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Spermatogenesis

As just noted, spermatogenesis occurs in the seminiferous tubules that form the bulk of each testis (see [link] ). The process begins at puberty, after which time sperm are produced constantly throughout a man’s life. One production cycle, from spermatogonia through formed sperm, takes approximately 64 days. A new cycle starts approximately every 16 days, although this timing is not synchronous across the seminiferous tubules. Sperm counts—the total number of sperm a man produces—slowly decline after age 35, and some studies suggest that smoking can lower sperm counts irrespective of age.

The process of spermatogenesis begins with mitosis of the diploid spermatogonia ( [link] ). Because these cells are diploid (2 n ), they each have a complete copy of the father’s genetic material, or 46 chromosomes. However, mature gametes are haploid (1 n ), containing 23 chromosomes—meaning that daughter cells of spermatogonia must undergo a second cellular division through the process of meiosis.

Spermatogenesis

This figure shows the steps in spermatogenesis. The left panel shows a flow chart that outlines the different steps in the formation of sperm. The right panel shows a micrograph with the cross section of a seminiferous tubule.
(a) Mitosis of a spermatogonial stem cell involves a single cell division that results in two identical, diploid daughter cells (spermatogonia to primary spermatocyte). Meiosis has two rounds of cell division: primary spermatocyte to secondary spermatocyte, and then secondary spermatocyte to spermatid. This produces four haploid daughter cells (spermatids). (b) In this electron micrograph of a cross-section of a seminiferous tubule from a rat, the lumen is the light-shaded area in the center of the image. The location of the primary spermatocytes is near the basement membrane, and the early spermatids are approaching the lumen (tissue source: rat). EM × 900. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)

Two identical diploid cells result from spermatogonia mitosis. One of these cells remains a spermatogonium, and the other becomes a primary spermatocyte    , the next stage in the process of spermatogenesis. As in mitosis, DNA is replicated in a primary spermatocyte, and the cell undergoes cell division to produce two cells with identical chromosomes. Each of these is a secondary spermatocyte. Now a second round of cell division occurs in both of the secondary spermatocytes, separating the chromosome pairs. This second meiotic division results in a total of four cells with only half of the number of chromosomes. Each of these new cells is a spermatid    . Although haploid, early spermatids look very similar to cells in the earlier stages of spermatogenesis, with a round shape, central nucleus, and large amount of cytoplasm. A process called spermiogenesis    transforms these early spermatids, reducing the cytoplasm, and beginning the formation of the parts of a true sperm. The fifth stage of germ cell formation—spermatozoa, or formed sperm—is the end result of this process, which occurs in the portion of the tubule nearest the lumen. Eventually, the sperm are released into the lumen and are moved along a series of ducts in the testis toward a structure called the epididymis for the next step of sperm maturation.

Questions & Answers

Describe the system s that maintain the internal environment of a human body
Nora Reply
an organism is a living being that had a cellular structure and that can independently perform all physiological functions needed for life.
Nwecho Reply
a tissue is a group of similar cells that work together to perform a particular function
Nwecho
chemical level, cellular level, tissue level, organs level, organ systems, organisms
Nwecho Reply
they're reproduction but also produces hormones dus they're endocrine system
Nwecho
cells are smallest independent functional unit of a living organism
Nwecho
an organ is an anatomically distinct structure of the body composed of two or more tissue
Nwecho
an organ system is a group of organs that work together to perform a major function.
Nwecho
Structural Organization of the human body.
Tammy
What is a cavity
Isaac Reply
Permanently damaged areas in teeth that develop into tiny holes
MASLAH
what is meant by epithelial tissue
Zahid
What is the difference between regional anatomy and systematic anatomy?
Andrew Reply
Regional anatomy is the study of the interrelationships of all of the structures in a specific body region, such as the abdomen. ... In contrast, systemic anatomy is the study of the structures that make up a discrete body system—that is, a group of structures that work together to perform a unique
Tammy
Pls is that all
Petra
regional anatomy studies structures that contribute to specific body region example the thoracic region while systematic anatomy studies structures that contribute to specific body systems example respiratory system
Nwecho
so meaning of dissect
Mary Reply
it is the dismembering or the cutting of living organism to study the anatomical structure of it body
Kwasi
what are lymph nodes
Memory Reply
what is the best book that shows unit 1 about cell unit 2 about tissue unit 3 about embroyology
Abraham Reply
2
Hellen
to understand structure of body able to understand function of system. to understand how to build human body and function
Dereje Reply
hi
Neela
to determine body structures
Petra Reply
to know the use of each and every part of our body
Petra
to understand how our body structures work to support our lives
Petra
Is this a question?
Tammy
So what was the question?
Thamie
All the body work together to make the whole organism life possible
Kwasi
what is the importance of conversation
Hellen
To be able to identify the parts of the body and their functions
Hodasi
ok
Hodasi
Ideas are shared during conversation also informations are given
Hodasi
it reduces cost
Kwasi
what is carbon dioxide respiratory system why?
Prachi Reply
Carbon dioxide (CO2) is involved with the chemical process of cellular respiration. It is produced as a cellular waste product during the decomposition reactions and serves an important role in maintaining the appropriate acid-base balance in the body.
Tammy
thank you
Prachi
You're welcome!
Tammy
i have not under stood human heart
Simbwa Reply
means?
Dilshan
why a man became wild at the time of sexual intercourse. reason?
Soul
what is anatomy
philemon Reply
what is anatomy in terms of medicine
philemon
it is the study of human and animal form by observing and examined them and sometimes dissecting them and view the tiny thing by the use of microscope
Kwasi
anatomy is simply the scientific study of the body's structures
Petra
study of human body and animal
Crystal
why a man becomes wild at the time of sexual intercourse
Soul
Anatomy is the study of structure of the human body.
Tammy
Physiology is the study of the functions of the human body
Tammy
what is the difference between regional anatomy and systematic anatomy?
Andrew
study of body And animal structure.
Sohail
Describe early studies into the working of human body.
Tonny Reply
please guys help me to answer this question; Define the two divisions of the skeleton ?
Jonathan Reply
two example of appendicular skeleton
Jonathan
upper limb ;eg humerus n lower limb;eg tibia
BRIAN
what is a metabolism?
Kheth Reply
Metabolism is the sum total of all the chemical processes in the body. It is divided into an anabolic(building up) and catabolic(breaking down) metabolism)
Jonas

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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