BL Session 12 - Embryology Flashcards Preview

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Flashcards in BL Session 12 - Embryology Deck (38)
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What is embryology?

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

- It includes molecular, cellular and structural factors.

- The understanding embryogenesis has the potential to treat disease, particularly repairing damaged cells/tissues/organs.

- Research also involves studies around embryonic stem cells.


Identify the features of the female reproduction system.


Outline the steps of oogenesis


Identify the necessary circumstances for fertilisation.

- Fertilisation normally occurs in the ampullary region of the Fallopian tube

- Sperm must be introduced into the female reproductive tract within 5 days before ovulation.

- Sperm are viable for 5 days

- Secondary oocyte viable for 12-24 hours

- Sperm initially incapable of fertilisation and thus requires capacitation, meaning the tail of the sperm moves faster, causing the plasma membrane to alter.


Because 50% of the implanting embryo’s genome is derived from the father, sperm are a foreign bodies – should they be rejected?

- Interestingly, both men and women can produce antibodies against sperm, and this is one of the causes of infertility.

- The surface proteins in sperm cells are “non-self” even for the male who produces them.

- Antibodies against a foreign protein can only be formed if there is contact with the blood.

- In the testes, Sertoli cells form a barrier made of specialised cell membrane structures called tight junctions, to avoid contact between blood cells and sperm cells, but when the barrier is broken by different type of injury, 


Define the following terms:

- Embryonic age

- Gestational age

- Germinal stage

- Embryonic period

- Foetal period.

- Embryonic age: time since fertilisation.

- Gestational age: time since last menstruation; that is embryonic age minus 2 weeks.

- Germinal stage: time from fertilisation to the end of the second week

- Embryonic period: time from the third to end of the eight week

- Foetal period: time from the beginning of the ninth week to birth at 38 weeks


Outline the features and steps in implantation.

- Before the blastocyst can implant it has to lose the zona pellucida. The zona pellucida is thought to prevent the morula/blastocyst adhering to the oviduct. The process of losing the zona pellucida is called hatching.

- It is mostly about (potential lack of) nutrition!

I. The zona pellucida stops the morula enlarging.

II. Morula and blastocyst use anaerobic and aerobic pathways.

III. The trophoblast becomes the yolk sac and placenta

- The implantation site determines the site of formation of the placenta.

- Normal implantation off the blastocyst occurs in the superior and posterior wall of the uterine cavity.

- The fertilised human oocyte migrates through the tube and implants itself on the 6th day in the endometrium


Distinguish between histiotrophic and haemotrophic nutrition.

- Histiotrophic nutrition: nutrition provided to the embryo not from the maternal blood. Important in humans up to the 12th week.

- Haemotrophic nutrition: nutrition provided by the mother’s blood. Important in humans from 12th week on.


What are abnormal fertilisation sites?

- Ovarian

- Infundibular

- In the fallopian tube (most frequent ectopic),

- Interstitial

- In the lower uterus segment (placenta praevia)

- Abdominal

- In the pelvic area.


Describe the role and properties of the following terms:

- Bilaminar embryonic disc

- Yolk sac

- Amniotic cavity

- Chorionic cavity

- Bilaminar embryonic disc: refers to the epiblast and the hypoblast, evolved from the embryoblast. These two layers are sandwiched between two balloons: the primitive yolk sac and the amniotic cavity.

- Amniotic cavity: the closed sac between the embryo and the amnion, containing the amniotic fluid.

- Yolk sac: a membranous sac attached to an embryo, formed by cells of the hypoblast adjacent to the embryonic disk.

- Chorionic cavity: the space surrounding the primary yolk sac and amniotic sac, except where the connecting stalk attaches to the cytotrophoblast of the blastocyst.


Why is the second week of development known as the week of 2s?

- The trophoblast differentiates into 2 layers – the cytotrophoblast and syncytiotrophoblast.

- The embryoblast forms 2 layers – the epiblast and hypoblast – the bilaminar embryonic disc.

- The hypoblast contributes to the formation of two cavities – the yolk sac and chorionic cavity.


What is the embryonic period?

- Weeks 3-8

- During this period:

I. Period of greatest change

II. All major structures and systems are formed

III. Greatest risk of major congenital malformation (i.e. teratogenesis) due to environmental exposure to drug therapy


Describe the results and processes involved in early embryonic development

- Result – foundations laid for the development of the body systems

- Processes:

I. Sufficient cells

II. Of the right type

III. In the right place


What are some key events and processes in early development?


Outline the process of gastrulation.

- Occurs in the third week of development, marking the start of the embryonic period.

- The bilaminar disk is converted to a trilaminar disk consisting of three germ layers: ectoderm, mesoderm and endoderm

- The primitive streak forms in the caudal epiblast, leading to migration and invagination of epiblast cells

- This process ensures the correct placement of precursor tissues to allow subsequent morphogenesis to occur.


Identify and describe the germ layers derivatives.

- Ectoderm – organs and structures that maintain contact with the outside world e.g. nervous system, epidermis.

- Mesoderm – supporting tissues e.g. muscle, cartilage, bone, vascular system.

- Endoderm – internal structures e.g. epithelium of GI tract, respiratory tract and parenchyma of glands


Outline the features of situs inversus.

- Complete mirror-image viscera

- Commonly results from immotile cilia

- No associated morbidity (usually)

- Problems arise if there is both normal and mirror-image disposition


Discuss left-right asymmetry.

- Prior to gastrulation the embryonic disk is bilaterally symmetrical

- However, in the body there are clear left vs right differences:

I. Thoracic viscera – left lung has 2 lobes while the right has 3

II. Abdominal viscera – liver on right, stomach and spleen on the left


What is neurulation?

Neurulation: refers to the folding process in vertebrate embryos, which includes the transformation of the neural plate into the neural tube. The embryo at this stage is termed the neurula.


What are somites?


Identify and describe some somite derivatives.

- Dermatome - skin section i.e. dermis

- Myotome - muscle section i.e. muscles

- Sclerotome - hard tissue section i.e. bones


Discuss the implication of segmentation

- Organisation of mesoderm into somites gives rise to repeating structures

I. Vertebrae

II. Ribs

III. Intercostal muscles

IV. Spinal cord segments

- Guides innervation


Outline embryonic folding.

- Folding draws together the margins of the disk

I. Creating a ventral body wall

II. Pulling amniotic membrane around the disk: embryo becomes suspended within the amniotic sac

III. Pulling connecting stalk ventrally


- At the end of the fourth week:

I. The nervous system has started to form

II. Segments have appeared, assigning specific tasks to specific cells

III. The embryo has folded, putting everything in the right place


Suggest in general terms one adult derivative for the splanchic layer of the lateral plate mesoderm

- The lateral mesoderm will split into two layers: the somatic layer and the spanchnic layer. 

- The splanchnopleuric layer forms the circulatory system. Spaces within the lateral plate are encolsed and forms the intraembryonic coelem. 


Why do you think the buccopharyngeal membrane and the cloacal membrane have no mesoderm?

- The buccopharyngeal and cloacal membrane have no mesoderm as these membranes form the upper and lower parts of the GI tracct. 

- Mesoderm derives into muscle, cartilage and bone, which are not part of the GI tract, hence, not necessary in essential membranes of the GI tract.


Saccrococcygeal teratomas are large abnormal growths in the saccrococcygeal region and are the most common tumours in newborns. Given that the developmental basis for these tumours is persistence of the primitive streak beyond the time when it should normally regress, suggest why these tumours can be composed of many discrete tissues.

- The primitive streak is a transient structure whose formation, on day 15 of human development, marks the start of gastrulattion, the process in which the inner cell mass is converted into the trilaminar disc, which is comprised of the three germ layers. 

- The primitive streak gives rise to the mesoderm which is a derivative pf supporting tissues e.g. muscle, cartilage and bone. Hence, if these sort of tumours involve the persistence of the primitive streak, then it consists precursor cells of the mesoderm, expaining why it can be composed of many discrete tissue types. 


What are embryonic stem cells? What ethical issues are posed by their use?

- Embryonic stem cells are pluripotent stem cells derived from the inner cell mass of a blastocyst. 

- Many of the debates surrounding human embryonic stem cells concern issues such as what restrictions should be made on studies using these types of cells. 

- At what point does one consider life to begin? Is it just to destroy an embryo cell if it has the potential to cure countless numbers of patients?


What can umbilical cord stem cells be used for?

Umbilical cord blood collected at birth is a rich source of stem cells that can be used in reasearch and in the clinic to treat diseases of the blood and immune system.


Where can adult stem cells be found. You have already learnt about their use in helping treat the complications of an intestinal disease - which disease? Adult stem cells are increasingly used to treat diseases of another system. Which system?

- Adult stem cells have been identified in many organs and tissues, including the brain, bone marrow, peripheral blood, blood vessels, skeletal muscle, skin, teeth, etc

- Adult stem cells have been used to treat many diseases of the immune system such as MS, Diabetes Type I and RA


Why is Caesarean section indicated in placenta praevia?

- Placenta previa is when the placenta covers part or all of the cervix during the last months of pregnancy. 

- This condition can cause severe bleeding before or during labor. 

- Bed rest is often the recommended treatment 

- If heavy bleeding occurs, an emergency C-section delivery may be necessary.