Testosterone in the context of Leydig cell

Castration is any action, surgical, chemical, or otherwise, by which a male loses use of the testicles: the male gonad. Surgical castration is bilateral orchiectomy (excision of both testicles), while chemical castration uses pharmaceutical drugs to deactivate the testes. Some forms of castration cause sterilization (permanently preventing the castrated person or animal from reproducing); it also greatly reduces the production of hormones, such as testosterone and estrogen. Surgical castration in animals is often called neutering.

Castration of animals is intended to favor a desired development of the animal or of its habits, as an anaphrodisiac or to prevent overpopulation. The parallel of castration for female animals is spaying. Castration may also refer medically to oophorectomy in female humans and animals.

An ox (pl.: oxen), also known as a bullock (in British, Australian, and Indian English), is a large bovine, trained and used as a draft animal. Oxen are commonly castrated adult male cattle, because castration inhibits testosterone and aggression, which makes the males docile and safer to work with. Cows (intact females) or bulls (intact males) may also be used in some areas.

Oxen are used for ploughing, for transport (pulling carts, hauling wagons and even riding), for threshing grain by trampling, and for powering machines that grind grain or supply irrigation among other purposes. Oxen may be also used to skid logs in forests, particularly in low-impact, select-cut logging.

A testicle, also called testis (pl. testes) is the male gonad in all gonochoric animals, including humans, and is homologous to the ovary, which is the female gonad. Its primary functions are the production of sperm and the secretion of androgens, primarily testosterone.

The release of testosterone is regulated by luteinizing hormone (LH) from the anterior pituitary gland. Sperm production is controlled by follicle-stimulating hormone (FSH) from the anterior pituitary gland and by testosterone produced within the gonads.

The fight-or-flight or the fight-flight-freeze-or-fawn (also called hyperarousal or the acute stress response) is a physiological reaction that occurs in response to a perceived harmful event, attack, or threat to survival. It was first described by Walter Bradford Cannon in 1914 to which he referred to as "the necessities of fighting or flight" in 1915. His theory states that animals react to threats with a general discharge of the sympathetic nervous system, preparing the animal for fighting or fleeing. More specifically, the adrenal medulla produces a hormonal cascade that results in the secretion of catecholamines, especially norepinephrine and epinephrine. The hormones estrogen, testosterone, and cortisol, as well as the neurotransmitters dopamine and serotonin, also affect how organisms react to stress. The hormone osteocalcin might also play a part.

This response is recognised as the first stage of the general adaptation syndrome that regulates stress responses among vertebrates and other organisms.

Male (symbol: ♂) is the sex of an organism that produces the gamete (sex cell) known as sperm, which fuses with the larger female gamete, or ovum, in the process of fertilisation. A male organism cannot reproduce sexually without access to at least one ovum from a female, but some organisms can reproduce both sexually and asexually. Most male mammals, including male humans, have a Y chromosome, which codes for the production of larger amounts of testosterone to develop male reproductive organs.

In humans, the word male can also be used to refer to gender, in the social sense of gender role or gender identity.

The endocrine system is a messenger system in an organism comprising feedback loops of hormones that are released by internal glands directly into the circulatory system and that target and regulate distant organs. In vertebrates, the hypothalamus is the neural control center for all endocrine systems.

In humans, the major endocrine glands are the thyroid, parathyroid, pituitary, pineal, and adrenal glands, and the (male) testis and (female) ovaries. The hypothalamus, pancreas, and thymus also function as endocrine glands, among other functions. (The hypothalamus and pituitary glands are organs of the neuroendocrine system. One of the most important functions of the hypothalamus—it is located in the brain adjacent to the pituitary gland—is to link the endocrine system to the nervous system via the pituitary gland.) Other organs, such as the kidneys, also have roles within the endocrine system by secreting certain hormones. The study of the endocrine system and its disorders is known as endocrinology.The thyroid secretes thyroxine, the pituitary secretes growth hormone, the pineal secretes melatonin, the testis secretes testosterone, and the ovaries secrete estrogen and progesterone.

The rut (from the Latin rugire, meaning "to roar") is the mating season of certain mammals, which includes ruminants such as deer, sheep, camels, goats, pronghorns, bison, giraffes and antelopes, and extends to others such as skunks and elephants. The rut is characterized in males by an increase in testosterone, exaggerated sexual dimorphisms, increased aggression, and increased interest in females. The males of the species may mark themselves with mud, undergo physiological changes or perform characteristic displays in order to make themselves more visually appealing to the females. Males also use olfaction to entice females to mate using secretions from glands and soaking in their own urine.

During the rut (known as the rutting period and in domestic sheep management as tupping), males often rub their antlers or horns on trees or shrubs, fight with each other, wallow in mud or dust, self-anoint, and herd estrus females together. These displays make the male conspicuous and aid in mate selection.

Progestogens, also sometimes written progestins, progestagens or gestagens, are a class of natural or synthetic steroid hormones that bind to and activate the progesterone receptors (PR). Progesterone is the major and most important progestogen in the body. The progestogens are named for their function in maintaining pregnancy (i.e., progestational), although they are also present at other phases of the estrous and menstrual cycles.

The progestogens are one of three types of sex hormones, the others being estrogens like estradiol and androgens/anabolic steroids like testosterone. In addition, they are one of the five major classes of steroid hormones, the others being the androgens, estrogens, glucocorticoids, and mineralocorticoids, as well as the neurosteroids. All endogenous progestogens are characterized by their basic 21-carbon skeleton, called a pregnane skeleton (C21). In similar manner, the estrogens possess an estrane skeleton (C18), and androgens, an androstane skeleton (C19).

A steroid is an organic compound with four fused rings (designated A, B, C, and D) arranged in a specific molecular configuration.

Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and as signaling molecules. Examples include the lipid cholesterol, sex hormones estradiol and testosterone, anabolic steroids, and the anti-inflammatory corticosteroid drug dexamethasone. Hundreds of steroids are found in fungi, plants, and animals. All steroids are manufactured in cells from a sterol: cholesterol (animals), lanosterol (opisthokonts), or cycloartenol (plants). All three of these molecules are produced via cyclization of the triterpene squalene.

In organic chemistry, a ketone /ˈkiːtoʊn/ is an organic compound with the structure R−C(=O)−R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group −C(=O)− (a carbon-oxygen double bond C=O). A ketone derived from an alkane is an alkanone. The simplest ketone is acetone (where R and R' are methyl), with the formula (CH₃)₂CO. Many ketones are of great importance in biology and industry. Examples include many sugars (ketoses), many steroids, e.g., testosterone, and the solvent acetone.

Sex-determining region Y protein (SRY), or testis-determining factor (TDF), is a DNA-binding protein (also known as gene-regulatory protein/transcription factor) encoded by the SRY gene that is responsible for the initiation of male sex determination in therian mammals (placentals and marsupials). SRY is an intronless sex-determining gene on the Y chromosome. Mutations in this gene lead to a range of disorders of sex development with varying effects on an individual's phenotype and genotype.

SRY is a member of the SOX (SRY-like box) gene family of DNA-binding proteins. When complexed with the steroidogenic factor 1 (SF-1) protein, SRY acts as a transcription factor that causes upregulation of other transcription factors, most importantly SOX9. Its expression causes the development of primary sex cords, which later develop into seminiferous tubules. These cords form in the central part of the yet-undifferentiated gonad, turning it into a testis. The now-induced Leydig cells of the testis then start secreting testosterone, while the Sertoli cells produce anti-Müllerian hormone. Effects of the SRY gene, which normally take place 6–8 weeks after fetus formation, inhibit the growth of female anatomical structure in males. The gene also contributes towards developing the secondary sexual characteristics of males.

An androgen (from Greek andr-, the stem of the word meaning 'man') is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors. This includes the embryological development of the primary male sex organs, and the development of male secondary sex characteristics at puberty. Androgens are synthesized in the testes, the ovaries, and the adrenal glands.

Androgens increase in both males and females during puberty. The major androgen in males is testosterone. Dihydrotestosterone (DHT) and androstenedione are of equal importance in male development. DHT in utero causes differentiation of the penis, scrotum and prostate. In adulthood, DHT contributes to balding, prostate growth, and sebaceous gland activity.

Gynecomastia (also spelled gynaecomastia) is the non-cancerous enlargement of one or both breasts in men due to the growth of breast tissue as a result of a hormone imbalance between estrogens and androgens. Physically speaking, gynecomastia is completely benign, but it is associated with significant psychological distress, social stigma, and dysphoria.

Gynecomastia can be normal in newborn male babies due to exposure to estrogen from the mother, in adolescent boys going through puberty, in older men over the age of 50, and in obese men. Most occurrences of gynecomastia do not require diagnostic tests. Gynecomastia may be caused by abnormal hormone changes, any condition that leads to an increase in the ratio of estrogens/androgens such as liver disease, kidney failure, thyroid disease and some non-breast tumors. Alcohol and some drugs can also cause breast enlargement. Other causes may include Klinefelter syndrome, metabolic dysfunction, or a natural decline in testosterone production. This may occur even if the levels of estrogens and androgens are both appropriate, but the ratio is altered.

The African bush elephant (Loxodonta africana), also known as the African savanna elephant, is a species of elephant native to sub-Saharan Africa. It is one of three extant elephant species and, along with the African forest elephant, one of two extant species of African elephant. It is the largest living terrestrial animal, with fully grown bulls reaching an average shoulder height of 3.04–3.36 metres (10–11 ft) and a body mass of 5.2–6.9 tonnes (11,000–15,000 lb); the largest recorded specimen had a shoulder height of 3.96 metres (13 ft) and an estimated body mass of 10.4 tonnes (23,000 lb). The African bush elephant is characterised by its long prehensile trunk with two finger-like processes; a convex back; large ears which help reduce body heat; and sturdy tusks that are noticeably curved. The skin is grey with scanty hairs, and bending cracks which support thermoregulation by retaining water.

The African bush elephant inhabits a variety of habitats such as forests, grasslands, woodlands, wetlands and agricultural land. It is a mixed herbivore feeding mostly on grasses, creepers, herbs, leaves, and bark. The average adult consumes about 150 kg (330 lb) of vegetation and 230 L (51 imp gal; 61 US gal) of water each day. A social animal, the African bush elephant often travels in herds composed of cows and their offspring. Adult bulls usually live alone or in small bachelor groups. During the mating season, males go through a process called musth, a period of high testosterone levels and heightened aggression. For females, the menstrual cycle lasts three to four months, and gestation around 22 months, the longest of any mammal.