Tissues and Integumentary System: Structure and Function

Tissue: The Building Blocks of Organs

Definition and Overview

Tissues are groups of cells with similar structure that work together to perform specific functions. They are fundamental building blocks of the body's organs, consisting of both cells and an extracellular matrix.

• Cells: The living component of tissue, specialized for particular functions.

• Extracellular Matrix: Non-living material that surrounds the cells, providing structural and biochemical support.

Four Basic Types of Tissue

• Epithelium: Covers body surfaces and lines cavities.

• Connective Tissue: Provides support and connects other tissues.

• Muscle Tissue: Responsible for movement.

• Nervous Tissue: Controls and coordinates body activities.

Epithelium

Structure and Classification

Epithelium consists of tightly packed cells that cover body surfaces or line internal cavities. Epithelial tissues are classified based on two criteria: the number of cell layers and the shape of the cells.

• Number of Layers:

  • Simple Epithelium: Single layer of cells.

  • Stratified Epithelium: Multiple layers of cells.

• Cell Shape:

  • Squamous: Flat, scale-like cells.

  • Cuboidal: Cube-shaped cells.

  • Columnar: Taller than they are wide.

Example: The alveoli of the lungs are lined by simple squamous epithelium, allowing efficient gas exchange.

Types of Epithelial Tissues

• Simple Epithelium: Squamous, Cuboidal, Columnar (ciliated and nonciliated)

• Pseudostratified Epithelium: Appears layered but is a single layer; can be ciliated or nonciliated.

• Stratified Epithelium: Squamous, Cuboidal, Columnar, Transitional

Table: Epithelial Tissue Classification

Type	Number of Layers	Cell Shape	Example Location
Simple Squamous	1	Flat	Alveoli of lungs, lining of blood vessels
Simple Cuboidal	1	Cube	Kidney tubules
Simple Columnar	1	Tall	Lining of digestive tract
Stratified Squamous	Multiple	Flat (surface)	Epidermis of skin, oral cavity
Transitional	Multiple	Variable	Urinary bladder

Functions of Epithelial Tissue

• Protection (e.g., skin)

• Absorption (e.g., intestines)

• Secretion (e.g., glands)

• Filtration (e.g., kidney glomeruli)

Connective Tissue

Overview and Functions

Connective tissue supports, connects, and binds other tissues and organs. It is characterized by relatively few cells and abundant extracellular matrix, which consists of ground substance and fibers.

• Ground Substance: Gel-like material that holds tissue together; in bone, it is hardened by calcium salts.

• Fibers: Collagen (strength), Reticular (support), Elastic (flexibility)

• Origin: All connective tissues arise from embryonic mesenchyme.

Types of Connective Tissue

• Connective Tissue Proper: Loose (areolar, adipose, reticular) and dense (regular, irregular, elastic)

• Specialized Connective Tissue: Cartilage (hyaline, elastic, fibrocartilage), Bone, Blood

Table: Types of Connective Tissue

Type	Main Features	Example Location
Areolar (Loose)	Loose arrangement of fibers, supports epithelia	Under epithelia, around organs
Adipose	Fat storage, insulation	Subcutaneous tissue, around kidneys
Dense Regular	Parallel collagen fibers, strong	Tendons, ligaments
Dense Irregular	Irregularly arranged fibers, withstands tension	Dermis of skin
Hyaline Cartilage	Firm, glassy matrix	Ends of long bones, nose, trachea
Elastic Cartilage	Flexible, elastic fibers	External ear
Fibrocartilage	Thick collagen fibers, strong	Intervertebral discs
Bone	Hard, calcified matrix	Skeletal bones
Blood	Fluid matrix (plasma), transports cells	Blood vessels

Muscle Tissue

Types and Functions

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

• Skeletal Muscle: Voluntary, striated, multinucleated; moves bones.

• Cardiac Muscle: Involuntary, striated, branched; found in heart walls, pumps blood.

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

Table: Comparison of Muscle Tissue Types

Type	Striations	Nuclei	Location	Control
Skeletal	Yes	Multiple	Attached to bones	Voluntary
Cardiac	Yes	One (sometimes two)	Heart	Involuntary
Smooth	No	One	Walls of hollow organs	Involuntary

Nervous Tissue

Structure and Function

Nervous tissue is responsible for controlling and coordinating body functions. It consists of two main cell types:

• Neurons: Generate and conduct electrical impulses. Each neuron has a cell body, dendrites (receive signals), and an axon (transmits signals).

• Neuroglia (Supporting Cells): Nourish, protect, and support neurons; do not conduct impulses.

Integumentary System (Skin)

Overview and Functions

The integumentary system is the largest organ system, accounting for about 7% of total body weight. It serves as a protective barrier and has several key functions:

• Protection from injury and infection

• Prevents dehydration

• Thermoregulation (via sweat glands and blood vessels)

Layers of the Integument

• Epidermis: Outermost layer; keratinized stratified squamous epithelium.

• Dermis: Middle layer; strong, flexible connective tissue with nerves and blood vessels.

• Hypodermis (Subcutaneous Layer): Deepest layer; mostly adipose tissue, anchors skin to underlying structures.

Cells of the Epidermis

• Keratinocytes: Produce keratin for protection.

• Melanocytes: Produce melanin pigment.

• Merkel Cells: Sensory receptors for touch.

• Langerhans Cells: Immune defense.

Layers of the Epidermis (from superficial to deep)

• Stratum Corneum: Outermost, many layers of dead keratinized cells.

• Stratum Lucidum: Clear layer, only in thick skin (palms, soles).

• Stratum Granulosum: 1-5 layers, cells secrete glycolipids for waterproofing.

• Stratum Spinosum: Several layers, contains mature keratinocytes and Langerhans cells.

• Stratum Basale: Deepest, single layer of young keratinocytes, Merkel cells, and melanocytes.

Dermis

• Papillary Layer: Superficial, contains dermal papillae (finger-like projections).

• Reticular Layer: Deeper, 80% of dermis, dense with collagen fibers for strength.

• Contains two vascular plexuses (cutaneous and subpapillary) for temperature regulation.

Hypodermis

• Also called superficial fascia or subcutaneous layer.

• Mainly adipose tissue; provides insulation and anchors skin to muscles.

Thick vs. Thin Skin

• Thick Skin: Found on palms and soles; has all five epidermal layers, including stratum lucidum.

• Thin Skin: Covers most of the body; lacks stratum lucidum, thinner stratum corneum.

Key Terms

• Lumen: The inner open space or cavity of a tubular organ (e.g., blood vessel, duct).

• Basement Membrane: Thin layer anchoring epithelium to underlying connective tissue.

Additional info: For laboratory identification, students should be able to recognize tissue types and skin layers under the microscope, as well as identify accessory cells and structures in skin models.