Embryo Block 1

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What is gestational age?: - calculated from first day of menstral cycle (LNMP)
What is conceptional age?: - calculated from day of fertilization
- 2 weeks less than gestational age
What is expected date of delivery?: - add nine months and 7 days to LNMP (gestational age)
Embryo Fetus Neonate Infancy: 1. 1st to 8 weeks
2. 9th week onwards
3. First 28 days after birth
4. First year of life
What is gametogenesis?: Conversion of primodial germ cells into mature male and female gametes via meiosis and cytodifferentiation
Development of Primordial germ cells?: Yolk sac --> gonadal ridge (dorsal body wall)
What do primordial germ cells induce?: - primary sex cords which lead to male and female gonads
What happens if primordial ger cells don't migrate to the gonadal ridge?: - they form tumors
When are the gonads indifferent?: - before 7 weeks
What is sex determined by?: - SRY gene on the short arm of the y chromosome
What does the SRY gene code for?: - Testis Determining Factor
1. N number 2. Ploidy: 1. number of like or homologus DNA strands
2. number of like or homologus chromosomes
Aneuploidy: - one or a few chromosomes above or below the normal number
Where does Meiosis occur?: - in the germ cells
What are the products of meiosis?: - 4 gametes with 23 chromosomes and 1N DNA
What are the stages of Meiosis 1?: - synapsis: pairing of 4 homologous duplicated chromosomes
- crossing over: exchange of segments of DNA
- alignment: 46 chromosomes separate from each other
- cell division: 2 secondary gametocytes are formed (23, 2N)
What are the stages of Meiosis 2?: - No synapsis and crossing over
- alignment: 23 duplicated chromososmes align at metaphase plate
- Disjunction: 23 chromosomes separate to form 23 sing chromosomes
- Cell division: 4 gametes (23 single chromosomes, 1N)
Stages of spermatogenesis: 1. Spermatocytogensis
2. Meiosis
3. Spermiogenesis
When do primordial germ cells arrive at the gonads?: - Week 4
How long to primordial germ cells stay dormant in males?: - week 4 - puberty
What happens to primordial germ cells at puberty in Males?: - differentiate into type A spermatogonia
How do Type A spermatogonia form Type B spermatogonia?: - via mitosis
What do Type B spermatogonia give rise to?: - primary spermatocyte
What do primary spermatocytes do?: - undergo meiosis to form secondary spermatocytes
What do secondary spermatocytes give rise to?: - 4 secondary (halploid) spermatids which give rise to mature sperms
What is spermiogenesis?: - from late spermatid to spermatozoa
What is sperm capacitation?: - capacity to fertilize an oocyte
Where does capicitation occur?: - Female genital tract
How does capacitation occur?: - removal of surface coating proteins and unmasking of enzymes
Where is sperm motility aquired?: - epidydimis
When do primordial germ cells arrive in gonads and differentiate into oogenia?: - week 4
When are all primary oocytes formed?: - 5th month of fetal life
How long do primary oocytes remain dormant?: - from prophase of meiosis 1 till puberty
What occurs to primary oocytes at puberty?: - completes meiosis 1 to form two daughter cells
- secondary oocyte and first polar body (later degenerates)
What occur during meiosis 2 involving secondary oocyte?: - secondary oocyte stops at metaphase of meiosis 2
- if fertilization occurs, then completes meiosis 2 to form mature oocyte and secondary polar body
Increased paternal age is associated with what chromosomal abnormality?: - Achondroplasia
What chromosome abnormality is Down syndrome?: - Trisomy 21
What is Down Syndrome associated with?: 1) esophageal atresia
2) Congenital Heart Disorders
3) abnormal facial features
4) esophageal atresia
5) acute lymphocytic leukemia
6) Alzheimers disease
What are symptoms of Turners syndrome?: 1) web neck
2) widely spaced nipples
3) infertility
Kleinfelter's Syndrome: - gynecomastia
- XXY
What is the ovarian cycle?: - changes in the ovary
What is the menstrual cycle?: - changes in the endometrium
What hormones control Ovarian cycle?: - Gonadotropins: FSH and LH
- from the pars distalis of the pituitary gland
What occurs during Ovarian cycle?: - Only one oocyte of several primordial follicles matures and ruptures during ovulation
What is corpus luteum?: - After ovuluation, the follicle is converted to corpus luteum in which oocyte is released
What are the three stages of Ovarian cycle?: - Follicular phase: 1-13 days
- Ovulation phase: 14 (rupture of follicle releasing oocyte)
- Luteal phase: 15-28 (presence of corpus luteum activity)
Where does follicle rupture in ovulation?: - at stigma at center of swelling of follicle
When is secondary oocyte released with granulosa cells?: - 12-24 hours after LH surge
What is corpus luteum formed under the influence of?: - LH
What does corpus luteum secrete?: - progesterone and small amounts of estrogen
What happens to corpus luteum if no fertilization occurs?: - forms corpus albicans by 10-12 days
What happens to corpus lutuem if fertilization occurs?: - continues to first 20 days of pregnancy as corpus luteum of pregnancy
What hormone is needed to maintain pregnancy?: - progesterone
What hormones influence Menstrual cycle?: - estrogen and progesterone
What occurs during first five days of menstrual cycle?: - uterus sheds endometrium
What is the proliferative phase of mestrual cycle?: - Epithelium regenerating under influence of estrogen
What is secretory phase of menstrual cycle?: - secretions under influence of progesterone
What are two layers of endometruim of uterus?: 1) stratum functionalis: undergoes cyclical changes, shed during menses
2) stratum basalis: gives rise to basal layer, permanent layer
What is the menstrual phase of menstrual cycle?: - 1st day of menstrual cycle: lasts 3-5 days, functional layer sloughed off
What is proliferative phase of menstrual cycle?: - last 9 days
- growth of ovarian follicles
- controlled by estrogen secreted by follicle
What is secretory phase?: - 13 days, progesterone dependent
What happens in secretory phase if fertilization occurs?: - blastocyst implants about 6th or 20th day of normal cycle
What happens in secretory phase if fertilization does not occur?: - secretory endometrium enters an ischemic phase
- falling hormone levels (especially progesterone) cause cconstriction of arteries in endometrium
What is fertilization?: - contact of sperm with secondary oocyte
- ends with fusion nuclei of sperm and ovum
How does sperm penetrate oocyte?: - acrosomal cap of sperm head releases enzyme hylarunidase that allows passage through corona radiata
- acrosome also release acrosin and neuraminidase which lyses zona pellucida
- sperm passes through zona and zona/cortical reaction occurs that makes the plasma membrane of the ovum impermeable to other sperms
What is a female pronucleus?: - Nucleus of mature oocyte
What is male pronucleus?: - Nucleus of the sperm (tail denerates)
What is a zygote?: - Fusion of male and female pronucleus
When is fertilization complete?: - Within 24 hours of ovulation
When is Early Pregnancy Factor produced and what is its function?: - 24-48 hours after fertilization
- produced by ovary
- immunosupressant, prevents zygote from being destroyed
What is In Vitro Fertilization?: - sperm cultivated with unfertilized egg in test tube and then transplanted into uterus
What is Gamete Intra Fallopian Transfer? (GIFT): - gametes of male and female injected into femaleâ€™s fallopian tube for fertilization to occur
What is Zygote Intra Fallopian Transfer? (ZIFT): - egg is fertilized outside the body and then implanted into fallopian tube
What is Intracytoplasmic sperm injection? (ICSI): - fertilization in which a sperm is directly injected into an egg to achieve fertilization. ICSI done for male infertility
What is Intrauterine insemination?: - a catheter tube is inserted through cervix into uterus to deposit sperm
What is a blastula?: - Division of zygote which will implants in uterus(blastomeres)
What is cleavage?: - Process in which zygote divide within 24 hours of fusion
What is compaction?: - Blastomeres align against each other by interacting with surface glycoproteins
- Outer cells form tight junctions which form trophoblast
- Inner cells develop gap junctions which develop embryo
What is Morula?: - Solid ball of 12 or more blastomeres
What does trophoblast give rise to?: - The placenta
What is a blastocyst cavity?: - Fluid filled spaces between central blastomeres
- Increases in size as zona pellucida degenerates
Where does blastocyst attach?: - Endometrium adjacent to embryonic pole
When does this attatchment occur? (implantation): - 6 days post fertilization
What does trophoblast differentiate into?: - Inner cytotrophoblast
- Outer synctiotrophoblast (invades endometrium during implantation)
When is blastocyst completely embedded in uterus?: - 10th-11th day
Where does normal implantation occur?: - Upper posterior wall of the uterus
What is an ectopic pregnancy?: - Implantation anywhere apart from the uterus
Where is the most common place for ectopic pregnancy?: - Fallopian tube
Where is amniotic cavity located?: - At embryonic pole b/w trophoblast and epiblast
What does the inner cell mass differentiate into?: - Epiblast: facing amniotic cavity
- Hypoblast: facing the blastocyst cavity
Where does the yolk sac come from?: - Blastocyst cavity
How does the Amnion form?: - Amnioblasts delaminate from the epiblast and form membrane surrounding amniotic cavity
What two structures give rise to primary yolk sac?: - Exocoelomic membrane
- Exocoelomic cavity
**cells migrate from hypoblast to form membrane which surrounds blastocyst cavity which is now called exocoelomic cavity
What is extraembryonic mesoderm derived from and where is it located?: - Derived from hypoblast
- Located around amnion and primary yolk sac
What is extraembryonic coelum derived from?: - Isolated cavities in extraembryonic mesoderm
What is the connecting stalk?: - embryonic mesoderm attatches wall of amniotic cavity to trophoblast
- coelem does not develop here
What does connecting stalk give rise to?: - Umbilical cord
What two layers does the extraembryonic mesoderm form?: - Somatopleuric extraembryonic mesoderm: lines trophoblast and outside of amniotic cavity
- Splanchno extraembryonic mesoderm: lines outside of yolk sac
When does Secondary yolk sac form?: - As extraembryonic coleom forms
- Primary yolk sac decreases in size
- Exocoelmic vescicle is degenerates (remnant)
What forms the chorion?: - Extraembryonic somatic mesoderm
- Trophoblast
**coleom now called chorionic cavity
What are predisposing factors of ectopic pregnancy?: - Previous history of PID/Salpingitis
(pelvic inflammatory disease/inflammation of fallopian tubes)
- Previous surgery on tubes or close to tubes
- Previous history of ectopic pregnancy
- Intra Uterine Device
- Advanced maternal age
- Smoking
What is gastrulation?: - Process by which the bilaminar disc is converted to trilaminar disc
What are two places where the mesoderm does not reach?: - Prochordal plate (cranium)
- Chrodal reion (cloacal membrane)
What is primitive streak?: - Thickened linear band formed by migrating cells of epiblast at beginning of 3rd week
Where is primitive streak located?: - Caudal end of embryo
What does primitive streak grow to form?: - Primitive node at its cranial end
What does prochordal cavity form in the future?: - mouth
What does cloacal membrane form in the future?: - anus
How does intraembryonic mesoderm form?: - Displaced cells migrated from hypoblast
When does the primitive streak degenerate and what does it become?: - around 4th week and beomes insignifican structure of sacrococcygeal region
What happens if primitive streak persists?: - Becomes sacrococcygeal teratoma
What is and how does the notochordal process form?: - A median cellular cord that is formed by cells which have migrated cranially from the primitive node
Where is the notochord located?: - Extends from primitive node to prochordal plate
What is the prochordal plate?: - Where endoderm and ectoderm fuse
What are the two regions on the embryo where the disc is bilaminar?: - Prochordal plate: forms oropharyngeal membrane
- Cloacal membrane: site of future anus
What defines primitive axis of the embryo?: - The notochord- gives rigidity
What does the notochord give rise to?: - Vertebral column
How does Neurenteric Canal form?: - The primitive pit extends into notochordal process.
- Cells of process fuses with endoderm.
- Located between yolk sac and primitive cavity
**if persistence occurs, then have neurenteric cysts
What is allantois?: - Outpouching from yolk sac extending into connecting stalk
- Occurs around day 16
- Involved w/ development of urinary bladder as it will form urachus
What is neurulation?: - Processes involved in formation of neural tube
What does the neural tube give rise to?: - Brain and spinal cord
When is neurulation complete?: - end of 4th week
How does neuroectoderm form?: - notochord induces overlying ectoderm
How does neural groove form?: - Neural plate invaginates in longitudinal plane
Where are folds of neural groove prominent?: - Cranial region
How does neural tube form?: - Neural folds move towards each other and begin to fuse converting neural plate to neural tube
What are neuropores?: - Openings at cranial and caudal end of neural tube
When is neuralation complete?: - During 4th week when neuropores close
What happens if two openings of neural tube do not fuse?: - Severe malformations of the brain
What are neural crest cells?: - Specialized cells at surface ectoderm and neuroectoderm
What happens to neural crest cells when neural tube is formed?: - Separate into two parts and migrate ventrolaterally
What are dervitives of neural crest cells?: 1) Dorsal root ganglia and ganglia of ANS
2) Schwann cells
3) Piamater and arachnoid
4) Melanocytes
5) Adrenal medulla
6) Skeletal and muscular components of the head
What three parts is the intraembryonic mesoderm divided into along sides of the notochord and neural tube?: 1) Paraxial mesoderm
2) Intermediate mesoderm
3) Lateral plate mesoderm
What are somites?: - Balls of paraxial mesoderm on either side of the neural tube
- Give rise to axial skeleton and associated musculature
What are chordomas?: - Tumors of notochordal remnants in bone
- Arise anywhere in skeleton from base of skull to coccyx
What are neural tube defects?: - occur due to defect in neurulation
- common birth defects
What causes neural tube defects?: - Multifactoral: genetic and environmental
- Folate deficiency
- Chromosomal abnormality (Trisomy 13, 18. 21)
- Maternal hyperthermia
- Maternal diabetes
- Alcohol abuse
- Drugs like valproate (anti epileptic)
What should pregnant women take to prevent neural tube defects?: - Folic acid
What is raschischisis?: - Failure of fusion of vertebral arches and neural tube with consequent exposure of neural tissue
What is cranioschisis?: - Congenital failure of skull to close usually accompanied by defect in development of the brain
- Associated with anencephaly
What is anencephaly?: - Defect in closure of neural tube during fetal development.
- Marked defective development of the brain together with absence of brain and spinal cord
What is meningocele?: - Only meninges are protruding
What is meningomyelocele?: - Brain and spinal cord are protruding out of body
What is decidua?: - Phase after implantation of endometrium
- Under influence of progesterone
- Decidual cells derived from connective tissue cells which have increased glycogen and lipid content
What layer of deciduas gives rise to placenta?: - Deciduas basalis
What is the chorion made up of?: - Trophoblast
- extraembryonic mesoderm
What is Chorion Laeve?: - Chorionic villi associated w/ deciduas capsularis disappears and leave a bare area known as Chorionic leave
What is Chorion Frondosum?: - Chorionic villi associated with deciduas basalis will develop further to form placenta
What is Primary Chorionic Villi?: - Cytotrophoblast plus synchotrophoblast
What is secondary chorionic villi?: Cytotrophoblast plus syncytiotrophoblast plus extraembryonic mesoderm
When does the cytotrophoblastic layer gradually start disappearing?: - As placenta ages
What is cytotrophoblastic shell?: - Area where tertiary villi invades layer between syncytiotrophoblast and decidua
Where do maternal blood vessels empty?: - Intervillous space of cytotrophoblastic shell
When does growth of placenta continue until/completely form?: - 20th week of gestation
What is the fetal component of the placenta?: - Chorionic villi
What is the maternal component?: - Decidua basalis
What is placenta divided by?: - Placenta septa (composed of villi) that project toward chorionic plate
- Placenta divided into cotyledons
- Maternal cotyledons form placenta
What is placenta membrane?: - Separates maternal and fetal blood
- Composed of:
1) endothelium of fetal blood vessels
2) Connective tissue of villus
3)Cytotrophoblast
4)Syncytiotrophoblast
- After 20th week, placenta has formed, membrane is smaller, allowing more gas exchange
What is the function of the placenta?: - Metabolism-synthesizes glycogen, cholesterol, and fatty acids that serve as energy sources for fetus
- Transport:
- Oxygen, CO2
- Vitamins, glucose
- Steroid hormones (not proteins)
- Electrolytes
- IgG antibody
- Drugs
- Infection agents
- Small amount of blood
- Endocrine:
- HCG
- Human chorionic sommatomammotropin
- Human chorionic tyrotropin
- Human chorionic adreno-corticotropin
- Progesterone and estrogen
Where is HCG produced?: - placenta
When is HCG detectable in blood or urine?: - 1-2 days after implantation
When do HCG reach a peak?: - 8-10 weeks of gestation
What is the function of HCG?: - Stimulates corpus luteum and maintains pregnancy
- Forms basis of urine pregnancy test
What gives rise to the umbilical cord?: - Connecting stalk
What is the umbilical cord covered by?: - Amnion
Which vein of the umbilical cord degenerates?: - Right umbilical vein
What forms Whartonâ€™s Jelly?: - Extraembryonic mesoderm
What is the umbilical cord a remnant of?: - Yolk sac
What composes the fetal membrane?: - Fused amnion and chorion along with deciduas
What is amniotic fluid?: - Clear yellowish fluid present in the amniotic sac covering the fetus
What is the major contribution to amniotic fluid?: - Urine from the fetus
How is amniotic fluid circulated?: - Exchange through amniochorionic membrane
- Amniotic fluid swallowed by fetus and is absorbed in respiratory and digestive tracts
What is oligohydraminos?: - Decrease in amniotic fluid
- Due to excessive swallowing of amniotic fluid, carried away in blood from placenta and discharged
What is polyhydraminos?: - Increase in amniotic fluid
- Could be due to problem w/ swallowing
What is pulmonary hypoplasia?: - If too little amniotic fluid, lungs will not develop
What is the function of amniotic fluid?: - Shock absorption
- Freedom of movement
- Promotes symmetrical growth of fetus
- Maintains constant temperature around fetus
- Barrier for infection
- Normal lung development
What is amniocentesis?: - Amniocentesis is a common prenatal test in which a small sample of the amniotic fluid surrounding the fetus is removed and examined.
- Do not perform before 14 weeks of pregnancy b/c not enough amniotic fluid
What is chorionic villus biopsy?: - Take biopsy of chorionic villus from vagina round 8-10th week of pregnancy
- 10th week is better
- procedure performed to see if there is an abnormality in fetus

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