Lecture 17: Adaptive Tissue Responses

Question 1

Cells response to injury (stress) in 3 major ways- adaptive, reversible injury with or without degeneration or death.
Stresses places on cells often cause modification of those cells without death
Stressors can be pathological or physiological (i.e. normal stimuli)

Answer 1

Refer to slide 5

Question 2

Cells and tissue vary in their ability to adapt. This is dependant on: ?

Answer 2

• The state of differentiation (3 types- labile, stable or permanent)
• particular vulnerability to certain agents
• blood supply
• nutrition
• previous state of cell

Question 3

Adaptive changes are ______changes in Mature cells and tissue ____growth has occurred

Answer 3

Adaptive changes are reversible changes in Mature cells and tissues after growth has occurred

• atrophy
• hypertrophy
• hyperplasia
• metaplasia

Question 4

What is atrophy? what does it involve in the adaptive response process.
what are the mechanisms
What are the causes of atrophy

Answer 4

-a reduction in the size or amount of the organ, tissue or cell
-due to a decrease in the size and/or number of its specialised cells/ organelles
-results of physiological (e.g. thymus) or pathological (e.g.: disuse) stimuli
8

Mechanisms of atrophy
-An increase in APOPTOSIS (programmed cell death) is responsible for the decrease in number of cells
-the remaining cells survive at a small size-fewer mitochondria, myofilaments and ER
-reduction in cells size assosiaed with catabolism > anabolism (proteolysis via ubiquitinisation (regulatory protein)- hormones, cytokines, with increase autophagic vacuoles.
9

Causes of Atrophy:
-inadequate nutrition 
-decreased Blood supply 
-loss of innervation 
-decreased workload (disuse)
-prolonged pressure 
-decrease in hormonal stimulation 
-physiological (eg Thymus)
-aging 
10

Question 5

Hypertrophy is?
Causes?
Mechanisms?

Answer 5

It is a
-increase in some of an organ or tissue due to an increase in the size of its specialised cells
-cells with increased workload that cannot divide e.g.: muscle
-general increase in the number of organelles which increases the size of the cells (limited by SA: vol)
17

Causes:
Compensatory:
-removal of kidney
-increased workload- striated and cardiac muscle

Hormonal:–> pregnancy causes uterine atrophy
17

Mechanisms:
trophic triggers:
-growth factors
-hormones
-cytokines 
-may be produced endogenously or exogenously --> increase in gene expression 
-physical triggers 
18

Question 6

Hyperplasia is?
Causes?
Mechanisms
physiologial or pathological

Answer 6

it is an increase in the size of an organ or tissue due to a increase in the number of specialised cells
-may be due to a physiological or pathological causes

Physiological hyperplasia:

a) compensatory/ reactive:
- haematopoietic system after blood loss
- mesenteric lymph noses
b) hormonal:
- cyclical changes in mammary gland or endometrium

Pathological hyperplasia:
-hormonal excess:
  -XS erythropoitin-polycythemia
  -XS estrogen- dysmenorrhea 
-reparatory- to restore architecture or function 
-infectious organisms 
30

Question 7

Metaplasia is?

Answer 7

-a change from one type of specialised, fully differentiated adult cell to another adult cell type (often less specialised)
-a protective response
-howevere some functions are lost
-reprogramming stem cells by cytokines, growth factors and ECM components
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Question 8

Dysplasia is

Answer 8

Disordered growth

• not an ATR, principally in epithelium
• often occurs in metaplastic/ hyper plastic epithelium
• loss in uniformity of individual cells plus loss in architectural organisation
• may progress to neoplasia

Question 9

summary

Answer 9

-the response of a cell to a stimulus is a continuum.
-continued stress may cause cell death even after an adaptive response.
-the cell may respond in abnormal ways to continued stress – hyperplasia
and metaplasia may lead to dysplasia
and neoplasia.
-ATR are reversible whereas neoplasia involves irreversible genetic change
BUT the transition between the 2 can be difficult to distinguish.