Physiology is the study of the physical and chemical processes associated with functions and activities of a living organism or its parts, from cell physiology to the physiology of exercise. It investigates biological mechanisms, often using the tools of chemistry and physics.

Activities such as reproduction, metabolism, growth, etc. involve the cells, tissues, organs, organ systems and structure of the body. Physiology is thus closely linked with anatomy, and can be described as functional anatomy.

What is circulation?
Circulation is a system of vessels in which both required substances (such as nutrients, antibodies, water, and oxygen) and waste products within animals are moved when and where needed. Vertebrates have closed circulatory systems.
Link: Circulatory System

What is metabolism?
Metabolism is the continuous creation and breaking down within an animal of many thousands of kinds of chemicals crucial to life. The physical and chemical changes comprising metabolism release heat; when measured, that heat is the metabolic rate.

An animal must have energy to fuel all of its functions, including breathing, movement, temperature regulation, etc., and that energy is acquired through the metabolism of food. Animals maintain body temperature and minimize energy loss using physiological and behavioural mechanisms.
Link: Metabolism and energetics

What do muscles do?
Muscles act in conjunction with the skeletal system to produce movement (locomotion). They are integral parts of most organs, blood vessels and glands, and provide force needed for their function. They can also be a major source of heat.
Link: Muscles

What does the nervous system do?
It controls complex behaviours. First, it collects, processes, and analyzes information. Then, it generates coordinated output. It is partly responsible for homeostasis. The nervous system works in conjunction with the endocrine system by responding to stimuli and then adjusting body processes.
Link: The nervous and endocrine systems

What is osmoregulation?
Water moves in and out of cells by osmosis. Water moves from an area with a high concentration of water and a low concentration of solutes to an area with a low concentration of water and a high concentration of solutes.
The regulation of water and ion concentrations in the body is called osmoregulation, and the process is critical to life. The balance of water and ions is maintained by intake and excretion. The major structures that are involved in osmoregulatory processes are the skin (or integument), the respiratory surface, the kidney, and the salt gland.
Link: Osmoregulation and excretion

What is respiration?
On a cellular level, respiration is the process whereby food is oxidized (using oxygen), creating energy that is harvested for physiological processes and waste products (including carbon dioxide). It is chemically very similar to the burning of wood, but it occurs in a very slow, controlled manner. At the level of the whole organism, respiration is the process by which the animal takes in oxygen that is used in cellular respiration and releases the carbon dioxide waste.
Link: Respiration

What is sensory reception?
Animals use their sensory organs to collect information from their surroundings. The sensory receptor cells transmit signals via neurons to the brain, where other neurons process the data. In this way, animals respond to the messages they receive from the world around them.
Link: Sensory reception, chemoreception, mechanoreception and photoreception

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