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 = 37oC = 98.6oF

• 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 = 37oC = 98.6oF

• 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

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 ….

Readings

• Chp. 1: p2-20. Book pages corresponding to notes.

• Clinical connections: p 10