Introduction Physiology: Study of the function and relationship of the various organ systems

The body Made of 40% solid particles and 60% H2O The percentage of H2O varies with age, sex Babies: up to 80% H2O Older, slim person: 60%

Figure 1.4

Fluid compartments 2/3 cell fluid (intracellular fluid=ICF) 1/3 fluid outside the cell  extracellular fluid (ECF) - 80% interstitial fluid (IF) - 20% circulating fluid – mostly plasma + CSF + eye and ear fluid

Figure 1.5

Homeostasis The process of maintaining a constant internal environment despite changing external environment Components: - Sensors - Integrating center - Effectors

Regulatory mechanisms: Negative feedback: the most common Positive feedback: rare (ex:blood coagulation, parturition) Most parameters controlling body function (heart rate, breathing rate, blood pressure, blood glucose..) are maintained within a narrow range

Negative feedback If a parameter value increases, body mechanisms works to bring the value down, within normal range The most common mechanism

Positive feedback As a value increases, the body reacts to increase the value further Example: parturition (labor and delivery) and blood clotting

Regulation of body temperature Body heat is a by-product of muscle contraction Heat losses or gains are due to: - convection: transfer of energy through moving gases or liquids - conduction: transfer of heat energy between objects in direct contact - radiation: transfer of energy through electromagnetic waves - evaporation: loss of heat when water is evaporating

Body temperature regulation Normal body temperature = 37 o C = 98.6 o F If external temperature is high  body reacts to cool down -skin: flush appearance due to blood vessel dilation, sweating -Heart rate increases -Respiratory rate increases If external temperature is low  body reacts to warm up -skin: pale appearance due to blood vessel constriction, goose bumps -Heart rate decreases -Respiratory rate decreases -Muscle shivering

Figure 1-4

Mechanism of regulation Temperature receptors in the skin and deep within the body send temperature information to the temperature integrating center in the hypothalamus The integrating center makes a decision about the adjustments to be made Effectors in charge of adjusting the temperature are activated

If body temperature is too cold:

Body temperature regulation Normal body temperature = 37 o C = 98.6 o F If external temperature is high  body reacts to cool down -skin: flush appearance due to blood vessel dilation, sweating -Heart rate increases -Respiratory rate increases

Pathology of temperature regulation: heat exhaustion -A person is working in the sun, is hot, sweat and drinks large amount of water -The electrolytes (salts) lost through sweating are not replaced  risk of seizures, loss of consciousness and death -Treatment: give fluids and electrolytes (ex: gatorade)

Pathology of temperature regulation: heat stroke A person is working in the sun, is hot. The sun increases body and especially brain temperature -If the brain temperature reaches too high level, the brain becomes unable to react  sweating stops -Body temperature reach very high levels  the person dies

So what is fever? Body temperature can be as high as o C ( o F), despite external temperatures being much cooler. Pathogens invade the body  macrophages fight against the infection and in the process secrete a special compound, a pyrogen. A pyrogen has the ability to reset the body’s internal temperature to a higher level When it does, the body reacts to increase its temperature  shivering, …  fever When the body has won its battle against the pathogen, the macrophages no longer secrete pyrogen. However, the body temperature is high  the temperature center in the hypothalamus direct the body to cool down  sweating ….

Readings Chp. 1: p2-20. Book pages corresponding to notes. Clinical connections: p 10