Spermatogenesis and Oogenesis Overview

Spermatogenesis and Oogenesis

• A spermatozoon has a head, neck, middle piece, and tail
• Spermatogenesis stages are summarized in Fig. 2.5
• Spermatozoa develop from spermatids
• Spermiogenesis is the process of spermatid to spermatozoon conversion (Fig. 2.6)
• Oogenesis stages are summarized in Fig. 2.8
• An ovarian follicle is a structure containing a developing ovum surrounded by follicular cells, with a fluid-filled cavity (Fig. 2.12)
• Ovarian follicles have a cellular covering called theca interna, which produces oestrogens (Fig. 2.13)
• Follicle size increases and bursts to expel the ovum, a process called ovulation
• The corpus luteum forms from enlarged follicular cells after ovulation (Fig. 2.17)
• The corpus luteum secretes progesterone, essential for pregnancy maintenance

Mature Spermatozoon Structure

• A highly specialized, mobile cell
• Possesses a head, neck, middle piece, and tail (Fig. 2.1)
• An axial filament passes through the middle piece, extending to the tail
• Measures approximately 60 µm in length
• Head is piriform (pear-shaped), measuring 4 µm in length

Spermatogenesis

• Gamete formation in males occurs during the reproductive period (puberty to old age)
• Takes place in the seminiferous tubules of the testes
• Cells of varying sizes and shapes (Fig. 2.4) are found within tubules
• Spermatogenesis stages include spermatogonia (types A and B), primary spermatocytes, secondary spermatocytes, spermatids, and spermatozoa (Fig. 2.5)
• Spermiogenesis (Figs 2.2 and 2.6) is the process where a spermatid transforms into a spermatozoon

Oogenesis

• Gamete formation in females occurs during the reproductive period (puberty to menopause)
• Takes place in the ovary, specifically within the follicles
• Involves oogonia, primary oocytes, secondary oocytes, and ova (Fig. 2.8)
• Primary oocytes remain in prophase of the first meiotic division until maturation
• Approximately 40,000 primary oocytes are present at birth
• The process involves the first and second meiotic divisions, and produces one ovum and polar bodies
• Stages in oogenesis and the structures involved are shown in Fig. 2.8

Ovarian Follicles

• Structures surrounding and protecting developing ova (oocytes)
• Formation includes flattened stromal cells surrounding oocytes, developing follicular cells, and later theca interna and externa (Fig. 2.9)
• They undergo various stages of development, including primordial, primary, secondary, and tertiary follicle stages
• Rupturing of follicles marks ovulation (Fig. 2.10 and 2.15)

Ovulation

• The expulsion of an ovum or secondary oocyte from the ovary
• Triggered by factors including high LH concentration and prostaglandins, which cause follicular wall contractions

Corpus Luteum

• Forms after ovulation from ruptured follicular cells
• Primarily secretes progesterone.
• Duration of existence depends on fertilization; if no fertilization, it degenerates (corpus albicans) (Fig. 2.18)
• Maintains pregnancy during early stages (corpus luteum of pregnancy)

Differences between Spermatogenesis and Oogenesis

• Spermatogenesis produces four spermatozoa from one primary spermatocyte, while oogenesis produces one ovum and polar bodies from one primary oocyte
• Spermatogenesis is a continuous process throughout the reproductive period, whereas oogenesis is cyclical, with pauses between cycles
• Spermatocytes form in the seminiferous tubules of the testes, while oocytes form in the follicles of the ovaries

This quiz focuses on the processes of spermatogenesis and oogenesis, detailing the stages of development for spermatozoa and ova. Key structures such as ovarian follicles and the corpus luteum are discussed, alongside their functions in reproduction. Test your understanding of these essential biological processes.