Reproductive system flashcards

Reproductive system:

Primary sex organs of male and females are the gonads. 

• Ovaries in females

• Testes in males

Secondary sex organs (male): 

• Paired ductus deferens

• Single prostate gland

• Paired seminal vesicles

• Scrotum and penis

• Paired bulbourethral glands

Functions of primary sex organs:

1. Produce gametes (sex cells)

2. Secrete hormones 

Functions of secondary sex organs:

1. Epididymis: Site of maturation and storage of sperm. Fluid is acidic due to waste products from sperm

2. Seminiferous tubule: Site of sperm production

3. Vas deferens: Propel and conduct the fluid containing the sperm cells from the epididymis to the urethra 

4. Seminal vesicles: Secretes alkaline fluid rich in fructose and prostaglandins to neutralize the acid from epididymis. Fructose provides nutrition for sperm cells and prostaglandins produce contractions in females to facilitate sperm movement.

• Seminal vesicle fluid forms 60% of semen

5. Prostate gland: Secretes thin milky alkaline fluid which helps to combat acidic vaginal secretions and fluid in epididymis. Secretions form about 30% of semen volume.

Semen contains about 120 million sperm cells per milliliter. 

List the pathway of the sperms from the seminiferous tubules through the various structures into the urethra:

1. Rete testis

2.  Vasa Efferentia

3. Epididymidis

4. Vas deferens

5. Ejaculatory duct

6. Prostatic urethra (Prostate gland)

7. Urethra

Erectile tissues of penis:

1. Double corpora cavernosa

2. Single corpus spongiosum

Testes descend as the fetus develops. Some factors that influence its descent are:

• Hormones (testosterone)

• Gubernaculum, fibrous cord that guides the descent of scrotum

This occurs about 1-2 months before birth. 

Why does the scrotum need to descend?

It needs to go outside the body so the temperature of the testis can be cooler. This is the crucial temperature in which sperm can be made.

Cryptorchidism:

Testes do not descend downwards, this will lead the man to become infertile. Sometimes they will remove the testis because it can no longer descend and there is a risk for testicular cancer. Other times, if it is not too late, a hormonal injection can be given so the testes will descend on their own.

Erection: Caused by parasympathetic nerve signals.

Ejaculation: Caused by sympathetic nerve signals.

• Emission: Movement of semen into urethra

Structure of testes & sperm cells:

• Cells of leydig: Secrete hormones (testerone)

• Spermatogonia: Germ cells or stem cells that divide to form the sperm cells

• Sertoli cells: Provide nutrients and support to sperm cells. Also have tight junctions between them that form a blood testis barrier to prevent harmful substances and toxins in the blood from coming in contact with sperm cells.

Sperm cells are made of many parts. Here’s a few:

• Acrosome: Located at the tip of the sperm. Contains enzymes that help in digesting the thick wall of the egg during fertilization

• Nucleus: Contains 23 chromosomes (haploid)

• Mitochondrial spiral: Synthesize ATP needed for movement 

• Microtubules: Lashing movements of tail help in propulsion of the sperm

Spermatogenesis:

1. Spermatogenesis begins with the spermatogonia which divides mitotically into a primary spermatocyte. (Diploid)

2. This primary spermatocyte will then undergo meiosis I to create two secondary spermatocytes. (Haploid)

3. Secondary spermatocytes will then undergo meiosis II to form four spermatids. (Haploid)

Each primary spermatocyte will give rise to four spermatids.

What are the stem cells in the seminiferous tubules called? How many chromosomes do these cells have?

These stem cells are spermatogonia and they are diploid (46 chromosomes)

Here’s a quick rundown of meiosis:

Meiosis:

Consists of two cell divisions. Results in 4 haploid daughter cells. 

1. Begins with DNA replication (just like mitosis), this will produce two identical copies of chromosomes called sister chromatids.

2. The first cell division separates the homologous pairs to produce haploid cells

Notice how the sister chromatids are still attached in telophase I. In meiosis II they are finally separated and look like this:

Meiosis I daughter cells may also look diploid but they only have two copies of one homologous chromosome. “However, remember that the mother cell has four individual chromosomes. The daughter cell doesn’t have four individual chromosomes—it has two sets of sister chromatids. A set of sister chromatids is simply two identical copies of a single homologous chromosome.”

This is very different in a female. In females, only one primary oocyte gets good nutrients and cytoplasm, while the other one receives poor nutrients. The one that receives poor nutrients is known as the polar body, and dies. This doesn’t just happen in meiosis I, but meiosis II as well.