Definitions and descriptions
There are currently 91 terms in this directory beginning with the letter H.
Haemophilia A (Factor Viii deficiency)
Is the most common of the hereditary clotting factor deficiencies and are caused by deficiency of factor Viii. The inheritance is sex linked but up to 33% of patient have no family history and result from spontaneous mutation.
Haemophilia B (Factor ix deficiency)
Is due to deficiency of clotting factor ix. Presentation as in Haemophilia A, this is less common 20%
Hair cells (HAIR SELLS)
Cells with specialized microvilli (called stereocilia) found in the inner ear; the receptors for hearing (cochlea), static equilibrium (utricle and saccule), and motion equilibrium (semicircular canals).
Hair root (HAIR ROOT)
The site of mitosis at the base of a hair follicle; new cells become the hair shaft.
Haploid number (HA-ployd)
Half the usual number of chromosomes found in the cells of a species. Characteristic of the gametes of the species (human _ 23).
Hard palate (HARD PAL-uht)
The anterior portion of the palate formed by the maxillae and the palatine bones.
Haversian system (ha-VER-zhun)
The structural unit of compact bone, consisting of a central haversian canal surrounded by concentric rings of osteocytes within matrix (Syn.—osteon).
Heart Failure is a clinical syndrome characterized by typical symptoms (e.g. breathlessness, ankle swelling and fatigue) that may be accompanied by signs (e.g. elevated jugular venous pressure, pulmonary crackles and peripheral oedema) caused by a structural and/or functional cardiac abnormality, resulting in a reduced cardiac output and/or elevated intracardiac pressures at rest or during stress.
Heart murmur (HART MUR-mur)
An abnormal heart sound heard during the cardiac cycle; often caused by a malfunctioning heart valve.
Heartburn (pyrosis) is the feeling of substernal burning, often radiating to the neck. Caused by the reflux of acidic (or, rarely, alkaline) material into the esophagus, it is highly specific for GERD.
Heat exhaustion (HEET eks-ZAWS-chun)
A state of weakness and dehydration caused by excessive loss of body water and sodium chloride in sweat; the result of exposure to heat or of strenuous exercise.
Heat stroke (HEET STROHK)
An acute reaction to heat exposure in which there is failure of the temperatureregulating mechanisms; sweating ceases, and body temperature rises sharply.
Heimlich maneuver (HIGHM-lik ma-NEW-ver)
A procedure used to remove foreign material lodged in the pharynx, larynx, or trachea.
A coil or spiral. Double helix is the descriptive term used for the shape of a DNA molecule: two strands of nucleotides coiled around each other and resembling a twisted ladder.
Parasitic worms belong to the animal kingdom. These are metazoan organisms with highly differentiated structures. Medically significant groups include the trematodes (flukes or flatworms), cestodes (tapeworms), and nematodes (roundworms).
A laboratory test that determines the percentage of red blood cells in a given volume of blood; part of a complete blood count.
A technique for providing the function of the kidneys by passing the blood through tubes surrounded by solutions that selectively remove waste products and excess minerals; may be life-saving in cases of renal failure.
The protein in red blood cells that contains iron and transports oxygen in the blood.
Lysis or rupture of red bloodcells; may be the result of an antigen–antibody reaction or of increased fragility of red blood cells in some types of anemia.
A hereditary blood disorder characterized by the inability of the blood to clot normally; hemophilia A is caused by a lack of clotting factor 8.
Hemopoietic tissue (HEE-moh-poy-ET-ik)
A bloodforming tissue, primarily the red bone marrow; lymphatic tissue produces some lymphocytes.
Hemorrhoid disease is due to enlargement or thrombosis of the veins in the external or internal hemorrhoidal plexus
Prevention of blood loss; the mechanisms are chemical clotting, vascular spasm, and platelet plug formation.
A chemical that inhibits blood clotting, an anticoagulant; produced by basophils. Also used clinically to prevent abnormal clotting, such as following some types of surgery.
Hepatic duct (hep-PAT-ik DUKT)
The duct that takes bile out of the liver; joins the cystic duct of the gallbladder to form the common bile duct.
Hepatic portal circulation (hep-PAT-ik POOR-tuhl)
The pathway of systemic circulation in which venous blood from the digestive organs and the spleen circulates through the liver before returning to the heart.
This is the term referring to inflammation of the liver, which may result from various causes, both infectious i.e. viral, bacterial, fungal and parasitic organisms and non-infectious e.g. alcohol, drugs, autoimmune and metabolic diseases.
Inflammation of the liver, most often caused by the hepatitis viruses A, B, or C.
It is an acute viral infection caused by Herpes simplex virus hominis (types HSV1, HSV2) acquired by close contact with an infected individual.
Herpes simplex (HER-peez SIM-pleks)
A virus that causes lesions in the skin or mucous membranes of the mouth (usually type 1) or genital area (usually type 2); either type may cause death or mental retardation of infants of infected women.
Herpes Simplex Keratitis
It is an inflammatory condition of the cornea caused by Herpes Simplex Virus.
Herpes Zoster (Shingles)
It is due to resurgence or reactivation of the Varicella zoster virus infection which also causes chickenpox.
Herpes Zoster Ophthalmicus
Occurs when Varcella Zoster reactivates in the trigeminal ganglion and passes down the ophthalmic division of the trigeminal nerve.
Heterotopic ossification is defined as bone formation in no osseous tissues. Usually occurs in trauma such as fractures and surgical procedures, the exact cause remains unknown.
Hexose sugar (HEKS-ohs)
A six-carbon sugar, such as glucose, that is an energy source (in the process of cell respiration).
Hip bone (HIP BOWNE)
The flat bone that forms half of the pelvic bone; consists of the upper ilium, the lower posterior ischium, and the lower anterior pubis.
Part of the brain in the temporal lobe on the floor of the lateral ventricle; it is essential for the formation of new memories.
An inflammatory chemical released by damaged tissues as part of innate immunity; stimulates increased capillary permeability and vasodilation.
The state in which the internal environment of the body remains relatively stable by responding appropriately to changes.
Homologous pair (hoh-MAHL-ah-gus)
A pair of chromosomes, one maternal and one paternal, that contain genes for the same characteristics.
The secretion of an endocrine gland that has specific effects on particular target organs.
Human leukocyte antigens (HLA) (HYOO-man LOOkoh-sight AN-ti-jens)
The antigens on white blood cells that are representative of the antigens present on all the cells of the individual; the “self” antigens that are controlled by several genes on chromosome number 6; the basis for tissue typing before an organ transplant is attempted.
Humoral immunity (HYOO-mohr-uhl 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.—antibody-mediated immunity).
Hyaline membrane disease (HIGH-e-lin MEM-brayn)
A pulmonary disorder of premature infants whose lungs have not yet produced sufficient pulmonary surfactant to permit inflation of the alveoli.
Hydrochloric acid (HIGH-droh-KLOR-ik ASS-id)
An acid secreted by the parietal cells of the gastric pits of the stomach; activates pepsin and maintains a pH of 1–2 in the stomach.
Hydrogen bond (HIGH-droh-jen BAHND)
A weak bond that helps maintain the three-dimensional shape of proteins and nucleic acids.
A higher than normal blood level of carbon dioxide (usually _45–50mmHg).
Hyperglycaemia in Pregnancy
Gestational Diabetes Mellitus (GDM) is any degree of glucose intolerance first recognized in pregnancy. Diabetes in pregnancy refers to those with pre-existing diabetes, whether diagnosed or not.
Refers to an elevation in potassium concentration ≥5.5 mmol/l. Kidney failure and use of medications use are common causes. Severity of hyperkalaemia may be mild (5.5-6), moderate 6.1- 6.5 and Severe >6.5. Severity grading increases once there is ECG changes.
Hypermetropia (Long sightedness)
This is a condition where patients have difficulty in seeing near objects. It is less manifested in children as they have a high accommodative power.
Farsightedness; an error of refraction in which only distant objects are seen clearly.
Hypertension is elevation of Blood Pressure SBP ≥ 140 mmHg and DBP ≥90 mmHg measured at least three separate occasions. Hypertension is a major independent risk factor for the development of CAD, stroke, and renal failure.
Symptomatic severe hypertension SBP 180mmHg and/or DBP >110 mmHgwithout evidence of target organ damage, such as pulmonary edema, cardiac ischemia, neurologic deficits, or acute renal failure.
Hyperthyroidism is a condition in which an overactive thyroid gland is producing an excessive amount of thyroid hormones that circulate in the blood. Graves' disease, multinodular goiter (TMNG), inflammation of the thyroid gland (thyroiditis) and excessive iodine intake are the most common cause of hyperthyroidism.
Having a greater concentration of dissolved materials than the solution used as a comparison.
Increase in size of a body part, especially of a muscle following long-term exercise or overuse.
Hypocholecalciferolemia (Vitamin D Deficiency)
This disease is characterized by hypocalcemia and or hypophosphatemia. The acceptable concentration of Vitamin D is between 30-60ng/Ml.
Hypopharyngeal cancer includes tumors arising from the pyriform sinus, posterior pharyngeal wall, postcricoid region. It is associated with tobacco use, alcohol consumption, and Plummer–Vinson syndrome.
Hypophyseal portal system (high-POFF-e-SEE-al PORtuhl)
The pathway of circulation in which releasing hormones from the hypothalamus circulate directly to the anterior pituitary gland.
The part of the brain superior to the pituitary gland and inferior to the thalamus; its many functions include regulation of body temperature and regulation of the secretions of the pituitary gland.
1. The condition in which the body temperature is abnormally low due to excessive exposure to cold. 2. A procedure used during some types of surgery to lower body temperature to reduce the patient’s need for oxygen.
Hypothyroidism is a condition in which a person's thyroid hormone production is below normal. Common causes of the disease are chronic autoimmune thyroiditis, post-surgery and post radioactive iodine.
Having a lower concentration of dissolved materials than the solution used as a comparison.
Hypovolemic shock (HIGH-poh-voh-LEEM-ik SHAHK)
A type of circulatory shock caused by a decrease in blood volume.