Structure of Sperm

AIPMT Biology Aspirants, read out the next AIPMT Biology Study material/ Notes of Structure of Sperm, important for AIPMT Biology.Free online notes for AIPMT.

  • Sperm is a microscopic structure which is about 60µm long.
  • Anton van Leeuwenhoek is known for discovery of sperm. Sperm is initially considered as parasite living within semen.
  • 300 million sperm complete the process of spermatogenesis each day.
  • Sperm is basically divided into head and tail. Tail further consists of neck, middle piece and end piece.
  • So, in other way sperm can be divided into following parts: Head, Neck, Middle piece and Tail.
  • Sperm is covered by the plasma membrane from head to tail.
  • Head: Sperm head is an elongated, pointed structure. Sperm head consists of Nucleus and Acrosome. Nucleus of sperm is an elongated haploid nucleus (having 23 highly condensed chromosomes). Acrosome is a cap-like structure present at the anterior end of nucleus which is filled with enzymes that help sperm penetrate ovum to bring fertilization. Enzymes present in acrosome include Hyaluronidase and Proteases. Acrosome is formed mainly from the golgi apparatus.
AIPMT-Biology-Representation of structure of Sperm

Representation of structure of Sperm

  • Neck: Neck of sperm is present just behind the head. It is the constricted region that contains centrioles which form the microtubules that comprise the remainder of the tail.
  • Middle piece: It contains numerous mitochondria arranged in a spiral fashion, which provide the energy (ATP) for locomotion of sperm tail that facilitate sperm motility essential for fertilisation and energy also required for sperm metabolism.
  • End piece: It is the terminal, tapering portion of the tail.
  • Human male ejaculates about 200 to 300 million sperms during coitus (intercourse).
  • After ejaculation, sperm do not survive for more than 48 hours within the female reproductive tract.
  • Sperms released from the seminiferous tubules, are transported by the accessory ducts. Secretions of epididymis, vas deferens, seminal vesicle and prostate are essential for maturation and motility of sperms.

Semen: Seminal plasma along with the sperms constitutes the semen.

  • Semen consists of secretions of seminiferous tubules, seminal vesicles, prostate, and bulbourethral glands.
  • In a normal ejaculation of 2.5 – 5ml of semen, approx. 50–150 million sperm/mL are found. If the number falls below 20 million/mL, male is likely to be infertile.
  • Semen has alkaline pH of 7.2–7.7 due to the higher pH and larger volume of fluid from the seminal vesicles.
  • Seminal fluid also provides sperm with a transportation medium, nutrients, and protection from acidic environment of the male’s urethra and the female’s vagina.
  • Prostatic fluid gives semen a milky appearance, and fluids from the seminal vesicles and bulbourethral glands give it a sticky consistency.
  • After ejaculation, semen coagulates within 5 minutes.
  • Capacitation: Sperm undergo functional changes in the female reproductive tract before they fertilize an ovum. These changes are called as capacitation. It causes sperm to beat / move more fastly and prepares its plasma membrane to fuse with the egg plasma membrane.
  • Hemospermia: Presence of blood in semen caused by inflammation of blood vessels lining the seminal vesicles.
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