Histology of the Male Gonads and Meiosis

Question 1

What are the different compartments of the testis?

Answer 1

the lobuli testis

Question 2

What do the septae testis converge to form, and what does this structure contain?

Answer 2

the septulae testis extend throughout the testis and converge to form the mediastinum testis which contains the characteristic epithelium-lined spaces of the rete testis

Question 3

What is the path of the efferent ductules in the testis?

Answer 3

The efferent ductules lead from the rete testis to the head of the epididymis.

Question 4

What are the histological features of the efferent ductules?

Answer 4

their irregular-shaped lumina present a characteristic epithelium consisting of high and low areas

Question 5

Where does spermatogenesis take place?

Answer 5

within the walls of the seminiferous tubules

Question 6

What are the histological features of the seminiferous tubules?

Answer 6

A transverse section of a seminiferous tubule shows some of the cell types recognised in spermatogenesis as they develop from the periphery towards the lumen of the tubule - spermatocytes, spermatids and spermatozoa. Three or more stages of the cycle of the seminiferous epithelium may be recognised in a single transverse section of a tubule; and, as spermatogenesis also proceeds in a wave-like manner along the tubules, different stages of cell development and differentiation will be seen in longitudinal and oblique sections.

Question 7

Where are the spermatogonia located?

Answer 7

They occupy a position along the basement membrane together with the Sertoli cells. There are two types of spermatogonia, Type A and Type B spermatogonia; The Type B spermatogonia differentiate into primary spermatocytes.

Question 8

What are the types of spermatogonia?

Answer 8

There are two types of spermatogonia, Type A and Type B spermatogonia; The Type B spermatogonia differentiate into primary spermatocytes.

Differentiation of Type B spermatogonia into primary spermatocytes requires a movement of the cells from one compartment within the seminiferous tubules to another. It also requires that the Type B spermatogonium enters the S phase of the cell cycle.

Question 9

What is the chromosomal and DNA complement of a newly formed primary spermatocyte prior to it entering into the first meiotic division?

Answer 9

…

Question 10

Describe the histological features of primary spermatocytes.

Answer 10

These cells are seen in the long prophase, which is characteristic of meiotic division. They have large round nuclei and appear away from the basement membrane. The chromosome filaments may appear thicker (due to pairing of homologous chromosomes) and either aggregated at one side of the nucleus (polarised) or more evenly distributed throughout the nucleus.

Question 11

Describe the histological features of secondary spermatocytes.

Answer 11

Medium sized round cells that are not often present in sections as they divide quickly (in approximately 8 hours) to form spermatids. They lie close to the lumen. Their nuclei, which are much smaller than that of a primary spermatocyte, are more densely stained, the chromatin being in irregular masses and not in the form of distinct chromosomes.

Question 12

Describe the histological features of spermatids

Answer 12

These cells occur near the lumen in close association with the cytoplasm of Sertoli cells; their structure varies with the stage of differentiation. Early spermatids have a spherical heterochromatic nucleus and eosinophilic cytoplasm (round spermatids). In more mature spermatids the nuclear head is ovoid and embedded in the Sertoli cell cytoplasm. The nucleus of a nearly mature spermatid is in the form of a thin ovoid plate and often appears as a deeply stained basophilic rod enclosed by the Sertoli cell cytoplasm. Note the sperm tails extending into the lumen. Note also the fine structural changes in spermiogenesis.

Question 13

Describe the histological features of Sertoli cells.

Answer 13

The nucleus of a Sertoli cell is slightly granular, lightly stained, contains a prominent nucleolus, may have a triangular shape and be either near or at a distance from the basement membrane. Note the fine structural details of Sertoli cells in Fig. 18.11-18.12b of Kerr’s Atlas of Functional Histology (demonstration copies on benches). The nuclei of Sertoli cells are usually paler staining than those of the spermatogenic cells and the apex of the nucleus usually points towards the lumen of the tubule.

Question 14

List the functions of Sertoli cells.

Answer 14

Sertoli cells secrete factors that regulate spermatogenesis and the activity of Leydig cells. They secrete activin and inhibin, which either increase or inhibit spermatogenesis. They secrete angrogen binding protein (ABP), which maintains a high level of androgens around developing spermatogenic cells. They also phagocytose spermatid excess cytoplasm (residual body) and assist in the spermatogenic movement of sperm and in spermiation.

Question 15

What is the ‘blood testis barrier’?

Answer 15

The blood testis barrier refers to the tight junctions between Sertoli cells, membranous cisternae and parallel intervening actin filament bundles. It divides the seminiferous tubule into:

1. The basal compartment: spermatogonia and early primary spermatocytes
2. Adluminal compartment: differentiating spermatocytes and spermatids

Question 16

What is the significance of androgen-binding protein?

Answer 16

Androgen binding protein (ABP) complex maintains high levels of androgens around developing spermatogenic cells (x200 normal levels). Androgens are very important in spermatogenesis.

Question 17

What are the characteristics of a Leydig cell at the LM level?

Answer 17

The interstitial cells of Leydig are located in the interstitial tissue near the blood capillaries and between the seminiferous tubules. These cells have round nuclei and pale-staining cytoplasms, which give them a bubbly appearance (like many steroid-producing cells). The cells contain abundant sER. They are usually large in size compared to other cells in the CT.

Question 18

What are the characteristics of a Leydig cell at the EM level?

Answer 18

1. Crystals of Reinke: protein units in hexagonal arrays
2. Lipfuscin granules: derived from lysosomes
3. Lipid droplets
4. Large amounts of sER
5. Mitochondria with tubular cristae

Question 19

What is the role of interstitial cells (of Leydig)?

Answer 19

The interstitial cells of Leydig secrete testosterone, which is the major male sex hormone. Its functions include:

1. Promoting development of male sex organs in early fetal development
2. Promoting male sexual characteristics
3. Promoting spermatogenesis
4. Increasing basal metabolism and physical energy
5. Promoting bone growth and increasing bone density
6. Increasing muscle growth, thickness of skin, and sebaceous gland secretion

Question 20

What is the chromosomal composition of primary and secondary spermatocytes?

Answer 20

Primary spermatocytes have a 2n chromosome number but they have double the amount of DNA (duplex chromatid chromosomes).

Secondary spermatocytes have 23 chromosomes (n) of which each is 2 chromatids joined by centromere. They therefore have double the required amount of DNA.

Question 21

What is the significance of intercellular bridges between cells of seminiferous epithelium?

Answer 21

The intercellular bridges ensure that a whole network of cells undergo development at the same time (allows controlled spermatogenesis).

Question 22

What effect does FSH have on developing spermatozoa?

Answer 22

FSH stimulates Sertoli cells to produce androgen-binding protein (ABP), thereby stimulating spermatogenesis. FSH also stimulates Sertoli cells to produce inhibin, which provides negative feedback to the anterior pituitary to decrease FSH secretion.

Question 23

What affect does temperature have on developing spermatozoa? How is this controlled?

Answer 23

The process of spermatogenesis is highly sensitive to temperature. Normal spermatogenesis requires 2-3 degrees Celsius lower temperatures than core body temperature. This is achieved in three ways:

1. Dartos muscle of the scrotal skin
2. Cremaster muscle in spermatic cord: elevates testes on exposure to cold and during arousal – warmth reverses the process.
3. Panpiniform plexus of the spermatic cord: returning venous blood cools the incoming arterial blood. This is a heat exchange unit.

Question 24

What are the phases of the cell cycle? During which phase is the DNA duplicated?

Answer 24

1. Interphase: the cell synthesises RNA and producing protein to grow in size.
2. Gap O (GO): there are times when the cell will leave the cycle and quit dividing. This may be temporary resting period or more permanent.
3. Gap I (G1): cell increase in size in gap 1, produce RNA and synthesis protein. There is a checkpoint at this time that everything is okay to begin DNA synthesis.
4. S Phase: to produce two similar daughter cells, the complete DNA instructions in the cell must be duplicated. DNA replication occurs during the S (synthesis) phase.
5. Gap 2 (G2): during the gap between DNA synthesis and mitosis, the cell will continue to grow and produce new proteins. At the end of this gap is another checkpoint to determine if the cell is ready to enter M (mitosis) and divide.
6. Mitosis (M phase): cell growth and protein production stop at this point in the cell cycle. All of the cell’s energy is focused on the complex and orderly division into two similar daughter cells. As with G1 and G2, there is a checkpoint in the middle of mitosis that ensures the cell is ready to complete cell division.

Question 25

What are the phases of mitosis? Briefly, what are the key events in the phases?

Answer 25

1. Interphase: DNA replicates, the cell centrioles divide, and proteins are actively produced.
2. Prophase: the nucleolus fades and chromatin (replicated DNA and associated proteins) condenses into chromosomes. Each replicated chromosome comprises two chromatids, both with the same genetic information. Microtubules of the cytoskeleton, responsible for cell shape, motility and attachment to other cells during interphase, disassemble. The building blocks of these microtubules are used to grow the mitotic spindle from the region of the centrosomes.
3. Prometaphase: nuclear envelope breaks down so there is no longer a recognisable ucleus. Some mitotic spindle fibres elongate from the centrosomes and attach to kinetochores, protein bundles at the centromere region on the chromosome where sister chromatids are joined. Other spindle fibers elongate an doverlap each other at the cell centre.
4. Metaphase: chromosomes align at the center of the cell.
5. Anaphase: spindle fibers shorten, kinetochores separate and the chromatids (daughter chromosomes) are pulled apart and begin moving to the cell poles.
6. Telophase: the daughter chromosomes arrive at the poles and the spindle fibers that have pulled them apart disappear.
7. Cytokinesis: spindle fibers begin to break down until only that portion of overlap is left. It is in this region that a contractile ring cleaves the cell into two daughter cells. Microtubules then reorganise into a new cytoskeleton for the return to interphase.

Question 26

How many chromosomes does the human genome contain? How many pairs of autosomes? What are the sex chromosomes?

Answer 26

The human genome contains 23 pairs of genomes. Of these, 22 pairs are autosomes. The females the sex chromosomes are the 2 X chromosomes, males have one X chromosome and one Y chromosome.