H Flashcards
H Zone
The central region of a sarcomere corresponding to the location of the thick filaments where there is no overlap with thin filaments; the H zone reduces in size upon contraction.
Habituation
A process by which repeated stimulation of a neuron results in a decreased response.
Hair Cell
Ciliated sensory cells of vertebrates that react to mechanical stimuli (particularly to vibrations). They are the basis of the senses of hearing and balance, and of the lateral line systems of fishes and amphibians.
Haldane Effect
The effect of oxygen on hemoglobin–carbon dioxide binding.
Half-Life
A period of time required for half of a population of molecules to be converted to another form; often applied to radioactive decay.
Heart
A muscular pumping structure.
Heart Rate
The number of times the heart beats in a given period of time; typically measured as beats per minute.
Heat
The kinetic energy associated with the movement of atoms and molecules.
Heat Capacity
The amount of thermal energy required to increase the temperature of 1 g of a substance by 1°C.
Heat of Vaporization
The heat needed to cause a liquid to become gaseous, expressed per unit mass.
Heat Shock Proteins
A class of molecular chaperones that increase in abundance in response to elevated temperature; the term includes members of genetically related proteins that are constitutive and do not increase in expression in response to thermal stress.
Heater Tissues
A general term for tissues that serve to elevate regional or systemic temperature of an animal, such as the heater organ of billfish.
Helicobacter pyloric
A bacterium that infects gastric pits, creating conditions that can lead to a gastric ulcer.
Hematocrit
The proportion of whole blood that is occupied by red blood cells.
Heme
A metal-binding porphyrin derivative that is incorporated into enzymes (e.g., cytochromes) and non-enzyme proteins (e.g., hemoglobin).
Hemerythrin
An iron-containing respiratory pigment found in sipunculids, priapulids, brachiopods, and annelids; lacks heme.
Hemimetabolous Insect
see also holometabolous insect
Type of insect that possesses immature stages (nymphs) that resemble the adults, except in lacking fully formed wings.
Hemocoel
Collective name for the sinuses in the open circulatory systems of many invertebrates.
Hemocyanin
A respiratory pigment found in arthropods and mollusks consisting of one or more protein molecules complexed directly to copper molecules.
Hemocytes
Generalized term for blood cells. Most commonly used for the blood cells of invertebrates.
Hemoglobin
A respiratory pigment consisting of a globin protein complexed to an ironcontaining porphyrin molecule called heme.
Hemolymph
The circulatory fluid of arthropods.
Hemopoietic Factor
A regulatory protein that induces the synthesis of red blood cells; erythropoietin, for example.
Henderson-Hasselbalch Equation
The mass action equation for the dissociation of carbonic acid (H2CO3) to bicarbonate (HCO3−) and hydrogen ions (H+); important in respiratory physiology.
Henry’s Law
One of the ideal gas laws; describes the dissolution of a gas in a liquid, stating that the amount of gas dissolved in a liquid is related to the partial pressure and the solubility of that gas.
Hepatocyte
The dominant cell type in a liver.
Hepatopancreas
An invertebrate tissue that serves the same roles as the vertebrate liver and pancreas.
Hering-Breuer Inflation Reflex
A respiratory reflex that reduces breathing in response to overinflation of the lungs; involved in the termination of a breath.
Hermaphrodite
An animal that possesses both male and female reproductive tissues either simultaneously or sequentially.
Hertz
A frequency of 1 per second (1 Hz = 1 sec−1).
Heterodimer
A quaternary structure of two dissimilar monomers
Heterothermy
A thermal strategy in which the body temperature (TB) varies either spatially or temporally.
Hexose
A general name for monosaccharides with six carbons; includes glucose and fructose.
Hibernation
A form of dormancy that occurs as a result of low ambient temperature and persists for long periods.
Hindbrain
The posterior portion of the vertebrate brain, consisting of the cerebellum and brainstem.
Hippocampus
A part of the vertebrate brain that is involved in the formation of memories.
Histamine
An amino acid; a regulatory molecule that is released from mast cells in response to an immunological challenge.
Histone
A protein that reversibly binds to DNA, altering its ability to be transcribed.
Holocrine Secretion
A type of secretion in which entire cells burst, releasing their internal contents.
Holometabolous Insect
An insect in which juvenile stages, dissimilar from the adult, undergo dramatic metamorphosis.
Homeostasis
A state of internal constancy that is maintained as a result of active regulatory processes.
Homeothermy
A thermal strategy of an animal (a homeotherm) that has a relatively constant body temperature (T_B).
Homeoviscous Adaptation
A process whereby cells alter the composition of cellular membranes to ensure that fluidity remains constant to compensate for the effects of a change in the external environment.
Homing
A movement that returns an animal to its home range.
Homodimer
A molecule composed of two identical subunits.
Homologs
see also paralogs, orthologs
Genes that are descended from a common ancestor, without intervening duplication events.
Homology
Similar in structure and/or function due to shared ancestry.
Homoplasy
A trait shared by taxa as a result of convergent evolution rather than shared ancestry.
Hormone
Type of chemical messenger that is carried in the blood and thus can act across long distances. Classically defined as a substance released from an endocrine gland and active at very low concentrations.
Humoral Immunity
The fluid elements of the immune system that do not involve cells.
Hydration Shell
A coating of water bound to the surface of an ion or molecule.
Hydrofoil
A surface, teardrop shaped in profile, that moves through water to generate lift. An aquatic version of an aerofoil.
Hydrogen Bond
A class of weak (noncovalent) bond in which an electropositive hydrogen atom is shared by two electronegative atoms.
Hydrolysis
The breaking of a covalent bond by introducing a water molecule; –H is added to one product and –OH to the other.
hydrophilic
A molecule is hydrophilic (“water loving”) if it dissolves more easily in water than in an organic phase, such as a lipid bilayer.
Hydrophobic
A molecule is hydrophobic (“water hating”) if it dissolves more easily in a lipid phase than in water
Hydrophobic Interactions
Weak interaction between two nonpolar groups or molecules arising through their mutual aversion to water.
Hydrostatic Pressure
Pressure exerted by a fluid at rest.
Hydrostatic Skeleton
A closed water-filled sac that acts as a semisolid support for an animal.
Hydroxyl Ion
OH−.
Hypercapnia
Higher than normal carbon dioxide levels.
Hyperglycemia
An elevated blood glucose level.
Hyperosmotic
A solution that has a higher osmolarity than another solution.
Hyperplasia
An increase in the number of cells in a tissue or organ.
Hyperpnea
Rapid Breathing.
Hyperpolarization
A change in the membrane potential of a cell from its normally negative
resting membrane potential to a more negative value; a relative increase in the negative charge on the inside of the cell membrane.
Hypertension
A condition in which arterial blood pressure is elevated above the normal level.
Hyperthermia
An elevation in body temperature (TB) above a desired point.
Hypertonic
A solution that has a combination of osmolarity and solute profile that leads to the efflux of water from the cell, resulting in a decrease in cell volume.
Hypertrophy
An increase in the size of cells in a tissue or organ.
Hyperventilation
Breathing rate or depth that is greater than needed for either oxygen supply or carbon dioxide removal.
Hypocapnia
Lower than normal carbon dioxide levels.
Hypoglycemia
Low levels of glucose in the blood.
Hypometabolism
A period when metabolic rate is lower than the normal resting rate.
Hypoosmotic
A solution that has a lower osmolarity than another solution.
Hypothalamic-Pituitary Portal System
A system of blood vessels within the hypothalamus and pituitary that carries hypothalamic hormones to the pituitary, where they regulate the release of pituitary hormones.
Hypothalamus
A region of the vertebrate forebrain that is involved in controlling body temperature, thirst, hunger, and many other physiological processes. Regulates the function of the pituitary.
Hypothermia
A decrease in body temperature (T_B) below a desired point.
Hypotonic
A solution that has a combination of osmolarity and solute profile that leads to the influx of water into the cell, resulting in an increase in cell volume.
Hypoventilation
Breathing rate or depth that is less than required for adequate gas exchange. For air breathers this usually involves insufficient breathing to allow the removal of carbon dioxide, rather than insufficient for oxygen supply; causes elevated blood carbon dioxide (hypercapnia) and respiratory acidosis.
Hypoxemia
Lower than normal blood oxygen levels.
Hypoxia
see also hypoxemia
Lower than normal oxygen; usually referring to environmental oxygen levels.
Hypoxic Pulmonary Vasoconstriction
Reduction of the diameter of the blood vessels in the lungs in response to low levels of oxygen in the lungs.
