Homeostasis and Water Balance in Biosciences

• Study notes on the foundations of biosciences, module 1 around homeostasis and water balance

Learning Objectives

• Recognize the molecule of water's structure and property
• Elucidate water role in cell metabolism
• Identify regulation mechanisms regarding bodily water balance

Atomic and Molecular Structure of Water

• Water presents an irregular tetrahedral structure
• Oxygen binds with two hydrogens, forms simple covalent polar bonds
• High oxygen electronegativity causes partial charges
• Water has a dipolar character
• Pure water is electrically neutral
• Water molecules interconnect through hydrogen bridges
• Oxygen electronegativity is 3.5; Hydrogen electronegativity is 2.1
• Angle between hydrogen atoms is 104.45°
• Distance between oxygen and hydrogen atoms is 0.9584 Å

Molecular Geometry and Charge Distribution

• The geometry and polarity of the bonds define charge distribution within the molecule
• A molecule is polar if its charge centers (+ and -) aren't aligned

States of Water

• Hydrogen bridge is at 0.18 nm
• Covalent bond is at 0.10 nm

Physico-Chemical Properties

• A solid's volume is found from amount of water displaced
• Water's physico-chemical properties are linked to biological functions
• Water molecules bind using hydrogen bonds
• Forces among water molecules in liquid bulk are balanced
• Surface interactions are like an elastic skin, supports small insects
• High oxygen electronegativity causes partial negative charges (δ-) on the oxygen atom and partial positive charges (δ+) on the hydrogen atoms
• The high tension results in the capillary effect

Water's Physico-chemical Properties

• A specific heat is the amount of calories needed to raise one gram of a substance
• Vaporization heat is amount of heat needed to evaporate one gram of substance at boiling temperature, 536 calories for water
• A dielectric constant involves two masses with opposite electric charges attract in a vacuum with a force indirectly proportional to the square of their separation distance
• Attraction force is proportional to 1/distance^2
• Any medium between two masses reduces attraction force, determined by medium electrical constant
• Important to measure the ability to keep ions apart
• Surface tension occurs from mutual attraction between liquid molecule, cohesion reduces the surface

Physico-chemical Properties of Water

• High boiling temperature
• Maximum density at 4 degrees C
• High specific heat
• High vaporization heat
• High heat conductivity
• High dielectric constant
• Capacity of hydration or ion solvation
• Solvent of amphipathic molecules
• Solvent for polar compounds of non-ionic nature
• High surface tension

Dissociation Constant

• Equation for dissociation of water: H2O + H2O ⇄ H3O+ + OH-
• Dissociation constant K = [H+][OH-]/[H2O]
• One gram of water contains 3.46 × 10^22 molecules
• Probability of a hydrogen atom existing as a hydrogen ion in pure water is about 1.8 × 10^-9
• One liter of water equals 55.56 mol, probability is 1.8 × 10^-9
• Molar concentration of H+ or OH- ions in pure water is probability (1.8 x 10^-9) times molar concentration of water (55.56 mol/L); resulting in 1.0 × 10^-7 mol/L
• Kw (ion product) = (K)[H2O] = [H+][OH-] = (1.8 × 10^-16 mol/L)(55.56 mol/L) = 1.00 × 10^-14 (mol/L)^2

Movement of Water and Solutes across Biological Membranes

• Three types of movement: Simple diffusion, facilitated diffusion, and active transport

Osmosis

• Physical phenomena, water movement via semipermeable membrane without expending energy
• Osmolarity is the total molecular concentration of osmotically active particles in a solution, osmoles or milliosmoles per liter of solvent
• Osmolality is the total molecular concentration of osmotically active particles in a solution, osmoles or milliosmoles per kg of solvent
• Example of osmolality calculation: 2Na+ glucose+BUN / 18 / 2.8

Osmolarity

• Fluid's total solute concentration with a normal value of 290 +/- 10 mOsm/l(milliosmoles)
• Milliosmoles is determined by number of particles in solution, a particle produces a milliosmol regardless of size/charge
• Osmotic pressure: related to osmolarity and non-ionizable solutes
• A non-electrolyte solute produces an osmotic push/force of one milliosmol
• Examples: 1 mmol C6H12O6 (glucose) = 1 milliosmol, 1 mmol Urea = 1 milliosmol
• Electrolyte solute produces osmotic force equal to liberated ions
• Examples: 1 mmol NaCl = 2 miliosmoles, 1 mmol CaCl2 = 3 miliosmoles
• Van't Hoff equation: Π = i.c.R. T, relating osmotic pressure (Π) which is the product of Van't Hoff factor (i), concentration of solutes (c), ideal gas constant (R), absolute temperature (T)

Tonicity

• Refers to osmotic pressure of a solution compared to plasma
• Isotonic solutions have the same osmotic pressure as plasma
• In hypotonic solutions, lower osmotic pressure than cell causes water to enter the cell, inflating it, and can even cause it to burst (turgescence)
• In hypertonic solutions, higher osmotic pressure than the cell causes water to exit the cell, causing it to shrink (plasmolysis)

Biological Importance of Water

• Universal solvent
• Propels enzymatic reactions
• Fluidifies branching pulmonary reactions
• Regulates body temperature
• Transports substances throughout tissues
• Eliminates waste
• Human body water percentage ranges from 100% to 50% depending on age

Osmolarity Calculations

• Calculation formula: Na+ x 1.86 + glycemia/18 + urea/2.8
• Reference plasma range: 285 - 295 mOsmol/kg H2O
• Reference urine range: > 100 a 1,200 mOsmol/kg H2O

Body Water Distribution

• Extracellular space (EEC) is ≈ 25% of body mass, includes vascular area with (5% plasma and 1-3% lymph), 15% is interstitial, inbetween cells and tissues, connecting and bone matter, 1–3% of the body is transcellular and is a component of fluids in the body
• Intracellular space (EIC) ≈ 40% of the liquid body mass which is 2/3 body weight
• Normal osmolarity for all spaces is around 280

Balance of Water

• Intracellular water ≈ 28 L
• Interstitial water = 10.5 L
• Water in plasma = 3.51 L
• Total output around 2300 ml a day
• Total input around 2300ml a day

Water Balance

• Daily intake: 2,500 ml
  • Includes sensible (visible) intake through free liquids (1,200 ml) and hidden water (1,000 ml)
  • Includes insensible (not visible) intake through oxidative water (300 ml) from protein, carbohydrates, and lipids
• Daily output: 2,500 ml
  • Includes sensible output through urine (1,500 ml) and feces (100 ml)
  • Includes insensible output through lungs (400 ml) and skin (500 ml)

Elimination of Metabolic Waste

• Transpires through catabolism
• Including the deamination of fatty acids
• Through pigments
• Through Organs
• Including excretion
• Excreting urea, uric acid, and the degradation of nucleic acids

Loss of Water & Dissolved Salts

• Sensitive demographics: infants, and elders are at greater risk of dehydrations
• Affected tissues: Blood , Intestinal track, and the kidneys
• Equilibrium is dynamic: According to your needs
• Recuperation
  • Drinking more liquids
  • Consuming solids with high water volume
  • Through H2O Metabolic Processes
• Body composition is 60-70% water
• An adult of 70kg losses around 2L/day - that needs replenishing
• Loss through:
  • Urination (Urine)
  • Bowl movements (heces)
  • Sweat
  • Expired air

Dehydration (DH) Causes

• Loss via:
  • Vomiting
  • Diarrhea
  • Polyuria
  • Intense perspiration
• Lack of water consumption via:
  • Nausea
  • Stomatitis or throat infection
  • Fever for Children
  • Refusal to intake of liquids

Dehydration (DH) Symptoms and Diagnosis

• Symptoms:
  • Vomiting is common with diarrhea, elevated urine production, abnormal sweating
  • Limited liquid consumption
  • Sunken eyes
  • Dry and sticky around tongue or in mucosa membrane
  • Depressed Fontanelles on infants
  • Skin tent, failure for skin to snap back upon being pinched
• Diagnosis
  • Testing: To search for abnormalities in electrolyte, also test Ht, osmolarity, to show how water level has been affected in tissues , looking for urea levels or any creatine
  • Examining physically by monitoring:
    • Hypotension to signify blood pressure
    • Measuring any Tachycardia

Physiology of Dehydration (DH)

• High temperatures
• Reduction in Cerebral activity or vasodilation around periphery/skin leading to poor function
• Reduced blood flow
• Cramping from loss of salts
• Lack of perspiration leads to heat strokes

Osmoregulation vs Volume Regulation

• Osmoregulation details the plasma osmolality
  • The process to detect if the body is hypo
  • Involves Osmoreceptors, and The Hypothalamus
  • Is affected by thirst to maintain H2O balance
• Volume regulations deals with
  • The circulatory system functioning at capacity
  • Involves the carotid, afferent arteriole, and the auricle
  • The system is affected by Salt, H2O, or Sodium to monitor homeostasis when the circulatory system signals otherwise

Hydroelectrolytic Solutions

• Hydroelectrolytic solutions can balance electrolyte, and rehydrate
• Assists or makes administrations of medicine easier
• Cristalloids are sugar based and help maintain the intravascular system to continue circulating
• Colloids are higher level molecules so their job assist with water retention in certain parts of the body

Volume Receptors Locations

• Volume receptors exist:
  • Cardiopulmonary
    • Carotid Artery
    • Aoritc Arch
    • Afferent arteriole in the kidney
• Volume Receptors function to:
  • Affect the pressure with blood volume
  • Kidneys also act a a volume regulator through juxtaglomerular and macula densa

Volume Effectors

• The System includes
  • the nervous system
  • Angiotensin II
  • Renal exertion for Sodium
  • Glomerular filtration
  • Aldosterone production
  • PNA levels control pressure of arteries for function

Nephron

• Nephritic function
• Including filtration, reabsorption control and secretion for water and nutrients
• Nephron includes: A renal, a proximal or distal and a collecting tube
• There must a steady state osmotic function controlled
• The loop of Henle is where there where there can either a semiimpermeable or more permeable membrane to allow the kidney to control water levels

Neurohumoral Regulation of Tubular Transport

• The neurohumoral relates to blood vessels (Hem-) and water
• The kidney's Renin travels to the glomerulus to create Angiotensin, converting to Aldosteron.
• This affects the system by:
  • affecting Sodium tubular production or absorption.
  • controlling kidney’s blood dynamic
  • and or gland in Aldosterone production.

RAA (Renin-Angiotensin-Aldosterone)

• Parts Included are Renin, Angiotensin, Adosteron, and the tubules and gland where the magic is happening

Renin-Angiotensin-Aldosterone System

• The Kidney plays a crucial role in stabilizing the entire system by using filtration and enzyme that goes the arteries to function
• The heart and lungs come together to send a signal to control pressure
• Aldosterone helps by absorption of salt

Vasopressin

• Vasopressin has a critical function in hormone transportation in the organ.

Antidiuretic Hormone (Vasopressin) - Regulation

• ADH is affected from blood terminal signals that affect water retention
• Factors like strong pain, sicknesses, and lack of temperature levels also come into play and affect the Vasopressin function

Antidiuretic Hormone (Vasopressin): functions

• ADH has several functions where it acts by consolidating memory and lowering secretion - as well as regulating core pressure,
• The kidneys act the core to ensure balance