Introduction to Physiology
Anatomy tells you where the engine parts sit. Physiology tells you why the engine runs.
It is 2 a.m. on a children's ward in Kano. A toddler with diarrhoea has stopped crying, his eyes look sunken and his lips are dry. The nurse on duty does not need a machine to tell her something is wrong: she can read the body's own signals. Learning to read those signals, and to understand what produces them, is what this course is about.
Definition of Physiology
In Anatomy you learn the parts of the body: where the heart sits, what a cell membrane is made of, how many bones are in the hand. Physiology asks the next question: how do those parts work, and how do they work together to keep you alive?
Physiology is the study of the functions of the body and its parts: how cells, tissues, organs and systems work, and how they work together to keep the body alive. The word comes from Greek physis (nature) and logos (study).
The two subjects are inseparable. Structure suits function: the walls of the air sacs in the lungs are extremely thin because gases must diffuse across them quickly; the red cell has no nucleus, which leaves more room for haemoglobin. Whenever you meet a structure, ask "what job does this shape make possible?"
Characteristics of Living Things
Every living organism, from a bacterium to you, shows a set of characteristics of life. Textbooks group them slightly differently, but the classic list has seven.
Some textbooks phrase these as the basic life processes: metabolism, responsiveness, movement, growth, differentiation (unspecialised cells becoming specialised ones) and reproduction. The two lists describe the same thing; know both, and be able to define each item in a sentence.
Metabolism is the sum of all the chemical reactions in the body. Catabolism breaks large molecules down and releases energy; anabolism builds large molecules from small ones and uses energy.
Survival Needs of the Body
| Need | Why the body needs it |
|---|---|
| Oxygen | Cells use it to release energy from food; without it brain cells are damaged within minutes |
| Nutrients | Supply energy and the raw materials for growth and repair |
| Water | About 60% of adult body weight; the medium for chemical reactions and transport |
| Normal body temperature | Enzymes work best near 37 °C; much hotter or colder and reactions fail |
| Suitable atmospheric pressure | Needed for air to enter the lungs and for oxygen to diffuse into blood |
Pause & think
Back to the toddler in Kano. Which survival need is most obviously under threat, and how can the nurse tell?
Quick check
Did it land?
Spotted a mistake?