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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
Q

principles of cleavage

A

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

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26
Q

what does cleavage form?

A

transforms the zygote into a solid ball of cells = morula after 12-16 cells stage within 3 days of fertilisation

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27
Q

purpose of cleavage

A

to generate a multicellular embryo - morula from a single large cell - zygote.

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28
Q

what is a morula?

A

solid ball (mulberry) of 12-16 cells (blastomeres)

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29
Q

what is compaction?

A

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

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30
Q

what is the inner cell mass of embryo?

A

embryoblast

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31
Q

what is the outer cell mass of embryo?

A

trophoblast

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32
Q

what is a blastocyst?

A

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

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33
Q

what is parthenogenesis?

A

process where an unfertilised egg goes on to develop into a new individual

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34
Q

embryonic germ disc

A

cluster of embryonic cells (inner cell mass) at the embryonic pole of the blastocyst that gives rise to tissues of the embryo proper

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35
Q

what is the bilaminar embryonic germ disc?

A

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.

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36
Q

what makes up the bilaminar embryonic germ disc?

A

2 layers of the embryoblast - epiblast and hypoblast

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37
Q

what does the bilaminar embryonic germ disc do?

A

establishes and defines the primitive dorsal-ventral axis of the embryo
epiblast = dorsal
hypoblast = ventral

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38
Q

primitive streak

A

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

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39
Q

role of primitive streak

A

a morphogenic inductive centre
development marks the start of gastrulation
defines all major body axes of developing embryo

40
Q

what axes does the primitive streak define?

A

cranial-caudal
medial-lateral
left-right
dorsal-ventral

41
Q

What is gastrulation?

A

the process of epiblastic cells moving through the primitive streak - leads to transformation of the bilaminar germ disc into a trilaminar germ disc

42
Q

What constitutes the trilaminar germ disc?

A

ectoderm
mesoderm
endoderm

43
Q

process of gastrulation

A

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
Q

purpose of gastrulation

A

formation of primitive streak and establishment of body axes

formation of embryonic body plan

45
Q

clinical implications of errors of gastrulation

A 
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
Q

what is sirenomelia

A

infants born with partial or complete fusion of the legs- mermaid syndrome

47
Q

What is caudal dysplasia

A

congenital disorder in which fetal development of the lower spine is abnormal

48
Q

What is dextrocardia?

A

where the heart is positioned on the right side

49
Q

what are laterality and heart defects?

A

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
Q

clinical implications of errors of gastrulation

A

outflow tract defects - transposition of great vessels, pulmonary stenosis
atrial and ventricular isomerisms
atrial and ventricular inversions
situs inversus and dextrocardia

51
Q

embryonic body plan and folding

A

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
Q

germ layers

A 
endoderm
extraembryonic mesoderm
intraembryonic mesoderm
ectoderm
notochord - structural element that forms part of vertebrae
53
Q

what is the placenta?

A

meeting point of fetal and maternal circulations

54
Q

role of placenta

A

serves as the fetal lungs, kidneys and GI tract
protective barrier
hormone synthesis

55
Q

what does the placenta develop from?

A

trophoblast

56
Q

whom does the placenta belong to?

A

fetus

57
Q

layers of trophoblast

A

trophoblast splits into 2 layers - syncytiotrophoblast and cytotrophoblast

58
Q

syncytiotrophoblast

A

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
Q

Crytotrophoblast

A 
inner layer with specialised functions:
proteolytic enzyme secretion 
endometrial invasion
villous formation
angiogenesis
60
Q

where are the 2 layers of the trophoblast?

A

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
Q

what is the blood supply of the uterus?

A

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
Q

what mechanisms contribute to vascular development of the uterus?

A

growth factors
cytokines
angiotensin II
natural killer cells

63
Q

what happens to spiral arteries?

A

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
Q

vascular development of fetus

A

villi grow into intervillous space, which are well -perfused with fetal blood from umbilical vessels
covered by microvilli creating a large surface area

65
Q

placental villi

A

project into intervillous space and create large surface area for gas exchange
there is a layer of syncytiotrophoblast covering the vessels

66
Q

blood flow between mother and fetus

A

2 separated flows so are not in direct contact

67
Q

blood supply of mother

A

in intervillous space pressire = 10-15mmHg
flow = 500-600mL/min
uterine contractions compromise flow

68
Q

blood supply of fetus

A

capillary pressure = 30mmHg

flow = 450 mL/min at term

69
Q

anatomy of placenta

A

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
Q

umbilical cord anatomy

A

carries fetal blood
2 arteries - deoxygenated from fetus to placenta
1 vein - oxygenated from placenta to fetus
come from internal iliacs

71
Q

what happens to placenta when there are multiple fetuses?

A

monochorionic diamniotic twins - share placenta but have separate amnions
2 cord attachments
monchorionic triplets - 2 umbilical connections off one placenta

72
Q

where is the placenta located?

A

superior to fetus on ultrasound

73
Q

hormone activity of placenta

A

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
Q

transfer function of placenta

A 
O2/ CO2
nutrients = glucose and lipids 
waste products = urea and bilirubin
hormones = cortisol
immunological = antibodies
drugs
75
Q

drug transfer across placenta

A

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
Q

placental transfer mechanisms

A 
passive diffusion
facilitated diffusion
active transport
endo/pinocytosis
osmosis
77
Q

what transfers across the placenta via passive diffusion?

A

steroids
fatty acids
fat soluble, small and unionised

78
Q

what transfers across the placenta via facilitated diffusion?

A

glucose

mainly via GLUT1 - insulin independent

79
Q

what transfers across the placenta via active transport

A

amino acids
iron
calcium
specific mechanisms for each

80
Q

what transfers across the placenta via endo/pinocytosis

A

immunoglobulins

only IgG - small

81
Q

What transfers across the placenta via osmosis?

A

water - follows electrolyte movement

82
Q

placental transfer of O2/CO2

A

simple diffusion

83
Q

what aids fetal oxygen carriage?

A

polycythaemia
higher oxygen affinity of fetal haemoglobin
bohr effect - shoft in haemoglobin oxygen curve by changes in local environment

84
Q

placenta as barrier

A

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
Q

maternal immune system

A

fetus is a foreign tissue
slight immunosuppression prevents rejection
maternal auto-immune disease may lead to recurrent miscarriages

86
Q

what are the mechanisms of immunosuppression in pregnant mothers

A

placental secretion of phosphocholine - immune cloak
trophoblast has reduced antigenic expression
suppression of maternal cytotoxic T cell activity
placental barrier to maternal lymphocytes

87
Q

Rhesus diseasen

A

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
Q

why can only rhesus antigen cause fetal haemolytic disease?

A

because ABO antibodies are IgM so too large to cross the placenta
Rh D antibodies are IgG so small enough to cross

89
Q

How is rhesus disease presented?

A

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
Q

common abnormalities in placenta/ umbilical cord

A

placental praevia
placental abruption
prolapsed cord
pre-eclampsia

91
Q

placental praevia

A

placenta lies close/ across cervix
4 grades
presents with bleeding during pregnancy
normally painless

92
Q

placental abruption

A

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
Q

prolapsed cord

A

cord bulges through cervix when membranes rupture

fetal head compresses cord during contractions cutting off umbilical flow

94
Q

pre-eclampsia

A

complex disease originating in placenta leading to multiple problems for mother and baby

95
Q

how does pre-eclampsia occur?

A

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
Q

what happens in pre-eclampsia?

A 
hypertension
fluid retention
coagulopathy
renal damage
convulsions
liver damage 
growth retardation

Physiology 2 (20 decks)

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