Animal reproductive system

Eggs of various birds, a [[turtle, various cartilaginous fish, a cuttlefish and various butterflies and moths. (Click on image for key)|right|thumb|link=File:Adolphe_Millot_oeufs-fixed.jpg#Key]]

thumb|Cloaca of a red-tailed hawk

Estradiol (E2), also called oestrogen, oestradiol, is an estrogen steroid hormone and the major female sex hormone. It is involved in the regulation of female reproductive cycles such as estrous and menstrual cycles. Estradiol is responsible for the development of female secondary sexual characteristics such as the breasts, widening of the hips and a female pattern of fat distribution. It is also important in the development and maintenance of female reproductive tissues such as the mammary glands, uterus and vagina during puberty, adulthood and pregnancy. It also has important effects in many

type of steroid hormone

Oviparous animals are animals that reproduce by depositing unfertilized egg cells or fertilized zygotes outside the body (i.e., by laying or spawning) in metabolically independent incubation organs (eggs), which nurture the embryo into moving offspring (hatchlings) with little or no embryonic development within the mother. This is the reproductive method used by most animal species, as opposed to viviparous animals that develop the embryos internally and metabolically dependent on the maternal circulation, until the mother gives birth to live juveniles.

mammalian protein found in Homo sapiens

Gonadotropins are glycoprotein hormones secreted by gonadotropic cells of the anterior pituitary of vertebrates. They are central to the complex endocrine system that regulates normal growth, sexual development, and reproductive function. The hormone family includes the mammalian hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH), the placental/chorionic gonadotropins, human chorionic gonadotropin (hCG) and equine chorionic gonadotropin (eCG), as well as at least two forms of fish gonadotropins. LH and FSH are secreted by the anterior pituitary gland, while hCG and eCG ar

thumb|Ovipositor of Tettigoniidae|long-horned grasshopper (the two cerci are also visible)

steroid-producing cells in the interstitial tissue of the testis

thumb|400x400px|Diagram of a human spermatozoa showing the acrosome

The allantois ( ; : allantoides or allantoises) is one of the four membranes of the extraembryonic tissue arising from the yolk sac. It is a hollow sac-like structure filled with clear fluid that forms part of the developing conceptus in an amniote that helps the embryo exchange gases and handle liquid waste. The other extraembryonic membranes are the yolk sac, the amnion, and the chorion. In mammals these membranes are known as fetal membranes.

thumb|upright=1.4|A broken wild bird eggshell

Dihydrotestosterone (DHT, 5α-dihydrotestosterone, 5α-DHT, androstanolone or stanolone) is an endogenous androgen sex steroid and hormone primarily involved in the growth and repair of the prostate and the penis, as well as the production of sebum and body hair composition.

thumb|The claspers of a spotted wobbegong shark (Orectolobus maculatus) thumb|The claspers of a young spinner shark (Carcharhinus brevipinna) thumb|Life restoration of the extinct chimaera Ischyodus, showing the presence of a cephalic clasper on the head of males (as well as a pelvic clasper) but absent in females In biology, a clasper is a male anatomical structure found in some groups of animals, used in mating. thumb|300x300px|A close up view of a chimaera clasper (Hydrolagus collie). Note the many small tooth-like projections covering the exterior surface. thumb|Illustration of Harpagofut

thumb|The ventral side (underside) of a female American lobster, a member of the class [[Malacostraca. The gonopores are at the bases of the third walking leg, pointing towards the animal's tail.]] A gonopore, sometimes called a gonadopore, is a genital pore in many invertebrates. Hexapods, including insects, have a single common gonopore, except mayflies, which have a pair of gonopores. More specifically, in the unmodified female, it is the opening of the common oviduct, and in the male, it is the opening of the ejaculatory duct.

darts that some snails shoot into each other during mating

thumb|Aedeagus of Pentodon idiota thumb|Photomicrograph of the aedeagus of water scavenger beetle [[Tormissus linsi (from above)|right|220px]]

thumb|Spermatheca of Acanthoscurria geniculata (Brazilian Giant White Knee Tarantula) thumb|Variety of the structure of spermathecae in Phlebotominae (Diptera, Psychodidae) thumb|Female tarantula molt

physical barrier between the blood vessels and the seminiferous tubules of the animal testes

Estetrol (E4), or oestetrol, is one of the four natural estrogenic steroid hormones found in humans, along with estrone (E1), estradiol (E2), and estriol (E3). Estetrol is a major estrogen in the body. In contrast to estrone and estradiol, estetrol is a native estrogen of fetal life. Estetrol is produced exclusively by the fetal liver and is found in detectable levels only during pregnancy, with relatively high levels in the fetus and lower levels in the maternal circulation.

The discharge, by sperm, of a single, anterior secretory granule following the sperm's attachment to the zona pellucida surrounding the oocyte. The process begins with the fusion of the outer acrosomal membrane with the sperm plasma membrane and ends

Hyperestrogenism, hyperestrogenic state, or estrogen excess, is a medical condition characterized by an excessive amount of estrogenic activity in the body.

Hypergonadism is a condition where there is a hyperfunction of the gonads. It can manifest as precocious puberty, and is caused by abnormally high levels of testosterone or estrogen, crucial hormones for sexual development. In some cases, it may be caused by a tumor, which can be malignant, but is more commonly benign. Anabolic steroids may also be a major cause of high androgen and estrogen functional activity. Other possible causes include head injuries and brain inflammatory diseases. Hypergonadism may contribute to symptoms such as precocious puberty and abnormal facial hair growth in fema

medical condition

endocrine organ found in true toads

Gonocytes are the precursors of spermatogonia that differentiate in the testis from primordial germ cells around week 7 of embryonic development and exist up until the postnatal period, when they become spermatogonia. Germ cells operate as vehicles of inheritance by transferring genetic and epigenetic information from one generation to the next. Male fertility is centered around continual spermatogonia which is dependent upon a high stem cell population. Thus, the function and quality of a differentiated sperm cell is dependent upon the capacity of its originating spermatogonial stem cell (SSC

hormones activity during sexual motivation

class of ways animals produce their young