Body's Extracellular Environment

Composition of the Extracellular Environment

The extracellular environment consists of all body fluids and substances outside the cells. It plays a crucial role in supporting cell function and communication.

• Extracellular fluid (ECF): Includes interstitial fluid, plasma, and transcellular fluids.

• Extracellular matrix (ECM): A network of proteins (e.g., collagen, elastin) and polysaccharides that provide structural and biochemical support to surrounding cells.

• Functions: Provides nutrients, removes waste, and facilitates cell signaling.

Cellular Mechanisms for Adherence and Communication

• Cell adhesion molecules (CAMs): Proteins on the cell surface that help cells stick to each other and to the ECM.

• Junctions: Tight junctions, desmosomes, and gap junctions enable physical connection and communication between cells.

• Signaling: Cells use contact signaling, chemical signaling (e.g., hormones, neurotransmitters), and electrical signaling to communicate.

Tissues: Types, Structure, and Function

Definition and Classification of Tissues

Tissue is a group of similar cells that perform a common function. Histology is the study of tissues. The four main tissue types are:

• Epithelial tissue

• Connective tissue

• Muscle tissue

• Nervous tissue

Epithelial Tissue

• Structure: Sheets of tightly packed cells covering body surfaces and lining cavities.

• Functions: Protection, absorption, filtration, excretion, secretion, and sensory reception.

• Specializations: Microvilli (increase surface area), cilia (movement of substances).

• Properties: Polarity, avascularity, high regenerative capacity.

Types of Epithelial Tissue (by cell layers and shape)

Lab linked objective: Differentiate between epithelial tissues by structure and function.

Glands: Exocrine vs. Endocrine

• Exocrine glands: Secrete products into ducts (e.g., sweat, salivary glands).

• Endocrine glands: Release hormones directly into the bloodstream (e.g., thyroid, pituitary).

• Structural difference: Exocrine glands have ducts; endocrine glands are ductless.

Multicellular Exocrine Glands

• Structural classification: Simple (unbranched duct) vs. compound (branched duct).

• Functional classification: Merocrine (exocytosis), apocrine (part of cell pinched off), holocrine (cell ruptures).

Connective Tissue

• Structure: Cells scattered within an abundant extracellular matrix.

• Functions: Support, protection, insulation, storage, transport.

• Specializations: Vary by type (e.g., bone is mineralized, blood is fluid).

Types of Connective Tissue

Lab linked objective: Identify dense regular, dense irregular, elastic, and cartilage tissues.

Membranes: Serous vs. Mucous

• Serous membranes: Line body cavities not open to the exterior; secrete serous fluid (e.g., pleura, pericardium).

• Mucous membranes: Line cavities open to the exterior; secrete mucus (e.g., respiratory, digestive tracts).

• Differences: Structure (epithelial type), location, and secretion type.

Tissue Repair

• Phases: Inflammation, organization (granulation tissue formation), regeneration, and fibrosis (scar formation).

• Growth factors: Proteins that stimulate cell division and tissue repair.

• Variables affecting repair: Nutrition, blood supply, age, type of tissue damaged.

Cellular Structure and Membrane Transport

Plasma Membrane Structure

• Phospholipid bilayer: Hydrophilic heads face outward, hydrophobic tails inward.

• Proteins: Integral (span membrane) and peripheral (surface-bound) proteins serve as channels, receptors, enzymes.

• Carbohydrates: Attached to proteins/lipids, function in cell recognition.

Membrane Transport Mechanisms

Cellular Structures: Structure and Function

• Nucleus: Contains genetic material (DNA), controls cell activities.

• Nucleolus: Site of ribosome synthesis.

• Ribosome: Protein synthesis.

• Golgi apparatus: Modifies, sorts, and packages proteins/lipids.

• Smooth endoplasmic reticulum (ER): Lipid synthesis, detoxification.

• Rough ER: Protein synthesis (with ribosomes attached).

• Lysosome: Digestion of cellular waste.

• Peroxisome: Breakdown of fatty acids, detoxification.

• Mitochondria: ATP production (cellular respiration).

• Microtubules, microfilaments, intermediate filaments: Cytoskeleton, cell shape, movement.

• Cilia and flagella: Movement of cell or substances across cell surface.

Cell Cycle Events

• Interphase: Cell grows, DNA replicates.

• Prophase: Chromosomes condense, spindle forms.

• Metaphase: Chromosomes align at cell equator.

• Anaphase: Sister chromatids separate.

• Telophase: Nuclear envelope reforms, chromosomes decondense.

• Mitosis: Division of nucleus.

• Cytokinesis: Division of cytoplasm, two daughter cells form.

Example: During tissue repair, cells undergo mitosis to replace damaged cells, and the process is regulated by growth factors and the cell cycle.

Additional info: The above content is expanded and organized based on the provided study guide objectives, with academic context added for clarity and completeness.