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USMLE - pathoma - Chapter 1 > Cellular injury > Flashcards

Cellular injury Flashcards

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USMLE® Step 1 flashcards
1
Q

When does cellular injury occur?

A

The cellular injury occurs when a stress exceeds the cell’s ability to adapt

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2
Q

What affects the likelihood of cellular injury?

A
  1. Type of stress
  2. severity of stress
  3. type of cells affected
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3
Q

Name examples of injury in different types of cells.

A
  1. Neurons are more susceptible to ischaemic injury compared to skeletal muscle
  2. Slow developing ischaemia (renal artery atherosclerosis) results in atrophy
  3. Acute ischaemia (renal artery embolus) results in injury.
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4
Q

Name some common causes of cellular injury.

A
  1. Inflammation
  2. Nutritional deficiency/excess
  3. Hypoxia
  4. Trauma
  5. Genetic mutations
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5
Q

What is definition of hypoxia?

A

Low oxygen delivery to issue - important cause of cellular injury

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6
Q

What is the pathology of hypoxia?

A
  1. Oxygen is the final electron acceptor in the electron transport chain of oxidative phosphorylisation.
  2. Decreased oxygen impairs oxidative phosphorylation resulting in decreased ATP production
  3. Lack of ATP distrupts cellular functions
    - Na+/K+ pump - sodium and water build up in cells
  • Ca2+ pump results in Ca2+ build up in the cytosol of the cell
  • Anaerobic glycolysis - lactic acid build up results in low ph - denaturing proteins and DNA.
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7
Q

Name 3 things caused by hypoxia?

A
  1. Ischaemia
  2. Hypoxaemia
  3. Decreased O2 carrying capacity of blood.
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8
Q

What is the definition of ischaemia?

A

Decreased blood flow to an organ

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9
Q

What are the causes of ischaemia?

A
  1. Decreased arterial perfusion e.g. Atherosclerosis
  2. Decreased venous drainage (Budd-Chiari syndrome - blockage of hepatic veins)
  3. Shock - generalised hypotension resulting in poor tissue perfusion.
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10
Q

What is the definition of hypoxemia?

A

Low partial pressure of oxygen in the blood (PaO2 <60 mmHg / SaO2 <90%)

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11
Q

What are the causes of hypoxemia?

A
  1. High altitude - decreased barometric pressure results in reduced partial pressure of O2
  2. Hypoventilation - increased PaCO2 results in decreased Pao2
  3. Diffusion defect - Thickened diffusion barrier (Interstitial pulmonary fibrosis) reduces O2 diffusion
  4. Ventilation/Perfusion mismatch
    - Blood bypasses oxygenated blood e.g. right - left shunt
    - Oxygenated air cannot reach blood e.g. atelectasis
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12
Q

Examples of how reduced oxygen carrying capacity arises with Hb loss?

A
  1. Anaemia -

2. Carbon monoxide poisioning - CO binds hemoglobin more avidly than oxygen

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13
Q

What are the classic findings of CO poisioning?

A
  1. Cherry red appearance of skin

2. Headaches, may lead to coma or death.

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14
Q

Describe the physiology of methemoglobinemia?

A
  1. Oxidant stress e.g. sulfa and nitrate drugs or in new borns
  2. Iron in haem is oxidised to Fe3+
  3. Fe3+ cannot bind to oxygen
  4. PaO2 is normal, SaO2 decreased
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15
Q

What is the classic finding in methemoglobinemia?

A

Chocolate coloured blood.

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16
Q

What is the treatment of methemoglobinemia?

A

IV methylene blue - reduces Fe2+ back to Fe3+ state.

17
Q

Hall marks of reversible injury in hypoxia

A

Cellular swelling
1. Cytosol swelling results in loss of microvillli and membrane blebbing (protrusions of membrane)

  1. Swelling of RER - dissociation of ribosomes and decreased protein synthesis
18
Q

Hallmarks of irreversible injury in hypoxia

A
  1. Plasma membrane damage
    - cytosolic (fluid portion of cytoplasm found in organelles) enzymes leaking into serum
    - additional calcium entering into the cell
  2. Mitochondrial membrane damage results in
    - loss of the electron transport chain in the inner mitochondrial membrane
    - Cytochrome c (mitochondrial protein) leaking into cytosol activating apoptosis
  3. Lysosome membrane damage results in hydrolytic enzymes leaking into the cytosol - in turn activated by high intracellular Ca2+

RESULTING IN CELL DEATH

USMLE - pathoma - Chapter 1 (5 decks)

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