Lecture 1 Flashcards
(111 cards)
1
Q
Divides the body into left and right parts
A
Sagittal plane
2
Q
Divides the body into superior and inferior parts
A
Transverse plane
3
Q
Divides the body into anterior and posterior parts
A
Frontal (coronal) plane
4
Q
Vertical plane, divides the body into right and left
A
Sagittal plane
5
Q
Midsagittal plane - sagittal plane exactly at midline
A
Median plane
6
Q
Set off from midline
A
Parasagittal plane
7
Q
The study of the origin and development of an organism
A
Embryology
8
Q
Prenatal period
A
Before birth
38 weeks from conception to birth
9
Q
Embryonic period
A
First 8 weeks
All major organs formed
10
Q
Fetal period
A
Remaining 30 weeks
Organ grow larger and become more complex
11
Q
Major embryological event in embryonic period
A
Organs form three primary germ tissues called the ectoderm mesoderm endoderm.
Emergence of the basic body plan.
12
Q
Germ cells become gametes
A
Gametogenesis
13
Q
Explain primordial germ cells (PGCs)
A
From where gametes come from
- Male gamete = sperm
- Female gamete = oocyte
- Gametogenesis meiosis and mitosis
- Cytodifferentiation maturation
They’re formed in the epiblast, 2nd week.
14
Q
Somatic cells
A
23 homologous pairs of chromosomes
22 autosomes 1 sex chromosomes
15
Q
Meiosis I
A
Duplication of 46 chromosomes into sister chromatids (diploid number)
16
Q
Meiosis II
A
Haploid number of chromosomes
Each gamete = 23 chromosomes
17
Q
Results of meiosis
A
- Genetic variy
- 1 cross over
- 2 random distribution of homologous chromosomes to daughter cells
- Haploid number of chromosomes
18
Q
Critical events in meiosis
A
- Crossover
- Formation of polar bodies
Females = 1 mature 3 polar bodies Male = 4 mature
19
Q
Oogonia become mature oocytes
A
Oogenesis
20
Q
Maturation of oocytes begins before birth
A
PGC - gonad of a genetic female - oogonia - several mitotic division - end of 3rd month - primordial follicle - primary oocytes some arrested at meiosis 1, prophase
5th mo = 7m germ cells - cell death - atresia
7th mo = majority of oogonia have degenerated
21
Q
Maturation of oocytes continues at puberty
A
Near time of birth = all primary oocytes have started prophase 1 entering diplotene (resting) stage
Arrested state of primary oocytes - due to presence of oocyte maturation inhibitor (OMI)
22
Q
Oocytes from birth to puberty
A
At birth = 600k - 800k
Childhood = 40k at the beginning of puberty
Puberty = 500
23
Q
Females at puberty
A
- Meiosis I resumes shortly before ovulation
- Meiosis 2 happens before the nucleus of the secondary oocyte returns to its resting stage (meiosis 2, metaphase 2) - prior to ovulation
- Meiosis 2 is complete when the oocyte is fertilized
- fertilization = cell degeneration 24hrs after ovulation
24
Q
Males at puberty
A
- Spermatogenesis
- Spermatogonia to spermatozoa
- Meiosis I - secondary spermocytes
- Meiosis 2 - spermatids
- Spermiogenesis - spermatids to spermatozoa
25
Events on the first week of development
1. Ovulation
2. Fertilization
3. Implantation
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Events on the first week of development
1. Ovulation
2. Fertilization
3. Implantation
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Phases of fertilization
1. Penetration of the corona radiata
2. Penetration of zona pellucida
3. Fusion of oocyte and sperm cell membranes
3. 1 cortical and zonal rxns - 1 sperm penetrates ovume.
3. 2 resumption of 2nd meiotic div - oocyte finishes meiosis
3. 3 metabolic activation of the egg
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Main results of fertilization
1. Restoration of the diploid number of chromosomes
2. Sex determination of the new individual
XX = female
XY = male
= Chromosomal axe
3. Initiation of cleavage
**Without fertilization, oocyte usually degenerates 24 hrs after ovulation.
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Cleavage facts
1. Begins 12 hour post fertilization
2. Zygote divides into 2 cells - series mitosis ensue
= 46 chromosomes in zygote = 46 chromosomes in both daughter cells
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Each cleavage division
Divided cells = blastomeres
16 cell stage (3 days after fertilization)
=Morula (mulberry)
= Enters the uterus after 3 days in the oviduct
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Morula
2 cell masses
- inner cell mass - embryo proper
- outer call mass - trophoblast - placenta
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Blastocyst
Morula - entering the uterine cavity, floats freely
Morula begins to accumulate fluid (penetrate the ZP) and forms a cavity (blastocele) between its inner cells
Once the cavity appears it is now called a blastocyst
Blastocyst has fluid filled inner cavity
Evolves from morula on day 5
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Day 6 events
1. Trophoblasts over the embryoblast pole begin to penetrate between the epithelial cells of the uterine mucosa
2. hCG secreted by the trophoblasts
3. Implantation
34
hCG is produced
Human chorionic gonadotropin
1. Produced by the trophoblasts starting on day 6
2. A hormone
3. Causes endometrium of uterus to grow and proliferate
4. Prevents the menstrual cycle from occurring
5. Why a female misses her periods when she is pregnant
35
Week 2
1. Implantation continues
2. Erosion of maternal blood vessels
3. Complete immersion into endometrium of uterus
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Day 8
1. Blastocyst partially embedded in the endometrial stroma
2. Trophoblast differentiates into two layers
= Inner layer of mononucleated call
A. Cytotrophoblast
B. + Mitotic figures
C. Migrate into the syncytiotrophoblast - fusion - individual cell membranes are lost
= Outer multinucleated cells
A. Syncytiotrophoblast
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Embryoblast
Differentiates into 2 layers
1. Small cuboidal cells adjacent to cavity
= Hypoblast
2. High columnar cells adjacent to the amniotic cavity (within the epiblast
= epiblast
Forming a bilaminar germ disc
Amnioblasts - epiblast adjacent to the cytotrophs
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Day 9
1. Blastocyst more deeply embedded
2. Trophoblast development progresses - at the embryonic pole with the appearance of vacoules in the syncytium - fusion - forms large lacunae - lacunar stage
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Abembryonic pole
1. Formation of Heuser's membrane (exocoelomic) lines inner surface of cytotrophoblast
2. Heuser's membrane with the hypoblast forms the lining of the primitive yolk sac (exocoelomic cavity)
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Day 11 and 12
1. Blastocyst completely embedded, producing a slight protrusion into the uterine lumen
2. Establishment of the uteroplacental circulation
- trophoblast continues to erode more and more sinusoids, maternal blood begins to flow through the trophoblastic system
* Formation of the extramebryonic mesoderm (EEM)
3. Formation of large cavities in the EEM - confluence of cavities - EE coelom or chorionic cavity = surrounds the primitive yolk sac and amniotic cavity
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Lines the cytotrophoblast and amnion
EE somatopleuric mesoderm
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Lines the yolk sac
EE splanchopleuric mesoderm
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Day 13
1. + Of villous structures in the trophoblast
2. Formation of primary villi
3. Formation of secondary yolk sac or definitive yolk sac (proliferation of the hypoblast)
4. + Exocoelomic cysts found in the chorionic cavity
5. Expansion EE coelom forming chorionic cavity
6. EEM lining the inside of the cytotrophoblast called the chorionic plate
7. Connecting stalk is traversed by the EEM
= With development of blood vessels = umbilical cord
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End of week 2
Two apposed cell discs: epiblast (floor of the amniotic cavity); hypoblast (roof of the secondary yolk sac)
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Cephalic region of the hypoblastic disc
Buccopharyngeal membrane or oropharyngeal membrane
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Week 2 events - week of twos
1. Trophoblast - differentiates into cyto and syncytio
2. Embryoblast - into epiblast and hypoblast
3. EEM - splits into somatopleure and splanchnopleure
4. 2 cavities - amniotic and yolk sacs
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Establishment of all germ layers. Ecto, meso, endo.
Gastrulation
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Week 3 events
1. Appearance of primitive streak
2. Formation of the notochord
3. Cloacal membrane formation
4. Allantois (16th day)
6. Primary villi with mesenchymal core where small capillaries arise
7. Establishment of the body axes
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After invagination, some displace the hypoblast
Endoderm
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Lie between epiblast and new endoderm
Mesoderm
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Cells remaining in the epiblast
Ectoderm
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Controls cell migration and specification from streak cells
1. 1 down - regulating E-cadherin (binds epiblast)
1. 2 into the mesoderm by regulating BRACHYURY (T) expression
Fibroblast growth factor 8
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Inhibit nodal activity; establishing cranial end of embryo
Cerberus and Left 1
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Absent in caudal end; + nodal expression =
Establish and maintain primitive streak
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Primitive streak is formed...
1. Nodal upregulates genes responsible for :
A. Dorsal and ventral mesoderm formation
B. Formation of head and tail structures
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BMP4 with FGF
1. Mesoderm is centralized
| 2. Antagonized by CHORDIN, noggin and follistatin = dorsal mesoderm
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Maintains node, induces regional specificity in the forebrain and midbrain
HNF-3B
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Activates inhibitors of BMP4, regulate head dev't
GOOSECOID
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It's expression is induced by FGF8; restricted to left side by accumulation of serotonin (activate MAD3 - restricts Nodal to left)
Nodal
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Establish midline; prevent Nodal from crossing over to right
Midline genes - SHH, lefty 1, ZIC3
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Upregulated by Lefty2, HB gene establish left sidedness
PITX2
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Restricted right LPM; probably regulate effector genes for establishing right handedness
SNAIL
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Once this is formed, genes regulate formation of dorsoventral mesoderm and head and tail structures
Once primitive streak is formed
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By cascade of genes
Heart, spleen, main lobe of liver on the right
Left-right asymmetry
65
What period is in the 3rd to 8th week
Embryonic period
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This period is characterized by development of structures (organs)
Embryonic period
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Characterized by growth of those structures
Fetal period
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Formation of the 3 germ layers
1. Primitive streak (groove) on dorsal surface of epiblast
2. Gastrulation: invagination of epiblast cells
3. Days 14-15: they replace hypoblast becoming endoderm
4. Day 16: mesoderm (a new third layer) formed in between
5. Epiblast cells remaining on surface: ectoderm
69
Are epithelial tissue (form sheets of tissue)
Ectoderm and endoderm
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Is a m mesenchyme tissue
Mesoderm
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Are star shaped and do not attach to one another, therefore migrate freely
Mesenchyme cells
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Beginning of 3rd week
1. Disk shaped ectodermal germ layers - broader ciphalic part
2. Appearance of notochord and prechordal mesoderm - overlying ectoderm thickens
= Neural plate
= It's cells - neuroectoderm
= Initial process of neurulation
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Notochord
1. Days 16-18
2. Primitive node epiblast cells invaginate and migrate anteriorly with some endoderm cells
3. Rod defining the body axis is formed
4. Future site of the vertebral column
74
Neural plate forms the neural tube
Neurulation
75
Neurulation process
1. lengthening of the neural plate NP and body axis thru convergent extension
- lateral to medial movement of cells in ectodermal and mesodermal plan
2. As the NP lengthens, it's lateral edges elevate forming neural folds, the depressed midregion is the neural groove.
3. Neural folds fuse in the midline, beginning at the cervical region (5th somite), then cranial and caudal directions forming neural tube.
4. Communication between cranial and caudal ends of NT with amniotic cavity is via anterior and posterior neuropores
5. Cranial neuropore closed at day 25 (18-20 somite stage)
6. Caudal neuropore closed at day 28 (25 somite stage)
7. Neurulation is complete
76
Neurulation 3rd to 8th week
1. Notochord signals overlying ectoderm
2. Neurulation - when complete, the CNS is represented by a closed tube with narrow caudal end, the spinal cord; broader cephalic end; the brain vesicles
3. Closure of neural tube: begins at end of the week 3; complete by end of week 4 (folic acid important for this step)
4. Extends cranially (eventually brain) and caudally (spinal cord)
5. Neural crest, lateral ectodermal cells, pulled along and form sensory nerve cells and other structures.
77
Mesoderm begins to differentiate
1. Lateral to the notochord week 3
| 2. Extends cranially and caudally (from head to tail or crown to rump)
78
Division of mesoderm into three regions
1. Somites: 40 pairs of best segments (repeating units, like building blocks) by end week 4
2. Intermediate mesoderm: just lateral to somites
3. Lateral plate: splits to form coelom (cavity)
79
Divisions of the mesodermal lateral plate
1. Somatic mesoderm: apposed to the ectoderm
2. Splanchnic mesoderm: apposed to the endoderm
3. Coelom in between will become the serious cavities of the ventral body cavity:
A. Peritoneal
B. Pericardial
C. Pleural
80
About what months are all major organs are in place in at least a rudimentary form
2 months
81
BMP 4 regulating factors: ectoderm
1. It's inactivation induces neural plate formation
| 2. It's inactivation in the hindbrain and spinal by: WNT3a and FGF
82
Cranially inactivation is caused by
Noggin
Chordin
Follistation
83
Regulating factors mesoderm
SHH
WNT proteins, BMP4, FGF
NT3
84
Produced by notochord and floor plate of the neural tube induces sclerotome
Since Hedgehog SHH
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Muscle forming regions
WNT proteins
BMP4
FGF
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Secreted by dorsal ntube
NT3
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Regulating factors endoderm
Homeobox genes (Drosophila)
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Homeobox genes Drosophila
1. Craniocaudal patterning
| 2. HOXA, HOXB, HOXC, HOXD
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Gut tube and body cavities end of 3rd weej
1. Ntube - elevates and closes dorsally
2. Gut tube - rolls and closes ventrally
Tube on top of a tube
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It holds the tubes together
LP - visceral (splanchnic), parietal (somatic)
Mesoderm
91
Space between visceral and parietal layers
Primitive body cavity
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Parietal layer + ectoderm
Lateral body wall folds
Meet in the midline at the end of the 4th week and fuse closing the ventral let wall aided by growth of head and tail regions
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Curving of the embryo
Fetal position
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Parietal layer of the peritoneum, pleura, pericardium
Parietal mesoderm
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Visceral layer of p p p
Visceral mesoderm
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Peritoneum doubles
Mesentery
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Pathway for vessels, nerves, and lymphatics
Mesentery
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Divides the body cavity into thoracic and peritoneal cavity
Diaphragm
99
Diaphragm is developed from:
1. Septum transversum (central tendon)
2. Pleuroperitoneal membranes
3. Dorsal mesentery of the esophagus
4. Muscular components from somites At C3-5
Phrenic nerve also arise from C3-5
100
Components of placenta
1. Fetal - from the chorion frondosum or villous chorion
| 2. Maternal portion - from decidua basalis
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Functions of placenta
1. Exchange of gases
2. Exchange of nutrients and electrolytes
3. Transmission of maternal Abs, providing the fetus with passive immunity
4. Production of hormones: progesterone, estradiol, hCG, somatomammotopoin
5. Detoxification of drugs
102
Umbilical cord surrounded by amnion containd
1. 2 umbilical arteries
2. 1 umbilical vein
3. Wharton jelly - protection for the vessels
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2 amnions 2 chorions 2 placentas
Dizygotic or fraternal twins
104
2 amnions 1 chorion 1 placenta
Monozygotic or identical twins
105
1 amnion 1 chorion 1 placenta
Conjoined twins
106
Where epiblasts (flask shaped) invaginate to form Endo and mesoderms
Primitive streak
107
Steps of the formation of notochord
1. From the prenotochordal cells and hypoblast (later replaced endodermal cells)
2. Further forms a midline axis = basis of axial skeleton
3. Underlies the neural tube
4. Prechordal plate (PP) forms between the tip of the notochord and bp membrane
* Pp = induction of forebrain
108
Where is the cloacal membrane formed
End of the embryonic disc
109
End of 3rd week
1. Ecto, meso, endodermal established in the head region.
| 2. Tissue and organ differentiation begins in cephalocaudal direction
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Establishment of the body axes
1. Anteroposterior (AP), dorsoventral, left-right
2. Prior to and during gastrulation
Ap = signaled by cells at the posterior margin of embryonic disc (posterior marginal zone PMZ)
PMZ- induces primitive streak formation, establishes cranial to caudal axis in embryo
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Small diverticulum extending into the connecting stalk; posterior wall of the yolk sac
Allantois
