henle ?
The tonicity of urine will change from isotonic to both very hypertonic and very hypotonic solutions
Describe the reabsorption process in distal tubule
The lumenal fluid is hypo osmotic to the peritubular fluid
Describe the reabsorption process in the collecting ducts
The osmolarity of the lumenal fluid is always less than the increasing osmolarity of the medullary interstitial fluid
What is specific about the location of aquaporins
They are present in the apical membrane in response to hormonal signal
They are permanently present in the basolateral membrane
What happens if the walls are impermeable to water ?
Excretion of a large volume of urine with low osmolarity
What happens if the walls are permeable to water ?
Excretion of low volume of urine with high osmolarity
Define excretion
Elimination of solute and water from the body
To what corresponds the amount excreted ?
Amount filtered + amount secreted - amount reabsorbed
What is the filtered load ?
Glomerular filtration rate X plasma concentration
On what is the excretion rate dependent ?
- filtered load (GFR x plasma concentration)
- rate of secretion
- rate of reabsorption
What happens if excretion rate > filtration load
Solute is secreted in the tubule
What happens if excretion rate < filtration load
Solute is reabsorbed from the tubule
What is the normal arterial pH ?
7.4
Why is it important to keep pH in range ?
- essential for protein 3D structure
What if pH < 7.35
Acidosis
Causing depression of central nervous activities, arrhythmia, potassium retention
What if pH < 6.8
Acidosis with fatal consequences such as coma and respiratory failure
What if ph > 7.45
Alkalosis
Increasing CNS excitability and potassium depletion
What if pH > 8
Alkalosis with fatal consequences such as muscle seizures and convulsions and spasms of respiratory muscles
Explain the bicarbonate buffer system
CO2 + H20 <=> H2C03 <=>H+ + CO3-
Where H2C03 is proportionate to CO2
So pH = 6.1 + log ((HCO3-)/(CO2)
Therefore in order to maintain pH at 7.4 the ratio between both must be 20:1
Which structures are responsible of the removal of H+ ions (causing acidity)
- kidneys
- lungs
What are the defense mechanisms against acid-base disturbance ?
- buffers
- respiratory compensation
- renal compensation
Describe the action of buffers
Immediate action but limited in time. Cannot reverse the change in pH
Describe the action of respiratory compensation
- acts within minutes
- true homeostatic mechanism
- if higher ventilation : lower CO2 : higher pH
- if lower ventilation : higher CO2 : lower pH
Describe the renal compensation in case of acid-base imbalance
If pH increases : low H+ secretion, low HCO3- reabsorption
If pH decreases : higher H+ secretion, higher HCO3- reabsorption and production
