3rd. part 2

• Penile urethra


  • Lined by transitional epithelium which may change from stratified squamous before or at the urethral opening in some species
  • Glands may or may not be present in the lamina propria-tela submucosa in stallion and boar
  • No muscularis mucosae
  • Typical tunica muscularis
• Penis


  • Consists of a root, body, and glans
  • Body is encapsulated- dense white fibrous connective tissue of tunica albuginea- well-developed in animals with fibrous type penis (boar and ruminants)
  • Body contains erectile tissue, smooth muscle, skeletal muscle and the urethra
  • Erectile tissue consists of dense white fibrous connective tissue rich in elastic fibers and sinuses; these sinuses can be engorged with blood
  • Animals with vascular type penis- horse, carnivores and man- have well developed erectile tissue
  • Glans penis- well developed in primates, stallion and dog; covered by penile portion of prepuce (a reflection of the skin); may contain erectile tissue, bone (os penis), cartilage and dense white fibrous connective tissue (bull)
  • Covered by stratified squamous epithelium
• Erectile Mechanism


  1. Under erotic stimulation, helicine arteries (branches of artery of the penis) become filled with blood; helicine arteries open into erectile tissues

  2. Cavernous or erectile tissue becomes filled with blood

  3. Peripherally located thin-walled veins become occluded against tunica albuginea- this enhances rigidity

  4. During detumescence, the helicine arteries contract and regain their initial tone

  5. The pressure in occluded veins is reduced

  6. Blood is drained from cavernous tissue and normal blood flow through the penis is resumed
• Ovary


  • Paired structures and are the counterpart of the testis in males
  • Has both exocrine (production of ova) and endocrine (production of hormones estrogen and progesterone) functions
  • Covered by a surface epithelium (a modification of the visceral epithelium, also called germinal epithelium) which is continuous with the mesovarium
  • Underneath the germinal epithelium is a capsule of dense white fibrous connective tissue called the tunica albuginea ovarii, which is similar but thinner than its counterpart in the testis
  • The parenchyma is divided into 2 zones: an outer cortex and inner medulla; in the mare, the cortex and medulla are reversed in position, the cortex is located in the deep zone of the ovary and only connects with the surface via the ovulation fossa
  • The ovarian cortex contains many follicles in various stages of development, atretic follicles, corpora lutea, interstitial cells and stromal elements (loose connective tissue)
  • The ovarian medulla contains large vessels, lymphatics, nerves and loose connective tissue rich in elastic and reticular fibers and strands of smooth muscles
  • The cortex is sometimes referred to as the functional part of the ovary and the medulla the vascular part
• Ovarian follicles


  • Primordial follicles
  • Primary follicles
  • Developing follicles
  • Vesicular follicles or Graafian follicle or tertiary follicles
• Primordial follicles


  Smallest and the most numerous of the follicles found on the periphery of the cortex beneath the tunica albuginea; consist of a large primary oocyte surrounded by a single layer of flat or squamous follicular cells
• Primary follicles


  Consist of a single layer of cuboidal granulosa cells around the oocyte; eventually, several layers of granulosa cells are formed around the oocyte as maturation advances at the same time, they gradually move deeper and nearer the medulla (in most animals expect the horse) for nourishment
• Developing follicles


  Bigger than the primary follicles and are characterized by several layers of follicular cells and the appearance of antrum, a space which separates the primary oocyte from the surrounding follicular cells
• Vesicular follicles or Graafian follicle or tertiary follicles


  The largest among the ovarian follicles; as they increase in size, they occupy a large part of the ovarian cortex and eventually bulge from the surface of the ovary, a mature follicle will have the following parts: primary oocyte- the young ovum, zona pellucida- a clear membrane immediately surrounding the ovum, corona radiata- a layer of radially arranged granulosa cells above the zona pellucida, cumulus oophorus- a cluster of follicular cells that surround the corona radiata and anchor the primary oocyte to the membrana granulosa, antrum- a cavity or space created by reorganization of the follicular cells; it is eventually filled with follicular fluid or liquor folliculi, membrana granulosa- several layers of follicular cells that surround the antrum; the cells secrete the hormone estrogen, it is enclosed by a connective tissue stroma of the cortex called the theca folliculi, the theca folliculi is consists of 2 layers, an inner cellular layer consisting of fibroblasts and an outer fibrous layer composed mainly of collagen fibers
• Corpora lutea


  Structures formed from the mature follicles after ovulations; during ovulation, the mature follicle ruptures and liquor folliculi is discharged; the mature wall of the ruptured mature follicle collapses and become folded and the follicular cells of the membrana granulosa become enlarged, accumulate lipid and are transformed into plump, pale staining polygonal cells called lutein cells which fill up the antrum; the new body formed by these lutein cells is now called corpus luteum; the lutein cells secrete the hormone progesterone
• Atretic follicles


  Follicles that degenerate and do not reach maturity; characterized by shrunken primary oocyte & granulosa cells that are undergoing dissolution
• The Ovarian Cycle


  1. Proestrus stage- there is accelerated growth of the primordial follicles as influenced by FSH

  2. Estrus stage- the period of ovulation when the mature follicle ruptures and the primary oocyte is released; during or after the release, the primary oocyte undergoes meiosis to give rise to the secondary oocyte and the first polar body

  3. Metestrus stage- characterized by the development of the corpus luteum and its subsequent secretion of progesterone; progesterone initiates the development of the uterine wall in preparation for pregnancy

  4. Diestrus- a short period of quiescence characterized by maximum development of the corpus luteum and maximum secretion of progesterone; if pregnancy does not occur, the later part of diestrus is characterized by involution of the corpus luteum and its conversion into a corpus albicans, the period of quiescence is quite long, occurring between breeding seasons and the stage is referred to as anestrus; during anestrus, the ovary is relatively quiet, the corpus luteum continues to involute and follicular development is arrested
• Species variation


  • The ovaries in mare are bean-shaped due to the presence of the ovulation fossa or fossa ovarii, an indentation at the attached border of the ovary
  • In the sow, the ovaries appear lobulated because of the presence of many follicles, corpora lutea or both
  • In the bitch, the corpus luteum persists throughout a period equal to the normal gestation period whether pregnancy occurs or not
• Oviducts or Uterine (Fallopian) tubes


  • The site of fertilization or union of the ovum and spermatozoa; the oviduct is divided into four regions: infundibulum- the funnel-shaped portion which has finger-like projections called fimbriae, ampulla- the longest portion of the oviduct, isthmus- the short narrow part of the oviduct near its connection with the uterus, intramural part- the short terminal part of the oviduct which extends through the wall of the uterus
  • Tunica mucosa- is extensively folded so that the lumen is almost obliterated; there are only irregular spaces in between folds of mucosa; lining epithelium is simple columnar intermittently ciliated; cells without cilia are called peg cells; lamina propria has loose connective tissue without glands; muscularis mucosae is absent
  • Tunica submucosa- blends with the lamina propria; it is also with loose connective tissue without glands
  • Tunica muscularis- typical except in the isthmus where it is composed of three layers; inner longitudinal, middle circular and outer longitudinal smooth muscle layers
  • Tunica serosa- typical
• Uterus


  • The site of implantation of the fertilized ovum; has 3 regions: horns, body and cervix; in most domestic species the uterus is bicornuate, with two prominent horns, a body and a cervix; in primates including women, the uterus is simplex with a prominent body, two small horns and cervix; the cervix serves as a valve to close off the uterus from the vagina; in the bitch, it possesses glands similar to those which occur in the body and horns of the uterus; while in other species the cervix is usually devoid of glands
  • Endometrium- the innermost layer and corresponds to the tunica mucosa of tubular organs; lining epithelium is simple columnar although patches of pseudostratified columnar may be encountered in the sow and cow; lamina propria is composed of loose connective tissue and contains simple or branched tubular uterine glands; in ruminants, there are areas of the lamina propria which are highly vascularized and are devoid of uterine glands, these areas are called uterine caruncles and are the eventual sites for attachment of the fetal cotyledons
  • Myometrium- corresponds to the tunica muscularis of tubular organs; it consists of two layers of smooth muscle fibers- a thick inner circular and a thinner outer longitudinal layer; a layer of blood vessels, the stratum vasculare is found in between the muscle layers
  • Perimetrium- corresponds to the tunica serosa of a tubular organ; it is very similar to the tunica serosa however, more lymphatic vessels may be present
• Uterine Changes during Estrous Cycle

  1. Proestrus- the lining epithelium of the uterus hypertrophies and is invaded by neutrophils; there is increased vascularity, congestion and occasional hemorrhage in the lamina propria

  2. Estrus- the lining epithelium continues to proliferate and is now being invaded by agranulocytes; the lamina propria remains congested, edematous and hemorrhagic; the uterine glands start to proliferate and the secretory activity of the glandular cells is increased

  3. Metestrus- continued proliferation and coiling of the uterine glands, continued secretory activities of the epithelial and glandular cells and disappearance of edema in lamina propria

  4. Diestrus- maximum glandular proliferation and extensive coiling of uterine glands; if fertilization occurs, the maximum secretory activity of epithelial and glandular cells are maintained; if there is no fertilization, vascularity of the lamina propria decreases, secretory activity ceases and the lining and glandular cells involute

  5. Anestrus- characterized by a thin endometrium lined by simple cuboidal epithelium and few simple straight uterine glands
• Cervix


  • The neck of the uterus; thick walled, muscular, and rich in elastic fibers
  • Tunica mucosa-submucosa forms high primary folds with secondary and tertiary folds
  • Lining epithelium is simple columnar in most species with many mucigenous cells and goblet cells; some ciliated epithelial cells are seen in certain species; in pregnancy, mucus secretion thickens to form the cervical seal
  • Intraepithelial and simple tubular subepithelial glands are seen in ruminants
  • In the sow, more than 90% of lining epithelium is stratified squamous that undergoes cyclical alterations similar to that of the vagina
  • Lamina propria is dense irregular connective tissue
  • Tunica muscularis is with inner circular and outer longitudinal smooth muscle layers
  • Elastic fibers are present in the circular layer; both muscles and elastic fibers are important in re-establishing cervical structure after parturition
  • Tunica serosa is loose connective tissue
• Vagina


  • Tunica mucosa- it is highly folded; the lining epithelium is stratified squamous non-keratinized; in the cow isolated foci of goblet cells are present in the cranial portion of the vaginal epithelium; in the bitch, intraepithelial glands have been observed during the estrus stage
  • Lamina Propria- it is dense white fibrous connective tissue with lymphatic nodules
  • Muscularis mucosae- is absent
  • Tunica submucosa- blends with and has the same features as the lamina propria
  • Tunica muscularis- consists of two-three layers of smooth muscle fibers- inner longitudinal, middle circular and outer longitudinal, the inner longitudinal layer is of variable occurrence
  • Tunica serosa- it is present in the cranial portion of the vagina and is replaced by the tunica adventitia caudally
• External Genitalia

  • Consists of the vestibule, clitoris, and the vulva
  • Vestibule- very similar in structure to the caudal portion of the vagina; also called the cavity of the vagina and has the following features: Tunica mucosa- the lining epithelium is stratified squamous non-keratinized epithelium with extensive lymphocytic infiltration, the lamina propria consists of loose and dense connective tissue and contains vestibular glands, compound tubuloalveolar mucous glands; in the cow the glands are concentrated near the clitoris, muscularis mucosae is absent, Tunica submucosa- blends with and has the same structure as the lamina propria, Tunica muscularis- has two
• Vestibule


  Very similar in structure to the caudal portion of the vagina; also called the cavity of the vagina
• Vestibule


  • Mucosa - stratified squamous non-keratinized epithelium with extensive lymphocytic infiltration
  • Lamina propria - loose and dense connective tissue, contains vestibular glands, compound tubuloalveolar mucous glands
  • Muscularis mucosae is absent
  • Submucosa - blends with and has the same structure as the lamina propria
  • Muscularis - has two distinct layers, inner longitudinal and outer circular
  • Adventitia - the fourth and outermost layer
• Clitoris


  Homologue of the penis, consists of body, glands and prepuce, contains erectile tissue and is surrounded by dense fibrous connective tissue
• Vulva


  Consists of the labia and the rima pudendi or the external urogenital opening
• Labia


  • Folds of integument composed of typical integumentary structures, only one pair is developed in domestic animals and they correspond to the labia minora in women
  • Outer surface covered with stratified squamous non-keratinized epithelium
• Placenta


  A membrane formed by the union of the fetal membranes with the endometrium of the uterus
• Classification of placenta based on distribution of chorionic villi

  • Diffuse placenta
  • Cotyledonary placenta
  • Zonary placenta
  • Discoidal placenta
• Layers of placental membrane

  • Maternal side: Endothelial lining of blood vessels, Connective tissue in lamina propria, Lining epithelium of endometrium
  • Fetal side: Lining epithelium (trophoblasts) of chorion, Loose connective tissue of chorioallantoic membrane, Endothelial lining of allantoic blood vessels
• Types of placenta based on contributions from fetal chorion and maternal endometrium

  • Epitheliochorial
  • Syndesmochorial
  • Endotheliochorial
  • Hemochorial
  • Hemoendothelial
• Combined classification of placenta

  • Diffuse epitheliochorial
  • Cotyledonary epitheliochorial
  • Zonary endotheliochorial
  • Discoid hemochorial
• Avian female reproductive system

  • Only left ovary and oviduct are functional
  • Ovary has cortex and medulla, no antrum in follicles
  • Oocyte surrounded by granulosa cells, theca cells form corpus luteum
  • Oviduct has infundibulum, magnum, isthmus
  • Uterus (shell gland) produces egg shell
  • Thick muscular vagina propels egg to cloaca
• The eyeball is a globe-shaped structure with 3 layers surrounding the refractive components
• Sclera


  • Episclera - outermost transparent layer
  • Sclera proper - middle layer, DWFCT rich in elastic fibers
  • Lamina fusca - inner layer, DWFCT rich in elastic fibers, contains pigments
• Cornea


  • Epithelium - nonkeratinized stratified squamous
  • Bowman's membrane - basement membrane and collagenous fibers
  • Substantia propria - bulk of cornea, collagenous fibers
  • Descemet's membrane - separates substantia propria from endothelium
  • Endothelium - large squamous or cuboidal cells
• Corneal repair and transplant is rapid for superficial wounds, but deep wounds heal slowly. Species differences in corneal susceptibility and repair
• Choroid


  • Epichoroid - avascular, loose CT, chromatophores
  • Lamina vasculosa - large vessels in loose CT
  • Tapetum - fibrous or cellular layer that reflects light
  • Choriocapillary layer - rich in capillaries
  • Elastic membrane - Bruch's membrane
• Ciliary body


  • Covered by pigmented epithelium and non-nervous columnar cells
  • Areolar CT rich in elastic fibers, extensive capillary network, smooth muscle (ciliary muscle)
  • Bounded by elastic lamina, internal to this is the ciliary epithelium (pars ciliaris retinae)
• Iris


  • Extension of the choroid into the anterior compartment
• Iris

  • Oriented radially
  • Distal margin defines the pupil
  • Rostral border covered by endothelium reflected from posterior lining of cornea
  • Stroma consists of areolar C.T., blood vessels, chromatophores and smooth muscle- the sphincter pupilae and dilator pupilae
  • Sphincter pupilae located along the caudal border
  • Caudal border covered by same cells as ciliary body, forming the pars iridica retinae
  • Corpora nigra (iridial granules) occur along the pupillary margin in horses and ruminants
• Nervous tunic

  Consists of the retina
• Retina

  • Responsible for reception and transduction of light stimuli and transmission of nerve impulses to the brain
  • Point of transition from retina to non-photosensitive epithelial cells is called the ora ciliaris retinae in domestic animals and the ora serrata in man
  • Epithelial and pigment cells form a bistratified layer, with the rostral continuation called the pars ciliaris retinae and the caudal layer called the pars iridica retinae
  • Has 10 distinct layers