Physiology Flashcards
What passes through Fenestrated Capillary Cells?
Non-formed elements I.e. Not cells (less than 100 nm)
What drains the Glomerulus?
An efferent arteriole
What is the main function of the Kidney?
To maintain a stable internal environment
What processes are undergone by the kidney?
Filtration, reabsorption and secretion
What is the Glomerulus?
The filtering unit of the kidney
What is the Renal Blood Flow?
25% of cardiac output
How is blood flow changed in the kidney?
By changing Afferent and/or Efferent arteriolar resistance
How is Renal Blood Flow calculated?
Q = ΔP/R
What is the renal arterial pressure?
80 - 200 mm Hg
What happens if renal arteriole pressure increases?
Renal resistance will increase proportionally
What is the Myogenic Theory of autoregulation of RBF?
Increased arterial pressure stretches the blood vessels, causing reflex contraction of smooth muscle in the blood vessel walls and consequently increased resistance to blood flow
Where is autoregulation of RBF controlled?
At the level of the Afferent arteriole
What happens when blood pressure is increased according to the Myogenic theory of autoregulation of RBF?
Resistance is increased
RBF is kept constant
GFR is increased
What happens when blood pressure decreases according to the Myogenic theory of autoregulation of RBF?
Resistance is decreased
RBF is kept constant
GFR is increased
What are the effects of the SNS on RBF?
⍺1 receptors (more common on afferent arterioles) stimulate vasoconstriction, decreasing RBF and GFR
What are the effects of high levels of Angiotensin II on RBF?
It causes vasoconstriction of both afferent and efferent arterioles (efferent more than afferent), increasing resistance and decreasing RBF
What are the effects of low levels of Angiotensin II on RBF?
It produces an increase in GFR by preferentially constricting efferent arterioles
What are the effects of Atrial Natriuretic Peptide on RBF?
It causes dilation of afferent arterioles and constriction of efferent arterioles, increasing RBF and GFR
What are the effects of Prostoglandins on RBF?
It causes vasodilation of both afferent and efferent arterioles
What are the effects of Dopamine on RBF?
Low dosages dilate renal arterioles, increasing RBF
What is Ultrafiltrate composed of?
It is composed of Water and all of the small solute of blood (not proteins or blood cells)
What is the pathway for ultrafiltration of plasma from the glomerulus to the Bowman space?
Fenestrated capillary endothelium > Capillary basement membrane > Visceral epithelial cell layer (podocytes) of Bowman Capsule
What is the Ultrafiltration Coefficient determined by?
The hydraulic conductivity of the glomerular capillary wall and the total capillary surface area available for filtration
What determines the GFR?
The Starling Equation
SNGFR = Kf x (∆P-∆𝜋)
SNGFR = Kf x [(Pgc −Pbs)−(𝜋gc −𝜋bs)]
How is hydrostatic pressure in glomerular capillaries changed?
It is change by changing the resistance of the afferent and efferent arterioles
How is hydrostatic pressure changed in Bowman’s space?
it can be changed by obstructing urine flow
How is oncotic pressure in glomerular capillaries changed?
It is changed by changing the plasma protein concentration.
What happens to oncotic pressure in glomerular capillaries when plasma protein concentration is increased?
It is increased
Net ultrafiltration and GFR is decreased
What happens to oncotic pressure in glomerular capillaries when plasma protein concentration is decreased?
It is decreased
Net ultrafiltration pressure and GFR is increased
What is the filtration fraction?
It is the fraction of the Renal Plasma Flow that is filtered across the glomerular capillaries
It expresses the relationship between the GFR and RPF
What is the normal filtration fraction?
20%
What happens if the filtration fraction is increased?
It produces increases in the protein concentration and oncotic pressure in glomerular capillaries of peritubular capillary blood
What is Renal Clearance?
It is the volume of plasma completely cleared of a substance by the kidney per unit time
What does it mean if a substance has high renal clearance?
It is completely removed on a single pass of blood through the kidneys
What substances have high renal clearance?
Inulin, Fructose, Polymers, Para-aminhippuric acid
What does it mean if a substance has a low renal clearance?
It is not removed well
What substances have low renal clearances
Protein, Glucose
How is GFR measured?
Using a substance that:
- Is freely filtered across the glomerular capillaries without size or charge restrictions
- Cannot be reabsorbed or secreted by the renal tubule
- cannot alter the GFR when infused
What can be used to measure GFR?
Inulin (must be injected intravenously)
What are the patterns of reabsorption?
Complete Reabsorption - The filtered substance is completely reabsorbed and is not present in urine
Zero Reabsorption - The Filtered substance is not reabsorbed and is present in its entirety (or close to) in the kidney
Regulated and Variable reabsorption - Reabsorption is dependant on the circumstances
How does tubular transport work?
Through Vectorial transport - the net movement of substance from tubular fluid to blood or vice versa
How is the proximal tubule adapted to bulk reabsorption of glomerular filtrate?
The epithelial cells have microvilli on their apical surface to provide large area and the basolateral membrane has folds
How is Na+ absorbed in the early proximal tubule?
Na+ is mainly absorbed with HCO3- and organic solutes, i.e. glucose and amino acids
How is Na+ in the late proximal tubule?
Na+ is mainly absorbed with Cl-
How much Na+ and what else is reabsorbed in the same amount?
67%, water is reabsorbed in the same amount
What is isosmotic reabsorption?
The tight coupling between Na+ and water reabsorption
What is reabsorbed in the proximal tubule?
65% of water, sodium, potassium and chloride
100% of glucose and amino acids
85%-90% of bicarbonate
What is the purpose of secretion in the proximal tubule?
To rapidly clear endogenous solutes and medications from the circulation
What is absorbed in the thick ascending limb of the loop of henle and what are the effects?
Sodium, potassium, chloride, bicarbonate and magnesium are reabsorbed. Water is not absorbed. This lowers tubular osmolarity.
What are the types of Nephrons?
Cortical (superficial) and Juxtamedullary (deep)
What is a nephron?
The functional unit of the kidney
What are the nephron segments?
The Bowman’s capsule, the Proximal Convoluted Tubule, the Proximal Straight Tubule, the Loop of Henle, the Distal Convoluted Tubule, the Collecting Duct
What is Renal Plasma Flow?
The portion of RBF that Is only plasma
What is the Paracellular transport pathway?
Passive transport where molecules travel between individual cells
What is the Transcellular Transport Pathway?
When molecules travel through cells
What does Sodium/Potassium ATPase transport?
It transports 3 Na+ out of the cell and 2 K+ into the cell
What is the purpose of Sodium/Potassium ATPase?
It creates a Na+ concentration gradient and a voltage gradient
What modes of transport are utilised by Sodium/Potassium ATPase?
Both active and passive transport mechanisms
What are the methods of water transport in the tubule?
Paracellular, transcellular and solvent drag/bulk transport
What is the renal threshold of reabsorption
The maximum amount of any given substance to be reabsorbed
What happens if the renal threshold is exceeded?
The additional substances are lost to the urine
What is the difference between Peritubular Capillary absorption and regular capillary absorption?
Peritubular capillaries reabsorb fluid across their entire length whereas regular capillaries filer along their 1st half and reabsorb along their 2nd half
What is the primary function of the Proximal Tubule?
To reabsorb as much of those substances the body needs as possible
What is the transport mechanism of Cl- reabsorption in the Proximal Tubule?
The Paracellular mechanism
How much HCO3- is reabsorbed by the Proximal Tubule?
About 80%
What is the function of the parathyroid hormone in the proximal tubule?
It inhibits Phosphate reabsorption
