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Human Development > Implantation and Placental Function > Flashcards

Implantation and Placental Function Flashcards

1
Q

How can you tell if you are pregnant by using progesterone

A
  • day 21 progesterone level should be greater than 30mmol-1 per litre
  • if it is less than 30mmol-1 then pregnancy hasn’t happened
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2
Q

where does fertilisation take place

A

oviduct

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3
Q

where does implantation takes place

A

uterus

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4
Q

What are the two ways in which the embryo signals the mother

A
  1. It establishes a physical and nutritional contact, this is required for a supply of nutrients leading to growth – this is placentation
  2. It signals its presence to the mother, by preventing luteal regression this is called maternal recognition of pregnancy
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5
Q

what are the key stages in implantation

A
  1. first differentiation step
  2. apposition
  3. adhesion
  4. invasion
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6
Q

describe the key stages in implantation

A
  1. First differentiation step
    - About 6 days after fertilisation the cells of the blastocyst will have differentiated into the outer cell layer – the trophectoderm and the inner cell mass, the trophectoderm will become the placenta and the inner cell mass the foetus
  2. Apposition
    - This is the positioning of the blastocyst within the uterine cavity
  3. Adhesion
    - The cells of the trophoblast fix to maternal tissues and to each other
    - This is achieved via a group of cell adhesion molecules including lamin and fibronectin together with cell surface receptor for these molecules
  4. Invasion
    - The trophoblast, through proteolytic processes, penetrates into the maternal decidua and endometrial spiral arteries
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7
Q

when do trophoblasts differetnate

A

day 6-7

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8
Q

what do trophoblasts differentiate into

A

blastocysts - these attach to the uteruine wall

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9
Q

what two things do trophectoderm differentiate into

A

cytotrophoblast and syncytiotrophoblast

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10
Q

describe cytotrophoblast

A
  • Have single nucleus

- Divide rapid in vivio

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11
Q

describe syncytiotrophoblast

A
  • Derived from fused cytotrophoblasts
  • Multinucleated
  • Do not divide
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12
Q

describe how the placental formation take place

A
  • Trophoblasts form villous stuctures
  • Cytotrophoblasts break through trophoblast shell
  • Invade through decidual tissue
  • Trophoblasts reach maternal spiral arteries
  • Spiral arteries are converted from narrow to wide vessels – happens when the cytotrophoblasts reach the spiral arteries
  • This allows a much greater flow of maternal blood around the villi
  • Villous trophoblast is the barrier between maternal and foetal circulation
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13
Q

what are the spiral arteries converted form narrow to wide vessels in the placental formation

A
  • this happens when the cytotrophoblasts reach the spiral arteries
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14
Q

maternal and foetal blood….

A

blood never mix and there are always cells between them

- the Villous trophoblast is the barrier between maternal and foetal circulation

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15
Q

what is the blood supply like during early development

A
  • At the early stage of development there is very little maternal blood supply to the embryo, the embryo exists in a relatively hypoxic environment
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16
Q

what is smooth muscle and endothelium replaced by in a spiral artery

A
  • it is replaced by the trophoblast cells in a spiral artery
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17
Q

what happens if fertilisation and implantation occur

A
  1. Corpus luteum does not degenerate because of hCG.
  2. Progesterone levels do not fall because progesterone secretion is maintained by the corpus luteum (oestrogen levels do not fall either)
  3. Progesterone maintains the endometrium and becomes what is called the decidua.
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18
Q

what can cause a miscarriage

A
  • hCG is produced immediately and goes up to 8-10 weeks of pregnancy and then fall dramatically, doesn’t stop being secreted till after deliveiry
  • if the hormones don’t match up then it is a miscarriage
  • round about 12 weeks you have a luteal placental shift, if the two things don’t match up then the endometrium will start to break down and you get a miscarriage
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19
Q

what is an ecotopic pregnancy

A
  • pregnancies that implant in the oviduct of the fallopian tube most commonly they can happen elsewhere
20
Q

what is a placental praaevia

A
  • this is when the placenta goes over the cervix
    – don’t want it over the cervix because then the mother can’t give birth while in labour and she will haemorrhage – have Caesarion in order to give birth
21
Q

describe the structure of the placenta

A
  • Discoid diam 15-20cm
  • Weight approx 500g
  • Thickness 2.5cm at the centre
22
Q

describe the position of the placenta

A

upper uterine segment 99.5%
posterior surface 2/3
anterior surface 1/3

23
Q

what aerate surfaces of the placenta

A
  • foetal – smooth, glistening and covered in aminion
  • umbilicila cord is inserted in the centre with vessels radiating from it
  • maternal - dull, greyish and divided into 15-20 cotyledons
  • Each cotyledon is formed of branches of one main villus stem covered by the decidua basalis
24
Q

where does the amniotic fluid come form

A

aminon

- it is supplemented by lung secretions and urine

25
Q

how many arteries and veins go to the placental fetes

A
  • 2 x umbilical arteries to the placenta

- and one umbilical vein

26
Q

what do the arteries and veins take to the placental foetus

A
  • there are umbilical arteries which there are 2 of they carry away the waste and carbon dioxide, the umbilical vein takes oxygen and nutrients to the baby
27
Q

where is the main site of exchange in the placenta

A
  • main site of exchange are capillary networks in terminal branches of chorionic villi
28
Q

why is the placenta necessary

A
  • Foetus requires nutrition

- Luteal regression needs to be prevented

29
Q

what is the function of the placenta

A
  • Site for exchange of gases (02 and C02) and other molecules between maternal and fetal blood
  • Nutrient exchange
  • Waste exchange – carbon dioxide, urea, metabolic waste, bilirubin
  • Synthesis of proteins and enzymes
30
Q

describe other things in the foetal blood supply

A
  • 80 - 100 spiral arteries open directly into the intervillous spaces
  • Low pressure blood (10mmHg in the relaxed uterus)
  • Return via venous pathways in decidual plate of placenta
31
Q

how often is blood exchanged

A
  • Villi bathed in maternal blood (the blood is exchanged 3-4 times a min)
32
Q

foetal haemoglobin has a …

A
  • Fetal haemoglobin has more affinity and carrying capacity than adult haemoglobin
33
Q

what does the rate of diffusion of gas between the maternal and foetal blood depend on

A

Rate of diffusion depends on

  • maternal/fetal gases gradient
  • maternal and fetal blood flow
  • placental permeability
  • placental surface area
34
Q

how are substances diffused across the placenta

  • H20 and electrolytes
  • Glucose
  • Amino acids
  • Fatty acids
  • Large proteins and cells
  • Waste products
A
  • H20 and electrolytes - simple diffusion
  • Glucose - facilitated diffusion via glucose transporter proteins (GLUTs)
  • Amino acids - active transport via transporter proteins (accumulative or exchangers)
  • Fatty acids – simple diffusion
  • Large proteins and cells – pinocytosis
  • Waste products, eg urea – simple diffusion
35
Q

what does the placenta allow through it

A
  • IgG antibodies
  • Hormones
  • Antibiotics
  • Sedatives
  • some viruses, eg rubella
  • some organisms, eg treponema pallida (syphilis)
36
Q

what does the placenta not allow through it

A

the placental will not let large molecules such as heparin and insulin through

37
Q

what foetal related cells can cross the placenta

A
  • granulocytes
  • trophoblasts cells
  • nucleated red blood cells
  • primitive counterparts
  • lymphocytes
  • gametocytes
38
Q

describe what happens when you are rhesus negative and your baby is rhesus positive

A
  • in the first pregnancy the red blood cells from the fetus will go into the maternal circulation and there is sensitisation to the fetal cells but there is no response
  • in the second pregnancy the antibodies from the mother will pass to the baby and destroy the red blood cells
  • happens when the mother is rhesus negative and baby is rhesus positive
39
Q

what is the placenta do in terms of endocrine function

A

The placenta is an important endocrine organ for pregnancy – it produces both protein and steroid hormones

40
Q

what does hCG do (human chorionic gonadotropin)

A
  • synthesis of hCG begins before implantation
  • maintains corpus luteum = progesterone and oestrogen secretion during early pregnancy
    resembles LH
41
Q

what does hPL do (Human placental lactogen)

A
  • increases free fatty acids by its lipolytic action
  • inhibits gluconeogenesis
  • it promotes fetal growth
  • it promotes mammary duct proliferation
  • exhibits lactogenic effects
  • resembles GH
42
Q

describe the changes that the placenta goes through when producing oestrogen and progesterone

A
  • Placenta produces progesterone and oestrogen from cholesterol precursors and in concert with the fetal adrenal gland
  • By the end of the first trimester, the placenta produces enough to maintain pregnancy and the corpus luteum is no longer needed.
43
Q

what does human placental growth hormone do

A

Regulation of maternal blood glucose levels to ensure adequate fetal glucose supply
low maternal blood glucose levels = gluconeogenesis in the maternal liver

44
Q

what does insulin like growth factor do

A
  • Similar structure to insulin

- Stimulates proliferation and differentiation of the cytotrophoblast.

45
Q

what does relaxin do and what produces it

A

Produced by decidual cells

Softens the cervix and pelvic ligaments in preparation for childbirth.

46
Q

why is the foetus not rejected by the maternal immune system

A
  1. HLA expression – trophoblast cells express HLA G this is not recognised by the maternal system so it is not rejected
  2. Infiltrating leucocytes secrete IL-2 which regulates the immune system
  3. Decidual reaction when the decidual cells become swollen and tightly compacted together around the developing fetus thus forming a barrier between mother and implanting embryo
47
Q

what are pathologies that are associated with abnormal placental development

A
  • Pre-eclampsia
  • Intrauterine growth restriction
  • Early miscarriage

Human Development (28 decks)

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