Anatomy & physiology terms

35 terms

Acid-base balance: Keeping blood pH within a narrow range (7.35–7.45). Bicarbonate buffers acid, the lungs adjust carbon dioxide by changing ventilation, and the kidneys excrete H⁺ and reabsorb bicarbonate. A pH below 7.35 is acidosis and above 7.45 alkalosis; each is classed as respiratory or metabolic by its origin, and the other system tries to compensate.
Anterior pituitary: The front lobe of the pituitary gland. Under the control of releasing and inhibiting hormones from the hypothalamus, it secretes growth hormone, thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH) and prolactin. Hormones from the target glands suppress its secretion by negative feedback. A functioning tumor can make too much of one of these hormones.
Antidiuretic hormone: A hormone made in the hypothalamus and released from the posterior pituitary that increases water reabsorption in the collecting ducts of the kidney. It is secreted when plasma osmolality rises, concentrating the urine. Deficiency (diabetes insipidus) causes large volumes of dilute urine; inappropriate excess (SIADH) causes water retention and hyponatremia. Monitor intake and output, weight and sodium in these clients.
Arterial blood gas: Measurement of pH, PaCO₂, PaO₂, bicarbonate (HCO₃⁻) and oxygen saturation in arterial blood. Approximate adult normal values: pH 7.35–7.45; PaCO₂ 35–45 mmHg; HCO₃⁻ 22–26 mEq/L; PaO₂ 80–100 mmHg. Interpret in order: look at the pH, decide whether the respiratory (PaCO₂) or metabolic (HCO₃⁻) component matches it, then assess compensation. A modified Allen test is commonly done before a radial sample.
Autonomic nervous system: The part of the nervous system that controls internal organs, blood vessels and glands involuntarily. The sympathetic division drives the "fight or flight" response, raising heart rate and blood pressure, dilating bronchi and pupils and slowing digestion; the parasympathetic division drives "rest and digest", slowing the heart and stimulating digestion and elimination. Many drugs, such as beta blockers and anticholinergics, act through this system.
Basic tissue types: A tissue is a group of cells with a similar structure that work together as a unit, with the intercellular matrix between them; histology is the study of tissues. The body has four basic tissues: epithelial tissue, which covers surfaces and lines cavities; connective tissue, which binds and supports structures; muscle tissue, which contracts to produce movement; and nervous tissue, which conducts impulses. Organs are built from combinations of these tissues.
Blood-brain barrier: A selective barrier, formed by tight junctions between brain capillary endothelial cells, that limits the passage of many substances from blood into brain tissue. It protects the brain from toxins and pathogens but also keeps many drugs out of the central nervous system. In newborns, very high bilirubin levels can cause kernicterus, a form of brain damage.
Body fluid compartments: Most body water is inside cells: intracellular fluid makes up about 60% of body fluid volume (about 40% of body weight), and the rest is extracellular. Extracellular fluid is made up of interstitial fluid and plasma. Fluid moves between compartments according to osmotic and hydrostatic pressure; shifts from plasma into the interstitium cause edema, and the "third spacing" seen in burns causes hypovolemia. Infants have a higher proportion of water.
Body membranes: Thin layers of tissue that cover the body, line its cavities and wrap the organs inside them. Mucous membranes line cavities open to the outside (the digestive, respiratory, excretory and reproductive tracts); serous membranes, such as the pleura around the lungs, line the closed thoracic and abdominopelvic cavities, cover their organs and secrete a thin fluid that reduces friction. Synovial membranes, made of connective tissue only, line freely movable joints and secrete lubricating synovial fluid; the meninges protect the brain and spinal cord.
Bone tissue: The connective tissue with a hard matrix that forms the skeleton. Compact bone is made of osteons (Haversian systems): rings of matrix around a central canal carrying blood vessels, with osteocytes in small spaces (lacunae) between the rings. Spongy bone is made of plates and bars called trabeculae, with red bone marrow in the spaces between them. Osteoblasts form bone and osteoclasts break it down; the balance between them keeps bone healthy, and its loss leads to osteopenia and osteoporosis.
Cardiac conduction system: Specialized cardiac muscle cells that start and coordinate each heartbeat: the sinoatrial (SA) node, atrioventricular (AV) node, bundle of His, right and left bundle branches and Purkinje fibers. The SA node, the natural pacemaker, fires 60–100 times a minute. If it fails, the AV node (40–60/min) and the ventricles (20–40/min) take over with slower escape rhythms. This pathway underlies the ECG waveform.
Cardiac output: The volume of blood the heart pumps in one minute: heart rate multiplied by stroke volume (CO = HR × SV). Stroke volume depends on preload, afterload and contractility. Falling cardiac output shows as hypotension, cool extremities, reduced urine output and altered mental status.
Cartilage: A tough but flexible connective tissue. Hyaline cartilage covers joint surfaces (articular cartilage), forms the costal cartilages joining the ribs to the sternum and supports the tracheal wall, keeping the trachea from collapsing. Fibrocartilage forms the intervertebral discs and the pad of the pubic symphysis. Elastic cartilage gives flexible support to structures such as the external ear. In children, the epiphyseal plate, where long bones grow in length, is also hyaline cartilage.
Connective tissue: Tissue that binds structures together and gives organs and the body a framework and support, with relatively few cells in an abundant intercellular matrix. It stores fat, transports substances, protects against disease and helps repair tissue damage. Common cells are fibroblasts, macrophages and mast cells. Its types include loose and adipose tissue, the fibrous tissue of tendons and ligaments, elastic tissue, cartilage, bone and blood. Most types have a good blood supply, and its cells divide more slowly than epithelial cells. Cancers of bone and soft tissues are sarcomas.
Electrocardiogram: A recording of the heart's electrical activity through electrodes placed on the skin. The P wave shows atrial depolarization, the QRS complex ventricular depolarization and the T wave ventricular repolarization; the PR interval is normally 0.12–0.20 seconds and the QRS shorter than 0.12 seconds. It reveals arrhythmias, ischemia and electrolyte disturbances. Place the electrodes correctly and help the client stay still.
Epithelial tissue: Tissue made of tightly packed cells with very little intercellular matrix that covers body surfaces, lines body cavities and hollow organs and forms most glands; it rests on connective tissue through a basement membrane. It is named by cell shape (squamous, cuboidal, columnar) and by the number of layers (simple or stratified). Its roles include protection, secretion, absorption, filtration and diffusion. The epithelium lining the mouth and intestines divides quickly, so chemotherapy damages it, and most cancers (carcinomas) arise from epithelial cells.
Gas exchange: The diffusion of oxygen from the alveoli into pulmonary capillary blood, and of carbon dioxide in the other direction. Elastic alveolar walls give a large surface area for this exchange. Pneumonia, pulmonary edema and emphysema impair it, causing hypoxemia and hypercapnia. Monitor respiratory rate, saturation, mental status and arterial blood gases.
Glandular epithelium: Epithelium specialized to produce and secrete substances. Exocrine glands release their product through ducts onto a surface; examples are sweat, sebaceous and mammary glands and the digestive enzyme glands. Endocrine glands are ductless; their hormones pass directly into the blood and act only on cells with receptors for them. The pancreas has both an exocrine part (digestive enzymes) and an endocrine part (insulin and glucagon). Cancers that arise in secretory epithelium are called adenocarcinomas.
Glomerular filtration rate: The volume of plasma the kidneys filter through the glomeruli per unit time, the main measure used to assess kidney function. A GFR of 90 mL/min/1.73 m² or more is normal, and it declines with age. In practice an estimate (eGFR) is calculated from serum creatinine; an eGFR below 60 mL/min/1.73 m² for more than 3 months indicates chronic kidney disease. Renally cleared drugs are adjusted to the GFR.
Hemostasis: The process that stops bleeding after vessel injury: vasoconstriction, formation of a platelet plug and a clot reinforced by fibrin through the coagulation cascade, followed later by fibrinolysis, which dissolves the clot. Platelet count, PT/INR and aPTT assess the process. Anticoagulants and antiplatelet drugs act on different steps, so monitor clients taking them for signs of bleeding.
Homeostasis: The body keeping its internal environment, such as temperature, blood glucose, blood pressure and pH, within narrow limits despite outside changes. It works mainly through negative feedback, which reverses a rise or fall in a body condition to restore stability.
Inflammation: The protective vascular and cellular response to tissue injury or infection. Its five cardinal signs are redness, heat, swelling, pain and loss of function; vasodilation and increased permeability bring leukocytes to the site. Watch wounds and catheter sites for these signs and help distinguish inflammation from infection.
Mean arterial pressure: The average pressure in the arteries over one cardiac cycle, calculated from the systolic and diastolic pressures. It is monitored closely in shock and sepsis; in septic shock the target is a MAP of at least 65 mmHg.
Muscle tissue: Tissue with a good blood supply that contracts to produce movement, using the proteins actin and myosin. Skeletal muscle is striated, multinucleated and voluntary; it moves bones and maintains posture. Smooth muscle is spindle-shaped, with one nucleus and no striations, and is involuntary; it lies in the walls of the stomach, intestines, bladder, uterus and blood vessels. Cardiac muscle is found only in the heart; its branching, striated cells, each with one nucleus, are joined by intercalated discs and contract involuntarily.
Nephron: The structural and functional unit of the kidney, about a million in each. Blood is filtered in the glomerulus and Bowman capsule; water, electrolytes and glucose are reabsorbed and wastes secreted along the proximal tubule, loop of Henle, distal tubule and collecting duct. Aldosterone and ADH fine-tune water and sodium balance in the distal segments. Diuretics act on different parts of the nephron.
Nervous tissue: Tissue in the brain, spinal cord and nerves that controls body activities through electrical impulses. Neurons generate and conduct impulses; each has a cell body, dendrites that carry impulses toward it and a single axon that carries them away. Sensory (afferent) neurons carry impulses to the central nervous system, and motor (efferent) neurons carry them to muscles and glands. Neurons do not divide, so a destroyed neuron is not replaced. Supporting cells, the neuroglia, do not conduct impulses but nourish and protect neurons.
Neuroglia: The supporting cells of nervous tissue, which do not conduct impulses; unlike neurons, they can divide. They bind, nourish and protect neurons, and some are phagocytic. The white, fatty myelin sheath around axons is made by Schwann cells in the peripheral nervous system and by oligodendrocytes in the central nervous system; the gaps are the nodes of Ranvier. Peripheral fibers can regenerate thanks to the Schwann cell covering, but central fibers do not. In multiple sclerosis, the immune system damages myelin in the central nervous system.
Osmosis and tonicity: Osmosis is the movement of water across a semipermeable membrane from the side with fewer dissolved particles to the side with more. Tonicity describes a fluid's effect on cell volume: isotonic fluids (e.g., 0.9% sodium chloride) leave cell volume unchanged, hypotonic fluids draw water into cells and swell them, and hypertonic fluids pull water out of cells. This is why fluid overload and cerebral edema are monitored when IV fluids are chosen and infused.
Oxyhemoglobin dissociation curve: The S-shaped curve relating the partial pressure of oxygen in blood (PaO₂) to hemoglobin oxygen saturation. On its flat upper part, as in the lungs, saturation changes little when PaO₂ varies; on its steep part, a small fall in PaO₂ releases much oxygen to the tissues. Rising CO₂, acidosis and a higher temperature shift the curve to the right, so hemoglobin gives up oxygen more readily; a left shift holds oxygen more tightly and impairs delivery to tissues. Pulse oximetry (SpO₂) estimates saturation; an arterial blood gas measures PaO₂ (normally 80–100 mmHg).
Pituitary gland: A small gland in the sella turcica at the base of the brain that, together with the hypothalamus, controls many other endocrine glands. The anterior lobe (adenohypophysis) secretes growth hormone, TSH, ACTH, FSH, LH and prolactin; the posterior lobe (neurohypophysis) stores and releases ADH and oxytocin made in the hypothalamus.
Preload and afterload: Preload is the stretch of ventricular muscle fibers at the end of diastole, set mainly by venous return. Afterload is the resistance the ventricle must overcome to eject blood, influenced by systemic vascular resistance and blood pressure. In heart failure, diuretics reduce preload and vasodilators reduce afterload, easing the work of the heart.
Renin-angiotensin-aldosterone system: A hormone system that regulates blood pressure and fluid volume. When kidney perfusion falls, renin is released; angiotensinogen becomes angiotensin I and then, through ACE, angiotensin II. Angiotensin II constricts blood vessels and stimulates aldosterone, which retains sodium and water and increases potassium excretion. ACE inhibitors and angiotensin receptor blockers target this system.
Surfactant: A slippery substance secreted in the alveoli that lowers surface tension and keeps alveoli from collapsing on expiration. It reaches adequate levels only late in pregnancy, so deficiency in preterm infants causes neonatal respiratory distress syndrome. Antenatal corticosteroids are given to women at risk of preterm birth to mature the fetal lungs, and surfactant can be given to the infant.
Thermoregulation: Regulation of body temperature by the hypothalamus, balancing heat production (metabolism, shivering) against heat loss (radiation, conduction, convection, evaporation). Newborns lose heat quickly because of their large surface area and little subcutaneous fat, and regulation weakens in older adults. In fever, pyrogens raise the hypothalamic set point, and vasoconstriction and shivering raise the core temperature to match it; in hyperthermia such as heatstroke, heat gain outstrips heat loss, and physical cooling is the main treatment.
Tissue repair: The replacement of damaged tissue. Tissues whose cells keep dividing, such as the epidermis and the lining of the gut, replace lost cells with the same cell type (regeneration), whereas neurons and cardiac muscle that dies in an infarction are not replaced, and the loss is permanent. Wound healing passes through hemostasis, inflammation, proliferation and maturation: proliferation forms new epidermis, pink granulation tissue with new capillaries and collagen, and in maturation collagen deposition forms a scar. Protect granulation tissue during dressing changes.