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Fertilization

Fertilization, pregnancy, development

QuestionAnswer
Accomplishing Fertilization Need viable sperm + viable secondary oocyte Sperm life = 24 - 72 hours oocyte = 12-24 Hours Coitus must take place 72 hours before ovulation no later than 24 after.
Sperm Transport + Capacitation Capacitation = sperm membrane become thin, fragile and fluid because of the depletion of cholesterol.
Acromosomal Reaction Sperms release hydrolytic enzymes from acromosome = required for fertilization. Acromosomal reaction occurs when sperm are in vicinity of oocyte. - For sperm to reach Oocyte corona radiata must be broken down by hydrolytic enzymes.
Acromosomal Rxn Contd First few 100 sperm to reach corona radiata make path for latter sperm to reach oocyte. Receptors in Oocyte pull nucleus of sperm into cytoplasm of oocyte.
Blocks to Polyspermy (prevent oocyte from being fertilized by more than 1 sperm)- Fast Block "Fast block to polyspermy" - Plasma membrane of sperm + oocyte contact eachothers sodium channels/oocyte membrane opens.-> exrracellular Na enters + depolarizes membrane (pos. inside repels pos. sperm)
Slow Block to Polyspermy Cortical Rxn - depolarization causes Ca ions to be released into cytoplasm of oocyte.The contents of these vesicles surrounds the egg, swells with water and gels, pushing other sperm away from the egg and blocking their entry.
Completion of Meiosis II and Fertilization Release of Ca stimulates oocyte to complete 2nd meiotic divisio. 2nd polar body formed ->oocyte has haploid nucleus. Ovum + Sperm nuclei swell and approach. mitotic spindle forms between them. nuclear membrane ruptures, M + F chromosomes comb.=dip.zygote
Pre-Embryonic Development Cleavage + blastocyst formation -rapid cell division following fertilization -Zona pellucida breaks down, blastocyst = fluid filled. Outer layer = Trophoblast -> helps placenta act as an endocrine organ
Pre-Embryonic Development II Blastocyst floats free in uterus for 2-3 days while endometrium develops (produces a chemical signal when developed)-> sensed by the trophoblast-> induced to adhere to endometrium.
Pre-Embryonic Development III BC = blastocyst Trophoblast cells begin to divide and form 2 layers of cells: inner = Cytotrophoblast; outer = syncytiotrophoblast -> invades endometrium, digests uterine cells, blastocyst begins to burrow. Proliferating endometrium cells eventually completely cover BC
Pre-Embryonic Development IV Menstration does not occur because trophoblast cells secrete HCG which acts on corpus luteum and stimulates it to keep producing progesterone and estrogen, takes over from decrease LH conc b/c of neg feedback
Placentation Formation of Placenta. Link between baby and mother. Cytotrophoblast produces chorion. Chorion develops fingerlike chorionic villi. Space formed by syncytiotrophoblast + digested endometrial cells = lacunae
Placentation II recieves blood from maternal arteries and drains into maternal veins. Surronds chorionic villi. -Embryonic blood vessels form in villi. connect to fetal circulation through 2 umbilical arteries. 1 vein. Placenta fully formed by 3rd month of pregnancy.
Placentation III Site of nutrient, excretory, gas exchange surface for fetus -> endocrine organ. HCG stimulates corpus luteum to continue producing estrogens + progesterone w/in time placenta secretes estrogen + progesterone STOPS producing HCG-> corpus luteum degenerates
Placentation IV Estrogen + Progesterone inhibit GnRH. Therefore no FSH/LH so no maturation of new follicles.Estrogen + progesterone increase thru out pregnancy, encourage growth, prep mammary glands for lactation
Effects of Pregnancy on Mother: Anatomical and Metabolic Changes -female repro organs vascularized + engorged with blood -Increased pigementation of facial skin -enlargement of uterus - displacement of abdominal cavity/thoraic -change in centre of gravity -pelvic ligments widen (relaxin)
Effects of Pregnancy on Mother: Physiological Changes -Breasts: HPL -> maturation of breasts for lactation -Gastrointestinal system - increased levels of estrogen + progesterone causes excess salivation + nausea (morning sickness) -displacement of uterus -> heartburn, constipation
Effects of Pregnancy on Mother: Physiological Changes II Urinary system - mother also disposing fetal wastes ->increased urine formation. compression of bladder b/c of growing uterus. more urination.
Effects of Pregnancy on Mother: Physiological Changes III Respitory System - nasal muscosa engorged with blood. nose bleeds. compression of thoraic cavity ↓ residual volume ↑ breathing frequency + difficulty breathing later in pregnancy. Cardiovascular sys - body water ↑ 25-40% b/c ↑ plasma volume
Partruition Giving birth/labour. events that expell infant from uterus. THEORIES OF INITIATION OF LABOUR: during last few weeks of pregnany estrogen levels highest. b/c of stimulation of placenta by adrenocortical hormones released from fetus.
Partruition II High E. levels stimulate uterine muscle cells to produce receptors for oxytocin. ->antagonizes effect of progesterone. myometrium contracts. As birth nears -> fetus secretes oxytocin which makes placenta produce/release prostaglandins
Partruition III Prostaglandins stimulate uterine muscle contraction. myometrium produced receptors for oxytocin resp. so contractions b/c more numerous + vigorous
Partruition IV Emotional + Physical stresses induce hypothalamus of mother -> oxytocin release. more contractions "true labour" - fetus moves down cervix. pos feedback. pressoreceptors stimulated -> send afferent impulses to hyp. -> stim pit to release more oxytocin
Adjustments of the Infant to Extrauterine Life First Breath = building levels of Co2 ↓O2. change in temp + stress. Surface tension must be overcomed to fill the lungs. surfacant distributed thoughout alveolar fluid -> breathing easier
Adjustments of the Infant to Extrauterine Life II Cardiovascular Changes - umbilical arteries + vein contrict during birth. outer segments fibrose are eventually sloughed off.
Lactation production of milk by mammary glands. ↑ estrogen, progesterone, hpl--stimulate hypothalamus to release PRL--> prolactin. after birth prolactin↓ -receptors in nipples send afferent impulses to hypothalamus -->prh released in bursts, stimulates glands
Lactation II Oxytocin "let down" reflex -> release milk from glands by binding to receptors of myoepithelial cells -> contract + expel milk from nipples +ive feedback ends when baby stops sucking --> stops secretion of oxytocin
First Trimester embryological + early fetal development. rudiments of major organs appear. 1. Cleavage 2. Implantation 3. Placentation 4. Embryogenisis
First Trimester - Formation of Amniotic Cavity Aminotic Cavity -> results from separation of inner cell mass from the trophoblast. Gastrulation + Germ Layer Formation -> Gastrulation cells in spec areas of surface moves toward a central line. forms 3 distinct layers
First Trimester - Germ Layers - Ectoderm Superficial cells. Integumentry system (hair, glands), pharyngeal cartilage, neural tissue - brain + spinal chord. pituitary, mucous epithelium, salivary glands
First Trimester - Germ Layers - Endoderm Cells that face blastocyst. become thyroid, pancreas, resp epithelium, mucous glands, exocrine, liver, bladder, stem cells
First Trimester - Germ Layers - Mesoderm Middle layer. Between ecto and endo. becomes skin, muscular system, cardiovascular system, adrenal cortex, kidneys, lymphatic system, repro, lining of organs
Extraembryonic Membranes Yolk Sac (endo + Meso) Amnion (ecto + Meso) Chorion (Meso + Trophoblast)
Extraembryonic Membranes II Yolk Sac-site of blood cell formation Amnion-contains amniotic fluid which surrounds + cushions developing fetus. Allantois (endo+meso) ->gives rise to urinary bladder.
Extraembryonic Membranes III Chorion - blood vessels develop = rapid transit system for nutrients linking embryo to trophoblast. ->chorionic villi as enlarge more maternal blood vessels eroded. Moves slowly thru lacunae; chorionic blood vessels pass close by
Extraembryonic Membranes IV fetal hemoglobin = high affinity for o2 than maternal hemoglobin - fetal hemo takes o2 from maternal. maternal blood re-enters venous system thru broken walls of small uterine veins. - no mixing of fetal/maternal blood.
Hormones HCG - indicator of pregnancy. resembles LH. maintains corpus luteum; promotes secretion of progesterone so endometrial lining remains functioning -> pregnancy ends w/ the absence of it. Human Placental Lactogen - helps prep mammary glands for milk prod.
Hormones II Relaxin - increases flexibility pelvis expands during delivery. dilation of cervix. - suppresses release of oxytocin release + delays labour labour contractions Progesterone + E. -maintain endometrial lining + continue pregnancy.
Second + Thrid Trimesters -developing fetus dependent on maternal organ for: nourishment, respiration, waste removal. -mother must absorb enough vitamin, o2, nutrients for herself + fetus + eliminate wastes
Labour + Delivery Dilation -> Expulsion -> Placental Stage
Created by: zeenat