Altered Cells and Tissues: Cellular Adaptation and Maladaptation

Levels of Structural Organization: The human body is organized hierarchically as follows: * Cells: The basic functional unit. * Tissues: Groups of similar cells performing a specific function (e.g., epithelial tissue, smooth muscle tissue). * Organs: Structures composed of different tissues working together (e.g., Stomach, Liver, Small Intestine). * Organ Systems: Groups of organs that coordinate to perform complex functions (e.g., Digestive System).
Cellular Components and the Plasma Membrane: * Plasma Membrane: Functions as a semi-permeable barrier that separates intracellular components from the extracellular environment. * Phospholipid Bilayer Structure: * Polar Heads: Hydrophilic (water-attracting) portions facing the exterior and interior fluids. * Fatty Acid Tails: Hydrophobic (water-repelling) portions located in the membrane interior. * Membrane Proteins: * Integral Proteins: Embedded within the lipid bilayer. * Transmembrane Proteins: Span the entire width of the membrane. * Channel Proteins: Form pores for substance passage. * Peripheral Proteins: Attached to the exterior or interior surfaces. * Cytoplasm: The fluid-filled space within the cell membrane.

Major Organelles: * Endoplasmic Reticulum (ER): Involved in protein and lipid synthesis. * Golgi Apparatus: Responsible for packaging and distributing cellular products. * Lysosomes: Contain enzymes for digestion and waste removal. * Peroxisomes: Break down fatty acids and detoxify substances. * Proteasomes: Degrade unneeded or damaged proteins. * Mitochondria: The energy-producing centers of the cell. * Nucleus: Contains the genetic material (DNA). * Cytoskeleton: Provides structural support and facilitates movement.
The 6 Habits of Highly Effective Cells: * Transportation: Moving substances in and out. * Ingestion: Taking in nutrients and materials. * Secretion: Releasing manufactured products. * Respiration: Transforming fuel into energy. * Communication: Signalling between cells. * Reproduction: Cellular division and differentiation.

Passive Transport: * Requires no energy expenditure. * Movement occurs from areas of high concentration to low concentration. * Diffusion: Movement of particles. * Osmosis: Movement of water across a membrane.
Facilitated Transport: * Still classified as passive (requires no energy). * Requires a specific transport protein to facilitate the movement of substances across the membrane.
Active Transport: * Requires energy in the form of Adenosine Triphosphate ( $ATP$ ). * Moves substances against the concentration gradient (from low to high concentration). * Involves the conversion of $ATP \rightarrow ADP$ .
Ingestion (Endocytosis): * The process of bringing large substances into the cytoplasm via vesicles. * Pinocytosis: Ingestion of small liquid-containing vesicles. * Phagocytosis: Ingestion of large particles, including whole cells, bacteria, and cell components. A phagosome is formed and subsequently fuses with a lysosome for digestion.

Secretion (Exocytosis): * Cellular products are packaged into vesicles by the Golgi apparatus and transported out of the cell through the plasma membrane.
Respiration: * Metabolic processes that transform fuel molecules into energy and waste products. * Aerobic Respiration: Produces $ATP$ using oxygen ( $O_2$ ). * Anaerobic Respiration: Produces $ATP$ without the use of oxygen ( $O_2$ ).
Communication: * Controlled by receptor-ligand binding. * Signals control cellular behavior and function. * Feedback mechanisms are essential to prevent cellular damage.
Reproduction: * Mitosis: Cell division resulting in identical daughter cells. * Meiosis: Specialized division for reproductive cells. * Differentiation: The process that directs the development of specific cell types.

Adaptive Mechanisms: Protective measures to prevent harm to tissues and cells. Cells change in size, number, or form to meet work demands. Adaptation ideally stops once the stressor is removed.
Types of Adaptations: * Atrophy: A decrease in cell size to become more efficient; often occurs due to reduced stimulation or workload. * Hypertrophy: An increase in cell size and total tissue mass. * Hyperplasia: An increase in the number of cells in an organ or tissue; occurs in cells capable of mitotic division (e.g., epidermis, GI tract). * Metaplasia: The replacement of one adult cell type with another adult cell type. * Dysplasia: Deranged cell growth resulting in cells that vary in size, shape, and organization; often a precursor to malignancy.