Human Anatomy and Physiology Chapter 27 – Reproductive System

The Reproductive System Functions: Produce sex cells (eggs and sperm) Permit the joining of the sex cells Provide an environment for the development of a fertilized egg (only in the female)

Male Reproductive System The male gonads (organs that produce sex cells) are the testes. The testes are held within the scrotum Optimum sperm production occurs at about 3° C cooler than internal body temperature The scrotum helps to regulate the temperature of the testes The dartos and cremaster muscles Figures 27.1 and 27.2

Male Reproductive System The penis contains erectile tissue – Figure 27.4

Male Reproductive System Inside the testes there is a series of coiled tubes called seminiferous tubules (ST) these are the site of sperm production they have a total length of nearly half a mile! Outside the ST are the interstitial or Leydig cells that produce testosterone Figure 27.3

Male Reproductive System (cont.) Spermatogenesis about 400 million sperm are produced each day! Inside the ST there are two cell types: Spermatogenic cells – these will become sperm Sertioli cells (sustentacular cells) – help nourish the germ cells They also form the blood-testis barrier Figure 27.8

Male Reproductive System (cont.) Germ Cells Spermatogonia – around the periphery of the ST Divide by mitosis to start the process of sperm production One cell  spermatocyte, One cell  spermatogonia The spermatocytes then proceed through meiosis to produce functional sperm cells Figure 27.8

Male Reproductive System (cont.) Mature sperm have three distinct parts: head - nucleus and acrosome midpiece - contains mitochondria tail - flagellum for motility Figure 27.9

Male Reproductive System (cont.) Sperm produced in the testes mature in the epididymis They are also stored here for as long as several months the epididymis is connected to the urethra by a long tube called the vas deferens (ductus deferens) vasectomy - severing of the vas deferens Figure 27.1 and Figure from other text

Male Reproductive System (cont.) Before leaving the body, sperm are mixed with a fluid seminal fluid + sperm = semen

Male Reproductive System (cont.) Seminal fluid is produced by three glands: seminal vesicles – (60%) mucus, fructose, fibrinogen, prostaglandins prostate gland – (30%) enzymes, clotting factors bulbourethral gland – (5%) mucus The remaining 5% of semen is composed of sperm Normal sperm count is 75-400 million sperm per ml of semen Figure 27.1

Male Reproductive System (cont.) Hormonal Regulation in Males Hypothalamus – Gonadotropin-releasing hormone (GnRH) Stimulates the release of the gonadotropins from the anterior pituitary gland: Luteinizing Hormone (LH) – increases testosterone production in the Leydig cells Follicle-Stimulating Hormone (FSH) – binds to Sertioli cells and stimulates sperm cell production Figure 27.10

Male Reproductive System (cont.) Puberty – onset of sexual maturity Human chorionic gonadotropin is produced by the placenta during fetal development This stimulates the release of testosterone for initial male sex organ development After birth, very little testosterone is produced until puberty

Male Reproductive System (cont.) At puberty the hypothalamus increases GnRH secretion This in turn increases LH and FSH secretion resulting in testosterone production Effects of testosterone Development and enlargement of male reproductive system Stimulates hair production on face, legs, chest, pubic region (and back, occasionally)

Male Reproductive System (cont.) Increases rate of sebaceous gland secretion Can result in acne Increases metabolism, RBC production, and protein synthesis Causes rapid bone growth (but also stimulates the closure of the epiphyseal growth plate)

Female Reproductive System The female gonads are the ovaries the ovaries alternate in producing one egg per month The ovaries also produce estrogen and progesterone (the female sex hormones) Anatomy - Figures 27.11 and 27.14

Female Reproductive System (cont.) Oogenesis There are many follicles within the ovaries each follicle contains an immature egg there are about 2 million follicles at birth 300,000-400,000 at puberty only ~400 are ever released as mature eggs the egg is released from the ovaries during ovulation The corpus luteum is a hormone-secreting gland in the ovary Figures 27.12 and 27.19

Female Reproductive System (cont.) Puberty Marked by menarche (the first menstrual period) Reproductive organs and breasts enlarge and develop Puberty results from estrogen and progesterone production

Female Reproductive System (cont.) The Menstrual Cycle Typically the cycle lasts 28 days Includes both the ovarian and uterine cycles

Female Reproductive System (cont.) The Ovarian Cycle: Days 1-14 are the Follicular Phase Day 14 – Ovulation Days 14-28 are the Luteal Phase

Female Reproductive System (cont.) The Follicular Phase Early in the cycle GnRH secretion increases Effect? FSH and LH stimulate the development of a follicle and The production of estrogen by the ovary

Female Reproductive System (cont.) A surge of LH results in ovulation It also leads to the development of the corpus luteum The corpus luteum secretes estrogen and progesterone If fertilization does not occur, the cells of the corpus luteum degenerate Estrogen and progesterone secretion then rapidly declines and the cycle starts over Figures 27.21 and 27.22

Female Reproductive System (cont.) The Uterine Cycle: Days 1-5: Menstrual Phase the endometrium is sloughed off Days 6-14: Proliferative Phase endometrium thickens and prepares for pregnancy Caused by estrogen and progesterone Days 15-28: Secretory Phase endometrium continues to thicken and secretions increase Figure 27.22, Figure from other text, and CD

Female Reproductive System (cont.) Menopause - period when uterine cycles and ovulation cease usually occurs between the ages of 45 and 55

Fertilization and Pregnancy Fertilization occurs in the fallopian tubes If the egg is fertilized, human chorionic gonadotropin is released This keeps the corpus luteum from degenerating and stops the uterine cycle The embryo can become embedded in the uterine wall Figures from other text and 28.4

Fertilization and Pregnancy Timing of intercourse: The egg is only viable for 12-24 hours after ovulation Sperm cells can survive for 24-72 hours Therefore intercourse must occur between days 11-15 in the menstrual cycle Even given the right timing, fertilization is not certain Figure 28.2 and other figure

Fertilization and Pregnancy Twins: Fraternal – 2 eggs released and fertilized Identical Twins – 1 egg separates to form 2 babies Figures from other text

Methods of Birth Control Table and Figures from other text

Methods of Birth Control Discussion

Infertility 15% of all couples in the US cannot have children these couples would be considered sterile Another 10% have fewer children than they wish these couples are termed infertile The most frequent causes of infertility in females are: blocked oviducts endometriosis - presence of uterine tissue outside the uterus The most frequent cause of infertility in males is: low sperm count

Alternative Methods of Reproduction Artificial Insemination - sperm are placed in the vagina by a physician sperm from donor concentrated sperm from husband with low sperm count In Vitro Fertilization - sperm and egg are mixed in a test tube fertilized egg is placed in the female’s uterus

Alternative Methods of Reproduction (cont.) Gamete Intrafallopian Transfer - eggs and sperm are mixed in a test tube they are immediately injected into the fallopian tubes Surrogate Mothers - individuals donate eggs and/or sperm the surrogate mother carries the fetus