OVERVIEW OF LIFE SUPPORT FUNCTIONS

By Dr. Arnold B. Fonollera, D.D.M.

Associate ProfessorMedical Physiology

Basis of Integrated Human Physiological Function

• Inquire into the fundamental cellular mechanisms.

• Awareness of ‘microfunction’ while keeping an eye on the interweaving of functions in the service of whole body coordination.

• Complementary approach

• In order to understand any phenomenon of life, it is always necessary to go back to the properties of the organic elements which constitute the principle.

Healthy Function

• There are certain things which must go on all the time to maintain life.

• There are ways and means of moving around and performing tasks.

• There are means of perceiving and of interacting with our surroundings, with people and with events.

• Along with these are the processes of growing, maturing, reproducing and ageing-life cycle

Relation of Physiology to Health and Medical Science

• Under threat, the urgent concern is to maintain essential living functions.

• The first goal of recovery and rehabilitation after illness or injury is the ability to carry out the basic activities of daily life

• The ideal of health is a full life, which requires the maintenance of all perceptions, activities and interactions, for the purposes of work and leisure and for a proper and satisfying progress through a full life span.

LIVING FUNCTIONSCells and Whole Organisms

• Whatever the size of the organism, the functions of respiration, nutrition, metabolism and excretion must proceed continuously.

• Exchanges between the external and internal environment– Oxygen moves in because a diffusion gradient

created by cells– Nutrients are allowed or actively assisted to enter– Unwanted substances are kept out, or having

entered are extruded– Products are either utilized or assisted to leave– Concentrations of different solutes are maintained

at different levels inside and outside the cell.– Osmotic equilibrium is maintained so that the cell

neither swells nor shrink

• Every cell have highly complex mechanisms to achieve all these.

The Internal Environment• The conditions that prevail within the body of

an organism, particularly with respect to the composition of the tissue fluid.

• The concept of an internal environment was first proposed by the French physiologist Claude Bernard (1813–78), who stated that maintenance of a constant internal environment was necessary for the survival of an organism in a varying external environment.

• Selective absorption of materials across cell membranes plays a large part in controlling the internal environment of both animals and plants.

• In addition, the body can regulate body fluids

by the action of hormones and the nervous system.

Interface with the Outside• Life-support functions involve 2-

way transport between cells and the outside world.

• The world extends as a tube through the body from mouth to anus. All of its contents are outside.

• Every cavity or lumen that borders the outside world from the inside is lined by epithelial tissue.

• Epithelium originated from the ectoderm

• All are in continuity with the skin

Epithelial Borders• Function on behalf of the whole body by taking

in, keeping in, keeping out or extruding substances as appropriate to the body just as every cell does in its own environment– Air in the lungs is a portion of the atmosphere.– Urine in the bladder and the ureters has already left

the true inside of the body.– Sperm that left the testes and egg that left the ovary

are essentially outside.– The fetus is attached but not truly inside the mother’s

body in the uterus.

3 Major Epithelial Functions• Protection– Impregnable to unwanted substances and microorganisms– Tight junctions

• Secretion – Extrude substances on the surface or lumen.– Defensive, excretory, facilitative

• Mucus- GIT,GUT, RT• Sweat- skin• Surfactant- alveolus• Enzymes- GIT• Hydrogen ions and ammonia

• Transfer of Substances– Absorption

• Intestinal lining – water, nutrients and minerals• Kidney tubules – plasma filtrate• Exocrine glands – selective reabsorption• Gallbladder – reabsorption to adjust bile composition

Transport of Substances• Passive – Alveolar surfaces – diffusion of respiratory gases– Water absorption in the GIT and GUT

• Active– Maintenance of osmotic gradients through movement of

sodium ions

Life Support FunctionsRespiration

• Keeping up the supply of oxygen is the most persistently urgent of all physiological functions. It cannot be allowed to lapse.

• The body has no method for storing any significant amount of oxygen. All the oxygen is in transit in the lungs and blood.

• Myoglobin, hemoglobin, dissolved O2 in tissue fluid.

• Three minutes worth.• Continuity depends on maintaining:– Oxygen level in blood by breathing– Rate of delivery by heart pumping

Rate of Oxygen Usage per unit mass of Tissue

• Heart - greatest• Brain – moderate although above

average from the whole resting body• Cerebral cortex (Memory and conscious

thought, speech, motor and sensory functions) – will never recover if oxygen is suspended for more than a few minutes.

• Brain stem – breathing, heart can continue during oxygen deprivation longer than the cortex.

• Liver and GIT – oxygen use can be depressed or suspended for a while without threat to life.

Energy BalanceNutrients

• Absorbed for immediate use or stored as reserves of metabolic fuels.

• Most tissues store nutrients but the brain stores least of all.

• Glucose – most immediate fuel from stored glycogen or by glucose intake.

• Respiration at tissue level – combustion of fuel– Interaction between oxygen and

organic nutrients releases energy and carbon dioxide and water.

Exchanges of Water, Solutes and HeatBody Water

• Total body mass is about 2/3 water• Cells contain 2/3 of that water.• Interstitial fluid – water in between cells vary between different

tissues.• Cell membrane• Bilayer of phospholipids• Passage is by being lipid-soluble or by passing through holes• Solute concentrations vary on the two sides• Permeabilities vary among solutes in a continuous movement of

dynamic equilibrium• Semi-permeable – freely permeable to water than to many solutes• Total concentration of particles must be in balance on the two

sides or else the cell would shrink or swell by osmosis

Water: largest constituent of body; 55-65% of body weight

• Intracellular Fluid– 66.6%– Within cells– High potassium

• Extracellular Fluid– 33%– Interstitial, space

surrounding cells – Intravascular; 7-8% of

total body water, 20-25% of ECF

– High sodium

Osmotic pressure (concentrations of all solutes in a fluid compartment) is equivalent between ECF and ICF compartments

Distribution of Water

WATER TO BODY MASS

Intracellular and Extracellular(Total Body Water)

Blood Plasma and Interstitial fluid and lymph(Extracellular Fluid)

The Essence of Water

• Generated by cell metabolism yet we need to take it continuously to support life

• The body is continuously losing water for 2 reasons:– A volume of water in excess of which is produced

metabolically is needed as vehicle for the excretion of wastes. Transport products via the blood to depots (liver) where they are chemically altered for watery excretion thru the GIT or GUT.

– Environment less than 100% humidity creates water loss by evaporation from the skin and the lungs. Heat in excess during metabolism must be evaporated to maintain temperature. Exchanges with the outside is influenced by climatic conditions.

The need for a control mechanism• Water ingested and metabolically

produced must match the loss.• We do not simply guess the right

amount to drink.• Thirst is a physiological guide but

can be affected by social habits.• Excess is dealt by increased output

of urine• The body has a means of making

precisely the right corrections.• Detectors for the concentration or

dilution of internal fluids.• Tendency to increase concentration

is the stimulus leading to thirst and smaller urine volume.

Water Control Mechanisms• Body fluid homeostasis: stability in the osmolality of body fluids

& volume of plasma.• Mechanisms: intrinsic to body fluids & cardiovascular system

– Osmotic movement of water across cell membranes buffers ECF osmolality

– Osmotic movement of water across capillary membranes buffers acute changes in plasma volume

– Venous compliance/capacitance - veins thin walled & distensible. Volume loss, veins collapse. Conversely, volume accumulates in veins when blood volume expanded

– Glomerular Filtration (GFR) - drop in blood pressure reduces GFR & decreases urine volume, whereas a rise in BP increases GFR and promotes urinary fluid loss. Kidneys so efficient that development of hypertension indicates renal dysfunction

Movement of FluidsMovement and distribution by different physical mechanisms

• Mechanical pumping –heart and smooth muscles of blood vessels

• Hydrostatic forces – resistance exerted by walls of blood vessels against the pumping force of the heart. – Hydrostatic pressure decreases from

the arteries to the veins– Hydrostatic pressure is also susceptible

to gravity. Pressure difference occur depending on the vertical distance from the heart.

– Mechanical function also affects pressure. Capillaries are leaky, so hydrostatic pressure always force some fluid out.

• Osmosis – net movement of water were solute particle concentration is higher than in an adjacent region, separated by a barrier which is impermeable to at least some solutes.– Osmolality (measure of solute concentration)– Higher in blood plasma than interstitial fluid– Increase fluid intake in the GUT, osmosis redistribute

water between blood, interstitial fluid and cells– Concentration of urine causes water retention

• Solvent drag – water is pulled across some boundaries by persisting osmotic gradients maintained by the active movement of solutes.– Pumping of sodium across cell membranes results in the

movement of water– Absorption by the gut– Reabsorption from the kidney– Reabsorption by gall bladder

Movement of Substances In and Out of Cells• Passive Diffusion– Ability to permeate the membrane– Soluble in the medium (O2 and CO2)– Squeeze between molecules of the medium(water)

• Facilitated Diffusion– Net movement is also down a diffusion gradient

• There is greater net movement of one substance than of other substances with similar mass and solubility, given the same concentration gradient.

• There is a valu for concentration gradient at which the diffusion rate levels off to a maximum

– If passive diffusion is downhill, facilitated diffusion is being pulled or pushed downhill.

• Carrier-mediated - Sugars and amino acids are transported across gut walls and from ECF into cells

• Metabolic energy is not required because the carrier itself maybe rolling “downhill”.

Active Transport• Substance is pulled “uphill”• Reguires metabolic energy• Gradients are against movement• Continuous transport of sodium

ions out of all cells by sodium pumps.

• Many substances move in and out of cells because of the direct or indirect effect of the active movement of sodium ions.

• Main pump actively exchange Na for K

• Other pumps exchange Na for Ca or Mg

Transport SystemThe circulation of the Blood• Exchange of O2 and CO2 between tissues and

lungs• Collect absorbed nutrients from the GIT and

deliver to the liver for processing and storage and to all other tissues for utilization

• Collect products of metabolism from all tissues and delivery to the liver and kidneys for recycling and disposal

• Redistribute heat and delivery to the skin if it needs to be lost

• Refreshment of tissue fluid• Communicate between different tissues and

organs by means of hormones

Trivial Facts about Blood

• ¼ of the blood volume (more than a liter) flows every minute through the kidneys where 1/10 of this volume if filtered off

• A small amount of urine is formed for the excretion of nitrogenous waste and of excess wastes and solutes.

• A drop of blood on the average has a chance of flowing through one of the kidneys once every 4 minutes

• It also has a chance of flowing through the lungs once every minute.