L. 36 Body Fluid Compartments

What is water content throughout the Different stages of life?

What creates differences in water content?

• ~80% at birth

• 50-60% in adults

• 45% in elderly adults

• Sex differences, fat deposition, muscle mass

What are the tissue specific water contents

• 80% lung

• 85% brain

• 80% heart

• 75% liver

• 50% blood

• 25% bone

• 10% teeth

How are fluids distributed?

• 60% of total body weight fluids are in…

  • Intracellular fluid (ICF) ~67%

  • Extracellular Fluid (ECF) ~33%

    • ECF is made of

      • ~80% Interstitial Fluid (IF)

      • ~20% Plasma

      • ~1% “negligible fluids”

What fluids have a negligible contribution to overall fluid balance?

• lymph (interstitial fluid)

• Transcellular fluids

  • Intraocular (eye)

  • Peritoneal (abdominal space)

  • Pleural (lung)

  • Cerebrospinal (brain/spinal)

  • Digestive (GI tract)

  • Synovial (joints)

Solute vs solvent?

Solute: the thing dissolved in a solvent (ions)

Solvent: any fluid into which solute is dissolved (water)

What is osmosis

• passive diffusion of water from an area of low solute concentration to higher solute concentration from a semipermeable membrane

Osmolartity vs osmolality

• R: concentrations of all solutes/volume unit of solvent (temp dependant)

• L: concentration of solutes/ unit weight of solvent (temp indépendant)

Which area that hold the body’s water content is most resistant to change in volumes?

• intracellular because it’s not good for cells

What is the main for water storage compartment Responsible for water regulation

• the extracellular fluid (ECF)

How is water distributed between compartments to regulate balance

• through osmosis

Which compartments does water balance happen between in IFC

• the interstitial fluid (IF) and plasma

Which compartments does water balance happen between in ECF

• plasma and IF

• GI tract and IF

How does ICF get transported into plasma?

• via action of hormones

Tonicity?

The ability of osmolarity to modifie the ICF volume by altering water movement

In normal conditions how does the plasma osmolarity compare to RBC osmolarity? What is this called?

• plasma and RBC osmolarity match each other

• Meaning they’re isotonic

What does Isotonic mean

• no net water movement between IF and ICF

What is 0.9% NaCl in mmol?

[130-140mmol] NaCl

What does Hypertonic mean? Which direction?

• high osmolarity in IF relative to ICF

• Water moves out of IF by osmosis

What is given to patients who require ECF replacement therapy or as a drug diluent

• Saline (0.9% NaCl)

• Or D5W (5% dextrose)

What does Hypotonic mean? Which direction?

• low osmolarity in IF relative to ICF

• Water moves in to IF by osmosis

How is osmolarity governed in body fluid compartments?

A few major solutes

• Major cations

  • Na+ (high in ECF, low in ICF)

  • K+ (high in ICF, low in ECF)

  • (Remember action potentials)

• Major Anions

  • Cl- (high in ECF, low in ICF)

  • HCO3- (higher in ECF than ICF)

• Other ions and protein

  • HPO4 2- (high in ICF, low in ECF) for nucleic acid synthesis, makes sense to be higher in ICF

  • Ca2+ (high in ECF, low in ICF)

  • Mg2+ (higher in ICF, low in ECF)

  • Protien (is anionic (high in ICF low in ECF)

What are 3 forms of transport across membranes?

• Passive

  • Co-transport (2+ electrolytes)

    • Symport: same direction

    • Antiport: opposite direction

• Facilitated

  • Uses protein transporters in membrane as passive mechanism (ex. GLUT1 in beta cell membrane)

• Active

  • Primary: Uses energy from ATP hydrolysis

  • Secondary: uses electrochemical solute gradient to move against gradient (Na+/K+ antiporter pump)

How is Na+K+ gradient maintained in ICF and IF?

• by primary active transport

• ATP hydrolysis required, remember Na+ greater outside of the cell, K+ greater inside the cell

What is CCCs? What does it do?

• Cation-coupled Chloride Channels

• Uses Na+ or K+ to co-transport Cl-

  • Secondary: K-Cl co-transporter (KCC2) or Na-K-Cl co-transporter NKCCL1

how is chlorine transported aside form CCCs?

ATP gated channels

• Cl- transported down gradient that was established by other channels in lung epithelium from ICF to IF

How is HCO3- transported out of plasma?

• It’s coupled to Cl- transported down gradient in RBCs (chloride shift)

What happens when CO2 enters the RBC? What catalyses this?

• CO2 reacts with H2O and forms HCO3-

• Carbonic Anhydrase (CA) catalyses this

How does HCO3- get moved out of the RBC after it’s synthesis?

• alongside Cl-, its exchanged thru secondary antiport (HCO3- out, Cl- in) mechanism (chloride shift)

• By band 3 protein AE1 (maintains electrical neutrality), forms H-Hb

What happens when O2 enters the RBC from alveoli?

• it dissociates and H-Hb and Hb-CO2 form again

• Chloride shift reverses

What is Ca2+ important for?

• blood clotting

• Signaling

What are the major 3 ions making up the bone? What regulates these ions in the ECF

• Ca2+

• HPO4 2-

• Mg2+

• dietary intake, excretion

• Formation/reabsorption of bone

What are the two main physical forces controlling fluid movement?

• osmotic pressure

• Hydrostatic pressure

What is osmotic pressure? Why?

• Force of solutes to make fluids move inwards

• Solvents on both sides of the blood vessel, solvent wants to move into blood vessel because less solvents

What is hydrostatic pressure? Why?

• Blood pressure against capillary wall (fluid movement outwards)

• Blood creates force toward outside blood vessel walls

What is the balance of forces when filtration occurs

Osmotic pressure is less than hydrostatic pressure

What is the balance of forces when no net movement occurs

Osmotic is equal to hydrostatic pressure

What is the balance of forces when reabsorption occurs

• osmotic is greater than hydrostatic pressure

Which pressure allows nutrient delivery to tissues?

• hydrostatic pressure

Which pressure allows tissues to remove waste from themselves?

• Osmotic pressure

What are the names form active and passive transport of nutrients accross GI epithelium? Which is the major mechanism for glucose transport?

• Active - Transcellular

  • Nutrient moves up/down gradient through cells and out other side

  • The major mechanism for glucose transport

• Passive - Paracellular

• - moves down concentration gradient, between cells through tight junctions

  • For amino acids and some glucose

Which side has the apical domain/ which side is the apical side?

The side of the cell wall that’s touching the intestinal lumen (inner side)

Which side has the basolateral domain/ which is the basaolateral side?

The side facing extracellular space

Which layer has the highest concentration of glucose in the GI?

• the cell layer (not intestinal lumen, not extracellular space)

How is dehydration sensed?

• decrease in blood volume (pressure)

• Increased blood osmolality (too high [Na+])

What does decreased blood pressure trigger?

• Generation of the hormone Angiotensin II

What does increased osmolality and dry mouth trigger?

• osmoreceptors in hypothalamus

What does Angiotensin II and osmoreceptors in the hypothalamus trigger in common?

The brain’s thirst centre

What does water consumption do?

• decrease blood osmolality

• Increased blood pressure

What can cause over hydration?

what counts as over hydration?

• a compromised or immature kidney function

• Certain medications (anti-depressants)

• Consumption of over 20L/day

Hyponatremia?

• Caused by over hydration

• Low [Na+] in blood

• Water moves into IF and ICF down it’s concentration gradient

• disorientation, fatigue, nausea, vomiting, tissue swelling, muscle cramps

AVP?

• Arginine VasoPressin (AKA anti-diuretic Hormone, ADH)

• Released from pituitary during dehydration to increase body water content

  • Constricts arteriols

  • Promotes water reabsorption in kidneys (not peeing it out)

What do diuretic agents do? Common examples of them?

Increase amount of water filtration from blood (usually results in more peeing)

Alcohol and caffeine

AVP disorders? Symptoms? Different types? Treatment?

• a lot of pee (Hypotonic pee)

• Excessive thirst

• Dehydration

• AVP deficiency (former: central diabetes insipidus)

  • Not enough production of AVP from pituitary

• AVP resistance (former: nephrogenic diabetes insipidus)

  • Resistance to action of AVP on Kidney → no water reabsorption

• Gestational AVP deficiency (former: gestational diabetes insipidus)

  • AVP degraded too fast because of placental enzyme vasopressinase (the cleaving AVP enzyme)

• AVP replacement (DDAVP)

• discontinuing certain medications

Which fluid’s volume increases in edema?

IF volume

Edema? Causes?

• Increased water volume in tissues (mostly IF)

• tissue swelling

• Pitting of skin

• Pregnancy

• Menstruation

• Tissue injury

• Infections

• Allergy

• Lymphatic disorders

• Heart/kidney failure - pulmonary edema

• Liver disease (lower proteins → decreased osmotic pressure)

• Vasodilators (blood pressure)

• Non steroidal anti-inflammatory drugs (NSAIDs, Advil

What does edema look like?

Puffy