Cell Transport, Tissue Repair, Apoptosis vs Necrosis

• Passive transport across membranes does not use additional energy
• Active transport occurs when a cell uses energy to transport substances
• Two types of active transport:

  • Primary active transport: uses chemical energy like ATP
  • Secondary active transport: uses an electrochemical gradient as a source of energy
• Membrane proteins are specific and selective, working against a concentration gradient
• Example of primary active transport:

  • Three cytoplasmic Na+ bind to pump protein
  • Na+ binding promotes hydrolysis of ATP, releasing energy
  • Phosphorylation causes the pump to change shape, expelling Na+ to the outside
  • Two extracellular K+ bind to pump
  • K+ binding triggers release of the phosphate, and the pump resumes its original conformation
  • Pump protein binds ATP, releases K+ to the inside, and Na+ sites are ready to bind Na+ again
• Secondary active transport uses energy to transport molecules across a membrane, relying on the electrochemical potential difference created by pumping ions in/out of the cell
• Vesicular transport includes endocytosis and exocytosis:

  • Endocytosis: moves substances into the cell
  • Exocytosis: moves substances out of the cell
  • Both processes require the expenditure of energy (ATP)
• Types of endocytosis:

  • Phagocytosis ("cellular eating"): cell engulfs solid material and forms a phagosome
  • Pinocytosis ("cellular drinking"): cell membrane engulfs extracellular fluid
  • Receptor-mediated endocytosis: cell detects and engulfs specific material via specialized receptors
• Membrane transport is medically relevant as it helps in maintaining homeostasis, providing nutrients to cells, and keeping cells isotonic
• Tissue repair involves different types of injuries like abrasions, contusions, lacerations, punctures, and burns
• Main actions during wound healing:

  • Regeneration: repair with the replacement of the same cells and tissue
  • Fibrosis: different cell types replace damaged cells with connective tissue and scar tissue
• Stages of repair:

  • Inflammation stage: release of inflammatory chemicals, capillary dilation, and blood entry with WBCs
  • Organization: blood clot replaced with granulation tissue, highly vascularized
  • Regeneration: surface epithelial cells replace dead cells with new cells
• Regeneration capacity of tissues varies:

  • Epithelial, bone, and connective tissue regenerate well
  • Smooth muscle regenerates fairly well
  • Skeletal muscle and cartilage regenerate poorly
  • Cardiac muscle and nervous tissue have little to no regenerative capacity
• Uncontrolled inflammation may indicate infection during tissue repair
• In multicellular organisms, the distance for substances to enter cells is larger due to a higher surface area to volume ratio
• Multicellular organisms require specialised exchange surfaces for efficient gas exchange of carbon dioxide and oxygen due to their higher surface area to volume ratio
• Primary intention healing involves completely cleaning the wound and suturing the wound edges together
• Secondary intention healing involves leaving the wound to heal on its own, developing granulation tissue, scabbing, and eventually scarring (fibrosis)
• Tertiary intention healing includes completely cleaning the wound, letting it heal on its own, and later suturing the wound edges together
• Necrosis is the premature death of cells in living tissue caused by external factors like infection, toxins, or trauma
• Treatment for wound healing includes stopping bleeding, cleaning wounds with water or saline, removing debris, deciding on primary, secondary, or tertiary intention healing, dressing the wound with sterile gauze, bandaging with wrap material, and changing the dressing and bandage daily
• Antibiotics for wound healing are not necessary unless there are visible signs of infection to prevent the development of drug-resistant bacteria like MRSA
• Apoptosis is the process of programmed cell death involving cell changes like blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, and chromosomal DNA fragmentation
• Apoptosis is controlled by a diverse range of cell signals, either extracellularly (extrinsic inducers) or intracellularly (intrinsic inducers), which positively or negatively affect apoptosis
• Causes of apoptosis include glucocorticoids, extreme heat, ionizing radiation, nutrient deprivation, viral infection, hypoxia, and extreme increased intracellular calcium concentration
• Necrosis is the premature death of cells in living tissue caused by external factors like injury, infection, cancer, poisons, inflammation, or lack of blood flow
• Necrosis does not activate the immune system for phagocytosis like apoptosis, leading to a build-up of dead tissue and cell debris that may require surgical removal (debridement)
• Necrosis can release harmful chemicals into surrounding tissue, triggering further cell death and potentially leading to gangrene if enough contiguous tissue necrotizes
• Apoptosis involves single cells, is energy-dependent, causes cell shrinkage, maintains membrane integrity initially, involves nuclear condensation, and forms apoptotic bodies
• Necrosis involves sheets of cells, is energy-independent, causes cell swelling, loses membrane integrity early, lacks nuclear condensation, and leads to leakage of cellular contents and an inflammatory response