MEDICAL BIOLOGY, HUMAN ANATOMY, PHYSIOLOGY AND PATHOLOGY - Ya.I. Fedoniuk 2010

ANATOMY, PHYSIOLOGY, PATHOLOGY

CHAPTER 7. THE NUTRITIONAL PROCESS AND ITS PATHOLOGY

ANATOMY AND PHYSIOLOGY OF THE DIGESTIVE ORGANS

BODY TEMPERATURE AND ITS REGULATION

Human body Temperature is maintained at a relatively constant level, regardless of ambient temperature fluctuations.

This temperature constancy is known as isothermia. Isothermia is characteristic only of warm-blooded, or homeothermic, animals. It is absent in cold-blooded, or poikilothermic, animals, whose body temperature depends on Changes in the external environment.

Isothermia is essential for the normal functioning of human Organs. Changes in body temperature alter the Structure AND Functions of Proteins and Nucleic Acids, reaction rates of Enzymes, and the permeability of Cell membranes.

Overheating of the body, when body temperature rises above 37 °С, is called hyperthermia, whereas cooling, when body temperature drops below 35 °С, is referred to as hypothermia.

For humans, the upper lethal temperature threshold is 43 °С. The lower limit is 26 °С, at which cardiac arrest occurs.

In homeothermic organisms, the temperature of different body parts varies.

Skin temperature depends on the ambient temperature and ranges from 28 °С

in the distal extremities to 33–34 °С on the skin of the trunk and HEAD. The temperature of Muscles and Internal Organs is characterized by constancy and is higher. The highest recorded temperature is in the Liver at 38 °С.

In practice, body temperature is measured in the axillary fossa (36.6 °С), the Oral Cavity (36.7–37 °С), and the rectum (37.3–37.6 °С). Body temperature fluctuates throughout the day. The lowest temperature is observed at 3:00–4:00 AM, after which it gradually rises, reaching its peak at 4:00 PM, and then begins to drop again. Daily temperature fluctuations are within ± 1.0 °С. Body temperature can rise sharply to 38–39 °С during muscular exertion, depending on the intensity of the workload. After the activity ceases, body temperature rapidly drops back to normal values.

Isothermia in humans can be maintained only through a balance between heat production and heat loss across the entire Organism. This is achieved via physiological mechanisms of thermoregulation (neural and endocrine).

Thermoregulation is conventionally divided into chemical and physical.