Animal Reproduction: Terminology and Processes

Androgen

A male sex hormone, such as testosterone; a type of hormone that promotes the development and maintenance of male sex characteristics.

Artificial insemination (AI)

When semen is placed into the cervix.

Conceptus

The production of conception being the embryo/fetus together with the surrounding membranes(s).

Corpus luteum

Produces progesterone that in turn allows and maintains pregnancy.

Estrous

An adjective describing the estrous cycle.

Estrus

A noun denoting the time of heat.

Function of the gonads

To produce gametes and sex hormones.

Gonad

The ovary in females and testis in males; the primary reproductive organ.

Libido

The desire to mate.

Monoestrous

Where there is a single estrus followed by an absence of ovarian activity.

Polyestrous

Where an animal will show repeated estrus separated by 16-23 days depending on the species.

Reflex ovulators

Show estrus but require mating to ovulate.

Pregnancy recognition

When the conceptus signals its presence to the mother to allow pregnancy to continue.

Primordial germ cell

Migrates to the site destined to be the gonad; cells become gonocytes in the developing gonad and ultimately become gametes.

Progesterone

The hormone that is essential to the maintenance of pregnancy.

Sertoli cells

In the seminiferous tubules of the testis; they function as 'nurse cells' for developing spermatozoa.

Testis

The primary male reproductive organ because it produces spermatozoa and the male reproductive hormone testosterone.

Vas deferens

Connects the epididymis with the urethra; provides an environment suitable for survival of spermatozoa and the additions of the secretions of the accessory glands resulting in semen.

Seminiferous tubules

Hollow structure in which the germ cells differentiate to spermatozoa.

Epididymis

A coiled structure also in the scrotum; functions include storage of quiescent but live spermatozoa before ejaculation, maturation of spermatozoa, and addition of nutrients to the semen for spermatozoa to use for movement.

Male accessory sex glands

Situated along the pelvic portion of the urethra; comprises of vesicular gland, prostate gland, and bulbourethral glands; it varies depending on species.

Ampullary gland

Surrounds the terminal part of the ductus deferens.

Seminal vesicles

Produces secretions that are added to the spermatozoa.

Capacitation

The process that spermatozoa undergo to gain the ability to fertilize an egg after ejaculation.

Fructose

A sugar present in seminal fluid that provides energy for spermatozoa.

Prostaglandins

Compounds in seminal fluid that stimulate contraction of the female reproductive tract.

Prostate Gland

Gland that produces slightly alkaline secretions added to spermatozoa to neutralize lactic acid.

Bulbourethral Gland

Gland found in all domestic animals except dogs, located in the dorsal aspect of the pelvic urethra.

Accessory Sex Glands

Glands with well-developed soft tissue capsules and internal septum, rich in smooth muscle fibers responsible for expelling secretions.

Urethra

Tube that connects the bladder and vas deferens, through which urine and semen are expelled.

Corpus Cavernosum

Spongy tissue surrounding the urethra in the penis that becomes rigid during sexual arousal.

Sigmoid Flexure

A structure in bulls, rams, and boars that aids in extending the penis from the sheath.

Os Penis

A bone found in the penis of dogs, cats, and most primates that facilitates erection.

Fibroelastic Penis

Type of penis with small blood spaces divided by tough fibroelastic tissue, enclosed by thick tunica albuginea.

Musculocavernous Penis

Type of penis with larger blood spaces and a more delicate tunic, requiring a larger volume of blood for erection.

Prepuce

The cutaneous sheath around the free part of the penis in a quiescent state.

Cowper's Gland

Gland also known as the bulbourethral gland, which secretes fluid to clean the urethra.

Pudendal Nerve

Nerve that delivers sensory input to the spinal cord, playing a role in erection and ejaculation.

Nitric oxide

Activates relaxation of corporal cavernosal smooth muscle tissue resulting in increased blood flow into the penis resulting in an erection.

Autonomic nerves

Involved with emission of seminal fluid.

Motor input

To the bulbospongiosus muscles causes expulsion of seminal fluid.

Spinothalamic nerves

Involved with integrating complex signaling related to reproduction.

Avian male reproductive tract

Entirely inside the body.

Testes

Produce sperm and then sperm travels through a vas deferens to the cloaca.

Papillae

Serve as the mating organs in avian males.

Castration in roosters

Called caponization.

Ovary

Principal function is to produce ova; develops in follicles associated with other cells.

Follicle development stages

Develops from primary, to secondary, to tertiary follicle.

Graafian follicle

Fully mature follicle that produces estradiol.

Luteinizing hormone (LH)

Stimulated by estradiol and triggers ovulation of ova.

Zona pellucida

Thin membrane surrounding the ovum during ovulation.

Corpus hemorrhagicum

Remnants of a follicle after ovulation that first forms a bloody or red body.

Luteolysis

Process by which the corpus luteum breaks down for the corpus albicans.

Infundibulum

Catches the ovum in the oviduct.

Oviduct

Functions to move the ovum to the uterus and is the site for fertilization.

Zygote

The ovum after fertilization.

Uterus

Site where the embryo implants and the fetus develops.

Endometrium

Glandular layer of the uterus.

Myometrium

Layer of smooth muscles in the uterus.

Bicornuate uterus

Has two large uterine horns, a uterine body, and a single cervix, found in porcine, canine, feline, ruminants, and equine.

Pyometra

Life-threatening, inflammatory bacterial infection of the uterus in mature intact female canines.

Cervix

Barrier between the uterus and vagina, normally constricted with a mucus plug.

Vagina

Site for insemination and becomes part of the birth canal during the birth process.

Vulva

External opening consisting of labia majora, labia minora, and clitoris.

Hen reproductive system

In almost all species of birds, only the left ovary and oviduct are functional.

Magnum

It functions by adding concentrated egg white proteins and membranes to the egg. The ovum spends 2-3 hours here.

Isthmus

It functions by adding fluid to egg white. The ovum spends 1-2 hours here.

Germ cells

Cells that give rise to gametes and play a key role in sexual differentiation by affecting gonad development.

Sex-determination system

A biological system that determines the development of sexual characteristics in an organism.

XY sex chromosomes

Mammals having XY (or much less commonly XXY) sex chromosomes will develop testes.

XX or X0 individuals

Develop as a female with two ovaries.

Sry gene

The principal gene controlling the sex of a mammal, located on the Y chromosome, which in virtually all cases leads to the development of testes.

W and Z chromosomes

Female birds have a W and Z chromosome, and males have two Z chromosomes.

Gonadotropin Releasing Hormone (GnRH)

A modified peptide with 10 amino acid residues, also called LH-releasing hormone.

Gonadotropin Inhibiting Hormone (GnIH)

Inhibits the release of both gonadotropins, LH and FSH, in both mammals and birds.

Follicle-Stimulating Hormone (FSH)

A glycoprotein hormone produced by the anterior pituitary gland.

Testosterone

The male sex hormone, a steroid synthesized from cholesterol.

Estrogens

Female sex hormones such as estradiol, estrone, and estriol, produced by the follicle before ovulation.

Oxytocin

A peptide hormone produced by the posterior pituitary gland that causes uterine contractions during the birthing process and milk to be let down from the mammary gland.

Gametogenesis

A biological process by which diploid or haploid precursor cells undergo cell division and differentiation to form mature haploid gametes.

Spermatogenesis

Occurs throughout the life of the male animal, except in seasonal breeders when it is restricted to the breeding season.

Oocytes

The number of oocytes in the ovary is established at birth.

Follicular Atresia

Loss of oocytes after ovulation or by cell death.

Cell Division

Requires duplication of the genome by mitosis (or meiosis).

Nuclear Mitochondria Replication Factors

Released from the nucleus to stimulate mitochondrial multiplication.

Meiosis

A type of cell division in sexually reproducing organisms that reduces the number of chromosomes in gametes (the sex cells, or egg and sperm).

Hormones Required for Spermatogenesis

Spermatogenesis requires the hormone FSH and testosterone.

Processes of Spermatogenesis

Involves three distinct processes as the cells progress from primary spermatocytes, to secondary spermatocytes, to spermatids, to sperm.

Oogenesis

Begins when the 2n oogonium undergoes mitosis, producing a primary oocyte.

Primary Oocytes

Arrest in prophase I before birth.

Secondary Oocyte

Results from meiosis of one oocyte per menstrual cycle, arrests in metaphase II and produces a polar body.

Completion of Meiosis

Occurs upon ovulation and sperm entry, resulting in a polar body and a fertilized egg.

Development of the Follicle

Maturation of a follicle proceeds from primordial follicles.

FSH and LH Roles

FSH stimulates the growth of a tertiary follicle, and LH stimulates the production of estrogen by granulosa and theca cells.

Mature Follicle

Ruptures and releases the oocyte.

Corpus Albicans

A scar on the surface of the ovary that is a remnant of ovulation.

Primary Follicle

The oocyte is surrounded by a single layer of cuboidal cells and a basement membrane.

Bovine Oocytes Size

Normally about 0.1 mm in diameter.

Secondary Follicle

Located near the surface of the ovary, with the oocyte usually about 120 μm in diameter.

Pre-ovulatory Follicle

Bulges from the surface of the ovary before ovulation and contains the ovum surrounded by zona pellucida and cumulus oophorus.