Download Pregnancy ch. 18 - Catherine Huff`s Site

Pregnancy,
Development and
Lactation
Chapter 18
Species Development
• Species can only be perpetuated if
pregnancy, development of offspring
and lactation are appropriately carried
out.
Fertilization
• Copulation- the act of breeding allowed by the
female during estrous (heat) period.
– Usually in a mounted position
• Intromission- the insertion of the penis into
the vagina.
• Ejaculation- when the semen is deposited in
the upper portion of the vagina
– Horse and pig deposit semen directly into uterus
through open cervix.
Transport of Spermatozoa
• Start actively swimming as soon as
deposited trying to make their way to
oviducts.
– Would take over an hour under own
power
– Are helped out by uterine contractions
• Copulation causes posterior pituitary gland
to release oxytocin which causes smooth
muscle of reproductive tract to contract
helping spermatozoa to the ovum.
Capacitation
• Series of changes that spermatozoa
undergo in the female reproductive
tract to increase chances of
fertilization.
– Changes of ion movement through cell
membranes
– Increase in cell’s metabolic rates
– Increase in rate of use of simple sugars for
energy production.
– Allows acrosome enzymes to be released.
Fertilization of the Ovum
• Spermatozoa are programmed to seek out
something large and round and attempt to
penetrate it.
– Some try to fertilize non-ovum things.
• Once ovum is found, many spermatozoa may
swarm around it and start tunneling through
the layers.
– Process aided by enzymes of acrosome.
• Once one spermatozoa penetrates ovum,
change in membrane prevents any other
sperm from entering.
The Zygote
• Once ovum is fertilized, it becomes a zygote.
• Male pronucleus- the nucleus of the male
spermatozoan immediately after fertilization.
• Female pronucleus- the nucleus of the ovum
immediately after fertilization.
– Each pronucleus carries haploid number
– Join together to get diploid number
• This joining establishes genetic information for
offspring.
Cleavage
• The rapid division of the zygote once single
nucleus has been established.
• Cell divides rapidly but overall size remains
the same because are dividing so quickly do
not have time to grow.
• Once zygote is a solid mass of cells, is in
morula stage.
• During this time, zygote is moving down ovum
to uterus
– Propelled by cilia and muscular contractions
Blastocyst
• Cells of morula stage continued to
divide and hollow cavity is formed in
center of zygotic cell.
• Once bump of cells on one side is
developed, this is now the blastocyst.
Implantation
• The means by which the blastocyst makes
itself a home by attaching itself to the lining
of the uterus (endometrium).
• Once blastocyst comes to rest beside uterine
lining, enzymes produced by blastocyst
dissolve away some lining and implants itself
into this pit in the lining.
• Placenta begins to form as soon as
implantation occurs.
– Way of transporting oxygen and nutrients to
blastocyst.
Terminology
• Embryo-what developing offspring is
referred to during early part of
pregnancy.
• Fetus- What developing offspring is
referred to during later part of
pregnancy.
The Placenta
• Life-support system of the developing
fetus.
• Fetus is a parasite on mother during
pregnancy.
• Grows along with fetus to enable for
appropriate transfer of waste products,
etc.
Structure of the Placenta
• Multi-layered, fluid-filled
membranous sac.
• Develops around embryo and is
connected to it by umbilical
cord.
– Smaller connections between
outermost layer of placenta and
lining of uterus.
• This is where exchange of nutrients
and wastes takes place.
• Fetal and maternal blood does not mix
but runs in close proximity to one
another.
Structure of Placenta Continued…
• 3 layers of placenta
– 1. Amnion
• Forms amniotic sac directly around fetus
– 2. Allantois
• Outside amniotic sac and forms allantoic sac.
– 3. Chorion
• Outside of allantoic sac and attaches to uterine
lining.
• Linked to fetus by umbilical cord.
The umbilical cord
• Link between the fetus and nutrient and waste
exchange structures of the placenta.
• Cordlike in structure
– Contains umbilical arteries (2) and umbilical vein.
• Umbilical arteries carry unoxygenated, waste filled
blood from fetus to placenta
• Umbilical vein carries nutrient and oxygen rich blood
back from placenta to fetus.
– Contains drainage tube from fetus’ urinary bladder
(urachus)
• Tube runs from the cranial tip of fetus’ bladder through
umbilical cord to allantoic sac.
• Fetus does not produce urine but do produce fluid that
must be eliminated.
Attachment to the Uterus
• Where chorion attaches to lining of the
uterus.
• Type of attachement varies among
species and is one of four types:
–
–
–
–
1. Diffuse Attachment
2. Cotyledonary Attachment
3. Zonary Attachment
4. Discoid Attachment.
Diffuse Attachment
• Means that attachment sites are spread
diffusely over the whole surface of the
placenta and the whole lining of the
uterus.
• No small, limited areas of attachment.
• Found in pigs and horses
• Detaches easily from uterine lining and
is passed after the delivery of the
newborn.
Cotyledonary Attachment
• Most complicated type and is somewhat opposite of
diffuse attachment.
• Areas of attachment are small, separate, and
numerous.
• Placentome- attachment sites.
• Cotyledon- area on surface of the placenta
• Caruncle-area on surface of uterus (mushroom-like).
– Cotyledon and caruncle interdigitate with one another.
• Each placentome must separate completely for
placenta to pass after birth.
– If not completely passed, may be retained and can cause
other problems.
Zonary Attachment
• Placenta attaches to the uterus in beltshaped area that encircles the
placenta.
• Found in dogs and cats
• Detaches easily after delivery.
Discoid Attachment
• Area of attachment between placenta
and uterus is a single-disk shaped area.
• Found in humans and other primates
Pregnancy
• Also called gestation period
• Time from implantation to delivery of the
newborn.
• Judge time by time since fertlization.
• Is divided into three segments called
trimesters
– 1st- period of the embryo implanting and
organizing and placental development
– 2nd- embryo now called fetus and is fetal
development period. Parts are taking shape and
differentiating.
– 3rd- fetal growth. All parts grow dramatically
Gestation Periods
Species
• Cat
• Dog
• Cow
• Elephant
• Ferret
• Goat, Sheep
• Hamster
• Horse
• Human
• Pig
• Rabbit
Approx Gestation Period
2 mo (56-69 days)
2 mo (59-68 days)
9 mo (271-291 days)
21 mo (615-650 days)
6 w (42 days)
5 mo (143-155 days)
3 w (19-20 days)
11 mo (321-346 days)
9 mo (280 days)
3 mo, 3 w, 3 d (110-116 days)
1 mo (30-32 days)
Parturition
•
•
•
•
Birth process
Lungs of newborn become functional
Goes from parasite to independent being.
Parturition is triggered by size and weight of uterus
and changing hormone levels.
– Progesterone of dam declines
– Progesterone has kept myometrium from contracting
– Increased levels of glucocorticoid hormones stimulate rise
in estrogen levels
– These increase sensitivity to oxytocin, released from
posterior pituitary gland.
• Oxytocin stimulates contractions which starts labor process
3 Stages of Labor
• 1. Uterine Contractions
– Presses fetus against uterus
– Causes cervix to gradually dilate
– Dam may appear restless in this stage.
• 2. Delivery of the Newborn
– Combination of uterine and abdominal muscle
contractions
– “Water” or amniotic and allantoic sacs rupture.
• 3. Delivery of the placenta
– Placenta separates from wall of the uterus and is
expelled by uterine contractions.
– Dam often eats the placenta.
Labor Continued
• Multiparous animals: the second and
third stages of parturition intermix with
one another.
– Newborn and placenta are delivered
alternatively.
– Next newborn will not be delivered
typically until previous placenta has been
expelled.
Parturition: normal
presentation
Dystocia
• “difficult birth”
• Most common cause is that fetus is too
large to pass or is in wrong orientation
for delivery.
• May have to Repell the fetus or deliver
through Cesarean section.
• If fetus is dead, may have to be removed
in segments- called Embryotomy.
Parturition: abnormal
presentations
Delivery
Placental Delivery
Whelping/ Parturition
Normal Presentation
Presentation of two sacs
Involution of the Uterus
• After parturition is complete, uterus gradually
returns to nonpregnant size.
• Process is called involution.
• At placental attachment sites, endometrium
sloughs into uterus and areas heal over.
• Myometrium contractions continue slowly,
pushing contents through birth canal.
• Will pass from bright red blood, to dead tissue
over course of weeks to about a month.
Mammary Glands and Lactation
• Play an important role during neonatal
period.
• Mammary glands are specialized skin
glands.
• Produce colostrum and milk which are
crucial to early life.
• Present in both males and females
– Females secrete appropriate hormones for
them to become functional
Species Differences
• Number, size and location varies from
animal to animal.
• Cattle, sheep and goats only have one
opening per teat
• Dogs have up to 20 openings per nipple.
Number of Mammary Glands for
Common animals
SPECIES
NUMBER OF GLANDS
Cats
Horses
10
2
Dogs
Humans
10
2
Cattle
Pigs
4
14
Udder of the Cow
• Udder is term used for mammary glands.
• Exaggerated in size, but composition is similar to
other animal’s mammary glands
• 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
• Suspended by strong suspensory ligaments that
allow it to stretch.
– Acts as a shock absorber.
Udder Continued
• Mastitis- infection of the mammary
gland
– Since are separate, is unlikely to spread
from one quarter to another.
– Can spread through bloodstream.
Alveoli and Duct System
• Alveoli- milk-secreting units of the mammary gland
• Alveolar duct- alveoli secrete milk into tube
– Similar in make up to Alveoli found in lungs.
• Ducts empty into large space called gland sinus
which is continuous with the teat sinus which is
where milk is extracted by suckling young.
• Tip of teat has streak canal- passageway from teat
sinus to outside.
– Surrounded by elastic fibers and ringlike sphincter muscle
that keeps it closed to prevent leakage.
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
mammary alveoli and duct systems to
develop
• Influenced by FSH and LH on ovaries
– Certain drugs may inhibit normal
mammary gland development
Lactation
• Process of milk production
• Begins at end of pregnancy and is
obvious at time of parturition.
• Prolactin and Growth Hormone from
anterior pituitary gland and hormones
from adrenal cortex are involved with
the starting of lactation.
Colostrum
• “First milk” or “premilk”.
• Contains large amounts of proteins, lipids, and amino
acids than milk and high levels of essential vitamins.
– Antibodies for defense
• Supplies important nutrients and defenses that
newborn can not receive elsewhere.
– If does not receive within first few hours, body can no longer
process appropriately.
• Has laxative effect to clear meconium ( first feces)
from newborn’s intestinal tract.
• Involved with passive immunity from dam to newborn
• Those without appropriate colostrum tend to be
weaker and do not grow as rapidly.
• Why we wait for vaccines.
Maintenance and Lactation
• Lactation continues as long as mammary
gland is emptied regularly.
• Physical stimulation of nipple.
• This sends nerve impulses to brain which
continues stimulation of appropriate
hormones for milk production.
• When nursing stops, signal stops.
– Will lead to involution of the mammary gland or
“drying up”.
Milk Letdown
• Immediate effect of nursing or milking
• Milk accumulates high up in mammary gland
in alveoli and small ducts and does not move
down until Milk letdown occurs.
• Oxytocin causes myoepithelial cells around
the alveoli and small ducts to contract
– Squeezes milk down the large ducts and sinuses.
– Can take from few seconds to minute for milk to
flow freely.