ANPH 209 - Module 2

Objectives

• Identify the main tissue types and discuss their roles in the human body

• Identify the four types of tissue membranes and the characteristics of each that make them functional

• Explain the functions of various epithelial tissues and how their forms enable their functions

• Explain the functions of various connective tissues and how their forms enable their functions

• Describe muscle tissue characteristics and how these enable function

• Discuss nervous tissue characteristics and how these enable information processing and control of muscular and glandular activities

Four Types of Tissues

• Epithelial: covers body surfaces, lines hollow organs, body cavities, ducts, and forms glands

• Connective: protects, supports, binds organs, stores energy as fat, provides immunity

• Muscular: generates the physical force needed for movement and body heat

• Nervous: detects changes in the body and responds, enabling control of activities

Tissue Examples

• Nervous tissue: brain, spinal cord, nerves

• Epithelial tissue: lining of GI tract organs and other hollow organs; skin surface (epidermis)

• Muscle tissue: cardiac muscle, smooth muscle, skeletal muscle

• Connective tissue: fat and other soft padding tissue, bone, tendons

• The four tissue types are exemplified by nervous tissue, stratified squamous epithelial tissue, cardiac muscle tissue, and connective tissue

Epithelial Tissue

Overview

• Have their own nerve supply

• Are avascular (lack their own blood supply); nutrients/waste come from surrounding connective tissue vessels

• Have a high rate of cell division for renewal/repair

• Play roles in protection, filtration, secretion, absorption, and more

• Types:

  • Covering and lining epithelium (skin surface, lining of cavities/organs)

  • Glandular epithelium (secretory portion of glands: thyroid, adrenal, sweat glands, etc.)

Covering and Lining Epithelium

Classification

• Classified by:

  • Arrangement of cells into layers: Simple vs Stratified

  • Shapes of cells: Squamous, Cuboidal, Columnar

• Common examples (layers/shapes):

  • Simple squamous epithelium

  • Stratified squamous epithelium

  • Simple cuboidal epithelium

  • Stratified cuboidal epithelium

  • Pseudostratified (columnar)

  • Simple columnar epithelium

  • Stratified columnar epithelium

• Simple epithelium:

  • Single layer of cells; functions in diffusion, osmosis, filtration, secretion, absorption

• Pseudostratified epithelium:

  • Appears to have multiple layers due to differing nuclei positions; all cells contact the basal surface

• Stratified epithelium:

  • Two or more layers; primarily protective

Cell Shapes and Functions

• Squamous: thin cells; allows rapid passage of substances

• Cuboidal: tall as they are wide; may have microvilli; functions in secretion/absorption

• Columnar: much taller than wide; may have cilia or microvilli; specialized for secretion/absorption

Specific Types

• Simple squamous epithelium:

  • Structure: single layer; nucleus flattened/oval/spherical

  • Functions: diffuse/filtration; protective lubricating substances

  • Locations: endothelium lining heart, blood vessels, lymphatic vessels; mesothelium lining serous membranes (pericardium, pleura, peritoneum)

• Simple cuboidal epithelium:

  • Structure: cube-shaped; central round nuclei

  • Functions: secretion and absorption

  • Locations: kidneys, thyroid gland

• Simple columnar epithelium:

  • Structure: tall column cells; oval nuclei at base; may be nonciliated or ciliated

  • Functions: absorption and secretion of mucus and enzymes

  • Specializations: microvilli (absorption) and goblet cells (mucus secretion); cilia for movement in certain tracts

  • Locations: digestive tract (nonciliated), uterine tubes and uterus (ciliated), larger bronchioles (ciliated)

• Pseudostratified columnar epithelium:

  • Structure: appears layered due to nuclei at different levels; all cells contact the basale but not all reach the apical surface in all cases

  • Function: secretes mucus; ciliated forms move mucus

• Stratified squamous epithelium:

  • Structure: several cell layers; outermost cells are flat

  • Function: protects against abrasion

  • Locations: lining of esophagus, mouth, vagina

• Stratified cuboidal epithelium:

  • Function: protective tissue; secretion and protection

  • Locations: sweat glands, salivary glands, mammary glands, some portions of male/female urethra

• Stratified columnar epithelium:

  • Function: protection and secretion; relatively rare

• Transitional epithelium (urothelium):

  • Function: allows urinary organs to expand and stretch

  • Locations: bladder, ureters, urethra

Glandular Epithelium

• Endocrine glands:

  • Secretions are hormones released into interstitial fluid, then into bloodstream

  • Hormones travel to targets with receptors; part of endocrine regulatory system

  • Examples: anterior pituitary, thymus, adrenal cortex, gonads

• Exocrine glands:

  • Secretions reach epithelial surface via ducts (e.g., mucous, sweat, saliva, breast milk)

  • Secretions into GI tract lumen are exocrine (technically outside the body)

• Gland structure (unicellular vs multicellular):

  • Unicellular: goblet cells in mucous membranes

  • Multicellular exocrine glands: develop from simple epithelium to secretory surface that secretes into cavities or ducts

• Duct structure: simple (single duct) or compound (divided into branches)

• Gland shapes: tubular, alveolar (acinar), tubuloalveolar (tubuloacinar)

• Patterns: simple tubular, simple coiled tubular, simple branched tubular, simple alveolar, simple branched alveolar, compound tubular, compound alveolar, compound tubuloalveolar, etc.

• Examples: merocrine sweat glands (eccrine), sebaceous glands (oil) in skin, gastric glands, intestinal glands, mammary, salivary glands, pancreas, etc.

Cell-to-Cell Junctions

• Types (basic):

  • Tight junctions: seal adjacent cells, restrict paracellular transport

  • Adherens junctions: cadherin-based connections; anchor actin filaments to each other via plaque

  • Desmosomes: button-like spots; connect intermediate filaments of cells; resist shearing

  • Gap junctions: connexons form channels allowing cytoplasmic exchange and electrical coupling

  • Hemidesmosomes: attach epithelial cells to the basement membrane via integrins

• Components referenced in diagrams: transmembrane glycoproteins (cadherins), integrins, plaque proteins, basal lamina

Connective Tissue

Overview, Cells, and Fibers

• Connective tissue is the most abundant and widely distributed tissue

• General functions:

  • Binds tissues together, supports/strengthens tissue

  • Protects and insulates internal organs

  • Compartmentalizes and transports substances (e.g., blood), stores energy as fat, immune responses

• General features:

  • Highly vascularized and has a nerve supply (except cartilage and dense connective tissue in some cases)

• Cells and fibers in connective tissue:

  • Fibroblasts: produce fibers and ground substance

  • Adipocytes: fat storage

  • Mesenchymal cells: stem-like; can differentiate into other CT cells

  • Macrophages: phagocytosis of bacteria and debris

  • Mast cells: release histamine (inflammatory mediator)

  • Neutrophils and Eosinophils: immune response

  • Plasma cells: secrete antibodies

• Extracellular matrix:

  • Ground substance: between cells and fibers; varies from fluid to gelatinous; supports/binds cells, stores water, facilitates exchange between blood and cells

  • Fibers: collagen (tensile strength), elastic fibers (stretch), reticular fibers (supportive network)

Classification

• Mature connective tissue types:

  • Loose connective tissue (areolar): includes adipose and reticular tissue

  • Dense connective tissue: binds muscles to bones (tendons) and binds bones to each other (ligaments)

  • Cartilage: hyaline, fibrocartilage, elastic cartilage

  • Bone tissue (osseous): rigid support with mineralized matrix

  • Liquid connective tissues: blood and lymph

Loose Connective Tissue

• Adipose tissue:

  • Adipocytes store triglycerides; energy reserve; insulating layer

• Reticular tissue:

  • Network of reticular fibers forming supportive framework for soft organs

Dense Connective Tissue

• Dense regular connective tissue:

  • Collagen fibers in parallel bundles; fibroblasts aligned along fibers

• Dense irregular connective tissue:

  • Collagen fibers interwoven in a mesh-like network; withstands multi-directional stress

Cartilage

• Cartilage characteristics:

  • Dense network of collagen fibers and elastic fibers embedded in chondroitin sulfate

  • Chondrocytes reside in lacunae

  • Perichondrium surrounds cartilage; two layers: outer fibrous and inner cellular

  • Avascular and aneural (no blood vessels or nerves) except perichondrium; growth is slow

• Types:

  • Hyaline cartilage: provides support with some flexibility; chondrocytes in lacunae

  • Fibrocartilage: strong with collagen fibers; chondrocytes in lacunae

  • Elastic cartilage: contains elastic fibers; chondrocytes in lacunae

• Growth and repair:

  • Interstitial growth: growth from within the tissue

  • Appositional growth: growth at the outer surface of the tissue

Bone Tissue, Blood, and Lymph

• Bone tissue (osseous):

  • Bones are organs composed of bone tissue plus other CT components

  • Osteocytes reside in lacunae within a mineralized matrix

  • Compact and spongy bone structures

• Blood and lymph (liquid CT):

  • Connective tissue with liquid extracellular matrix (plasma in blood)

Muscular Tissue

• General features:

  • Consists of elongated cells called muscle fibers (myocytes)

  • Cells use ATP to generate force

  • Primary functions: movement, posture, heat generation, protection of organs

• Classifications and features:

  • Skeletal muscle:

  • Long cylindrical fibers, striated, multiple peripheral nuclei

  • Voluntary movement; attached to bones; responsible for locomotion and heat production

  • Cardiac muscle:

  • Striated, single central nucleus; intercalated discs

  • Involuntary control; pumps blood; found in heart

  • Smooth muscle:

  • Non-striated, spindle-shaped cells, single nucleus

  • Involuntary control; moves contents through organs and regulates flow of blood in vessels

• Locations:

  • Skeletal: attached to bones and around openings such as mouth and anus

  • Cardiac: heart walls

  • Smooth: walls of blood vessels, GI tract, respiratory pathways, stomach, intestines

Nervous Tissue

• Composition:

  • Neurons (nerve cells)

  • Neuroglia (supporting cells)

• Structure of a neuron:

  • Cell body (soma) contains nucleus and mitochondria

  • Dendrites: receive signals and transfer impulses to the soma

  • Axon: carries action potentials away to other excitable cells

• Function:

  • Transmit and receive impulses; generate and propagate electrical signals

  • Neurotransmitter release at synapses

  • Coordinates activities of muscles and glands

• Examples in tissue diagrams:

  • Neuron in spinal cord; axon and dendrites depicted; myelin sheath in some neurons

Excitable Cells and Electrical Activity

• Excitable cells include neurons and muscle fibers

• Capable of producing electrical signals (action potentials) in response to stimuli

• Action potentials propagate along cellular membranes to trigger responses

• Neurotransmitter release mediates communication between cells

Tissue Homeostasis and Repair

Tissue Injury and Repair

• When tissue damage is extensive, stroma (supportive tissue) and parenchymal cells participate in repair

• Inflammation is the initial healing step

• Key cellular players:

  • Fibroblasts divide rapidly

  • New collagen fibers are produced

  • New blood capillaries form to supply healing materials

  • Granulation tissue forms to restore vascular supply and provide a scaffold for repair

• Wound healing progression:

  • Clotting occurs, forming a scab

  • Epithelial cells multiply and cover the granulation tissue

  • Epithelium thickens and area contracts as it matures

  • Inflammatory mediators and white blood cells infiltrate the injured area

Aging and Tissues

• Tissue healing tends to be faster in young individuals

• Fetal surgery often leaves no scars due to tissue properties

• Younger tissues have better nutritional state, blood supply, and metabolic rate

• Aging affects extracellular components and tissue function

• Changes in glucose usage, collagen, and elastic fibers contribute to aging and tissue mechanics

Tissues & Cancer

• Carcinogenesis involves abnormal cell division and invasion of underlying tissues

• Indicators of cancer include changes in cell size, nucleus size, and tissue organization

• Carcinoma can disrupt normal tissue structure and function

Important Terminology and Concepts

• Epithelial tissue features: nerve supply, avascularity, high turnover, roles in protection, filtration, secretion, absorption

• Gland types and secretions: endocrine (hormones) vs exocrine (ducted secretions)

• Glandular structures: unicellular vs multicellular; duct patterns; tubular, alveolar, tubuloalveolar configurations

• Cell junctions: tight, adherens, desmosomes, gap junctions, hemidesmosomes

• Connective tissue components: cells (fibroblasts, adipocytes, macrophages, mast cells, WBCs, plasma cells, mesenchymal), fibers (collagen, elastic, reticular), ground substance

• Cartilage properties: avascular, perichondrium, lacunae, growth patterns (interstitial vs appositional)

• Bone and blood as specialized connective tissues

• Muscle tissue properties: striations (skeletal, cardiac), intercalated discs (cardiac), smooth muscle lack of striations

• Nervous tissue function: neurons vs neuroglia; electrical excitability; synaptic signaling

• Tissue repair sequence: inflammation → granulation tissue → collagen deposition → epithelial restoration

• Aging effects on tissues: healing rates, scar formation, extracellular matrix changes

• Cancer progression indicators: cellular and tissue architecture disruption