Male Reproductive System PDF

Chapter 26 Sexual Reproduction and The Male Reproductive System  Anatomy terminology (in a professional setting) is NOT inappropriate Penis Femur Testicles Nasal cavity Scrotum Blood Sperm...

Chapter 26 Sexual Reproduction and The Male Reproductive System  Anatomy terminology (in a professional setting) is NOT inappropriate Penis Femur Testicles Nasal cavity Scrotum Blood Sperm Plasma Semen Artery Vagina Vein Labia Major Ulna Clitoris Smooth muscle Ovaries Lymph Uterus Aorta  Sexual Reproduction and Development Expected Learning Outcomes – Identify the most fundamental biological distinction between male and female. – Define primary sex organs, secondary sex organs, and secondary sex characteristics. – Explain the role of the sex chromosomes in determining sex. – Explain how the Y chromosome determines the response of the fetal gonad to prenatal hormones. – Identify which of the male and female external genitalia are homologous to each other. – Describe the descent of the gonads and explain why it is important.  The Two Sexes Male and female gametes (sex cells) combine their genes to form a zygote (fertilized egg) – One gamete has motility: sperm (spermatozoon) Parent producing sperm considered male Parent with a Y chromosome is male – Other gamete contains nutrients for developing embryo: egg (ovum) Parent producing eggs considered female Anyone lacking a Y chromosome is female In mammals, female is the parent that provides a sheltered internal environment and prenatal nutrition of the embryo Overview of the Reproductive System Male reproductive system serves to produce sperm and introduce them into the female body – Males have a copulatory organ (penis) for introducing their gametes into the female reproductive tract Female reproductive system produces eggs, receives sperm, provides for the union of the gametes, harbors the fetus, and nourishes the offspring – Females have a copulatory organ (vagina) for receiving the sperm Overview of the Reproductive System Reproductive system consists of primary and secondary sex organs – Primary sex organs (gonads) Produce gametes (testes or ovaries) – Secondary sex organs: organs other than the gonads that are necessary for reproduction Male—system of ducts, glands; penis delivers sperm cells Female—uterine tubes, uterus, and vagina receive sperm and harbor developing fetus Overview of the Reproductive System Secondary sex characteristics—features that further distinguish the sexes and play a role in mate attraction – Develop at puberty to attract a mate – Both sexes Pubic and axillary hair and their associated scent glands, and the pitch of the voice – Male Facial hair, coarse and visible hair on the torso and limbs, relatively muscular physique – Female Distribution of body fat, breast enlargement, and relatively hairless appearance of the skin Chromosomal Sex Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. X XX = Determination X female Sperm Egg Our cells contain 23 pairs Y XY = of chromosomes X male – 22 pairs of autosomes – 1 pair of sex chromosomes (XY males: XX females) Males produce half Y- carrying sperm and half X-carrying sperm All eggs carry the X chromosome  Chromosomal Sex Determination Sex of child determined by type of sperm that fertilizes X mother’s egg X XX = female – X-carrying sperm Sperm Egg fertilizes the egg: female Y – Y-carrying sperm X XY = male fertilizes the egg: male  Prenatal Hormones and Sexual Differentiation For the first ~7 weeks, a fetus is sexually undifferentiated Gonads begin to develop at 5 or 6 weeks as gonadal ridges Two sets of ducts adjacent to each gonadal ridge – Mesonephric (wolffian) ducts develop into male reproductive system; paramesonephric ducts degenerate – Paramesonephric (müllerian) ducts develop into female reproductive tract; mesonephric ducts degenerate Important to note that BOTH are present until about week 7  Prenatal Hormones and Sexual Differentiation SRY gene (sex-determining region of Y chromosome)-In males, codes for a protein, testes-determining factor (TDF), that initiates development of testes – Begin to secrete testosterone at 8 to 9 weeks – Stimulates mesonephric ducts to develop into the male anatomy – At same time the testes secrete müllerian-inhibiting factor (MIF) causing degeneration of the paramesonephric ducts  5-6 week embryo SRY(+ testosterone) ~week 6-7 SRY + testosterone 7-9 week embryo  Hormonal Control of Sex Androgens (e.g., testosterone) - development of male reproductive organs - development of secondary sexual characteristics - more prevalent in males Estrogens (e.g., estradiol) Progestins (e.g., progesterone) - pubertal development of female reproductive traits - estrogens involved in masculinization too! NOTE: Estrogen levels are always high in pregnancy If estrogen was the hormone that directed the female development, all fetuses would be feminized Female development occurs in absence of androgen hormones  Development of the External Genitalia Similarity of external genitalia of both sexes: 1. Genital tubercle becomes the head (glans) of the penis or glans clitoris 2. Pair of urogenital folds encloses urethra of male forming the penis or forms the labia minora 3. Pair of labioscrotal folds becomes either scrotum or labia majora Genitalia is undifferentiated until ~ week 9 By week 12, either male or female genitalia are distinctly formed Male and female organs that develop from the same embryonic structure are homologous – Penis is homologous to the clitoris – Scrotum is homologous to the labia majora  Development of 1. Genital tubercle External Genitalia 2. Urogenital fold 6 weeks 3. Labioscrotal fold Tail! 8 weeks ~12 weeks Male Female = differentiation  Development of External Genitalia Male Female Developing glans Urethral groove 10 weeks Anus Glans of penis Glans of clitoris Urethral orifice Labia minora ~12 weeks Labia majora = Scrotum differentiation Perineal raphe  Descent of the Gonads Both male and female gonads initially develop high in the abdominal cavity near the kidneys, and migrate into the pelvic cavity (ovaries) or scrotum (testes) Gubernaculum—a connective tissue cord extends from the gonad to the floor of the pelvic cavity – Guides migration in males and females Descent of testes covers a substantial distance – See next page Ovaries descend to lesser extent – Lodge on inferior brim of the lesser pelvis – Gubernaculum becomes a pair of ligaments that supports the ovary and the uterus  Descent of the Testis Pass through the inguinal canal around 7 months Position of testes becomes important later in spermatogenesis Testes accompanied by elongating testicular arteries and veins, lymphatic vessels, nerves, spermatic ducts, and extensions of internal abdominal oblique muscle 3-month fetus 8-month fetus 1-month-old infant Parietal Closed proximal peritoneum Muscular wall of abdomen portion of Epididymis vaginal process Inguinal canal Testis Ductus deferens Figure 27.5 Spermatic cord Pubic symphysis Vaginal process Tunica vaginalis Vaginal process Gubernaculum Scrotum Scrotal swelling Penis Gubernaculum  Male Reproductive Anatomy Expected Learning Outcomes – Describe temperature regulation in the scrotum – Describe the structure and functions of the male reproductive system – Describe the pathway taken by a sperm cell from its formation to its ejaculation, naming all the passages it travels. – State the names, locations, and basic functions of the male accessory reproductive glands. Male Reproductive Anatomy Fig. 26.3  The Scrotum The human testes reside in the scrotum and have adapted to this cooler environment – Cannot produce sperm at core body temperature of 37°C – Must be held at about 35°C Scrotum has three mechanisms to regulate temperature of the testes 1. Cremaster muscle: strips of the internal abdominal oblique muscle Cold temperatures>contracts and draws testes upward toward body Warm temperatures>relaxes suspending testes further from the body 2. Dartos muscle: subcutaneous layer of smooth muscle Cold temperatures>contracts, wrinkling the scrotum, holding testes against warm body Reduces heat loss The Scrotum Fig. 26.6  The Scrotum Scrotum has three mechanisms to regulate temperature of the testes 3.Pampiniform plexus: an extensive network of veins from the testes that surrounds the testicular artery and spermatic cord – Countercurrent heat exchanger— without the pampiniform plexus, warm arterial blood would heat the Heat testis and inhibit sperm production – Removes heat from the descending arterial blood – By the time it reaches the testis, the blood is 1.5° to 2.5°C cooler Arterial blood cools as it descends Testis Venous blood carries Heat away as it ascends Pathway of a sperm 1. Seminiferous tubule Sperm development 2. Rete testis Sperm partially mature here 3. Efferent ductules Ciliated to move sperm 4. Head/Body of Epididymis Sperm mature here (~20 days) 5. Tail of Epididymis Sperm stored (40-60 days) Reabsorbed if not used 6. Ductus (Vas) deferens Vasectomy- severe the vas deferens = birth control Fig. 26.4  Pathway of a sperm (contd.) 7. Ampulla End unites with seminal vesicle 8. Ejaculatory duct Last of spermatic ducts 9. Urethra Sperm now actively swimming Accessory Glands 1. Seminal vesicles- secretes to ejaculatory duct Forms 60% of semen 2. Prostate gland- secretes to prostatic urethra Thin milky secretion forms 30% of semen 3. Bulbourethral glands- secretes to urethra During sexual arousal, they produce a clear slippery fluid that lubricates the head of the penis in preparation for intercourse Protects the sperm by neutralizing the acidity of residual urine in the urethra Fig. 26.5 About 10% of semen  Sperm and Semen Expected Learning Outcomes – Understand meiosis and the outcome of this cell division – Describe the sequence of cell types in spermatogenesis, and relate these to the stages of meiosis. – Describe the composition of semen and functions of its components.  Sperm and Semen Spermatogenesis—process of sperm production in seminiferous tubules Involves three principal events 1. Remodeling of large germ cells into small, mobile sperm cells with flagella 2. Reduction of chromosome number by one-half in sperm cells (unites with egg to return to 46) 3. Shuffling of genes so new combinations exist in the sperm that are different from the parents Ensures genetic variation in the offspring Four sperm cells produced from one germ cell by meiosis Basics of Gamete Formation * Formation of sperm (spermatozoa) * Begins at puberty; continues throughout life We are diploid (two sets of homologous chromosomes; one maternal, one paternal) = 2n (46 chromosomes) Meiosis = a type of cell division that yields Haploid (1n) cells (gametes like sperm and egg)  Basics of Gamete Formation Meiosis I: Chromosomes replicate in preparation for division Synapses formed between homologous chromosomes tetrads Crossing-over (recombination) occurs; maternal and paternal chromosomes swap genetic material Homologous chromosomes drawn to opposite ends of cell during anaphase Haploid chromosome number (reduction division of meiosis) Meiosis II: same as basic cell division (mitosis) except chromosomes are NOT replicated at start Haploid daughter cells result SUMMARY: Meiosis reduces chromosomal number by half (from diploid [2n] to haploid [1n]) Through crossing over, meiosis yields genetic variability! No 2 gametes are alike. Basics of Gamete Formation Fig. 26.1  Spermatogenesis Puberty- testosterone rises Spermatogenic cells in epithelial walls of seminiferous tubules are reactivated and begin mitosis Spermatogonia (2n) Mitosis Type A daughter cells (2n) (maintain germ line; spermatogonia) Type B daughter cells (2n) (destined to become sperm) Growth Primary spermatocyte (2n) Meiosis I Secondary spermatocyte (1n) Meiosis II Spermatids (non-motile) Fig. 26.7 Spermiogenesis Production of ‘tailed’ sperm from spermatids 1. Acrosomal enzymes packaged by Golgi apparatus 2. Acrosome is formed at anterior end of nucleus 3. Microtubules arrange to begin forming the flagellum 4. Mitochondria multiply rapidly and position themselves along flagellum (WHY?) 5-6. Excess cytoplasm is removed (‘streamlining’) 7. Mature sperm is born! (About 70 days from being a type B spermatocyte) Fig. 26.8 Hormonal Control of Male Reproduction Fig. 26.9  Semen Semen (seminal fluid)—fluid expelled during orgasm 2 to 5 mL of fluid expelled during ejaculation – 60% seminal vesicle fluid, 30% prostatic fluid, and 10% sperm and spermatic duct secretions Normal sperm count 50 to 120 million/mL Lower than 20 to 25 million/mL: infertility  Semen Cont. – Stickiness of semen promotes fertilization Clotting enzyme from prostate activates proseminogelin Converts it to a sticky fibrinlike protein: seminogelin Entangles the sperm Sticks to the inner wall of the vagina and cervix Ensures that semen does not drain back into vagina 20 to 30 minutes after ejaculation, serine protease from prostatic fluid breaks down seminogelin, and liquifies the semen Sperm become active Prostaglandins thin the mucus of the cervix, stimulate peristaltic waves in uterus and uterine tubes  Semen Two requirements for sperm motility: 1.Elevated pH Prostatic fluid buffers vaginal acidity from pH 3.5 to 7.5 2.Energy source Seminal vesicle secretions provide fructose and other sugars to the mitochondria of the sperm  Male Sexual Response Expected Learning Outcomes – Describe the blood and nerve supply to the penis. – Explain how these govern erection and ejaculation.  Male Sexual Response Publication of research by William Masters and Virginia Johnson (1966) – Divided intercourse into four recognizable phases Excitement Plateau Orgasm Resolution – Led to therapy for sexual dysfunction – Sexual intercourse is also known as coitus, coition, or copulation  Anatomical Foundations Internal pudendal (penile) artery enters root of the penis and divides in two – Dorsal artery: travels under skin on dorsal surface Supplies blood to skin, fascia, and corpus spongiosum – Deep artery travels through the core of the corpus cavernosa Gives off smaller helicine arteries that penetrate the trabeculae and enter lacunae Dilation of deep artery fills lacunae causing an erection When penis is flaccid, most blood comes from the dorsal artery Many anastomoses unite deep and dorsal arteries – Deep dorsal vein drains blood from penis  Anatomical Foundations Innervation of penis – The glans has an abundance of tactile, pressure, and temperature receptors – Dorsal nerve of penis and internal pudendal nerves lead to integrating center in sacral spinal cord – Both autonomic and somatic motor fibers carry impulses from integrating center to penis Sympathetics induce an erection in response to input from the special senses and to sexual thoughts Parasympathetics induce an erection in response to direct stimulation of the penis  Excitement and Plateau Excitement phase is characterized by vasocongestion (swelling of the genitals with blood), myotonia (muscle tension), and increases in heart rate, blood pressure, and pulmonary ventilation – Bulbourethral glands secrete their fluid – Initiated by a broad spectrum of erotic stimuli – Erection of penis is due to parasympathetic triggering of nitric oxide (NO) secretion – Causing dilation of deep arteries and filling of lacunae with blood – Vasocongestion can also cause the testicles to become 50% larger during excitement  Excitement and Plateau Plateau phase—the variables such as respiratory rate, heart rate, and blood pressure stay increased – Marked increased vasocongestion and myotonia – Lasts for a few seconds or a few minutes before orgasm  Orgasm and Ejaculation Orgasm or climax—a short but intense reaction that is usually marked by the discharge of semen – Lasts 3 to 15 seconds – Heart rate, blood pressure, and breathing greatly elevate  Orgasm and Ejaculation Ejaculation occurs in two stages – Emission: sympathetic nervous system stimulates peristalsis which propels sperm through ducts as glandular secretions are added – Expulsion: semen in urethra activates somatic and sympathetic reflexes that stimulate muscular contractions that lead to expulsion Sympathetic reflex constricts internal urethral sphincter so urine cannot enter the urethra and semen cannot enter the bladder Ejaculation and orgasm are not the same – Can occur separately  Resolution Resolution phase—body variables return to preexcitement state – Sympathetic signals constrict internal pudendal artery and reduce blood flow to penis – Penis becomes soft and flaccid (detumescence) – Cardiovascular and respiratory responses return to normal Refractory period—period following resolution in which it is usually impossible for a male to attain another erection or orgasm – May last from 10 minutes to a few hours Neural Control of Male Sexual Response Neural Control of Male Sexual Response