Pacemaker
/ˈpeɪsˌmeɪkər/
The sinoatrial node of the heart; it sets the rate and rhythm of cardiac contraction.
Pancreas
/ˈpæŋkriəs/
A large gland behind the stomach that secretes digestive enzymes and the hormones insulin and glucagon.
Parasympathetic
/ˌpærəsɪmpəˈθɛtɪk/
The part of the autonomic nervous system that conserves energy as it slows the heart rate and increases intestinal activity.
Parathyroid Hormone
/ˌpærəˈθaɪrɔɪd ˈhɔːrmoʊn/
A hormone secreted by the parathyroid glands that is important in bone remodeling and calcium regulation.
Parietal Cell
/pəˈraɪətəl sɛl/
Cells in the stomach lining that secrete hydrochloric acid and intrinsic factor.
Passive Transport
/ˈpæsɪv ˈtrænspɔːrt/
Movement of ions and other atomic or molecular substances across cell membranes without need of energy input.
Pathogen
/ˈpæθədʒən/
A bacterium, virus, or other microorganism that can cause disease.
Pepsin
/ˈpɛpsɪn/
The chief digestive enzyme in the stomach, which breaks down proteins into polypeptides.
Pericardium
/ˌpærɪˈkɑːrdiəm/
The membrane enclosing the heart, consisting of an outer fibrous layer and an inner double layer of serous membrane.
Peristalsis
/ˌpɛrɪˈstælsɪs/
The involuntary constriction and relaxation of the muscles of the intestine, creating wave-like movements that push the contents forward.
Phagocytosis
/ˌfæɡəsaɪˈtoʊsɪs/
The ingestion of bacteria or other material by phagocytes and amoeboid protozoans.
Pharynx
/ˈfærɪŋks/
The membrane-lined cavity behind the nose and mouth, connecting them to the esophagus.
Phospholipid
/ˌfɒsfoʊˈlɪpɪd/
A lipid containing a phosphate group in its molecule; a major component of all cell membranes.
Pituitary Gland
/pɪˈtjuːɪˌtɛri ɡlænd/
The 'master gland' of the endocrine system, located at the base of the brain.
Plasma
/ˈplæzmə/
The colorless fluid part of blood, lymph, or milk, in which corpuscles or fat globules are suspended.
Platelet
/ˈpleɪtlət/
A small colorless disk-shaped cell fragment without a nucleus, found in large numbers in blood and involved in clotting.
Pleura
/ˈplʊərə/
Each of a pair of serous membranes lining the thorax and enveloping the lungs.
Pons
/pɒnz/
The part of the brainstem that links the medulla oblongata and the thalamus.
Proprioception
/ˌproʊprioʊˈsɛpʃən/
The sense of self-movement and body position.
Proximal
/ˈprɒksɪməl/
Situated nearer to the center of the body or the point of attachment.
Pulmonary Circulation
/ˈpʊlməˌnɛri ˌsɜːrkjʊˈleɪʃən/
The portion of the circulatory system which carries deoxygenated blood away from the right ventricle, to the lungs, and returns oxygenated blood to the left atrium.
Purkinje Fibers
/pɜːrˈkɪndʒi ˈfaɪbərz/
Specialized conducting fibers in the ventricles of the heart that allow for rapid electrical signaling.