Chapter 13: Reproduction

• Chapter overview:– Chapter 13 presents the anatomy and

physiology of reproduction, including:• anatomical views and parts identification

• estrous cycle and gestation

• new developments and related technologies

Selected Reproduction Terms:

• Puberty - sexual maturity

• Ovulation - release of ovum (egg) from ovary

• Copulation - the act of mating

• Fertilization - union of male and female sex cells

• Conception - becoming pregnant

Selected Reproduction Terms:

• Estrous cycle - the interval between two estrus periods

• Estrus - the time of receptivity to mating during the estrous cycle; also termed “heat”

• Gestation - pregnancy

• Parturition - the act of giving birth

Reproductive Tract: Male Mammals

• Scrotum - container for the testes external to the body; functions in temperature regulation

• Testicles - paired within the scrotum

• Epididymis - long tortuous tubule encased and lying along the surface of the testis

Reproductive Tract: Male Mammals

• Vas deferens - simple tubule carrying sperm from the epididymis to the ampulla or urethra

• Ampulla - widened area at juncture of vas deferens and urethra; not found in all species

• Urethra - single tubule leading from vas deferens through penis to exit

Reproductive Tract: Male Mammals

• Sigmoid flexure - curvature in the penis structure of bull and boar allowing for extension during mating

• Accessory glands - glands associated with the male reproductive tract to provide fluids for volume, nutrient source, and protection of the sperm

Terms: Male Reproduction

• Castration - removal or destruction of the testes by surgical or other physical or chemical methods

• Cryptorchid - male mammal with one or both testicles failing to descend into the scrotum

Reproductive Tract: Female Mammals

• Ovary - structure containing the reproductive cells (ova); paired

• Infundibulum - associated with each ovary; captures the ova after ovulation

• Oviduct - tubule connecting infundibulum to the uterine structure; site of fertilization

Reproductive Tract: Female Mammals

• Uterine horn - leads from oviduct to body of uterus; well developed in litter-bearers, small or absent in nonlitter-bearers; implantation occurs here in many litter-bearing species

• Uterus - body of the uterine structure between cervix and horns; site of implantation in nonlitter-bearers

Reproductive Tract: Female Mammals

• Cervix - muscular opening between uterus and vagina; remains reasonably constricted except for relaxation to allow birth

• Vagina - structure external to the cervix; accepts penis of male for mating

• Vestibule - general area of vagina posterior to entrance of urethra

Major Hormones of Reproduction:

• Testosterone - produced in cells of Leydig in testis; causes growth of reproductive tract, development of male physical character, and onset of sexual drive

• Estrogen - produced in cells lining mature ovarian follicles; induces estrus, mammary duct growth, and development of secondary sex character

Fetal Membranes:

• Membranes develop from the fetus to provide contact for nourishment and a protective barrier– Amnion: innermost membrane surrounding

fetus– Chorion: outer layer making contact with

uterus– Allantois: layer fused with amnion and chorion

to create a fluid filled space

“Freemartins” in Bovines:

• Occurrence: female born twin to a male

• Result: female generally has incomplete reproductive tract; over 90% are infertile

• Reason: fetal membranes anatomose (connect); compounds from male fetus inhibit normal development of female

Estrus Synchronization:

• Manipulation of estrous cycle to synchronize ovulation and breeding of female groups

• Generally focus on use of prostaglandin injection protocols to lyse the corpus luteum

Superovulation:

• Manipulation of ovulation to dramatically increase simultaneous release in a single genetically superior individual

• Generally involves use of follicle stimulating hormone and prostaglandin

• Multiple ova may be fertilized in vivo or in vitro

• Ova are manually collected from dam• Recipient females are utilized to implant

fertilized ova

Embryo Transfer (ET):

• Transferring embryos from one genetically superior female to another

• Embryos may be recovered from a donor female or may be fertilized and grown in vitro

• Often linked with superovulation• Transfer of frozen embryos also common,

allowing longer-term storage• Also used to expand populations of endangered

species

Cloning:

• An ovum recovered from a female is enucleated and genetic material from a diploid donor cell is inserted

• The new cloned embryo is implanted in a recipient female

• An offspring is created from one genetic parent

• Note: natural born identical twins are actually clones of each other

Transgenics:

• Transgenic - an animal with the genetic makeup of more than two parents

• What: recombinant technology creating the inclusion portions of foreign DNA into DNA of another cell via splicing techniques

• Why: to attempt to “insert” a cure or control for a genetic disease; to create organisms that produce pharmaceuticals; to advance the science of medicine