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Gestationplacentationlactation Gestationplacentationlactation Presentation Transcript

  • Gestation
    • The period of
    • fetal development beginning with fertilization and ending with parturition
    Leonardo da Vinci, "The Foetus in Utero," 1489
  • Fertilization
    • Zygote: diploid cell resulting from the fusion of the male and female pronuclei (syngamy)
    • Embryo: organism in the early stages of development; not recognizable as a member of a specific species
  • Cleavage
    • Following fertilization the zygote undergoes several mitotic divisions inside the zona pellucida (overall size does not change).
    • 1 st cleavage yields a 2 celled embryo,
      • each cell is called a blastomere and is totipotent
    • Divisions continue rapidly until the 32 cell stage
  • Preattachment development of the embryo Senger, pg 286 8-cell embryo morula early blastocyst hatched blastocyst
  • Maternal Recognition of Pregnancy
    • Necessary to prevent luteolysis
    • Occurs prior to implantation/placentation
    • Differs among species
  • Pregnancy Recognition Signals
    • Cow – bovine interferon tau (bIFNt); produced by conceptus, days 15-16 of gestation are critical
    • Sheep – ovine interferon tau (IFNt); produced by conceptus, days 13-14 of gestation
    • Sow – Estradiol; produced by conceptus and causes a reroute of PGF 2 α ; must occur days 11-12
    • Mare – Protein/estrogen complex and embryo migration; beginning day 12 embyro must migrate 12-15 times per day
    Senger, pgs 291-295
  • Differentiation
    • Formation of three germ layers
    • Formation of the extraembryonic membranes (placenta)
    • Formation of organs
    • Rapid changes in relative size
  • Three Embryonic Germ Layers
    • Inner cell mass (ICM) = embryo
    • Trophoblast = chorion
    Ectoderm Nervous system, skin, hair Mesoderm Muscle, skeleton, Cardiovascular system, Reproductive system Endoderm Digestive system, lungs, endocrine system Senger, pg 81-82 ICM Blastocoele
  • Extraembryonic Membranes Senger, pg 290
  • Function of Fetal Membranes and Fluids Yolk Sac – Originates from fetal midgut. Nutrient supply for early embryo. Absorbs uterine sectretions from endometrium to stimulate early embryonic development. Amnion – Innermost membrane directly surrounding the fetus. Protects from injury and provides lubrication for parturition. Prevents lung collapse and opens digestive tract. Allantois – Originates from the gut and forms the umbilicus. Supports blood vessels. Reservoir of nutrients and wastes. Chorioallantois: product of fusion between the allantoic and chorionic membranes Chorion – Outermost membrane in direct contact with uterine tissue. Becomes vascularized by allantoic vessels. Site of hormone production, nutrient and gas exchange.
  • Placenta
    • PLACENTA: organ of nutrient and waste exchange between the fetal blood and maternal blood
    • PLACENTAL SHAPE: defines the proportion of surface area shared between fetal membranes and maternal uterine tissue where exchange occurs
    • PLACENTAL TYPE: defines the structure of cell layers separating fetal blood from maternal blood
  • Placental Shapes
    • Diffuse – noninvasive
    • Cotyledonary – placentomes are the point of high throughput maternal/fetal contact
    • Zonary/Discoid – invasive; most direct contact between fetal and maternal blood
    Senger pgs 308-310
  • Diffuse Placenta Uterine Endometrium Fetal Chorion Senger, pg 308
  • Cotyledonary Placenta Senger, pg 310
  • Cotyledonary Placenta Fetus Umbilicus Placentomes
  • Types of Placentas Maternal Blood Maternal endothelium Maternal connective tissue Maternal epithelium Fetal epithelium Fetal connective tissue Fetal endothelium Fetal Blood Type = degree of invasiveness, based on layers separating maternal blood from the fetal epithelium Least Invasive epitheliochorial synepitheliochorial endotheliochorial Most Invasive hemochorial
    • Cow Cotyledonary Epitheliochorial
    • Ewe Cotyledonary Synepitheliochorial
    • Sow Diffuse Epitheliochorial
    • Mare Diffuse Epitheliochorial
    • Dog, Cat Zonary Endotheliochorial
    • Primates Discoid Hemochorial
    • Rodents Discoid Hemochorial
    Placentation by Species
  • Hormones Produced by the Placenta
    • equine Chorionic Gonadotropin: maintains primary CL, responsible for formation and maintenance of accessory CL.
    • human Chorionic Gonadotropin: maintain CL
    • Progesterone: in some species (ewe, mare, woman) the placenta takes over progesterone production later in gestation.
    • ~”progesterone block” – inhibits myometrial contractions
    • Estrogen: peak of E2 signals preparturient period in some species
    • Placental Lactogen: stimulates growth of fetus and mammary glands
    • Relaxin: softens connective tissue in the cervix and relaxes pelvic ligaments
    • Fetal Growth
    • Growth : period of development from embryo to fully developed fetus, prior to parturition
    • Example of development relative to time for the bovine
    • Calcification of Bone Matrix 70 days
    • Extensive Bone Formation 180 days
    • Tooth Formation 110 days
    • Hair, eyes, muzzle 150 days
    • Hair over entire body 230 days
  • Relative Development Cleavage Differentiation Growth More than 50% of the total weight of the fetus at parturition is gained during the last two months of gestation fertilization ZP Disintegration parturition placentation Shift from classification as embryo to fetus
  • Days 45-147 Days 11-45 Days 0-10 Sheep Days 68-336 Days 15-68 Days 0-14 Mare Days 28-113 Days 7-28 Days 0-6 Sow Days 45-283 Days 13-45 Days 0-12 Cow Growth Differentiation Cleavage Species
  • Parturition The process by which the uterus expels the products of conception
  • Stages of Parturition
    • Stage I – preparatory stage involving cervical dilation and positioning of the fetus in the birth canal via myometrial contractions.
    • Stage II – time of hard labor and expulsion of the fetus.
    • Stage III – expulsion of the placental membranes and subsequent uterine involution.
  • Brief Definitions
    • Dystocia – difficult birth
      • Usually refers to calving difficulty
        • i.e., absolute or relative
    • Presentation – direction of fetal delivery
      • Anterior, posterior, or transverse
        • i.e., anterior = head first
    • Position – orientation of the fetus
      • Dorsal or ventral side up or lateral
    • Posture – location of the legs, head, and neck
      • relates to normal/abnormal posture
  • Cattle
    • Dystocia is the major cause of calf loss
      • Relative Dystocia – normal sized calf and a small birth canal
      • Absolute Dystocia – abnormally large calf and a normally sized birth canal
        • Most common cause of dystocia is from an oversized calf
    • Hiplock – shoulders of the calf “lock” onto the bones of the pelvis during delivery
      • Results in the calf getting stuck in the birth canal
  • Cattle
    • Stages:
      • Stage I – lasts from 1-4 hours (seldom noticed)
      • Stage II – begins with the rupture of the allantochorion
        • Should allow for 2-3 hours for a normal birth to occur without interfering
      • Stage III – begins after expulsion of the fetus
        • Lasts up to 4 – 5 hours after fetal expulsion
    • Presentation:
      • Anterior
    • Position:
      • Dorsal side up
    • Posture:
      • Front legs first (slightly offset), bottom of hooves facing down, and nose between front legs
  • Sheep
    • The process of parturition in the sheep is very similar to that in cattle
    • Twins are present if a front and rear leg appear together
  • Swine
    • Duration of farrowing (parturition):
      • 4 – 48 minutes per piglet
    • Presentation:
      • Anterior or posterior
    • Position:
      • Dorsal or ventral side up
    • Posture:
      • Not specific
  • Horses
    • Foaling time is difficult to predict
      • Relaxation of the sacrosciatic ligament
      • Distended mammary glands - days
        • Waxing – within 48 hours
  • Foaling
    • Stages:
      • Stage I – lasts ~ 1 hour
        • Restlessness, sweating in flanks
      • Stage II – very rapid, lasts ~ 10-20 minutes
      • Stage III – lasts from 1-12 hours
  • Horses
    • Presentation:
      • Anterior
    • Position:
      • Dorsal side up
    • Posture:
      • Front legs first (slightly offset), bottom of hooves facing down, and nose between front legs
    • It is crucial that the foal is born within 30 minutes of the beginning of stage II. Failure to do so, will most likely lead to the death of the foal.
      • Due to the “crushing” of the umbilical cord between the foal and the dam
        • deprives the foal of oxygen
  • Hormones of Parturition
    • ACTH – induces parturition in response to fetal stress
    • Fetal Cortisol – induces the release of PGF 2alpha and produces the enzymes needed to convert placental progesterone to estradiol
    • Placental Progesterone – maintains pregnancy and will be converted to estradiol during parturition
    • Estradiol – enhances secretions of female tract (lubrication) and myometrial contractions, as well as enhance the receptors for PGF 2alpha and oxytocin
  • Hormones of Parturition
    • PGF 2alpha – enhances myometrial contractions, induces luteolysis and the release/secretion of relaxin
    • Relaxin – relaxes the pelvic ligaments, allowing them to stretch for expulsion of the fetus
    • Oxytocin – enhances myometrial contractions (produces the most forceful contractions)
  • Induction of Parturition **Not Recommended Unless the Life of the Dam or the Fetus is Threatened**
    • Inducing parturition can enhance reproductive management by controlling the time of parturition
      • Dangerous unless parturition is impending (within one day of occurring)
      • Retained placenta often occurs
        • Forcing expulsion of the fetus and the fetal membranes (i.e., the placenta) before the placenta is ready to detach from the uterus
  • Agents Used to Induce Parturition
    • Cattle
      • Glucocorticoids
      • Prostaglandins
      • Estrogens
    • Sheep
      • Glucocorticoids
        • If given after day 140, response within 48hrs
    • Swine
      • Glucocorticoids
      • Prostaglandins
        • If given after day 110, response within 30hrs
    • Horses
      • Glucocorticoids
      • Prostaglandins
        • All or none response
    Oxytocin: Works well, but the dose and timing are extremely important. All impending signs of parturition must be present. (general rule: give ~ 1hr before parturition)
  • Senger, pg 321
  • synepitheliochorial Cotyledonary IFNtau 147 days Sheep epitheliochorial Diffuse Migration-estrogen/protein 336 days Mare epitheliochorial Diffuse Estrogen 113 days Sow epitheliochorial Cotyledonary IFNtau 283 days Cow Placental Type Placental Shape Pregnancy recognition signal Gestation Length Species
  • Lactation
  • Neuroendocrine Reflex Arc
    • Teat stimulation (suckling)
    • Stimulation of nerves in the spinal cord
    • Nerve signals to the brain
    • Release of oxytocin from posterior pituitary into blood
    • Oxytocin received by the mammary tissue
    • Contraction of alveoli
    • Contraction of ducts
    • Milk ejection
    1 3 2 4 5 6 7 8 5
  • Mammary Gland Anatomy Tissue of Mammary Gland: Secretory cells Alveoli Myoepithelial cells Ducts Blood Vessels
  • Mammary Gland Anatomy
  • Initiation of Lactation: (lactogenesis) 1. Increased formation and development of duct system 2. Increased formation and development of secretory cells 3. Development of capacity for milk synthesis    
  • Hormones Required for Lactation   1. Estrogen : stimulates duct growth 2. Progesterone : stimulates alveolar development 3. Growth Hormone (somatotropin): stimulates milk production 4. Thyroid Hormones: enhance development and function of mammary tissue 5. Corticoids: enhance synthesis of enzymes necessary for milk biosynthesis 6. Prolactin: initiation of lactogenesis 7. Oxytocin: stimulate myometrial contractions to release milk from alveoli to ducts 8. Insulin: maintain function and survival of secretory cells 9. Placental Lactogen: general mammary tissue growth Adrenalin: prevents milk ejection; blocks secretion of oxytocin, causes vasoconstriction in mammary gland Administration of bST to dairy cattle increases milk production 15-40%. Suggested that bST stimulates insulin-like growth factor-1 (IGF-1) which stimulates the secretory cells.