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)
What are the effects of growth hormone (GH)?
Stimulates glycogenolysis by the liver –> raises plasma glucose level –> makes glucose available for glycolysis
Represses glucose uptake by muscles and adipose tissue
Stimulates lipolysis
Stimulates amino acid uptake –> protein synthesis
Causes production of IGF ( insulin like growth factor in the liver
What is the effect of GnRH? (gonadotrophin releasing hormone)
Increases hypothalamic GnRH secreting neurones activity
= increase of FSH and LH up to age 10
(follicle stimulating hormone and luteinising hormone)
= puberty
- In females, ovarian follicles begin to mature
- In males Leydig cells mature in response to
LH –> testosterone secretion,
spermatogenesis
How is the adult body maintained?
Through cell renewal
What cells are renewed by stems cells?
Skin epidermis
Intestinal epithelium
Blood cells
Olfactory neurones (e.g. in rodents)
What cells are renewed without stem cells?
Insulin producing Beta cells
Hepatocytes in the liver
What cells do not renew?
(as known so far)
Auditory receptor cells (in the ears)
Photoreception cells (in the eyes)
What are undifferentiated stem cells?
Lack tissue specificity or specialized functions
What can stem cells that are able to differentiate do?
Give rise to specialised cell types via differentiation
What are stem cells that are self renewing ?
Capable of renewing themselves by cell division for long periods
i.e undifferentiated state maintained after cell division in at least one daughter cell
What embryonic stem cells?
Pluripotent - can differentiate into any part of the body
What are adult stem cells?
Multipotent - can differentiate into more than one type of cell
But can only differentiate to a cell within the same lineage
What are examples of adult stem cells?
Hematopoietic stem cells
Dermal papilla cells, hair follicle stem cells
Intestinal stem cells
Mesenchymal stem cells
Satellite cells - in muscles
What are some of the factors of aging?
- Reduction of hormones (GF, FSH, LH)
- Accumulation of mutations and epigenetic changes in the genome
- Accumulation of mutations in mitochondrial DNA
What is quiescence?
Cell cycle arrest at G0 due to a lack of nutrition, no stimuli for cell divsion
What is senescence?
Where cells go from G0 to cell death eventually even though the cells were metabolically active.
- Because the chromosome becomes shorter and shorter at their ends (telomere)
- Chromosome without telomere is detected as a DNA damage and cell cycle is stopped
What is the importance of telomere in stem cell replication?
- Telomere is a repetitive DNA sequence at the end of chromosomes - protects the chromosome from damage and end fusion
- DNA replication of that region requires telomerase
- Stem cells express high levels of telomerase so can replicate without a loss of the telomere region
- Telomere shortening is a way for cells to count divisions. Getting rid of old cells and guarding against uncontrolled cell division
