RGD - Male Reproductive System Lesson

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Male Reproductive System

The reproductive system is a set of organs within an organism that work together to produce offspring. This system of organs also functions to produce important accessory substances such as fluids, hormones, and pheromones. Unlike the other body systems that you have studied, the organs in the reproductive system will differ depending upon the gender of the individual.  These differences allow for the individuals of each gender to combine genetic material in the process of intercourse to produce an offspring. Sexual reproduction (as opposed to asexual reproduction) is beneficial to humans because it increases the genetic variation of the offspring.   This increases the probability of greater genetic fitness of the offspring.

Anatomy of the Male Reproductive System

The male reproductive system includes both internal and external structures. The external structures include the:

  1. penis
  2. scrotum
  3. testicles

The internal organs of the male reproductive system include the:

  1. vas deferens
  2. accessory sex organs (seminal vesicles, prostate gland, bulbourethral glands)

The scrotum is a loose, pouch-like sack of skin that hangs behind the penis, containing the testicles. This structure has two functions: protection and climate control. For optimal sperm development, the testes must be at a temperature slightly cooler than normal body temperature. Special muscles in the wall of the scrotum allow it to contract and relax, moving the testicles closer to the body for warmth and protection or vice versa.

The testicles are the primary reproductive organs of the male reproductive system. They are located inside of the scrotum and have both exocrine and endocrine functions. Their endocrine function is the production of the male sex hormone testosterone. The exocrine function of the testicles is the production of sperm, the male gamete.  

Seminiferous tubules form coiled masses within the testes and are the site of spermatogenesis, a process that creates sperm. Seminiferous tubules empty into tubules that eventually drain into the epididymis.

The epididymis is a highly coiled tube that is about 20 feet long. The epididymis provides a temporary storage site where the sperm mature. The sperm develop as they pass through the epididymis is a process that takes about 20 days.

Mature sperm are transported to the urethra via the vas deferens in preparation for ejaculation. The vas deferens extends through the inguinal canal into the pelvic cavity. The end of the vas deferens empties into the ejaculatory duct which passes through the prostate gland (an accessory sex gland) to merge with the urethra. It is these structures that are cut and clamped as a form of permanent birth control during a procedure called a vasectomy.

Accessory sex glands include the seminal vesicles, prostate gland, and the bulbourethral glands. The primary purposes of the accessory sex glands are to produce seminal fluid (semen) and to clean and lubricate the urethra. Just below the urinary bladder is the location of the seminal vesicles and prostate. Sac-like pouches called the seminal vesicles produce fructose that provides sperm with a source of energy, helping with their ability to move. The fluid from the seminal vesicle is alkaline, which helps semen to neutralize the acidity of the vaginal tract. Most of the fluid in semen is made up of secretions from the seminal vesicles. The walnut-sized prostate excretes a milky-white fluid that helps to nourish the sperm, giving it better motility, longer survival, and better protection of genetic material. Lastly, the bulbourethral glands, also known as the Cowper's glands, are pea-sized structures located on the sides of the urethra just below the prostate gland. These glands produce a clear, slippery fluid that empties directly into the urethra. This fluid serves to lubricate the urethra and to neutralize any acidity that may be present within it due to residual drops of urine.

The penis is the male organ for sexual intercourse and urination. Semen and urine leave the penis through the urethra. The penis is composed of two main parts: the shaft and glans (head of the penis). Spongy erectile tissue, rich in blood vessels, can be found inside the penis that allows it to expand and contract. All males are born with a foreskin (a fold of skin covering the head of the penis), but some receive a procedure called circumcision within a few days of birth to remove the foreskin. This is an elective procedure (since it is not medically necessary) that is performed due to religious beliefs, hygiene concerns, or cultural and social reasons.

Functions of the Male Reproductive System

The male reproductive system has three main functions:

  • Produce, maintain, and transport sperm (male gametes) and protective fluid (semen)
  • Discharge sperm within the female reproductive tract
  • Produce and secrete testosterone (male sex hormone)

Sperm are male gametes or reproductive cells. When a male gamete meets a female gamete, it joins with (fertilizes) it, to form a new organism.

Sperm are male gametes or reproductive cells.

Human gametes are haploid as opposed to their diploid somatic cell counterparts. They are formed through a meiotic process in the gonads called gametogenesis. Gametogenesis differs between the sexes. In males, the production of mature sperm cells, or spermatozoa, is the result of a process called spermatogenesis that occurs in the seminiferous tubules. Spermatogenesis begins at the initiation of puberty and continues throughout the lifetime of a male. Once this process starts, millions of sperm are produced every day with very little interruption until death. Spermatogenesis starts with one diploid spermatogonium that has 23 pairs or 46 chromosomes (like a normal body cell). This cell divides by meiosis, resulting in four haploids containing only 23 total chromosomes. Review the process of spermatogenesis in the graphic and video below.

Spermatogenesis

 

As you learned in the endocrine system module, testosterone is the main sex hormone in males. Testosterone has two major roles:

  1. During the teen years, testosterone causes the reproductive organs to mature and other male traits, such as hair growth on the face and muscle growth, to develop.  
  2. During adulthood, testosterone helps with the production of sperm.

 

Disorders of the Male Reproductive System

Learn about common disorders of the male reproductive system in the learning object below.

 

Review the anatomy of the male reproductive system in the learning object below:

 

video Male Reproductive System from source:   http://www.ck12.org/life-science/Male-Reproductive-System-in-Life-Science/lecture/Male-Reproductive-System/  

video Spermatogenesis from source:   http://www.ck12.org/life-science/Human-Sperm-in-Life-Science/lecture/Spermatogenesis/ Links to an external site. 

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