Embryology and Pregnancy- Growth and Development (1)

Question 1

What is fertilisation?-the first trimester

3 steps?

Answer 1

• Fertilisation allows the transmission of genes from the parents.
• It restores the diploid number of chromosomes.
• It initiates the development of the embryo

STEPS IN FERTILISATION

• Contact of sperm and egg
• Entry of the sperm,just one sperm into the egg.
• Fusion of egg and sperm nuclei

Question 2

Outline the implantation of the first trimester?

Answer 2

Enzymes are secreted by the trophoblast, these allow the trophoblast to push its way into the uterine lining by liquefying the endometrial cells.

Once it has been buried in the endometrium, it starts to excrete human chorionic gonadotropin (hCG), this rescues the corpus luteum and therefore, the secretion of progesterone and estrogens are sustained. The pregnancy is established and pregnancy test would be positive.

Question 3

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Answer 3

Question 4

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Answer 4

Question 5

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Answer 5

Question 6

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Answer 6

Question 7

What process forms the 3 primary germ layers of an embryo?

Answer 7

All the structures in the developing embryo start from three primary germ layers. formed in process called GASTRULATION. The folding (INVAGINATION) of these layers starts to form the body axis.

Question 8

What are the 3 primary embryonic germ layers?

Answer 8

Mesoderm

Ectoderm

Endoderm

Question 9

Explain the mesoderm?

Answer 9

Mesoderm- this layer will develop into the embryonic heart and primitive circulatory system.

It forms the skeletal and cardiac muscle, bone and cartilage, connective tissues, blood, bone marrow, the lymphatic system, the endothelium of blood vessels and lymph vessels and the dermis of the skin.

Question 10

Explain the ectoderm?

Answer 10

Ectoderm- this gives rise to the neural tube, which goes on to form the brain and spinal cord. It also forms the nervous tissue, epidermis of the skin, hair follicles, nails, mammary glands, the lens, cornea and internal muscles of the eye, the epithelium of the oral and nasal cavity and the salivary glands.

Question 11

Explain the endoderm?

Answer 11

Endoderm- this forms a single tube lined with mucous membrane in the embryo-this tissue goes on to form the lining of the GI tract, bladder, lungs and vagina etc

Question 12

What is organogenesis?

Answer 12

• The 4th to 8th week from the start of the last menstrual period is the period during which the embryo starts to develop all the major organs.
• The term organogenesis refers to this period in which all the major body systems begin to develop.
• There is a dramatic change in shape and size as the flat tri-laminar embryonic disk forms a three dimensional cylinder, in a process called embryonic folding. This folding is caused by the different growth rates of the various tissues.
• The head and spinal cord are formed, there is the formation of a primitive gut.
• By the fourth week the upper limbs begin their development.
• During this period the developing embryo is very vulnerable to damage and permanent abnormalities in organs or final body structure can occur, some of which are incompatible with life