Growth and Development of Organisms Flashcards
What are the 5 key stages of the human life cycle?
Embryonic development –> Growth –> Puberty –> Maintenance –> Ageing
What is embryogenesis?
The formation and development of an embryo
When is an embryo structure formed?
The overall structure is formed by the first two months of pregnancy.
The rest of the gestation period is mostly growth (3cm - 5cm)
When does pregnancy begin?
Day 1 of the last menstrual period
What is the germinal period?
Week 0 - 4
just the egg
what weeks is a foetus formed?
3rd - 8th week
When is the first trimester?
Week 0 - 13
When is the second trimester?
Week 13 - 26
When is the third trimester?
Week 27 - 38
What is the critical period?
The developmental stage when an embryo is susceptible to toxic agents (teratogens)
Varies depending on organ but usually corresponds to the stage of active differentiation and morphogenesis
What are some possible teratogens? (toxic agents)
medications – e.g. thalidomide (sedative drug)
alcohol, tobacco, caffeine
environmental chemicals
viral infection
What is the critical period for the CNS in humans?
Week 3 - 16
(moderately sensitive till week 38)
What is the critical period for the heart in humans?
Week 3 - 8
What was the critical period of thalidomide?
day 34 - 51 (week 4 - 8)
- mothers who took thalidomide in this period had babbies affected - born with major malformations
When does implantation occur?
Occurs at the blastocyst stage - day 8 - 9 after fertilisation.
Once implanted the embryo develops, embryonic disk is formed - one layer of cells - cells then proliferate
What are the 3 germ layers formed following gastrulation (when the blastocyst has formed)?
Ectoderm - smaller top layer
Mesoderm - middle layer
Endoderm - large bottom layer
What is the derivative of the ectoderm?
- surface ectoderm (epidermis of skin)
- nervous system
- neural crest cell derivatives
What is the derivative of the mesoderm ?
- Dermis ( inner layer of skin)
- Muscles
- Skeleton
- Urogenital organs (except urinary bladder)
- Blood, vasculature, spleen
What is the derivative of the endoderm?
- digestive system (gut, liver, pancreas)
- respiratory system
- urinary bladder
- thyroid, parathyroid
What is the main function between week 0-10 in the gestational period?
Morphogenesis and Differentiation
What is the main function between week 10-20 in the gestational period?
Rapid growth
What is the main function between week 20-30 in the gestational period?
Protein accumulation
What is the main function between week 30-40 in the gestational period?
Fat accumulation
What hormones are involved in growth?
- Growth hormone (GH)
- Insulin - like Growth Factor - 1 (IGF-1)
- Gonadotrophin releasing hormone (GnRH)
- Gonadal steroids ( Androgens, Oestrogens, Progesterone)
- Others ( Thyroid hormones, calcitonin, parathyroid hormone, corticosteroids)
