Study Guide: Tissues and Membranes in Anatomy & Physiology

Epithelial Tissue

Structural and Functional Characteristics

Epithelial tissue forms the covering or lining of all internal and external body surfaces. It serves as a barrier, protective layer, and is involved in absorption, secretion, and sensation.

• Cellularity: Composed almost entirely of tightly packed cells with minimal extracellular matrix.

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

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

• Regeneration: High capacity for cell division and repair.

Types of Epithelia: Classification, Functions, and Locations

• Simple Squamous Epithelium: Single layer of flat cells; allows diffusion and filtration. Location: Alveoli of lungs, lining of blood vessels.

• Simple Cuboidal Epithelium: Single layer of cube-shaped cells; secretion and absorption. Location: Kidney tubules, glands.

• Simple Columnar Epithelium: Single layer of tall, column-like cells; absorption and secretion. Location: Digestive tract lining.

• Stratified Squamous Epithelium: Multiple layers; protects against abrasion. Location: Skin, mouth, esophagus.

• Pseudostratified Columnar Epithelium: Appears layered but all cells touch the basement membrane; secretion and movement of mucus. Location: Respiratory tract.

• Transitional Epithelium: Multiple layers, can stretch; allows urinary organs to expand. Location: Urinary bladder.

Glands: Definition and Types

• Gland: A cell or group of cells specialized to secrete substances.

• Exocrine Glands: Secrete products into ducts (e.g., sweat, salivary glands).

• Endocrine Glands: Release hormones directly into the bloodstream (e.g., thyroid, pituitary glands).

Comparison: Exocrine glands have ducts; endocrine glands are ductless.

Connective Tissue

Common Characteristics and Composition

Connective tissue supports, binds, and protects other tissues and organs. It is characterized by cells scattered within an abundant extracellular matrix.

• Cells: Fibroblasts, adipocytes, macrophages, etc.

• Extracellular Matrix: Protein fibers (collagen, elastic, reticular) and ground substance.

Types and Functions

• Loose Connective Tissue: Cushions organs, provides support. Example: Areolar tissue.

• Dense Connective Tissue: Provides strength and flexibility. Example: Tendons, ligaments.

• Adipose Tissue: Stores fat, insulates, and cushions.

• Cartilage: Supports and reinforces; resists compression. Example: Hyaline cartilage in joints.

• Bone: Supports, protects, stores minerals.

• Blood: Transports gases, nutrients, wastes.

Muscle Tissue

Types, Structure, and Locations

Muscle tissue is specialized for contraction and movement. There are three main types:

• Skeletal Muscle: Long, cylindrical, multinucleated cells; striated; voluntary control. Location: Attached to bones.

• Cardiac Muscle: Branched, striated cells with intercalated discs; involuntary. Location: Heart wall.

• Smooth Muscle: Spindle-shaped, non-striated cells; involuntary. Location: Walls of hollow organs (e.g., intestines, blood vessels).

Comparison: Skeletal muscle is voluntary and striated; cardiac is involuntary and striated; smooth is involuntary and non-striated.

Nervous Tissue

General Characteristics

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

• Neurons: Transmit electrical impulses.

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

Function: Forms the brain, spinal cord, and nerves; responsible for sensation, integration, and response.

Covering Membranes

Serous Membranes: Structure and Function

Serous membranes are thin sheets of tissue that line body cavities not open to the outside and cover organs within these cavities.

• Structure: Consist of a layer of simple squamous epithelium (mesothelium) and underlying connective tissue.

• Function: Secrete serous fluid to reduce friction between moving organs.

• Examples: Pleura (lungs), pericardium (heart), peritoneum (abdominal organs).