Skeletal, muscular and integumentary systems - structure, function and care
Skeleton: framework, protection, storage
There are 206 bones: 80 axial (skull 22, vertebral column 26, ribs 24 and sternum, hyoid) and 126 appendicular (limbs and girdles). Bones give shape and support, protect organs (skull–brain, rib cage–heart and lungs, vertebrae–spinal cord), act as levers for muscles, store calcium and phosphorus, and form blood cells in the red marrow of long bones, sternum and pelvis.
Muscle tissue
Skeletal muscle is striated, voluntary and multinucleate and tires quickly; smooth muscle is unstriated, involuntary and found in the gut, bronchi and blood-vessel walls; cardiac muscle is striated yet involuntary, with intercalated discs, and works without rest. Biceps and triceps are antagonistic - one flexes while the other extends. Contraction needs ATP; during hard exercise anaerobic respiration builds lactic acid, causing cramp.
Skin
Epidermis (keratin, melanin), dermis (sweat and sebaceous glands, hair follicles, nerve endings, capillaries) and subcutaneous fat. The skin protects against microbes and UV, regulates temperature by sweating and vasodilation, makes vitamin D in sunlight, excretes small amounts of water and salt, and carries touch, pain and temperature sensation.
Care
Weight-bearing exercise, calcium with vitamin D from sunlight, milk and green leafy vegetables, good posture, and turning a bedridden patient at regular intervals to prevent pressure sores.
Worked example
A 60-year-old woman fractures her wrist after a minor fall and has lost height. Minor trauma plus height loss suggests osteoporosis: after menopause, falling oestrogen reduces calcium deposition, so bone mass drops. Care means calcium and vitamin D, weight-bearing exercise and fall-proofing the home.
Marks-losing traps
Cardiac muscle is striated but involuntary; melanin lies in the epidermis while glands lie in the dermis; rickets in children (soft, bowed bones) is not osteoporosis in adults; bone is living tissue with blood vessels and nerves.