Introduction • Physiology: Study of the function and relationship of the various organ systems
Dec 21, 2015
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%
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
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
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
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 ….