Pregnancy & Lactation

Pregnancy & LactationFertilizationAfter breeding, the sperm and egg unite to form a zygote. After the nuclei have fused the zygote becomes an embryo. Embryos do not have any anatomical form.FertilizationFetus is the potential offspring still within the uterus. Conceptus is the product of conception which includes:EmbryoMembranesplacenta

Development of zygoteAfter fusion of nuclei, the zygote undergoes a series of mitotic division. The first division creates a two celled embryo.These cells are called blastomeres. Each blastomere undergoes divisions yielding 4, 8, and 16 daughter cells.Twins are derived from blastomeres of a 2-celled embryo that divide independently.

DevelopmentWhen a solid ball of cells is formed and blastomeres cant be counted, the embryo is called a morula. During this stage, fluid fills the cell and creates a cavity called a blastocoele. When a distinct cavity is recognized, the embryo is called a blastocyst. After growing, the blastocyst starts to crack the membrane and now becomes a free-floating embryo in the uterus.

Developmenthttp://www.youtube.com/watch?v=cO6vFYH7QJA

DevelopmentAs the hatched blastocyst continues to grow, it forms three different layers known as the endoderm, ectoderm, and mesoderm.

EctodermCNSSense organsMammary glandsSweat glandsSkinHairMesodermCirculatorySkeletalMuscleReproductive tractsKidneysUrinary ductsEndodermDigestive LiverLungsPancreasThyroid glandOther glandsBreak timehttp://www.youtube.com/watch?v=WpK9XNAQfH4

PlacentasPlacentaThe placenta is a transient organ of metabolic interchange between mother and offspring. Also produces a variety of hormones. Placentas have 4 different membranes:AllantoisYolk sacAmnionChorionPlacental MembranesYolk SackIn birds to nourish embryoIn mammal a source of blood cells and primordial germ cellsAmnionNon-vascular, fluid filledFluid produced by fetusProtective cushionRuptures at birth 14Placental Membranes AllantoisBlood vesselsFuses with chorionBrings blood vessels to chorionChorionOutermost membraneAttachment to mother

15ChorionAllantochorion(Chorioallantois)Allantois CavityCotyledonAmniotic CavityAmnionYolkSack16PlacentaThe functional unit of the placenta is the chorionic villus. Placentas are classified according to their chorionic villi.The four classifications are:DiffuseZonaryDiscoidCotyledonaryPlacentaDiffuse:Pig & horseCharacterized by having uniform distribution of the villi covering the surface. Microcotyledons are the functional interface between mother and offspring

PlacentaZonary:Dogs & catsA prominent region of exchange that forms a zone around the middle of the conceptus.

PlacentaDiscoid:Rodents & primatesCharacterized by having one or two distinct adjacent discs.These discs interface with the endometrium and provide nutrient and metabolic waste exchange.

Art

PlacentaCotyledonaryRuminants (cows, sheep, goats, deer, etc.)Characterized by having numerous, button-like structures called cotyledons.Cotyledons are the placental unit for blood vessels and connective tissue.A placentome consists of a fetal cotyledon and a maternal cotyledon.

Re-cap

Breakhttp://www.youtube.com/watch?v=Yk9n48ZB8XQ

Stand up and shake off your handsParturitionParturitionA complex cascade of eventsTriggered by the fetus

Separated into three stages:1. Initiation of contractions2. expulsion of fetus3. expulsion of membranes

Stage 1LaborInitiated by fetus Fetus becomes stressed due to lack ofNutrientsOxygenSpaceThis stress leads to a series of hormone secretions initiating contractions and dialation.Stage 1 comparisonCow 2 to 6 hoursDog 6 to 12 hoursHorse 1 to 4 hoursAlpaca 2 to 6 hoursHuman 8+ hoursStage 2 Expulsion of the fetusAs the hormones increase so do the contractionsAs the contractions increase, the feet and head of the fetus put pressure on the membranes causing them to rupture.As the fetus enters the birth canal, they become hypoxic causing stronger contractions. Positive feedback loopStage 2 comparisonCow 30 to 60 minDog 6 hoursHorse 12 to 30 min Alpaca 5 to 90 minHuman 2 hoursStage 3Membrane expulsionIn most species, stage three quickly follows stage 2.Easy process Retained placentaCan cause disease, need to be removed manuallyStage 3 comparisonCow 6 to 12 hoursDog 15 minutesHorse 1 hourAlpaca 45 to 180 minHuman 1 hour or lessDystociaDifficult birthDifficulties usually occur in the second stage due to the fetus not positioned correctly.Other causesSize of fetusImproper rotation (head comes first) multiple birthsPuerperiumThe period after birth in which the reproductive tract returns to non-pregnant conditions. 4 events of puerperiumMyometrial contractionsEndometrial repairResumption of ovarian functionElimination of bacteriaLactation