General embryology

Question 1

what are processes in human development?

Answer 1

• Begins with fertilization of an ovum
• Cell division
• Cell migration
• Programmed cell death
• Differentiation
• Growth
• Cell rearrangement
• Development does not stop at birth

Question 2

what are developmental periods?

Answer 2

-Prenatal:Embryonic, Fetal
-Postnatal: Infancy,Childhood, Puberty,Adolescence,Adulthood
Note: Birth is a dramatic event during development resulting in a change in environment

Question 3

what are phases in prenatal development?

Answer 3

-The first two, when combined, constitute the embryonic stage. (Embryo)
I. Phase
-Fertilization -> Week 4: Involves cellular proliferation, migration and some differentiation of cell populations
-Few congenital defects result during this period; if severe, the embryo is lost
2. Phase
-Weeks 4-8: morphogenesis (differentiation of all major internal and external structures)
-Extreme vulnerability to teratogens/defects
3.The third is the fetal stage.(Fetus)
Mainly growth and maturation

Question 4

control of development

Answer 4

• development results from genetic plans in the chromosomes
• Embryonic development is essentially a process of growth (mitosis) and increasing complexity (morphogenesis and differentiation) of structure and function
• Developmental potential becomes more restrictive as tissues acquire the specialized features necessary for increasing their sophistication of structure and function
• Choices are made based on cues from immediate surroundings (INDUCTION)

Question 5

what is induction?

Answer 5

• All cells of the zygote are initially the same but differentiate into idfferent populations that have assumed particular shapes, functions, and rates of turnover.
• An inducer is the agent that provides cells with the signal to enter this process. Each compartment of cells must be competent to respond to the induction process.

Question 6

what is competence?

Answer 6

• Ability to respond to an inducer.

- Windows of competence vary for different populations of cells

Question 7

what is differentiation?

Answer 7

The process of responding to an inducer to “change” to what it is supposed to be.

Question 8

what are the players in induction, competence, differentiation?

Answer 8

homeobox genes, growth factors, retinoic acid and other regulatory molecules

Question 9

what is paracrine regulation?

Answer 9

A growth factor produced by one cell acts on another

Question 10

what id autocrine regulation?

Answer 10

A cell recaptures its own product.

Question 11

what happens in the 1st week of fetus development?

Answer 11

• Human development begins with fertilization or formation of the zygote
• Gametogenesis is the process of forming the generative cells (gametes): egg, sperm
• Meiosis is a special cell division that takes place in germ cells

Question 12

meiosis

Answer 12

-Diploid germ cells develop haploid gametes through spermatogenesis in the male and oogenesis in the female
-Division 1 – reduction division – chromosome # reduced from diploid to haploid when homologous chromosomes pair and separate
Division 2 – follows the 1st without interphase and the chromosomes divide

Question 13

what are importance of meiosis? EXQ

Answer 13

• Maintains the constancy of the chromosome number
• Results in a random assortment of genetic material
• Relocates segments of maternal and paternal chromosomes between the gametes

Question 14

how does gamete production occur?

Answer 14

• Spermatogenesis begins in the male at puberty (13-16) and continues into old age
• Oogenesis begins before birth in the female and is completed after puberty (12-15) and continues to menopause (permanent cessation of menses)

Question 15

abnormal gametogenesis

Answer 15

• Disturbances of meiosis during gametogenesis result in the formation of abnormal gametes.
• Some of these are not compatible with life.
• Others result in a variety of developmental issues (e.g., Down’s Syndrome)

Question 16

Gamete transportation

Answer 16

Refers to the way the oocyte and sperms meet each other in the ampulla of the uterine tube, the usual site of fertilization.

Question 17

sperm transport

Answer 17

• 200-600 million sperms are deposited around the external os of the uterus and in the fornix of the vagina during intercourse.
• Pass slowly through the cervical canal by movements of their tails; vesiculase (seminal glands) coagulates some semen to form a vaginal plug
• Cervical mucus also increases and becomes less viscous, allowing easier movement of sperms
• Ejaculate volume averages 3.5 ml (2-6) and the sperms move about 2-3 mm/minute depending on pH of environment

Question 18

maturation of sperm

Answer 18

• Freshly ejaculated sperm are unable to fertilize oocytes
• Capacitation - ~ 7 hrs; glycoprotein coat and seminal proteins are removed from acrosome; membrane components are extensively altered (occurs in uterus or uterine tube)
• Intact acrosome binds to the ZP3 glycoprotein on the zona pellucida
• Encounter with the corona radiata cells - acrosome rx – acrosome membrane perforates causing release of hyaluronidase and acrosin from the acrosome that facilitates fertilization (acrosome rx)

Question 19

gamete viability

Answer 19

• Human oocytes are usually fertilized within 12 hrs of ovulation
• Most human sperms probably do not survive more than 48 hrs in the female genital tract
• There is short term storage and release of sperms in the folds of the cervical mucosa which probably enhances the probability of fertilization

Question 20

fertilization

Answer 20

• Usual site of fertilization is in the ampulla of the uterine tube, the longest and widest part
• Tales sperm 5-45 minutes to reach ampulla with only about 200 making the journey
• If oocyte is not fertilized it degenerates and is resorbed
• Complex event which begins w/ the contact of the egg and sperm and ends with the intermingling of the maternal and paternal chromosomal material at metaphase of the first mitotic (cleavage) division of the zygote