Spermatogenesis | spermatozoa | spermatid and sperm morphology
hi guys in this article we know about spermatogenesis spermatozoa spermatid and sperm morphology.as we know that gametogenesis is the process of formation and differentiation of haploid gametes like a sperms and OVA from the diploid primary germ cells that is known as gametogonia.
There is two types of gametogonia spermatogonia and oogonia present in primary sex organ calls gonads (testes in male and ovaries and female) respectively.
Spermatogenesis is continuous process and it is completed in about 74 days in human beings. Seasonal breeding animals the testis undergo testicular cycle in which the testis and their spermatogenic tissues become functional only in the specific breeding season.
so in some seasonal breeding mammals like that bat, otter and llama testis enlarge become functional and descend into scrotum in breeding season while become reduce and non-functional and send into abdomen in other season.
But in human beings, lion, bull and horse the testis lies permanently in the scrotum and as per spermatogenesis occurs throughout the year in human male testes descend into the respective scrotal sac during 7th month of development under the stimulation of follicular stimulating hormone which was secreted from pituitary glands. but in some other mammals like elephant, Dolphin ,whale and seal testis lies permanently in the abdomen.
definition of spermatogenesis is the formation of haploid microscopic and functional male gametes that is known as a spermatozoa or sperm cell from the diploid reproductive cells that is known as spermatogonia present in the testis of male organism.
And spermatogenesis process is compromise of two steps formation of spermatid and spermiogenesis that is formation of sperm from spermatid. Formation of spermatid compromise of three phases
Spermatogenesis steps:- there are two spermatogenesis steps
A) formation of spermatid
Formation of spermatid have three steps
1) multiplicative phase:- it involves the Rapid mitotic division of diploid primary germ cells called spermatocytes present in germinal epithelium of seminiferous tubules of testis. the cells are on differentiated and have large and chromatin reach nucleus this form large number of diploid and rounded sperm mother cells are spermatogonia.
Some spermatogonia act as stem cells and go on dividing and adding new cells by repeated mitotic division so forming large population of spermaticgenic tissues these are called as type A spermatogonia and some of other spermatogonia move inward and enter into growth phase this type of spermatogonia is known as B type.
2) growth phase :- it is characterized by spermatocytogenesis in which diploid spermatogonia increase in size by the accumulation of nutritive materials derive from germinal cells in the cytoplasm and replication of DNA and forms diploid primary spermatocytes.
3) maturation phase:- it is characterized by meiosis the diploid primary spermatocytes undergoes meiosis that is reductional division and form two haploid cells known as secondary spermatocytes. Each secondary spermatocytes containing 23 chromosomes in the case of human beings and it is immediately followed by meiosis II cell division that is known as equational cell division in each secondary spermatocyte to form two haploid spermatids each of which has 23 chromosomes. So each of diploid spermatogonia produce four haploid spermatids.
B) spermiogenesis :- it is transformation of a non-motile rounded haploid spermatid into functional and motile spermatozoa is known as spermiogenesis there man is to increase the sperm motility and it involve following changes:-
1) nucleus become condensed, narrow and anteriorly pointed due to loss of material like RNAs , nucleolus and most of protein
2) a part of Golgi body of a spermatic form the acrosome while the lost part of Golgi body is called Golgi rest
3) centrioles of a spermatic form the neck of sperm cells
4) distal centrioles give rise to axoneme
5) mitochondria form a spiral ring behind-the-neck around the distal centriole and proximal part of this is known as nebenkern
6) most of cytoplasm is lost but some cytoplasm forms sheath of tail of sperms.
7) the spermatids mature into spermatozoa in deep folds of cytoplasm of the sertoli cells which also provide nourishment to them. mature spermatozoa are released in lumen of seminiferous tubules is known as spermiation.
Spermatozoa are haploid containing half number of chromosomes, oval, rounded, motile structure also known as sperm cells and that is male sex cells that carries man genetic material and they are tiny object that cannot be seen without microscope.
in healthy men one ejaculation usually content between 40 millions to 60 million sperm cells.sperms have oval had a short middle and long tail they moved by whiping their tails. sperm fertilizes a woman’s egg by breaking through the membrane that Surround the egg.
Nutrition of sperm cells
As we know that mature spermatozoa are released in lumen of seminiferous tubules where they get nutrition and development nursing by sertoli cells of seminiferous tubules and sertoli cells is act as nursing cell that provide nutrition to developing spermatozoa.
Motility in sperm cells
Sperm motility is the ability of a sperm to move efficiently this is important factor which help in fertilizing the egg because sperm need to move through the female genital tract or reproductive tract to reach the fertilizer egg .poor sperm count have less motility and can be cause of male factor infertility.
Sperm pathway is approach of sperm to ovum during the copulation male inserts its erectile penis in the vagina of female and release about 3.5 ml of seminal fluid this process is known as ejaculation. seminal fluid content as many as 200 to 300 million sperm.
this ensure the reaching of a number of sperm to the ovum is many sperm are killed by acidity of female genital tract and many as enulf by phagocytes of the vaginal epithelium so that only about hundred sperm reach the fallopian tube. The sperms cells swims in the seminal fluid by lacing movement of the rate of 1 to 4 mm per minute.
The sperm swims towards the fallopian tube through the uterus it is added by aspiratory action of the uterus and peristaltic movement of fallopian tube.
Capacitation :- capacitation is the phenomenon of physiological maturation of sperms inside the female genital tract. it occurs in the presence of viscous fluid secreted from the secretary cells of epithelial lining of oviduct mucosa. it takes about 5 to 6 hours.
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Spermatozoa or sperm cell is haploid male gamete whose primary function is to fuse with ovum to restore diploid condition and to transmit paternal character to new offspring.
Sperm morphology consist of structure of spermatozoa or sperm. Structure of sperm of mammalian sperm is mini microscopic flagellated and motile gametes with no nutritive material, protective envelops and most of cell organelles like ribosome endoplasmic reticulum etc are absent, the whole body of sperm is envelop by plasma membrane only it is basically formed of four parts
1) head of sperm :- sexy shape of red berries in different mammals it is generally oval and flat in men and formed of two parts acrosome and nucleus.
Acrosome is a small cap like-pointed structure present at the tip of nucleus. it is formed from part of Golgi body of spermatid. during the sperm entry the acrosome secrets lytic enzyme called as hyaluronidase which helps in the penetration of ovum.
Nucleus of sperm is long narrow and pointed but it is Flat and oval in human sperm it is formed by condensation of nuclear chromatin of spermatid and loss of RNA, nucleolus and acidic protein. Chemically the nucleus is formed of deoxy ribonucleoprotein DNA that is carrier of genetic information
2) Neck :- neck is the smallest part of spermatozoa and may be indistrict. it is formed of two centrioles perpendicular to each other and is formed from centrosome of spermatid. they have proximal centriole and distal centriole and their micro tubule structure having 9 + 0 arrangement.
3) middle piece :- middle piece of sperm lies behind the neck and it is cylindrical in human sperm it is formed of mitochondrial spiral around the proximal part of axoneme. the mitochondria are the Carriers of oxidative enzyme and the enzyme which are responsible for oxidative phosphorylation so the middle piece is known as powerhouse of sperm.
4) tail of sperm :- it is the longest part of a sperm it is cylinder and tapering part it is formed of two parts Central and contractile and microtubule part known as exoneme. And Outer part is known as protoplasmic sheath. Microtubules of Agro names are arranged in 9 + 2 arrangement. tail shows lacing movement which provide forward push to the sperm.