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Pregnancy, Development and Lactation

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Title: Pregnancy, Development and Lactation


1
Pregnancy, Development and Lactation
  • Chapter 18

2
Species Development
  • Species can only be perpetuated if pregnancy,
    development of offspring and lactation are
    appropriately carried out.

3
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.

4
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.

5
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 cells metabolic rates
  • Increase in rate of use of simple sugars for
    energy production.
  • Allows acrosome enzymes to be released.

6
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.

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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.

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10
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

11
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.

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13
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.

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15
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.

16
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.

17
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.

18
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.

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21
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.

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24
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.

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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.

27
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.

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29
Zonary Attachment
  • Placenta attaches to the uterus in belt-shaped
    area that encircles the placenta.
  • Found in dogs and cats
  • Detaches easily after delivery.

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31
Discoid Attachment
  • Area of attachment between placenta and uterus is
    a single-disk shaped area.
  • Found in humans and other primates

32
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

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35
Gestation Periods
  • Species Approx Gestation Period
  • Cat 2 mo (56-69 days)
  • Dog 2 mo (59-68 days)
  • Cow 9 mo (271-291 days)
  • Elephant 21 mo (615-650 days)
  • Ferret 6 w (42 days)
  • Goat, Sheep 5 mo (143-155 days)
  • Hamster 3 w (19-20 days)
  • Horse 11 mo (321-346 days)
  • Human 9 mo (280 days)
  • Pig 3 mo, 3 w, 3 d (110-116 days)
  • Rabbit 1 mo (30-32 days)

36
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

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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.

39
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.

40
Parturition normal presentation
41
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.

42
Parturition abnormal presentations
43
Delivery
44
Placental Delivery
45
Whelping/ Parturition
Normal Presentation Presentation of two sacs
46
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.

47
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

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49
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.

50
Number of Mammary Glands for Common animals
SPECIES NUMBER OF GLANDS
Cats Horses 10 2
Dogs Humans 10 2
Cattle Pigs 4 14
51
Udder of the Cow
  • Udder is term used for mammary glands.
  • Exaggerated in size, but composition is similar
    to other animals 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.

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Udder Continued
  • Mastitis- infection of the mammary gland
  • Since are separate, is unlikely to spread from
    one quarter to another.
  • Can spread through bloodstream.

54
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.

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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

58
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.

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60
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 newborns 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.

61
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.

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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.

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