Chapter 20 - Pregnancy, Development and Lactation

Question 1

Breeding and Fertilization of the Ovum

Answer 1

Erection
Copulation
Ejaculation
Sperm
Transport
Fertilization

Question 2

Erection

Answer 2

 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

Question 3

Copulation

Answer 3

 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

Question 4

Ejaculation

Answer 4

 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

Question 5

The Transport of Spermatozoa

Answer 5

 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

Question 6

Capacitation

Answer 6

 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

Question 7

Fertilization of the Ovum – in the Oviduct

Answer 7

 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

Question 8

Gestation hormone

Answer 8

Progestin - ovary

Question 9

The Zygote

Answer 9

 The ovum, once it is fertilized
 Male pronucleus and female pronucleus joined
*Each contain haploid chromosome number
* Join together to restore diploid chromosome number

Question 10

Breeding hormones

Answer 10

Estrogen - ovary
Oxytocin- Posterior Pituitary

Question 11

parturition hormones

Answer 11

Relaxin - Placenta
ACTH - anterior pituitary (fetus)
glucocorticoids -adrenal glands (fetus)
estrogens - placenta
prostaglandin F2 alpha -placenta and uterine wall (dam)
Oxytocin - posterior pituitary (fetus)

Question 12

Lactation hormones

Answer 12

growth hormone – anterior pituitary
prolactin- anterior pituitary
oxytocin - posterior pituitary

Question 13

The Zygote

Answer 13

 The ovum, once it is fertilized
 Male pronucleus and female pronucleus joined
*Each contain haploid chromosome number
* Join together to restore diploid chromosome number

Question 14

Cleavage

Answer 14

 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

Question 15

Implantation

Answer 15

 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

Question 16

The Placenta

Answer 16

 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

Question 17

sacs (placenta)

Answer 17

 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

Question 18

Placental Attachments comparative anatomy

Answer 18

(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

Question 19

The Umbilical Cord

Answer 19

 The link between the fetus and the nutrient waste exchange structures of the placenta
 Cord contains:
* Umbilical arteries (2)
* Umbilical vein (1)
* Urachus (1)

Question 20

Gestation

Answer 20

 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

Question 21

Parturition

Answer 21

 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

Question 22

Parturition hormones

Answer 22

 2 hormones
*Estrogen – increases myometrium sensitivity to oxytocin
* Oxytocin
* Myometrium contractions
* Milk letdown

Question 23

First Stage of Labor

Answer 23

– uterine contractions
* Myometrium contracts
* Fetus is pressed down against cervix
* Cervix gradually dilates

Question 24

2nd stage of labor

Answer 24

actual delivery of the newborn
*Amniotic and allantoic sacs of the placenta rupture
* Uterine and abdominal muscles contract in rhythmic pattern
* Newborn is delivered

Question 25

Third stage of labor

Answer 25

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!

Question 26

Involution of the Uterus

Answer 26

 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

Question 27

The Mammary Glands

Answer 27

 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

Question 28

Udder of Cow

Answer 28

 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”

Question 29

The Alveoli and Duct System (cows)

Answer 29

 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

Question 30

Mares, Ewes, Goats

Answer 30

 2 mammary glands in one udder

Question 31

Mammary Gland Development

Answer 31

 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

Question 32

Hormones in Mammary Gland Development

Answer 32

 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

Question 33

Mammary Glands & Lactation

Answer 33

 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

Question 34

Lactation

Answer 34

 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

Question 35

Lactation Physiology

Answer 35

 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

Question 36

Colostrum

Answer 36

 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

Question 37

Maintenance of Lactation

Answer 37

 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”

Question 38

Milk Letdown

Answer 38

 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

Question 39

Morula

Answer 39

Solid mass of cells
Found in upper section of the oviduct, known as the isthmus
Does not have a cyst (open area)

Question 40

Blastocyst

Answer 40

hollow ball of cells
Found in endometrium of the uterus
implantation occurs

Question 41

Labor Comparative Anatomy

Answer 41

**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

Question 42

Nipples comparative anatomy

Answer 42

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