embryology reviewer

8/18/2019 Embryology Reviewer

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First Semester Comparative Vertebrate Embryology - Laboratory

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thickness of chromosomes means

advance pairing.

o Pachytene – Complete pairing and

eventual exchange of chromosomal

arm, the cells seems to be haploid,

chromosomes shorten and thicker.o Diplotene – Chromosomes partly

split, relaxation of pairing, presence

of “chiama”, configuration of “x”,

cross, or loop

o Diakinesis – progressive

condensation by means of coiling,

chromosomes are in their shortest

and thickest appearance.

The nucleus goes through the metaphase,

anaphase, and telophase – first maturation

division.

Secondary Spermatocyte

Smaller than the primaries

Chromosomes are not that evident

Spermatids

Half the size of the secondary spermatocyte

Possess haploid set of chromosomes but

not capable of functioning as male gamete

SPERMIOGENESIS – transformation of

spermatids to spermatozoa.o May be observed in the inner region

of the lobe

o Major nuclear and cytoplasmic

changes that will eventually

terminate in the formation of

functional gamete.

o Elongation of spermatid – cytoplasm

sloughed off.

o Tail Sheath – surrounding the tail

filament, grows back from

centrosomeo Head – Condensation and

elongation of chromatin mass

o Middle Piece – contains the

centrosome and mitochondria

o Tail

Spermatozoa

Exhibit long, thin, darkly staining head with

distinct tails.

Tail measures 7-8 times longer than the

head. Abundant at the distal region of the testis.

Histology of Frog’s Testis

Mesorchium

Portion of the peritoneum that suspends the

testis to the dorsal body wall.Tunica Albuginea

Outer connective tissue that covers the

testis

Known as septula or intertubular connective

tissue

Seminiferous tubule

Much-coiled tubule containing the clusters

of spermatogenic cells undergoing the same

stage of development and the sertoli cells

Connected to the vas deferens

Cells going through same stage are found ina cluster or group within the tubule.

Spermatocysts

Cluster of similar cells undergoing the same

stage of development

Surrounded by follicle cells

Formed from primary spermatogonium and

its associated follicle

Spermatogonia

Small, closely packed cells with granular oval

nucleus.

o

Primary Spermatozoa – fastened tothe walls of the seminiferous tubule

o Residual Spermatozoid – Source of

germ cell proliferation

Active Spermatogenesis – short season in

summer, begins with a rapid succession of

mitotic division

The millions of sperm came from

comparatively large number of gonia by

repeated mitotic division, maturation, and

spermatogenesis.

The seminiferous tubules do not containpermanent population of sperm cells.

Primary Spermatocyte

Very large cell, spherical, with large

vesicular nuclei

Characteristic meiotic prophase

configurations of chromosomes can be seen.


Result of the first meiotic division

Half of the size of the primaries and lietowards the lumen of the tubule.


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flakes, most common gonia, last

stage before primary spermatocyte

o Intermediate- chromophilic

chromatin in the form of delicate

crustor flake, has prominent nuclei

appearing in the center.

Primary Spermatocyte

Significantly large in size

Nuclei larger than the spermatogonia

The chromosomes are very much visible and

the nuclear membrane is disintegrated

already.

Visible stages:

o Interphase – Similar to gonia B,

finely granular nucleus with pale

nucleolus, exist for about 6 hours.o Prophase I

o Metaphase I

o Anaphase I

o Telophase I


Result of first meiotic division of the primary

spermatocyte

Pale stained granular chromatin

Twice the diameter of spermatids.

Spermatids

Result of second meiotic division

Lie next inward beyond the spermatocyte

layer in the seminiferous tubule

Nuclei quite round, small size (2/3 of primary

oocyte), pale staining properties, and

position above the level of primary

spermatocyte – IMPORTANT CLUES

DNA undergoes progressive condensation

Decrease of nuclear size due to the

elimination of nuclear sap.

Spermatozoa

Deeply stained when matured

The heads are buried at the Sertoli cells

Matured spermatozoa becomes free of the

nurse cells and pass into the ducts

*The histology of Chick’s Testis is also the same as

mouse’s testis

OOGENESIS Process of producing egg

Products of meiotic division which is

responsible for haploid condition

Formation of Polar bodies

o Produced after first meiotic division

o Smaller than egg

o

Due to unequal cytokinesiso Provides the ovum a much greater

amount of cytoplasm and store

food.

o Non functional

After meiosis, the ootid quickly change into

the mature egg cell or ovum

It takes place within the follicles of the ovary

o The ovary is covered by continuous

sheet of epithelium called the

germinal epithelium

Mesovarium The mesentery that attached the ovary to

the body wall

Route for blood vessels to and from the

ovary.

Ovary

Divided into two parts

o Central Medulla – consist largely of

connective tissue and blood vessels,

appear more or less continuous with

the mesovariumo Peripheral cortex – business part of

the ovary

HISTOLOGY OF FROG OVARY

A large sac of yolk with heavier and larger

granules concentrated toward the animal

hemisphere

Surrounded by a coat necessary for retaining

the shape, aids in cleavage and gastrulation

Mesorvarium Double-layered extension of the peritoneum

Attachment to the dorsal body wall

Theca externa

Outermost connective tissue surrounding

the ovary

Continuous with the mesovarium

Ruptures during ovulation

Theca interna

Inner connective tissue surrounding theovary and each egg


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Follicle Cells

Derived from oogonia

Contains oval and granular nuclei

Surrounds the developing oocyte

Ovarian Follicle

Collective term for theca externa, theca

interna, follicle cells

Oogonia

Located at the periphery of the ovary and

much smaller than the oocyte

No pigment and contains a little yolk

Each cluster of oogonia represents a future

ovarian unit.

The majority of oogonia never mature intoova.

Oocytes

Bigger than the oogonia

Lightly stained at the center is the germinal

vesicle or immature nucleus.

Distinction to primary and secondary oocyte

is not possible

Vitelline Membrane

Non-cellular transparent membranebetween follicle cells and each mature egg

cells.

Derived from ovum and follicle cells

Developed during maturation process.

Perivitelline Space

Fluid-filled space formed between the egg

and the vitelline membrane after

fertilization

Shows compensatory shrinkage.

HISTOLOGY OF CAT OVARY

Germinal epithelium

Forms the outer surface

Epithelial lining of the ovary

Cuboidal cells

Tunica albuginea

Layer of fibrous connective tissue below the

germinal epithelium

Stroma

Another layer of connective tissue below the

Tunical albuginea

Made up of connective tissue fibers and

spindle shaped cells.

Oogonium Potential ovum with vesicular nucleus with a

prominent nucleolus

Embedded at the stroma and in clusters.

Primary Follicle Stage

Surrounded with single layer of flattened

follicular cells.

Structures of Follicle Stage Cells

Follicles

o

Single layer of cells that surroundsthe developing germ cell

o Have dark stained nuclei and maybe

squamosal or low cuboidal.

Oogonium

o Potential ovum surrounded by single

layer of follicle cells

o Spheroid and has a vesicular nucleus

with a prominent nucleolus

Growing Follicle Stage

Immediately succeeds the primary folliclestage

Proliferated by mitotically dividing cells and

are now several layers thick.

Increased in size and complexity.

Structures

Follicle Cells

o Several layers thick, low columnar or

cuboidal cells enclosing the oocyte

Antrum

o

Follicular cavityo Formed by the union of spaces

between the follicle cells

o Precipitation of proteins in the fluid

may give the cavity a granular

appearance.

Liquor Folliculi

o Viscous follicular fluid secreted by

follicle cells.

Oogonium or Primary Oocyte

o The probable stage of development

of the cell in the growing follicle


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o Hardly distinguishable from each

other

Zona Pellucida

o Deeply staining membrane

surrounding the egg cell and

separating it from the follicle cells

Graafian follicle

Large follicle that bulges on the free surface

of the ovary

Structures

Antrum

o Fluid-filled cavity, now it is bigger.

o Lined by stratum granulosum, thick

layer of follicle cells

Cumulus Oophorus o Eccentric mound of follicle cells

surrounding egg cells

o Includes the oocyte, zona pellucida,

amd surrounding granulose cells

Primary oocyte

o Stage of development at this point

o Has a heavy nuclear envelope

Stratum Granulosum

o Layers of follicle celss boredering the

Graafian, excluding the cumulus

oophorus Corona Radiata

o Layer of follicle cells of the cumulus

oophorus that lie nearest to the

oocyte

Zona Pellucida

Liquour Folliculi

Theca folliculi

o The stroma immediately adjacent to

the follicle

Theca interna

o

Inner layer between the thecainterna and the granulose cells

o Richly vascularized

o Cells are secretory

Theca Externa

o Outer layer of the capsule composed

of spindled shaped dense connective

tissue fibers

Atretic Follicles

o Unsuccessful follicles undergoing

degenerative process

o

Shows antrum scattered follicle cells

o Exhibited by the presence of

collapsed zona pellucida

o Corpus atretica – mass of tissue

regressing corpus luteum

Corpus lutea

o

Masses of granular tissueo Result from the ovulation of egg

cells from follicles.

o Responsible for the production of

progesterone

o Lightly stained, follicles converging

at the middle portion

o Lutein Cells, Capillaries, Capsule

Corpus Albicans

o Found in the central portion of the

ovary.

o

Non-functional corpus luteum whenfertilization does not take place

o Pale stain in its central portion

Periovarial Membrane

o Peritoneum of the ovary which

continues into the Oviduct

Periovarial Space

o Space between the periovarial

membrane and the ovary

Oviduct

o Convoluted structure that is found

alongside of the ovary o Attached to the periovarial

membrane

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