Growth and Development of Organisms Flashcards
Define the term embryogenesis
The formation and development of an embryo
Define the term embryology
The branch of biology and medicine concerned with the study of embryos and their development.
Define the term ‘developmental biology’
Studying the mechanism of how changes are controlled at cellular, molecular and genetic levels
What is the critical period?
The developmental stage when embryo is susceptible to toxic agents (teratogens)
Usually corresponds to the stage of active differentiation and morphogenesis
Varies depending on the organ
List possible teratogens
- medications – e.g. thalidomide (sedative drug)
- alcohol, tobacco, caffeine
- environmental chemicals
- viral infection
What are the two ways to count the age of the embryo?
From fertilisation (giving the full term to be 38 weeks) From day 1 of the last menstrual period (giving the full term to be 40 weeks)
Name the three germ layers in embryos
ectoderm, mesoderm, endoderm
What are the derivatives of the ectoderm?
- surface ectoderm (mainly epidermis of the skin)
- the nervous system
- neural crest cell derivatives (melanocytes, some of skull bones, adrenal medulla)
What are the derivatives of the mesoderm?
- dermis (inner layer of the skin)
- muscles
- skeleton (bones and cartilages except in the head)
- urogenital organs (except urinary bladder)
- blood, vasculature, spleen
What are the derivatives of the endoderm?
- the digestive system (gut, liver, pancreas)
- the respiratory system
- urinary bladder
- thyroid, parathyroid
Name some of the hormones involved in growth
Growth hormone (GH), Insulin-like Growth Factor-1 (IGF-1) Gonadal steroids (Androgens, Estrogens, Progesterone) Others (Thyroid hormones, corticosteroids, parathyroid hormone, calcitonin)
Describe the effect of growth hormone
It stimulates glycogenolysis by the liver, raising plasma glucose level which make available for use.
Glucose uptake by muscle and adipose tissue is repressed
Lipolysis and amino acid uptake is stimulated
It causes production of IGF in the liver
What can be renewed by stem cells?
Skin epidermis
Intestinal epithelium
Blood cells
Olfactory neurons (e.g. in rodents)
What can renew without stem cells?
Insulin producing β-cells
Hepatocytes in liver
What doesn’t renew (as far as we know)?
Auditory receptor cells
Photoreception cells
Describe stem cells
Undifferentiated: lack tissue-specificity or specialised functions
Able to differentiate: can give rise to specialised cell types via differentiation
Self-renewal: capable of renewing themselves by cell division for long periods
Define the term ‘growth’
An increase in the size/number of cells, which results in the enlargement of all/part of an organism
Define the term ‘development’
Changes an organism undergoes throughout its lifetime. It includes differentiation and morphogenisis
Define the term ‘differentiation’
The changes in a cell’s structure and function from an immature, generalised cell to a mature, specialised cell
Define the term ‘morphogenesis’
The change in shape of tissues, organs, and the entire organism
Name the three stages of pre-natal development
Germinal period
Embryonic period
Fetal period
Germinal period
First 14 days after fertilisation when germ layers form
Embroyonic period
Week 2-8 after fertilisation, when the major organ systems form
Fetal period
Last 30 weeks of pregnancy, when the organ systems grow and mature.
How is the body structure maintained?
By replacing old cells with new cells
What’s the key difference between pluripotent and multipotent stem cells?
Pluripotent cells can give rise to all of the cell types that make up the body. Multipotent cells can develop into more than one cell type, but are more limited than pluripotent cells.
Where are pluripotent stem cells found?
Embryonic stem cells
Where are multipotent stem cells found?
Adult stem cells
When do embryos become fetuses?
At 60 days (about 8 weeks)
What happens to the genome as you age?
You accumulate mutations and epigenetic changes in the genome. At the age of 70, a somatic cell has 2000 gene ‘scars’, traces of quick DNA repairs. There’s also an accumulation of mutations in mitochondrial DNA, x100 more frequently than nuclear DNA
What are telomeres?
Repetitive DNA sequences (GGGTTA) at the end of chromosomes. At birth, babies have about 2,000, which falls to a few hundred in old age. They form loops so that the end of the chromosome won’t be recognised as broken DNA, protecting it from damage.
Why can human cells only divide a limited number of times?
The telomeres get shorter and shorter with each division. Chromosome without a telomere is detected as DNA damage and the cell cycle is arrested by p53 –> cell senescence
What is cellular senescence?
Cellular senescence is defined as irreversible cell cycle arrest driven by a variety of mechanisms, including telomere shortening, that culminate in the activation of the p53 tumor suppressor.
What does replication of the telomere region require?
DNA replication of this region requires telomerase (cannot be done by usual DNA replication method)
Why are stem cells able to replicate without the loss of the telomere region?
Stem cells express high levels of telomerase, hence are able to replicate without a loss of the telomere region
Why aren’t differentiated cells able to replicate without the loss of the telomere region?
Most differentiated cells express only a low level of telomerase therefore lose 100-200 nucleotides (15-30 repeats) every cell division
Why is telomere shortening useful?
Telomere shortening is a mechanism for cells to ‘count’ cell division: to get rid of old cells, and also to self-guard against uncontrolled cell division
