235-21 Male Reproductive Anatomy & Physiology PDF

Today’s Learning Objectives What is the biological advantage of sexual reproduction? What happens to cause a baby to become a girl or boy? What are indifferent gonads? Which parent is driving the sex of the baby, why? Compare the fate of the homologous structures identified during se...

Today’s Learning Objectives What is the biological advantage of sexual reproduction? What happens to cause a baby to become a girl or boy? What are indifferent gonads? Which parent is driving the sex of the baby, why? Compare the fate of the homologous structures identified during sex development What can go wrong during sex development and why? Biologically, what is puberty and why does it come about? How are sperm produced in the testes? What is controlling this process? Trace a sperm cell though the reproductive tract to ejaculation, what structures did it pass and what were the functions of these structures? What is the physiology of erection? Male Fertility Approx semen volume for each ejaculation is 1.5-5.0 mL. There are generally 60 to 150 million sperm per milliliter of ejaculate. A sperm count < 20 million/ml semen is called oligospermia and is considered less fertile. – May be caused by heat, drugs, or anabolic steroids On a population level, the average sperm count dropped from 104 million to 49 million per milliliter from 1973 through 2019. Normal sperm counts are considered to be over 40 million per milliliter. 2 Chat with a Neighbor What is the difference between gender and sex?  First, Some Definitions Sex Biological classifications of male and female Based on chromosomes and anatomy Gender Social classifications Based on sex, gender roles and self-identity  Gender Gender Identity How a person self-identifies Male, female, non-binary, etc. Gender expression The outward manifestation of gender Based on social constructs  Sex Chromosomal Sex XX and XY Anatomical Sex Based on Genitalia: Male and Female Clinical Example: Klinefelter Syndrome 47 XXY People with these conditions are genetically infertile and have lower amounts of testosterone and estrogen as well as other physiological issues. 7 Chat with a Neighbor: Review Question How do humans procreate? Try to remember as much as you can from past education (try not to look forward). Draw or write down what happens to allow for the human species to continue. Hint: How many chromosomes do we have?  Human Life Cycle 1. Genes from two individuals are combined in random ways to produce a new individual. - Allows for genetic variation and adaptability to a changing environment 1. Gametes (sperm and ova) form in the gonads (testes and ovaries) via meiosis (cuts chromosome number in half) 2. Ova and sperm fused in fertilization to restore original chromosome number. 3. The new individual progresses from zygote → embryo → fetus 9 Autosomal and Sex Chromosomes Each zygote gets: – 23 chromosomes from mother, – 23 from father. Produces 23 pairs of homologous chromosomes (diploid) 22 pairs are autosomal chromosomes = have the same (but not identical) genes on them. The last pair are the sex chromosomes. 10 Formation of Testes and Ovaries After fertilization, the gonads and associated structures are identical in males and females. Embryonic gonads can become either testes or ovaries. The signal that determines is called testis-determining factor (TDF), coded for by a gene on Y chromosome called SRY gene. Access the text alternative for slide images 11 Our current understanding of sex determination SRY gene on Y chromosome is necessary for development of testes and production of (more) testosterone AMH: Regresses female reproductive anatomy  Development of External Genitalia Identical in males and females for 6 weeks Both sexes have labioscrotal swelling, genital tubercle, urethral folds. Testosterone masculinizes these into scrotum, prostate gland, spongy urethra, and penis. Without testosterone, these become labia and clitoris. 13  Masculinization Caused by testosterone Converted to DHT (dihydroxytestosterone), the active hormone DHT necessary for the development and maintenance of the male external genitalia 14  Disorders of Embryonic Sexual Development Hermaphroditism: Both ovarian and testicular tissue exist in the body. Some people have an ovary on one side and a testis on the other, while others have fused ovotestes. Due to a problem in zygotic mitosis where some cells receive the short arm of the Y chromosome with its SRY gene and some do not 15  Clinical Example: Disorders of Sexual Development Pseudohermaphroditism: The individual has ovaries or testes, but accessory structures are not complete or are inappropriate for genetic sex. Female pseudohermaphroditism: may be due to excessive secretion of adrenal androgens in a female = congenital adrenal hyperplasia. Top Model Hanne Gaby Odiele Male pseudohermaphroditism: may be Says She Is Intersex due to testicular feminization syndrome whereby testes make testosterone but testosterone receptors don’t work. (e.g. Androgen Insensitivity Syndrome) 16 Onset of Puberty Secretion of FSH and LH is elevated at birth and stays high for the first 6 months of postnatal life Declines to almost nothing until puberty. Puberty begins with a release of LH (pulsatile). – This results in increases in testosterone or estradiol-17β (estrogen) secretion. – These hormones produce secondary sex characteristics. 17 Age of Onset of Puberty Depends on activity levels, amount of body fat Leptin secreted by adipose cells required for onset of puberty. Exercise may inhibit GnRH secretion by hypothalamus More active, slimmer girls begin puberty later Melatonin from the pineal gland may play a role, but not yet proven in humans 18 Think-Pair-Share With a partner, review the process of meiosis, using the primary spermatocyte below. Male Reproductive System 20  Male Sex Organs Ductus (vas) deferens Head of epididymis Efferent ductule Rete testis Straight tubule Body of epididymis Duct of epididymis Tail of epididymis Sagittal section through testis and epididymis, anterior aspect to the right 21 Cross-Section of the Testis Sertoli Cells Stimulate germ cells (sperm); Secrete inhibin, which inhibits FSH secretion  Endocrine Control of the Testes LH secretion is controlled by rising testosterone secretion through negative feedback. FSH secretion is controlled by testosterone and inhibin secretion. Inhibin is released from Sertoli cells of seminiferous tubules. Access the text alternative for slide images 24 Hormonal Control of Spermatogenesis Testosterone required to stimulate meiosis and early spermatid maturation. Testosterone secreted by Leydig cells after stimulation by LH. FSH enhances spermatogenesis through action of Sertoli cells that are stimulated FSH ensures optimal fertility 25 Spermatogenesis Germ cells from yolk sac migrate to the testes early in embryonic development Diploid spermatogonia first go through mitosis to increase the number of cells One daughter cell (primary spermatocyte) continues through meiosis; other daughter cell remains spermatogonia After meiosis I → 2 secondary spermatocytes. After meiosis II → 4 spermatids. Process occurs as the cells move toward the lumen of the seminiferous tubules 26  Spermiogenesis Maturation of spermatids into functioning spermatozoa Acrosome, a cap of digestive enzymes, forms Mitochondria concentrated in spirals in the mid- piece 27  Male Accessory Sex Organs Spermatids move from seminiferous tubules → Spermatic cord straight tubule → rete testis Blood vessels and nerves → efferent ductules → epididymis. Ductus (vas) deferens Testis The epididymis is the site of Head of epididymis Seminiferous Efferent ductule sperm maturation and tubule Rete testis storage; sperm become Straight tubule Lobule Septum motile (spermiogenesis) Body of epididymis Tunica albuginea Tunica vaginalis In ejaculation, spermatozoa Duct of epididymis Cavity of tunica vaginalis move from the epididymis Tail of epididymis → vas deferens → Sagittal section through testis and ejaculatory duct → urethra. epididymis, anterior aspect to the right 28  Male Accessory Sex Organs The seminal vesicle and prostate gland add fluid to sperm to form semen. Seminal fluid: contains fructose – Prostaglandin Prostate fluid: contains citric acid, calcium, and vesiculase – Vesiculase: enzyme that causes coagulate after ejaculation – Fibrinolysis cause semen to then become more liquid, freeing the sperm – Proteolytic enzymes 29 Male Reproductive Anatomy  Prostate Cancer Benign prostatic hyperplasia (BPH): 40-50% of men in fifties, 80% of men in eighties  Review Question Outline the pathway a sperm cell takes from production to ejaculation Erection Results from blood flow into erectile tissues of penis: – corpora cavernosa, corpus spongiosum Due to parasympathetic nerve-induced vasodilation of arterioles leading to corpora cavernosa 33 Erection  Nitric Oxide and Erection Activates guanylate cyclase to produce cGMP → Closes Ca2+ channels → Decreases cytoplasmic Ca2+ levels → Relaxes muscles Venous outflow of blood is partially blocked during an erection. 35 Control of the Erection Controlled by hypothalamus and sacral region of spinal cord Can occur due to: – Conscious sexual thought (hypothalamus → spinal cord → penis) – Or sensory stimulation (penis → spinal cord → penis) 36 Emission and Ejaculation Emission: the movement of semen into the urethra. Ejaculation: the forceful expulsion of semen from the urethra. Both are under sympathetic nervous system control. Contraction of smooth muscles in the tubules, seminal vesicle, prostate, and muscles at base of penis is involved in ejaculation. Remember cooperation of the parasympathetic and sympathetic divisions of the ANS? 37 What do you think happens when you “fracture” your penis? Click to the next slide if you want to see what a penile fracture looks like! (NSFW) Male Fertility Approx semen volume for each ejaculation is 1.5-5.0 mL. There are generally 60 to 150 million sperm per milliliter of ejaculate. A sperm count < 20 million/ml semen is called oligospermia and is considered less fertile. – May be caused by heat, drugs, or anabolic steroids On a population level, the average sperm count dropped from 104 million to 49 million per milliliter from 1973 through 2019. Normal sperm counts are considered to be over 40 million per milliliter. 40 Are there any forms of male birth control? If so, what? Male Contraception: Vasectomy Most widely used and reliable form of male contraception Vas deferens is cut, tied to prohibit sperm transport. Does not affect testosterone production or ejaculation. 70% of men develop antisperm antibodies 42 Other Types of Male Contraception Condoms Suppressing FSH, GnRH, LH—research is ongoing Calcineurin—interferes with sperm motility and fertilization Vasalgel—an injected gel placed in the vas deferens to block sperm transport 43