The Reproductive System - Male and Female Structures, Estrus Cycle, and Parturition

The Reproductive System - Male Structure

  • Description of Male Structures

    • Scrotum

    • Also known as the scrotal sac

    • External pouch that encloses and supports the testes

    • Keeps the testes outside of the body for temperature regulation

      • Important for the survival and development of sperm

    • Perineum

    • Area between the scrotum and the anus

    • Testes

    • Male sex glands that produce spermatozoa

    • Also referred to as male gonads

    • Singular form is testis

    • Divided into compartments containing coiled tubes called seminiferous tubules

    • Epididymis

    • Tube located at the upper part of each testis

    • Secretes a portion of semen, stores semen before ejaculation

    • Provides a passageway for sperm

    • Divided into three sections: head, body, and tail

    • Runs down the length of the testicle, turns upward, and narrows

    • Sperm collected here becomes motile

    • Ductus Deferens

    • Narrow tube that connects to the epididymis

    • Carries sperm into the pelvic region toward the urethra

    • Enclosed by the spermatic cord

    • Acts as the excretory duct of the testes

    • Accessory Sex Glands

    • Seminal Vesicles

      • Opens into the ductus deferens where it joins the urethra

      • Secretes a thick, yellow substance that nourishes sperm and increases semen volume

    • Ejaculatory Duct

      • Formed by the union of the ductus deferens and the duct from the seminal vesicles

      • Passes through the prostate and enters the urethra

    • Prostate Gland

      • Single gland surrounding or near the urethra

      • May be well-defined or diffuse depending on the species

      • Secretes a thick fluid that aids in sperm motility

    • Bulbourethral Glands

      • Two glands located on either side of the urethra

      • Secrete thick mucus that acts as a lubricant for sperm

    • Urethra

    • Tube passing through the penis to the exterior

    • Serves both reproductive and urinary systems

    • Penis

    • Male sex organ that carries reproductive and urinary products outside the body

    • Prepuce

      • Retractable fold of skin covering the glans penis

    • Structural differences among species

      • Example: Dogs have an os penis (a bone in the penis)

      • Example: Cats have barbs on the penis

    • Composed of erectile tissue that fills with blood to achieve erection

    • Sigmoid Flexure

      • An S-shaped bend in the penis of some species

The Reproductive System - Female Structure

  • Description of Female Structures

    • Ovaries

    • Pair of organs located in the caudal abdomen of females

    • Also called gonads

    • Produce estrogen, progesterone, and ova (eggs)

    • Eggs develop in the ovaries and are expelled during ovulation

    • Uterine Tubes

    • Also known as fallopian tubes

    • Paired tubes extending from the cranial portion of the uterus to the ovaries (not attached to the ovaries)

    • Distal end has a funnel-shaped opening called the infundibulum

      • Contains fringed extensions called fimbriae that capture the egg upon ovulation

    • Proximal end connects to the uterine horns

    • Transports eggs from the ovary to the uterus and sperm from the vagina and uterus

    • Fertilization occurs here

    • Uterus

    • Thick-walled, hollow organ with muscular walls and a mucous membrane lining

    • Houses the developing embryo during pregnancy

    • Located dorsal to the urinary bladder and ventral to the rectum

    • Cervix

    • Caudal continuation of the uterus

    • Marks the cranial extent of the vagina

    • Contains ringlike sphincters to prevent foreign substances entering the uterus

    • Typically closed except during estrus when it relaxes for sperm entry

    • Closed during pregnancy by a mucous plug

    • Vagina

    • Muscular tube lined with mucosa

    • Extends from the cervix to the outside of the body

    • Accepts the penis during copulation

    • Serves as passage for semen, excretions, and offspring

    • Vulva

    • External female genitalia

    • External opening to the urogenital tract

      • Consists of vaginal orifice, vestibular glands, clitoris, hymen, and urethral orifice

    • Perineum

      • Area between the vaginal orifice and the anus

    • Labia

      • Fleshy borders or edges of the vulva

    • Vaginal Orifice

      • Entrance from the vagina to the outside

    • Vestibular Glands

      • Secrete mucus to lubricate the vagina

    • Clitoris

      • Sensitive erectile tissue located in the ventral portion of the vulva

    • Urethral Orifice

      • Found where the vagina and the vulva join; often associated with a vestigial hymen

    • Mammary Glands

    • Milk-producing glands in females

    • Number of glands varies by species

The Estrus Cycle

  • Definition

    • The heat cycle that occurs at the onset of puberty and continues throughout an animal's life

    • The ability to reproduce begins at puberty and varies among species

    • The estrus cycle prepares the uterus to accept a fertilized ovum

  • Stages of the Estrus Cycle

    • Proestrus

    • Period before sexual receptivity

    • Involves secretion of FSH (Follicle Stimulating Hormone) by the anterior pituitary gland

    • FSH causes follicular development in the ovary

    • FSH stimulates ovarian estrogen release, preparing the reproductive tract for pregnancy

    • Estrus

    • Period when the female is receptive to males

    • FSH levels decrease, while LH (Luteinizing Hormone) levels increase

    • Leads to follicle rupture and egg release (ovulation)

    • Commonly termed “in heat” or standing heat

    • Metestrus

    • Short period after sexual receptivity

    • Corpus luteum forms and produces progesterone

    • Progesterone ensures proper implantation and maintenance of pregnancy

    • If not pregnant, the CL decreases in size

    • The term is mostly used in cattle cycles

    • Diestrus

    • Phase of inactivity after metestrus

    • Observed in polyestrous animals before the next proestrus

    • Anestrus

    • Period where the animal is sexually quiet

    • Long phase seen in seasonally polyestrous and seasonally monestrous animals

  • Parturition (Birth)

    • Stages of Birth

    • Stage 1

      • Dilation of the cervix

    • Stage 2

      • Uterine contractions and expulsion of fetus

    • Stage 3

      • Separation of placenta from the uterus

  • Uterus Parts

    • Cornus

    • Horn: Cranial end with two horns leading to uterine tubes

    • Corpus

    • Middle portion or body of the uterus

    • Cervix

    • Neck: Caudal portion of the uterus extending into the vagina

  • Layers of the Uterus

    • Perimetrium

    • Membranous outer layer

    • Myometrium

    • Muscular middle layer

    • Endometrium

    • Inner layer