Aughey E., Frye F.L. Comparative veterinary histology with clinical correlates

Подождите немного. Документ загружается.

181

11.38 Section of a seminiferous tubule of a mature

green iguana (Iguana iguana). Three spermatogonia are

shown in mitosis (arrows). Primary spermatocytes (1) and

many tailed spermatozoa (2) lie within the centre of the

tubule. H & E. ×200.

11.38

11.39 A section of the testis of a panther chameleon

(Chamaeleo pardalis). A nest of large interstitial cells

containing finely granular cytoplasm can be seen in the

lower third of this image (arrows). H & E. ×200.

11.39

Reptiles utilize internal fertilization. Male chelo-

nians possess a single erectile penis that is often heav-

ily pigmented and is covered by lightly keratinized

and mucous epithelium. Male snakes and lizards pos-

sess paired erectile intromittant organs, called

hemipenes, that contain fibrovascular tissue that,

when involuted, invaginates. When erect the outer

surface is covered with keratinized epithelium.

Additional flamboyant spines, flounces and other sex-

ual adornments are species specific. The hemipenes

receive lubrication from mucous glands that are

located within the lumen of the hemipenial sheath. In

some reptiles, modified sebaceous glands are associ-

ated with the hemipenes and their sheaths (11.41).

Male crocodilians possess a relatively small erec-

tile penis that superficially resembles that of higher

vertebrates; it even has a glans-like swelling at its

distal end. The surface is covered with lightly ker-

atinized epithelium without horny projections.

Male tuataras lack an erectile intromittant

organ. Internal fertilization is accomplished by

cloacal apposition during which semen is trans-

ferred to the female and enters the proctodeum por-

tion of the cloaca.

11.40 Inactive testis of a green sea turtle (Chelonia

mydas). The seminiferous tubles are lined only by

sustentacular cells and a few spermatogonia. H & E. ×100.

11.40

11.41 Inverted (detumescent) hemipenis of a Carolina

anole lizard (Anolis carolinensis). The organ is composed

of spongy fibrovascular tissues containing many arterial

and venous channels (1), and stratified lightly cornified

squamous epithelium (2). Lobules of glandular tissue,

similar to sebaceous glands, lie at the base of each

hemipenis and furnish lubrication and scent-rich

secretions to the erectile intromittant organ.

H & E. ×50.

11.41

Male Reproductive System

182

Comparative Veterinary Histology with Clinical Correlates

11.4411.43

Clinical correlates

True hermaphroditism occurs occasionally in

reptiles but is usually only discovered at

necropsy. The condition can involve one gonad

of each sex, one or more ovotestes or separate

masses of ovarian and testicular tissue.

A Bidder’s organ is normally present in male

bufonid toads. This interesting structure is a cap-

like mass of ovarian tissue attached to the cra-

nial pole of the testis (11.42). It is unclear why

androgenic and ovarian hormone secretion do

not each suppress their opposites.

As in domestic animals, the reptilian or

amphibian testis can be the site of inflammatory

disorders, atrophy and fibrosis (11.43), and neo-

plastic disease (11.44). Malignant tumours are

more prevalent than benign variants.

11.42 Bidder’s organ in a western toad (Bufo boreas). Although similar to

hermaphroditic gonadal tissue, Bidder’s organ is a normal constituent found

in some bufonid amphibians and consists of a cap-like assemblage of

pigmented ovarian tissue, including yolked follicle-like structures attached

to the cranial pole of each testis. The presence of ovarian tissue does not

suppress spermatogenesis. H & E. ×50.

11.43 Testicular fibrosis in a blood python (Python

curtus). The seminiferous tubules are atrophic and

widely separated from each other by wide bands of

mature fibrocollagenous connective tissue. H & E. ×20.

11.44 Sustentacular (Sertoli) cell tumour from a

snake. Note large nests of pale-staining sustentacular

cells. H & E. ×100.

11.42

12.1

183

The female reproductive system consists of the

ovaries, uterine tubes (oviducts or Fallopian tubes),

uterus, vagina and vestibule. The external genitalia

are the vulva, labia, clitoris and external urethral

orifice.

Ovaries

Cortex and medulla

The ovaries have an exocrine function, the produc-

tion of the egg or female gamete, and an endocrine

function, the production of female sex hormones.

Each ovary is divided into an outer parenchymatous

zone cortex and an inner vascular zone medulla

12. FEMALE REPRODUCTIVE SYSTEM

12.1 Ovary (cat). (1) Parenchymatous

zone with primary follicles (2) and

secondary follicles (3). (4) Vascular

zone. H & E. ×7.5.

(12.1), except in the mare where there is no zonal

division. The cortex of each ovary is covered by a

simple squamous or cuboidal epithelium that is con-

tinuous with the mesothelium of the visceral peri-

toneum (the germinal epithelium), except at the hilus

where blood vessels and nerves enter and exit from

the gland. Beneath the epithelium is a layer of dense

connective tissue, the tunica albuginea. Deep to that

is the ovarian or cortical stroma, containing ovarian

follicles in various stages of development. The ovar-

ian stroma consists of spindle-shaped cells arranged

in whorls surrounding the ovarian follicles. In car-

nivores, particularly the cat, numerous specific inter-

stitial cells are present in the stroma. They are small,

round, epithelioid cells with a round nucleus and

they stain poorly (12.2).

12.2 Ovary. Parenchymatous zone

(cat). (1) Primary follicles; the large

oocyte is surrounded by flattened

nurse cells. (2) Cellular ovarian

stroma. The specific interstitial cells

are arrowed. H & E. ×250.

12.2

The medulla is highly vascularized and consists

of fibroelastic connective tissue and some smooth

muscle (12.3). Channels, lined with (densely stain-

ing) cuboidal epithelium and called the rete ovarii,

are conspicuous components of the medulla in car-

nivores and ruminants (12.4). They are derived from

the mesonephric tubules during embryogenesis.

Development of the follicles

Primordial follicles are the least developed and most

numerous follicles of the ovary, lying just below the

tunica albuginea. Each consists of a primary oocyte

surrounded by a layer of simple squamous follicle

(nurse) cells (see 12.2). The primary oocytes origi-

nate in the late embryonic/early postnatal ovary

from oogonia and are surrounded by a flattened

layer of nurse cells. Further development is arrested

until puberty, when a regular cycle of events results

in the passage of one or more follicles into the

lumen of the uterine tube during reproductive

cycles. A number of follicles begin to grow, and the

primary oocyte accumulates yolk and enlarges from

60 +m to between 100 and 120 +m in diameter.

Concomitantly, an acidophilic, translucent mem-

brane, the zona pellucida, forms around the oocyte

(12.5). The nurse cells become cuboidal, then

columnar, then stratified and begin to accumulate

fluid in the intercellular spaces. The follicle now

comes under the influence of follicle-stimulating

hormone from the pituitary gland and continues to

grow to become a secondary follicle, with a C-

shaped, fluid filled space, or antrum (12.6). Its cells

are now called the granulosa layer. The follicle

secretes oestradiol, the female sex hormone that

prepares the endometrium to receive the fertilized

egg. The ovarian stroma condenses around the

developing follicle to form an inner layer, the theca

interna, which is cellular and vascular, and an outer

layer, the theca externa, which is composed of

fibrous connective tissue.

The follicle continues to increase in size, mov-

ing to the surface of the ovary to become a vesicu-

lar [tertiary (mature) Graafian] follicle. The oocyte

is surrounded by a multilayer of granulosa cells, the

cumulus oophorus (12.7 and 12.8). Ordinarily, a

mature vesicular follicle contains a single oocyte.

The follicles of certain animals (carnivores, sows

and ewes) may, however, contain up to six oocytes.

Maximum size is reached just before ovulation.

184

Comparative Veterinary Histology with Clinical Correlates

12.3 Ovary. Vascular zone (bitch). (1) The ovarian stroma

is very vascular. (2) Smooth muscle cells. H & E. ×125.

12.3

12.4 Ovary. Vascular zone (sheep). Tubules of the reti

ovarii are arrowed. H & E. ×125.

12.4

12.5 Ovary. Parenchymatous zone (sheep). (1) The oocyte

is surrounded by the granulosa layer. (2) Ovarian stroma.

H & E. ×125.

12.5

185

12.6 Ovary. Secondary follicle

(bitch). (1) The oocyte is surrounded

by the amorphous zona pellucida.

(2) The granulosa cells are stratified.

(3) Fluid accumulates to begin

antrum formation. (4) Ovarian

stroma concentrates around the

follicle to form the theca. H & E.

×62.5.

12.6

12.7 Ovary. Tertiary follicle (cow).

(1) The oocyte surrounded by the

zona pellucida is embedded in a

mound of granulosa cells, the

cumulus oophorous. (2) Theca or

capsule of ovarian stroma. H & E.

×62.5.

12.7

12.8 Ovary. Parenchymatous zone

(cat). The cuboidal epithelium is

arrowed. (1) Tunica albuginea is a

thin layer of connective tissue.

(2) Primary follicles. (3) Vescicular

(tertiary) follicle with a large fluid

filled antrum (4) lined by granulosa

cells (5) and encapsulated by the

vascular theca interna (6) and the

fibrous theca externa (7). Gomori’s

trichrome. ×62.5.

12.8

Female Reproductive System

Ovulation

At ovulation the primary oocyte divides into sec-

ondary oocytes, one cell retaining most of the cyto-

plasm; completion of meiosis occurs at fertilization.

The follicle breaks open, releasing the oocyte, which

passes into the uterine tubes. The follicle collapses

and the granulosa cells, together with those of the

theca interna, hypertrophy, expanding into the cav-

ity to form the granulosa lutein and theca lutein cells

of the corpus luteum (12.9 and 12.10). They are

arranged in long cords separated by vascular con-

nective tissue. The luteal cells secrete progesterone

which, with the oestradiol, prepares the uterus for

possible conception. With regression of the corpus

luteum, stromal elements move in and replace the

dead cells with collagen to form a scar: the corpus

albicans (12.11 and 12.12). Although many pri-

mordial follicles begin the process outlined above,

few become mature. The majority undergo a degen-

erative regression. They are called anovular or atretic

follicles and can be recognized by the irregular out-

line of the follicle and the separation of the granu-

losa cells (12.13). Cells of the theca interna

hypertrophy and the zona pellucida becomes

swollen. Eventually, the entire follicle is resorbed.

186

Comparative Veterinary Histology with Clinical Correlates

12.9 Ovary. Parenchymatous zone

(sheep). (1) The pale vacuolated cells

are part of the corpus luteum.

(2) Ovarian stroma. H & E. ×62.5.

12.9

12.10 Ovary. Parenchymatous zone

(sow). (1) Cords of large densely

stained luteal cells are separated by

(2) blood vessels. H & E. ×125.

12.10

187

12.11 Ovary. Parenchymatous zone

(sheep). (1) Ovarian stroma. (2) Dense

white connective tissue. (3) Active

fibroblasts replacing degenerating

luteal cells. H & E. ×125.

12.11

12.12 Sheep. Parenchymatous zone

(sheep). The central pale staining

area is dense white connective tissue

(scar tissue) and represents a later

stage in the development of a corpus

albicans. H & E. ×250.

12.12

12.13 Ovary. Parenchymatous zone

(bitch). Atretic follicle. (1) The

granulosa cells are separating; spaces

are present between them. (2) The

oocyte is no longer in contact with

the lining granulosa cells. H & E.

×125.

12.13

Female Reproductive System

Uterine tubes (oviducts)

The uterine tubes are long flexuous musculo-

membranous tubes. They consist of an expanded

cranial end, the infundibulum, which is close to the

ovary; a middle segment, the ampulla; and a cau-

dal narrow part or isthmus that opens into the ipsi-

lateral horn of the uterus. The epithelium is simple

or pseudostratified columnar with secretory and

188

12.14 Transverse section (TS) uterine

tube (sheep). (1) The lumen is lined

by a pseudostratified epithelium

thrown into deep folds. (2) The

lamina propria has deposits of dark

brown pigment. (3) The muscularis

is for the most part circular smooth

muscle fibres. (4) The serosa is

loose vascular connective tissue

with prominent blood vessels.

H & E. ×62.5.

12.14

12.15 TS uterine tube (cow). The lining epithelium is

pseudostratified columnar with ciliated and non-ciliated

cells.The deep mucosal folds are cut in transverse section

giving the appearance of mucosal glands (arrowed).

H & E. ×125.

12.15

ciliated cells. The lamina propria has longitudinal

folds giving it a glandular appearance. In some

breeds of sheep (blackface and crosses), pigment

cells are present. The muscularis is mainly a layer

of circular smooth muscle, thickening at the junc-

tion with the uterine horn, with an outer layer of

longitudinal muscle. The serosa is loose vascular

connective tissue with prominent blood vessels

(12.14 and 12.15).

Comparative Veterinary Histology with Clinical Correlates

189

Uterus

The uterus is bicornuate, with right and left horns

(cornua), a body (corpus) and a neck (cervix)

(12.16–12.23, all illustrations in transverse sec-

tion). The uterine wall in the cornua and corpus

has three layers: an inner endometrium (mucosa),

a middle myoemetrium (muscularis) and an outer

perimetrium (serosa).

Endometrium

The epithelial lining of the endometrium is simple

cuboidal or columnar in the mare and carnivores,

and pseudostratified in the sow and ruminants. In

ruminants, ciliated cells may be present. The lam-

ina propria is a deep layer of vascular connective

tissue, with simple tubular endometrial glands that

open into the lumen of the uterus. These glands are

12.16 TS uterus (cat).

(1) Endometrium with simple straight

tubular glands. (2) Myometrium with

circular and longitudinal smooth

muscle. H & E. ×7.5.

12.16

12.18 TS uterus (bitch). (1) The lining epithelium is simple columnar.

(2) The endometrial glands are lined by tall columnar epithelial cells

with a basal nucleus. (3) The lamina propria is very cellular with

many small blood vessels. H & E. ×125.

12.18

12.17 TS uterus (mare). Only the

endometrium is present. The lining

epithelium is simple columnar; the

endometrial glands are slightly coiled

at the base (arrowed). H & E. ×62.5.

12.17

Female Reproductive System

190

12.19 TS uterus (cow). (1) The endometrial glands are

markedly coiled. (2) Thick layer of myometrium. H & E.

×100.

12.19

12.21 TS uterus (sheep). Only part of

a caruncle is present; the connective

tissue is very cellular and well

vascularized. H & E. ×125.

12.22 TS uterus. Caruncle (sheep).

Local deposits of pigment (melanin)

are present in the connective tissue

of some breeds of sheep. H & E. ×250.

12.21

12.20 TS uterus (cow). The myometrium is split by the

stratum vasculare (arrowed.). H & E. ×100.

12.20

12.22

12.23 TS uterus. Intercaruncular area

(sheep). The endometrial glands

(arrowed) are confined to the

intercaruncular area. H & E. ×100.

12.23

Comparative Veterinary Histology with Clinical Correlates