Biological Science 13 (Reproductive System and Development)

Reproductive System and Development

Day 22:

Female Reproductive Structures ^[1] 

A. Reproductive System

The human reproductive system is responsible for a great variety of people, because each person has possible genes for everything (one from each parent). One gene is expressed and the other is not, but both can be passed down to children. I have brown eyes, but I probably have my parents green eye gene also. The reproductive system takes all the genetic information and puts only half in eggs and sperm (gametogenesis, using meiosis I and II), so that when the egg and sperm combine, they have exactly enough genes. Which half is used for each egg and sperm is random, so many possibilities are possible for humans (unlike cheetahs which are almost identical clones). 

1. Male and Female Reproductive Structures and Their Functions

Both reproductive structures must produce gametes with half the normal DNA. The female reproductive structures must also facilitate the growth of a zygote into a baby, and allow the baby to leave the body during birth. The male reproductive structures must allow sperm to exit the body near enough to the cervix for fertilization to occur and also produce a buffer to keep sperm from being killed by the acid of the female reproductive system.

Male Reproductive Structures ^[2] 

Prostate Cancer is the 4th most lethal cancer for men, drinking tea and eating soy help:


"I think the most important finding is that consumption of both soy and tea has a synergistic effect," says study author Jin-Rong Zhou, adding that each appears to reinforce the power of the other to fight cancer... statistical data showed that China had one of the lowest prostate cancer risk profiles in the world... Ultimately, both tea-soy combinations inhibited angiogenesis, a process in which tumors grow blood vessels to stay alive. ^[3] Read more.

A. Gonads

• Female Gonads: Ovaries (hold eggs which are made before birth, releasing them monthly after puberty and produces estrogen).
• Male Gonads: Testes (make sperm in the seminiferous tubules and produces testosterone in the interstitial cells).

B. Genitalia

• Female: The ovaries store eggs, which pass through the fallopian tubes, into the uterus, through the cervix and out the vagina. 
• Menstruation/Fertilization: The lining of the uterus thickens every month (normally), growing more blood vessels. The egg (oocyte), becomes a secondary oocyte and enters the uterus. If fertilization occurs, the embryo releases human Chorionic Gonadotropin (hCG) (testable by pregnancy tests, cause of nausea), which releases hormones preventing menstruation and triggering the placenta to create progesterone and estrogen.
• Gonadotropin Releasing Hormone (GnRH) made in the hypothalamus releases the gonadotropins: Folicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) from the anterior pituitary, these stimulate the growth of the oocyte/follicle and trigger maturation/ovulation (respectively). ^[4] Further Details.
• Estrogen made in the ovaries normally inhibits luteinizing hormone and folicle stimulating hormone, but once it reaches a threshold it causes a surge of luteinizing hormone that triggers ovulation. ^[5] 
• The corpus luteum, which remains in the ovary after expelling the oocyte into the Fallopian tube, prevents the endometrium from shedding by secreting estrogen and progesterone. If fertilization does not occur the corpus luteum dies, estrogen and progesterone levels drop, the endometrium dies and sheds, and the menstrual cycle restarts.  ^[6] Further Details.

The Menstrual Cycle ^[7] Further Details.

 (Thank You Isometrik)

• Male: Inside the testes sperm is made (in the seminiferous tubules, inside the testicle) and stored (inside the epididymis, on top of the testicle). The sperm travels through the vas deferens, the ejaculatory duct, and exits the body via the urethra. 
• Male Accessory Structures: The prostate secretes alkaline fluid to protect the sperm from female acidity, citric acid, fibrinolysin (to liquefy the semen) and acid phosphate. The seminal vesicles secrete fructose to provide energy for the sperm, prostaglandins, flavins (florescent). Bulbourethral glands (Cowper's glands) produce a lubricant to help sperm swim. The interstitial cells of the testis produce testosterone. ^[8] 

C. Differences Between Male and Female Structures

Male reproductive organs develop from female structures. Ovaries drop into the scrotum in males. Erectile clitoris tissue become the penis in males. The skin of the vagina forms the skin of the scrotum in males. Testicles need to be away from the body, because too much heat kills sperm. The male reproductive system is connected to the urinary tract, the female reproductive system in separate. All the eggs of a female are created before birth. Males do not produce sperm until around age 12. Thus, females are about 12 year more mature then males, not surprisingly.

2. Gametogenesis by Meiosis

• Female Gametogeneis: Making eggs with half the DNA for a child, at birth females have all the eggs they will ever have stored in their ovaries. 
• Eggs are frozen in Meiosis I (at prophase) until puberty (when meiosis I begins to reach completion monthly), there is too much DNA (diplotene) in the eggs until ovulation occurs, allowing meiosis II (meiosis II pauses in metaphase II and continues when the egg nucleus contacts sperm) to occur, reducing the DNA in half. ^[5] 
• Male spermatogenesis occurs in the seminiferous tubules. The names of the sperm keep changing. Spermatogonium until mitosis, then primary spermatocyte (required puberty), until meiosis I, then secondary spermatocyte, until meiosis II, then spermatid (having the correct amount of DNA, half a normal cell), then sperm (after maturing) or spermatozoa (same thing as sperm). ^[5] 
• Sperm is made at about 70,000/minute, each sperm takes 70-74 days to develop. ^[9] 

3. Ovum and Sperm

Ovum and sperm have half the normal DNA each, they combine to form a complete set of DNA that grows into a complete individual about 25% of the time, miscarriage occurs nearly 75% of the time in humans (counting early miscarriage of zygotes ext.).

A. Differences in Formation

Male VA Female (Gametogenesis) [5]
Male	Female	Difference
Spermatogonium (2n)	Oogonium (2n)	Spermatogonium made fresh. Oogonium all done before birth.
Primary spermatocyte	Primary oocyte	Primary oocye pauses at prophase I
Secondary spermatocyte	Secondary oocyte	Secondary oocyte pauses at metaphase II
Sperm	Ovum	Between the secondary spermatocyte and the sperm, there's the spermatid.

B. Differences in Morphology

Sperm are small and move with a flagella, using sugar for energy. Eggs are very large spheres that don't move.

C. Relative Contribution to Next Generation

Sperm contributes only half the DNA; eggs contribute half the DNA, mitochondria, organelles and epigenetics).^[5] 

4. Reproductive Sequence (Fertilization, Implantation, Development, Birth)

• Fertilization: the sperm and egg meet, then combine nucleus and DNA (forming a zygote).
• Implantation: the zygote then grows into a morula (by dividing via mitosis), keeps dividing into a blastocyst and sticks to the wall of the uterus.
• Development: gastrulation (development of 3 layers: mesoderm, ectoderm, endoderm and a pore) and organogenesis (organ development) occur.

B. Embryogenesis

The process of making an embryo. 

Embryogenesis ^[10] 

1. Stages of Early Development (Order and General Features of Each)

Zygote 1-15 cells.

Morula 16-127 cells/4 divisions (solid ball).

Blastocyst 128 cells/7 divisions (hollow ball).

Gastrula many cells (3 layers, pore/blastopore).

Then embryo... ^[11] 

A. Fertilization

Sperm + Egg -> Zygote 

The sperms release hormones to weaken the egg membrane as a team, then one sperm causes a acrosomal reaction allowing it to penetrate the membrane and enter the egg, the egg goes through a cortical reaction preventing more sperm from entering, meiosis II occurs and the sperm and egg nuclei fuse).^[5] 

B. Cleavage

Zygote -> Morula (solid ball, produced by repeated mitotic divisions)

C. Blastula Formation

Morula -> Blastocyst (hollow ball, implants on the uterus)

D. Gastrulation

The trilaminar (three layers) ball of cells that goes on to form organs. The blastopore become the mouth (protosomes) or the anus (in humans/deutrostomes). ^[12] 

Gastrulation ^[13] 

I. First Cell Movements

The surface cells (blue in the above picture) migrate inwards forming a blastopore.

II. Formation of Primary Germ Layers (Endoderm, Mesoderm, Ectoderm)

The three cell layers are the endoderm (cells migrate inwards), the mesoderm (cells the the middle, the Oreo filling cells if you will) and the ectoderm (cells that remain outside).

E. Neurulation

The ectoderm becomes a tube that forms the brain and spinal cord, as well as the skin and all nerves.

2. Major Structures Arising out of Primary Germ Layers

Endoderm makes: inside tube stuff, gut, lungs, digestive organs (liver and pancreas).

Mesoderm makes: muscle, blood, bone, internal organs (kidney and gonads).

Ectoderm makes: skin and nerves (including the brain). This means skin is exposed neural tissue, that concept is where the term neuromuscular therapist (for massage therapist) has its basis. The Color of Distance, by Amy Thomson is a great book (fiction) about creatures that display their emotion, heal themselves, communicate and experience the world mostly with their skin. In reality, we as humans are very much like those creatures. Our skins are the boundary and contact, with each other and the world in which we live.


Day 23:

C. Developmental Mechanisms

The cells of the body have a destiny (specialization) to become a certain type of cell, based on the way we use our body we change some cells to do different things, when the cell is at a certain point (determination) they can no longer change (can't teach an old dog new tricks), the point when the cell starts to preform its function (differentiation) is the end of development. 

Long Overview of Development (14 Minutes) ^[14] 

1. Cell Specialization

The destiny of each individual cell to become a specific type of cell as it grows. The cell starts to develop a certain way, but can change still.

A. Determination

The point of no return for a growing cell.

B. Differentiation

The concept that stem cells can become other types of cells, adopting different shapes, sizes, contents and functions.

C. Tissue Types

The tissue types are explained in detail in this post.

They are epithelial (skin and linings), connective (blood, bone, tendons, ligaments, fat, cartilage and basement membranes), nervous (neurons and supporting cells) and muscle (skeletal, smooth and cardiac).

2. Cell Communication in Development

The body communicates on all levels. On the level of tissues, cells speak to each other. Inducer (the cell talking) tells the responder (the cell listening) to change.

3. Gene Regulation in Development

• Differential Gene Transcription: genes are limited by transcription factors, histones proteins are modified (methylations, acetylations) to wrap around DNA turning genes off or on, DNA is modified (methylations), to turn genes on and off, as well.
• Differential RNA Processing: RNA may not be transcribed if it doesn't leave the nucleus, RNA can be spliced in different ways to regulate genes.
• Translation Regulation: mRNA are used to different extents, selective inhibition of translation of stored RNA occurs in the oocyte (translation occurs as needed after fertilization).
• Post-Transnational Regulation: some proteins are inactive without modifications, proteins can be marked for ubiquitin degradation. ^[5] 

4. Programmed Cell Death

The name of intensional cell death is apoptosis. Capases are the proteases that digest the cell. This type of cell death can be used for remodeling the shape of the body as it grows. 

Relevant Links:

More Details: Male Reproductive System
More Details: Female Reproductive System
More Details: Development (Zygotes & Embryos)
Find Out About: Prostate Disorders
Find Out About: American Chemical Society (ACS) Citation Style
Free Text Books: Anatomy, Biochemestry, Biology, Genetics, Immunology, Microbiology

Today, I am starting to use the American Chemical Society Citation Style to cite my sources. I will have to go back and cite my sources in earlier posts soon...

Footnotes:

1. Brenda. [Untitled Diagram of Female Reproductive System]. Brenda's A & P Eportfolio. [Online]. Apr 14, 2011. http://blm1128.blogspot.com/2011/04/objective-79-locate-structures-of-male.htm (retrieved Jul 01, 2012). 
2. [Untitled Diagram of Male Reproductive System]. The Health Success Site. [Online].
http://www.thehealthsuccesssite.com/what-is-prostate-cancer.html (retrieved Jul 2, 2012).

3. Bouchez, Colette. Soy-Tea Combo May Thwart Prostate Cancer. HealthScoutNews. [Online]. 
http://www.thehealthsuccesssite.com/what-is-prostate-cancer.html (accessed Jul 2, 2012).

4. Gonadotropin-Releasing Hormone. Wikipedia. [Online]. Jun 14, 2012.
http://en.wikipedia.org/wiki/Gonadotropin-releasing_hormone (accessed Jul 02, 2012).

5. Reproductive System. MCATReview.org. [Online]. 2008. 
http://mcat-review.org/reproductive-system-development.php (accessed Jul 02, 2012).

6. Corpus Luteum. Wikipedia. [Online]. Jun 08, 2012.
http://en.wikipedia.org/wiki/Corpus_luteum (accessed Jul 02, 2012).

7. Menstrual Cycle. Wikipedia. [Online]. Jul 02, 2012.
http://en.wikipedia.org/wiki/Menstrual_cycle (accessed Jul 02, 2012).

8. Slomianka, Lutz. Male Reproductive System. Blue Histology. [Online]. 2009.  http://www.lab.anhb.uwa.edu.au/mb140/corepages/malerepro/malerepro.htm (accessed Jul 2, 2012).

9. Spermatogenesis. Wikipedia. [Online]. Apr 23, 2012. 
http://en.wikipedia.org/wiki/Spermatogenesis#Spermiogenesis (accessed Jul 02, 2012).

10. Human Fertilization and Embryogenesis. [Video]. Health Science. [Online]. 2012.
http://healthscience.synthasite.com/ (retrieved Jul 01, 2012). 

11. Embryogenesis. Wikipedia. [Online]. May 26, 2012. 
 http://en.wikipedia.org/wiki/Embryogenesis#Fertilization_and_the_zygote (accessed Jul 02, 2012).

12. Freeman, S. Biological Science; Pearson: Ontario [Online] 2011. p 774.

http://www.pearsoned.ca/highered/showcase/freeman/pdf/9780321632203_ch34.pdf (accessed Jul 02, 2012).

13. Blastula. Drawing. Wikipedia. [Online]. May 17, 2012. 
http://en.wikipedia.org/wiki/File:Blastula.png (accessed Jul 01, 2012).

14. Andersen, P. Development: Timing and Coordination. [Video]. BozemanScience.com. [Online]. Sep 14, 2011.
http://www.bozemanscience.com/science-videos/2011/9/14/024-development-timing-and-coordination.html  (retrieved Jul 01, 2012).