Tissues and Membranes: Structure, Function, and Classification in Anatomy & Physiology

Chapter 4: Tissues and Membranes

Preparation of Tissue Samples for Microscopy

To study tissues under a microscope, samples must be properly prepared. This process ensures that cellular structures are preserved and visible for examination.

• Fixation: Preserves tissue structure by preventing decay and autolysis, typically using chemicals like formalin.

• Slicing: Thin sections of tissue are cut using a microtome to allow light to pass through for microscopy.

• Staining: Application of dyes (e.g., hematoxylin and eosin) to highlight different cellular components and structures.

Chapter 4.2: Epithelial Tissue

Special Features and Functional Characteristics of Epithelial Tissue

Epithelial tissue covers body surfaces, lines cavities, and forms glands. It serves as a protective barrier and is involved in absorption, secretion, and sensation.

• Cellularity: Composed almost entirely of closely packed cells with minimal extracellular material.

• Polarity: Has an apical (free) surface and a basal (attached) surface.

• Attachment: Basal surface is attached to a basement membrane.

• Avascularity: Lacks blood vessels; nutrients diffuse from underlying tissues.

• Regeneration: High capacity for renewal due to frequent cell division.

Classification of Epithelia

Epithelia are classified by the number of cell layers and the shape of the cells at the apical surface.

• Simple epithelium: Single layer of cells.

• Stratified epithelium: Multiple layers of cells.

• Cell shapes: Squamous (flat), cuboidal (cube-shaped), columnar (tall and column-like).

Types of Epithelia: Functions and Locations

Type of Epithelia	Main Function(s)	Location(s)
Simple Squamous	Diffusion, filtration, secretion	Alveoli of lungs, lining of blood vessels (endothelium), serous membranes
Simple Cuboidal	Secretion, absorption	Kidney tubules, ducts of small glands, ovary surface
Simple Columnar	Absorption, secretion of mucus and enzymes	Digestive tract lining, gallbladder, uterine tubes (ciliated)
Pseudostratified Columnar	Secretion (mainly mucus), propulsion of mucus by cilia	Trachea, upper respiratory tract
Stratified Squamous	Protection from abrasion	Skin (keratinized), mouth, esophagus, vagina (non-keratinized)
Stratified Cuboidal	Protection	Largest ducts of sweat glands, mammary glands, salivary glands
Stratified Columnar	Protection, secretion	Rare; male urethra, some glandular ducts
Glandular	Secretion	Glands (endocrine and exocrine)

Definition of Gland

A gland is a structure composed of one or more cells that synthesizes and secretes a particular product (such as hormones, enzymes, or sweat).

Exocrine vs. Endocrine Glands; Multicellular vs. Unicellular Glands

• Exocrine glands: Secrete products into ducts that open onto body surfaces or into body cavities (e.g., sweat, salivary glands).

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

• Unicellular glands: Single-celled, such as goblet cells that secrete mucus.

• Multicellular glands: Composed of many cells, often with complex duct structures.

Classification of Multicellular Exocrine Glands

• Structural classification: Simple (unbranched duct) or compound (branched duct); tubular, alveolar, or tubuloalveolar secretory units.

• Functional classification: Merocrine (secrete by exocytosis), holocrine (entire cell ruptures), apocrine (apical part of cell pinches off).

Chapter 4.3: Connective Tissue

General Characteristics and Elements of Connective Tissue

Connective tissue is the most abundant and widely distributed tissue type in the body, providing support, protection, and binding of other tissues.

• Functions: Support, protection, insulation, storage, and transport (e.g., blood).

• Characteristics: Cells are separated by abundant extracellular matrix; varying degrees of vascularity.

• Structural elements:

  • Ground substance: Unstructured material filling the space between cells.

  • Fibers: Collagen (strength), elastic (flexibility), reticular (support).

  • Cells: Fibroblasts, chondrocytes, osteocytes, adipocytes, and others.

Types of Connective Tissue and Their Functions

Type	Main Function(s)	Location(s)
Areolar (Loose)	Wraps and cushions organs; holds tissue fluid	Under epithelia, around organs
Adipose (Loose)	Stores energy, insulates, cushions	Under skin, around kidneys and eyes, within abdomen
Reticular (Loose)	Forms soft internal skeleton (stroma) for support	Lymph nodes, bone marrow, spleen
Dense Regular	Attaches muscles to bones or bones to bones; withstands tensile stress	Tendons, ligaments
Dense Irregular	Withstands tension from many directions	Dermis of skin, fibrous capsules of organs and joints
Elastic (Dense)	Allows recoil after stretching	Walls of large arteries, certain ligaments, bronchial tubes
Hyaline Cartilage	Supports and reinforces; resists compressive stress	Ends of long bones, nose, trachea, larynx, costal cartilages
Elastic Cartilage	Maintains shape while allowing flexibility	External ear, epiglottis
Fibrocartilage	Absorbs compressive shock	Intervertebral discs, pubic symphysis, menisci of knee

Chapter 4.4: Muscle Tissue

Types of Muscle Tissue: Structure and Location

Muscle Type	Structures	Body Locations
Skeletal	Long, cylindrical, multinucleate cells; striated	Attached to bones
Cardiac	Branched, striated, usually uninucleate; intercalated discs	Walls of the heart
Smooth	Spindle-shaped, non-striated, single nucleus	Walls of hollow organs (e.g., intestines, blood vessels)

Chapter 4.5: Nervous Tissue

General Characteristics of Nervous Tissue

Nervous tissue is specialized for communication via electrical and chemical signals. It consists of two main cell types:

• Neurons: Excitable cells that transmit electrical impulses.

• Neuroglia (glial cells): Support, protect, and nourish neurons.

Found in the brain, spinal cord, and peripheral nerves.

Chapter 4.6: Membranes

Structure and Function of Cutaneous, Mucous, and Serous Membranes

Membrane	Location	Structure	Functions
Cutaneous	Skin (external body surface)	Keratinized stratified squamous epithelium over connective tissue	Protection, prevents water loss
Mucous	Lines body cavities open to exterior (digestive, respiratory, urogenital tracts)	Epithelium over loose connective tissue (lamina propria)	Secretion, absorption, protection
Serous	Lines closed ventral body cavities (pleura, pericardium, peritoneum)	Simple squamous epithelium (mesothelium) over areolar connective tissue	Secretes serous fluid to reduce friction

Chapter 4.7: Tissue Repair

Process of Tissue Repair

Tissue repair involves a series of steps to restore tissue integrity after injury. The process includes:

1. Inflammation: Damaged cells release chemicals that cause blood vessels to dilate and become permeable, allowing immune cells to enter the area.

2. Organization: Granulation tissue forms, new blood vessels develop, and fibroblasts produce collagen fibers to bridge the gap.

3. Regeneration: Epithelial cells proliferate and migrate over the granulation tissue, restoring the original tissue structure. In some cases, fibrosis (scar formation) occurs if regeneration is incomplete.