Embryo pt.2 Flashcards
Describe the characteristic signs of carnegie stage 22
- Development of the eyelids and the external ear canal
- Tragus and antitragus (parts of ear)
- Nasal septum
- Secondary palate
Describe the characteristic signs of carnegie stage 23
- 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
What is considered to be the most critical stage of prenatal development?
The embryonic period is the most critical, as flaws in that period can lead to major alterations in structure and function of the fetus
How important is the embryonic period?
- 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
Which time period can be considered as “infancy”?
Approximately first year of life
What time period does the term neonate define?
An infant age 1 month or younger
What can postnatal development be divided into?
- Infancy
- Childhood
- Puberty
- Adulthood
Describe the growth of the baby in terms of size during infancy
- Rapid growth
- The total length increases by about one half and weight is usually tripled
Which time period can be considered as “childhood”?
Between infancy and puberty
Describe the amount of teeth a baby has by the end of infancy
By 1 year od age, most infants have six to eight teeth
Which time period can be considered as “puberty”?
The period when humans become functionally capable of reproduction
Describe the growth of the baby in terms of size during childhood
- 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
How long does puberty last for males and females?
- 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
What happens during puberty?
- Secondary sexual characteristics develop
- Reproductive function begins
- Sexual dimorphism becomes more apparent
What is teratology?
Branch of embryology and pathology concerned with the production, developmental anatomy, and classification of malformed embryos and fetuses
What is a gamete?
Refers to any germ cells, whether its a sperm or oocyte
What is gametogenesis?
The process of formation of gametes from primordial germ cells
What happens at the end of gametogenesis when it comes to chromosome number?
During gametogenesis, the chromosome number is reduced by half
What does gametogenesis involve?
Involves a specialized cell division called meiosis
Describe the process of meiosis during gametogenesis?
- 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
Which processes involved meiosis?
Only gametogenesis
What is gametogenesis in males called?
Spermatogenesis
What is gametogenesis in females called?
Oogenesis
What are differences between male and female gametogenesis? What are its implications?
- 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
How do the X and Y chromosomes pair up during gametogenesis?
- 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
How long does spermatogenesis take?
About two months