Gametogenesis

📌 Definition & Site
🖇 Gametogenesis = process of forming male & female gametes (sex cells).
🟠 Site: Gonads → Testes in males, Ovaries in females.
🟣 Types:

• Spermatogenesis → sperm formation.
• Oogenesis → ovum (egg) formation.

📌 🟠 Spermatogenesis (Male Gamete Formation)
🖇 Definition: Transformation of spermatogonia into mature spermatozoa.
🖇 Site: Seminiferous tubules of testis.
🖇 Onset: Begins at puberty (13–16 years) and continues for life.
🖇 Duration: Around 64 days.

🚨 Steps:

1. Spermatocytogenesis → cell division.
2. Spermiogenesis → maturation (no further division).

🟣 Spermatocytogenesis:

• Spermatogonia (46, XY) divide by mitosis:
  • Type A → renew stem cells.
  • Type B → grow into Primary Spermatocytes.
• Primary Spermatocyte (4n DNA) → 1st meiotic division → two Secondary Spermatocytes (23, X or 23, Y).
• Secondary Spermatocytes → 2nd meiotic division → Spermatids (haploid).

🟣 Spermiogenesis (Maturation):

• Nucleus → forms sperm head.
• Golgi apparatus → forms acrosomal cap covering anterior 2/3 of nucleus.
• Centrioles → form tail (flagellum).
• Mitochondria → form spiral sheath in midpiece to supply energy.
• Cytoplasm → removed by Sertoli cells.

🟠 Structure of Mature Sperm:
Head contains nucleus and acrosome.
Neck contains centrioles.
Tail divided into three parts: middle piece (mitochondria), principal piece (motility), and end piece.

📌 🟣 Seminal Fluid
🖇 Formation: Mixture of sperms from testis and secretions from seminal vesicles, prostate, and bulbo-urethral glands.

🖇 Characters:
Thick, white, gelatinous fluid.
Volume 3–5 ml per ejaculation.
Characteristic odor.
Alkaline in reaction.
Sperm count 200–600 million per ejaculation.
More than 80% motile.
Less than 10% abnormal forms.

🖇 Functions:
Fructose provides energy for sperms.
Prostaglandins aid motility and transport.
Alkaline nature neutralizes vaginal acidity.

🚨 Anomalies:
Azoospermia → no sperms.
Oligospermia → fewer than 20 million sperms.
Immotile sperms or Necrospermia → dead sperms.
Abnormal shapes → dwarf, giant, double head, or double tail.

📌 🟠 Sperm Transport
In males → from epididymis to urethra through vas deferens, with secretions added to form seminal fluid.
In females → deposited in vagina (posterior fornix), passes through cervical canal into uterus, then reaches uterine tube.
About 400 sperms reach the ampulla.
Fertilization power lasts 24 hours.
Only one sperm fertilizes the ovum.

📌 🟣 Oogenesis (Female Gamete Formation)
🖇 Definition: Transformation of oogonia into mature ovum.
🖇 Site: Cortex of ovary.
🖇 Onset: Begins during intrauterine life and continues until menopause.

🚨 Stages:

1. Prenatal (Intrauterine):
   Oogonia (46, XX) multiply by mitosis and form Primary Oocytes (4n DNA).
   Each primary oocyte starts meiosis I but stops in prophase until puberty.
2. Postnatal (Before Ovulation):
   At puberty, each month a primary oocyte completes meiosis I → forms one Secondary Oocyte and one First Polar Body.
3. At Ovulation:
   Secondary oocyte begins meiosis II but stops at metaphase.
   If fertilization occurs → meiosis II completes, producing a Mature Ovum and Second Polar Body.
   If no fertilization → the secondary oocyte degenerates within 24 hours.

🟠 Number of Oocytes:
At birth → 1–2 million primary oocytes.
At puberty → about 40,000 remain.
Throughout reproductive life → around 480 oocytes are ovulated.

📌 🟣 Comparison Between Male & Female Gametes
Male gametes (sperms) are very small and highly motile, with little cytoplasm and two types (22+X, 22+Y).
Female gametes (ova) are large, immobile, have abundant cytoplasm with yolk, and only one type (22+X).
Primary spermatocytes form after puberty, but no new primary oocytes form after birth.

📌 🚨 Clinical Points
Azoospermia and Oligospermia cause male infertility.
Abnormal sperm motility or shape reduces fertilization chances.
If fertilization doesn’t occur within 24 hours, the secondary oocyte degenerates leading to infertility.