Reproduction+in+Human

= Sexual reproduction = toc Sexual reproduction is the formation of a new individual following the union of two ** gametes **. In humans and the majority of other eukaryotes — plants as well as animals — the two gametes Gametes need = Sex Organs of the Human Male = The reproductive system of the male has two major functions: The male reproductive system contains two main divisions: the testes where sperm are produced, and the penis. In humans, both of these organs are outside the abdominal cavity.
 * differ in structure ("anisogamy") and
 * are contributed by different parents.
 * motility to be able to meet and unite
 * food to nourish the developing embryo.
 * production of sperm
 * delivery of these to the reproductive tract of the female.

Having the testes outside the abdomen facilitates temperature regulation of the sperm, which require specific temperatures to survive about 2-3 °C less than the normal body temperature i.e. 37°C.



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//Testes//
he //testes// are the male reproductive glands. Within each testis are over 800 coiled //seminiferous tubules//, Each testis is packed with over 800 coiled ** seminiferous tubules ** (laid end to end, they would extend more than 20 meters) where spermatogenesis occurs. They produce several thousand spermatozoa each second. Between the tubules, groups of other cells secrete the hormone testosterone. The ends of the tubules combine to form a single complex tubule, named the //epididymis//, which forms the exit duct from a testis. The testes are contained in the //scrotum//, a pouch of skin, connective tissue, and smooth muscle. Each testis is supported by a//spermatic cord// of fibrous tissue, along which run blood and lymph vessels, nerves, and the //deferent duct// (//vas deferens//) which carries the spermatozoa from the epididymis. The scrotum supports the testes external to the main parts of the body, maintaining a temperature of approximately 34 °C, which is required for successful production of spermatozoa. If the testicles remain too close to the body, it is likely that the increase in temperature will harm the spermatozoa formation, making conception more difficult. This is why the testes are carried in an external pouch viz. scrotum rather than within the abdomen; they normally remain slightly cooler than body temperature, facilitating sperm production.

// Seminal Vesicles //
The //seminal vesicles// are two pouches of fibrous muscular tissue, lined with columnar epithelium, lying behind the bladder. They join the deferent ducts, forming ejaculatory ducts. The seminal vesicles secrete a viscous fluid which provides an energy source for spermatozoa.

//Ejaculatory Ducts//
The // ejaculatory ducts // connect the separate deferent ducts and the seminal vesicles together, and link through the prostate gland into the urethra.

// Prostate Gland //
The //prostate gland// surrounds the urethra immediately below the bladder. It has an outer layer of fibrous tissue and smooth muscle, and a central core of glandular material. It secretes a thin lubricating fluid via numerous ducts into the urethra.

// Urethra //
The //urethra// in the male serves the dual purpose of carrying urine, and semen. The urethra originates at the bladder, passes through the prostate gland (where it is joined by the ejaculatory ducts), and along the length of the penis, to end at the external urethral orifice. The flow of fluid along the urethra is controlled by two sphincters, as described for the urinary system.

//Penis//
The //penis// is formed from three columns of erectile tissue and smooth muscle, supported by fibrous tissue. The urethra runs through the central //corpus spongiosum//, with lateral columns, the //corpora cavernosa//, on either side. The corpus spongiosum expands into the tip of the penis, or //glans penis//, which is normally covered by the //prepuce// or //foreskin//. (The prepuce is often surgically removed on health or religious grounds). The penis has a relatively large blood supply. In response to parasympathetic nervous stimulation, this increases, causing erection

Semen
// Semen // is the fluid passed out of the urethra (into the female vagina) during ejaculation. It consists of: an energy giving fluid from the seminal vesicles, a lubricating fluid from the prostate gland, mucus, and spermatozoa.

//Spermatozoa// resemble minuscule tadpoles in form, having an elongated round ‘head’, and a ‘tail’ with which they are able to propel themselves. They are amongst the smallest of structures in the body, being around 0.05mm in total length. 1ml of semen contains approximately 100 million spermatozoa.

Sperm production — spermatogenesis — takes place in the ** testes **.

An adult male manufactures over 100 million sperm cells each day. These gradually move into the **epididymis** where they undergo further maturation. The acidic environment in the epididymis keeps the mature sperm inactive.

In addition to making sperm, the testis is an ** endocrine gland **. Its principal hormone, ** testosterone **, is responsible for the development of the secondary sex characteristics of men such as the beard, deep voice, and masculine body shape. ** Testosterone is also essential for making sperm. **



Sperm
Sperm cells are little more than flagellated nuclei. Each consists of
 * a head, which has
 * an **acrosome** at its tip and
 * contains a haploid set of chromosomes in a compact, inactive, state.

=** //Female Reproductive System// **= The main purposes of the // female reproductive system // are the production of the eggs, or ova, and the protection of a fertilised ovum during its development into a baby In addition, the breasts provide milk for feeding the young infant during the early months of its life.
 * a **midpiece** containing mitochondria and a single centriole.
 * a **tail** which is a flagellum.



//Uterus//
The //uterus// is a hollow muscular organ in which a foetus develops after fertilisation. There are three main parts of the uterus: **Body**. This is the main part. **Fundus**. This is the area above the Fallopian tubes. **Cervix**. This is the opening into the uterus from the vagina. The uterus is composed from three layers of tissue: **Perimetrium**. (outer layer) This is formed by folds of peritoneum, enclosing the uterus, except at the sides, where the Fallopian tubes enter. **Myometrium**. (middle layer) This is formed from smooth muscle fibres and areolar tissue, together with blood vessels. **Endometrium**. (inner layer) This is formed from columnar epithelium, containing many mucus secreting glands. The uterus is supported in position, mainly by a system of ligaments, but with additional support from adjacent organs.

//Vagina//
The //vagina// is a tube, approximately 80mm long, which forms the external entry to the uterus. It is composed of stratified epithelium, supported by a layer of smooth muscle, with an outer layer of areolar tissue. The vagina does not contain secretory cells, but is kept moist by secretions from the uterus.

//Fallopian Tubes//
The //Fallopian tubes// (also known as //uterine tubes//) provide pathways for the transport of ova from the ovaries to the uterus. Being continuous with the uterus at their medial ends, they are composed from the same tissue layers, although the inner lining is ciliated. The lateral ends of the tubes divide into a number of projections, or //fimbriae//. The fimbriae ‘reach out’ towards the ovaries in order to catch ova as they are released during ovulation.

// Ovaries //
The //ovaries// are the female reproductive glands. Each ovary has a central medulla, composed of fibrous tissue, around which is a cortex made up from a framework of connective tissue containing ovarian follicles. Each //ovarian follicle// contains one ovum.

Ovulation
In response to hormonal stimulation from the pituitary gland, approximately every 28 days, one ovarian follicle matures and ruptures. This releases the ovum into the peritoneal cavity, where it is ‘caught’ by one of the fimbriae of the nearby Fallopian tube. The cilia in the Fallopian tube, together with peristalsis, propel the ovum towards the uterus. Prior to ovulation, the maturing follicle cells produce the hormone //oestrogen//. This causes a thickening of the endometrium in preparation for a fertilised ovum. After ovulation, the follicle lining cells develop into the //corpus luteum// through the action of luteinising hormone. They then secrete the hormone progesterone. This causes an increase in mucus secretion within the endometrium, in order to assist the movement of spermatozoa towards the ovum.

Menstruation
When the ovum is not fertilised, progesterone secretions from the corpus luteum cease, through their own action in inhibiting the production of luteinising hormone. About 14 days after ovulation, the internal lining of the uterus begins to break up, and is discharged, together with some blood and other secretions, via the vagina.

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