external respiration

External respiration

Inside the lungs, oxygen from the air is exchanged for waste carbon dioxide from the bloodstream. This process of external respiration takes place in hundreds of millions of microscopic sacs called alveoli. Oxygen from inhaled air diffuses from the alveoli into the pulmonary capillaries surrounding them, and is pumped through the bloodstream. Carbon dioxide from […]

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Pulmonary ventilation, or breathing, is induced by changes in the volume of the lungs and the air pressure within them. During normal inhalation the diaphragm and external intercostal muscles contract, and the ribcage elevates. As the volume of the lungs increases, air pressure in the lungs drops below atmospheric pressure, and air rushes in. During […]

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Specialized nervous system cells called neurons make this messaging possible. At one end of a neuron are dendrites that receive a messaging signal. In the neuron’s axon, a chain reaction moves the message to the synapse, where the signal is transferred. Before this process begins, the neuron is polarized with a net positive charge outside […]

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smoth muscle tissue

Smooth muscle tissue

Smooth muscle tissue is in the walls of hollow organs throughout the body. The tissue contracts and relaxes to contain substances and move substances through the body. Smooth muscle contractions are involuntary actions managed by impulses that travel through the autonomic nervous system to the smooth muscle tissue. The arrangement of cells in smooth muscle […]

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fat bone formation

Flat bone formation

The development of the skeleton’s flat bones begins as certain mesenchymal cells, at specific points within embryonic fibrous connective tissue, develop into osteoblasts. The osteoblasts cluster together, secrete bone matrix, and develop into osteocytes that deposit calcium and other mineral salts that harden the forming bone matrix. The bony regions spread out into thin columns […]

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heart funtion

Heart function

The heart is a muscular organ that functions as a double pump to control blood flow. The heart of an adult male is slightly larger than that of an adult female; on average a normal adult heart is about the size of a fist and weighs approximately 300 grams — less than one pound. The […]

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hear camb

Heart chambers

The heart has four hollow chambers: the left and right ventricle and the left and right atrium. Each chamber has a different function. The right atrium receives oxygen-depleted blood and empties it into the right ventricle. This blood then flows to the lungs for gas exchange. Oxygenated blood from the lungs enters the left atrium, […]

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paired muscle

Paired muscle actions

Movement of the skeleton often involves pairs of muscles that perform opposing actions, like flexing and extending or bending and straightening. Muscles involved in these paired actions are categorized as agonists and antagonists. A muscle that contracts to generate the main force of an action is called the prime mover, or the agonist, for that […]

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Skeletal Muscle Function

Skeletal muscle contractions

The muscular, nervous, and skeletal systems interact to produce movement. Messages travel through the nervous system to the skeletal muscles that attach to bones throughout the body. The fibrous appearance of skeletal muscles is created by the arrangement of proteins inside the cells that form muscle tissue. Motor neurons of the nervous system connect with […]

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