Pregnancy & Lactation Student Notes PDF

PREGNANCY & DR. JACQUELINE MOBLEY AHS 2202 LACTATION IN THIS LECTURE WE WILL DISCUSS… Breeding Fertilization Implantation Placental development & function Parturition Lactation BREEDING A little recap…. Estrus vs. estrous Estrogen drives behavioral...

PREGNANCY & DR. JACQUELINE MOBLEY AHS 2202 LACTATION IN THIS LECTURE WE WILL DISCUSS… Breeding Fertilization Implantation Placental development & function Parturition Lactation BREEDING A little recap…. Estrus vs. estrous Estrogen drives behavioral and physical changes of estrus Male responds to visual, olfactory and behavioral cues Female behavioral changes Increased activity/restlessness Vocalization/phonation Mounting Lordosis (mating posture) Tail flagging COPULATION /MATING Timing: estrus Occurs in the mounting standing position in most domestic animals Intromission = insertion of the penis into the vagina Followed by thrusting & ejaculation WHAT HAPPENS TO THE EJACULATE? 1. Retrograde transport 2. Phagocytosis by neutrophils in the vagina & uterus 3. Transport to oviduct Rapid transport → 5 minutes post ejaculation Sustained transport → trickle effect Thi s Photo by Unknown Author i s l icensed under CC BY-NC-ND HOW DO SPERMATOZOA MOVE SO QUICKLY? Spermatozoa do not swim solely on their own to the oviduct Spermatozoa transport is facilitated by Estrogen stimulates myometrial contractions Prostaglandins in the semen increasing tone & motility of the uterus/oviduct Oxytocin release from posterior pituitary inducing contractions Cilia in oviducts actively carry sperm in Thi s Photo by Unknown Author i s l icensed under CC BY waves SPERM MATURATION IN THE FEMALE REPRO TRACT Spermatozoa are not initially completely fertile Capacitation Changes that occur to spermatozoa in the female that make them fertile Seminal plasma proteins are removed by the female tract environment Exposes molecules that can now bind to the zona Thi s Photo by Unknown Author i s l icensed under CC BY-SA pellucida of the ovum Acrosome reaction Enzymes are released to allow attachment and penetration of zona pellucida FERTILIZATION Sperm penetrates the zona pellucida Sperm binds to the oocyte plasma membrane Oocyte undergoes cortical reaction Cortical reaction releases enzymatic granules Results in the “zona block” and “vitelline block” Prevents polyspermy  PREGNANCY Thi s Photo by Unknown Author i s l icensed under CC BY-ND  THE ZYGOTE Zygote: the fertilized ovum Sperm nucleus becomes the male pronucleus Ovum nucleus becomes the female pronucleus Ootid: male & female pronucleus are visible in single cell Syngamy: fusion of the male & female pronuclei Forms the diploid chromosome number  CLEAVAGE DIVISIONS Cleavage The process of rapid mitosis that occurs after formation of the zygote 1st cleavage division of the zygote creates 2 blastomeres Division is fast resulting in many cells but overall size is unchanged Morula 2-celled embryo becomes a morula when >8 cells Looks like a raspberry Gradually a hollow cavity forms Thi s Photo by Unknown Author i s l icensed under CC BY-NC Early blastocyst Fluid accumulates within the morula and the structure becomes a blastocyst  BLASTOCYST The blastocyst is composed of the Inner cell mass (ICM) → becomes the body Trophoblast → becomes the chorion, which becomes the fetal placenta Enzymes produced by the blastocyst break down the zona pellucida The blastocyst squeezes out Free-floating embryo arises **As this entire process occurs, the fertilized ovum 1. Zona pellucida makes its way down the oviduct to the uterus** 2. Trophoblast 3. Blastocyst cavity 4. Inner cell mass  IMPLANTATION Blastocyst implants itself in the uterine endometrium How? Enzymes Multiparous species? Randomly space themselves throughout Blastocyst is implanted…now what? “Maternal recognition of pregnancy” Luteolysis must be prevented Hormones involved vary between species  THE PLACENTA Placenta functions Nutrient and waste removal Hormonal production for maintenance of pregnancy & induction of parturition The placenta attaches to the lining of the uterus Chorion of fetus Endometrium of the dam Umbilical cord attaches the fetus to the placenta Thi s Photo by Unknown Author i s l icensed under CC BY-NC-ND Fetal and maternal blood does not mix  PLACENTAL STRUCTURE Membranes form 2 sacs around the fetus Amnion: layer immediately around the fetus Aminotic sac is the space formed by the amnion Allantois is the layer around the amnion Allantoic sac is the space between the amnion & the allantois Chorion attaches to the uterine lining The chorion is linked to the fetus by the umbilical cord NUTRIENT EXCHANGE THROUGH THE PLACENTA Degree of separation of maternal & fetal layers varies Epitheliochorial – endometrium epithelium & chorion epithelium intact Sow & mare Syndesmochoral – endometrial epithelium transiently erodes & regrows Ruminants Endotheliochorial – endometrial epithelium completely eroded Maternal capillaries are directly exposed to the epithelial cells of chorion Hemochorial – direct contact between chorionic epithelium and maternal pools of blood Primates & rodents  THE UMBILICAL CORD The umbilical cord is the link between the fetus & the placenta Umbilical cord contains: Umbilical arteries → unoxygenated, waste- filled to the placenta Umbilical vein → nutrient & O2 rich blood to the fetus Urachus → fetal urine away from the bladder to the allantoic sac Remember patent urachus?  PLACENTAL ATTACHMENT The area where maternal and fetal vessels intertwine 4 types Diffuse Cotyledonary Zonary Discoid Thi s Photo by Unknown Author i s l icensed under CC BY-NC DIFFUSE PLACENTAL ATTACHMENT Attachment is diffuse over the entire surface of the placenta & uterus Pigs, horses, camelids Loosely attached, easily passed after birth  COTYLEDONARY PLACENTAL ATTACHMENT Attachment sites are small, discrete and numerous Placentome Each attachment site Cotyledon (placenta side) + caruncle (maternal side) = placentome Ruminants Placental detachment sometimes is incomplete, potentially dangerous & life- threatening metritis ensues ZONARY PLACENTAL ATTACHMENT Belt-shaped attachment encircles the placenta Dogs & cats Placenta is rarely retained with zonary placental attachment DISCOID PLACENTAL ATTACHMENT Single, discrete disc-shaped attachment site Humans, primates, rabbits, rodents  Gestation = fertilization to delivery 3rd trimester: fetal 1st trimester: embryo 2nd trimester: fetus growth stage GESTATION (PREGNANCY) Gestation length Pigs: 3 mos, Cats: 56-69 Dogs: 59-68 Horse: 11 Cattle: 9 3 weeks, 3 days (2 mos) days (2 mos) mos mos days PARTURITION (BIRTH) Hormonal changes trigger birth Before birth: Relaxin (placenta) relaxes the ligaments of the pelvis Fetal stress releases ACTH and fetal cortisol Placenta releases Prostaglandin F2alpha (PGF2⍺) Luteolytic to the CL Progesterone drops Estrogen rises Oxytocin sensitivity of the myometrium increases Myometrial contractions occur  STAGES OF LABOR Stage 1 Stage 2 Stage 3 Uterine contractions Rupture of the water Delivery of the placenta Cervix relaxes & dilates bags Delivery of the newborn  Contractions of the uterus to return to original size Sloughing of the UTERINE myometrium INVOLUTION Healing of the placental attachment sites Decreases chances of hemorrhage LACTATION  Function: production of colostrum & milk CHARACTERISTICS OF THE MAMMARY Present in both males & females GLANDS Hormones initiate the function of the mammary glands in females  Quantity Wide range among species Horses 2 Swine 14 SPECIES Location DIFFERENCES Inguinal only (cattle) to entire ventrum (cats, dogs, pigs) Number of openings on teets One per teat in cattle, sheep, goats Up to 20 per teat in dogs UDDER OF THE COW Four mammary glands (quarters) Each quarter is separate Mastitis in one quarter does not affect the others The udder weighs up to 100 lb at milking time Median & lateral suspensory ligament supports this weight Median = elastic fibers Lateral = collagenous fibers ALVEOLI AND DUCT SYSTEM Alveoli are the location of milk production Arranged like clusters of grapes around an alveolar duct Ducts converge into larger ducts Largest ducts empty into the gland sinus dorsal to the teat Teat Streak canal forms the passage from the sinus to the outside Elastic fibers and a ring-like sphincter Thi s Photo by Unknown Author i s l icensed under CC BY-SA muscle surround it Sphincter prevents leakage and protects the teat from ascent of microbes MAMMARY GLAND DEVELOPMENT Initial development occurs during puberty Estrogen & progesterone develop alveoli & ducts Prolactin & growth hormone also necessary for duct & alveoli changes 3rd trimester Prolactin, ACTH and placental lactogen further develop alveoli in final stages of pregnancy LACTATION Lactation is the Prolactin is the Oxytocin is the process of milk primary hormone hormone of milk production of milk production ejection COLOSTRUM Colostrum is produced in the first 2-3 days Higher amounts of proteins, lipids, amino acids and vitamins, growth factors Supplies important nutrients to newborn Antibodies/immunoglobulins Passive immunity Absorbed through gut of the newborn If not sufficient intake, failure of passive transfer may occur  MAINTENANCE OF LACTATION Milk production continues so long as suckling & emptying of the mammary gland continues Nerve impulses from teat stimulation have a positive feedback “Drying up” or mammary gland involution Gradual decrease & stop of lactation Thi s Photo by Unknown Author i s l icensed under CC BY Decreased stimulation Prolonged pressure buildup within the mammary gland (pressure atrophy) MILK LET-DOWN Milk produced and stays in the alveoli and small ducts Sensory impulses are received by the brain Anterior pituitary produces prolactin Posterior pituitary produces oxytocin Oxytocin causes contraction of myoepithelial cells of the alveoli and ducts Oxytocin is the hormone of milk ejection Milk is squeezed into the larger ducts & sinuses Baby consumes milk THE END