1. REPRODUCTIVE SYSTEM - 1
LECTURE 18
CH 20

2. 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

3. 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)

4. 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.

5. 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

6. Turner’s Syndrome XO

7. 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.

8. Male Reproductive System

9. Vasectomy

10. Male Reproductive System

11. 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.

12. 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.

13. Nitric Oxide and Erection

14. 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

15. 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.