2A notes (tissues, membranes)

• 1. Merocrine secretion: Products are released by exocytosis, where vesicles fuse with the plasma membrane (e.g., salivary glands, most sweat glands).

  2. Apocrine secretion: A portion of the apical cytoplasm, containing the secretory product, pinches off from the cell (e.g., mammary glands).

  3. Holocrine secretion: The entire cell accumulates secretory product and then ruptures, releasing the product and cell fragments (e.g., sebaceous oil glands).

Connective Tissue

• The most abundant and diverse tissue type in the body, serving to support, connect, and protect other tissues.

• Components:

  • Cells: Various cell types specific to the connective tissue.

  • Protein Fibers:

    • Collagen fibers: Provide tensile strength.

    • Elastic fibers: Allow for stretch and recoil.

    • Reticular fibers: Form delicate, supportive frameworks.

  • Ground Substance: An amorphous material filling the space between cells and fibers, varying in consistency from fluid to gel to solid.

• Functions:

  • Binding organs together.

  • Providing structural support.

  • Energy storage (adipose tissue).

  • Transport (blood).

  • Immune protection.

• Types of Connective Tissue:

  • Loose Connective Tissue: Characterized by loosely arranged fibers.

    • Areolar: Functions as a universal packing material, found beneath epithelia.

    • Adipose: Stores fat, provides cushioning, and insulates.

    • Reticular: Forms the framework (stroma) of lymphoid organs like the spleen and lymph nodes.

  • Dense Connective Tissue: Contains densely packed fibers.

    • Dense regular: Fibers are arranged parallel, providing high tensile strength in one direction (e.g., tendons, ligaments).

    • Dense irregular: Fibers are irregularly arranged, providing strength in multiple directions (e.g., dermis of the skin).

    • Elastic: Contains a high proportion of elastic fibers, allowing for stretch and recoil (e.g., walls of large arteries).

  • Supporting Connective Tissue:

    • Cartilage: A firm, flexible tissue (e.g., hyaline cartilage, elastic cartilage, fibrocartilage).

    • Hyaline- primarily collagen fibers, evenly dispersed, provides support with some flexibility (joints)

    • Elastic- primarily elastic fibers with some collagen, maintains shape while allowing extreme flexibility (tip of nose and ears)

    • Fibrocartilage- primarily dense collagen fibers, minimal elastic fibers, resists strong compression and tension (kneecap and intervertebral discs)

    • Bone: Hard, rigid tissue, very minimal collagen

    • providing support and protection.

  • Fluid Connective Tissue:

    • Blood: Functions in the transport of nutrients, gases, and waste products throughout the body.

Muscle Tissue

• Skeletal Muscle:

  • Voluntary control.

  • Striated (appears striped under a microscope).

  • Primarily responsible for movement of bones and the body.

• Cardiac Muscle:

  • Involuntary control.

  • Striated.

  • Found exclusively in the heart, its contractions pump blood.

• Smooth Muscle:

  • Involuntary control.

  • Lacks striations.

  • Located in the walls of internal organs (e.g., stomach, intestines, blood vessels), facilitating the movement of substances through them.

Nervous

• Serves as the body's main control and communication system.

• Neurons: Specialized cells that generate and transmit electrical messages.

• Glial cells (Neuroglia): Provide protection, support, and nourishment to neurons.

• Predominantly found in the brain, spinal cord, and peripheral

Organs and Integration: Example the Stomach

• An organ is a structure composed of at least two different tissue types working together to perform specific functions.

• Stomach tissue integration:

  • Epithelial tissue: Lines the stomach lumen, secreting digestive acid and enzymes.

  • Connective tissue: Provides structural support, contains blood vessels for nutrient supply, and nerves for regulation.

  • Smooth muscle: Three distinct layers churn and mix food, facilitating mechanical digestion.

  • Nervous tissue: Regulates muscle contractions and glandular secretions, coordinating digestive processes.

Body Membranes

• Mucous Membrane:

  • Preforms absorptive, protective, and secretory functions and is formed from epithelium and lamina propria CT

  • Digestive tract, respiratory, urinary and reproductive

• Serous Membrane:

  • Lines closed ventral body cavities (e.g., thoracic and abdominopelvic cavities).

  • Composed of two layers: a parietal layer that lines the cavity wall and a visceral layer that covers the organs within the cavity.

  • Produces a thin, slippery serous fluid that lubricates the surfaces, reducing friction between organs and cavity walls.

• Cutaneous Membrane (Skin):

  • A dry membrane that forms the external covering of the body.

  • Consists of a keratinized stratified squamous epithelium (epidermis) attached to a thick layer of connective tissue (dermis).

  • Its primary function is to protect against water loss and physical jury.

• Synovial Membrane:

  • Lines the cavities of freely movable joints (e.g., knee, shoulder).

  • Composed of loose areolar connective tissue with specialized cells (synoviocytes).

  • Secretes synovial fluid, which lubricates the joint and nourishes the articular cartilage.