Overview of Tissues and Integumentary System in Anatomy & Physiology

Tissues of the Human Body

Epithelial Tissue

Epithelial tissue covers body surfaces, lines internal cavities, and forms glands. It is classified based on cell shape and the number of layers.

• Simple Squamous: Single layer of flat cells; allows for diffusion and filtration. Example: Alveoli of lungs.

• Simple Cuboidal: Single layer of cube-shaped cells; involved in secretion and absorption. Example: Kidney tubules.

• Simple Columnar: Single layer of tall, column-like cells; often contains goblet cells that secrete mucus. Example: Lining of the digestive tract.

• Pseudostratified Ciliated Columnar: Appears layered but all cells touch the basement membrane; often contains goblet cells and cilia. Example: Lining of the trachea.

• Transitional: Multiple layers that can stretch; found in organs that expand. Example: Urinary bladder.

• Stratified Squamous: Multiple layers of flat cells; protects against abrasion.

  • Keratined: Surface cells are dead and filled with keratin (e.g., skin epidermis).

  • Non-keratinized: Surface cells are alive and moist (e.g., lining of mouth).

Connective Tissue

Connective tissue supports, binds, and protects other tissues and organs. It has diverse forms and functions.

• Adipose: Stores fat; composed of adipocytes. Example: Subcutaneous fat.

• Areolar: Loose connective tissue with fibroblasts; provides support and flexibility. Example: Underlies most epithelia.

• Blood: Fluid connective tissue; transports gases, nutrients, and wastes.

  • Erythrocytes: Red blood cells; carry oxygen.

  • Leukocytes: White blood cells; immune defense.

• Hyaline Cartilage: Provides support and flexibility; contains chondrocytes in lacunae. Example: Nose, trachea, ends of long bones.

• Elastic Cartilage: Contains elastic fibers; maintains shape and flexibility. Example: External ear.

• Fibrocartilage: Strongest cartilage; resists compression. Example: Intervertebral discs.

• Bone/Osseous: Rigid tissue; osteocytes in lacunae. Example: Skeleton.

• Dense Regular Elastic (Elastin): Parallel elastic fibers; allows stretch. Example: Ligaments.

• Dense Regular Collagenous (Collagen): Parallel collagen fibers; strong, resists pulling. Example: Tendons.

• Dense Irregular: Collagen fibers in multiple directions; provides strength. Example: Dermis of skin.

Muscle Tissue

Muscle tissue is specialized for contraction and movement.

• Skeletal: Voluntary, striated muscle attached to bones; responsible for body movement.

• Cardiac: Involuntary, striated muscle found only in the heart; responsible for pumping blood.

• Smooth: Involuntary, non-striated muscle found in walls of hollow organs (e.g., intestines, blood vessels).

Nervous Tissue

Nervous tissue is responsible for transmitting electrical impulses throughout the body.

• Neurons: Nerve cells that generate and conduct electrical signals.

• Neuroglial Cells: Support, protect, and nourish neurons.

Integumentary System

Structure of the Skin

The skin is composed of two main layers: the epidermis and the dermis, with underlying hypodermis (subcutaneous tissue).

• Epidermis: Outermost layer; composed of stratified squamous epithelium.

• Dermis: Deeper layer; contains connective tissue, blood vessels, nerves, and appendages.

• Hypodermis: Subcutaneous layer; primarily adipose tissue (not always considered part of the skin).

Layers of the Epidermis

The epidermis consists of several distinct layers (from deep to superficial):

• Stratum Basale: Deepest layer; site of cell division.

• Stratum Spinosum: Provides strength and flexibility.

• Stratum Granulosum: Cells begin to die and accumulate keratin.

• Stratum Lucidum: Present only in thick skin (e.g., palms, soles).

• Stratum Corneum: Outermost layer; dead, keratinized cells.

Dermis Structure

• Papillary Layer: Superficial dermal layer; forms dermal papillae that interlock with the epidermis.

• Reticular Layer: Deeper dermal layer; dense irregular connective tissue.

• Adipose Tissue: Fat storage, insulation, and cushioning.

Skin Appendages and Associated Structures

• Capillaries: Small blood vessels in the dermis; supply nutrients and aid in thermoregulation.

• Hair Follicle: Structure from which hair grows.

• Hair Shaft: Visible part of the hair above the skin.

• Hair Root: Portion of hair below the skin surface.

• Hair Papilla: Contains blood vessels that nourish the growing hair.

• Root Hair Plexus: Nerve endings wrapped around hair follicle; sense hair movement.

• Arrector Pili Muscle: Smooth muscle attached to hair follicle; causes "goosebumps" when contracted.

• Sebaceous Gland: Secretes sebum (oil) into hair follicles; lubricates skin and hair.

• Eccrine Sweat Gland: Produces watery sweat for thermoregulation.

Summary Table: Major Skin Layers and Features

Layer/Structure	Main Features	Function
Epidermis	Stratified squamous epithelium; multiple sublayers	Protection, barrier
Dermis	Papillary and reticular layers; connective tissue	Support, elasticity, houses appendages
Hypodermis	Adipose tissue	Insulation, energy storage
Hair Follicle	Invagination of epidermis into dermis	Hair production
Arrector Pili Muscle	Smooth muscle	Hair erection (goosebumps)
Glands (Sebaceous, Eccrine)	Associated with hair follicles or skin surface	Lubrication, thermoregulation

Additional info:

• Some connective tissue types (e.g., dense regular elastic) are less commonly discussed but are important for specialized functions such as in ligaments.

• The hypodermis is not always considered a true skin layer but is functionally important.