Female Reproductive System | Histology | Anjani Mishra

Female Genital System of Animals

 Written By Anjani Mishra

Female Genital (reproductive) system of animals

Fig: Female genitalia of cow where the roof of vagina and vulva have been removed

Fig: Genital organs of cow

General Features of F.G.S.

The female genital system consists of following organs;

A. The pair gonads,

     1. The ovaries

B. The female genital duct

    1. Fallopian Tube / Uterine tube

          Infundibulum

          Ampulla

          Isthmus

    2. Uterus

          Horn of uterus

          Body of uterus

          Neck of uterus/Cervix/os-uteri

    3. Vagina

Accessory organ

    1. Mammary gland (Accessory gland)

Ovary

Gross

The ovary is the main female reproductive organ where the female germ cells or ovum are produced. They are classified as double glands (mixed glands), since they produce both exocrine (cytogenic) and endocrine(hormones) secretions.

They are slightly flattened, oval bodies, measuring about 4 cm in length, 2 cm in width, and 1cm in thickness. One lies on each side of the uterus on the lateral wall of the pelvic cavity.

Histology

1. Covering

The free surface of the ovary is covered by a single layer of cuboidal cells known as germinal epithelium (serous covering). Beneath the epithelium there is a poorly delineated layer of dense connective tissue, the tunica albuginea (fibrous coat). It is covered by a layer of small columnar epithelial cells. The fibrous coat encloses the stroma, a reddish-white vascular substance.

(Note:-Stroma- foundation, supporting tissue of an organ,opposite of parenchyma)

2. Internal structure

The ovary is divided into two zones;

           A)  An inner medulla, and

           B)  An outer cortex.

There is no distinct line of demarcation between the two zones.

Fig: Ovary, queen

2. Corpus luteum,  3. Cortex,  6. Growing follicle,  7. Medulla,  

A) Medulla

• A central deeper portion is the medulla that consists of loose connective tissue, rich in elastic fibers and containing numerous large blood vessels, lymphatics, and nerves. 
• The stroma contains scattered strands of smooth muscle fibers.

B) Cortex

• The outer broad peripheral layer is the cortex, consists of a compact cellular stroma that contains the ovarian follicles. 
• The stroma is composed of networks of collagen fibers and spindle shaped cells, arranged in irregular whorls. These stromal cells contribute to the growth of the theca folliculi.
• The follicles may be seen in all stages of development, and the appearance of the ovarian cortex depends upon the age of the individual and the stages of ovarian cycle. 
• Before puberty only primary, or primitive follicles are seen. Sexual maturity is characterized by the presence of growing follicle and their end products (corpus luteum). 
• After menopause, follicles disappear and the cortex eventually becomes a narrow region of fibrous connective tissue.

Ovarian follicles

• An ovarian follicle consists of an oocyte surrounded by one or more layers of follicular cells, or granulosa cells.
•  Ovarian follicles are embedded in the stroma of the cortex. 
• A basal lamina underlies the follicular cell and marks the boundary between the follicle and the surrounding stroma.

There are several stages of follicular development and three types can be distinguished.

1. Premordial follicle

2. Growing follicle

            A. Primary

            B. Secondry

3. Mature, or graafian follicle

1. Premordial follicle

• The follicles that are formed during fetal life are primordial follicles. 
• It consists of a primary oocyte enveloped by a single layer of flattened follicular cells. 
• The oocyte is a spherical cell about 25um in diameter. It has a large nucleus and nucleolus.  

Fig: Premordial follicle

Fig: Ovary, queen

11. Primary follicle,  12. Primordial follicle,  13. Stroma

2. Growing follicle

  A. Primary follicle

        It consists of ovum which is surrounded by a single layer or multiple layers of cuboidal follicular epithelium or stratified epithelium. It is further classified into two types based on layer of follicular cells.

     i) Unilaminar primary follicle

     ii) Multilaminar primary follicle

 i) Unilaminar primary follicle

• As long as only a single layer of follicular cells encircles the oocyte, the follicle is called a "unilaminar primary follicle." 
• At this stage, the glycoprotein rich zona pellucida begins to form between the oocyte and        the follicular cells.
• A definite connective tissue capsule is absent around the follicle.
• The oocyte is a spherical cell about 30-40um in diameter.  
• It has a large vesicular nucleus.              
• Nucleolus is indistinct.
• Cytoplasm contains fine granules.

Fig: Unilaminar primary follicle

ii. Multilaminar primary follicle

•  Forming several layers of cells around the primary oocyte, the follicle is called “multilaminar primary follicle,” and follicular cells become to known as granulosa cells.
•  During this stage, the zona pellucida thickens and the theca folliculi begins to form. 
• The stroma immediately around the follicle differentiate to form the theca folliculi.
•  A definite connective tissue capsule is present around the follicle.

Fig: Multilaminar primary follicle

  B. Secondry follicle

• The multilaminar primary follicles continues to develop and increase in size, reaching upto 200um in diameter.
• Continued protiforation of the granulosa cells depends on follicle stimulating hormone (FSH).
• Irregular small spaces are found in the follicular mass, called antrum which is filled with fluid, called liquor folliculi.

  The theca folliculi forms 2 layer ;

  a) Theca interna – Cotaining a rich vascular network and steoid-secreting (estrogen) cuboidal cells  with abuudant smooth endoplasmic reticulam (SER)

   b) Theca externa – Consisting mostly of fibrous connective tissue.

 

3. Mature / Graafian follicle

• Continued proliferation of granulosa cells and liquor folliculi results in the formation of a mature (graafian) follicle.
• A relatively thick membrane is formed around the surface of the ovum known as zona pellucida.
• The ovum is pressed to one side of the follicle by the expansion of the antrum.
• The follicular epithelial cell immediately surrounding the ovum to form corona radiata.
• Granulosa cells surrounding oocyte remain intact and form the cumulus oophorus.
• The antrum is surrounded by a follicular epithelial cells, known as membrana granulosa.
• The theca externa gradually merges with the ovarian stroma.
• A connective tissue sheath is present around the follicular epithelium known as theca folliculi, composed of theca interna and theca externa.
• Theca folliculi separated from the membrana granulosa by a membrane, known as follicular basement membrane.

Fig: Mature, or graafian follicle

Fig: Ovary, queen

  1. Antrum,  4. Cumulus oophorus,  8. Membrana granulosa,  9. Oocyte, cytoplasm

 14. Theca externa,  16. Theca interna

Fallopian tube/Uterine tube

The wall of fallopian tube or uterine tube is composed of;

        1.  Mucosa

                  i) Lamina epithelia

                  ii) Lamina propria

       (Note:- Lamina muscularis mucosa is absent)
       2. Sub-mucosa

       3. Muscularis externa

       4. Serosa

Fig: Diagram of fallopian tube

1. Longitudinal muscle fiber,  2. Circular muscle fiber,  3. Lamina propria,  4. Fold of mucosa,  

5. Epithelium,  6. Mesothelium(peritoneum) 

 Fig: Fallopian tube, fimbria of infundibulum, mare

      3. Simple Columnar epithelium, ciliated, 6. Lamina propria, 7. Muscularis, 9. Serosa,

     10. Sub-mucosa

  1. Mucosa

        i) Lamina epithelia- It bears simple columnar epithelium, parts of which are pseudo-stratified ( as in ruminant and swine). Only parts of its cells are ciliated.

     ii) Lamina propria- It consists of connective tissue containing cells, vessels, and muscle   

                                      fibers. The propria lacks gland
 2. Sub-mucosa- It consists of connective tissue together with large blood vessels, nerves and continuous with lamina propria as there is no muscularis mucosa.

  3. Muscularis externa

           It is rich in elastic tissue and made up chiefly of circular fiber bundles, but isolated longitudinal and oblique bundles also occur. It becomes thicker towards the uterus and blends into the circular uterine muscle layers. It undergoes special contraction during estrus, which probably serve to propel the ovum towards the uterus.

 4. Serosa

           It is loose, thick and continuous with peritonium and broad ligament. The sub-serosa contains many vessels and peripheral to these, a continuous layer of longitudinal muscle fiber is present

Uterus

The uterus is a thick walled hollow muscular organ which continues cranially with the uterine tube and caudally opens into the vagina.

It lies almost entirely within the abdominal cavity in the adult. 

It consists of two horns the body, and the neck(cervix). In domestic animals, three main regions of the uterus are distinguished as:

 a) Horn of uterus,

 b) Body of uterus, &

 c) Neck of uterus/cervix/os-uteri (internal and external os)

Fig: Uterus, horn, x.s., bitch

2. Endometrial gland,  5. Myometrium(circular),  6. Myometrium(longitudinal),

7. Stratum vasculare

The wall of uterus consists of three coats, namely;

1. Mucosa (Endometrium)

        i) Lamina epithelia- lined with simple columnar epithelial cells. Some cells are ciliated   

                                         &  some are non-ciliated.

                  a)  Horn- Simple columnar epithelium (ciliated)

                  b)  Neck and body- Simple columnar epithelium (non-ciliated)

                  c)  Neck of uterus/cervix/os-uteri

                              Internal os- Simple columnar epithelium (non-ciliated)

                              External os- stratified squamous epithelium (non-keratinized)

       ii) Lamina propria- connective tissue layer containing tubular glands known as uterine glands.

2. Muscularis (Myometrium)

• It is a thick layer of smooth muscle fibers, arranged both circularly and longitudinally.
• The muscularis(myometrium) layer is divided into thick inner circular and a thinner outer longitudinal layer invested by stratum vasculare, which contains numerous large blood vessels and nerves.
• The stratum vasculare is not very distinct in swine and man, where as in case of cow, located within the outer half of the circular muscle.
• I n some places particularly in the body and horn of uterus, the inner layer contains few oblique fibers and show reticular arrangement. During pregnancy, these muscle fibers increase in number and size under the influence of oestrogen.

3. Serosa (Perimetrium)

• The stratum vasculare, and the layer of longitudinal muscle continues together with the broad ligament of uterus, which invests and suspends the uterus.
• The stratum vasculare corresponds to the sub-serosa. The longitudinal muscle layer should be interpreted as a muscularis serosae.

 Vagina

                                                       Fig: Diagram of vaginal wall

1. Stratified squamous epithelium,  2. Lymphoid tissue,  3. Stroma of L.C.T.,  4. Muscular coat(chiefly longitudinal),  5. Small nerve cell,  6. Blood vessels,  7. Adipose tissue in the C.T. coat

 Fig: Vagina, bitch

6. Lamina propria,  9. Stratified epithelium

The wall of vagina consist of three classical layers: namely;

1. Mucosa

     i) Lamina epithelia - lined by stratified Squamous epithelium (non-keratinized)

    ii) Lamina propria - composed of dense connective tissue, elastic fibers, neutrophil &    

                                    lymphocyte.

2. Muscularis

             i) Inner thin circular

            ii) outer thick longitudinal

At the caudal part of vagina, there is spincter, composed of skeletal muscle.

3. Fibrosa

merged with surrounding connective

Vaginal vestibule- Some lymph nodules are present in the wall close to clitoris. The wall also contains major vestibular mucous gland which provide lubrication to the vaginal vestibule, called Bartholin's gland or "Gland of Bartholin". It is homologous to the male bulbourethral gland.

Fig: Vaginal vestibule

  3. Columnar cells,  4. Duct,  13. Vestibular epithelium

The Clitoris

                       Fig: Clitoris of cow

Structure

• The clitoris is rich in elastic fiber and consists of corpus cavernosum clitoridis, the glans, and the prepuce which continues with the vestibular mucosa.
• The corpus cavernosum clitoridis is homologous to the corpus cavernosum penis. It posses a heavy tunica albuginea with many vessels and nerves.
• The corpus cavernosum clitoridis of solipeds and women is well developed and equipped with abundant musculature. 
• In ruminants there is less cavernosus tissue. In cat and sow varying quantities of fat cells are present in the trabeculae and cavernosus tissue. They are also found to a slight extend in solipeds and in larger quantities in ruminants.
• The end of the corpus cavernosum clitoridis is capped by the richly innervated glans. The glans clitoridis resembles the glans penis structurally. 
• A true erectile body is present in the glans clitoridis only in the bitch and mare. Ruminants have only a fibroelastic cover on the distal end of the corpus.
• The preputium clitoridis, composed of the non-glandular cutaneous mucosa of the vestibule has parietal and visceral parts as in the male. It also contain lymph nodules. The space between these two layer of prepuce is the fossa clitoridis. The fossa is distinct in solipeds and bitch. In the ewe and cat there is only a slight indication of it, and it is absent in the cow and sow. 

Estrus Cycle – The term estrus means the time of strong mating tendency shown by a female. It is also properly termed by breeders as heat.

A series of structural and physiological changes that take place in the female reproductive organs from one estrus to another. The rhythmic changes that take place in female from one estrus to another estrus is known as estrus cycle.

The term estrus is derived from Greek Word “Oistrus” mean Gadfly(mosquito), shows same behavior like estrus animal as cow.

The estrus cycle is characterized by four distinct phases of changes as –

1.     1.     Pro-estrus (18/19 - 21 days)
2.      Estrus (0 -1 day)
3.      Met-estrus (2 - 4 days)
4.      Di-estrus (5 - 16,17,18 days)

The ovarian cycle consists of two phases --

1.     1.   Follicular phase (proliferative stage)

              Pro-estrus, estrus

2.     2.   Luteal phase (secretory stage)

              Met-estrus, di-estrus

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