Introduction to Physiology

Study Notes

Physiology is the study of the functions of the different body systems, how they perform these functions and what factors affect them.
The human body is made up of multiple systems. These systems are composed of organs, which themselves are built from tissues. Tissues are ultimately made up of cells which are the basic structural units of the body.
Cells contain a cell membrane, and cytoplasm.
- Inside the cytoplasm is the nucleus, mitochondria, Golgi apparatus, lysosomes, ribosomes, centrosomes, and rough and smooth endoplasmic reticulum.
- These organelle structures perform specific functions within the cell.

Homeothermic animals (warm blooded) maintain a constant body temperature regardless of the environment. They include humans, birds, and other mammals.
Poikilothermic animals (cold blooded) have body temperatures that fluctuate based on the environmental temperature. They include amphibians and reptiles.

Body temperature can be measured using a clinical thermometer placed in various positions:
- Mouth (oral)
- Armpit (axillary)
- Rectum (rectal)

The normal human body temperature is 37°C (98.6°F) when measured orally.
It typically varies between 35.8°C to 37.3°C (96.4°F and 99.1°F).
Axillary temperature is 0.3°C to 0.6°C (0.5°F to 1°F) lower than oral temperature.
Rectal temperature is 0.3°C to 0.6°C (0.5°F to 1°F) higher than oral temperature.

Age:
- Infants have fluctuating body temperatures during their first few days of life due to an undeveloped temperature regulation system.
- Children have slightly higher body temperatures (0.5°C) than adults due to higher activity levels.
- Elderly individuals may have slightly lower body temperatures due to reduced heat production.
Sex:
- Women tend to have slightly lower body temperatures compared to men due to a lower basal metabolic rate.
- Temperatures may temporarily decrease during the menstrual phase.
Diurnal Variation:
- Body temperature is generally 1°C lower in the early morning and reaches its maximum (about 1°C above normal) in the afternoon.
After Meals:
- Body temperature increases slightly (0.5°C) after eating.
Exercise:
- Body temperature elevates during exercise due to increased heat production in muscles.
Sleep:
- During sleep, the body's temperature decreases by 0.5°C.
Emotion:
- Body temperature can rise during emotional states.
Menstrual Cycle:
- In women, the body temperature rises immediately after ovulation (0.5°C to 1°C).

Regulating body temperature depends on the balance between heat produced by the body and heat lost from the body.

Metabolic Activities:
- Most body heat is generated through metabolism, converting food into energy.
- Fat metabolism produces more heat than other nutrients.
Muscle Activity:
- Contracting muscles produce heat - this is why we get warm when we exercise.
Shivering:
- Involuntary muscle contractions generate heat to help maintain body temperature.
Specific Dynamic Action (SDA):
- The process of digesting and assimilating food also produces heat.
Hormonal Factors:
- Certain hormones, like thyroid hormone, influence metabolic rate and heat production.
Other Factors:
- Sun exposure, radiation from surrounding objects, and body temperature of other individuals contribute to heat gain.