Urinary System 2 Flashcards
Filtration membrane:
Prevents blood cells and large proteins from passing
Fenestrated endothelium
Filtration membrane: Blocks large, negatively charged ions
Basement membrane
Filtration membrane: allow water, glucose, ions and small molecules to pass
Filtration slits
Determines the direction and amount of filtrate produced
Net Filtration Pressure
Normal NFP amount
10mmHg
Formula for NFP
NFP = GBHP - (CHP + BCOP)
normal:
10 = 55 - (15 +30)
Percentage of renal plasma flow that becomes filtrate
Filtration fraction - typically 16-20%
The amount of filtrate formed per minute in all renal corpuscles, normally 105-120 mL/min.
Glomerular Filtration Rate (GFR)
Importance of Maintaining GFR: Too high or too low
Too high: Needed substances may not be reabsorbed and are lost in urine.
Too low: Wastes are not adequately removed from blood.
3 Modes for Regulation of GFR
- Renal autoregulation
- Neural regulation
- Hormonal regulation
Adjusts blood flow locally via the myogenic mechanism and tubuloglomerular feedback.
Renal autoregulation
Sympathetic nervous system adjusts GFR, especially in emergencies.
Neural regulation
Involves Angiotensin II and Atrial Natriuretic Peptide (ANP).
Hormonal regulation
Movement of solutes and water from renal tubules back into the blood (peritubular capillaries or vasa recta).
Reabsorption
Transfer of substances (wastes, toxins, excess ions) from blood into the tubules for excretion
Secretion
Reabsorption dominates:
100% of glucose and amino acids.
65% of water, sodium, potassium.
85-90% of bicarbonate (HCO₃⁻).
Proximal Convoluted Tubule (PCT):
Reabsorbs 15% of water (permeable to water, but not solutes).
Nephron Loop Descending limb
Reabsorbs Na⁺, K⁺, Cl⁻ through active transport.
Nephron Loop Ascending limb
Reabsorbs Ca²⁺ (regulated by PTH).
Reabsorbs small amounts of water, Na⁺, and Cl⁻.
Early DCT
Final adjustments depend on body needs:
Principal cells: Reabsorb Na⁺ and water (regulated by aldosterone and ADH).
Intercalated cells: Regulate pH by secreting H⁺ or reabsorbing bicarbonate (HCO₃⁻).
Secrete urea and K⁺.
Late DCT and Collecting Duct
Increases water reabsorption by stimulating aquaporins in collecting ducts.
Antidiuretic Hormone (ADH)
Increases Na⁺ reabsorption and K⁺ secretion.
Aldosterone
Increases Ca²⁺ reabsorption in the early DCT.
Parathyroid Hormone (PTH):
Inhibits Na⁺ reabsorption, leading to more water and Na⁺ excretion.
Atrial Natriuretic Peptide (ANP)
Two Types of Water Reabsorption
- Occurs in the DCT and collecting tubule.
- Allows precise control of water reabsorption by ADH.
- Adjusts urine volume by reabsorbing a portion (or all) of the remaining 15% of filtrate volume.
Facultative Water Reabsorption
- Normal volume: Approximately 1200 mL/day.
- Normal osmotic concentration: 600 - 1500 mOsm/L.
- Values differ from person to person and from day to day as the kidneys alter their function to maintain homeostasis.
Normal Urine
Dilute urine is produced in the absence of
ADH
Concentrated urine is produced in the presence of
ADH.
A mechanism in the nephron loop of juxtamedullary nephrons that allows the kidneys to produce concentrated urine.
Countercurrent Multiplication System:
secrete renin when:
There is intrarenal artery hypotension (low blood flow through kidneys).
Juxtaglomerular cells
activates angiotensinogen (from liver) into angiotensin I (AGI).
Renin
converts angiotensin I (AGI) into angiotensin II (AGII).
ACE
Vasoconstrictor that decreases GFR by constricting afferent arterioles.
Angiotensin II:
Acts on principal cells to increase reabsorption of Na+, Cl-, and H₂O, thereby increasing blood volume and pressure.
Aldosterone:
released by the posterior pituitary
Antidiuretic Hormone (ADH)
secreted by atrial cells in the heart when blood in the atria stretch the walls
Atrial Natriuretic Peptide (ANP):
secreted by the parathyroid glands when blood Ca²⁺ levels are low.
Parathyroid Hormone (PTH):
secreted by the parafollicular cells (C cells) of the thyroid gland when blood Ca²⁺ levels are high.
Calcitonin
