The major systems covered in the study of human physiology are as follows:
- Circulatory system – including the heart, the blood vessels, properties of the blood, and how circulation works in sickness and health.
- Digestive/excretory system – charting the movement of solids from the mouth to the anus; this includes a study of the spleen, liver, and pancreas, the conversion of food into fuel and its final exit from the body.
- Endocrine system – the study of endocrine hormones that carry signals throughout the organism, helping it to respond in concert. The principal endocrine glands – the pituitary, thyroid, adrenals, pancreas, parathyroids, and gonads – are a major focus, but nearly all organs release endocrine hormones.
- Immune system – the body’s natural defense system is comprised of white blood cells, the thymus, and lymph systems. A complex array of receptors and molecules combine to protect the host from attacks by pathogens. Molecules such as antibodies and cytokines feature heavily.
- Integumentary system – the skin, hair, nails, sweat glands, and sebaceous glands (secreting an oily or waxy substance).
- Musculoskeletal system – the skeleton and muscles, tendons, ligaments, and cartilage. Bone marrow – where red blood cells are made – and how bones store calcium and phosphate are included.
- Nervous system – the central nervous system (brain and spinal cord) and the peripheral nervous system. Study of the nervous system includes research into the senses, memory, emotion, movement, and thought.
- Renal/urinary system – including the kidneys, ureters, bladder, and urethra, this system removes water from the blood, produces urine, and carries away waste.
- Reproductive system – consisting of the gonads and the sex organs. Study of this system also includes investigating the way a fetus is created and nurtured for 9 months.
- Respiratory system – consisting of the nose, nasopharynx, trachea, and lungs. This system brings in oxygen and expels carbon dioxide and water.