Overview of Human Body - Definitions

Skeletal system

provides support and protection, stores calcium and other minerals, and forms blood cells.

Muscular system

provides movement, protection/support, and heat generation.

Skeletal muscle

long, multinucleated, striated fibers under voluntary control that produce strong, rapid contractions.

Cardiac muscle

striated, branched, involuntary cells connected by intercalated discs that produce rhythmic contractions to pump blood.

Smooth muscle

spindle-shaped, single-nucleus, non-striated, involuntary cells that produce slow, sustained contractions in walls of hollow organs.

Motor unit

one motor neuron and all of the skeletal muscle fibers it innervates.

Sarcomere

the contractile unit formed by thin actin and thick myosin filaments.

Sliding filament mechanism

muscle contraction mechanism in which actin and myosin filaments slide relative to each other, shortening the sarcomere.

Cross-bridge cycling

interaction in which myosin heads bind to actin during muscle contraction.

Digestive system

processes and digests food, breaks down sugars, proteins, and fats, absorbs nutrients and water, and eliminates indigestible waste.

Mucosa

GI layer involved in secretion and absorption.

Submucosa

GI layer containing blood supply and neural control.

Muscularis

GI layer responsible for motility and peristalsis.

Serosa

outer GI layer providing protection and support.

Cardiovascular system

circulates blood, transports oxygen and nutrients, removes carbon dioxide and metabolic wastes, regulates blood pressure, and distributes blood flow.

Actin

thin

Myosin

thick

Renal/urinary system

filters blood to form urine, regulates electrolytes and blood pH, maintains water balance and blood volume, eliminates metabolic waste, and stores/eliminates urine.

Nephron

functional unit of the kidney.

Filtration

selective filtering of fluid by glomerular capillaries.

Reabsorption

recovery of needed substances from tubular fluid.

Secretion

movement of substances into tubular fluid for elimination.

Excretion

final elimination of urine from the body.

Endocrine system

coordinates body functions through hormones released into the bloodstream.

Hormone

chemical messenger released into the bloodstream that travels to target tissues and acts through specific receptors.

Target cell

a cell that expresses the appropriate receptor for a particular hormone.

Nervous system

coordinates the body rapidly through electrical signaling.

Neurotransmitter

signaling molecule that crosses a synaptic cleft.

Female reproductive system

produces oocytes and sex hormones, supports embryo/fetal development, and nourishes newborns through lactation.

Placenta

structure that supports fetal development.

hCG

hormone detectable in urine during pregnancy.