Chapter 18 - Developmental Biology Flashcards
What is embryology?
Study of the development of a unicellular zygote into a complete, multicellular organism
What occurs over the 9 months of pregnancy?
Unicellular human zygote undergoes cell division, cellular differentiation, and morphogenesis in preparation for life outside the uterus
What are the 2 early developmental stages?
Fertilization and cleavage
Describe fertilization:
- Time period?
- Where is occurs?
- Twins?
- Fertilized ovum within 12-24h after ovulation
- Occurs in latereal, widest portion of oviduct
- More than one fertilized egg result in twins
Describe cleavage:
- What does it increase?
- What does it result in?
- First complete cleavage? Second? Third?
- Types of embryonic cells?
Early embryonic development is characterized by a series of rapid mitosis decisions known as cleavage
- Increases cell number without corresponding growth in cell protoplasm; also, increases surface-area-to-volume ratio which improves gas/nutrient exchange
- Results in progressively smaller cells with increasing ratio of nuclei to cytoplasm
- First complete cleavage of zygote occurs 32h after fertilization; second occurs 60h; third occurs 72h which is 8-celled and reaches the embryo
- Cell division continues until morula is formed; blastulation begins when morula develops into blastocoel (blastula); implants on uterus
How does emergency contraception work?
Blocks implantation
What is an ectopic pregnancy?
Embryo implants elsewhere than the uterus
- Usually aborts
What occurs during gastrulation?
After week 2, the embryo is fully implanted in the uterus and the cell migrations transform single cell layer of blastula into 3-layered structure called a gastrula:
- Ectoderm: Integumentary system (epidermis, hair, nails, mouth, anal canal)
- Endoderm: Epithelial lining of respiratory and digestive tract, and liver, pancreas
- Mesoderm: Musculoskeletal system, circulatory system, excretory system,. gonads, connective tissue, digestive/respiratory organs
What is neurulation? What develops? What does its inductive effect cause? What does it do once its formed?
At the end of gastrulation, regions of the germ layer develop into a nervous system (week three)
- The notochord develops along longitudinal axis of embryo just under the dorsal layer of ectoderm
- It has an inductive effect on overlying ectoderm causing it to bend inward to form a grove along the dorsal surface of the embryo; fuse and form a close tube that gives rise to the brain and spinal cord (CNS)
- Once formed it detached from surface of ectoderm
What are neural crest cells?
Cells at the tip of each neural fold which migrate laterally and give rise to components of the peripheral nervous system
- Includes: Sensory ganglia, autonomic ganglia, adrenal medulla, and schwann cells
What happens if the neural tube does not close properly? What can decrease this chance of occurring?
Spina bifida
- Folic acid consumption during pregnancy
What are the three stages of development?
1) Organogenesis: Body organs form; cells differentiate and change physical shape to proliferate and migrate
2) Growth: Organs increase in size
3) Gametogenesis: Eggs develop in women and sperm develop in men = permits reproduction
How does the fetus receive oxygen? What is it called?
Through a specialized circulatory system from its mother which supplies oxygen and nutrients, and removes CO2 and waste
- Placenta and umbilical cord
What is the placenta and umbilical cord composed of and how does it form?
Outgrowths of 4 extra-embryonic membranes formed through development:
- Amnion: Thin, tough membrane containing watery amnionic fluid; acts as shock absorber of external pressure during gestation and localized pressure from uterine contractions
- Chorion: Placenta formation begins with chorion, a membrane that completely surrounds the amnion; assists in transfer of nutrients from mother to fetus
- Allantois: Develops as an outpacing of gut; blood vessels of this portion enlarge and become umbilical vessels which connect fetus to developing placenta
- Yolk sac: Site of early development of blood vessels, becomes associated with umbilical vessels
What is gestation? How long does it last?
Human pregnancy
- 9 months
- 266 days
How is gestation subdivided?
1) First Trimester
2) Second Trimester
3) Third Trimester
Describe the first trimester:
- What develops?
- When does the heart beat?
- What forms?
- How long is the embryo at 5 weeks, 6 weeks, and at 3 months?
- When does bone form?
- Have most of the organs formed; what about the brain?
- Major organs begin to develop
- Heart beats at ~22 days
- Eyes, gonads, limbs and liver start to form
- 5 week embryo is 10mm long; 6 week embryo is 15mm long; 3 months fetus is 9cm long
- Cartilaginous bone forms into bone at week 7
- Most organs are formed at week 8 and the brain is fairly developed
Describe the second trimester:
- What does the fetus do?
- Can it move?
- Facial features?
- Toes/fingers?
- Length?
- Grows a lot
- The fetus can move
- The fetus has facial features
- Fingers and toes elongate
- End of month 6, 30-36cm
Describe the third trimester:
- What development occurs here?
- Antibodies?
- Growth rate?
- Rapid growth and further brain development
- Antibodies are transported by highly selective active transport from mother to fetus
- Growth rate slow and fetus is less active (less room to move)
How is child birth accomplished?
Labour: A series of strong uterine contraction
What are the 3 stages of labour?
1) First Stage: Cervix thins and dilates, and the amniotic sac ruptures, releasing its fluid contents; mild contractions
2) Second Stage: Rapid contractions resulting int he birth of the baby
3) Third/Final Stage: Uterus contracts to expel placenta and umbilical cord
What are congenital disorders? How are they caused?
- Birth defect that can present a wide variety of symptoms, even death
- Errors during fetal development and/or often caused because of deleterious genes or problems with gestation environment
What is a teratogen?
Chemical and biological agents that can cause disorders
- Ex. Alcohol, drugs, tobacco, bacteria, viruses
What is a vertical transmission?
When a mother passes on an infection directly to her developing offspring during development or birth
What are some environmental factors that can lead to birth defects?
Poor nutrition, radiation, physical trauma or restraint
What is experimental embryology?
- What do scientists hope to do?
A field that aims to investigate effects and other factors on development
- Hope to identify risk factors for women who could become pregnant and treatments applicable throughout human life cycle
How does seed formation occur?
Zygote divides mitotically to form mass of cells called an embryo
What does a plant embryo consist of?
1) Epicotyl: Precursor to upper stem/leaves
2) Cotyledons: Seed leaves; dicots have 2, monocots have 1
3) Hypocotyl: Lower stem and root
4) Endosperm: Feeds embryo; in dicots it absorbs the endosperm
5) Seed Coat: Develops from the outer covering of the ovule; embryo and seed coat together comprise the seed
How do seeds develop and disperse?
In most fruit, seeds develop in the ovary walls at the base of the flower and other pistil components
- The fruit enables the seed to be carried/dispersed effectively by air, water, or animals
- The seed is released from the ovary and may germinate under proper conditions (i.e. temperature, moisture, and oxygen)
How do plants grow?
Growth in higher plants is restricted to embryonic cells called meristem cells
- Undergo active cell reproduction
- Gradually elongate and differentiate into cell types characteristic to the species
What are the 2 types of meristem?
1) Apical: Tips of roots/stems; growth occurs in length
2) Lateral: Located between xylem/phloem; growth occurs in diameter
- Not active in monocots
- Dominant in dicots
