Anatomy and Physiology of Tissues

Chapter 4: Tissues

Introduction

  • The human body is composed of four primary tissue types: muscular, nervous, epithelial, and connective.

  • Connective tissue is the most abundant tissue type in the body.

  • Histology is the study of tissues, and a trained professional in this field is called a histologist.

Tissue Organization

  • Tissues are formed when groups of cells combine.

  • These cells are held together by proteins attached to their plasma membranes.

Four Main Tissue Types

  • Epithelial Tissue: Known for covering surfaces and lining body cavities.

  • Connective Tissue: The most abundant type, responsible for connecting and supporting different tissues and organs.

  • Muscular Tissue: Facilitates body movement and generates heat.

  • Nervous Tissue: Controls bodily functions and systems.

Epithelial Tissue

  • Functions as a covering or lining and forms the majority of glands (organs).

Terminology

  • Epithelium: Refers to more than one layer of epithelial tissue.

  • Avascular: Epithelium lacks blood vessels but possesses a basal surface for nutrient absorption.

Polarity

  • The apical surface interacts with the external environment.

Basement Membrane

  • Epithelial tissue is attached to a basement membrane, which consists of epithelial and connective tissues.

  • Composed of collagen fibers (the strongest type) along with specific proteins and carbohydrates.

  • Serves as a selective barrier between the epithelium and connective tissue, providing nutrients through the basement membrane and apical surface.

  • Epithelium is highly innervated, having a large nerve supply.

  • Epithelium actively regenerates through mitosis to replace older cells.

Anatomy of Epithelium

  • Columnar cells form the epithelium, with connective tissue located beneath.

  • The basement membrane lies between the epithelium and connective tissue.

  • The apical surface is the most superior part of the epithelium.

  • The basal surface is the bottom layer of the epithelium that makes contact with connective tissue.

Physiology of Epithelium

Epithelium protects the body from several factors:

  • Protection: Provides external and internal covering to protect against dehydration, abrasion, and destruction.

  • Selective Permeability: Controls which substances can penetrate, acting as a first line of defense for internal organs.

  • Secretion: Glands with ducts extending to the apical surface secrete substances via exocrine or endocrine glands (preferably exocrine).

  • Sensation: Receptors at nerve endings provide senses such as touch, pressure, temperature, and pain.

  • Specialized Epithelium (Neuroepithelium): Responsible for senses like sight, taste, smell, hearing, and balance (equilibrium).

Classification of Epithelial Tissue

Based on cell shape and number of layers:

Cell Shapes

  • Squamous: Flat cells.

  • Cuboidal: Cube-shaped cells.

  • Columnar: Tall and slender cells.

Cell Layers

  • Simple: One layer of cells.

  • Stratified: Multiple layers of cells.

  • Pseudostratified: Appears stratified but is only one layer.

  • Transitional: Shows columnar, cuboidal, and squamous cells.

Squamous

  • Some are keratinized (dead skin, not undergoing mitosis) and some are non-keratinized (continue to divide).

  • Major physiology is diffusion.

Cuboidal

  • Performs absorption and secretion.

  • Stratified cuboidal is rare.

Columnar

  • Some are ciliated (have hair-like structures to move secretions).

  • Pseudostratified columnar appears stratified due to nuclei location but is simple.

  • Transitional shows all three cell shapes for epithelium.

Connective Tissue

  • Divided into proper, cartilage, bone, and blood.

  • The most abundant tissue type whose name implies function: connects structures and allows nutrient transport.

Muscle Tissue

  • Three types: skeletal, smooth, and cardiac.

  • Skeletal attaches to bone (750+ muscles) for movement and body heat.

  • Smooth moves fluids and solids.

  • Cardiac forms the heart.

Nervous Tissue

  • Composed of two cell types: neurons and neuroglia.

  • The name of the cell is also the name of the tissue.

Classifying Epithelium

  • Start with the number of cell layers (simple or stratified) and then the shape of the cell at the apical surface.

Simple Epithelium

  • One cell layer with a basal surface making contact with the basement membrane.

  • Simple squamous epithelium's major function is diffusion.

  • Columnar, cuboidal, and squamous can perform filtration, absorption, or secretion.

  • Examples: lining air sacs of lungs, small and large intestines, and blood vessels.

Stratified Epithelium

  • Two or more layers of cells.

  • Only the basal layer makes contact with the basement membrane.

  • Found lining the pharynx, esophagus, and skin.

  • Cells in the basal layer are stem cells, replacing old and injured cells.

Pseudostratified Epithelium

  • Simple epithelium, one layer thick, but appears layered due to the nuclei location.

Classifying Epithelium by Cell Shape

Squamous

  • Flat, like floor tiles under a microscope, with a flat nucleus in the center.

Cuboidal

  • Slightly equal on all sides, cube-shaped with a round nucleus in the center.

Columnar

  • Twice the length as in width (tall and slender).

  • The nucleus is oval and located towards the bottom of the cell.

Transitional

  • Change shape when stretched (columnar, cuboidal, and squamous when at rest).

  • Example: the bladder.

Anatomy of Epithelium (Cell Shapes)

Squamous

  • Flat cells with a flat nucleus located almost at the top center.

Cuboidal

  • Cube-shaped cells with a round nucleus located directly in the center.

Columnar

  • Cells are twice in length than they are in width. Shaped like a column.

  • The nucleus is oval and located towards the bottom of the cell (most of the time).

Transitional Epithelium (All Cell Shapes)

  • Shows all cell shapes: columnar (basal surface, nucleus at the top), cuboidal (cube-shaped, round nucleus in the center), and squamous cells.

Microscopy of Epithelium

  • Simple squamous is one layer.

  • Simple cuboidal is not layered.

  • Simple columnar is nonciliated (no hair-like structures).

  • Goblet cells (glands) secrete mucin (dehydrated protein) that turns into mucus when hydrated.

Glands (Formed by Epithelium Tissue)

  • Classified according to their anatomy and physiology.

  • Usually multicellular organs. Goblet cells are unicellular exceptions.

Function

  • Glands usually secrete electrolytes (sodium and chloride), hormones, enzymes, and waste.

Classification

  • Endocrine glands: no duct, secretions go directly into the bloodstream or interstitial fluid (internal use).

  • Exocrine glands: have a duct, secretions are not used internally (external environment).

Endocrine Glands

  • Produce hormones (chemical messengers).

Exocrine Glands

  • Include sweat glands (pseudoriferous), mammary glands, and salivary glands.

  • Goblet cell is the only unicellular exocrine gland.

  • Multicellular exocrine glands have grape-like clusters called acini that produce secretions released through a duct.

Exocrine Gland Anatomy

  • Acinus (singular): one grape-like cluster. Acini (plural): multiple grape-like clusters.

  • Simple glands: one unbranched duct.

  • Compound glands: branched ducts.

  • Tubular glands: the secretion portion is shaped like a tube.

  • Acinar glands: the secretion portion is shaped like a grape.

  • Tubuloacinar glands: secretion portions resembling a tube and a grape-like cluster.

Exocrine Gland Physiology

Classification

  • Merocrine, apocrine, and holocrine glands (all exocrine).

Merocrine

  • Package secretions into vesicles and release them into the duct.

  • Examples: most sweat glands, lacrimal glands, and salivary glands.

Apocrine

  • Pinch off a portion of their plasma membrane to become their secretion.

  • Examples: mammary glands and some sweat glands in the axillary, pubic, and edges of the fingertips.

Holocrine

  • Accumulate secretions in a cell, causing the cell to disintegrate.

  • Examples: sebaceous glands (oil-producing glands).

Connective Tissue

Components

  • Cells, fibers, and ground substance

Examples

  • Tendons, ligaments, adipose tissue (body fat), cartilage, bone, and blood.

Functions

  • Attachments, support, protection, and transport

Specific Functions

  • Physical protection (e.g., bones).

  • Support and structural framework.

  • Binding of structures.

  • Storage (adipose tissue and bone: minerals - calcium & phosphorus).

  • Transport of nutrients and wastes (blood).

  • Immune protection (blood cells in plasma).

Characteristics

  • Identified by cells, fiber types, and ground substance.

  • Elements: cells (like meatballs), fibers (like noodles), and ground substance (like sauce) to hold everything together.

Major Classes

  • Proper, cartilage, bone, and blood

Cell Types
Immature Cells

  • Fibroblasts (produce fibers: collagen, elastic, and reticular).

  • Chondroblasts (immature cartilage cells).

  • Osteoblasts (immature bone cells).

  • Hematopoietic (stem cells in red bone marrow that make blood cells: erythrocytes, leukocytes, and thrombocytes).

Mature Cells

  • Chondrocytes (maintain cartilage matrix).

  • Osteocytes (maintain bone integrity).

  • Adipocytes (fat cells store nutrients and provide insulation).

  • Leukocytes (mature white blood cells respond to injury).

  • Mast cells (start the inflammatory response).

  • Macrophages (phagocytic cells that eat dead cells or foreign invaders).

Fiber Types

  • Collagen fibers (strongest, resist stretching, cable-like, white).

  • Reticular fibers (thinner, branching, tough but flexible; found in stroma - lymph nodes, liver, spleen).

  • Elastic fibers (stretch and return to shape, branching, wavy, recoil; formed by elastin protein).

Ground Substance

  • Non-living material that holds fibers and cells in place.

  • Can be viscous, semi-solid (gel-like), or solid.

  • Protein fibers form the extracellular matrix around cells.

  • Protein components: glycosaminoglycans (GAGs) and proteoglycans (sugars attached to proteins).

Connective Tissue Proper

Loose Connective Tissue

  • Components are spaced out, easily identifiable under a microscope.

Types

  • Areolar: Layer around internal organs with all three fibers (collagen, elastic, reticular), leukocytes, fibroblasts, and semi-solid or viscous ground substance.

  • Adipose: Formed by adipocytes (fat cells) and stores energy reserves; offers insulation.

  • Reticular: Has reticular fibers; leukocytes and fibroblasts; located in immune-related areas (spleen, lymph nodes, thymus, and bone marrow).

Dense Connective Tissue

  • Compact, stacked tightly together.

Types

  • Dense Regular: Ground substance; fibroblasts; collagen fibers with a pattern (tendons and ligaments).

  • Dense Irregular: Collagen fibers without a pattern.

  • Elastic Connective Tissue: Primarily elastic fibers instead of collagen (has fibroblasts, but elastic cartilage has cartilage cells).

Cartilage

Elastic Cartilage

  • Located in the ears and epiglottis.

  • Can be stretched and returned to shape.

Structure

  • Chondrocytes are located inside spaces known as lacunae.

Fibrocartilage

  • Toughest cartilage that resists compression, absorbs shock, and bears weight.

  • Located in intervertebral discs, knee pads (meniscus), and pubic symphysis.

Hyaline Cartilage

  • Most abundant type of cartilage.

  • Found in the nose (the portion you touch), trachea (keeps it inflated), ribs (attaching to the sternum), and every joint (so bones don't directly contact).

Bone (Connective Tissue)

  • Osteon is the building unit.

  • Osteocytes are located within the osteon (mature bone).

Fluid Connective Tissue

Two Types

  • Blood and lymph.

  • Liquids are classified as connective tissue because of the nutrients they supply.

Blood

  • Cells: erythrocytes and leukocytes (not thrombocytes - platelets).

  • Ground substance: plasma.

  • Does not have fibers.

Lymph

  • Cells and plasma.

  • Does not have erythrocytes.

Muscular Tissue

Types

  • Skeletal, cardiac, and smooth.

Skeletal Muscle

  • Striated (stripes), with dark and light stripes indicating protein alignment.

  • Does not branch.

Cardiac Muscle

  • Striated and has intercalated discs (openings between cells).

  • Branches.

Smooth Muscle

  • Not striated (smooth appearance).

  • Fusiform (tapered at the edges).

Nervous Tissue

Consists Of

  • Neurons and neuroglia

Neuron Structure

  • Soma (cell body).

  • Processes: dendrites (short, numerous) and axon (single, long).

Neuron Function

  • Dendrites collect information and transfer it to the cell body.

  • The cell body integrates information and forms a response.

  • The response travels from the cell body to the axon (longer tail).

Tissue Problems

Scurvy

  • Vitamin C deficiency affects connective tissue.

  • Results in weakness, gum problems, hemorrhages, and abnormal bone growth.

  • Fixed by vitamin C supplements or foods high in vitamin C.

  • Connective tissue fibers are weak and cannot hold things in place properly.

Atrophy

  • Shrinkage of tissue due to a decrease in cell size and number.

  • Normal with age or in bedridden individuals.

Necrosis

  • Tissue death (though can be reversed with techniques after the year of February).

Hypertrophy

  • Increase in cell size within a tissue.

Hyperplasia

  • Increase in cell number within a tissue.

Neoplasia

  • Abnormal increase in cell number, often referring to a tumor.


Scurvy

  • Vitamin C deficiency affects connective tissue.

  • Results in weakness, gum problems, hemorrhages, and abnormal bone growth.

  • Fixed by vitamin C supplements or foods high in vitamin C.

  • Connective tissue fibers are weak and cannot hold things in place properly.

Atrophy

  • Shrinkage of tissue due to a decrease in cell size and number.

  • Normal with age or in bedridden individuals.

Necrosis

  • Tissue death (though can be reversed with techniques after the year of February).

Hypertrophy

  • Increase in cell size within a tissue.

Hyperplasia

  • Increase in cell number within a tissue.

Neoplasia

  • Abnormal increase in cell number, often referring to a tumor.


Immature Cells

  • Fibroblasts (produce fibers: collagen, elastic, and reticular).

  • Chondroblasts (immature cartilage cells).

  • Osteoblasts (immature bone cells).

  • Hematopoietic (stem cells in red bone marrow that make blood cells: erythrocytes, leukocytes, and thrombocytes).

Mature Cells

  • Chondrocytes (maintain cartilage matrix).

  • Osteocytes (maintain bone integrity).

  • Adipocytes (fat cells store nutrients and provide insulation).

  • Leukocytes (mature white blood cells respond to injury).

  • Mast cells (start the inflammatory response).

  • Macrophages (phagocytic cells that eat dead cells or foreign invaders).