Reproductive System. Lab Exercise 39. Objectives. Introduction

Transcription

1 Lab Exercise Reproductive System Objectives - You should be able to identify the principal organs of both the male and female reproductive system and state their functions - Be familiar with the maturation process of sperm and eggs and be able to identify structures associated with this process Introduction Reproduction takes many forms, from simple binary fission to the complex formation of male and female gametes that unite to produce offspring. Each species has evolved reproductive mechanisms that suit its environmental conditions. Some species have extremely high mortality rates and therefore produce numerous offspring to insure that at least some will survive to reach reproductive age. Others devote much energy to only one or two offspring at a time to enhance their chance of survival. Sexual reproduction is considered more adventitious than asexual reproduction because it increases the genetic diversity of the species. While this may not mean much to an individual organism, genetic diversity enhances survival of the species. If the gene pool is diverse due to combining genes from haploid gametes, some of the individuals may have the genetic make-up necessary to survive environmental changes. In this unit we will focus on the reproductive systems of humans. To begin this exercise, go to the Mammalian Systems section of the BiologyOne DVD and select the Reproductive System. 1

2 Activity.1 Male Reproductive System Activity.2 Testes From the introductory screen of the Reproductive System simulation, click on the forward arrow in the lower right to study the structure of the male reproductive system. The following is a summary of these structures and their functions. testes- The site of production for sperm and the male hormone testosterone. epididymis- Where sperm are stored and mature. scrotal sac- Houses the testes outside the body. vas deferens- The vessel which transports sperm away from the epididymis. seminal vesicle-a pair of glands that produce an alkaline solution of fructose. Solutions from these glands make up about 60% of the semen volume. They are located just dorsal to the bladder. prostate gland - This gland surrounds the urethra just below the urinary bladder. It secretes about a third of the volume of semen, secreting alkaline fluids and enzymes that help to activate the sperm. Click on the forward arrow to study the microscopic structure of a testis. Look for and identify the seminiferous tubules, interstitial cells, spermatogonium, primary spermatocytes, spermatids, and sperm. Within the testes are hundreds of tightly coiled seminiferous tubules, where sperm production occurs. Looking at a cross section through a seminiferous tubule, you will be able to see cells at all stages of sperm development. The outermost layer of cells are stem cells which will give rise to developing sperm. These are called spermatogonia. A spermatogonium will differentiate into a primary spermatocyte. The primary spermatocyte is diploid and, through the first division of meiosis, will form haploid secondary spermatocytes. The spermatids, found to the center of the tubules, have completed meiosis and will begin to take on the typical characteristics, a head and a tail. Found outside and around the seminiferous tubules are interstitial cells. The interstitial cells produce the hormone testosterone. Make your own drawing of these in the Results Section. bulbourethral gland- Glands which produce an alkaline mucus fluid. The function is not fully known, but it is believed to aid in lubrication prior to ejaculation and may neutralize remaining urine in the urethra. Also called the Cowper s gland. urethra- Vessel with a dual role. Transports both urine and semen. A sphincter (muscular ring) is located at the base of the bladder to prevent passage of urine simultaneous with semen. penis- The male structure responsible for delivering sperm and urine. After becoming familiar with these organs, label the diagram of the male reproductive system in the Results Section. 2

3 Activity.3 Female Reproductive System Activity.4 Ovaries Click on the forward arrow in the lower right to study the structures of the female reproductive system. These structures and a brief summary of their functions is given below. ovaries- The sites for production of eggs and the hormones estrogen and progesterone. oviducts- The vessel through which the egg passes from the ovary to the uterus. Also, the site where fertilization of the egg occurs. uterus- The primary portion of the muscular structure where development of the fetus takes place. The endometrium (inner lining of the uterus) is where a new embryo implants. If fertilization of the egg does not occur, the endometrium is sloughed away, resulting in the female menstrual period (menses). cervix- Muscular ring at the base of the uterus providing entrance from the vagina. Click on the forward arrow in the lower right to view the anatomical structure of the ovary and developmental stages of follicles. There are five screens in this tutorial that show the follicles at various stages of their development. Click on the forward arrow to advance through these. Study the micrographs of the ovary. Look for and identify the primordial follicles, primary follicles, secondary follicles, Graffian follicles and corpus luteum. From the day she is born, all of the eggs a female will produce are in her ovaries, waiting to be released. The eggs are housed in fluid-filled follicles and are surrounded by steroid-producing supporting cells called granulosa cells. Each month, several follicles will begin to ripen or mature and fill with fluid. Those just beginning this development are called primary follicles. As more fluid accumulates, a secondary follicle appears. One follicle will no doubt develop more quickly than the others, and this somehow inhibits further development of the others. As a result, the human ovary usually releases only one egg per cycle. vagina- Muscular tube averaging from 3-4 inches in the female, which receives the penis and semen. Also serves as the birth canal. Test your ability to identify these structures by labeling the diagram of the female reproductive structure in the Results Section. As the follicle matures (under the control of the hormone FSH), more fluid accumulates and pushes the granulosa cells aside, leaving a large cavity called the antrum. Only the egg itself, attached to a string of granulosa cells, protrudes into the center of the antrum. This very mature follicle is known as the Graffian follicle. Finally, with a surge of the hormone LH (luteinizing hormone), the egg ruptures from the follicle and enters the Fallopian tube (oviduct). The emptied follicle undergoes drastic changes. It becomes a bloody mass called the corpus hemorrhagicum and, as the blood is absorbed, differentiates to the corpus luteum (CL). For a while, the corpus luteum will secrete progesterone and estrogen. These hormones act on the uterus to prepare it for possible implantation of the fertilized egg. Eventually, the CL will degenerate and regress to a much smaller corporus albicans (white body) before it is completely digested. As you observe these structures, make your own drawings of them in the Results Section. 3

4 Lab Exercise Name Results Section Activity.1 Male Reproductive System

5 Activity.2 Testes seminiferous tubules 5

6 Activity.3 Female Reproductive System

7 Activity.4 Ovaries primordial follicles primary follicle secondary follicle Graffian follicle 7