Introduction

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

2. 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% The body

3. Figure 1.4

4. 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 Fluid compartments

5. Figure 1.5

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

7. 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

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

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

10. 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 Regulation of body temperature

11. 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 Body temperature regulation Normal body temperature = 37oC = 98.6oF

12. Figure 1-4

13. 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

14. If body temperature is too cold:

15. 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 Body temperature regulation Normal body temperature = 37oC = 98.6oF

16. 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 exhaustion

17. 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 Pathology of temperature regulation: heat stroke

18. Body temperature can be as high as 35-36oC (105-106oF), 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 …. So what is fever?

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