ATP Generation in Human Cells

ATP Generation

• ATP can be produced via aerobic and anaerobic pathways.
• Aerobic respiration requires oxygen and occurs in the mitochondria.
• Anaerobic pathway functions without oxygen, utilizing glycolytic oxidation from glucose/glycogen.

Impact of Oxygen and Glucose Supply

• Interrupted blood supply results in both oxygen and glucose deficit, causing complete ATP depletion and severe cell injury.
• Defects in oxygen transport (e.g., RBC issues, lung disease) compromise only oxygen supply, allowing some ATP generation through anaerobic means.

Tissues Dependent on Aerobic Respiration

• Myocardium cells, proximal tubular cells of kidneys, and CNS neurons rely solely on aerobic respiration, making them more sensitive to hypoxia.

Intracellular Lactic Acidosis

• Low oxygen levels lead to mitochondrial failure, switching to anaerobic glycolysis, resulting in lactic acid accumulation.
• This causes decreased intracellular pH, chromatin clumping, and disrupted cellular integrity.

Damage from ATP Depletion

• Reduced ATP affects sodium/potassium pumps, leading to increased intracellular sodium and cell swelling (hydropic swelling).
• Decreased ATP hinders phospholipid production, hampering cell membrane repair.

Reduced Protein Synthesis

• Membranes of the endoplasmic reticulum and Golgi apparatus swell, leading to ribosome detachment and diminished protein synthesis.
• Other cellular alterations include loss of microvilli, bleb formation, and myelin figures.

Irreversible Cell Injury

• Prolonged ischemia or hypoxia leads to continuous ATP depletion, reduced protein levels, decreased intracellular pH, and lysosomal enzyme leakage, culminating in cell death.
• Key features of irreversible injury include cytosolic calcium influx, activated phospholipases, proteases, endonucleases, and lysosomal enzymes.

Causes of Irreversible Cell Injury

• Calcium influx results in vacuole formation in mitochondria and deposition of calcium salts.
• Activated phospholipases damage cell membrane phospholipids, affecting membrane function.
• Intracellular proteases lead to cytoskeleton degradation.
• Activated endonucleases damage DNA, causing nuclear changes (pyknosis, karyorrhexis, karyolysis).

Microscopic Features of Cell Injury

• Hydropic swelling features swollen tubular epithelial cells, clear cytoplasmic vacuoles, and cytoplasmic blebs.
• Hyaline change presents as glassy, eosinophilic proteinaceous material in histological sections, appearing intracellularly (e.g., hyaline droplets in kidney) or extracellularly (e.g., hyaline arteriolosclerosis).

Mucoid Change/Degeneration

• Mucoid degeneration involves excessive mucus production from epithelial cells or connective tissues.
• Notable examples include catarrhal inflammation, cystic fibrosis, and mucin-secreting tumors.

Fibrinoid Necrosis

• Characterized by fibrin-like material deposition, it occurs in immunologic tissue injuries (e.g., immune complex vasculitis).

Apoptosis Mechanism

• Apoptosis is a programmed cell death process, distinct from necrosis, causing no inflammatory response.
• It can occur physiologically (e.g., hormonal tissue involution) or pathologically (e.g., tumor response to chemotherapy).

Molecular Processes in Apoptosis

• Initiators include the withdrawal of survival signals and the presence of injurious agents.
• Final phases involve caspase activation leading to nuclear and cytoskeletal damage, and disruption of membranes.
• Phagocytosis of apoptotic cells occurs through mechanisms like thrombospondin binding and phosphatidylserine exposure.

This quiz focuses on the processes of ATP generation in human cells, specifically through aerobic and anaerobic pathways. It explores the significance of oxygen in aerobic respiration and the role of glycolytic oxidation in anaerobic environments. Test your knowledge on how these mechanisms contribute to cellular energy.