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SA pathological processes > S7) Cellular Adaptations > Flashcards

S7) Cellular Adaptations Flashcards

1
Q

What determines the size of a cell population?

A
  • Rate of cell proliferation
  • Rate of cell differentiation
  • Rate of cell death by apoptosis
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2
Q

When does cell proliferation occur?

A
  • Cell proliferation occurs in physiological and pathological conditions
  • Excessive physiological stimulation can become pathological e.g. prostatic hypertrophy
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3
Q

What regulates normal cell proliferation?

A

Proto-oncogenes

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4
Q

Chemical signals from the microenvironment either stimulate/inhibit cell proliferation

Identify the four effects of chemical signals

A
  • Survive – resist apoptosis
  • Divide – enter cell cycle
  • Differentiate – take on specialised form and function
  • Die – undergo apoptosis
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5
Q

How can a cell population increase its numbers?

A

Increased growth occurs by:

  • Shortening the cell cycle
  • Conversion of quiescent cells → proliferating cells (enter cell cycle)
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6
Q

The restriction (R) point is the most critical checkpoint in the cell cycle.

What happens at this checkpoint?

A
  • Checkpoint activation delays cell cycle and triggers DNA repair mechanisms / apoptosis via p53
  • Majority of cells that pass R point will complete cell cycle
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7
Q

How is the cell cycle controlled?

A
  • Controlled by cyclins and cyclin dependent kinases (CDKs)
  • CDKs become active by binding with cyclins
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8
Q

What is cellular adaptation?

A

Cellular adaptation is the reversible state between a normal unstressed cell and an overstressed injured cell occurring when cells respond to challenges which are not completely pathological

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9
Q

What are the 5 different types of cellular adaptation?

A
  • Regeneration – multiply to replace loses
  • Hyperplasia – increase in number
  • Hypertrophy – increase in size
  • Atrophy – decrease in size/number
  • Metaplasia – replaced by a different type of cell
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10
Q

What is hyperplasia?

A

- Hyperplasia is an increase in tissue/organ size due to increased cell numbers

  • It is a response to increased functional demand and/or hormonal stimulation
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11
Q

Describe the occurrence and control of hyperplasia

A
  • Occurs in labile/stable tissues
  • May occur secondary to a pathological cause but the proliferation is a normal response
  • Remains under physiological control
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12
Q

Provide two examples of physiological hyperplasia

A
  • Increased erythrocyte production by bone marrow due to hypoxia
  • Proliferative endometrium under the influence of oestrogen
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13
Q

Provide two examples of pathological hyperplasia

A
  • Epidermal thickening in chronic eczema/psoriasis
  • Enlargement of thyroid gland due to iodine deficiency
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14
Q

What is hypertrophy?

A
  • Hypertrophy is an increase in tissue/organ size due to an increase in cell size without an increase in cell numbers
  • It is a response to increased functional demand and/or hormonal stimulation
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15
Q

Where does hypertrophy occur?

A
  • Occurs in labile (easily changed), stable and permanent tissues
  • Seen especially in permanent cell populations due to little/no replicative potential
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16
Q

Provide two examples of physiological hypertrophy

A
  • The skeletal muscle hypertrophy of a bodybuilder
  • The smooth muscle hypertrophy of a pregnant uterus (also involves hyperplasia) under the influence of oestrogen
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17
Q

Provide three examples of pathological hypertrophy

A
  • Ventricular cardiac muscle hypertrophy due to systemic hypertension / valvular disease
  • Smooth muscle hypertrophy due to intestinal stenosis
  • Bladder smooth muscle hypertrophy due to prostate gland enlargment
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18
Q

What is compensatory hypertrophy?

A

Compensatory hypertrophy is an increase in the size / function of an organ or part to counteract a structural or functional defect

e.g. if one kidney is removed the other enlarges

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19
Q

What is atrophy?

A
  • Atrophy is the shrinkage of a tissue / organ due to an acquired decrease in size and/or number of cell
  • Due to a reduced supply of growth factors and/or nutrients
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20
Q

What is happening in cell atrophy?

A
  • Shrinkage in the cell size to a point at which survival is still possible
  • Reduced structural components of the cell
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21
Q

Which processes underpin organ/tissue atrophy?

A

Organ/tissue atrophy is typically due to combination of cellular atrophy and apoptosis (programmed cell death)

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22
Q

Provide two examples of physiological atrophy

A
  • Ovarian atrophy in post-menopausal women
  • The decrease in size of the uterus after parturition
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23
Q

What are the 8 different pathological causes of atrophy?

A
  • Reduced functional demand/workload (atrophy of disuse)
  • Loss of innervation (denervation atrophy)
  • Inadequate blood supply
  • Inadequate nutrition
  • Loss of endocrine stimuli
  • Persistent injury
  • Aging (senile atrophy)
  • Pressure
24
Q

Provide an example for the following forms of pathological atrophy:

  • Atrophy of disuse
  • Denervation atrophy
A
  • Reduced functional demand/workload – muscle atrophy after disuse
  • Loss of innervation – wasted hand muscles after median nerve damage
25
Q

Provide an example for the following causes of pathological atrophy:

  • Inadequate blood supply
  • Inadequate nutrition
A
  • Inadequate blood supply – thinning of skin on legs with peripheral vascular disease
  • Inadequate nutrition – wasting of muscles with malnutrition
26
Q

Provide an example for the following causes of pathological atrophy:

  • Persistent injury
  • Loss of endocrine stimulus
A
  • Loss of endocrine stimuli – breast, reproductive organs
  • Persistent injury – polymyositis (inflammation of muscle)
27
Q

Provide an example for the following causes of pathological atrophy:

  • Aging
  • Pressure
A
  • Aging – brain, heart
  • Pressure – tissues around an enlarging benign tumour (secondary to ischaemia)
28
Q

What is metaplasia?

A

rare

  • Metaplasia is the reversible change of one differentiated cell type to another due to altered stem cell differentiation
  • Sometimes a prelude to dysplasia (abnormal development of cells) and cancer
29
Q

Where does metaplasia occur?

A
  • No metaplasia across germ layers
  • Occurs only in labile or stable cell types
30
Q

Provide two examples of metaplasia

A
  • Bronchial pseudostratified ciliated epithelium → stratified squamous epithelium due to effect of cigarette smoke
  • Stratified squamous epithelium → gastric glandular epithelium with persistent acid reflux (Barrett’s oesophagus)
31
Q

Does metaplasia predispose to cancer?

A

Epithelial metaplasia can be a prelude to dysplasia and cancer:

  • Barrett’s epithelium and oesophageal adenocarcinoma
  • Intestinal metaplasia of the stomach and gastric adenocarcinoma
32
Q

What is regeneration?

A

Regeneration is the replacement of cell losses by identical cells in order to maintain the size of a tissue or organ

33
Q

Which factors induce cells to regenerate?

A
  • Growth factors in the microenvironment
  • Cell-to-cell communication
34
Q

Describe the regenerative capacity of the following tissues:

  • Bone
  • Tendons
  • Articular cartilage
A
  • Bone – very good
  • Tendons – poor, heal very slowly as they have few cells and few blood vessels
  • Articular cartilage – poor (avascular)
35
Q

Describe the regenerative capacity of the following tissues:

  • Adipocytes
  • Epithelia
  • Liver
A
  • Adipocytes – none, new fat cells are formed by undifferentiated cells that lie among the adipocytes
  • Epithelia – very good
  • Liver – very good
36
Q

Describe the regenerative capacity of the following tissues:

  • Mesothelia
  • Melanocytes
  • Smooth muscle
A
  • Mesothelia – good
  • Melanocytes – tend to regenerate too little / too much
  • Smooth muscle – very good
37
Q

Describe the regenerative capacity of the following tissues:

  • Striated muscle
  • Peripheral nerves
  • Central Nervous system
A
  • Striated muscle – limited, regeneration via satellite cells
  • Peripheral nerves – regenerate well, sprouting axons grow at 1-3 mm/day
  • Central nervous system – in humans, none
38
Q

What is reconstitution?

A
  • Reconstitution is the replacement of a lost part of the body
  • It requires the coordinated regeneration of several types of cells
  • E.g. regrowth of a lizard’s tail*
39
Q

What is aplasia?

A

Aplasia is the complete failure of a specific tissue/organ to develop

  • It is an embryonic developmental disorder e.g. aplasia of a kidney
40
Q

What is involution?

A

Involution is the normal programmed shrinkage of an organ, it overlaps with atrophy e.g. uterus after childbirth, thymus in early life

41
Q

What is hypoplasia?

A
  • Hypoplasia is the congenital underdevelopment or incomplete development of a tissue or organ (spectrum of aplasia)
  • There are an inadequate number of cells within the tissue which is present
  • E.g. renal hypoplasia, testicular hypoplasia in Klinefelter’s syndrome, hypoplasia of the chambers of the heart*
42
Q

What is atresia?

A

Atresia is the congenital imperforation of an opening (no orifice) e.g. atresia of the anus or vagina

43
Q

What is dysplasia?

A
  • Dysplasia is the abnormal maturation of cells within a tissue
  • It is potentially reversible but is often a pre-cancerous condition
44
Q

Benign prostatic hyperplasia (BPH) occurs in 80% of men by the 8th decade and is androgen dependent.

Which part of the prostate is affected and why is this important?

A
  • The periurethral area (transition zone)
  • The nodules that form press on the urethra and partially obstruct the flow of urine i.e. the patient experiences symptoms of bladder outflow obstruction
45
Q

What secondary effects can BPH have on the bladder?

A
  • Bladder muscle hypertrophy
  • Bladder distension
  • Urinary retention
46
Q

Does BPH predispose a patient to prostatic carcinoma?

A

No

47
Q

Psoriasis is a common inflammatory dermatitis which affects 1-2% of people. The skin develops scales and bleeds easily.

Which areas of the body are commonly affected?

A

The skin of the elbows, knees, scalp, ears

48
Q

How does the skin in psoriasis differ from normal skin macroscopically and microscopically?

A

Macroscopically – well-demarcated, pink–salmon-coloured plaques covered by loosely adherent scales which are silver/white in colour

Microscopically – marked epidermal thickening, decreased/absent granular layer, minute microabscesses of neutrophils, dilated blood vessels within dermal papillae

49
Q

What alterations occur in proliferation of the squamous cells in psoriasis and how is this achieved?

A
  • Psoriasis is a T cell-mediated disease (CD4+ and CD8+) with increased keratinocyte proliferation by unknown antigen
  • The T cells produce growth factors for keratinocytes and induce them to proliferate at approximately 10x the normal rate
50
Q

Apart from the skin which other parts of the body can be affected by psoriasis?

A
  • In 30-50% of cases the nails are also affected
  • In 5-10% of cases the joints are also affected (psoriatic arthritis)
51
Q

A 23 year old man is involved in a car accident in which his right leg is fractured in three places. He is immobilised in bed, because of other injuries for three weeks.

What changes can occur to his leg due to the immobilisation, and why?

A
  • Skeletal muscle atrophy due to a decrease in cell and tissue size as a result of decreased functional demand/workload
  • Osteoporosis of disuse due to increased bone resorption as a result of lack of mechanical stress on the bone
52
Q

What other conditions can occur as a result of prolonged immobilisation?

A
  • Decreased pulmonary ventilation
  • Thromboembolism
  • Pressure sores
53
Q

What is Barrett’s oesophagus?

A
  • Barrett’s oesophagus is the metaplasia of oesophageal stratified squamous epithelium to gastric/intestinal type epithelium
  • It occurs secondary to persistent acid reflux from the stomach into the oesophagus and predisposes to oesophageal adenocarcinoma
54
Q

can atrophy be reversed

A

reversible up to a point where its been months or years

less so when the parenchymal cells are replaced with connective tissue

55
Q

when can metaplasia be adaptive an useful

A
  • bone marrow destroyed by disease => splenic tissue turns into bone marrow
  • columnar epithelium -> stratified squamous epithelium to resist mechanical abrasions by stones

SA pathological processes (15 decks)

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