<< Chapter < Page Chapter >> Page >

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

what are the characteristics of blood
yeboah Reply
they are red in colour
Tawoi
Me phone no petandi meku doubt vunte nenu phone chesi cheputhanu
Mohan Reply
What is respiratory disease
Rita Reply
What are the importance of homeostasis in human body?
Pablo Reply
homeostasis
Abena
it help to keep our salt and water balance
Husna
Homeostasis regulates and mentain internal equilibrium (ie temperature and pH) of the body.
Edmund
maintain temp and ph so our enzyme works properly
Husna
The inability of the body regulating and maintaining the temp. and pH results in disease affection.
Edmund
formation of the bone
Ali Reply
.
mohamed
عاوز ايه يعني من الفورمايشن
Doctor
notes on cell theory and discovery
Masika Reply
Cell theory are a set of rules for overall knowledge on cells. The most famous set of rules include: All cells arise from other cells. The cell is the functional unit of life. The structure (organelles) and morphology of the cell indicates it's main functions.
Carmelo
Antonie Van L. was the first to actually observe alive microorganisms (such as protist and bacteria) in a microscope in the 1600s.
Carmelo
electro phisiology meand
aparna Reply
rouleaux formation factors
Hridya Reply
can anyone suggest me how to learn forearm and hand topic of anatomy?
Anjali Reply
can anyone suggest me how to learn forearm and hand anatomy topic?
Anjali
can anyone suggest me how to learn forearm and hand topic of anatomy? pls pls tell
Anjali
check out youtube videos for trickss and while learning the boness part keep the bone wid u and learn ..... hope it helps u
Subuhi
ohk
Anjali
formation of the bone
Ali
what is the space between d dura mater and pia mater
Uwakwe Reply
Subdural space
Juveriya
Actually sub dural space is space between dura and arachnoid mater And sub arachnoid space is space between arachnoid and pia mater
Juveriya
the smallest bone in the body
Bahja Reply
stapes is the smallest bone in human Body
dipayan
Yeah
Ridwan
what is cell membrane
Hajara
cell membrane is like a protective cover of a cell and it's cytoplasm
dipayan
thanks
Hajara
list two adpitive mechanism that control homeostasis condition
Hajara
positive and negative feedback Mechanism
dipayan
@Dipayan, a cell membrane encloses and surrounds the cytoplasm of the cell. It's structure varies between species of life (eukaryotes, archaea, bacteria), but it is mostly composed of phospholipid, arachidonic acid, proteins, glycoproteins, glycolipids, and cholesterol.
Carmelo
and the glycoprotein and polysaccharides of the cell membrane forms the glycocalyx which has several functions especially in a bacteria.
Norom
can we stain sputum samples?
Apai Reply
Yes
Dorcas
wat do we use in staining them?
Apai
gram stain
Mawuli
Hello
bona
zeel Nelson stain
bona
why the ganglion cyst bumps?
dipayan Reply
i think fats gather under the skin
Matthew
but there were some tissue is present
dipayan
plz Matthew clearly present your answer
dipayan
appilied physiology of umn and lmn lesion
Ananthan Reply
what is umn and imn
dipayan
I don't know
bona
saaa
Patricia
Upper motor neurons (UMN) are responsible for conveying impulses for voluntary motor activity through descending motor pathways that make up the upper motor neurons. UMN send fibers to the LMN, and that exert direct or indirect supranuclear control over the LMN of the cranial and spinal nerves.
Amit
What is your doubt
Mohan
Anatomy of functions of the skeletal system
Tobokwa Reply

Get the best Anatomy & Physiology course in your pocket!





Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Anatomy & Physiology' conversation and receive update notifications?

Ask