HISTOLOGY

4 types:

• Epithelial

• Connective

• Muscle

• Nervous

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Study of tissues -cells similar in structure and perform a common function

WHAT IS NECROSIS?

Necrosis is tissue death. It occurs if the blood supply to an area is stopped for too long. When this happens the tissues die due to a lack of oxygen to the cells.

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PREPARING TISSUES FOR MICROSCOPY

Fixed – preserved Artifacts – distortions not seen in living

tissue Sectioned – cut into slices thin enough

light can pass through Stained – organic dyes used to

enhance contrast

Transmission electron microscopy (TEM) – uses electrons for detailed contrast

Scanning electron microscopy (SEM) – 3D pictures of tissue surface

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EPITHELIAL TISSUE Covers a surface or lines a cavity Glandular epithelium – exocrine glands Forms boundaries

Basement Membrane: Network of protein fibers that forms barrier between epithelium and connective tissue

Protection Absorption – molecules pass into blood or

lymph Filtration – passage of solvent thru a

membrane Excretion – eliminate waste Secretion – release aqueous solution Sensory reception

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CHARACTERISTICS OF EPITHELIUM Polarity

Apical surface – exposed Microvilli

Increase surface area Allow absorption and secretion

Cilia Beat to move materials across surface

Basal Surface – attached Basal lamina – adhesive glycoproteins

Specialized Contacts Tight Junctions

Prevents passage of water and solutes Interlocking membrane proteins Basal adhesion belt binds cells together

Desmosomes Durable interconnections 2 types:

Button desmosomes- small disk Hemidesmosomes – half button shape

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MORE CHARACTERISTICS OF EPITHELIUM

Supported by connective tissue Reticular lamina – Extracellular collagen network

Avascular but innervated No blood vessels, nutrients obtained from diffusion Nerve supply

Regeneration Cells are continually replaced Epithelial cells only survive 1-2 days

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SQUAMOUS EPITHELIUM

Simple SquamousThin and flat cells, 1 LayerFunction: diffusion & filtrationFound: forms capillary walls

(endothelium), lining air sacs of lungs, kidneys, lining body cavities (mesothelium)

Stratified SquamousThin and flat cells, More than 1

layer, most common epitheliaFunction: protectionFound: in places of mechanical

stress, skin surface, lining tongue, mouth, esophagus, and anus 8

CUBOIDAL EPITHELIUM

Simple Cuboidal Box shaped cells, 1 layer Function: Secretion or

absorption Found: covering surface of

ovaries, lining kidney tubules, salivary ducts, and pancreatic ducts

Stratified Cuboidal Box shaped cells, 2 layers, rare Function: strengthen lumen

walls Found: ducts of large sweat

glands, salivary glands, mammary glands, and pancreas 9

COLUMNAR EPITHELIAL

Simple Columnar Tall, rectangular cells, 1 layer Function: absorption

(microvilli) & secretion Found: Lines stomach,

intestinal tract, excretion ducts, gall bladder

Pseudostratified Columnar Single layer irregularly

shaped cells (looks like multiple layers)

Function: protection, secretion

Found: Lining respiratory passageways (ciliated), and auditory tubes 10

TRANSITIONAL EPITHELIAL TISSUE

Transitional3-6 layers of rounded

cellsFunction: Withstands

stretchingFound: Lines urinary

bladder and portions of ureters and urethra

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EXOCRINE GLANDULAR EPITHELIA

Exocrine glands: excrete secretions usually thru ducts onto surface Unicellular

Goblet & mucous cells scattered among epithelial cells

Secrete mucin (glycoproteins & water) via exocytosis

Multicellular – Secretory sheet, classified by pattern of ducts

ex – mucin lining stomach

Mode of Secretion: Merocrine: via exocytosis

Ex. Skin Perspiration, Mucus Glands, Saliva, mammary glands (milk)

Apocrine: lose cytoplasm and secretory product Ex. Mammary glands (lipids)

Holocrine – cell fills with secretion then bursts and dies Ex. Sebaceous glands – oils from base of hair

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CLASSIFICATION OF CONNECTIVE TISSUES: 3 TYPESConnective Tissue Proper

Syrupy ground matrixEx. Loose (areolar, adipose) & Dense

(tendons & ligaments)Blood - Fluid Connective tissue

Cells suspended in watery ground substance w/dissolved proteins

Cartilage Supporting Connective TissueDense ground substance(Hyaline, Elastic, Fibrocartilage)

Bone Supporting Connective Tissue14

CONNECTIVE TISSUES

3 Main Components Specialized cells Mostly nonliving extracellular matrix that surrounds

cells Protein Fibers – collagen, elastic, reticular Ground Substance (fluid) – fills space between cells

Interstitial fluid, Cell Adhesion Proteins, Proteoglycans

Functions (vary widely) Binding & Supporting - framework Transport materials – fluid with dissolved material Storing Energy– fat in adipose tissue Insulating Protect Organs

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CONNECTIVE TISSUE PROPER: CELL TYPES

Fibroblasts Produce and maintain connective tissue fibers

and ground substance Local maintenance & repair permanent

Macrophages Defense: Engulf damaged cells and pathogens Release chemicals to stimulate immune

response Fixed or migrating (reinforcement)

Adipocytes Permanent fat cells store nutrients Droplet of lipid pushes nucleus to side

Mast Cells Mobile, found near blood vessels Have vesicles filled with chemicals to be

released after an injury or infection Heparin -anticoagulant Histamine – leaky capillaries Proteases & other enzymes 16

CONNECTIVE TISSUE FIBERS

CollagenLong, straight,

unbranched, flexible Elastic

Protein – elastinWavy, branched,

stretchy Reticular Fibers

Thin, branching interwoven network

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GROUND SUBSTANCE

Fills spaces between cells, surrounds fibers Connective tissue proper – clear, colorless,

syrupy to slow movement of pathogens

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LOOSE CONNECTIVE TISSUE Areolar Tissue

Contains all cells and fibers of connective tissue proper

Separates skin from muscles Provides padding Allows movement Extensive blood supply

Adipose tissue- 90% adipose cells Behind eyes, kidneys, heart,

abdomen, buttocks, and breasts

Reticular Tissue- dominated by reticular fibers Lymph nodes, bone marrow, and

spleen

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WHAT IS THE DIFFERENCE BETWEEN WHITE FAT AND BROWN FAT?

White fat Pale yellow in color Found in adults Used for insulation, long term energy storage, &

cushion Brown fat

Highly vascular, contains lots of mitochondria Found in infants and young kids Metabolically very active, breaks down lipids fast Instead of absorbing energy, it releases heat to

warm circulating blood to increase body temperature 21

DENSE (FIBROUS) CONNECTIVE TISSUEConsists of mostly collagen fibers Dense Regular – collagen

fibers are parallel to resist tension

Poorly vascularized Tendons – connect skeletal

muscle to bone Aponeuroses – flat

tendons (muscle to muscle or bone)

Ligaments – contain elastic fibers, connect bone to bone

Fascia – binds together muscles, bv, and nerves

Dense Irregular – meshwork of thick collagen fibers Provides support in many

directions (i.e. skin dermis) Joint and organ capsules

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FLUID CONNECTIVE TISSUES

BloodPlasma- watery matrix

w/dissolved proteinsRed blood cell (rbc)White blood cells (wbc)Platelets

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CARTILAGE SUPPORTING CONNECTIVE TISSUE:

Cartilage – gel w/embedded fibersChondrocytes – cells found in lacunae derived

from chondroblastsAvascular, therefore difficult to repairLacks nervesTypes:

Hyaline – tightly packed collagen fibers, tough but flexible Connects ribs to sternum, supports passageways of respiratory

tract, covers bone surfaces in joints, tip nose, embryonic skeleton Elastic – elastic fibers, resilient and flexible

Flap of outer ear (pinna), epiglottis, auditory tube Fibrocartilage – mostly collagen fibers, durable and tough

Between vertebrae, between pubic bones, around or within joints24

Hyaline Cartilage

Elastic Cartilage

Fibrocartilage

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BONE SUPPORTING CONNECTIVE TISSUE:

Osseous tissue: Bone

Matrix – hard calcium and flexible collagen, very little ground substance

Osteocytes found w/in lacunae

Lacunae surround blood vessels

Canaliculi extend from central (Haversian) canal 26

Osseous Tissue

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MUSCLE TISSUE Muscle tissue – interaction between the

myofilaments myosin and actin create a contraction, highly vascular

Skeletal – striated voluntary muscle Large, multinucleated cells (long and slender) Incapable of dividing, but produced through stem cells Striations (series of bands) Only contract when stimulated by nerves

Cardiac – striated involuntary muscle Smaller striated cells, single nucleus Interconnected by intercalated discs Limited ability to repair Pacemaker cells establish a regular rate of contraction

Smooth – nonstriated involuntary muscle Walls of blood vessels, hollow tube=like organs Small, slender cells w/ one nucleus Actin and myosin are scattered so no striations Can be repaired Can contract on own or by nervous system 28

NERVOUS TISSUE Specialized for conducting electrical impulses

and responding to stimuli 2 Types Cells:

Neurons – communicate thru electrical events Neuralgia – physical support for neural tissue,

supply nutrients to neurons

Long cells w/ 3main parts: Cell body w/ nucleus Dendrites – branching projections that receive info Axon – long projection (w/synaptic terminals)

relays info to other cells Limited ability to repair

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MEMBRANES Membranes - epithelia and connective

tissues combine to form 4 types of membranes: Mucous Membranes Serous membranes Cutaneous membranes Synovial membranes

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CUTANEOUS MEMBRANE

Aka Skin – covers surface of body, thick, dry

Stratified squamous epithelium and underlying dense connective tissue

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MUCOUS MEMBRANES

Mucosae – line cavities with exterior contactDigestive, respiratory, reproductive, and

urogentital tracts Epithelial surfaces kept moist Ex.

Simple columnar epithelia of dig. tractStratified squamous epithelia of mouthTransitional epithelia of urinary tract

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SEROUS MEMBRANES

Minimizes friction when organ moves Line internal subdivisions of ventral body

cavityParietal – lines inner surface of cavityVisceral – lines outer surface or organs

Simple epithelia supported by loose connective tissuePleura – covers pleural cavity and lungsPeritoneum – lined abdominal cavity and

associated organsPericardium – lines pericardial cavity and heart

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SYNOVIAL MEMBRANES

Lines articulation (joint) capsule Loose connective tissue and incomplete layer

of epithelial tissue Produce synovial fluid for smooth movements

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Synovial Membrane

Cutaneous Membrane

Mucous Membrane

Serous Membrane

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TISSUE INJURY AND REPAIR Inflammation

In response to pathogens, impact, abrasion, extreme temperatures, or chemical irritation

Mast cells release histamine and heparin that dilate blood vessels to induce swelling, warmth, redness and pain

RegenerationFibroblasts produce dense collagen fibers

called fibrous tissue (scar tissue) Fibrosis is the permanent replacement of

normal tissues with fibrous tissue (i.e. heart and muscle tissues) 37

TISSUES AND AGING

Speed and effectiveness of tissue repair decreases with age (change of hormones and lifestyle)

Epithelia gets thinner, bones become brittle, cardiac muscle fibers and neurons cannot be replaced

Osteoporosis – inactivity, low calcium, and decrease in estrogen result in poor bone strength

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