Cell theory

Cell Theory

  • Principles of Cell Theory:

    1. All living organisms are composed of one or more cells.

    2. Cells are the smallest units of life.

    3. New cells arise only from pre-existing cells through cell division.

Organization of Animal Bodies

  • All animal cells share similarities in:

    • Material exchange with surroundings.

    • Energy acquisition from organic nutrients.

    • Synthesis of complex molecules.

    • Reproduction.

    • Response to signals.

  • Animals begin life as a single fertilized egg, which divides and specializes into various cell types.

Cell Characteristics and Proteomes

  • Proteome: Different proteins expressed determine the characteristics of various cell types, despite identical DNA in each cell.

Cell Morphology

  • Eukaryotic cells exhibit significant variation in size and shape, even within cells having the same genome.

Types of Animal Tissue

  • There are four general types:

    1. Epithelial Tissue: Forms continuous sheets to cover/line surfaces.

    2. Connective Tissue: Supports and connects tissues.

    3. Nervous Tissue: Conducts electrical signals.

    4. Muscle Tissue: Facilitates movement.

Epithelial Tissues

  • Function: Cover organs, line cavities, protect and absorb.

  • Types based on layers:

    • Simple: Single layer.

    • Stratified: Multiple layers.

    • Pseudostratified: Appears stratified but is one layer.

  • Cell Shapes: Cuboidal, squamous, and columnar.

Connective Tissues

  • Functions include:

    • Connecting and supporting structures.

    • Comprising blood, adipose, bone, and more.

    • Formulating an extracellular matrix (ECM).

  • Types of ECM Proteins: Collagen and elastin (for strength and flexibility).

Blood Composition

  • Blood consists of red and white blood cells and platelets within plasma containing electrolytes and proteins.

  • Adipose tissue provides insulation and energy storage.

Nervous Tissue

  • Comprises complex networks of neurons that conduct electrical signals.

  • Functions include initiating and conducting impulses affecting muscles and glands.

Muscle Tissue

  • Specialized for contraction:

    • Types:

      • Skeletal Muscle: Voluntary movement.

      • Smooth Muscle: Involuntary control of tubes.

      • Cardiac Muscle: Involuntary, found in the heart.

Tissues and Organ Systems

  • Tissues: Groups of similar cells, over 200 types in humans.

  • Organs: Combinations of tissues performing specific functions.

  • Organ Systems: Collections of organs working together (e.g., digestive, nervous systems).

Homeostasis

  • Definition: Maintenance of stable internal conditions despite external changes.

  • Regulators: Actively maintain internal conditions, using more energy.

  • Conformers: Match internal environment with external, using less energy.

Homeostatic Variables

  • Variables like blood glucose levels fluctuate but are regulated by mechanisms ensuring stability.

  • Examples include temperature regulation, blood sugar, and pressure regulation.

Homeostatic Control Systems

  • Components of control include:

    • Set Point: Normal value.

    • Sensor: Monitors the variable.

    • Integrator: Compares sensor input with set point.

    • Effector: Initiates response to restore set point.

Feedback Mechanisms

  • Negative Feedback: Reduces output or activity to maintain the set point (e.g., temperature control).

  • Positive Feedback: Amplifies changes in a process until completion (e.g., childbirth, blood clotting).

Feedforward Regulation

  • Prepares the body for changes before they occur, optimizing responses and minimizing deviations.

Key Cell Processes

  • Six basic processes:

    1. Cell division

    2. Growth

    3. Differentiation

    4. Migration

    5. Apoptosis

    6. Cell connections

Body Fluids

  • Composed mainly of water.

  • Compartmentalized into intracellular (inside cells) and extracellular (outside cells) fluids.

  • Types of Extracellular Fluids: Plasma (blood) and interstitial fluid (between cells).

Cell Communication

  • Essential for coordinated activities within organisms.

  • Types of signaling include:

    1. Direct intercellular signaling

    2. Contact-dependent signaling

    3. Autocrine signaling

    4. Paracrine signaling

    5. Endocrine signaling.

Stages of Cell Signaling

  • Three stages:

    1. Receptor activation

    2. Signal transduction

    3. Cellular response.

  • Ligands bind to receptors affecting cellular processes.

Example of Signaling Pathway

  • Epinephrine: A fight-or-flight hormone influencing various body functions.

  • Involves a cascade of reactions leading to changes in cellular activity, such as increased heart rate.