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Body Logistics Flashcards

1
Q

What is embryology?

A

The study of progression from a single cell to a baby in 9 months.

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2
Q

Where does fertilisation usually occur?

A

In the ampullary region of the fallopian tube (also known as uterine tube)

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3
Q

Millions of sperm enter the female reproductive tract. Why does only one sperm fertilise the secondary oocyte?

A
  • Some die due to the acidic environment of the vagina
  • Cilia in the fallopian tube traps some sperm
  • Not all sperm have the optimum structure to allow them to swim through to the Fallopian tube
  • The secondary oocyte is covered in a protective layer of cells called the corona radiata. Only one sperm breaks through this and reaches the membrane as the corona radiata hardens after this occurs and the egg produces chemicals to prevent other sperm from entering.
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4
Q

When must sperm enter the female reproductive tract for fertilisation to occur?

A

5 days before ovulation

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5
Q

How long are sperm/secondary oocytes viable for?

A

Sperm=5 days

Secondary oocyte=12-24 hours

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6
Q

What do sperm require for fertilisation?

A

Capacitation- the tail of the sperm moves faster causing the plasma membrane to alter

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7
Q

How many cells does a zygote begin with?

A

2 cells

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8
Q

How does the egg and sperm combine to form a diploid set of chromosomes?

A

When the sperm reaches the membrane of the secondary oocyte, the membranes of the sperm and secondary oocyte fuse and the contents of the sperm enters the egg. The presence of the sperm pronuclei triggers the completion of meiosis II in the egg pronuclei. Microtubules pull the two pronuclei together to form a diploid set of chromosomes.

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9
Q

What are two potential mechanisms of a male contraceptive pill?

A
  1. Cell penetrating peptides that enter sperm and prevent them from moving.
  2. Blocking sperm power kick using a progesterone receptor antagonist. The progesterone receptor is on the sperms tail and the female hormone activates the receptor triggering a cascade of reactions that make the tail of the sperm move rapidly towards the egg.
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10
Q

Define embryonic age.

A

Time since fertilisation

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11
Q

Define gestational age.

A

Time since last menstruation. Embryonic age minus 2 weeks.

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12
Q

Define germinal stage.

A

Time from fertilisation to end of second week.

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13
Q

Define embryonic period.

A

Time from the third to end of eighth week

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14
Q

Define foetal period.

A

Time from beginning of ninth week to birth at 38 weeks.

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15
Q

What is hatching and why is it essential?

A

Hatching is the process of a blastocyst losing the zona pellucida. This is essential for implantation to occur.

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16
Q

What differentiates the morula and blastocyst?

A

Morula-By 3 to 4 days after fertilisation, the dividing cells of the embryo forms a spherical shape that looks like a mulberry.
Blastocyst-By 4 to 5 days after fertilisation, a cavity forms within this ball of cells.

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17
Q

When does implantation occur?

A

6th day after fertilisation

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18
Q

What is the function of the zona pellucida in the blastocyst/morula?

A

Prevents it from adhering to the oviduct
Stops morula from enlarging (limited food source) so cells divide by reduction division, more cells but overall structure remains the same size

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19
Q

Where does implantation usually occur?

A

Superior, posterior part of uterus in the endometrium

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20
Q

What is an ectopic pregnancy?

A

The blastocyst implants outside of the uterus, usually in one of the fallopian tubes.

21
Q

What is placenta previa?

A

The placenta is placed unusually low in the uterus. Caused by implantation of the blastocyst in the inferior part of the uterus.

22
Q

How do the morula and blastocyst acquire energy?

A

Anaerobic and aerobic pathways

Histiotrophic nutrition- not from maternal blood

23
Q

What is histiotrophic nutrition?

A

Nutrition provided to the embryo not from the maternal blood up to twelfth week after fertilisation.

24
Q

What is haemotrophic nutrition?

A

Nutrition provided by the mothers blood from twelfth week after fertilisation onwards.

25
What does the yolk sac and placenta develop from?
Trophoblast
26
Why is the second week of development known as the week of 2's?
Trophoblast differentiates into 2 layers: cytotrophoblast and syncytotrophoblast Embryoblast forms bilaminar disc: epiblast and hypoblast Hypoblast contributes to the formation of 2 cavities: yolk sac and chorionic cavity
27
What are teratogenic agents?
Capable of crossing placental barrier and disrupting development of the embryo during embryonic period to cause congenital malformation Viruses Ionising radiation Chemicals eg. Warfarin, thalidomide, isotretinoin (used to treat cystic acne), valproic acid
28
If teratogenic agents are exposed to the embryo during the germinal stage, what are the consequences?
Death of embryo
29
If teratogenic agents are exposed to the embryo during the embryonic period, what are the consequences?
Narrow windows during which different systems develop during this period so embryo is very sensitive and this can cause congenital malformations
30
What are the consequences of exposing an embryo to teratogenic agents after the embryonic period?
Risk of structural defects is very low, except for damage to CNS.
31
What is the difference between the syncytiotrophoblast and cytotrophoblast?
Syncytiotrophoblast- cells of trophoblast that merge together when the embryo becomes embedded in the uterine wall Cytotrophoblast- cells in trophoblast
32
How does the placenta form and when does this occur?
Day 11 Within the syncytiotrophoblast, lacunae form that merge together to form larger spaces. Capillaries in the endometrium dilate and become sinusoids. These capillaries merge with the syncytiotrophoblast and uterine glands appear that allow oxygenated blood and nutrients to flow in the spaces close to the embryo.
33
What happens during the second week of development?
Week of 2's Trophoblast differentiates into syncytiotrophoblast and cytotrophoblast Embryoblast forms epiblast and hypoblast (bilaminar embryonic disc) Hypoblast contributes to the formation of the yolk sac and chorionic cavity
34
How does the chorionic cavity form?
After the establishment of the uterine-placental circulation, a new population of cells (the embryonic mesoderm) appears between the cytotrophoblast and the primitive yolk sac. This and the hypoblast breaks down to form the chorionic cavity.
35
At the end of week 2 is the epiblast uniform disc or not?
Uniform disc
36
What is gastrulation? When does this occur?
Day 16. The bilaminar disc made up of epiblast and hypoblast is converted into a trilaminar disc made up of endoderm, mesoderm and ectoderm (derivatives of epiblast).
37
What determines the ultimate fate of invagination get epiblast?
Where in the primitive streak/node they invaginate into.
38
What does ectoderm, mesoderm and endoderm eventually form?
Ectoderm - organs and structures that maintain contact with the outside world eg. Nervous system, epidermis Mesoderm - supporting tissues eg. Muscle, cartilage, bone, vascular system (including heart and vessels) Endoderm- internal structures eg. Epithelial lining of GI tract, respiratory tract, parenchyma of glands
39
How does the uniform embryonic disc change to have left-right asymmetry?
During gastrulation, ciliated cells at the node of the primitive streak result in left-ward flow of signalling molecules Side-specific signalling cascades are initiated
40
What is situs inversus?
Complete mirror image viscera Commonly results from immotile cilia Problems usually only arise if there is both normal and mirror image viscera
41
What is the role of the notochord?
Solid rod of cells running in the midline of the mesoderm with an important signalling role. Directs the conversion of overlying ectoderm into neuroectoderm Slipper shape neural plate forms Edges of neuroectoderm elevate out of the plane of the disk and curl towards each other creating the neural tube
42
What are somites?
Organisation of paraxial mesoderm into segments either side of the neural tube. Somites form the building blocks of the musculoskeletal system.
43
What are the derivatives of somite?
Dermatome - dermis Myotome - muscles Sclerotium - bones
44
What is segmentation?
Organisation of mesoderm into somites gives rise to repeating structures eg, vertebrae, ribs, intercostal muscles, spinal cord segments. This guides innervation.
45
How many somites does an embryo have?
42-44 | Some disappear leaving 31 in total
46
What is the importance of embryonic folding?
Creates a ventral body wall Pulls the amniotic membrane around the disc so the embryo becomes suspended within the amniotic sac Pulls connecting stalk ventrally Creates primordium of the gut, puts the heart and the primordium of the diaphragm in the right place and creates a new cavity in the embryo
47
Why does folding occur?
Growth of the neural tube folds the cranial and caudal ends of the embryonic disc downwards Growth of the somites folds the lateral ends of the embryonic disc downwards
48
In which week of development does folding occur?
Embryonic period | 4th week of development
49
When does the primitive streak appear?
Embryonic period | 3rd week of development

zESA2 (21 decks)

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