Male Reproductive System
presentation lecture from: Evergreen University
Adolescence
* Puberty
* Burst of hormones activate maturation of the gonads: testes
* Begins: 9 – 14 yrs of age
* Abnormally early = precocious puberty
* Delayed = eunuchoidism
General Physical Changes
* Enlargement of the external and internal genitalia
* Voice changes
* Hair growth
* Mental changes
* Changes in body conformation and skin
* Sebaceous gland secretions thicken/increase acne
External Genitalia
* Gonads = testes undescended by birth= cryptorchidsim
* Scrotum
* Penis
Testes
* Each testis is an oval structure about 5 cm long and 3 cm in diameter
* Covered by: tunica albuginea
* Located in the scrotum
* There are about 250 lobules in each testis. Each contains 1 to 4 -seminiferous tubules that converge to form a single straight tubule, which leads into the rete testis.
* Short efferent ducts exit the testes.
* Interstitial cells (cells of Leydig), which produce male sex hormones, are located between the seminiferous tubules within a lobule.
scrotum
* consists of skin and subcutaneous tissue
* A vertical septum, of subcutaneous tissue in the center divides it into two parts, each containing one testis.
* Smooth muscle fibers, called the dartos muscle, in the subcutaneous tissue contract to give the scrotum its wrinkled appearance. When these fibers are relaxed, the scrotum is smooth.
* the cremaster muscle, consists of skeletal muscle fibers and controls the position of the scrotum and testes. When it is cold or a man is sexually aroused, this muscle contracts to pull the testes closer to the body for warmth.
Epididymis
* a long tube (about 6 meters) located along the superior and posterior margins of the testes.
* Sperm that leave the testes are immature and incapable of fertilizing ova. They complete their maturation process and become fertile as they move through the epididymis. Mature sperm are stored in the lower portion, or tail, of the epididymis
spermatic cord
* contains the proximal ductus deferens, testicular artery and veins, lymph vessels, testicular nerve, cremaster muscle and a connective tissue covering.
Duct System
* Sperm cells pass through a series of ducts to reach the outside of the body. After they leave the testes, the sperm passes through the epididymis, ductus deferens, ejaculatory duct, and urethra.
Ductus Deferens [vas deferens]
* a fibromuscular tube that is continuous with the epididymis.
* enters the abdominopelvic cavity through the inguinal canal and passes along the lateral pelvic wall, behind bladder & toward the prostate gland. Just before it reaches the prostate gland, each ductus deferens enlarges to form an ampulla.
* Sperm are stored in the proximal portion of the ductus deferens, near the epididymis
Ejaculatory Duct
* Each ductus deferens, at the ampulla, joins the duct from the adjacent seminal vesicle (one of the accessory glands) to form a short ejaculatory duct.
* Each ejaculatory duct passes through the prostate gland and empties into the urethra.
Urethra
* extends from the urinary bladder to the external urethral orifice at the tip of the penis.
* It is a passageway for sperm and fluids from the reproductive system and urine from the urinary system.
* divided into three regions: The prostatic urethra, the membranous urethra & the penile urethra (also called spongy urethra or cavernous urethra)
accessory glands
* are the seminal vesicles, prostate gland, and the bulbourethral glands. These glands secrete fluids that enter the urethra.
Seminal Vesicles
* glands posterior to the urinary bladder.
* Each has a short duct that joins with the ductus deferens at the ampulla to form an ejaculatory duct, which then empties into the urethra.
* The fluid is viscous and contains fructose, prostaglandins and proteins.
Prostate
* a firm, dense structure about the size of a walnut that is located just inferior to the urinary bladder.
* encircles the urethra as it leaves the urinary bladder.
* Numerous short ducts from the prostate gland empty into the prostatic urethra. The secretions of the prostate are thin, milky colored, and alkaline. They function to enhance the motility of the sperm.
Bulbourethral Glands
* small, about the size of a pea, and located near the base of the penis. A short duct from each enters the proximal end of the penile urethra.
* In response to sexual stimulation, the bulbourethral glands secrete an alkaline mucus-like fluid
Seminal Fluid or Semen
* a slightly alkaline mixture of sperm cells and secretions from the accessory glands.
* Secretions from the seminal vesicles make up about 60 percent of the volume of the semen, with most of the remainder coming from the prostate gland. The sperm and secretions from the bulbourethral gland contribute only a small volume.
* The volume of semen in a single ejaculation may vary from 1.5 to 6.0 ml. There are between 50 to 150 million sperm per milliliter of semen. Sperm counts below 10 to 20 million per milliliter usually present fertility problems.
penis
* is a cylindrical pendant organ located anterior to the scrotum and functions to transfer sperm to the vagina.
* consists of three columns of erectile tissue that are wrapped in connective tissue and covered with skin. The two dorsal columns are the corpora cavernosa. The single, midline ventral column surrounds the urethra and is called the corpus spongiosum.
* 3 parts: a root, body (shaft), and glans penis.
* The root of the penis attaches it to the pubic arch
* the body is the visible, pendant portion.
* The corpus spongiosum expands at the distal end to form the glans penis.
* The urethra, which extends throughout the length of the corpus spongiosum, opens through the external urethral orifice at the tip of the glans penis. A loose fold of skin, called the prepuce, or foreskin, covers the glans penis.
Erection
* Involves increase in length, width & firmness
* Changes in blood supply: arterioles dilate, veins constrict
* The spongy erectile tissue fills with blood
* Erectile Dysfunction [ED] also known as impotence
Hormones
* Follicle-stimulating hormone (FSH) stimulates spermatogenesis
* Interstitial Cell Stimulating Hormone (ICSH) stimulates the production of testosterone
* testosterone stimulates the development of male secondary sex characteristics & spermatogenesis.
Spermatogenesis
* Sperm are produced within the seminiferous tubules.
* Interspersed within the tubules are large cells which are the sustentacular cells (Sertoli's cells), which support and nourish the other cells.
* Early in embryonic development, primordial germ cells enter the testes and differentiate into spermatogonia
* Spermatogonia are diploid cells, each with 46 chromosomes (23 pairs) located around the periphery of the seminiferous tubules.
* At puberty, hormones stimulate these cells to begin dividing by mitosis. Some remain at the periphery as spermatogonia.
* Others become primary spermatocytes. Because they are produced by mitosis, primary spermatocytes, like spermatogonia, are diploid and have 46 chromosomes.
* Each primary spermatocytes goes through the first meiotic division, meiosis I, to produce two secondary spermatocytes, each with 23 chromosomes (haploid). Just prior to this division, the genetic material is replicated
* During meiosis I, one chromosome, goes to each secondary spermatocyte. In the second meiotic division, meiosis II, each secondary spermatocyte divides to produce two spermatids. There is no replication of genetic material in this division, but a single-stranded chromatid goes to each cell.
* As a result of the two meiotic divisions, each primary spermatocyte produces four spermatids.
* each spermatid has 23 chromosomes (haploid), one from each pair in the original primary spermatocyte.
* The final step in the development the spermatids formed from spermatogenesis become mature spermatozoa, or sperm.
* The mature sperm cell has a head, midpiece, and tail. The head, also called the nuclear region, contains the 23 chromosomes surrounded by a nuclear membrane. The tip of the head is covered by an acrosome, which contains enzymes that help the sperm penetrate the female gamete. The midpiece, metabolic region, contains mitochondria that provide adenosine triphosphate (ATP). The tail, locomotor region, uses a typical flagellum for locomotion.
Male Reproductive System.ppt
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