skeletal system

bone structure function

support, protect, movement, blood cell formation (hematopoiesis), and mineral storage

compact bone

dense, outer layer; organized into osteons (functional units)

spongy bone

inner porous layer; contains trabeculae and red marrow (where blood cells are made)

yellow marrow

found in the central cavity of long bones; stores fat

periosteum

fibrous outer layer covering of the bone

bone matrix

composed of collagen fibers (flexibility) and calcium/phosphate salts (hardness)

ossification

cartilage transforms to bone. Chondrocytes (cartilage cells) die off, and osteoblasts (bone-builders) secrete bone matrix

regulation

growth is regulated by growth hormone before puberty and gender hormones during/after puberty; bone stops growing when the epiphyseal plates (growth plates) close

osteoblasts

build new bone

osteoclasts

break down bone to release calcium into the blood

parathyroid hormone (PTH)

stimulates osteoclasts to increase blood calcium

thyroid (calcitonin)

stimulates osteoblasts to lower blood calcium and “store” it in bone

muscular systems characteristics

excitability (responds to stimuli), contractility (shortens), extensibility (stretches), and elasticity (returns to shape)

origin of muscular system

attachment to the stationary bone

insertion

attachment to the moving bone

synergistic

muscles work together

antagonistic

muscles working in opposition (biceps; triceps)

hierarchy

muscle → fascicle → muscle cell (fiber) → myofibril → sarcomere (the functional unit of contraction)

ATP sources

creatine phosphate and glycolysis (intense/short-term) vs. cellular respiration (light/moderate/long-term)

slow-twitch fibers

red; lots of myoglobin/mitochondria, endurance-focused

fast-twitch fibers

white, powerful, tires quickly, anaerobic

plasma

liquid portion containing waters, period, ions, and nutrients

formed elements

red blood cells, white blood cells, and platelets; all originate from stem cells in red bone marrow

clotting process

platelets stick to the wound → thrombin converts fibrinogen into fibrin (the “net” that traps cells) → plasmin eventually dissolves the clot

red blood cells (erythrocytes)

lose their nucleus as they mature to pack in more hemoglobin (which carries oxygen); they live ~120 days because they can’t repair

recycling RBC’s and WBC’s

recycled in the liver and spleen; the kidneys release erythropoietin (EPO) to stimulate more RBC production if oxygen is low