Spermatogenesis

Question 1

Which gene determines the sex of the embryo?

Answer 1

SRY gene

Question 2

Where do they germ cells migrate through in males?

Answer 2

The germ cells migrate via the seminiferous cords.

Question 3

What does the mesonephric duct do?

Answer 3

The mesonephric duct will promote the ejaculation of sperm cells.

Question 4

Where is the sperm produced?

Answer 4

The sperm is produced in the testis.

Question 5

What path does the sperm take after being produced?

Answer 5

It will move from the epididymis, through the vas deferens and into the urethra through the body of the penis.

Question 6

Where aer sperm cells released?

Answer 6

Sperm cells are released in the lumen of seminiferous tubules.

Question 7

Describe the structure of the testes.

Answer 7

The seminiferous tubules are separated by septums, creating structures called lobules.

The whole testes is surrounded by a connective tissue called tunica albuginea.

Each tubule is connected to the rete testis. The rete testis continues with efferent ductules that end with the epididymis. It will continue downwards reaching the vas deferens.

Question 8

Describe the 3 phases of spermatogenesis.

Answer 8

Proliferative (20 days) - during embryo development, germ cells are called spermatogonia stops initial proliferation until puberty. Once puberty arrives, the spermatogonia will resume proliferation and undergo differentiation, becoming primary spermatocytes.

Meiosis (24 days) - primary spermatocytes will move from the adluminal compartment and enter in meiosis. Secondary spermatocytes are formed which will undergo a second division forming spermatids.

Spermiogenesis (30 days) - cells will undergo remodelling to form the spermatozoa.

Question 9

What happens in the mitotic proliferative phase of spermatogenesis?

Answer 9

Starting from the basal layer are spermatogonium.

There are mainly 2 types, A pale and A dark. The dark one will start dividing via mitosis, giving rise to type A pale.

This will also be able to undergo meiosis, and will give rise to a differentiated type B spermatogonia.

Question 10

What happens in the spermatocyte (meiosis) phase of spermatogenesis?

Answer 10

After the mitotic process, spermatogonia B will stop proliferating and undergo an initial growth, becoming primary spermatocytes to start meiosis.

After meiosis I, secondary spermatocytes are formed, which will undergo a second meiotic division forming spermatids.

During mitotic division at the beginning, the cells will be continuously attached to each other. They will be separated in the last step of spermatogenesis.

The meiotic process is also continuous.

Question 11

What happens in the spermiogenesis phase of spermatogenesis?

Answer 11

The cell is a spermatid with a rounded shape, abundant cytoplasm and a big round nucleus.

Question 12

State the 4 phases that chracterise spermiogenesis.

Answer 12

• Golgi phase
• Cap phase
• Acrosomal phase
• Maturation phase

Question 13

Describe how the golgi phase characterise spermiogenesis.

Answer 13

Start observing formation of acrosomal granules, which comes from the GA. During this phase centrioles will move opposite the granules to form the tail.

Question 14

Describe how the cap phase characterise spermiogenesis.

Answer 14

The acrosomal vesicle has acquired a more localised area. The tail is starting to be formed and the shape of the cytoplasm becomes more elongated.

Question 15

Describe how the acrosomal phase characterise spermiogenesis.

Answer 15

The acrosome is almost complete in the maturation process and forms a cap on top of the nucleus. The nucleus changes colour, indicating the chromatin that was coiled with histones is now coiled with proteins called protamins.

Question 16

Describe how the maturation phase characterise spermiogenesis.

Answer 16

The cell will release the cytoplasm, forming the residue bodies. Cells will also separate from each other. The acrosomal cap is now called the acrosome and contains enzymes such as hyaluronidase, neuraminidase and acrosin, which will contribute to the penetration of the oocyte.

Question 17

What is a major difference of spermatogenesis compared to oogenesis?

Answer 17

Compared to oogenesis, spermatogenesis is a continuous phenomenon as there is a continuous production of spermatozoa.

In females there is an initial meiotic division in prophase with an arrested phase and another one in puberty.

Question 18

Why can different stages of spermatononia differentiation be observed in the semineferous tubules?

Answer 18

This is because there is an association of germ cells.

Spermatogonia A dark will generate a clone of spermatozoa every 16 days. After this, there will be 4 cycles of spermatogenesis in 74 days.

Question 19

What is the general structure of a semineferous tubule?

Answer 19

A series of cells can be observed one on top of the other, the lumen can be observed.

The tubule is surrounded by a layer of basal membrane.

Germ cells will differentiate at the level of the basal part of the tubules, then at a later stage, the differentiation into sperm cells can be observed at the level of the lumen.

Question 20

What are the histological components of a semineferous tubule?

Answer 20

The group of cells that will move from the basal lamina into the lumen are called seminiferous epithelium. This is because they form an epithelium towards the lumen.

Surrounding the tubules is a layer of fibroblast inside connective tissue. There are also isolated muscle cells called myoid cells that will contribute to the contraction of the tubules in releasing the spermatozoa.

Underneath is another type of connective tissue with capillaries and interstitial cells called Leydig cells, which produces testosterone.

There are 2 cells in the epithelium, the sertoli cells and germ cells.

Question 21

Describe the structure of sertoli cells.

Answer 21

They are considered tall cell
A collumbar shape. 
Very elaborate cytoskeleton.
Very active cell.
Tripartite structure of the nucleus, this is called a karyosome.

Question 22

What are the functions of sertoli cells?

Answer 22

These cells essential for spermatogenesis development, they also have a nutritional support as well as a mechanical support.

They have both exocrine and endocrine functions as they secrete factors necessary for the development of germ cells.

Question 23

Why is a blood testis barrier created?

Answer 23

Mature germ cells will be different from an immunological perspective from the basal cells or other cells of the body.

Therefore a blood testis barrier will need toseparate the basal compartment from the luminal apartment.

It has been demonstrated that this tight junction can open when germ cells need to go into the luminal department.

Question 24

How is a blood testis barrier created?

Answer 24

From the attachment of one sertoli cell to another with tight junctions.

Question 25

Describe the general structure of a spermatozoa.

Answer 25

The acrosomal cap is a large vesicle surrounding the nucleus.

Then an area called the connective piece (neck) surrounds the centrioles.

Then a tail that can be divided into a middle piece, a central piece and end piece.

In the middle piece are the mitochondria that wraps around the microtubules.

Question 26

What is the axoneme composed of?

Answer 26

The axoneme is composed by 9 doublets of microtubules and 2 in the centre.

Question 27

Is the sperm mobile at the moment of release?

Answer 27

The moment its released, the spermatozoa is not mobile. It will reach the motility stage in the epididymis.

Question 28

What is the difference between a cross-section of tubules in man vs in rodents?

Answer 28

In rodents, a cross section of the tubules will show one type of association cycle of cell.

While in man, there are mixed patterns along the tubule and no criteria for organization. Therefore several cycles can be observed in one cross section.

Question 29

Describe hormonal control in spermatogenesis.

Answer 29

Gonadotropin releasing hormone stimulates secretion from the anterior pituitary gland of FSH and LH.

Sertoli cells have receptors for FSH while leydig cells have receptors for LH. Therefore under the stimulation of FSH, sertoli cells will produce factors that will contribute to the differentiation of germ cells. These cells also release androgen-binding protein (ABP) in the luminal part that will bind to testosterone to promote the last phase of spermatogenesis.

Additionally sertoli cells will produce inhibin, which will have a negative action on the anterior pituitary gland, stopping the release of FSH.

Leydig cells will produce testosterone, which will act on the body for secondary effects.