{H zone}{}{Area in the center of the A band in which there are no actin myofilaments; contains only myosin.}

{hair follicle receptor}{}{A sensory receptor located in the structure in which hair develops.}

{Haversian system}{}{A central canal containing blood capillaries and the concentric lamellae around it; occurs in compact bone.}

{hemisphere}{}{Refers to half of the cerebrum of the brain.}

{hemoglobin}{}{Red, respiratory protein of erythrocytes; consists of 6% heme and 94% globin; transports oxygen and carbon dioxide.}

{hepatopancreatic ampulla}{}{Composed of the pancreatic duct and the common bile duct.}

{heterozygous}{}{Possessing two separate alleles of a gene.}

{holocrine}{}{Gland whose secretion is formed by the disintegration of entire cells [e.g., sebaceous gland; see also apocrine and merocrine].}

{homeostasis}{}{State of equilibrium in the body with respect to functions, composition of fluids and tissues.}

{homologous pair}{}{Pair of chromosomes each containing the same gene loci.}

{hormone}{}{Substance secreted by endocrine tissues into the blood that acts on a target tissue to produce a specific response.}

{human chorionic gonadotropin [HCG]}{}{Hormone produced by the embryo upon fertilization and division of embryonic cells.  The hormone maintains the corpus luteum, which allows the uterine lining to proliferate.}

{hyaline cartilage}{}{Gelatinous, glossy cartilage tissue consisting of cartilage cells and their matrix; contains collagen, proteoglycans, and water.}

{hydrogen bond}{}{Hydrogen atoms bound covalently to either N or O atoms have a small positive charge that is weakly attracted to the small negative charge of other atoms such as O or N; can occur within a molecule or between different molecules.}

{hydrophilic}{}{A polar substance; literally, water-loving.}

{hydrophobic}{}{A non-polar substance; literally, water-hating.}

{hyperextension}{}{Extension of a joint beyond its normal range.}

{hyperpolarization}{}{Increase in the charge difference across the cell membrane; causes the charge difference to move away from 0 mV.}

{hypertonic}{}{Solution that causes cells to shrink.}

{hypodermis}{}{Loose areolar connective tissue found deep to the dermis that connects the skin to muscle or bone.}

{hypoglossal nerve}{}{Cranial nerve XII; motor fibers transmit impulses to muscles that move the tongue.}

{hypophysis}{}{Endocrine gland attached to the hypothalamus by the infundibulum. Also called the pituitary gland.}

{hypothalamus}{}{Important autonomic and neuroendocrine control center beneath the thalamus.}

{hypotonic}{}{Solution that causes cells to swell.}