Embryo pt.2

Question 1

Describe the characteristic signs of carnegie stage 22

Answer 1

• Development of the eyelids and the external ear canal
• Tragus and antitragus (parts of ear)
• Nasal septum
• Secondary palate

Question 2

Describe the characteristic signs of carnegie stage 23

Answer 2

• Angle between the head and trunk amounts to 30 degrees
• The head makes 50%of the embryo’s size
• The head is rounded, the extremities lengthened and stand out from the body
• Chin
• Nasal pit
• Development of the external genital primordium

Question 3

What is considered to be the most critical stage of prenatal development?

Answer 3

The embryonic period is the most critical, as flaws in that period can lead to major alterations in structure and function of the fetus

Question 4

How important is the embryonic period?

Answer 4

• Considered most critical
• Over 90% of the structures of the human body are already established during the embryonic period and abnormal development frequently occurs in that time period

Question 5

Which time period can be considered as “infancy”?

Answer 5

Approximately first year of life

Question 6

What time period does the term neonate define?

Answer 6

An infant age 1 month or younger

Question 7

What can postnatal development be divided into?

Answer 7

• Infancy
• Childhood
• Puberty
• Adulthood

Question 8

Describe the growth of the baby in terms of size during infancy

Answer 8

• Rapid growth
• The total length increases by about one half and weight is usually tripled

Question 9

Which time period can be considered as “childhood”?

Answer 9

Between infancy and puberty

Question 10

Describe the amount of teeth a baby has by the end of infancy

Answer 10

By 1 year od age, most infants have six to eight teeth

Question 11

Which time period can be considered as “puberty”?

Answer 11

The period when humans become functionally capable of reproduction

Question 12

Describe the growth of the baby in terms of size during childhood

Answer 12

• During early childhood, there is active ossification, but as the child becomes older, the rate of body growth slows down
• Just before puberty growth accelerates, the prepubertal growth sprout

Question 13

How long does puberty last for males and females?

Answer 13

• Starts around 9-10 years old for females with the process largely completed by 16 years
• Starts from after 10-11 years old (earliest) for males with the process largely completed by 18 years

Question 14

What happens during puberty?

Answer 14

• Secondary sexual characteristics develop
• Reproductive function begins
• Sexual dimorphism becomes more apparent

Question 15

What is teratology?

Answer 15

Branch of embryology and pathology concerned with the production, developmental anatomy, and classification of malformed embryos and fetuses

Question 16

What is a gamete?

Answer 16

Refers to any germ cells, whether its a sperm or oocyte

Question 17

What is gametogenesis?

Answer 17

The process of formation of gametes from primordial germ cells

Question 18

What happens at the end of gametogenesis when it comes to chromosome number?

Answer 18

During gametogenesis, the chromosome number is reduced by half

Question 19

What does gametogenesis involve?

Answer 19

Involves a specialized cell division called meiosis

Question 20

Describe the process of meiosis during gametogenesis?

Answer 20

• Meiosis consists of two sequential cell divisions that result in four daughter cells
• During meiosis 1, the homologous (maternal and paternal) chromosomes are paired, seperated, and distributed to the two daughter cells
• The first meiotic division is a reduction division, chromosome number is reduced from diploid to haploid
• Meiosis 2 proceeds like mitosis in which the chromatids are distributed to the daughter cells (1n/1c), forming 4 daughter haploid cells

Question 21

Which processes involved meiosis?

Answer 21

Only gametogenesis

Question 22

What is gametogenesis in males called?

Answer 22

Spermatogenesis

Question 23

What is gametogenesis in females called?

Answer 23

Oogenesis

Question 24

What are differences between male and female gametogenesis? What are its implications?

Answer 24

• The primordial follicle in the ovary remains arrested in meiosis for years
• Oogenesis is arrested at prophase I of meiosis until adolescence (beginning with puberty)
• The long duration of the first meiotic division (up to 45 years) may account in part for the relatively high frequency of meiotic errors, leading to aneuploidy, that occur with increasing maternal age
• It has been shown that about 25% of the intermediates (cells forming during meiosis), in females and not males, that should mature into crossover products actually fail. So 1/4 cells is giving rise to an abnormal cell

Question 25

How do the X and Y chromosomes pair up during gametogenesis?

Answer 25

• The X and Y chromosomes are not homologous but they have homologous segments at the tip of their short arms
• They pair in these regions only

Question 26

How long does spermatogenesis take?

Answer 26

About two months