Chapter 20 - Pregnancy, Development and Lactation Flashcards
Breeding and Fertilization of the Ovum
Erection
Copulation
Ejaculation
Sperm
Transport
Fertilization
Erection
Enlargement and stiffening of the penis that prepares it for breeding
*Arteries dilate
*Veins are compressed
Sexual stimuli
*Smells and behavioral changes from the female
Copulation
The act of breeding
Allowed by the female during the estrus period
Positions:
*Standing with mounting the female from behind
*Kneeling (cushed) position
* Camels, llamas, alpacas
Mounting is followed by intromission, thrusting, and ejaculation
Ejaculation
The reflex expulsion of semen from the penis
Stage 1:
* Spermatozoa move from epididymis
* Fluids from accessory reproductive glands move into pelvic portion of urethra
* Sphincter muscle around neck of urinary bladder closes
Stage 2:
* Rhythmic contraction of smooth muscle around urethra
* Semen is pumped out into female reproductive tract
* Through cervix into the uterus
The Transport of Spermatozoa
Semen usually deposited in upper portion of vagina
*By swimming of spermatozoa
*By contraction of uterus and oviducts
*By action of cilia in oviducts
Spermatozoa must arrive at oviducts before ovum
* Capacitation to enhance fertility
Capacitation
Series of changes that spermatozoa undergo in the female reproductive tract to increase chances of successful fertilization of the ovum
*Ion movement through cell membrane
*Increase in cell’s metabolic rates
*Increase in rate of simple sugar use for energy production
*Exposure of enzymes in acrosome
Fertilization of the Ovum – in the Oviduct
Large number of spermatozoa find and swarm around the ovum
Many begin tunneling through corona radiata and zona pellucida
One spermatozoon will physically penetrate the cell membrane of the ovum = fertilization
* Genetic material is delivered into ovum’s cytoplasm
Ovum’s cell membrane blocks all other spermatozoa from entering
Gestation hormone
Progestin - ovary
The Zygote
The ovum, once it is fertilized
Male pronucleus and female pronucleus joined
*Each contain haploid chromosome number
* Join together to restore diploid chromosome number
Breeding hormones
Estrogen - ovary
Oxytocin- Posterior Pituitary
parturition hormones
Relaxin - Placenta
ACTH - anterior pituitary (fetus)
glucocorticoids -adrenal glands (fetus)
estrogens - placenta
prostaglandin F2 alpha -placenta and uterine wall (dam)
Oxytocin - posterior pituitary (fetus)
Lactation hormones
growth hormone – anterior pituitary
prolactin- anterior pituitary
oxytocin - posterior pituitary
The Zygote
The ovum, once it is fertilized
Male pronucleus and female pronucleus joined
*Each contain haploid chromosome number
* Join together to restore diploid chromosome number
Cleavage
Rapid mitosis of zygote
* 2 pronuclei join to form a single nucleus
*Each chromosome makes a copy of itself
* Zygote begins to rapidly divide
* number of cells increases, but overall size does not change
Zygote is moving down oviduct toward uterus
Cells in morula stage form blastocyst
Overall size of zygote does not change
Implantation
Blastocyst embeds itself in endometrium
*Enzymes dissolve away a small pit
* Multiple blastocysts are randomly spaced in multiparous species
Placenta begins to form as soon as blastocyst is implanted
The Placenta
Life-support system for the developing offspring
* Develops around embryo
* Connected by umbilical cord
Multilayered, fluid-filled membranous sacs
*Amnion - sac
*Allantois -sac
* Chorion
*Attaches to uterine lining
Where attached to uterus lining, exchange of nutrients & waste takes place
sacs (placenta)
Amnion: membranous layer immediately surrounding the fetus
* Forms the amniotic sac
* Fetus floats in amniotic fluid inside the amniotic sac
Allantois: layer surrounding amniotic sac; forms the allantoic sac, which accumulates wastes
Placental Attachments comparative anatomy
(A) Diffuse attachment – horse and pig
– Attachment sites spread diffusely over placenta and uterus
–placenta detaches easily
(B) Cotyledonary attachment – ruminants
–small, discrete, numerous attachment points (placentomes)
—placentomes have a cotyledon that joins the caruncle on the uterus
— Sometimes placentomes are retained in uterus which can lead to illness of the mother
(C) Zonary attachment – dog & cat
— Placenta attaches along a belt like zone
— Detaches fairly easily
(D) Discoid attachment – primates, rodents
— Single, discrete, disc-shaped attachment
The Umbilical Cord
The link between the fetus and the nutrient waste exchange structures of the placenta
Cord contains:
* Umbilical arteries (2)
* Umbilical vein (1)
* Urachus (1)
Gestation
Gestation period: time from fertilization of ovum to delivery of newborn
Divided into three segments (trimesters):
* First trimester – embryonic period
*Placenta develops
* Second trimester – fetal period
*Body tissues, organs, & systems develop
* Third trimester – fetal growth period
Parturition
The Birth Process
Triggered by multiple factors
*Size and weight of uterus and fetus
* Changing hormonal levels
Fetal changes after birth
* Lungs expand and begin to function
* Foramen ovale and ductus arteriosus close
Parturition hormones
2 hormones
*Estrogen – increases myometrium sensitivity to oxytocin
* Oxytocin
* Myometrium contractions
* Milk letdown
First Stage of Labor
– uterine contractions
* Myometrium contracts
* Fetus is pressed down against cervix
* Cervix gradually dilates
2nd stage of labor
actual delivery of the newborn
*Amniotic and allantoic sacs of the placenta rupture
* Uterine and abdominal muscles contract in rhythmic pattern
* Newborn is delivered
Third stage of labor
delivery of the placenta (afterbirth)
*Placenta separates from wall of the uterus
*Placenta is expelled by weaker uterine contractions
*Placenta is often eaten by dam
Post-partum examination – very important!
Involution of the Uterus
Uterus gradually returns to its non-pregnant size
Endometrium sloughs into lumen of uterus at sites of placental attachment
Myometrium continues mild contractions to move remaining uterine contents out through birth canal
May take from a few weeks to a month or more for involution to be complete
The Mammary Glands
Specialized skin glands
*Present in both male and female
* Normally only function in the female
*Vary among species
* Number, locations, openings per teat
Produce colostrum and milk
Very important during neonatal period
Udder of Cow
Four mammary glands (quarters)
Quarters are completely separate units from each other
Each quarter has its own milk-secreting systems and ducts leading down to separate teats
Slinglike arrangement of ligaments for support and attachment to body wall
Nipples are called “teats”
The Alveoli and Duct System (cows)
Milk-secreting units of mammary gland = alveoli
* Alveoli arranged like clusters of grapes around alveolar duct
Milk secreted into alveolar duct
* Smaller ducts join to form larger ducts
* Largest ducts empty into gland sinus
* Gland sinuses are continuous with teat sinuses
Milk accumulates in 2 large teat sinuses for milk letdown
Streak canal at tip of teat
Mares, Ewes, Goats
2 mammary glands in one udder
Mammary Gland Development
Develop in response to hormones produced at puberty
*Prolactin
* Growth hormone
*Estrogen
*Progesterone
* Thyroid-stimulating hormone
*Adrenocorticotropic hormone
Levels of various hormones must be balanced precisely for complete development
Hormones in Mammary Gland Development
Mammary glands develop in response to hormones produced at puberty
Prolactin and growth hormone directly encourage mammary gland development
Estrogen and progesterone encourage the mammary alveoli and duct systems to develop
Mammary Glands & Lactation
Specialized skin glands
* Colostrum – passive immunity
* Milk
Present in both males & females
Undeveloped until puberty
Lactation
* Milk production
*Begins towards end of pregnancy
* Continues as long as gland is emptied
Lactation
The process of milk production
Begins toward end of pregnancy
Obvious at time of parturition
Hormones involved in starting lactation
*Prolactin
* Growth hormone
* Hormones from adrenal cortex
Lactation Physiology
Physical stimulation of teat or nipple and regular removal of milk from the gland stimulates anterior pituitary to continue production of hormones that keep lactation going
Lack of hormonal stimulation combined with increased pressure in the mammary gland gradually causes lactation to cease
Colostrum
Pre-milk secretion
Contents:
* Larger amounts of proteins, lipids, and amino acids than milk
* High levels of various essential vitamins
* Laxative effect to help clear newborn’s meconium
* High levels of specific antibodies (passive immunity)
* Transfer of preformed antibodies from dam to newborn
Maintenance of Lactation
Once begun, lactation continues as long as mammary gland is emptied regularly
*Physical stimulation of the teat combined with regular milk removal
Lactation will gradually cease
* Lack of hormonal stimulation
*Increased pressure in mammary gland
*Involution of the mammary gland = “dries up”
Milk Letdown
Immediate effect of nursing or milking
Steps for milk letdown:
* Milk accumulates in alveoli and small ducts
*Physical stimulation of nipple or teat sends sensory nerve impulses to brain, to release oxytocin
* Oxytocin causes contraction of myoepithelial cells around alveoli and small ducts
* Milk is squeezed down into large ducts and sinuses
Morula
Solid mass of cells
Found in upper section of the oviduct, known as the isthmus
Does not have a cyst (open area)
Blastocyst
hollow ball of cells
Found in endometrium of the uterus
implantation occurs
Labor Comparative Anatomy
**Canine: labor term - whelping, newborn- pups, litter, ok breach
*Feline: labor term - Queening, newborn- kittens, litter, ok breach
*Equine: labor term -Foaling, newborn- foals, one. twins bad, not ok breach
*Bovine: labor term - Calving, newborn- calves. one twins ok if same sex. Freemartin is heifer calf with bull calf twin. She’s sterile, breach not ok.
*Ovine: labor term -lambing, newborn- lambs, twins good, not ok breach
*Porcine: labor term -farrowing, newborn- piglets, litter, ok breach
Nipples comparative anatomy
Location, Number of nipples, number glands
cats - inguinal/thoracic/abdominal-3 - 7, 10
cattle - inguinal-1, 4
dogs - inguinal/thoracic/abdominal-8 - 20, 10
goats- inguinal-1, 2
horses- inguinal-2 -4, 2
pigs -inguinal/thoracic/abdominal-2-3, 14
sheep -inguinal-1, 2
