Histology Chapter 5

Introduction to Tissues

• Tissues are categorized into four main types: epithelial, connective, nervous, and muscular.
• Functions of tissues stem from similar cells performing specific roles.
• Histology is the study of microscopic tissue anatomy.

Tissue Characteristics

• Tissues differ in cell types, functions, and matrix characteristics like fibrous proteins and ground substances (fluid or gel).

Epithelial Tissue

• Composed of sheets of cells that cover surfaces and line cavities, and make up most glands.
• Avascular with a high mitotic rate.
• Functions include protection, secretion, waste excretion, absorption, filtration, and stimulus sensing.

Epithelial Structure

• Basal surface faces blood supply while apical surface faces body surfaces or internal cavities.
• Simple epithelium consists of one layer, while stratified epithelium has multiple layers, named by the shape of apical cells.

Types of Simple Epithelia

• Simple Squamous: Thin, scaly cells facilitating rapid diffusion; found in alveoli and blood vessels.
• Simple Cuboidal: Cube-shaped cells; involved in absorption and secretion; located in glands and kidney tubules.
• Simple Columnar: Tall, narrow cells with microvilli for absorption and secretion; seen in the GI tract and uterus.

Types of Stratified Epithelia

• Stratified Squamous: Most widespread; deepest layers undergo mitosis; includes keratinized (skin) and nonkeratinized (oral cavity) types.
• Stratified Cuboidal: Rare; involved in secretion, seen in sweat glands.
• Stratified Columnar: Rare type with limited locations.

Connective Tissue Overview

• Composed of living cells within a non-living matrix; includes fibers (collagen, elastic, reticular) and ground substance.
• Primary functions: support, binding, protection, movement, immune response, storage, heat production, and transport.

Fibrous Connective Tissue

• Cells: Fibroblasts (create matrix), immune cells, adipocytes (store fat).
• Matrix: Contains collagen (strong), elastic (stretchy), and reticular (framework) fibers; ground substance is gelatinous, impacting tissue stiffness.

Types/Examples of Fibrous Connective Tissue

• Loose Connective Tissue: Gel-like; found beneath epithelial tissues.
• Dense Regular Connective Tissue: Parallel fibers; found in tendons and ligaments.
• Dense Irregular Connective Tissue: Random fiber orientation; located in skin dermis and organ capsules.
• Adipose Tissue: Stores energy, provides insulation and cushioning; brown fat is involved in heat generation.

Cartilage

• Flexible connective tissue with chondrocytes in lacunae, lacking blood vessels; heals slowly.
• Types of cartilage:
  • Hyaline Cartilage: Clear, in joints and respiratory structures.
  • Elastic Cartilage: Contains elastic fibers; found in ear and epiglottis.
  • Fibrocartilage: Strong, shock-absorbing; located in intervertebral discs and pubic symphysis.

Bone Tissue

• Calcified connective tissue categorized into spongy (porous, found in long bones) and compact (dense, arranged in cylinders).
• Osteons consist of a central canal surrounded by concentric lamellae, housing mature bone cells (osteocytes) within lacunae.

Blood

• Fluid connective tissue with a transportation function, containing erythrocytes (RBCs), leukocytes (WBCs), and platelets for clotting.
• Plasma acts as the blood's ground substance.

Nervous Tissue

• Responsible for communication through electrical and chemical signals.
• Composed of neurons (nerve cells) and neuroglia (supporting cells).
• Neurons consist of a cell body (neurosoma), dendrites (signal reception), and an axon (outgoing signal transmission).

Muscular Tissue

• Specialized for contraction; responsible for body movements, digestion, respiration, blood circulation, and heat production.
• Types include:
  • Skeletal Muscle: Long, striated cells under voluntary control.
  • Cardiac Muscle: Branched, striated cells forming the heart; involuntary, with intercalated discs.
  • Smooth Muscle: Fusiform cells with single nuclei; involuntary, found in hollow organ walls.

Glands

• Organs or cells that secrete useful products (endocrine or exocrine).
• Endocrine Glands: Ductless; secrete hormones into the bloodstream.
• Exocrine Glands: Use ducts to transport secretions to surfaces; some organs function as both.