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Physiology 2 > Embryology > Flashcards

Embryology Flashcards

1
Q

trimesters

A

3 three month periods of the 9 months from conception to birth

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2
Q

period of the egg

A

pre-embryonic period

from fertilisation of the egg to end of 3rd week with implantation of conceptus

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3
Q

period of the embryo

A

embryonic period/ period of organogenesis
from beginning of 4th week to end of 8th week
This is when each of the 3 germ layers are formed and give rise to specific tissues and organs.
By the end of this period the main organ systems have been established

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4
Q

what are the germ layers

A

ectoderm
mesoderm
endoderm

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5
Q

period of the fetus

A

fetal period from the beginning of 3rd month to birth. Period for maturation of embryonic organ systems and tissues

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6
Q

what are the different periods of pregnancy?

A

period of egg
period of embryo
period of fetus

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7
Q

when is the most risky time of pregnancy?

A

up to week 8 as there can be major morphologic abnormalities

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8
Q

when are primordial germ cells formed

A

they are specialised germ cells that are formed a generation earlier when the parents were embryos

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9
Q

what is the purpose of gametogenesis?

A

reduces chromosomal number to haploid

enhances genetic variability through random recombination

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10
Q

Pluripotent stem cells

A

embryonic stem cells
has the ability to form all mature cell types in the body except placental and extraembryonic cells
cannot form a whole organism

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11
Q

multipotent stem cell

A

adult stem cells
has the ability to form more than one closely related mature cell types in the body but not as varied as pluripotent cells
e.g. cord blood, bone marrow stem cells form erythrocyte, leucocyte and platelet

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12
Q

totipotent stem cells

A

has the ability to form all differentiated cell types in the body including placental and extraembryonic membrane cells. It could form a whole organism - e.g. zygote and first few generations of blastomeres

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13
Q

Clinical implications of gametogenesis

A

errors in gametogenesis could lead to chromosomal abnormalities that could result in birth defects or spontaneous abortions
errors in spermatogenesis could lead to spermatozoa morphological abnormalities that could affect male fertility

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14
Q

fertilisation

A

the process by which male and female gametes fuse to form a zygote, it occurs in the ampullary region of uterine tube/ oviduct

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15
Q

what are the phases of fertilisation?

A

phase 1 - penetration of corona radiate
phase 2 - penetration of zona pellucida
phase 3 - fusion of oocyte and sperm cell membranes

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16
Q

Draw the structure of an ovum

A

check from online diagram

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17
Q

Draw the structure of a sperm

A

check from online diagram

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18
Q

what is capacitation?

A

occurs in the female reproductive tract.
involves epithelial interactions between the sperm and mucosal surface of uterine tube - glycoprotein coat and seminal plasma proteins are removed from plasma membrane that overlies the acrosomal region of spermatozoa
only capacitated sperm can pass through the corona cells and undergo the acrosome reaction

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19
Q

acrosome reaction

A

induced by the zona proteins following binding of the acrosomal region of sperm with zona pellucida of oocyte. Acrosome reaction leads to release of enzymes needed to penetrate the zona pellucida

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20
Q

Cortical and zona reactions

A

following release of acrosome enzymes the sperm is able to penetrate the zona. The sperm’s contact with the plasma membrane of oocyte leads to release of lysosomal enzymes from cortical granules in the plasma membrane which becomes impenetrable to other spermatozoa. It also causes changes in permeability of zona pellucida. The enzymes alter the structure and composition of the zona pellucida to prevent polyspermy

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21
Q

what is the zona

A

glycoprotein shell surrounding oocyte that facilitates and maintains sperm binding

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22
Q

what is the purpose of fertilisation?

A

restores diploid chromosome number
zygote is produced after fertilisation and has a unique genome
it activates the egg to commence subsequent embryological development

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23
Q

clinical implications of fertilisation

A

physiological processes and anatomical framework relating to the release of gametes and fertilisation are used as basis for most contraceptive methods
male infertility could result from quality and quantity of sperm ejaculated
female infertility could result from a number of causes
infertility in males and females could be treated with various forms of Assisted Reproductive Technology

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24
Q

Cleavage

A

repeated series of rapid mitotic cell divisions of the large zygote to produce an increasing number of smaller daughter cells - blastomeres

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25
principles of cleavage
does not result in growth as there is no increase in protoplasmic mass it increases the nucleocytoplasmic ratio, with each cleavage the cytoplasm is partitioned as nuclei are replicated leading to increased number of smaller cells which approach the size of a typical body cell
26
what does cleavage form?
transforms the zygote into a solid ball of cells = morula after 12-16 cells stage within 3 days of fertilisation
27
purpose of cleavage
to generate a multicellular embryo - morula from a single large cell - zygote.
28
what is a morula?
solid ball (mulberry) of 12-16 cells (blastomeres)
29
what is compaction?
process of reorganisation and segregation of cells into inner cell mass and outer cell mass following cleavage it involves the establishment of inside-outside polarity and increase maximised cell-to-cell contact
30
what is the inner cell mass of embryo?
embryoblast
31
what is the outer cell mass of embryo?
trophoblast
32
what is a blastocyst?
a stage when the morula develops a fluid filled cavity - blastocoel with a compact inner cell mass at one side of the cavity - embryonic pole enclosed by a thin single- layered epithelium of trophoblast
33
what is parthenogenesis?
process where an unfertilised egg goes on to develop into a new individual
34
embryonic germ disc
cluster of embryonic cells (inner cell mass) at the embryonic pole of the blastocyst that gives rise to tissues of the embryo proper
35
what is the bilaminar embryonic germ disc?
outer and inner layers of the inner cell mass outer = epiblast inner = hypoblast following segregation of the blastomeres the outer cell mass mass forms the trophoblast which contributes to formation of the placenta and other fetal membranes inner cell mass gives rise to tissues of the embryo proper and the cells = embryoblast and constitute the germ disc.
36
what makes up the bilaminar embryonic germ disc?
2 layers of the embryoblast - epiblast and hypoblast
37
what does the bilaminar embryonic germ disc do?
establishes and defines the primitive dorsal-ventral axis of the embryo epiblast = dorsal hypoblast = ventral
38
primitive streak
transient thickened longitudinal midline structure at caudal end of epiblast of bilaminar embryonic germ disc which forms on day 15 of developing embryo it has a narrow depression - primitive groove with bulging regions either side at the cephalic/cranial end it is the primitive node - surrounds a small circular depression - primitive pit that is continuous with the primitive groove
39
role of primitive streak
a morphogenic inductive centre development marks the start of gastrulation defines all major body axes of developing embryo
40
what axes does the primitive streak define?
cranial-caudal medial-lateral left-right dorsal-ventral
41
What is gastrulation?
the process of epiblastic cells moving through the primitive streak - leads to transformation of the bilaminar germ disc into a trilaminar germ disc
42
What constitutes the trilaminar germ disc?
ectoderm mesoderm endoderm
43
process of gastrulation
commences with formation of primitive streak on 15th day, epiblastic cells ingress or invaginate through the primitive streak to form the mesoderm and endoderm while the remaining epiblastic cells become the ectoderm
44
purpose of gastrulation
formation of primitive streak and establishment of body axes | formation of embryonic body plan
45
clinical implications of errors of gastrulation
``` caudal dysplasia/ caudal regression syndrome/ caudal or sacral agenesis e.g. sirenomelia Dextrocardia laterality and heart defects ventricular septal defects atrial septal defects double outlet right ventricle ```
46
what is sirenomelia
infants born with partial or complete fusion of the legs- mermaid syndrome
47
What is caudal dysplasia
congenital disorder in which fetal development of the lower spine is abnormal
48
What is dextrocardia?
where the heart is positioned on the right side
49
what are laterality and heart defects?
disruption of the laterality pathway in specifying left and right sidedness in the progenitor heart cells causes many different types of heart defects such as: ventricular septal defects atrial septal defects double outlet right ventricle
50
clinical implications of errors of gastrulation
outflow tract defects - transposition of great vessels, pulmonary stenosis atrial and ventricular isomerisms atrial and ventricular inversions situs inversus and dextrocardia
51
embryonic body plan and folding
formation of the body plan involving extensive folding of the embryo embryonic body folding separates the embryo from its extraembryonic membranes - amnion and yolk sac converts the flat embryonic disc into a 3D body plan
52
germ layers
``` endoderm extraembryonic mesoderm intraembryonic mesoderm ectoderm notochord - structural element that forms part of vertebrae ```
53
what is the placenta?
meeting point of fetal and maternal circulations
54
role of placenta
serves as the fetal lungs, kidneys and GI tract protective barrier hormone synthesis
55
what does the placenta develop from?
trophoblast
56
whom does the placenta belong to?
fetus
57
layers of trophoblast
trophoblast splits into 2 layers - syncytiotrophoblast and cytotrophoblast
58
syncytiotrophoblast
direct contact with maternal blood outer layer of multiple fused trophoblast cells specialised systems for maternal - fetal transport barrier to unwanted material hormone secretion
59
Crytotrophoblast
``` inner layer with specialised functions: proteolytic enzyme secretion endometrial invasion villous formation angiogenesis ```
60
where are the 2 layers of the trophoblast?
Syncytiotrophoblast on the outside only on the side of the embryo that implants into the uterus wall Cytotrophoblast underneath the syncytiotrophoblast but surrounds the whole embryo
61
what is the blood supply of the uterus?
mainly supplied by uterine artery which is a branch of the internal iliac also contribution from ovarian artery arcuate artery runs circumferentially in myometrium spiral arteries invaded by cytotrophoblast cells and remodelled to create a low resistance/ high flow pathway
62
what mechanisms contribute to vascular development of the uterus?
growth factors cytokines angiotensin II natural killer cells
63
what happens to spiral arteries?
they funnel to generate a wide outflow into the intervillous space facilitated by NKs and extravillous cytotrophoblast cells endothelium is replaced by endovascular cytotrophoblast cells
64
vascular development of fetus
villi grow into intervillous space, which are well -perfused with fetal blood from umbilical vessels covered by microvilli creating a large surface area
65
placental villi
project into intervillous space and create large surface area for gas exchange there is a layer of syncytiotrophoblast covering the vessels
66
blood flow between mother and fetus
2 separated flows so are not in direct contact
67
blood supply of mother
in intervillous space pressire = 10-15mmHg flow = 500-600mL/min uterine contractions compromise flow
68
blood supply of fetus
capillary pressure = 30mmHg | flow = 450 mL/min at term
69
anatomy of placenta
weighs 20% of fetus size of dinner plate 15-20 discrete sections - cotyledons covered in 2 smooth membranes - amnion and chorion central umbilical cord insertion the exposed rough surface is adhered to the uterine wall
70
umbilical cord anatomy
carries fetal blood 2 arteries - deoxygenated from fetus to placenta 1 vein - oxygenated from placenta to fetus come from internal iliacs
71
what happens to placenta when there are multiple fetuses?
monochorionic diamniotic twins - share placenta but have separate amnions 2 cord attachments monchorionic triplets - 2 umbilical connections off one placenta
72
where is the placenta located?
superior to fetus on ultrasound
73
hormone activity of placenta
hCG - produced from blastocyst and supports pregnancy Oestrogen - production co-dependent on fetal adrenal function progesterone - produced independently by placenta human placental lactogen - anti-insulin action makes more glucose available for fetus other growth hormones - placental growth factor and insulin-like growth factors
74
transfer function of placenta
``` O2/ CO2 nutrients = glucose and lipids waste products = urea and bilirubin hormones = cortisol immunological = antibodies drugs ```
75
drug transfer across placenta
some drugs will be able to cross the placenta and impact the fetus, doctors have to consider this when prescribing drugs to pregnant women
76
placental transfer mechanisms
``` passive diffusion facilitated diffusion active transport endo/pinocytosis osmosis ```
77
what transfers across the placenta via passive diffusion?
steroids fatty acids fat soluble, small and unionised
78
what transfers across the placenta via facilitated diffusion?
glucose | mainly via GLUT1 - insulin independent
79
what transfers across the placenta via active transport
amino acids iron calcium specific mechanisms for each
80
what transfers across the placenta via endo/pinocytosis
immunoglobulins | only IgG - small
81
What transfers across the placenta via osmosis?
water - follows electrolyte movement
82
placental transfer of O2/CO2
simple diffusion
83
what aids fetal oxygen carriage?
polycythaemia higher oxygen affinity of fetal haemoglobin bohr effect - shoft in haemoglobin oxygen curve by changes in local environment
84
placenta as barrier
against microbes less efficient in early pregnancy when fetal immune system is less developed so infection risk is higher - rubella, CMV, toxoplasmosis maternal antibodies offer additional immune protection
85
maternal immune system
fetus is a foreign tissue slight immunosuppression prevents rejection maternal auto-immune disease may lead to recurrent miscarriages
86
what are the mechanisms of immunosuppression in pregnant mothers
placental secretion of phosphocholine - immune cloak trophoblast has reduced antigenic expression suppression of maternal cytotoxic T cell activity placental barrier to maternal lymphocytes
87
Rhesus diseasen
occurs when fetus is rhesus positive and mother is rhesus negative exposure to fetus blood during delivery triggers antibody production. antibodies are then in the maternal blood and can cause problems for future rhesus positive pregnancies as the antibodies cause haemolysis
88
why can only rhesus antigen cause fetal haemolytic disease?
because ABO antibodies are IgM so too large to cross the placenta Rh D antibodies are IgG so small enough to cross
89
How is rhesus disease presented?
anti-D is given to rhesus -ve mothers to prevent sensitisation - routinely at 28/34 weeks within 74 hrs postpartum if baby is Rh +ve at times of likely exposure - amniocentesis and termination
90
common abnormalities in placenta/ umbilical cord
placental praevia placental abruption prolapsed cord pre-eclampsia
91
placental praevia
placenta lies close/ across cervix 4 grades presents with bleeding during pregnancy normally painless
92
placental abruption
bleeding in plane between placental and uterus normally painful bleeding can be revealed - tracks down to cervix or concealed - behind placenta life-threatening for fetus
93
prolapsed cord
cord bulges through cervix when membranes rupture | fetal head compresses cord during contractions cutting off umbilical flow
94
pre-eclampsia
complex disease originating in placenta leading to multiple problems for mother and baby
95
how does pre-eclampsia occur?
placental vessels fail to develop normally placental perfusion becomes inadequate this is interpreted as shock from blood loss causes vasoconstricting substances to be released
96
what happens in pre-eclampsia?
``` hypertension fluid retention coagulopathy renal damage convulsions liver damage growth retardation ```

Physiology 2 (20 decks)

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