The Reproductive System Chapters 19,20

The Basic Structures The human reproductive system produces, stores, nourishes, and transports functional gametes. Fertilization is the fusion of male and female gametes. The reproductive system includes gonads (testes and ovaries), ducts, accessory glands and organs, and the external genitalia.

In males, the testes produce spermatozoa, which are expelled from the body in semen during ejaculation. The ovaries of a sexually mature female produce oocytes (immature ova) that travel along uterine tubes toward the uterus. The vagina connects the uterus with the exterior of the body.

The Male Reproductive System Spermatogenesis occurs in the testes and hormones from the hypothalamus, pituitary gland, and testes control male reproductive functions. Spermatozoa gravel along the epididymis, the ductus deferens, the ejaculatory duct, and the urethra before leaving the body. Accessory organs secrete products into the ejaculatory ducts and urethra. The scrotum encloses the testes, and the penis is an erectile organ.

In each testes, are a series of lobules In each testes, are a series of lobules. Seminiferous tubules within each lobule are the sites of sperm production. Between the seminiferous tubules are interstitial cells, which secrete sex hormones.

Seminiferous tubules contain spermatogonia, stem cells involved in spermatogenesis, and nurse cells, which sustain and promote the development of spermatozoa.

Sperm Each spermatozoon has a head, middle piece, and tail.

Pathway of Sperm Epididymis: regulates composition of the tubular fluid, recycles damaged spermatozoa. When leaving epididymis, spermatozoa are functionally mature but NOT mobile. Ductus deferens (vas deferens): goes from epididymis through inguinal canal into the body. Junction of seminal gland and ductus deferens creates ejaculatory duct which passes through the prostate gland and empties into the urethra.

Spermatogenesis Involves Three Processes 1. Mitosis: cell division of the spermatogonia produces spermatocytes 2. Meiosis: spermatocytes undergo meiotic cell division to produce immature gametes called spermatids. 3. Spermiogenesis: spermatids mature into spermatozoa which are shed into the lumen of the seminiferous tubule.

Seminal Gland (seminal vesicle): contributes 60% of volume of semen Seminal Gland (seminal vesicle): contributes 60% of volume of semen. Secretion contains fructose to nourish sperm Prostate Gland: secretes fluid that makes up about 30% of seminal fluid. It is slightly alkaline. Bulbo-urethral glands secrete an alkaline mucus that has lubricating properties Enzymes: seminal fluid includes a number of enzymes. A typical ejaculation is 3-5ml of semen which contains 20-100 million sperm/ml.

Hormones and Male Reproductive Function The pituitary gland releases FSH and LH FSH: promotes spermatogenesis LH (interstitial cell-stimulating hormone) causes the secretion of testosterone by interstitial cells. Testosterone: many functions Early(7th week to 6th months) causes the development of male duct system and accessory organs. Late (puberty) sexual maturation and appearance of secondary sex characteristics.

Female Reproductive System Oogenesis occurs in the ovaries and hormones from the pituitary gland and ovaries control female reproductive functions.

Ovaries Small, lumpy organs near the lateral walls of the pelvic cavity Responsible for The production of female gametes or ova The secretion of female sex hormones including estrogens and progestins The secretion of inhibin and the ovaries are involved in the negative-feedback control of FSH production

Oogenesis: ovum production Begins before a woman’s birth and continues until menopause. In the ovaries, the oogonia (stem cells) complete their mitotic divisions before birth. Between the 3rd and 7th months of fetal development the daughter cells (primary oocytes) begin meiosis. Meiosis stops at Prophase I and remains suspended until puberty 2 million oocytes in ovaries at birth; 400,000 remain at puberty

Follicle Development Specialized structures called ovarian follicles are the sites of oocyte growth and meiosis I. In the outer portion of each ovary are clusters of primary oocytes each surrounded by a single layer of follicle cells . This is the primordial follicle

At puberty the primordial follicles develop into primary follicles

The primary follicles gradually transform into secondary follicles with the accumulation of follicular fluid.

At the start of each ovarian cycle only a few secondary follicles are ready for further development. Under the influence of FSH, one follicle forms a tertiary follicle by days 10-14 of the ovarian cycle

Until this time, the primary oocyte has been suspended in Prophase I Until this time, the primary oocyte has been suspended in Prophase I. Rising levels of LH cause the primary oocyte complete meiosis I. This cell (secondary oocyte) is now haploid. A polar body has also been produced. The secondary oocyte begins meiosis II , but does NOT divide. Meiosis II will be completed ONLY if fertilization occurs.

Ovulation At ovulation the tertiary follicle releases the secondary oocytes into the pelvic cavity. The ciliated epithelium sweeps the secondary oocyte into the uterine tube.

The Luteal Phase The 14 day luteal phase begins at ovulation. The empty follicle collapses and forms the corpus luteum which releases progesterone. If fertilization does NOT occur, the corpus luteum degenerates after about 12 days and a new ovarian cycle begins.

The Uterus The uterus is a small pear-shaped organ about 3” long and 2” in diameter. The uterine wall is made up of an inner endometrium and a muscular myometrium and a perimetrium.

Uterine Cycle Averages 28 days in length Three phases: Menses: the degeneration of the endometrium triggered by a decline in progesterone. Proliferative Phase: epithelial cells multiply and spread across the surface of the endometrium. Stimulated by rising levels of estrogen. Uterine glands secrete a mucus rich in glycogen. Secretory Phase: Begins at ovulation. Uterine glands increase secretion and endometrium prepares for arrival of embryo. Stimulated by progestins and estrogens from corpus luteum. As hormone levels decline, the uterine cycle ends and menses begins.

See Spotlight on pages 660 and 661 in your book

Aging and Reproduction Females: menopause (ovulation and menstruation cease) occurs at ages 45-55 Males: male climacteric or andropause: occurs between ages 50 and 60 when levels of testosterone decrease and levels of FSH and LH increase.

Gestation consists of three stages of prenatal development First Trimester: all the basic components of the major organs systems appear Second Trimester: dominated by the development of organs and organ system to near completion Third Trimester: rapid fetal growth

Chapter 20: Development

Implantation