Definitions and descriptions

Definitions and descriptions

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There are currently 173 terms in this directory beginning with the letter A.
Abdomen (AB-doh-men)
Portion of the body between the diaphragm and the pelvis
Abdominal cavity (ab-DAHM-in-uhl KAV-i-tee)
Part of the ventral cavity, inferior to the diaphragm and above the pelvic cavity
Abducens nerves (ab-DEW-senz)
Cranial nerve pair VI. Motor to an extrinsic muscle of the eye
Abduction (ab-DUK-shun)
Movement of a body part away from the midline of the body
ABO group (A-B-O GROOP)
The red blood cell types determined by the presence or absence of A and B anti-gens on the red blood cell membrane; the four types are A, B, AB, and O
Abortion
It is a spontaneous loss of a fetus before it is viable (has the potential to survive outside the womb). The World Health Organization (WHO) defines it as expulsion or extraction of an embryo or fetus weighing 500 mg or less, approximately 24 weeks of gestation. Clinical features will depend on the types of  abortion.
Abscess
Abscess is a collection of pus caused by Staphylococcus aureus.
Absorption (ab-ZORB-shun)
The taking in of materials by cells or tissues
Accessory nerves (ak-SES-suh-ree)
Cranial nerve pair XI. Motor to the larynx and shoulder muscles
Accessory organs (ak-SES-suh-ree)
The digestive organs that contribute to the process of digestion, although digestion does not take place within them; consist of the teeth, tongue, salivary glands, liver, gallbladder, and pancreas
Acetabulum (ASS-uh-TAB-yoo-lum)
The deep socket in the hip bone that articulates with the head of the femur (from the Latin “little vinegar cup”)
Acetylcholine (as-SEE-tull-KOH-leen)
A chemical neuro-transmitter released at neuromuscular junctions, as well as by neurons in the central and peripheral nervous systems
Acid (ASS-id)
A hydrogen ion (H +) donor; when in solution has a pH less than 7
Acidosis (ASS-i-DOH-sis)
The condition in which the pH of the blood falls below 7.35
Acne
Acne is a multifactorial disease primarily of teenagers with follicular plugging and inflammation. It presents with polymorphic lesions including, papules and lesions involving the face, chest, shoulders and back.
Acne (AK-nee)
Inflammation of the sebaceous glands and hair follicles
Acoustic nerves (uh-KOO-stik)
Cranial nerve pair VIII. Sensory for hearing and equilibrium
Acquired immunity (uh-KWHY-erd im-YOO-ni-tee)
The immunity obtained upon exposure to a pathogen or a vaccine or upon reception of antibodies for a particular pathogen
Acromegaly (AK-roh-MEG-ah-lee)
Hypersecretion of growth hormone in an adult, resulting in excessive growth of the bones of the face, hands, and feet
Acrosome (AK-roh-sohm)
The tip of the head of a sperm cell, a modified lysosome; contains enzymes to digest the membrane of the ovum
Actin (AK-tin)
A contractile protein in the sarcomeres of muscle fibers; is pulled by myosin
Action potential (AK-shun poh-TEN-shul)
The changes in electrical charges on either side of a cell membrane in response to a stimulus; depolarization followed by repolarization
Active immunity (AK-tiv im-YOO-ni-tee)
The immunity provided by the production of antibodies after exposure to a foreign antigen; may be natural (recovery from disease) or artificial (reception of a vaccine)
Active immunization.
In active immunization, the immune system is stimulated by administration of vaccines to develop a disease-specific immunity.
Active site theory (AK-tiv SITE THEER-ree)
The process by which an enzyme catalyzes a specific reaction; depends on the shapes of the enzyme and the substrate molecules
Active transport (AK-tiv TRANS-port)
The process in which there is movement of molecules against a concentration gradient; that is, from an area of lesser concentration to an area of greater concentration. Requires energy
Acute Bronchitis
It is a self-limited inflammation of the bronchi due to upper airway infection. Acute bronchitis is one of the most common conditions associated with antibiotic misuse. This respiratory condition is generally caused by a virus. Pertusis is the only indication for antibacterial agents in the treatment of acute bronchitis. It is also known as chest cold, is short-term inflammation of the bronchi (large and medium sized airways) of the lungs.
Acute Epiglottitis (AE)
Epiglottitis is an acute infectious inflammation of the epiglottis, supraglottic and hypopharynx which occurs both in children and adults. It is commonly caused by Haemophilus influenzae. Epiglottitis is a potentially lethal condition especially in children. Edema of the epiglottis may cause acute airway obstruction.
Acute Kidney Disease
Acute kidney disease is a sudden decline in the glomerular filtration rate (GFR) resulting elevation of serum blood urea, creatinine and other waste products. Practically AKI is recognized when there is urine output of less than 0.5ml/kg/hour for >6 hours. Causes of AKI are classified as pre-renal, renal and post-renal causes and usually result in reversible kidney failure.
Acute Laryngo-tracheobronchitis
Acute Laryngo-tracheobronchitis (croup) is an acute inflammation of the larynx, trachea and bronchi which occurs in young children (usually between 6 months to 3 years of age). it arises as a result of narrowing of the airway in the region of the larynx. The most common cause is viral infection (particularly parainfluenza viruses) but may also be due to bacterial infection. The obstruction is due to inflammation and oedema.
Acute Necrotizing Ulcerative Gingivitis (ANUG)
It is a severe form of gingivitis and is characterized by rapid destruction of gingival tissue, particularly in the area of the interdental papilla. Patients usually present with soreness and bleeding of the gums and foul smell test (fetor-exore/ halitosis). Acute Necrotizing Ulcerative Gingivitis (ANUG) is also called Vincent's gingivitis or Vincent's gingivostomatitis. It is common in malnourished children and immunocompromised individuals espeially patients with diabetes and HIV/AIDs
Acute pancreatitis
It is due to sudden inflammation of the pancreas due to pancreatic enzymes auto digestion. Common risk factors which trigger the acute episode are presence of gallstones and alcohol intake.
Acute rhinitis
It is a viral inflammatory condition in the nasal mucous membrane, usually part of a more wide-spread infection of the upper respiratory tract.
Acute viral Hepatitis
It is a systemic infection predominantly affecting the liver caused by hepatotropic viral agents namely Hepatitis A virus (HAV), Hepatitis B virus (HBV),  Hepatitis C virus (HCV), HBV-associated delta agent or Hepatitis D virus (HDV), and the Hepatitis E virus (HEV); in most cases leads to self limiting disease but can take a fulminant course and lead to hepatic failure.
Adaptation (A-dap-TAY-shun)
The characteristic of sensations in which awareness of the sensation diminishes despite a continuing stimulus
Addison’s disease (ADD-i-sonz)
Hyposecretion of the hormones of the adrenal cortex, characterized by low blood pressure, dehydration, muscle weakness, and mental lethargy
Adduction (ad-DUK-shun)
The movement of a body part toward the midline of the body
Adenohypophysis (uh-DEN-oh-high-POFF-e-sis)
The anterior pituitary gland
Adenoid Hypertrophy
It is hypertrophy of the lymphoid tissues in the nasopharynx, presenting with mouth breathing, snoring and otitis media with effusion. It is reported mainly in children.
Adipocyte (ADD-i-poh-site)
A cell of adipose tissue, specialized to store fat
Adipose tissue (ADD-i-pohz TISH-yoo)
A connective tissue composed primarily of adipocytes; function is fat storage as a source of potential energy
Adrenal cortex (uh-DREE-nuhl KOR-teks)
The outer layer of the adrenal glands, which secretes cortisol and aldosterone
Adrenal glands (uh-DREE-nuhl)
The endocrine glands located on the top of the kidneys; each consists of an adrenal cortex, which secretes cortisol and aldosterone, and an adrenal medulla, which secretes epinephrine and norepinephrine (Syn.—suprarenal glands)
Adrenal medulla (uh-DREE-nuhl muh-DEW-lah)
The inner layer of the adrenal glands; secretes epinephrine and norepinephrine
Adrenocorticotropic hormone (ACTH) (uh-DREE-no- KOR-ti-koh-TROH-pik)
A hormone produced by the anterior pituitary gland that stimulates the adrenal cortex to secrete cortisol
Aerobic (air-ROH-bik)
Requiring oxygen
Afferent (AFF-er-rent)
To carry toward a center or main part
Afferent arteriole (AFF-er-ent ar-TIR-ee-ohl)
The arteriole that takes blood from the renal artery into a glomerulus; within its wall are juxtaglomerular cells that secrete renin
After-image (AFF-ter-IM-ije)
The characteristic of sensations in which a sensation remains in the consciousness even after the stimulus has stopped
Afterbirth (AFF-ter-berth)
The placenta delivered shortly after delivery of the infant
Age-related macular degeneration (AMD) (MAK-yoo- lar dee-jen-e-RAY-shun)
Loss of central vision because of the growth of abnormal blood vessels or bleeding in the retina
Agglutination (uh-GLOO-ti-NAY-shun)
Clumping of blood cells or microorganisms; the result of an antigen–antibody reaction
AIDS (AYDS)
Acquired immunodeficiency syndrome; caused by a virus (HIV) that infects helper T cells and depresses immune responses
Albumin (al-BYOO-min)
A protein synthesized by the liver, which circulates in blood plasma; contributes to the colloid osmotic pressure of the blood
Aldosterone (al-DAH-ster-ohn)
A hormone (mineralocorticoid) secreted by the adrenal cortex that increases the reabsorption of sodium and the excretion of potassium by the kidneys
Alimentary tube (AL-i-MEN-tah-ree TOOB)
The series of digestive organs that extends from the mouth to the anus; consists of the oral cavity, pharynx, esophagus, stomach, small intestine, and large intestine
Allele (uh-LEEL)
One of two or more different genes for a particular characteristic
Allergen (AL-er-jen)
A substance capable of stimulating an allergic response
Allergic rhinitis
It is an irritation of the nasal mucosa by an allergen in a previously sensitized individual. Common allergens include house dust (mite's faeces), pollens, cockroach antigen, animal dander, moulds (in-door)
Alopecia (AL-oh-PEE-she-ah)
Loss of hair, especially that of the scalp
Alpha cells (AL-fah SELLS)
The cells of the islets of Langerhans of the pancreas that secrete the hormone glucagon
Alveolar type I cell (al-VEE-oh-lar TIGHP WON SELL)
The simple squamous epithelial cell that forms the walls of the alveoli of the lungs
Alveolar type II cell (al-VEE-oh-lar TIGHP TOO SELL)
The septal cell in the lungs that produces pulmonary surfactant
Alveolar ventilation (al-VEE-oh-lar VEN-ti-LAY-shun)
The amount of inhaled air that reaches the alveoli andmparticipates in gas exchange; about 350–400 mL of a 500-mL tidal volume
Alveoli (al-VEE-oh-lye)
The air sacs of the lungs, made of simple squamous epithelium, in which gas exchange takes place
Alzheimer’s disease (ALZ-high-mers)
A progressive brain disease, of unknown cause, resulting in loss of memory, intellectual ability, speech, and motor control
Amblyopia (AM-blee-OH-pee-ah)
Impaired vision without apparent damage to an eye; often the result of lazy eye because the brain ignores the image from the lazy eye and the eye stops focusing
Amenorrhea (ay-MEN-uh-REE-ah)
Absence of menstruation
Amine/amino group (ah-MEEN/ah-MEE-noh)
The NH2 portion of a molecule such as an amino acid
Amino acid (ah-MEE-noh ASS-id)
An organic compound that contains an amino, or amine, group (NH2 ) and a carboxyl group (COOH). Twenty different amino acids are the subunit molecules of which human proteins are made
Amniocentesis (AM-nee-oh-sen-TEE-sis)
A diagnostic procedure in which amniotic fluid is obtained for culture of fetal cells; used to detect genetic diseases or other abnormalities in the fetus
Amnion (AM-nee-on)
An embryonic membrane that holds the fetus suspended in amniotic fluid; fuses with the chorion by the end of the third month of gestation
Amniotic fluid (AM-nee-AH-tik FLOO-id)
The fluid contained within the amnion; cushions the fetus and absorbs shock
Amoebiasis
Amoebiasis is an infection caused by the protozoa organism Entamoeba histolytica, which can cause colitis and other extra-intestinal manifestations. The infection is primarily acquired through ingestion of contaminated food and water and occasionally can be acquired through oral-anal sexual practices
Amoebic liver abscess
It is the most frequent extra-intestinal manifestation of Entamoeba histolytica infection which results from the invasion of the portal venous system from the colon leading to inflammation and subsequently abscess formation particularly involving the right lobe of the liver.
Amphiarthrosis (AM-fee-ar-THROH-sis)
A slightly movable joint, such as a symphysis
Amylase (AM-i-lays)
A digestive enzyme that breaks down starch to maltose; secreted by the salivary glands and the pancreas
Anabolic steroid (AN-ah-BAH-lik STEER-oyd)
A chemical similar in structure and action to the male hormone testosterone; increases protein synthesis, especially in muscles
Anabolism (an-AB-uh-lizm)
Synthesis reactions, in which smaller molecules are bonded together to form larger molecules; require energy (ATP) and are catalyzed by enzymes
Anaemia in Pregnancy
It is hemoglobin levels less than 11g/dl in early pregnancy and less than 10.5g/dl in the 2nd and 3rd trimester of pregnancy. Mild anemia- hemoglobin: 8-11g/dl; severe anemia- hemoglobin <7g/dl. Iron deficiency anemia during pregnancy has been associated with an increased risk of low birth weight, preterm delivery and perinatal mortality.
Anaerobic (AN-air-ROH-bik)
1. In the absence of oxygen.
2. Not requiring oxygen
Anal Fissures
These are painful linear ulcers in the anal canal. Young and middle aged adults most commonly affected. Primary fissure occur in the posterior midline. It can also be secondary to Crohn's disease, anal cancer, or infection such as syphilis, TB in which case they occur more lateral. Passage of hard stools is a common predisposition to primary fissures.
Anaphase (AN-ah-fayz)
The third stage of mitosis, in which the separate sets of chromosomes move toward opposite poles of the cell
Anaphylactic shock (AN-uh-fi-LAK-tik SHAHK)
A type of circulatory shock that is the result of a massive allergic reaction (from the Greek “unguarded”)
Anaphylaxis
It is an acute and often life-threatening immunologic reaction, frequently heralded by scalp pruritus, diffuse erythema, urticaria or angioedema. Bronchospams, laryngeal edema, hyperistalsis, hypotension and cardiac arrhythmia may occur. Antibiotic (especially penicillins), other drugs and radio-graphic contrast agents are the most common causes of serious anaphylactic reactions. Hymenoptera stings are the next most frequent cause, followed by ingestion of crustaceans and other food allergens.
Anastomosis (a-NAS-ti-MOH-sis)
A connection or joining, especially of blood vessels
Anatomic position (AN-uh-TOM-ik pa-ZI-shun)
The position of the body used in anatomic descriptions: The body is erect and facing forward, the arms are at the sides with the palms facing forward
Anatomy (uh-NAT-uh-mee)
The study of the structure of the body and the relationships among the parts
Ancylostomiasis
It is a hookworm disease caused by infestation of the small intestine with Ancylostoma duodenale or Necator americanus leading to anaemia and malnutrition.
Anemia (uh-NEE-mee-yah)
A deficiency of red blood cells or hemoglobin
Anencephaly (an-en-SEFF-ah-lee)
A congenital nervous system defect in which the cerebrum has not developed; is always fatal
Anesthesia
Anesthesia is a state of controlled reversible loss of consciousness usually accompanied by analgesia, muscle relation, amnesia and reflexia. It is usually induced for the purpose of facilitating surgery and other therapeutic or diagnostic procedures. It is a continuum of clinical services that range from monitored anesthe
Aneurysm (AN-yur-izm)
A localized sac or bubble that forms in a weak spot in the wall of a blood vessel, usually an artery
Angle closure Glaucoma
It is also known as congestive glaucoma and commonly affect people aged 40 years and above.
Anion (AN-eye-on)
An ion with a negative charge
Ano rectal syndrome (ARS)
Ano rectal syndrome is defined as soreness, burning, itching or other irritation of the rectum together with redness in the area of anus. Sometimes it is accompanied by diarrhea and it may occur as a toxic side effect of oral administration of certain broad spectrum antibiotics.
Antagonistic muscles (an-TAG-on-ISS-tik MUSS-uhls)
Muscles that have opposite functions with respect to the movement of a joint
Antepartum Haemorrhage
It is the bleeding from the birth canal after the 28th week of gestation. The main forms are placenta praevia and abruption placenta.

 
Anterior (an-TEER-ee-your)
Toward the front (Syn. ventral)
Anthrax
Anthrax is a bacterial disease caused by the spore forming Bacillus anthracis, a Gram positive, rod-shaped bacterium. it is a zoonotic disease whereby man is infected directly through contact with infected hides or inhalation of spores in the lungs or ingestion of infected meat. it can be cutaneous, pulmonary and/ or intestinal.
Antibody (AN-ti-BAH-dee)
A protein molecule produced by plasma cells that is specific for and will bond to a particular foreign antigen (Syn.—gamma globulin, immune globulin)
Antibody titer (AN-ti-BAH-dee TIGH-ter)
A diagnostic test that determines the level or amount of a particular antibody in blood or serum
Antibody-mediated immunity (AN-ti-BAH-dee-MEE- dee-ay-ted im-YOO-ni-tee)
The mechanism of adaptive immunity that involves antibody production and the destruction of foreign antigens by the activities of B cells, T cells, and macrophages (Syn.—humoral immunity)
Anticodon (AN-ti-KOH-don)
A triplet of bases on tRNA that matches a codon on mRNA
Antidiuretic hormone (ADH) (AN-ti-DYE-yoo-RET-ik)
A hormone produced by the hypothalamus and stored in the posterior pituitary gland; increases the reabsorption of water by the kidney tubules, and in large amounts causes vasoconstriction and is called vasopressin
Antigen (AN-ti-jen)
A chemical marker that identifies cells of a particular species or individual. May be “self ” or “foreign.” Foreign antigens stimulate immune responses
Antigenic (AN-ti-JEN-ik)
Capable of stimulating antibody production
Antiphospholipid Antibody Syndrome (APLAS) in Pregnancy
It is an autoimmune disease characterized by the presence of maternal circulation of one or more auto antibodies against membrane phospholipids. It is an acquired condition.
Antipyretic (AN-tigh-pye-RET-ik)
A medication, such as aspirin, that lowers a fever
Antiseptic (AN-ti-SEP-tik)
A chemical that destroys bacteria or inhibits their growth on a living being
Antithrombin (AN-ti-THROM-bin)
A protein synthesized by the liver that inactivates excess thrombin to prevent abnormal clotting
Antitoxin (AN-tee-TAHK-si
Antibodies specific for a bacterial toxin; used in treatment of diseases such as botulism or tetanus
Anus (AY-nus)
The terminal opening of the alimentary tube for the elimination of feces; surrounded by the internal and external anal sphincters
Aorta (ay-OR-tah)
The largest artery of the body; emerges from the left ventricle; has four parts: ascending aorta, aortic arch, thoracic aorta, and abdominal aorta
Aortic body (ay-OR-tik BAH-dee)
The site of chemoreceptors in the wall of the aortic arch; detect changes in blood pH and the blood levels of oxygen and carbon dioxide
Aortic semilunar valve (ay-OR-tik SEM-ee-LOO-nar VALV)
The valve at the junction of the left ventricle and the aorta; prevents backflow of blood from the aorta to the ventricle when the ventricle relaxes
Aortic sinus (ay-OR-tik SIGH-nus)
The site of pressoreceptors in the wall of the aortic arch; detect changes in blood pressure
Apgar score (APP-gar SKOR)
A system of evaluating an infant’s condition 1 minute after birth; includes heart rate, respiration, muscle tone, response to stimuli, and color
Aphasia (ah-FAY-zee-ah)
Impairment or absence of the ability to communicate in speech, reading, or writing. May involve word deafness or word blindness
Aphthous ulceration
Aphthous ulceration or recurrent aphthous stomatitis (RAS) are painful recurrent mucous membrane ulcerations. Usually affect the non-keratinized oral mucous membrane.
Aplastic anaemia
Aplastic anaemia is defined as pancytopenia resulting from aplasia of the bone marrow. Pancytopenia- a reduction in the blood count of all the major cell lines.
Aplastic anemia (ay-PLAS-tik uh-NEE-mee-yah)
Failure of the red bone marrow resulting in decreased numbers of red blood cells, white blood cells, and platelets; may be a side effect of some medications
Apneustic center (ap-NEW-stik SEN-ter)
The respiratory center in the pons that prolongs inhalation
Apocrine gland (AP-oh-krin)
The type of sweat gland (exocrine) found primarily in the axillae and genital area; actually a modified scent gland
Aponeurosis (A-poh-new-ROH-sis)
A flat tendon
Apparent (uh-PAR-ent)
1. Readily seen or visible.

2. An infection in which the patient exhibits the symptoms of the disease
Appendicitis (uh-PEN-di-SIGH-tis)
Inflammation of the appendix
Appendicular skeleton (AP-en-DIK-yoo-lar)
The portion of the skeleton that consists of the shoulder and pelvic girdles and the bones of the arms and legs
Appendix (uh-PEN-diks)
A small tubular organ that extends from the cecum; has no known function for people and is considered a vestigial organ
Aqueous (AY-kwee-us)
Pertaining to water; used especially to refer to solutions
Aqueous humor (AY-kwee-us HYOO-mer)
The tissue fluid of the eye within the anterior cavity of the eyeball; nourishes the lens and cornea
Arachnoid membrane (uh-RAK-noid)
The middle layer of the meninges, made of web-like connective tissue (from the Greek “spider-like”)
Arachnoid villi (uh-RAK-noid VILL-eye)
Projections of the cranial arachnoid membrane into the cranial venous sinuses, through which cerebrospinal fluid is reabsorbed back into the blood
Areolar connective tissue (uh-REE-oh-lar)
A tissue that consists of tissue fluid, fibroblasts, collagen and elastin fibers, and wandering WBCs; found in all mucous membranes and in subcutaneous tissue (Syn.—loose connective tissue)
Arrhythmia (uh-RITH-me-yah)
An abnormal or irregular rhythm of the heart
Arteriole (ar-TEER-ee-ohl)
A small artery
Arteriosclerosis (ar-TIR-ee-oh-skle-ROH-sis)
Deterioration of arteries with loss of elasticity that is often a consequence of aging or hypertension; a contributing factor to aneurysm or stroke
Artery (AR-tuh-ree)
A blood vessel that takes blood from the heart toward capillaries
Arthropod (AR-throw-pod)
Invertebrate animals characterized by an exoskeleton and jointed appendages; includes insects, spiders, ticks, mites, and crustaceans
Arthropods.
These animals are characterized by an external chitin skeleton, segmented bodies, jointed legs, special mouthparts, and other specific features. Their role as direct causative agents of diseases is a minor one (mites, for instance, cause scabies) as compared to their role as vectors transmitting viruses, bacteria, protozoa, and helminths.
Articular cartilage (ar-TIK-yoo-lar KAR-ti-lidj)
The cartilage on the joint surfaces of a bone; provides a smooth surface
Articulation (ar-TIK-yoo-LAY-shun)
A joint
Ascariasis
It is a small intestine infestation caused by Ascaris lumbricoides which leads to malnutrition, iron deficiency anaemia, impaired growth and cognition is susceptible hosts. It is most common infestation in children and it is acquired through ingestion of contaminated food and water.
Ascites (a-SIGH-teez)
An abnormal accumulation of fluid in the peritoneal space
Asthma
It is a chronic reversible obstructive inflammatory airways disease caused by constriction of bronchial smooth muscle causing bronchospasm, oedema of bronchial mucous membrane and blockage of the smaller bronchi with plug of mucous.
Asthma (AZ-mah)
A respiratory disorder characterized by constriction of the bronchioles, excessive mucus production, and dyspnea; often caused by allergies
Astigmatism (uh-STIG-mah-TIZM)
An error of refraction caused by an irregular curvature of the lens or cornea
Astrocyte (ASS-troh-site)
A type of neuroglia that forms the blood–brain barrier to prevent potentially harmful substances from affecting brain neurons
Asymptomatic (AY-simp-toh-MAT-ik)
Without symptoms
Atelectasis (AT-e-LEK-tah-sis)
Collapsed or airless lung, without gas exchange
Atherosclerosis (ATH-er-oh-skle-ROH-sis)
The abnormal accumulation of lipids and other materials in the walls of arteries; narrows the lumen of the vessel and may stimulate abnormal clot formation
Atlas (AT-las)
An irregular bone, the first cervical vertebra; supports the skull
Atom (A-tom)
The unit of matter that is the smallest part of an element
Atomic number (a-TOM-ik)
Number of protons in the nucleus of an atom
Atomic weight (a-TOM-ik WAYT)
The weight of an atom determined by adding the number of protons and neutrons
Atopic Eczema
It is a dermatitis/ Eczema on a background of atopy. Hence there is often a personal or family history of atopic disease (asthma, hay fever or atopic dermatitis).
ATP (Adenosine triphosphate)
A specialized nucleotide that traps and releases biologically useful energy
Atrial natriuretic peptide (ANP) (AY-tree-uhl NAY-tree- yu-RET-ik)
A peptide hormone secreted by the atria of the heart when blood pressure or blood volume increases; increases loss of sodium ions and water by the kidneys (Syn.—atrial natriuretic hormone)
Atrioventricular (AV) node (AY-tree-oh-ven-TRIK-yoo-lar NOHD)
The second part of the cardiac conduction pathway, located in the lower interatrial septum
Atrium (AY-tree-um) (Pl.—atria)
One of the two upper chambers of the heart that receive venous blood from the lungs or the body
Atrophy (AT-ruh-fee)
Decrease in size of a body part due to lack of use; a wasting
Attenuated (uh-TEN-yoo-AY-ted)
Weakened, or less harmful; used to describe the microorganisms contained in vaccines, which have been treated to reduce their pathogenicity
Auditory bones (AW-di-tor-ee)
The malleus, incus, and stapes in the middle ear
Auerbach’s plexus (OW-er-baks PLEK-sus)
The autonomic nerve plexus in the external muscle layer of the organs of the alimentary tube; regulates the contractions of the external muscle layer (Syn.—myenteric plexus)
Auricle (AW-ri-kuhl)
The portion of the outer ear external to the skull; made of cartilage covered with skin (Syn.—pinna)
Autoclave (AW-toh-clayve)
A machine that uses steam under pressure for sterilization
Autoimmune disease (AW-toh-im-YOON di-ZEEZ)
A condition in which the immune system produces antibodies to the person’s own tissue
Autonomic nervous system (AW-toh-NOM-ik NER- vuhs)
The portion of the peripheral nervous system that consists of visceral motor neurons to smooth muscle, cardiac muscle, and glands
Autosomes (AW-toh-sohms)
Chromosomes other than the sex chromosomes; for people there are 22 pairs of autosomes in each somatic cell
Axial skeleton (AK-see-uhl)
The portion of the skeleton that consists of the skull, vertebral column, and rib cage
Axis (AK-sis)
An irregular bone, the second cervical vertebra; forms a pivot joint with the atlas
Axon (AK-sahn)
The cellular process of a neuron that carries impulses away from the cell body
Axon terminal (AK-sahn TER-mi-nuhl)
The end of the axon of a motor neuron, part of the neuromuscular junction
Gafacom
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