Male Reproductive Physiology Lecture 1 PDF

Male Reproductive Physiology Assis. Prof. Dr. Ahmed Tawfeeq Neamah Lecture 1 Objectives: The student will be able to: Describe the anatomy and physiology of male reproductive organs. Understand the steps involved in spermatogenesis...

Male Reproductive Physiology Assis. Prof. Dr. Ahmed Tawfeeq Neamah Lecture 1 Objectives: The student will be able to: Describe the anatomy and physiology of male reproductive organs. Understand the steps involved in spermatogenesis. Describe the structure of sperm, acrosome reaction, and capacitation Identify various contraceptive methods in male and female. Introduction The male reproductive system consists of two essential elements: the gonads (testes) and the complex array of glands and ducts that constitute the sex accessory organs. The system encompasses testis, epididymis, vas deferens, ejaculatory duct, urethra, penis, and scrotum (Figure 1). The vas deferens is a thick, muscular tube that is bundled together inside the scrotum with connective tissue, blood vessels, and nerves into a structure called the spermatic cord. Accessory sex glands include seminal vesicles, prostate, and bulbourethral glands (Cowper’s glands). The main function of gonads is spermatogenesis and the production of sex hormones essential for reproductive function. The ducts are responsible for the storage of sperm and the transport of semen and urine. Epididymis aids with the storage of sperm and maturation of the sperm and acquisition of motility. Accessory sex glands produce seminal plasma constituents including fructose, citric acid, calcium, prostaglandins, and fibrinogen. The penis is the male organ of copulation. 1 Male Reproductive Physiology Assis. Prof. Dr. Ahmed Tawfeeq Neamah Testes are paired ovals structures each approximately 4 to 5 cm in length and are housed within the scrotum. The scrotum helps to keep testes temperature 2 to 4°C below core body temperature. Testes are surrounded by two distinct layers; the outer tunica vaginalis is a serous membrane that has both a parietal and a thin visceral layer. Beneath the tunica vaginalis is the tunica albuginea, a tough, white, dense connective tissue layer covering the testis itself and also invaginates to form septa that divide the testis into 300 to 400 structures called lobules (Figure 1). Within the lobules, sperm develop in structures called seminiferous tubules. The testis has up to 900 coiled seminiferous tubules, each averaging more than one-half meter long. Male reproductive functions can be divided into three major subdivisions: (1) formation of sperm—spermatogenesis; (2) performance of the male sexual act; and (3) regulation of male reproductive functions by sex hormones and other hormones. Figure 1. Structures of the male reproductive system. 2 Male Reproductive Physiology Assis. Prof. Dr. Ahmed Tawfeeq Neamah Spermatogenesis During the formation of the embryo, the primordial germ cells migrate into the testes and become immature germ cells called spermatogonia, which lie in two or three layers of the inner surfaces of the seminiferous tubules (Figure 2). Spermatogenesis occurs in the seminiferous tubules during active sexual life as the result of stimulation by pulsatile release of gonadotropin-releasing hormone (GnRH), release of anterior pituitary gonadotropic hormones follicle-stimulating hormone (FSH) and luteinizing hormone (LH). At puberty, spermatogonia, undergo mitotic division and differentiation. Two identical diploid cells result from spermatogonia mitosis. One of these cells remains a spermatogonium, and the other becomes a primary spermatocyte. The primary spermatocytes undergo meiotic division, reducing the number of chromosomes. In this two-stage process (Meiosis I and II), they divide into secondary spermatocytes and then into spermatids, which contain the haploid number of 23 chromosomes. The spermatids mature into spermatozoa (sperm) by the process of spermiogenesis. Spermatids mature into spermatozoa in deep folds of the cytoplasm of the Sertoli cells (also called sustentacular cells). Mature spermatozoa are released from the Sertoli cells and become free in the lumens of the tubules. Sertoli cells secrete special nutrients that are essential for sperm maturation, regulate spermatogenesis, and are stimulated by the FSH hormone. Sertoli cells also secrete androgen-binding protein (ABP), inhibin, and anti-Müllerian hormone (AMH). Tight junctions between Sertoli cells create the blood–testis barrier, which keeps bloodborne substances from reaching the germ cells and, at the same time, keeps surface antigens on developing germ cells from escaping into the 3 Male Reproductive Physiology Assis. Prof. Dr. Ahmed Tawfeeq Neamah bloodstream and prompting an autoimmune response. Testosterone is also essential for spermatogenesis and is produced in the testis by Leydig cells (also called interstitial cells). One production cycle, from spermatogonia through formed sperm, takes approximately 64-72 days. Both acidic medium and high temperature may have detrimental effects on sperm function. 4 Male Reproductive Physiology Assis. Prof. Dr. Ahmed Tawfeeq Neamah Figure 2. Steps of spermatogenesis 5 Male Reproductive Physiology Assis. Prof. Dr. Ahmed Tawfeeq Neamah The structure of Sperm Approximately 100 to 300 million sperm are produced each day. Each spermatozoon is composed mainly of a head, midpiece and a tail (Figure 3). The head comprises the condensed nucleus of the cell, with only a thin cytoplasmic and cell membrane layer around its surface. The midpiece is the central part of the sperm cell between the head and the tail and contains mitochondria. On the outside of the anterior two-thirds of the head is a thick cap called the acrosome that is formed mainly from the Golgi apparatus. The acrosome contains several enzymes similar to those found in lysosomes of the typical cell, including hyaluronidase and powerful proteolytic enzymes. These enzymes play important roles in allowing the sperm to enter the ovum and fertilize it. The tail of the sperm is called the flagellum. Back-and-forth movement of the flagellum provides motility for the sperm. The energy for this process is supplied in the form of ATP, which is synthesized by the mitochondria The central strand of the flagellum, the axial filament, is formed from one centriole. Once ejaculated into the female, the spermatozoa move up the uterus and then to the isthmus of the uterine tubes and undergo capacitation. This further maturation process involves two components: increasing the motility and the fertilization ability of sperm and preparation for the acrosome reaction. In this reaction, the stored enzymes in the acrosome are released when sperm come in contact with the ovum to facilitate sperm penetration of the ovum. 6 Male Reproductive Physiology Assis. Prof. Dr. Ahmed Tawfeeq Neamah Figure 3. The structure of human sperm 7 Male Reproductive Physiology Assis. Prof. Dr. Ahmed Tawfeeq Neamah Contraception Contraception encompasses a variety of methods designed to prevent pregnancy. Contraceptive methods are important for family planning along with other medical indications. Conception can be prevented by hormonally disrupting the menstrual cycle (Oral contraceptive pills OCP), by physically blocking the passageway (barrier methods or sterilization), or less successfully, by abstinence during fertile periods or withdrawal method. Implantation can also be impaired via the use of a foreign by intrauterine device (IUD) or surgical removal (Salpingectomy or Vasectomy). When considering contraceptive methods counseling should include efficiency, safety, acceptability availability, plans for pregnancy, health status, side effects and risks. Contraceptive methods include: For female: Combined oral contraceptive pills (COC) Progestin-only pills Injectables contraceptives Patch Intrauterine device (IUD) (e.g., Copper, Levonorgestrel IUD) Vaginal ring Diaphragm or cervical cap Female condom Lactational Amenorrhea Withdrawal Female sterilization (Salpingectomy) 8  Male Reproductive Physiology Assis. Prof. Dr. Ahmed Tawfeeq Neamah For male: Male condom Withdrawal Male sterilization (Vasectomy) Suggested further reading and online activities Search online for the meaning of the term “sperm maturation arrest” Compare the origin and function of AMH, testosterone and estrogen in male and female reproductive systems. Search Google images for testis biopsy histological sections and identify the different stages of spermatogenesis in the section. Visit this site: https://www.innerbody.com/htm/body.html References Hall J. and Hall M. (2021). Guyton and Hall Textbook of Medical Physiology. 14th ed. Elsevier. Barret K. (2019). Ganong’s Review of Medical Physiology. 26th ed. McGraw Hill Lange. Betts J., and Desaix P. (2022). Anatomy and Physiology. 2nd ed. OpenStax. McCance K. (2018). Pathophysiology: the biologic bases for disease in adults and children. 8th ed. Elsevier. Papadakis M. (2019). Current Medical Diagnosis and Treatment. 58th ed. McGraw Hill Lange. 9 Male Reproductive Physiology Assis. Prof. Dr. Ahmed Tawfeeq Neamah e-Book and application link: https://quiz.learn-future.com 10