REPRODUCTIVE SYSTEM - 1 LECTURE 18 CH 20

Human Life Cycle Adult has 46 chromosomes 23 pairs = diploid meiosis occurs in gonads -- leads to gametes -- each is haploid, has 23 chromosomes --each is unique because of certain steps in meiosis that create genetic variation -- meiosis is not mitosis a zygote is a fertilized egg

Each human adult has 46 chromosomes (23 pairs) Each pair is called a homologous chromosome 22 autosomes and one pair of sex chromosomes XX = female; XY = male Each pair has 2 alleles of each gene Alleles are variant forms of a gene Both may be active or one may be silenced by “genomic imprinting” which refers to epigenetic changes (DNA methylation or modification of histones)

In females, one of the two X chromosomes is inactive. This produces a visible Barr Body. An easy way to visually determine the sex of a cell.

A region of the Y chromosome has been shown to code for a sex-determining factor, which leads to the development of testes XX males had a region of the Y chromosome inserted into the X SRY for sex-determining Region of Y Develop w/in 50 days

Turner’s Syndrome XO

Endocrine Regulation of Reproductive System Regulated by the hypothalamus Gonadotropin Releasing Hormone (GnRH) stimulates the anterior pituitary to release LH and FSH. These are called the gonadotropins. “tropin” means “stimulating effect” -- the gonads are stimulated puberty begins with the release of LH, which stimulates the formation of sex hormones. -- a person becomes sexually mature, not necessarily emotionally mature.

Male Reproductive System

Vasectomy

Male Reproductive System

Changes in Blood Flow Cause Erection Cross section through relaxed penis (a) Normally, smooth muscles encircling the arterioles leading into the penis are contracted, limiting blood flow.

Changes in Blood Flow Cause Erection Cross section through erect penis Sexual stimulation triggers the release of NO from parasympathetic axons into the corpora cavernosua and penile arteries and smooth muscle. NO activates guanylate cyclase, which converts GTP to cGMP, which closes Ca2+ channels. The lowered Ca2+ causes the relaxation of smooth muscles and vessel dilation, leading to erection. (b) During sexual excitement, these muscles relax, and blood flows into spaces within the penis. The swelling penis squeezes off the veins leaving the penis, thereby increasing the pressure produced by fluids within the penis and causing it to become elongated and firm.

Nitric Oxide and Erection

Semen = Sperm + Secretions Secretions from epididymis aid sperm maturation Seminal vesicle secretes fructose and prostaglandins Prostate-gland secretions buffer pH in the acidic vagina Bulbourethral gland secretes mucus

The Structures Involved in Spermatogenesis Section of the testis Seminiferous tubules Epididymis Vas deferens Cross section of a seminiferous tubule Sertoli cells: Nourish the developing sperm Spermatogonia Leydig cells Lie between the seminiferous tubules Secrete testosterone (a) A section of the testis, showing the location of the seminiferous tubules, epididymis, and vas deferens. (b) Cross section of a seminiferous tubule. The walls of the seminiferous tubules are lined with Sertoli cells and spermatogonia. As spermatogonia undergo meiosis, the daughter cells move inward, embedded in infoldings of the Sertoli cells. There they differentiate into sperm (spermatazoa), drawing on the Sertoli cells for nourishment. Mature sperm are freed into the central cavity of the tubules for transport to the penis. Testosterone is produced by the interstitial cells in the spaces between tubules.