ANIMAL PHYSIOLOGY: Chapter 1: General concepts in physiology
1. Introduction
• Integrative physiology
o = making links between 2 or more, at first sight separated physiological systems
o Vb: Heart & kidney
▪ Kidney dictate the amount of RBC production → this changes the viscosity of the blood →
this changes the contraction force of the heart vb pumps harder for circulating thicker blood
▪ Opm: Both heart & kidney secrete hormones
o Vb: Fatness (body composition) & reproductivity
▪ Fat mass secretes hormones → these hormones negatively influence reproductivity vb
production of sperm, ovulation, ovary growth
• Communication (chapter 5)
o = neurocommunication (not voluntary; milliseconds) & endocrine system
o Vb: Different tissues communicate
▪ Vb: Muscle depleted of glycogen by exercising → muscles communicate to liver to produce
more glycogen
▪ Vb: Fat tissue communicates with testes or ovary
o Vb: Appetite, hunger, satiety regulation by hormones, hypothalamus, hypophysis
2. Body fluid compartments
• Total body water (TBW) (or Total body fluid):
o Varies between 45 – 70 % of body mass, dependent on:
▪ 1) age: water decreases with age
▪ 2) sex: independent of age, females have less water tov males
• Reden: due to having more fat as females, which has to do with reproductive
hormones/oestrogens
▪ 3) degree of fatness: the more fat, the less water
▪ 4) ….
o Opm: fluid = water, with dissolved ions, proteins, molecules etc
• Total body water (TBW) content:
o Varies between 45 – 70 % of body mass
o Fat contains 20% of the TBW, as preformed endogenous water
▪ Preformed: water is in between the adipocytes & is already a watermolecule
▪ Endogenous: water is already inside the body exogenous: water in food or drinks, thus
outside the body
▪ Gevolg: catabolization of fat tissue → gives energy & water to the animal/human
▪ Opm: leptin = a hormone secreted by fat tissue into the bloodstream of humans, to impair
and regulate feed intake behavior & reproductive processes
o Other body tissues contain 70% of the TBW
• Water location in the body:
o 1) 60 % Intracellular fluid (ICF)
▪ = cellular H2O = within the cell
▪ composition (ions, proteins, (ash?) in the water) is relatively stable
▪ represents ± 35 % of body mass
o 2) 40 % Extracellular fluid (ECF)
▪ = interstitial H2O, plasma H2O, Transcellular H2O (*) = outside the cell
▪ relatively unstable due to many different compartments (*)
▪ represents ± 22 -25 % of body mass
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, ▪ → important in homeostasis: if too much ECF → pathologies vb oedema
• Extracellular fluid (ECF) (*)
o Interstitial or intercellular fluid:
▪ Location: water between the cells
▪ composition plasma except low protein content
▪ → 17 % to 19 % of body mass
o Blood plasma
▪ Location: in the vascular system vb in venules, arteries, capillary beds etc
▪ separated from intercellular fluid by vascular endothelium (walls of the cells that make up
the vascular system)
• epithelium (walls of all other cells that make up tissues)
▪ → 4.6 % of body mass (species dependent)
o Transcellular water
▪ Location: e.g. cerebrospinal fluid, fluid in cavities (vb eyeballs), secretions of digestive
system, fluid in pericard (= small sack around heart), urine in kidneys, …
▪ separated from plasma by epithelium
▪ → ± 1.5 % of body mass
2.1 Determination body fluid compartment volumes
• Determination body fluid compartment volumes
o 1) Drying of an euthanized animal to know what water content was
▪ Disadvantage: direct - non-repeatable - invasive!
o 2) Principle of dilution (more used)
▪ 1) (intravenous) administration of a known quantity of a marker (e.g. dye or xenobiotic
substance) that diffuses entirely into the compartment of unknown volume
▪ 2) measuring the concentration of the marker in an aliquot (interested volume sampled)
taken from the compartment
▪ Opm: xenobiotic substance = substance foreign to the body
o 3) Dexa (Dual energy X ray absorptiometry)
▪ = a device to measure
• 1) (originally) the bone mineral density of astronauts (bec their bones become thin)
• 2) the body composition vb fat, protein, ash, water (TBW) content of animals
• 3) age related changes in body composition of animals
▪ Advantage: repeatable – not invasive
• Determination of:
o Total body water:
▪ marker must diffuse in both ICW and ECW
o Extracellular water (ECW):
▪ marker may not diffuse through cell membranes into the cells
o Intracellular water (ICW):
▪ cannot be measured by using a marker
▪ % total body water - % ECW 35 % of body mass
o Interstitial water
▪ cannot be measured by using a marker (spreads to all portions of ECF), thus measure all
other compartments and make a difference
▪ % ECV - % plasma volume - % transcellular water 17 % of body mass
o Plasma volume:
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, ▪ marker (Evans’ blue) binds completely to plasma proteins
▪ ± 4.6 % of body mass
o Blood volume (45-120 ml/kg BW (age & species-dependent):
▪ Blood volume (increase/decrease) regulates blood pressure & heartrate
▪ Calculation:
▪ Formulas: based on erythrocyte value OR hematocrit value (=Packed Cell Volume)
▪ Determination of hematocrit value
• Centrifugation of a blood sample results in packed RBC & cell-free plasma, separated
by buffy coat (WBCs, platelet)
• → hematocrit = Height of RBCs / Total height
o Note
▪ As about 9 to 10 % of plasma is trapped between blood cells after centrifugation, a
correction factor of 0.91 is suggested
• Hematocrit values (cell volume/ blood volume)
o Differ with sexes: men: 0.40-0.54; women: 0.37-0.47
▪ Reden: higher amount of RBC/hematocrit in male’s blood, because the level of metabolism
is higher in male tov female vb: more muscle content → needs more O2 → needs more RBC
to carry the O2
o Differ with sporters: hematocrit higher in endurance sporters
▪ Reden: sporters eat products to gain muscle mass & some products also induce production
of erythropoietine, which stimulates bone marrow to produce more RBC → to carry more
O2 & thus to have better prestations
▪ Opm: hematocrit also increased by training at high altitudes
o Differ with body size: the smaller the animal the higher the hematocrit, if you correct for bodyweight
o Differ with age: the younger the animal the higher the hematocrit, if you correct for bodyweight
(within species)
▪ Reden: due to the ratio between the surface & the weight of an animal
• → younger animals have a larger surface area compared with their weight,
compared to all animals
• → more heat is lost at a larger surface area → more heat should be produced to
maintain body T → more O2 needed for heat production → need a higher capacity
to transport O2 to the liver, muscles…
2.2. Composition of body fluids
• Composition of body fluids
o Differences between ions (K, Na ~ resting membrane potential), the concentration & proteins
between the intracellular fluid, plasma (intravascular fluid), and interstitial fluid
▪ → protein content in intracellular fluid is 4X higher tov plasma
▪ → protein content in plasma is 4X higher tov interstitial fluid
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, o Why is the plasma & interstitial fluid the same in terms of ions? Why a difference in proteins?
▪ Reden: ions (& small proteins) can pass through the pores of the endothelium of
bloodvessels large proteins cannot pass through the pores
▪ Cut-off value: 20kDa
▪ Opm: Cut-off value of 20kDa does not hold for all tissues: at the level of the gut & liver vb,
the pores are larger (cut-off value of 40kDa)
• Definitions
o Osmolarity: quantity of particles (ions, molecules) per liter of solution
o Osmolality: quantity of particles (ions, molecules) per kilogram of solution
▪ non-ionized molecules: molecular weight (g) per liter
• e.g. glucose: 180 g/l
▪ ionized molecules
• e.g. NaCl: 58.5/2 = 29.8 g/l
o Osmotic pressure: pressure to prevent osmosis (= 5.79 mm Hg for plasma)
• Principle of osmosis
o = a process, based on the principle of diffusion of a fluid (in which substances are dissolved) through
a semi-permeable membrane
▪ 1) The fluid (usually water) can pass through the membrane but not the substances
▪ 2) The direction of the fluid flow is from high to low concentration of fluid
o = passive transport of a fluid due to concentration differences of the dissolved particles (= the
driving force)
o Requirements:
▪ 1) presence of a semi-permeable membrane (only fluid can pass but not the particles)
▪ 2) initial difference in concentration of the particles (or fluid) at both sites of the membrane
o The fluid diffuses from the highest fluid concentration towards the lowest fluid concentration or
otherwise stated from low [substrate] to high [substrate]
▪ → at new equilibrium: iso-osmolarity at both sides of the membrane
▪ → changes in volume
▪ → induction of a hydrostatic (= OSMOTIC) pressure
o Note: diffusion of particles is not associated with changes in volume
• Total osmotic pressure
o about 280 mOsm/l !!
o about equal in intracellular and interstitial fluid
▪ (for ECF: 80 % of total osmotic pressure is due to Na+ and Clions)
▪ (for Intracellular: 50 % of total osmotic pressure is due to K + ions)
• Additional osmotic pressure in blood plasma = colloid oncotic pressure
o = pressure that works oppositely compared to the osmotic pressure/hydrostatic pressure (that
wants to push fluid out of the vascular system through the pores)
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