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Anatomy of Male Reproductive System

Testes, Spermatogenesis, Duct system, Urethra, Accessory glands, Seminal vesicles, Prostate, Penis.

Anatomy of the Male Reproductive System

The male reproductive system has organs that are involved in reproducing new individuals, just like the female reproductive system does. Along with the pair of testes, there are also several excretory organs, such as the penis, the bulbourethral glands, and seminal vesicles.

Testes

As the male gonads, or testes or testicles, begin to develop in the abdominal cavity, near the kidneys, they are found high in the abdominal cavity. The drops are deposited in the scrotum, a pouch right below the abdomen and anterior to the penis, after birth or during the last two months of pregnancy. Despite their location outside of the abdominal cavity, the testes are protected from injury by having a temperature about 3° C lower than the normal body temperature. Low temperatures are necessary for viable sperm to develop. Skin and subcutaneous tissue make up the scrotum. In the middle part of the testis, there is a vertical partition of subcutaneous tissue that divides the tissue into two sections, with one testis in each. Scrotal wrinkles are caused by the contraction of smooth muscle fibers in the subcutaneous tissue, which is called the dartos muscle. Relaxed, these fibers provide smoothness to the scrotum. In addition, the position of the scrotum and testes is controlled by the cremaster, which is made up of skeletal muscle fibers. A man's testes contract this muscle when he is cold or sexually aroused to stay warm.

Structure

The testicle is an oval structure with a diameter of 3 cm and a length of approximately 5 cm. Several bundles of fibrous connective tissue surround each testis, dividing it into many lobules using septa in the tunica albuginea. Approximately 250 lobules are present in each testis. One to four highly coiling seminiferous tubules line the lobules and form a straight tube leading into the rete testis. A short efferent duct excites the testes. Cells of Leydig (interstitial cells) are located between seminiferous tubules in a lobule and produce male sex hormones.

Spermatogenesis

Spermatogenesis occurs within the seminiferous tubules and produces sperm. Seminiferous tubules shown in transverse sections are packed with cells in different stages of development between the smaller cells and the larger ones that occupy the lumen of the tubule are large cells. It is these large cells that provide other cells with sustenance and nourishment (Sertoli's cells). As the embryo develops, primordial germ cells travel to the testes and differentiate into immature cells known as spermatogonia. The outermost edge of the seminiferous tubules contains spermatogonia, a diploid mitochondrion composed of 46 chromosomes (23 pairs). These cells divide by mitosis when they undergo puberty due to hormones. In mitosis, some daughter cells become spermatogonia at the periphery. As they approach the lumen, some undergo modifications and develop into primary spermatocytes. Primarily spermatocytes, like spermatogonia, undergo mitosis and have 46 chromosomes because they are produced during mitosis.

Every primary spermatocyte has got divided once at meiosis I, producing two secondary spermatocytes (haploid), each with 23 chromosomes. Before the division of the genetic material, a pair of chromatids called centromeres is joined to each chromosome, forming two strands. Every secondary spermatocyte receives one chromosome containing two chromatids during meiosis I. Second meiosis, or meiosis II produces two spermatocytes on every single secondary spermatocyte. It is not necessary to replicate genetic material during this division, but each cell receives a single strand of the chromatid. Primary spermatocytes divide twice during meiosis, producing four spermatids. As spermatogenesis occurs, cells divide twice but DNA replicates only once, resulting in 23 chromosomes in each spermatid, one from each pair of chromosomes seen in the original spermatocyte. It is thought that the immature cells are at the periphery of the tubule while the differentiated cells are closer to the center as the stages of spermatogenesis progress. Spermatogenesis and Mitosis differ in that Mitosis (and Oogenesis in the female) produce half as many chromosomes as the original cell. If sperm and egg nuclei are united, the number of chromosomes is restored. The sperm and egg cells produce double the number of chromosomes as the previous generation during mitosis. Spermiogenesis occurs at the end of the process of developing sperm. Spermatozoa, or mature sperm, form when spermatids from spermatogenesis mature. Sperm cells have ahead, an elongated midsection, and a tail. A nuclear membrane surrounds the 23 chromosomes that make up the head, also called the nuclear region. Acrosomes, which contain enzymes that help sperm penetrate the female gamete, cover the tip of the head. Adenosine triphosphate (ATP) is produced by mitochondria in the metabolic region of the midpiece. It uses a typical flagellum to move its tail or locomotor region. Once released into the seminiferous tubules, Sperm leave the testes. The gametes then enter the epididymis where they will complete their maturation and be ready to fertilize the female gamete. During puberty, males begin to produce sperm, and it continues throughout their lives. Approximately 74 days are needed for the entire process, beginning with the primary spermatocyte. Female sperm can survive in her reproductive tract for 48 hours after ejaculating.

Duct system

It takes sperm cells several ducts to travel from the inside to the outside. The sperm then travel through the epididymis, the ductus deferens, the ejaculatory duct, and the urethra after leaving the testicles.

Epididymis

Afferent ducts exit the testes and enter the epididymis, where the sperm leaves. There is two epididymis in each testis, which are long tube (about 6 meters long) and coil tightly around each other to form a comma-shaped organ. A sperm that leaves the testes is immature and unable to fertilize the ova. While moving through the epididymis, they undergo maturation and become fertile. Mature sperm are located at the tip of the epididymis.

Duct deferens

A fibromuscular tube, also known as vas deferens, connects the ductus deferens to the epididymis. From the posterior margin of the testes, it begins at the base (tail) of the epididymis, then sharply ascends. By entering the inguinal canal, the ductus deferens passes along the lateral pelvic wall to reach the abdominopelvic cavity. The ureter crosses over the posterior part of the bladder as it descends the bladder wall towards the prostate. Each ductus deferens enlarges into an ampulla as it approaches the prostate gland. A peristaltic movement propels sperm through the ductus deferens in the proximal portion, near the epididymis. The ductus deferens portion of the spermatic cord provides the testes with vascular and neural structures used by spermatogenesis. In addition to the ductus deferens, the spermatic cord contains lymph vessels, testicular nerves, and the cremaster muscle, which is used to elevate the testes during sexual stimulation and for warmth.

Ejaculatory duct

Each ductus deferens forms a short ejaculatory duct with the jointed duct from an adjacent seminal vesicle (an accessory gland). Each ejaculatory duct empties into the urethra via the prostate gland.

Urethra

At the tip of the penis, there is a urethral orifice connecting the urethra with the urinary bladder. Sperm and fluids are transported between the reproductive and urinary systems by this duct. Sphincters tighten to prevent urine from entering the urethra as reproductive fluids pass through the urethra. There are three regions of the male urethra. In the prostate gland, the urethra passes through the proximal end. As well as receiving the ejaculatory duct, which contains sperms and seminal vesicles' secretions, it is also in contact with several prostate gland ducts. Lastly, the membranous urethra runs through the pelvic floor. It is a short portion. Those with a penile urethra extend it to the outside at the external orifice, which is known as the spongy urethra or cavernous urethra. These ducts are connected to the penile urethra by bulbourethral glands.

Accessory glands

Sesamoid vesicles, prostate glands, and bulbourethral glands are some of the accessory glands of the male reproductive system. Fluids are secreted through these glands into the urethra.

Seminal vesicles

Pairs of saccular glands are situated posterior to the urinary bladder and are known as seminal vesicles. Ejaculatory ducts join at the ampulla with the ductus deferens to form the urethra, where they empty. The fluid during the ejaculatory process is viscous and contains fructose, fructose molecules, and sperm prostaglandins, which aid mobility and viability of sperm, as well as proteins that cause slight coagulation reactions in semen.

Prostate

Prostate glands are firm, dense structures situated just below the urinary bladder. A urethra surrounded and protected by a walnut-sized membrane, leaves the urinary bladder after leaving. There are short ducts that empty into the prostatic urethra from the prostate gland's substance. Alkaline, milky, thin, and milky-colored secretions are secreted by the prostate. Sperm motility is enhanced by these secretions.

Bulbourethral gland

The Cowper's glands are located near the base of the penis, and they are bulbourethral glands. A pea's size is similar to its size. The proximal end of the penile urethra is punctured by a short duct from each gland. A mucus-like alkaline fluid is secreted by the bulbourethral glands in response to sexual stimulation. This fluid helps neutralize urine residues left in the urethra, aids in lowering vaginal acidity and lubricates the tip of the penis during genital stimulation.

Seminal fluid

The sperm cells, or semen, are mixed with some secretions from the accessory glands to form a slightly alkaline solution. A majority of the semen is composed of secretions from the seminal vesicles, with the rest originating from the prostate gland. A small volume of sperm is provided by the bulbourethral gland and its secretions. An ejaculation can contain between 1.5 and 6.0 ml of semen. Semen typically contains between 50 and 150 million sperm per milliliter. Sperm counts less than 10 to 20 million per milliliter are usually associated with infertility. In an ejaculation, there are several million sperm, even though only one penetrates and fertilizes the ovum.

Penis

It functions to transfer sperm from the scrotum to the vagina. This cylinder organ is located anterior to the scrotum in males and functions as a male copulatory organ. Penises consist of three columns of erectile tissue covered by skin and covered with connective tissue. Corpora cavernosa refers to the two dorsal columns. The corpus spongiosum surrounds the body's urethra and is an isolated ventral column. In addition to its roots, body, and glans, the penis has three components. In addition to the root that joins the penis to the pubic arch, there is a visible body that hangs from the root. Glans penis is formed by the expansion of the corpus spongiosum distal end. There is an external urethral opening formed by the urethra, which extends to the tip of the glans penis along the length of the corpus spongiosum. There is a loose fold of skin covering the glans penis called the prepuce.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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