Reproductive System part 1.pdf

Reproductive System Marie A. Román Martínez, PhD Department of Biology Office hours: by appointment Email: [email protected] Copyright-This presentation is intended for educational purpose only. No part of this presentation may be reproduced or transmitted in any form without written permission. O...

Reproductive System Marie A. Román Martínez, PhD Department of Biology Office hours: by appointment Email: [email protected] Copyright-This presentation is intended for educational purpose only. No part of this presentation may be reproduced or transmitted in any form without written permission. Objectives 1. Define the key terms of reproduction. 2. Describe the locations and functions of the male reproductive organs. 3. Describe spermatogenesis. 4. Describe the actions of testosterone. 5. Describe the location and functions of the organs of the female reproductive system. 6. Describe oogenesis and the development of the corresponding ovarian follicles. 7. Describe the ovarian and menstrual cycles and their regulation by hormones. 8. Describe the structure of mammary glands and breasts. 9. Describe how various methods of birth control work. 10. Describe the common disorders of the reproductive system. 2 Reproductive System Marie A. Román Martínez, PhD Department of Biology Office hours: by appointment Email: [email protected] Copyright-This presentation is intended for educational purpose only. No part of this presentation may be reproduced or transmitted in any form without written permission. Reproductive System Reproduction is the process by which life is sustained from one generation to the next. The ovaries and testes are the gonads and form the gametes (sex cells). Other reproductive structures carry the gametes to where they may unite. Sexual maturation, formation of sex cells, and pregnancy are tightly controlled by hormones secreted by the pituitary gland and the gonads. 4 Male Reproductive System Primary functions of male reproductive system: Production of male sex hormones. Formation of sperm (male gamete). Placement of sperm in the female reproductive tract where one sperm can unite with a secondary oocyte (female gamete). Organs of male reproductive system: Paired testes Accessory ducts Accessory glands External genitalia 5 Testes Male gonads or sex glands. Septa divide testis into lobules. Each lobule holds several seminiferous tubules. Seminiferous tubules: Lined with spermatogenic epithelium. Formed of spermatogenic and supporting cells. 6 Testes Spermatogenic cells: Divide to produce sperm. Supporting cells: Support and nourish spermatogenic cells. Regulate sperm production. Interstitial cells: Fills spaces between seminiferous tubules. Produce testosterone, the primary male sex hormone. 7 Spermatogenesis Process that produces sperm by the division of spermatogenic cells. Begins at puberty and continues for lifetime. Controlled by follicle-stimulating hormone (FSH) and luteinizing hormone (LH) and by testosterone. 8 Steps of Spermatogenesis Spermatogonium: Large cell near basement membrane of spermatogenic epithelium. Contains 46 chromosomes. Divides by mitosis to form 2 cells with 46 chromosomes each. Type A spermatogonium remains a spermatogonium. Stem spermatogonium that will divide repeatedly by mitosis. Type B spermatogonium is pushed inward and becomes a primary spermatocyte. 9 Steps of Spermatogenesis Primary spermatocyte (46) Undergoes meiosis Meiosis consists of 2 successive cell divisions that reduce the number of chromosomes in the daughter cells in half. 10 Steps of Spermatogenesis Chromosome events Prior to meiosis I, chromosomes replicate. Each is composed of two chromatids joined at a centromere. During metaphase of meiosis I, chromosome align as homologous pairs. During cytokinesis of meiosis I, the members of each pair separate into different secondary spermatocytes. Each secondary spermatocyte receives only 23 replicated chromosomes. In meiosis II, chromatids separate into different daughter cells. 11 Steps of Spermatogenesis Spermatid (23 chromosomes) A total of 4 are formed. Each loses their cytoplasm and forms a flagellum. Forms a sperm containing 23 chromosomes. 12 Genetic Diversity of Sperm Is created by the following two mechanisms: 1. Random alignment of paired homologous chromosomes (on the cellular equator) during meiosis I. Daughter cells contain different combination of maternal and paternal chromosomes. 2. Crossover during meiosis I. Exchange of DNA between paired homologous chromosomes during meiosis I. Some chromosomes contain genes from both parents. 13 14 Sperm Anatomy Consists of three parts: Head Compact nucleus containing 23 chromosomes. Acrosome  covers the nucleus, contains enzymes that help the sperm penetrate a secondary oocyte. Neck Connects the head to the flagellum. Flagellum Enables movement. Middle piece, a principal piece, and an end piece. Middle piece contains mitochondria. Spermatogenesis https://anatomy.mheducation.com/html/apr.html?animal=human& 15 Male Reproductive System Accessory Ducts Carry sperm from testes to external environment of the body. Structures referred to as the male reproductive tract: Epididymis Ductus deferens (Vas deferens) Ejaculatory duct Urethra 16 Male Reproductive System Epididymis Comma shaped, tightly coiled tube along the top and back of the testis. Receives sperm from seminiferous tubules. Site of sperm maturation and storage: Mature as they slowly move (10-14 days). The mature sperm are stored in the epididymis until they are ejaculated. Sperm stored for more than two months are destroyed and absorbed. 17 Male Reproductive System Ductus deferens Extends from epididymis upward, merges with duct from the seminal vesicle. Uses peristalsis to move sperm. Ejaculatory Duct Enters the prostate and merges with urethra. During ejaculation, contracts to mix seminal vesicle secretions with sperm and push them into urethra. 18 Male Reproductive System Urethra Extends from the urinary bladder through the penis to the external environment. Two roles: Transport urine. Carries semen, during ejaculation. Cannot do both functions simultaneously. Accessory glands Three different exocrine glands make secretions involved in the reproductive process: Seminal vesicles Prostate gland Bulbo-urethral glands 19 Accessory Glands Seminal vesicles Paired glands on the back of the urinary bladder. Duct merges with the ductus deferens to form ejaculatory duct. Secretion: Is alkaline to help regulate pH of semen. Contains fructose and prostaglandins. Secretions compose about 60% of semen. 20 Accessory Glands Prostate Pear-shaped gland encircling the urethra where it exits urinary bladder. Ejaculatory duct passes through rear half of prostate to join with urethra. Secretes an alkaline, milky fluid into the urethra. Keeps sperm pH slightly alkaline. Has chemicals that activate swimming movements of sperm. Secretions compose about 30% of semen. 21 Accessory Glands Bulbo-urethral glands Two small, spherical glands below the prostate gland near the base penis. Secrete an alkaline, mucus-like fluid into urethra in response to sexual stimulation. Neutralizes acidity of urethra. Lubricates the end of the penis. 22 Semen Fluid that passes from urethra during ejaculation. All three glands contribute secretions, in addition to sperm and fluid from testes. Volume of ejaculate is 2-5 ml with approximately 50150 million sperm/ml. Composition: Slightly alkaline (pH=7.5): Neutralize acidity in male’s urethra and female’s vagina protects the sperm. Contains fructose from seminal vesicles. Swimming movements are activated by prostatic fluid. Prostaglandins from seminal vesicles: Stimulate reverse peristalsis in the uterus and uterine tubes, which accelerates the movement of sperm in the female reproductive tract. 23 Male External Genitalia Visible parts of male reproductive system. Includes the scrotum and penis. Scrotum: Sac of skin and subcutaneous tissue that holds testes. In midline behind penis. Testes migrate into the scrotum during 7th month of fetal development. Descent controlled by testosterone. Allows testes to be kept 2-3 ℉ below average body temperature. Necessary for viable sperm production. 24 Male External Genitalia Scrotum: Contains two muscle: 1. Dartos muscle Smooth muscle layer. 2. Cremaster Two thin ribbonlike skeletal muscles. Both are used to elevate and depress the testes. Elevated closer to the body in cold temperatures and depressed in warm temperatures. Adjust temperature of the testes. 25 Male External Genitalia Penis Copulatory organ. Composed of spongy erectile tissue. Enables penis to become enlarged and rigid during sexual stimulation. Three columns of erectile tissue compose the body of the penis. Corpora cavernosa: two columns located on the top of an erect penis. Corpus spongiosum: located on the bottom of an erect penis. Expands at the tip to form the glans penis, which contains numerous sensory receptors and the external urethral orifice. Prepuce loose sheet of skin that covers the glans. 26 Male reproductive system overview https://anatomy.mheducation.com/html/apr.html?animal=human& 27 Male Sexual Response In absence of sexual stimulation: Vascular sinusoids in erectile tissue contain small amount of blood. Penis is flaccid. Sexual stimulation initiates parasympathetic action potentials. Cause dilation of arterioles and constriction of venules supplying the erectile tissue. Erectile tissues become engorged with blood produces the erection Also stimulate secretion from bulbo-urethral glands. 28 Male Sexual Response Continued stimulation causes orgasm. Characterized by ejaculation of semen and feeling of intense pleasure. Sympathetic action potentials stimulate peristaltic contractions of most accessory ducts and glands. Forces semen into the urethra. Skeletal muscles contract rhythmically forcing semen out of urethra ejaculation. Immediately after ejaculation, vascular changes that produced erection are reversed. Sympathetic action potentials cause constriction of the arterioles and dilation of the venules, allowing the accumulated blood to leave the penis. Another orgasm is not possible for a period of time after ejaculation occurs. 29 Action of Testosterone Male sex hormones are collectively called androgens. Most important androgen in males. Produced primary by the testes. Testosterone secretion Fetal development Produced by adrenal glands. Promote formation of male sex organs. At puberty: Promotes maturation of male reproductive organs. Stimulates continuation of spermatogenesis. 30 Action of Testosterone At puberty: Promotes development of male secondary sex characteristics: Growth of body hair (axillary, face, and pubic regions) Increased muscular development. Development of heavy bones, broad shoulders, and narrow pelvis. Deepening of the voice due to the enlargement of the larynx and thickening if the vocal folds. Increase in rate of cellular metabolism. Increase rate of red blood cell production. Testosterone production starts to decline at about 40 years of age, resulting in a gradual decline in the functions of reproductive organs and secondary sex characteristics. 31 Hormonal Control of Reproduction in Males Onset of sexual development begins at ages 11 or 12 years, completing around 15 to 17 years. At puberty, hypothalamus secretes gonadotropin releasing hormone (GnRH). GnRH stimulates the anterior lobe of the pituitary gland to release two hormones: Luteinizing hormone (LH) Follicle-stimulating hormone (FSH) 32 Hormonal Control of Reproduction in Males Luteinizing hormone (LH) Promotes growth of interstitial cells of the testes. Stimulates production of testosterone by interstitial cells. Follicle-stimulating hormone (FSH) Acts on supporting cells and works with testosterone in the seminiferous tubules to stimulate spermatogenesis. 33 Regulation of Male Sex Hormone Secretion Controlled by negative-feedback mechanism. Keeps testosterone within healthy limits. As testosterone level increases, GnRH production is inhibited. Loss of GnRH, decrease LH and FSH production. Decrease in LH, decreases testosterone secretion by the interstitial cells. Decrease in FSH, decreases sperm production. 34 Regulation of Male Sex Hormone Hormone Secretion As testosterone level decreases, GnRH is secreted. GnRH causes LH and FSH to be secreted. LH increases testosterone production. FSH increases sperm production. Testosterone maintains the male reproductive organs and spermatogenesis. Inhibin is secreted by supporting cells. Secretion increases when sperm count is high. Decreases FSH secretion, which decreases sperm production. Secretion decreases when sperm count is low. FSH secretion increases, which increase sperm production. 35