Term
| after fertilisation rapid mitotic division of the zygote takes place. What is this known as? |
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Definition
cleavage.
the first division of the zygote begins about 24 hours after fertilisation and is completed about 6 hours later
By day 2 the 2nd cleavage is complete and there are four cells |
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Term
| by the end of the 3rd day of fertilisation there are 16 cells. the progressivley smaller cells produced by cleavge are known as what? |
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Definition
blastomeres.
successive cleavages produce a solid sphere of cells called a morula |
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Term
| when the morula enters the uterine cavity on day 4 or 5, a glycogen rich secretion (uterine milk) from the glands of the endometrium of the uterus passes into the uterine cavity and enters the morula through which part? |
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Definition
zona pellucida.
the uterine milk provides nouishment for the morula. At 32-cell stage this fluid enters the morula collecting between the blastomeres and reorganising them around a fluid filled cavity called the blastocyst cavity |
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Term
| during the formation of the blastocyst two distinct cell populations arise. what are they? |
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Definition
embryoblast AKA inner cell mass - located internally and develops into the embryo
trophoblast - the outer layer of cells forming wall of blastocyst. will form the outer chorionic sac surrounding the fetus and fetal portion of placenta. |
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Term
| on the 5th day the blastocyst hatches from the zona pellucida by digesting a hole in it and squeezing out. what is the next step? |
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Definition
Implantation.
attatchment into the vascular, glandular endometrial lining of the uterus |
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Term
| about 8 days post fertlisation, the trophoblast develops into 2 layers in the region between the blastocyst and the endometrium. name the two layers please |
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Definition
Syncytiotrophoblast - this contains no disctint cell boundaries
Cytotrophoblast - this forms between the embryoblast and the synctiotrophoblast and composed of distinct cells. |
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Term
| what do the two layers of the trophoblast become as they develop? |
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Definition
part of the chorion (one of the fetal membranes)
during implantation the synctiotrophoblast secrete enzymes(hyaluroniase) that let the blastocyst penetrate the uterus lining. |
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Term
| what secretes human chorionic gonadotrophin? |
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Definition
trophoblasts.
hCG has actions similar to LH. prevents degeneration of corpus luteum and sustains its progesterone and estrogen secretion. |
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Term
| during pregnancy the corpus luteum secretes progesterones and estrogens with help of hCG secreted from trophoblasts. what do these hormones do? (progesterone and estrogen) |
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Definition
| keep uterine lining in a secretory state, preventing periods |
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Term
| the embryoblast also differentiates into 2 layers. what are they? |
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Definition
hypoblast - primitive endoderm
epiblast - primitive ectoderm
together these form a flat disc known as the bilaminar embryonic disc
a small cavity appears in the epiblast enlargening to form the amniotic cavity |
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Term
| as the amniotic cavity enlargens a single layer of squamous cells form a domelike roof above the epiblast called the..... |
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Definition
amnion.
thus the amnion forms the roof of the amniotic cavity and the epiblast forms the floor |
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Term
| where do ectopic pregnanices occur? |
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Definition
in oviduct or body cavity
0.6% of pregnancies
symptoms : abdominal pain, uterine bleeding and a slower than normal rise in serum hCG |
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Term
| describe Gestational trophoblastic neoplasias |
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Definition
it happens 1 in 1000 conceptions
hydatidiform mole is benign
choriocarcinoma - malignant and may metastisise, may be fatal
with this condition you get high levels of hCG |
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Term
| when does the UK Human Fertilisation and Embryology Act 1990 forbid keeping or using a human embryo? |
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Definition
After the appearance of the primitive streak or after 14 days, whichever is earlier.
the primitive streak is the first sign of gastrulation where the embryonic disc forms the primary germ layers |
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Term
| how would nutrients get to the embryo on day 14 post fertilisation? |
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Definition
they can diffuse
3 weeks post fertilisation is when the heart starts beating and blood vessels form |
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Term
| characteristics of a 4 week fetus |
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Definition
5mm
20mg
heart beating
trachea, lungs, liver, pancreas
no kidneys waste discarded via allantois |
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Term
| characteristics of an 8 week fetus |
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Definition
28mm
2.7g
nail beds, sweat glands, hair follicles, cartilage, fingers, toes, thymus, thyroid, pituitary
embryonic kidney (metanephros)
@9weeks gonads differentiate
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Term
characteristics of 12 week fetus
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Definition
78mm
26g
epidermis, bone, CNS, brain and spinal cord
gall bladder
external genitalia |
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Term
| drugs such as teratogens are a risk in the first trimester. what is the effect of teratogens? |
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Definition
| Teratogens are substances or environmental agents which cause the development of abnormal cell masses during fetal growth, resulting in physical defects in the fetus. |
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Term
| smoking, alcohol and rubella virus are all risks in the first trimester. what consequences arise if a mother to be contracts rubella in the first trimester? |
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Definition
| Infection of the mother by Rubella virus during pregnancy can be serious; if the mother is infected within the first 20 weeks of pregnancy, the child may be born with congenital rubella syndrome(CRS) Spontaneous abortion may occur or baby may be still born. If the baby survives the infection, it can be born with severe heart disorders (Patent ductus arteriosus being the most common), blindness, deafness, or other life threatening organ disorders. |
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Term
| what is Patent Ductus Arteriosus (PDA)? |
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Definition
| Patent Ductus Arteriosus (PDA) is a congenital disorder in the heart wherein a neonate's ductus arteriosus fails to close after birth |
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Term
| the following are condtions associated with congenital rubella syndrome |
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Definition
cataract, glaucoma, retinitis and microphthalmos
sever bilateral deafness
patent ductus arteriosus, pulmonary stenosis, atrial septal defect, ventricular septal defect, valvular aortic stenosis and pulmonary hypertension,
thrombocytopenia, microcephalgy, mental retardation, growth retardation and late onset diabetes mellitus |
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Term
| what is Alpha-foetoprotein? (AFP) |
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Definition
AFP is a major plasma protein produced by the yolk sac and the liver during fetal development that is thought to be the fetal form of serum albumin.
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Term
| what can alpha-foetoprotein measure? |
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Definition
AFP is measured in pregnant women through the analysis of maternal blood or amniotic fluid, as a screening test for developmental abnormalities. It is increased in open neural tube defects and omphalocele and is decreased in Down syndrome
Elevation of AFP is used as one factor in the diagnosis of ataxia telangiectasia
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Term
define omphalocele
and ataxia telangiectasia |
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Definition
An omphalocele is a type of hernia, a a birth defect in which the infant's intestine or other abdominal organs stick out of the belly button.
Ataxia telangiectasia AKA Louis–Bar syndrome is a rare, neurodegenerative, inherited disease causing severe disability. Ataxia refers to poor coordination and telangiectasia to small dilated blood vessels, both of which are hallmarks of the disease |
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