Phagocytosis and Intracellular Killing Quiz

Damaged tissues release histamines, leading to increased blood flow (BF) and capillary leakage.

Histamines cause capillaries to leak, permitting phagocytes and complement factors (CF) to enter the wound site.

Phagocytes engulf bacteria, dead cells, and cellular debris to aid in tissue repair.

Platelets (PLTs) move out of capillaries to seal wounds.

The acute inflammatory response involves vascular and cellular events:

• Vascular events:
  • Vasodilation and increased BF
  • Increased vascular permeability
  • Formation of a fluid exudate
  • Three patterns of fluid leakage:

Histamine-mediated (transient, 30-60 minutes)

Cell-factor mediated (delayed, 2-3 hours)

Chemical toxin or burn-mediated (prolonged, 24 hours)

Cellular events:

• Margination: blood cells move nearer to the vessel wall, allowing for leukocyte rolling.
• Rolling: neutrophils bind to selectins on endothelial cells, facilitating their movement along the vessel wall.
• Adhesion: neutrophils attach firmly to the vessel wall, enabling transmigration.
• Transmigration (diapedesis): neutrophils squeeze between endothelial cells and the basement membrane to reach infected tissue.
• Chemotaxis: neutrophils are attracted to the site of tissue damage and move towards it in a directed manner.

Neutrophils respond to chemotactic factors through a process called chemotaxis, which is essential for their migration to the infected area.

Phagocytosis is the microbial activity of leukocytes, encompassing recognition, attachment, engulfment, and killing/degradation of pathogens.

Recognition and attachment involve interactions between pathogen surface molecules and phagocyte receptors, leading to receptor clustering and phagocytosis initiation.

Opsonization marks pathogens for ingestion by attaching immunoglobulins or complement components to their surfaces.

Engulfment entails the phagocyte surrounding the pathogen with its membrane and forming a phagosome, which later fuses with lysosomes to generate a phagolysosome for pathogen destruction.

Vulgaris infection affects dogs, cats, and horses.

Fibrocartilaginous embolism occurs in dogs and cats, leading to fibrocartilaginous infarcts which are classified as ischemic infarcts.

Ischemic infarcts are white, pale, and anemic, caused by arterial insufficiency in organs with end arteries.

Coagulative necrosis is a type of infarct characterized by tissue death due to lack of blood supply.

Hemorrhagic infarcts are red and result from venous insufficiency or hemorrhagic necrosis.

Infarcts can undergo various fates such as organization, scarring, sequestration, emollition, calcification, and regeneration.

Hemorrhagic infarcts are clinically important in the lungs, and are associated with bronchopneumonia in cats and dirofilaria immitis infections and endocrine disorders in dogs.

Cerebral stroke is a life-threatening event in which part of the brain is deprived of adequate oxygenation.

Ischemic strokes occur when the blood supply to the brain is interrupted, while hemorrhagic strokes result from bleeding into or around the brain.

Cerebral stroke is rare in domestic animals and is usually caused by head trauma.

Cardiac rhythm disorders can be analyzed through an electrocardiogram (ECG), which records the electrical activity of the heart.

The ECG recording consists of waves and leads, with their deflection and amplitude reflecting the direction of stimulation in the heart.

Abnormalities on the ECG can be caused by artifacts or physiological or pathological conditions.

Cardiac rhythm disorders include tachycardia, bradycardia, arrhythmia, persistent, paroxysmal, and heterotopic disorders.

Disorders in the flow of impulses can result in heart blocks, which affect the rate and origin of the cardiac rhythm.

Nomotopic disorders originate at normal sites such as the sinus node, while heterotopic disorders originate from abnormal sites.

Premature beats, supraventricular tachycardia, atrial flutter, and fibrillation, and ventricular tachycardia are common heterotopic disorders.