Experiment 8: Identification of Stages of Gamete Development - T.S. of testis and T.S. of ovary

AIM

To identify the stages of gamete development, i.e. T.S. of testis and T.S. of ovary through permanent slides.

PRINCIPLE

Gametogenesis is the process of formation of haploid gametes from diploid germ cells. In males it is called spermatogenesis in testis and in females oogenesis in ovary. Meiosis reduces chromosome number to half.

Spermatogenesis occurs in seminiferous tubules lined by germinal epithelium. Spermatogonia divide mitotically and differentiate through primary, secondary spermatocytes and spermatids to spermatozoa with support from Sertoli cells and testosterone from Leydig cells.

Oogenesis occurs in ovarian follicles. Primordial follicles develop into primary, secondary and Graafian follicles containing ovum and antrum cavity. After ovulation, ruptured follicle forms corpus luteum that secretes progesterone.

REQUIREMENTS

• Permanent slides of T.S. of testis and ovary
• Light and compound microscope
• Notebook
• Pencil and eraser
• Lens cleaning fluid and cleaning paper

PROCEDURE

1. First, clean the slide and microscope with the help of lens cleaning paper and cleaning fluid.
2. Fix the slide on the stage of microscope.
3. Observe the slide of testis and ovary first under the lower magnification and then under higher magnification.

OBSERVATION

T.S. of Mammalian Testis

Transverse section of testis shows many coiled seminiferous tubules embedded in interstitial tissue. Each tubule is lined by germinal epithelium that produces male germ cells. Various stages from periphery to lumen are visible.

Identification Characteristics

• The seminiferous tubules are easily seen in cross-section of testis.
• The presence of larger cells called Sertoli cell is the characteristic feature of this slide. These cells provide nutrition to the developing spermatozoa.
• The presence of interstitial cells or Leydig's cell is evident.

General Characteristics

• The transverse section of testis shows many seminiferous tubules embedded in interstitial tissues. These appear as coiled, circular structures.
• Each seminiferous tubule is lined on its inside by germinal epithelium which divides mitotically to produce male germ cells called spermatogonia.
• Various stages of development of sperm from spermatogonia are seen from periphery to the lumen of seminiferous tubules.
• All these stages are clearly visible in a transverse section of testis. The mature sperms are present in the centre and primary spermatocyte in the middle layer.
• Sertoli cells are prominent pyramid-shaped cells found in between the germinal cells. These cells provide nutrition to the developing spermatozoa.
• Leydig cells are seen in the interstitial tissue. They produce the hormone called testosterone responsible for development of male secondary sexual characters.

Key labels observed: Spermatogonium, Sertoli cell, Primary spermatocyte, Secondary spermatocyte, Spermatid, Spermatozoa.

T.S. of Mammalian Ovary

Transverse section of ovary shows mass of primordial follicles, interstitial tissue, antrum follicle and ovarian stroma lined by germinal epithelium. Various circular Graafian follicles are seen in stroma with blood vessels.

Identification Characteristics

• The presence of Graafian follicle is characteristic feature of mammalian ovary.
• Each Graafian follicle contains one ovum and a cavity called antrum.

General Characteristics

• The section of mammalian ovary shows the mass of primordial, interstitial follicle cell mass, antrum follicle tissues lined up by germinal epithelium. Ovarian stroma is present.
• The stroma is made up of connective tissue, blood vessels and nerve fibres.
• Various circular structures seen in stroma are Graafian follicles.
• In the later stages of follicle which separates the ovum and the cells around it except at one point.
• As this cavity enlarges, Graafian follicle becomes ready to release ovum.
• The mature follicle ruptures and releases ovum. The ruptured follicles form corpus luteum and release progesterone.
• All stages of oogenesis cannot be seen at same time, however, they can be seen when an ovary is observed for entire duration of menstrual cycle.

Key labels observed: Blood vessels, Primary follicle, Tertiary follicle showing antrum, Graafian follicle, Ovum, Corpus luteum.

RESULT

The transverse sections of testis and ovary of mice clearly show the developmental stages of sperms and ova by the process of gametogenesis.

CONCLUSION

Spermatogenesis shows centripetal differentiation from spermatogonia at periphery to spermatozoa in lumen, supported by Sertoli and Leydig cells. Oogenesis shows follicular development from primordial to Graafian stage and formation of corpus luteum, ensuring haploid gamete formation.

PRECAUTIONS

• The prepared permanent slide should be handled carefully.
• It should be observed initially under the low and then under the higher magnification of the microscope.
• The diagram of the structures seen in T.S. of ovary and testis should be drawn and should be labelled properly in order to develop understanding of the detailed structures.