Human sperm structure

Alaa Elsayed , M.D.

19 Jul 202006:18

Summary

TLDRThe human sperm is a complex motile cell composed of a head, neck, middle piece, and tail. The head contains 23 chromosomes within a nucleus, covered by an acrosome crucial for fertilization. Two centrioles within the sperm play a role in forming the mitotic spindle post-fertilization. The tail, divided into the principal and end pieces, lacks mitochondria and is supported by fibrous sheaths, with the axoneme at its core providing motility. This detailed structure is essential for sperm function and fertilization.

Takeaways

🌟 The human sperm is a motile cell composed of four main parts: head, neck, middle piece, and tail.
🔬 The sperm head is roughly 5 micrometers long and contains the nucleus with 23 chromosomes, which is crucial for fertilization.
🧬 The anterior two-thirds of the nucleus is covered by the acrosome, which contains enzymes that help in penetrating the oocyte.
🔧 The middle piece of the sperm contains two centrioles, which play a vital role in forming the mitotic spindles after fertilization.
🏋️‍♂️ The tail is composed of a principal piece and an end piece, with the principal piece lacking certain microtubules and instead having fibrous sheaths for support.
🏃‍♂️ The axoneme, found in the tail, has a '9+2' structural pattern, which is essential for sperm motility.
🔋 The middle piece is surrounded by tightly packed mitochondria, which provide the energy necessary for sperm movement.
🛡️ The connecting piece connects the head to the tail and is crucial for maintaining the integrity of the sperm structure.
🚫 Decapitated sperm, where the connecting piece is displaced, cannot swim and therefore cannot reach the oocyte.
🏁 The end piece of the tail is covered only by the plasma membrane, lacking the outer dense fibers and fibrous sheaths present in the principal piece.

Q & A

What are the four main parts of a human sperm?
-The four main parts of a human sperm are the head, neck, middle piece, and tail.
What does the sperm head resemble in shape?
-The sperm head resembles an egg with a narrow cranial part and a wider caudal part.
How long is the sperm head and what occupies most of its space?
-The sperm head is about 5 micrometers in length, and most of its space is occupied by the nucleus.
How many chromosomes does the nucleus contain and what is their role?
-The nucleus contains 23 chromosomes, which are the genetic material from the father required for fertilization.
What is the function of the acrosome and what does it contain?
-The acrosome is a cap covering the anterior two-thirds of the nucleus and contains proteolytic enzymes known as lysosomal enzymes, which help in digesting structures surrounding the oocyte to enable sperm penetration.
What are the two centrioles associated with the nucleus and where are they located?
-The two centrioles are the proximal centriole, located in the implantation fossa, and the distal centriole, located slightly distal at the neck region.
What is the significance of the proximal centriole after fertilization?
-The proximal centriole forms the mitotic spindles required for chromosome separation after fertilization.
What is the function of the connecting piece and how is it connected to the head and tail of the sperm?
-The connecting piece connects the head to the tail of the sperm. It is surrounded and connected by a banded structure, and displacement of this piece from the implantation fossa can result in the head separating from the tail.
What is the 9 plus 2 structural pattern and where is it found in the sperm?
-The 9 plus 2 structural pattern refers to the axoneme, which has two central microtubules surrounded by nine peripheral doublet microtubules. This pattern is found in the tail of the sperm.
How are the mitochondria arranged in the middle piece of the sperm and what is their role?
-The mitochondria in the middle piece are arranged in a tightly packed, helical pattern around the axoneme. They provide the energy required for sperm motility.
What are the two parts of the tail and how is the axoneme covered in each part?
-The tail consists of the principal piece and the end piece. In the principal piece, the axoneme is covered by two fibrous supports, the outer dense fibers (ODF) and the fibrous sheaths. In the end piece, the axoneme is directly covered by the plasma membrane without ODF and fibrous sheets.

Outlines

00:00

🌟 Sperm Structure and Function

This paragraph delves into the intricate structure of the human sperm, highlighting its four main parts: head, neck, middle piece, and tail. The head, measuring about 5 micrometers in length, houses the nucleus containing 23 chromosomes, essential for fertilization. The acrosome, a cap covering the anterior two-thirds of the nucleus, contains enzymes crucial for sperm penetration into the oocyte. The middle piece connects the head to the tail via the connecting piece and capitulum, with centrioles playing a vital role in forming the mitotic spindle post-fertilization. The tail, composed of the principal piece and end piece, lacks mitochondria and instead has fibrous sheaths supporting the axoneme, which is critical for sperm motility and energy provision.

05:01

🔬 Detailed Analysis of Sperm Tail

Paragraph 2 focuses on the tail of the sperm, which is divided into the principal piece and the end piece. Unlike other parts, the tail does not contain mitochondria. It is characterized by the absence of ODF 3 and 8, replaced by two longitudinal pillars of fibrous tissue. Fibro sheaths extend between these pillars, enveloping the axoneme. In the principal piece, the axoneme is covered by two fibrous supports: ODF and the fibro sheaths. In contrast, the end piece's axoneme is directly covered by the plasma membrane, lacking both ODF and fibrous sheets, indicating a structural adaptation for different functions along the tail.

Mindmap

Keywords

💡Sperm

Sperm, also known as spermatozoa, are the male reproductive cells involved in reproduction. In the video's context, sperm are described as having a complex structure, which is essential for their motility and ability to fertilize an egg. The script provides a detailed description of the various parts of a sperm cell, highlighting its role in the process of fertilization.

💡Head

The head of the sperm is a critical part, as it contains the genetic material necessary for fertilization. The video script describes it as being egg-shaped with a narrow cranial part and a wider caudal part, measuring about 5 micrometers in length. The head houses the nucleus, which contains 23 chromosomes, illustrating the importance of the sperm head in carrying the father's genetic information.

💡Acrosome

The acrosome is a cap-like structure covering the anterior two-thirds of the sperm's nucleus. It contains proteolytic enzymes, which are crucial during fertilization. As described in the script, these enzymes help digest the structures surrounding the oocyte, facilitating sperm penetration. The acrosome's function is vital for the successful fertilization of the egg.

💡Centrioles

Centrioles are cellular structures found in the sperm's neck region, with the proximal centriole located in the implantation fossa and the distal centriole slightly distal. The script explains that these centrioles are cylindrical and surrounded by nine peripheral triplet microtubules. After fertilization, the proximal centriole forms the mitotic spindles necessary for chromosome separation, demonstrating its critical role in early embryonic development.

💡Connecting Piece

The connecting piece is a banded structure that surrounds and connects the two centrioles. It is covered by a convex cap called the capitulum, which articulates with the concavity of the implantation fossa, linking the head to the tail of the sperm. The script mentions that displacement of the connecting piece can result in decapitated sperm, which cannot swim or reach the oocyte, emphasizing the structural integrity's importance for sperm motility.

💡Axonemal Complex

The axonemal complex, also known as the axoneme, is the backbone of the sperm's tail and is composed of a 9+2 structural pattern. The script describes it as having two central microtubules surrounded by nine peripheral doublet microtubules, supported by an outer dense fiber known as ODF. This complex is essential for sperm motility, as it provides the structural framework for the tail's movement.

💡Mitochondria

Mitochondria are the energy-producing organelles in cells, and in the sperm, they are tightly packed in a helical pattern around the axoneme in the middle piece. The script explains that these mitochondria provide the energy required for sperm motility, highlighting their importance in the sperm's ability to swim towards the oocyte.

💡Principal Piece

The principal piece is the main part of the sperm's tail, where the axoneme is covered by two fibrous supports: the outer dense fibers (ODF) and the fibrous sheaths. The script describes the absence of ODF numbers three and eight, which are replaced by two longitudinal pillars of fibrous tissue. This structural arrangement is crucial for the tail's flexibility and motility.

💡End Piece

The end piece is the terminal section of the sperm's tail, where the axoneme is directly covered by the plasma membrane without the presence of outer dense fibers or fibrous sheaths. The script indicates that this part of the tail does not contain mitochondria, suggesting a transition in the tail's structure as it approaches its tip.

💡Fertilization

Fertilization is the process by which a sperm cell unites with an egg cell to form a zygote, marking the beginning of embryonic development. The video script discusses various structures of the sperm, such as the acrosome and the enzymes it contains, that play a critical role in the fertilization process by enabling the sperm to penetrate and fuse with the oocyte.

💡Motility

Motility refers to the ability of the sperm to move independently, which is essential for reaching and fertilizing the oocyte. The video script details the structures that contribute to sperm motility, such as the axoneme, mitochondria, and the tail's fibrous supports. Understanding motility is crucial for appreciating the sperm's function in reproduction.

Highlights

The human sperm is a motile structure composed of four parts: head, neck, middle piece, and tail.

The sperm head is oval-shaped, resembling an egg with distinct cranial and caudal parts, measuring about 5 micrometers in length.

The nucleus occupies most of the sperm head's space, containing 23 chromosomes, which are essential for fertilization.

The acrosome, a cap covering the anterior two-thirds of the nucleus, contains proteolytic enzymes crucial for sperm penetration of the oocyte.

The implantation fossa is a small depression in the caudal part of the nucleus, associated with the proximal centriole.

Two centrioles are present in the sperm: one in the implantation fossa and one at the neck region, both playing roles in fertilization.

The centrioles are surrounded by a structure known as the connecting piece, which connects the head to the tail of the sperm.

Displacement of the connecting piece can lead to decapitated sperm, which cannot swim or fertilize oocytes.

The axoneme extends from the connecting piece to the end of the tail, forming the backbone of the sperm's tail.

The axoneme has a '9+2' structural pattern, with two central microtubules surrounded by nine peripheral doublet microtubules.

The axoneme is supported by an outer dense fiber known as ODF, forming the axoneme-ODF complex.

In the middle piece, the axoneme is surrounded by tightly packed mitochondria in a helical pattern, providing energy for sperm motility.

The tail of the sperm is composed of two parts: the principal piece and the end piece, with distinct structural features in each.

The principal piece is covered by two fibrous supports: ODF and fibrous sheaths, which are essential for sperm structure.

The end piece of the tail is directly covered by the plasma membrane, lacking ODF and fibrous sheaths.

The absence of certain ODF numbers and the presence of longitudinal pillars of fibrous tissue are unique to the sperm tail structure.