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Biology LibreTexts

25.8: Glossary: H

  • Page ID
    17832
  • habitat

    natural environment in which a species lives and to which it is adapted

    habitat loss

    destruction or disruption of a natural habitat, most often due to human actions such agriculture, forestry, mining, or urbanization

    hair

    filament made of tightly packed, keratin-filled keratinocytes that grows out a hair follicle in the dermis of the skin

    hair follicle

    structure in the dermis of skin where a hair originates

    hair root

    part of a hair that is located within the hair follicle and consists of living keratinocytes

    hair shaft

    part of a hair that is visible above the surface of the skin and consists of dead keratinocytes

    hallucinogen

    type of psychoactive drug that causes hallucinations and other perceptual anomalies, as well as subjective changes in thoughts, emotions, and consciousness

    haploid

    having only one chromosome of each type, or half the number of chromosomes of a diploid cell

    Hardy-Weinberg theorem

    founding principle of population genetics that proves allele and genotype frequencies do not change in a population in which the forces of evolution (mutation, natural selection, genetic drift, and migration) are not operating

    Hashimoto’s thyroiditis

    autoimmune disorder in which the immune system destroys the thyroid gland, causing insufficient secretion of thyroid hormones

    hearing

    ability to sense sound waves

    heart

    muscular organ in the chest that pumps blood through blood vessels when it contracts

    heart attack

    blockage of blood flow to heart muscle tissues that may result in the death of cardiac muscle fibers

    heat index (HI)

    number that combines air temperature and relative humidity to indicate how hot the air feels due to the humidity

    helminth

    parasitic worm such as tapeworm, pinworm, or hookworm

    hematopoiesis

    process in which red blood cells, white blood cells, and platelets are produced by red bone marrow

    hemisphere

    one of two halves (left and right) of the cerebrum of the human brain

    hemodialysis

    medical procedure for patients with kidney failure in which wastes and excess water are artificially filtered out of blood by passing it through a machine

    hemoglobin

    oxygen-binding protein containing iron that is the principal component of red blood cells

    hemoglobin C

    abnormal hemoglobin variant found mainly in West and North Africa that is a genetic adaptation to malaria

    hemoglobin E

    abnormal hemoglobin variant found mainly in South and Southeast Asia that is a genetic adaptation to malaria

    hemoglobin S

    abnormal hemoglobin variant found in sub-Saharan Africa, the Middle East, and India that is the single most effective genetic adaptation to malaria

    hemolytic disease of the newborn (HDN)

    type of anemia in which red blood cells in a Rhesus positive fetus are destroyed by antibodies to the Rhesus antigen produced by a Rhesus negative mother

    hemophilia

    any of several genetic disorders that cause dysfunction in the blood-clotting process, leading to uncontrolled bleeding from even minor injuries

    herbivore

    consumer that eats producers such as plants or algae

    herd immunity

    protection from infection of nonvaccinated people in a population because most of the people around them are vaccinated and immune to the infection

    heterotroph

    organism that obtains energy by consuming other organisms

    heterozygote

    organism that inherits two different alleles for a given gene

    high-altitude sickness

    acute illness that results from hypoxia at high altitude and includes symptoms such as fatigue, shortness of breath, headache, and dizziness

    histamine

    chemical released by injured or infected cells or by certain immune system cells that triggers inflammation or an allergic reaction

    homeobox gene

    one of many genes that regulate early development of the organism

    homeostasis

    condition in which a system such as the human body is maintained in a more-or-less steady state

    homeostat

    physiological mechanism that helps maintain homeostasis in an organism; also called homeostatic mechanism

    homeostatic imbalance

    condition in which cells may not get everything they need or toxic wastes may accumulate because of the failure of a homeostatic mechanism

    hominid

    any member of the family of the primate order that includes humans and great apes

    hominin

    any human or human ancestor that evolved after the human lineage diverged from the chimpanzee lineage about 6 million years ago

    Homo

    genus in which the only living species is Homo sapiens

    Homo denisova

    extinct species of archaic humans that lived in Asia beginning about 400,000 years ago and interbred with Neanderthals and early modern Homo sapiens; also called Denisovans

    Homo erectus

    early species in the genus Homo that first evolved about 1.9 million years ago in East Africa, migrated to Eurasia before going extinct about 800,000 years ago, and was probably ancestral to Homo heidelbergensis

    Homo floresiensis

    extinct species of archaic humans that lived on Flores Island in Indonesia from about 100,000 to 60,000 years ago and were very small in size

    Homo habilis

    first known species in the genus Homo that lived from about 2.5 to 1.4 million years ago in East Africa and probably was ancestral to Homo erectus

    Homo heidelbergensis

    transitional species in the genus Homo that probably evolved from Homo erectus about 800,000 years ago and evolved into Homo neanderthalensis and early Homo sapiensaround 200,000 years ago

    homologous chromosomes

    pair of chromosomes that have the same size and shape and contain the same genes

    homologous structure

    structure that is similar in related species because it was inherited from a common ancestor; or structure that develops from the same undifferentiated embryonic tissue in males and females of the same species, such as the testis and ovary in humans

    Homo neanderthalensis

    extinct species of archaic humans that lived in Europe and Asia between about 400,000 and 30,000 years ago; also called Neanderthals

    homozygote

    organism that inherits two alleles of the same type for a given gene

    hormonal contraception

    use of hormones such as estrogen and/or progesterone to prevent pregnancy by interfering with ovulation

    host

    species that is harmed in a parasitic relationship with another species

    human biology

    scientific study of the anatomy, physiology, genetics, evolution, and ecology of the human species

    human genome

    all of the DNA of the human species

    Human Genome Project

    international science project that sequenced all 3.3 billion base pairs of the human genome

    human immunodeficiency virus (HIV)

    virus transmitted through body fluids or mucous membranes that infects and destroys helper T cells and may eventually cause acquired immunodeficiency syndrome (AIDS)

    human papillomavirus (HPV)

    sexually transmitted virus that may cause genital warts and cervical cancer

    hunting and gathering

    type of subsistence strategy that includes hunting wild animals and gathering wild plants and that was utilized by humans from Homo erectus until at least 10,000 years ago

    hunting response

    process of alternating vasoconstriction and vasodilation in extremities that are exposed to cold

    hydrogen bond

    relative weak chemical bond that forms between molecules of the same substance, such as between molecules of water

    hydropower

    renewable, nonpolluting energy that can be obtained from moving water and used to generate electricity

    hyperopia

    vision problem in which close objects are out of focus but distant vision is unaffected; also called farsightedness

    hypersecretion

    secretion of more than the normal amount of a substance, such as secretion of too much hormone by an endocrine gland

    hypertension

    persistently high blood pressure, generally defined as 140/90 mm Hg or higher

    hyperthermia

    dangerous increase in core body temperature above 40.6 degrees C (105 degrees F)

    hyperthyroidism

    disorder in which the thyroid gland produces excessive amounts of hormones

    hypertrophy

    increase in the size of a structure, such as an increase in the size of a muscle through exercise

    hyperventilation

    breathing more quickly and shallowly than normal

    hyposecretion

    secretion of less than the normal amount of a substance, such as an endocrine hormone

    hypothalamus

    part of the brain that secretes hormones and connects the brain with the endocrine system

    hypothermia

    dangerous decrease in core body temperature below 34.4 degrees C (94 degrees F)

    hypothesis

    logical answer to a scientific question that may be tested in a scientific investigation

    hypothyroidism

    disorder in which the thyroid gland produces inadequate amounts of hormones

    hypoxia

    relative lack of oxygen, as, for example, at high altitude