The Reproductive System

Negative feedback

High testosterone levels inhibit the release of GnRH by the hypothalamus, causing a reduction in LH secretion and lowering testosterone levels to normal levels.

Release of Gonadotropin-Releasing Hormone (GnRH)

The hypothalamus secretes the hormone at a rate and pace that remains relatively steady. As a result, plasma levels of FSH, LH, and testosterone remain within a relatively narrow range throughout a man's reproductive life.

Spermiogenesis (physical maturation)

The last step of spermatogenesis, each spermatid matures into a single spermatozoon, or sperm. The process of spermiogenesis takes roughly 5 weeks to complete.

Meiosis II

The secondary spermatocytes soon enter this stage, which yields four haploid spermatids, each containing 23 chromosomes. For each primary spermatocyte that enters meiosis, four spermatids are produced.

It monitors and adjusts the composition of the fluid produced by the seminiferous tubules, It acts as a recycling center for damaged spermatozoa, and It stores and protects spermatozoa and facilitates their functional maturation.

Three functions of epididymis:

Mitosis

Spermatogonia undergo cell divisions throughout adult life. Once daughter cell from each division remains in place while the other is pushed toward the lumen (space) of the seminiferous tubule. The displaced cells differentiate into primary spermatocytes, which prepare to begin meiosis.

Nurse Cell Stimulation

Under FSH stimulation, and in the presence of the testosterone from the interstitial cells, nurse cells. 1 promote spermatogenesis and spermiogenesis, 2 secrete androgen-binding protein (ABP), and 3 secrete inhibin in response to factors released by developing spermatozoa.

pituitary gland

When stimulated by GnRH, the anterior lobe of the ___ releases luteinizing hormone (LH) and follicle-stimulating hormone (FSH).

Secretion of Follicle-Stimulating Hormone (FSH)

targets primarily the nurse cells of the seminiferous tubules.

Secretion of Luteinizing Hormone (LH)

targets the interstitial cells of the testes.

Mitosis of spermatogonium

Each division of a diploid spermatogonium produces two daughter cells. One is a spermatogonium that remains in contact with the basement membrane of the tubule, and the other is a primary spermatocycte that is displaced toward the lumen.

Interstitial Cell Stimulation

LH induces the secretion of testosterone and other androgens by the interstitial cells of the testes.

Maintains libido (sexual drive) and related behaviors, Stimulation of bone and muscle growth, establishment and maintenance of male secondary sex characteristics, and maintenance of accessory glands and organs of the male reproductive system.

Peripheral Effects of Testosterone:

Meiosis I

Prior to the start, each primary spermatocyte contains 46 individual chromosomes. At the end of meiosis I, the daughter cells are called secondary spermatocytes. Every secondary spermatocyte contains 23 chromosomes, each of which consists of a pair of duplicate chromatids.

Mitosis of spermatogonium, Meiosis I, Meiosis II, and Spermiogenesis (physical maturation).

Spermatogenesis Stages.

Androgen binding protein

binds androgens within the seminiferous tubules which elevates the local concentration of androgens and stimulates the physical maturation of spermatids.

Inhibin

depresses the pituitary production of FSH, and perhaps the hypothalamic secretion of gonadotropin-releasing hormone (GnRH). The faster the rate of sperm production, the more inhibin is secreted. By regulating FSH and GnRH secretion, nurse cells provide feedback control of spermatogenesis.

Nurse cell environment

facilitates both spermatogenesis and spermiogenesis.

Meiosis

is a special form of cell division involved in gamete production. In human, gametes contain 23 chromosomes, half the amount found in somatic cells. As a result, the fusion of the nuclei of a male gamete and a female gamete produces a cell that has the normal number of chromosomes (46), rather than twice that number. In the seminiferous tubules, meiotic divisions that begin with primary spermatocytes produce spermatids, the undifferentiated male gametes.

Male reproductive function

is regulated by the complex interaction of hormones from the hypothalamus, anterior lobe of the pituitary gland, and the testes. The interaction of positive and negative feedback loops keep testosterone levels within a relatively narrow range until late in life.

Spermatogenesis

is the process of spermatozoa formation. Creation of sperm.