5 - Renal Physiology Flashcards
What structure allows the kidney to maintain constant blood flow despite systemic pressure changes
Two capillary beds in series between arteries and veins
What is the typical composition of blood
44% red blood cells
1% other cells
55% plasma (includes albumin, fibrinogen, IgG, clotting factors, water, salts, hormones)
What are the three layers of the glomerular filtration barrier
- Capillary endothelium (fenestrated)
- Basement membrane
- Podocytes (with foot-like processes forming a filtration bed)
What characteristic helps prevent protein and cell passage in the glomerulus
Negatively charged glycoproteins in the filtration layers
What is required for filtration to occur in the kidney
Hydrostatic pressure – No pressure = No filtration
Where does reabsorption occur
In the lumen of the nephron, substances like ions, glucose, and amino acids are reabsorbed
What mechanisms are involved in reabsorption (5)
Co-transport
Active transport
Osmosis
Solvent drag
Passive diffusion
What factors affect reabsorption efficiency (2)
Flow rate of filtrate
Concentration of small molecules
(Note: Reabsorption is limited by the number of available transporters)
What are the roles of sodium-glucose transporters in glucose reabsorption
SGLT2: Reabsorbs 90% of filtered glucose
SGLT1: Reabsorbs remaining 10%
What is the main role of the Loop of Henle
Acts as a counter-current multiplier to concentrate urine and reabsorb water
How does the Loop of Henle achieve water reabsorption
- Na⁺ actively transported out of ascending limb
- Ascending limb is impermeable to water
- Water moves out of descending limb by osmosis
- Na⁺ diffuses out passively at the hairpin bend
What is the difference between secretion and excretion in the kidney
Secretion = movement of substances into nephron tubule (not necessarily excreted)
Excretion = substances that are eliminated in urine
What forms of nitrogen are secreted into the proximal convoluted tubule (PCT)
NH₃ (ammonia) from plasma
NH₄⁺ (ammonium) from the PCT cytosol
What systems regulate blood pressure and fluid balance (7)
Central/autonomic nervous systems
Cardiac output
Blood vessel tone
Renal function
RAAS (Renin-Angiotensin-Aldosterone System)
Catecholamines
ADH (vasopressin)
What are the main functions of aldosterone (4)
- Increases Na⁺ reabsorption in the distal tubule and collecting duct
- Promotes K⁺ secretion
- Stimulates Na⁺/K⁺ pump activity
- Reduces renin secretion (negative feedback)
How do granular cells regulate renin release
Act as baroreceptors in the afferent arteriole – low stretch = more renin release
How does low blood pressure affect Na⁺ delivery in the nephron
↓ BP → ↓ GFR → ↓ flow rate
More Na⁺ reabsorbed early in tubule
Less Na⁺ reaches the distal tubule
What increases angiotensinogen production
Corticosteroids
Oestrogen
Thyroid hormone
Angiotensin II
Plasma volume changes
What pH ranges define acidemia and alkalemia
Acidemia: pH < 7.35
Alkalemia: pH > 7.45
What does a U:P (urine to plasma) ratio >1 indicate
The kidney is concentrating solutes in the urine (hyperosmotic)
What does a U:P ratio = 1 indicate
Urine and plasma have equal solute concentration (isosmotic)
What does a U:P ratio <1 indicate
Kidney is diluting the urine (hypoosmotic)
What are the kidney’s 2 main tasks for acid-base balance
- Reabsorption of filtered bicarbonate (HCO₃⁻)
- Excretion of daily acid load
How does the kidney regulate acid-base balance
HCO₃⁻ reabsorption
H⁺ secretion
Ammonium (NH₄⁺) secretion
