Osmoregulation Flashcards
Intracellular fluid
Fluid/H2O inside the cell. Humans: 28L of total body H2O
• Extracellular fluid
Fluid outside the cell. Made up on interstitial and plasma
• Interstitial fluid
H2O between cells, internal environment. Humans: 11.2 L of total body H2O
• Plasma
Extracellular component of blood. Humans 2.8L of total body H2O
• Internal environment
Cells constantly consuming O2 and nutrients from internal environment, releasing CO2 and waste products to internal environment
External environment
Plasma has exchange with external environment through actions of lungs, intestines, and kidneys. Plasma also has free exchange with interstitial fluid, and thereby maintains constancy of internal environment
Osmoregulation
Maintenance of a nearly constant osmotic pressure in blood plasma
Ion regulation
Maintenance of a nearly constant concentration of inorganic ions in blood plasma
Volume regulation
Maintenance of a nearly constant water volume in blood plasma
Fluid balance
inputs and outputs. In order to maintain ECF osmolality and volume, must achieve H2O balance and Na+ balance
o Inputs: drinking and eating, metabolic H2O as result of cell respiration
o Outputs: Urinary H2O and solute loss, Fecal H2O and solute loss, and Evaporative H2O loss (breathing, sweating)
U/P ratio
Urine Concentration Solute(s)/Plasma Concentration Solutes(s) by varying U/P ratio, kidneys can modify blood plasma, affect interstitial fluid properties
- U/P = 1, isotonic urine
- U/P > 1 Hypertonic urine
- U/P
Kidneys:
Filter blood plasma, remove appropriate amount of H2O and plasma solutes
Kidney Renal artery:
Supply blood to kidney
Renal vein:
Drain blood
Ureters
Transport urine to bladder
Bladder
Holds urine
Cortex:
Outer region of kidney. Contains Glomeruli, proximal and distal tubules, and pertubular capillaries
Medulla
Loop of Henle, Vasa Recta capillaries (Humans have multiple medullary pyramids, rodents have a single medulla)
Glomerulus:
Site of filtration, plasma into nephrons
Nephron
site of reabsorption and secretion. About 800,000 per kidney in humans
Bowman’s capsule:
surrounds glomerular capillaries, collects ultrafiltrate leaving glomerular capillaries
Proximal tubule
60-70% of H2O and Na+ are reabsorbed into pertitubular capillaries.
All transport dependent on active pumping of Na+ and Na+K+ATPase
Have a lot of mitochondria
Distal Tubule:
- Depends on relative number of Na+ channels and Na+K+ATPase pumps
- Aldosterone (secreted if plasma volume is low) determines how many Na+ transport proteins are present
- DT H2O permeability matches Na+ reabsorption rate, equal reabsorption of Na+ and H2O increases plasma volume
Loop of Henle:
- H2O Reabsorption: only occurs in the descending limb of loop (AQP-1 present in these cells)
- Na+ reabsorption: only present in the ascending limb of loop necessary proteins present.
- Differential reabsorption of H2O and Na+ in this segment critical for forming concentrated urine (diluting plasma osmolarity)
- Creates a vertical osmotic gradient from cortex to papilla
Collecting ducts
many nephrons drain into individual collecting ducts to ureters. Have tubular reabsorption
AVP action → increase H2O reabsorption from CD, forming urine with higher U/P ratio
Filtration
125 ml plasma/min; 180L/day
Reabsorption:
movement from tubular lumen to blood; 178.5L/day
Secretion
movement from blood to tubular lumen; additional venue for rapidly removing substances from blood
Excretion:
anything not reabsorbed is excreted; 1.5L/day
Glomerular capillary
Highly permeable capillaries with loads of fenstra
Podocyte
inner epithelial layer of Bowman’s capsule, retrict filtration of large, negatively charged molecules (think proteins).
Blood pressure (PGC):
blood pressure within glomerular capillaries tends to force fluid out
Colloid osmotic pressure (𝛑GC):
Proteins aren’t filtered so osmolarity in glomerular capillaries slightly higher than that in bowman’s capsule, pulls H2O back in capillaries
Hydrostatic pressure (PBC):
Fluid in capsule exerts hydrostatic pressure, pushes fluid back into glomerular capillaries
Na+K +ATPase
found in Proximal Tubule, Distal Tubule
NKCC co-transporter
protein that aids in the active transport of Na, K and Cl-
Aquaporin (AQP-1, AQP-2, AQP-3):
Forms pores in membrane. AQP-1: Proximal tubule, AQP-2: collecting duct,
Single effect:
o Refers to the difference in osmotic concentration between the descending limb/interstitial fluid and adjacent ascending thick limb.
o Due to active Na+ transport of epithelial cells in ascending limb
o Due to high water permeability in descending limb, but no water permeability in ascending limb
Vasopressin (ADH/AVP/Antidiuretic):
o Regulates the body’s retention of water by
• Increasing water reabsorption in the kidney’s collecting duct
• Determines how many Na+ transport proteins are present
• Increases peripheral vascular resistance → increases arterial bp
