Tissue level of organization Sp_Fall (1)

Histology Overview

• Study of tissues– groups of similar cells and their extracellular matrix (ECM).

Objectives

• Identify and describe various tissue types and their functions.

• Differentiate between endocrine and exocrine glands: structure, function, location.

• Describe the structure and function of different membranes.

• Analyze how epithelial tissues' structure enables their functions.

• Understand connective tissues' characteristics and functions.

• Learn muscle tissue characteristics and their functional significance.

Definition of Tissue

• A tissue is a group of similar cells and their products that share an embryonic origin and collaborate in performing specific physiological or structural roles.

• Tissues are formed through the linking of cells to the ECM:

  • Extracellular Matrix (ECM):

    • Made of fibrous proteins providing support.

    • Ground substance fills spaces between fibers and cells, absorbing water.

Embryonic Origin of Tissues

• Layers of Germ Cells:

  • Ectoderm: Skin, Brain.

  • Mesoderm: Cardiac Muscle, Blood Cells.

  • Endoderm: Lung Cells, Thyroid cells.

Primary Tissue Classes

• Epithelial: Covers surfaces.

• Connective: Supports.

• Nervous: Controls.

• Muscular: Moves.

Nervous Tissue

• Function: Internal communication.

• Main Components: Brain, Spinal cord, Nerves.

Muscle Tissue

• Function: Contracts to facilitate movement.

• Types: Skeletal (attached to bones), Cardiac (heart), Smooth (hollow organs).

Epithelial Tissue Characteristics

• Composed of tightly packed cells: simple or stratified.

• Covers body surfaces and lines cavities.

• Forms linings of organs and constitutes glandular structures.

• Cells exhibit polarity, are connected by junctions, and lack blood vessels.

• Relies on underlying connective tissue for nourishment.

Basement Membrane

• Structure between epithelium and connective tissue.

• Composed of basal lamina and reticular lamina.

Cell Junctions

• Tight Junctions: Prevent molecules from passing between cells.

• Desmosomes: Anchor adjacent cells together.

• Gap Junctions: Allow communication between cells.

Simple vs. Stratified Epithelia

• Simple Epithelia: One cell layer; includes squamous, cuboidal, columnar types.

• Stratified Epithelia: Two or more layers; includes squamous, cuboidal, columnar, and transitional types.

Types of Simple Epithelia

• Simple Squamous: Allows for diffusion (e.g., found in blood vessels).

• Simple Cuboidal: Involved in secretion and absorption (e.g., kidney tubules).

• Simple Columnar: Absorptive surfaces (e.g., digestive tract).

• Pseudostratified Columnar: Appears stratified but is not; involved in secretion and movement.

Types of Stratified Epithelia

• Stratified Squamous: Protects underlying tissues; can be keratinized (skin) or non-keratinized (mouth).

• Stratified Cuboidal: Rare, found in some gland ducts.

• Stratified Columnar: Limited distribution; found in transition zones.

• Transitional: Specialized for the urinary system; cells change shape with filling.

Endocrine vs. Exocrine Glands

• Gland: Cells/Organs that secrete substances.

• Exocrine Glands: Maintain contact with surface via ducts (e.g., sweat glands).

• Endocrine Glands: Secrete hormones directly into the bloodstream; no ducts (e.g., thyroid).

Connective Tissue Overview

• Composed of cells dispersed in a matrix (includes fibers and ground substance).

• Types: fibrous, adipose, cartilage, bone, blood.

• Functions: support, protection, binding, storage.

Connective Tissue Types

• Loose Connective Tissue: Fills spaces between organs (e.g., Areolar, Adipose).

• Dense Connective Tissue: Provides strength (e.g., tendons, ligaments).

• Supporting Connective Tissue: Provides structure (e.g., cartilage, bone).

  • Cartilage Types: Hyaline (flexible), Elastic (elasticity), Fibrocartilage (shock absorption).

  • Bone Types: Compact and Spongy.

Fluid Connective Tissue

• Blood: Cells suspended in fluid ECM; includes RBCs, WBCs, platelets.

• Lymph: Contains lymphocytes; drains excess interstitial fluid.

Excitable Tissues

• Muscular and Nervous Tissues: Respond to stimuli through electrical and chemical signals.

• Membrane Potential: Basis for signaling in these tissues.

Tissue Injury and Repair

• Inflammation: Body's initial response to injury; characterized by redness, swelling, pain, heat.

• Tissue Repair Mechanisms: Regeneration (same type) vs. fibrosis (scar tissue).

• Necrosis: Accidental cell death; induces inflammation.

• Apoptosis: Programmed cell death; does not cause inflammation.