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Haploid is the designation given to a cell with a single set of chromosomes, characteristic of gametes. In humans, a single set is 23 chromosomes.


Hematoxylin and eosin (H&E) staining refers to the process in which hematoxylin and eosin reagents are used to visualize the morphology of tissue within sections. Hematoxylin commonly stains nuclei of cells blue while eosin acts as a counterstain, which will color other structures pink/red.

Histology is the study of cells and tissues at the microscopic level. It is a branch of anatomy dealing with tissue structure.

A histone is a protein located in the nucleus of eukaryotic cells that organizes DNA into compact structures.

Histotroph is the complex mixture of molecules secreted into or transported into the uterine lumen. Histotroph includes nutrient transport proteins, ions, mitogens, cytokines, lymphokines, enzymes, hormones, growth factors, proteases and their inhibitors, amino acids, glucose, fructose, vitamins, and other substances. Histotroph is a primary source of nutrition for mammalian conceptus development. In humans, its importance continues throughout the first trimester of pregnancy until hematotrophic nutrition is established.

The term homologous refers to chromosomes that have the same pattern of genes.

Hormonal contraception or hormonal birth control refers to any medication or medical preparation that contains either estrogen or progesterone or a combination of the two hormones that a woman takes in order to prevent a pregnancy from occurring. Hormonal birth control is often prescribed to treat other medical conditions, as well, such as acne, heavy periods, and relief for the symptoms of PCOS, endometriosis, etc. Hormonal contraception may be taken orally, implanted, injected, absorbed via a patch on the skin’s surface, or placed inside the vagina. Hormonal contraception acts by either preventing the ovulation of a matured egg from the ovary each month, by making the cervix more difficult for the sperm to pass through, or by making the lining of the uterus less capable of supporting the implantation of an embryo.

A hormone is a molecule synthesized by specialized cells in an organ that travels through the blood stream and affects other cells in the body.

Hormone (or endocrine) disruptors are substances that interfere with the proper functioning of the endocrine system (i.e., the production, release, transport, and regulation of hormones in the body). Classes of endocrine disruptors include synthetic chemicals found in the environment, plastics, pesticides, and various pollutants. Exposure to such substances has been linked to various pathologies in both animals and humans.

Hormone replacement therapy (HRT) is a medical treatment used to lessen the symptoms of menopause, such as hot flashes, night sweats, and vaginal dryness. Doctors may prescribe pills, creams, or skin patches containing the hormones estrogen or progesterone (alone or in combination) to mimic naturally-occurring levels of hormones produced by the ovaries prior to the onset of menopause.

Hormone therapy is a medical treatment for cancer. Because certain cancers are hormonally responsive, especially those involving the reproductive system, the goal of hormone therapy is to suppress tumor growth and spread by altering hormone production and activity in the body.

Hot flashes (or flushes) are common symptoms of menopause characterized by a sense of significantly increased bodily temperature, rapid heart rate, perspiration, and a flushed appearance of the face. Hot flashes occur with great frequency in the early stages of menopause, from a few times per week to multiple times per day. Though most menopausal women experience hot flashes to some degree, it is possible to go through menopause without ever experiencing a hot flash.


Human chorionic gonadotropin (hCG) is a protein hormone produced by a developing embryo which stimulates progesterone production essential for the maintenance of pregnancy. It can be detected in maternal blood as early as 10 days after fertilization occurs. It is often used as a biomarker to detect pregnancy.

Hydrocephaly refers to a build-up of cerebrospinal fluid in the brain. This is dangerous, as the excess fluid increases pressure and can compress and permanently damage the brain. Hydrocephaly usually accompanies spina bifida and is often a result of obstructed flow of cerebrospinal fluid in the ventricular system before birth.

A hydrogel is a polymer network that is highly swollen with water and has a solid-like structure.

The hymen is a ring of tissue on the rim of the vaginal opening. This tissue can be torn during sexual intercourse or other means of penetration, such as tampon use during menstruation.

Hyperovulation in humans refers to the production and release of more than one egg during a menstrual cycle. Hyperovulation can occur naturally or be stimulated via hormone treatments for the purposes of egg donation in third-party reproduction. Under normal conditions, when more than one egg is released, the chances of conceiving fraternal twins or triplets is increased. Stimulated hyperovulation involves several drugs and the careful monitoring of hormone levels and ovarian status using an ultrasound. Once mature, follicles are punctured during the egg retrieval procedure and evaluated for quality before being used for in vitro fertilization (IVF).

Hyperplasia is an increase in cell number in an organ or tissue, which could be an indication of abnormal or precancerous changes.

Hyperploidy is a state in which cells contain one or more extra chromosomes. Humans normally have 46 chromosomes per cell, but if a human has 47 or more chromosomes per cell, then that person is hyperploid. Trisomy 21 (commonly called Down Syndrome) is one example of hyperploidy because there are three copies of chromosome 21.

Hypoblast is the underside of the embryonic disk, which arose from the inner cell mass during the late blastula and early trophoblast stages of embryonic growth. These cells give rise to the yolk sac, the extra-embryonic tissue that will help support embryonic growth.

Hypogonadism is a condition of insufficient function of the gonads. The gonads produce gametes and sex hormones. In females, the ovaries produce ova (eggs), estrogens, and progestins; in males, the testes produce sperm and androgens. Sexual development and fertility may be impaired in hypogonadal individuals.

Hypoploidy is a state in which cells contain one or more fewer chromosomes than what is normal. Humans normally have 46 chromosomes per cell, but if a human has 45 or less chromosomes per cell, that person is hypoploid. One example of a hypoploid human disorder is Turner syndrome, where females have only one copy of the X sex chromosome.

The hypothalamus synthesizes and releases GnRH and is the portion of the brain that links the endocrine system to the nervous system. The release of GnRH stimulates the synthesis of gonadotrophins (LH and FSH) by the pituitary gland.

A hysterectomy is the surgical removal of a woman’s uterus.