Human Reproductive system

Stucture of reproduction organ in human

The Male Reproductive System

pictr 1. male reproductive organ

 The testes (testicles) are the male sex glands (gonads). Male sex cells (sperm cells) are produced in the testes. So is testosterone, the male hormone. This hormone is needed for reproductive organ function and for the development of male secondary sex characteristics. The testes are suspended between the thighs in a sac called the scrotum.

       Sperm travel from the testis to the epididymis. The epididymis is a coiled tube on top and the side of the testis. From the epididymis, sperm travel through a tube called the vas deferens. Eventually each vas deferens joins a semivesicle. The two seminal vesicles store sperm and produce semen. Semen is a fluid that carries sperm from the male reproductive tract. The ducts of the seminal vesicles join to form he ejaculatory duct. The ejaculatory duct passes through the prostate gland.

        The prostate gland, shaped like a doughnut, lies just below the bladder. The gland secretes fluid into the semen. As the ejaculatory ducts leave the prostate they join the urethra, which also runs through the prostate. The urethra is the outlet for urine and semen. The penis contains the urethra.

The penis is outside the body and has erectile tissue. When the man is sexually aroused, blood fills the erectile tissue. The penis becomes enlarged, hard, and erect. The erect penis enter the vagina of the female reproductive tract. The semen, which contains the sperm, is released into the vagina.

Female Reproductive organ

 The function of the external female reproductive structures (the genitals) is twofold: To enable sperm to enter the body and to protect the internal genital organs from infectious organisms. The main external structures of the female reproductive system include:

• Labia major: The labia major enclose and protect the other external reproductive organs. Literally translated as "large lips," the labia major are relatively large and fleshy, and are comparable to the scrotum in males. The labia major contain sweat and oil-secreting glands. After puberty, the labia major are covered with hair.

• Labia minor: Literally translated as "small lips," the labia minor can be very small or up to 2 inches wide. They lie just inside the labia major, and surround the openings to the vagina (the canal that joins the lower part of the uterus to the outside of the body) and urethra (the tube that carries urine from the bladder to the outside of the body).

• Bartholin's glands: These glands are located beside the vaginal opening and produce a fluid (mucus) secretion.

• Clitoris: The two labia minor meet at the clitoris, a small, sensitive protrusion that is comparable to the penis in males. The clitoris is covered by a fold of skin, called the prepuce, which is similar to the foreskin at the end of the penis. Like the penis, the clitoris is very sensitive to stimulation and can become erect.

The internal reproductive organs in the female include:

• Vagina: The vagina is a canal that joins the cervix (the lower part of uterus) to the outside of the body. It also is known as the birth canal.

• Uterus (womb): The uterus is a hollow, pear-shaped organ that is the home to adeveloping fetus. The uterus is divided into two parts: the cervix, which is the lower part that opens into the vagina, and the main body of the uterus, called the corpus. The corpus can easily expand to hold a developing baby. A channel through the cervix allows sperm to enter and menstrual blood to exit.

• Ovaries: The ovaries are small, oval-shaped glands that are located on either side of the uterus. The ovaries produce eggs and hormones.

• Fallopian tubes: These are narrow tubes that are attached to the upper part of the uterus and serve as tunnels for the ova (egg cells) to travel from the ovaries to the uterus. Conception, the fertilization of an egg by a sperm, normally occurs in the fallopian tubes. The fertilized egg then moves to the uterus, where it implants into the lining of the uterine wall.

spermatogenensys







The male testes have tiny tubules containing diploid cells called spermatogonium that mature to become sperm. The basic function of spermatogenesis is to turn each one of the diploid spermatogonium into four haploid sperm cells. This quadrupling is accomplished through the meiotic cell division detailed in the last section. During interphase before meiosis I, the spermatogonium’s 46 single chromosomes are replicated to form 46 pairs of sister chromatids, which then exchange genetic material through synapsis before the first meiotic division. In meiosis II, the two daughter cells go through a second division to yield four cells containing a unique set of 23 single chromosomes that ultimately mature into four sperm cells. Starting at puberty, a male will produce literally millions of sperm every single day for the rest of his life.



Oogenesys:



All materials necessary to begin development are stored in the egg.

a. Proteins-yolk (made in other organs (liver, fat bodies), transported to egg

b. Ribosomes and tRNA

• burst of protein synthesis after fertilization

c. Protective chemicals

• UV filters

• DNA repair enzymes

• antibodies

• alkaloids (and other protective molecules)

d. mRNA

• encode proteins for use in early development

• some localized regionally

e. Morphogenic factors

• initiate differentiation

• examples : transcription factors, paracrine factors

1. Early in embryogenesis, primordial germ cells migrate from the yolk sac endoderm to the genital ridge (developing ovary) where they take up residence and are called oogonia.​

2. These diploid oogonia undergo several mitotic divisions prior to or shortly after parturition, thus providing the developing ovary with a large supply of future ova (eggs).

3. When oogonia begin the first meiotic division, they are called primary oocytes.

4. Primary oocytes are arrested in prophase of Meiosis I until the female reaches sexual maturity. They grow in size during this arrested phase, but do not divide. A human female is born with about 2 million primary oocytes in her ovaries, but by the time of puberty only about 400,000 are left due to atresia (degeneration).

5. When the female reaches sexual maturity and under the influence of follicle stimulating hormone (FSH), a small number of primary oocytes are stimulated to continue through Meiosis I.

6. During this process the number of chromosomes is reduced from the diploid number (2N) to the haploid number (1N).

7. This division is uneven in that although the chromosomes are divided equally, most of the cytoplasm stays with the oocyte.  The smaller polar body contains half the chromosomes but only a small amount of cytoplasm and will eventually degenerate.

8.After a primary oocyte completes the first meiotic division, it is called a secondary oocyte (1N).  In most species Meiosis I is completed just before ovulation (release of the ovum from the ovary).  However, in horses and dogs Meiosis I is completed after ovulation. 

9. If a secondary oocyte is not penetrated by a sperm, it will degenerate.

10. If fertilization and pregnancy do not occur, a new cycle will begin in which FSH from the pituitary gland will stimulate a few more primary oocytes to continue through Meiosis I.  11. The process is the same as previously described and a secondary oocyte is formed.

12. However, some of the time a sperm will penetrate the zona pellucida and the secondary oocyte is stimulated to continue   through Meiosis II, forming a second polar body and a mature ovum (1N).  Again, the polar body contains half of the chromosome material, but little cytoplasm, and it eventually degenerates.

13. After a sperm enters the cytoplasm of the ovum, two pronuclei form, containing genetic material from the ovum or the sperm.

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14. Fertilization is complete when the two pronuclei fuse and restore the diploid chromosome number.   15. If fertilization is completed, the zygote undergoes several mitotic changes to become an embryo; otherwise it degenerates.

Structure of eggs

Ovum layers consist of :

a. Corona Radiatais granulosa cells that attach to outer part of oosit.

b. Pellusida Zone isglicoproteinthat enveloped to the oosit.

Oogenesis : sequence process of forming the ovum in ovarium.

FERTILIZATION 

Fertilization is the joining of a sperm and an egg. A sperm is a male gamete that isreleased into the vagina of a female during intercourse. In order for fertilization to occur there must be a mature ovum present. Every month one of the ovaries releases an egg which will meet one of the A 4 million sperm the male ejaculates into the vagina. The sperm swim through the cervix and into the uterus which lead to the fallopian tubes. This is where fertilization is most likely to take place. The high amount of sperm in the ejaculate is needed because only around 100 survive to enter reach the fertilization site.In order to penetrate the egg the sperm must first break through 2 barriers surrounding the ovum. The acrosome of sperm comes in contact with the corona radiata and releases digestive enzymes that break down a gelatinous layer around the egg called, the zona pellucida. Once a sperm reaches the plasma membrane of the egg it sets off a reaction that spreads across the membrane of the egg preventing other sperm from breaking through the egg membrane. Once the sperm reaches the inside of the egg it sheds its tail and the two nuclei fuse and now the 23 chromosomes from the egg and the 23 chromosomes of the sperm join and they become a zygote. Chromosomes contain all the information needed to determine the genetic structure of the new baby. Normally all human beings have two chromosomes that determine sex. A combination of X and Y makes a male or a combination of X and X makes a female. All ovum have X sex chromosomes where as sperm have both X or Y sex chromosomes. Therefore, the male gametes determine the sex of the baby.