Note:  You should also use the multimedia web program for this system.  Go back to the Histology Part 2 Index and click on Female Reproductive System under the heading "Multimedia Lessons, Reproductive System".

 

GROSS ANATOMY

The female reproductive system is composed of several distinct organs. These include the paired ovaries, paired uterine tubes, uterus (uterine horns), cervix, vagina, and the mammary glands.  The ovaries are both an exocrine organ producing cells, i.e., ova, and an endocrine organ, secreting hormones, i.e., estrogen and progesterone.  Note: in domestic animals the oviducts are usually called uterine tubes and the uterus is called uterine horns due to the structure of these organs.  

 

 

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Photographs of reproductive tract of miniature pig.  Note appearance of follicles in the ovary in "A" and "B".  Arrow in "B" indicates a corpus luteum.

Thanks to Dr. Larry Stein for providing these gross specimens.

OVARY

The surface of the ovary is covered withsurface epithelium, a simple epithelium which changes from squamous to cuboidal with age. Immediately beneath this surface epithelium there is a dense connective tissue sheath, the tunica albuginea ovarii.

In most species, the ovaries are composed of an outercortex and innermedulla (except in the mare where the cortical region is interior to the medulla).  The cortex is composed of ovarian follicles (developing oocytes with their associated follicular cells), interstitial gland cells and stromal elements.  Ovarian follicles are in different stages of development (least mature to most mature): primordial, primary, secondary, secondary-vesicular and mature.

 

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Micrograph of ovary (Lab slide 77). Note the developing follicles in the outer cortex and the blood vessels and nerves in the inner medulla.  Arrows indicate the tunica albuginea.

Primordial follicles:  

The primordial (quiescent) follicle consists of a primary oocyte and a single layer of flattened follicular cells.  As the follicle develops, alterations occur in the primary oocyte and the surrounding follicular cells.  The primary oocyte produces yolk granules and the follicular cells change from flattened to cuboidal or columnar. 

10ovarybL2.jpograph of ovary with developing follicles (Lab slide 77).

 

Primary follicles:

The primary follicle consists of a primary oocyte with a single layer of cuboidal/columnar follicular cells.  As development proceeds, the number of follicular cells increases by mitosis forming several layers around the primary oocyte. As these cells enlarge they release steroid hormones called estrogens of which estradiol is the dominant one prior to ovulation.  During each cycle, a few primary follicles will continue to develop into secondary follicles.


Secondary (antral, vesicular) follicles:  

The secondary follicle consists of several layers of cuboidal/columnar follicular cells, now collectively called the membrana granulosa which begin to secrete follicular fluid.   A thick, amorphous layer, the zona pellucida, forms between the primary oocyte and the membrana granulosa. Previously undifferentiated stromal cells now develop into two distinct layers around the developing follicle: the theca interna and the theca externa . Cells in the theca interna are large, rounded and epithelial-like; cells in the theca externa are smaller, fibroblasts. Both layers of theca cells are separated from the membrana granulosa cells of the follicle by a basement membrane. As the follicular fluid secreted by the membrana graulosa cells accumulates, small pockets of fluid between granulosa cells begin to appear. Usually in human females only one secondary follicle will continue to develop.

The secondary-vesicular follicle is characterized by the presence of pockets of follicular fluid within the membrana granulosa. As the follicle continues to develop, the separate pockets fuse to form one large pocket of fluid called the follicular antrum.  

 

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Micrograph of ovary with developing follicles
 (Lab slide 77).


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Micrograph of ovary with developing follicles 
(Lab slide 77).

Follicular atresia: At any stage in the development of a follicle, it can die and degenerate.  Such degenerate follicles are called atretic follicles and are fairly common.  Sometimes they appear to contain a dark pink-staining material which is probably the remains of the zona pellucida of the follicle.

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Micrograph of cat ovary.  Note the atretic follicle.

Corpus luteum formation:

After ovulation, hemorrhage into the remains of the follicle usually occurs resulting in a structure called a corpus hemorrhagicum.  This transitory structure develops into a corpus luteum. 

 

In most species LH from the pituitary gland initiates this luteinization and stimulates the granulosa cells to secrete progesterone.    The granulosa cells undergo hyperplasia (proliferation), hypertrophy (enlargement) and are transformed into granulosa lutein cells.   In several species, including the human, the accumulation of a yellow lipid pigment (lutein) and other lipids marks the transition to granulosa lutein cells.  The cells of the theca interna are also transformed into lipid-forming cells called theca lutein cells. The resulting structure is highly vascular.  If fertilization occurs, the corpus luteum persists and secretes progesterone.

 

If fertilization does not occur, the corpus luteum degenerates and is replaced by connective tissue forming a corpus albicans.

 

 

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Micrographs of ovary with corporus luteum (Lab slide 79).

OVIDUCT  

The uterine tubes (also called Fallopian tubes or oviducts):  

  1. transport the ovum from the ovary to the site of fertilization
  2. help transport spermatozoa, the haploid male gametes, from the site of deposition to the site of fertilization
  3. provide an appropriate environment for fertilization
  4. transport the fertilized ovum (embryo) to the uterine horns where implantation and further development may occur.

The uterine tubes can be divided into three major parts:

  1. the infundibulum
  2. the ampulla
  3. the isthmus
The oviduct (fallopian tube in humans) is a fairly typical tubular organ composed of a tunica mucosa with a lamina epithelialis and a lamina propria.  There is no lamina muscularis mucosae in the oviduct.

The tunica mucosa is highly branched and folded, especially in the infundibulum and ampulla.

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Scanning electron micrograph of the ampulla of the oviduct of a mouse.
 Double arrows indicate the outer edge of the tunica muscularis. 
 Note the highly folded tunica mucosa.  
The shaded area is enlarged in Figure B below.

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Scanning electron micrograph of the shaded area in Figure A.  Note lamina epithelialis and lamina propria.  Shaded area is enlarged in Figure C.

 

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Scanning electron micrograph of the 
shaded area in Figure B.  
The epithelium of the tunica mucosa is simple columnar and contains two types of cells: (1)ciliated; ciliary beating causes caudad fluid flow, to move the oocyte toward the uterus; (2)non-ciliated secretory cells termed "Peg cells"

Scanning electron micrographs showing the characteristics of the wall of the oviduct.  Note the highly folded tunica mucosa of the ampullary region of the oviduct.  The lamina epithelialis of the tunica mucosa is shown in higher magnifications in the stacked micrographs. Note the presence of epithelial cells with cilia as well as cells without cilia (Peg cells).  The peg cells are secretory in nature whereas the ciliated cells serve to propell the secretion of the peg cells toward the uterus along with an ovum, if present.  The ratio of ciliated to non-ciliated cells changes with the cycle of the female animal under the control of hormones from the ovary.

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Micrograph of oviduct of a pig (Lab slide 80).

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Micrograph of oviduct of a rat (Lab slide 81).  Note the different tunics.   There is no lamina muscularis mucosa in the female reproductive tract, but other layers are present.


UTERUS

Functions

  1. serves to receive the sperm in mares
  2. transports sperm from site of deposition to uterine tubes for fertilization
  3. provides suitable environment for 
    a. implantation of the embryo
    b. nourishment of the embryo & fetus during pregnancy
  4. provides mechanical protection of the fetus
  5. expels the mature fetus at the end of pregnancy

In the fundus and body of the uterus, the wall is divided into the 

  1. endometrium = tunica mucosa and tunica submucosa
  2. myometrium = tunica muscularis
  3. perimetrium= tunica serosa   

 

 
  • Endometrium.   The endometrium comprises the tunica mucosa and the tunica submucosa of the uterus.  In the tunica mucosa the lamina epithelialis is usually simple columnar except in the sow and ruminants where it may be pseudostratified columnar.  The lamina propria consists of loose connective tissue full of neutrophils and lymphocytes.  It blends with the underlying tunica submucosa since there is no lamina muscularis mucosae in the entire female reproductive tract.  Uterine glands are simple or branched tubular glands located in the lamina propria-tunica submucosa. Some regions of the endometrium in ruminants are void of glands and are highly vascular.  It is in these regions, called caruncles, that contacts between the uterus and the extraembryonic membranes are made.


  • Myometrium is the tunica muscularis of the uterus.  It is composed of a thick inner circular layer and a thinner outer longitudinal layer of smooth muscle.  The region in between the two layers of smooth muscle contains large blood vessels. 

 

  • Perimetrium is the tunica serosa of the uterus. It has the typical composition of loose connective tissue, but contains a large number of lymphatic vessels. 

The stratum vasculare is a layer of large blood vessels located between the inner and outer layers of smooth muscle of the myometrium.

In the sow the stratum vasculare is indistinct and in the cow it may be located in the outer half of the circular muscle layer.

 

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Micrographs of uterus of a rat (Lab slide 81).

VAGINA

The vagina serves and the receptacle for the penis during copulation and also expells the fetus at birth, serving as the birth canal.

 


 


Copyright 2002 Charlotte L. Ownby
Histology Part 2 Index