Cellular adaptation and tissue regeneration Flashcards
Explain the overview of adaptation and regeneration
- When normal cells are exposed to stress and increased demands, adaptation occurs. When there is an inability to adapt cell injury and death occurs
- When normal cells is exposed to injurious stimulus then cell injury and death occurs
- Repair regeneration occurs from cell injury
How is Hyperplasia and hypertrophy a cellular adaptation
- Cells respond to increased demand and external stimulation by hyperplasia or hypertrophy
How is Atrophy a cellular adaptation
- Cells respond to reduced supply of nutrients and growth factors by Atrophy
How is Metaplasia a cellular adaptation
- In some situations, cells change from one type to another, a process called metaplasia
What is Hyperplasia?
- Increase in the number of cells in an organ or tissue resulting in increased volume of the organ or tissue
- The process remains controlled
- May lead to cancerous proliferation
Is hyperplasia physiological or pathological?
- Can be physiological or pathological
What is the mechanism of hyperplasia?
- Increase local production of growth factors ->
- Increased expression of growth factor receptors of the responding cells. Activation of particular intracellular signalling pathways ->
- Production of transcription factors that turn on many cellular genes ->
- Cell proliferation
What is Hypertrophy?
- An increase in the size of cells due to synthesis of more structural components, resulting in an increase in the size of the organ
Is Hypertrophy physiological or pathological?
- Can be physiological (exercises leads to increase muscle fibre)
-or pathological (e.g. hypertension the heart needs to pump a lot harder)
What causes Hypertrophy?
- Caused by increased FUNCTIONAL DEMAND or by specific HORMONAL STIMULATION
Explain Cardiac hypertrophy
- under normal conditions due to exercise
- Adaptation response to increased work load is that the heart muscle fibre gets larger to increase the blood output
- Hypertrophic cardiac myocytes
Explain the mechanisms of hypertrophy
- Hypertrophy is the result of increased production of cellular proteins
- Induced by co-ordinated actions of mechanical sensors, growth factors and vaso-active agents
What are the two main biochemical pathways of hypertrophy mechanisms
- IGF1 -> PI3K -> Akt pathway (physiological)
- Ang II, ET-1, NA -> GPCR -> Galphaq/11 -> MAPK, PKC, PKA (pathological)
Explain the number and size of cells in these situations: 1) Hyperplasia, 2) Hypertrophy, 3) Combined hypertrophy and hyperplasia
1) Cell number increase, cell size the same
2) Cell size increase, cell number the same
3) Increase in cell size and cell number
What is Atrophy?
- Atrophy is the shrinkage (reduced size) of an organ or tissue from a decrease in cell size and number
- It represents a form of adaptive response and may culminate in cell death
When does physiological atrophy commonly occur?
- Physiological atrophy is common during normal foetal development
What does Pathological atrophy depend on?
- Pathological atrophy depends on the underlying cause and can be local or generalised
What are the causes of Atrophy, explain them
- Decreased workload (atrophy of disuse)
- Loss of innervation (denervation atrophy)
- Diminished blood supply: arterial occlusive disease
- Lack of nutrition
- Loss of endocrine stimulation
- Pressure atrophy (Tissue compressed)
Explain how decreased workload (atrophy of disuse) causes atrophy
- restriction to bed rest leads to skeletal muscle atrophy
Explain how Loss of innervation (denervation atrophy) causes atrophy
- Nerve damage leads to muscle atrophy
Explain what repair often consists of
- Repair most often consists of a combination of regeneration and scar formation and fibrosis by the deposition of collagen
The relative contribution of regeneration and scarring in tissue repair depends on what 2 things
- The ability of the tissue to regenerate
- The extent of the injury
In adult tissues the size of cell population is determined by
- The rate of cell proliferation, differentiation
- The rate of death by apoptosis
Differentiated cells incapable of replication is referred to as what
- Terminally differentiated cells
What are stem cells characterised by
- Their self-renewal properties
- Their capacity to generate differentiated cell linages
In early stages of embryonic development stem cells (embryonic stem (ES) cells) are what?
- They are pluripotent - they can generate all tissues of the body
What does Pluripotent stem cells turn into?
multipotent or unipotent stem cells (more restricted developmental potential), -> differentiated cells from the three embryonic layers
What is an Embryonic stem cells?
- The inner cell mass of blastocysts in early embryonic development contains pluripotent stem cells known as ES cells
What are Adult (somatic) stem cells?
- Stem cells present in adult tissues that continuously divide such as the bone marrow, the skin, and the lining of the GI tract
What are Induced pluripotent stem cells (iPSC)
- Differentiated cells of adult tissues can be reprogrammed to become pluripotent (transferring their nucleus to an enucleated oocyte; introducing the key genes).
What are the impact of stem cell research on Biology and Medicine
- To study the specific signals and differentiation steps required for the development of many tissues
- To produce knockout mice, an essential tool to study the biology of particular genes and to develop models of human disease
- To regenerate damaged organs
