Human Development Lecture 6 – The making part 1
Trimesters (period of 3 months);
• First trimester; most dangerous period, all the major organs appear.
o Mitosis, cleavage, hatching, implantation, placentation (teratogens)
o Embryological and early fetal development
• Second trimester; development of organs and shape and proportions change.
The fetus grows faster than the placenta. Amnion and chorion membranes
fuse. Bone formation occurs. Covered with fine hair (lanugo)
• Third trimester; Growth rate slows down, deposition of adipose tissue. Organ
systems become fully functional.
Birth defects;
The embryological period is most sensitive to
substances/toxic components.
Many birth defects can be prevented.
When does life begin?
1. Metabolic view; no point when life begins. Sperm and egg cell are as alive as
any other organism.
2. Genetic view; when there is fertilization.
3. Embryological view; at day 12. Earlier identical twins can form and this are 2
individuals with 2 different lives/personalities.
4. Neurological view; at 27 weeks, because then EEG should be defined
5. Ecological/technological view; at 23 weeks, when embryo can exist separately
from its maternal environment. When lungs are mature
6. The immunological view; around birth, because life begins when organism
recognize the distinction between self and non-self
7. The integrated physiological view; when baby is born
and umbilical cord is cut, because baby has become
independent of mother.
Pre-embryonic period (first 2 weeks); WEEK 1; zygote
to blastocyst, implantation
Cleavage; Zygote become pre-embryo
Sequence of cell divisions immediately after fertilization.
The zygote become pre-embryo which develops into
multicellular blastocyst
Cleavage end when blastocyst contact the uterine wall.
First divisions until morula generate identical cells; blastomeres
Morula is a (groter dan of gelijk aan) 16 cell stage
Blastocyst; hollow ball with inner cavity blastocoele and inner cell mass
(ICM) which will form the embryo. Outer layer is trophoblast, which become
the extraembryonic membrane; play role in implantation and supports
embryo’s growth.
Trophoblast secrete enzymes that erode through zone pellucida, the uterine fluid can
now feed the pre-embryo.
Trimesters (period of 3 months);
• First trimester; most dangerous period, all the major organs appear.
o Mitosis, cleavage, hatching, implantation, placentation (teratogens)
o Embryological and early fetal development
• Second trimester; development of organs and shape and proportions change.
The fetus grows faster than the placenta. Amnion and chorion membranes
fuse. Bone formation occurs. Covered with fine hair (lanugo)
• Third trimester; Growth rate slows down, deposition of adipose tissue. Organ
systems become fully functional.
Birth defects;
The embryological period is most sensitive to
substances/toxic components.
Many birth defects can be prevented.
When does life begin?
1. Metabolic view; no point when life begins. Sperm and egg cell are as alive as
any other organism.
2. Genetic view; when there is fertilization.
3. Embryological view; at day 12. Earlier identical twins can form and this are 2
individuals with 2 different lives/personalities.
4. Neurological view; at 27 weeks, because then EEG should be defined
5. Ecological/technological view; at 23 weeks, when embryo can exist separately
from its maternal environment. When lungs are mature
6. The immunological view; around birth, because life begins when organism
recognize the distinction between self and non-self
7. The integrated physiological view; when baby is born
and umbilical cord is cut, because baby has become
independent of mother.
Pre-embryonic period (first 2 weeks); WEEK 1; zygote
to blastocyst, implantation
Cleavage; Zygote become pre-embryo
Sequence of cell divisions immediately after fertilization.
The zygote become pre-embryo which develops into
multicellular blastocyst
Cleavage end when blastocyst contact the uterine wall.
First divisions until morula generate identical cells; blastomeres
Morula is a (groter dan of gelijk aan) 16 cell stage
Blastocyst; hollow ball with inner cavity blastocoele and inner cell mass
(ICM) which will form the embryo. Outer layer is trophoblast, which become
the extraembryonic membrane; play role in implantation and supports
embryo’s growth.
Trophoblast secrete enzymes that erode through zone pellucida, the uterine fluid can
now feed the pre-embryo.
