Intoduction To Embryology, Testis & Spermatogenesis - Nto, Nto Johnson
Intoduction To Embryology, Testis & Spermatogenesis - Nto, Nto Johnson
Intoduction To Embryology, Testis & Spermatogenesis - Nto, Nto Johnson
Zygote - a diploid cell resulting from the fusion of two haploid gametes; a
fertilized ovum.
Cleavage - is the division of cells in the early embryo.
The process follows fertilization, with the transfer being triggered by the
activation of a cyclin-dependent kinase complex.
The zygotes of many species undergo rapid cell cycles with no significant overall
growth, producing a cluster of cells the same size as the original zygote.
Morula (Latin, morus: mulberry) – is an early-stage embryo consisting of 16
cells (called blastomeres) in a solid ball contained within the zona pellucida.
Blastomere – is a type of cell produced by cleavage (cell division) of the zygote
after fertilization and is an essential part of blastula formation.
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Embryological terms
Neurula- the embryo may be referred to as neurula at the stage of
neurulation or formation of the neural tube
Embryo (Gr, embryon)
This refers to early stage of developing human being which extends
to the end of the 8th week.
At this stage the beginnings of all major structures are present
Gastrula- a three layered or trilaminar embryonic disc. The three
germ layers differetiate into the tissues and organs of the embryo.
Implantation – the process by which the blastocyst attaches to the
endometrium and embeds in it
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Embryological terms
Conceptus (L. concepto- derivatives of a zygote)
Refers to embryo and all structures that develop from it
placenta,amnion,chorionand yolk sac.
Primordium (L.Primus, first + ovchor – to begin)
Refers to first recognizable indication for development of an organ or
structure
Fetus (L. Unborn offspring)
The developing human after embryonic period.
The fetal period is from 9th week to birth.
Tissues and organs formed during the embryonic stage differentiate and
Embryological terms
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Trimester – period of three calendar months during a pregnancy.
The first trimester (12week, is most critical because embryonic and early fetal
development is occurring)
Abortion –
premature stoppage of development or premature expulsion of a conceptus
from the uterus or expulsion of an embryo or fetus before it is viable (capable of
living outside the uterus)
Congenital anomalies/malformations - these are birth defects or abnormalities of
development present at birth
Teratogen - an agent or factor which may cause birth defects or congenital
anomalies.
Teratology –the study of congenital malformations
Testes
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It is surrounded by a capsule
Testicular capsule is a dynamic membrane,
composed of three layers
An outer layer – tunica vaginalis
A middle layer – tunica albuginea
An Inner layer – tunica vasculosa
Testes
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Tunica vaginalis
Is made up of mesothelial cells
Has two layers, Visceral and Parietal
The serous cavity between the layers allows the testis to
move freely within it
Tunica albuginea
A thick dense fibroelastic connective tissue
Contains smooth muscle cell
It is thickened along the posterior border, mediastinum
testis
The mediastinum testis sends thin fibrous partitions,
septuli testis, that divide the interior of the testis into 250
Testes
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Each lobuli testis contains
1-4 seminiferous tubules
Embedded within a loose connective
tissue stroma
Interstitial tissue contains vessels, nerves,
and cells
*interstitial cells (leydig)
SPERMATOGENESIS
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Spermatogenesis by which haploid spermatozoa develop from germ cells in
the wall of the seminiferous tubule of the testis
It takes about 64 days to form a mature sperm in humans
The process begins with mitotic division (spermatocytogenesis) of stem cells
(Spermatogonia type A)
Spermatogonia type A (44+X+Y) divides mitotically to give rise to more type
A and also to type B
Spermatogonia type B (44+X+Y) grows and divides mitotically to form
primary spermatocyte
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SPERMATOGENESIS
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Golgi phase
Spermatids grow and become radially symmetrical, and begins to
develop polarity
The head forms at one end, Golgi apparatus forms enzymes that
will become the acromosome
The other end forms the middle piece, the mithochondria gather at
the distal centriole and begins to form the axoneme
Spermatid DNA becomes highly condenced, forming chromatin
Spermiogenesis
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Acrosomal phase
Golgi apparatus surrounds the condenced nucleus, forming the acrosomal cap
Acrosomal vesicle
Acrosome – hydrolytic enzymes: Hyaluronidase, Neuraminidase, Acid
phosphatase, Acrosin (zonalysin)
Formation of Tail
One of the centrioles of the cell elongates to become the tail of the sperm
Manchette (a temporary structure) assist in this elongation
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Spermiogenesis
Maturation phase
Residual bodies are shed
Formation of spermatozoa
Release of mature spermatoza > spermiation
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