INTRODUCTION TO CELLS & TISSUES

ByVijay Kapal

Graduate Studies Course CMM 5001

The Pathological Basis Of Disease

FertilizationFertilization of egg by the sperm

Egg + Sperm

(23 Chromo) (23 Chromo)

Fertilized egg (Zygote)

(46 Chromosomes)

Human body

Sperm

Ovum (Egg)

Sperm

Zygote

Implantation

Uterus

Uterine glands

Maternal blood vessels

Blastocyst

Zygote

3-layered Flat EmbryoEctoderm (1)

Mesoderm (3)

Endoderm (2)

Fertilized egg or Zygote (Single cell)

3-layers of cells

All Tissues & Organs of Human body

Nucleus

Cytoplasm

Cell membrane

Cell

Human Genome

Chromosomes (2N = 46)

Each cell has 46 chromosomes

Form 23 homologous pairs

Each parent contributes = 23

Autosomes = 44

Sex chromosomes = 2

(Male = XY, Female = XX)

Each autosome of a homologous pair look alike

But each sex chromosome do not look alike

Cell CycleNondividing cells (Fixed postmitotics)

Resting cells (Reverting postmitotics)

Methotrexate

Bleomycin Etoposide

Paclitaxel Vincristine Vinblastine Colchicine G0

G1

S

G2

M

Mitosis & MeiosisA Homologous Pair (2 Chromosomes)

1

2

46

1 pair

23 pair

Daughter Somatic Cells (2) Gametes (4)

2nd Division

1st Division

MeiosisTakes place only in testes and ovaries

Is a reductional division

Main purpose is to reduce the number of chromosomes from 2N to 1N in sperms & eggs

(Chromosomes of each homologous pair will separate from each other)

Homologous pair = 1 chromosome from each parent (at fertilization)

2N = 46 chromosomes (2 sets)

1N = 23 chromosomes (1set)So

Sperm = 1N chromosomes (23)

Egg = 1N chromosomes (23)

Fertilization restores chromosome number again to 2N = 46 chromosomes (2 sets)

Human Body

Cells

Tissues

Organs

Human body

CellTissue

Cell Organelles• Nucleus Chomatin, Transcription• Rough ER Protein synthesis & Segregation• Smooth ER Fat & Steroid synthesis & Detoxification• Golgi Complex Concentrating, Modifying & Packaging of

secretory products• Lysosomes Intracellular digestion• Peroxisomes Contain oxidative enzymes; Use catalase to degrade

H2O2 = H2O + O2• Mitochondria Oxydative phosphorylation & ATP production• Cell Membrane Lipid bilayer layer with intramembranous proteins• Cell cytoskeleton Actin filaments, Microtubules, intermediate filaments

Cell OrganellesMitochondria

Lysozome

Golgi

Nucleus

Rough ER

Cells, Tissues & Various Topics Of Research

• Subcellular localisation & trafficking of molecules and oganelles• Cell-cell and cell-extracellular matrix interactions• Cell cytoskeleton and receptor dynamics and functions• Cell and tissue differentiation and remodelling• Genetically engineered cells and tissues• Three-dimensional reconstructions, particularly of expression patterns

over time• Cell cycle and cell lineage analysis involving gene expression profiles• Apoptosis• Gene expression analysis from histological preparations• Functional genomics & proteomics• Techniques used in molecular histology

Epithelial Tissue

Outer layer of skin

Inner lining of trachea

Inner lining of ducts of sweat glands

General Features

• Diversity• Metaplasia• Lining and Covering• Basal Lamina• Renewal• Avascularity• Cell Packing• Derivation

Classifying Principles1. Number of cell layers:

1. Simple epithelia2. Stratified epithelia3. Pseudostratified epithelia

2. Shape of the surface cells:1. Squamous cells2. Cuboidal cells3. Columnar cells

3. Luminal surface modifications:1. Microvilli (Brush border)2. Cilia3. Stereocilia

Specific Epithelial Types• Simple squamous epithelium:• Simple cuboidal epithelium:• Simple columnar epithelium:• Pseudostratified epithelium:• Stratified Squamous epithelium:

a) Keratinizedb) Nonkeratinized

• Stratified cuboidal epithelium:• Stratified columnar epithelium:• Transitional epithelium:

Simple squamous Stratified squamous

Simple cuboidal stratified cuboidal

Simple columnar Pseudostratified

Transitional

Types of Epithelia

Full Empty

Bladder

Kidney (Epithelium)

Simple squamous

Simple cuboidal

Kidney Tubules

Small Intestine (Simple Columnar)

Absorptive cells

Nucleus

Brush border

Lamina propria

Lumen of gut

Esophagus (Stratified Squamous)

Epithelium

Lamina propria

Skin (Stratified Squamous)

Epidermis

(Epithelium)

Dermis

(Connective tissue)

Epithelium

Cilia

Ciliated cells

Goblet cells

Basal lamina

Lamina propria

Trachea (Pseudostratified Epithelium)

Ureter (Transitional Epithelium)

Epithelium

Lumen

Basal lamina

Lamina propria

Basal Lamina• Next to epithelia an acellular sheet like structure is the Basal Lamina.• Component Layers & Constinuent Macromolecules:

A. Component LayersLamina lucidaLamina densaB. Constituent MacromoleculesLamina lucida (Laminin that binds to cell surface integrins, collagen IV) Lamina densa (Type IV Collagen)Basement Membrane:Basal lamina accompanied by reticular lamina (Type III Collagen) is called the basement membrane.Functions:Forms sieve-like selective barrier between the epithelia & connective tissue.Aids in cell organization, cell adhesion & maintainence of cell shape.Has a role in maintaining specific cell function. Helps guide migrations of cells during development and regeneration of injured tissue

Polarity & Specialization of Epithelial CellsA. Specialization of the Apical Surface:

1. Microvilli (Enterocytes & Proximal convoluted tubule cells))2. Cilia (Trachea, Bronchus etc.)3. Stereocilia (Epididymis)4. Flagella

B. Specialization of the Lateral Surfaces:1. Zonula occludens (Tight junctions)2. Zonula adherens (Intermediate junctions)3. Macula adherens (Desmosomes)4. Gap junction (Nexus)

C. Specialization of the Basal Surface:1. Basal lamina2. Hemidesmosome3. Sodium-potassium ATPase

D. Intracellular Polarity:

Microvilli

Zonula occludens

Zonula adherens

Terminal web

Macula adherens

Gap junction

Nucleus

Hemidesmosome

Cell Junctions

Mucous Membranes

• Components of Mucous Membrane:1. Epithelium2. Basement membrane3. Lamina propria

Mucous Membrane

Epithelium

Basal lamina

Lamina propria

Serous Membranes

A. Components of Serous Membrane:1. Epithelium called mesothelium2. Basement membrane3. Submesothelial connective tissue layer

Functions of Epithelia1. Protection from:Mechanical traumaDehydrationPathogens

2. Secretion of:Hormones, milk, sweat etc.Enzymes, HCl, glycoproteins,Mucous & serous products

3. Lubrication of:Contents of GI tractFetus in birth canalJoints

4. Filtration of wastes: (Urine)

5. Absorption of food: (Aminoacids, Glucose, Fatty acids)

6. Neuroepithelium: (Taste, Smell, Hearing)

7. Reproduction: (Germ cells)

Major Types of Epithelial Cells A. Epithelial Cells Specialized for Transport:

1. Ion-transporting cells (Kidney tubules, Gall bladder etc.)2. Cells that transport by pinocytosis (Endothelial cells of blood capillaries

B. Absorption: (Enterocytes, Proximal convoluted tubule cells)C. Secretion:

1. Protein-secreting cells (Acinar cells of pancreas, Hepatocytes)2. Polypeptide-secreting cells (APUD cells)3. Mucous cells (Goblet cells)4. Serous cells (Acinar cells of pancreas & secretory cells of parotid salivary glands.5. Steroid-secreting cells (Adrenal cortex, Leydig cells etc.)

D. Contractile Epithelial Cells: (Myoepithelial cells of glands)

GLANDSA. Exocrine & Endocrine Glands:B. Classification of Exocrine Glands:

1. By structure:a) Number of cellsb) Duct systemc) Secretory portion2. By secretory producta) Mucous secretionb) Serous secretionc) Seromucous secretion3. By mode of secretiona) Merocrineb) Apocrinec) Holocrine

Unicellular Multicellular Simple tubular Coiled tubular Branched

Simple branched Simple acinar Compound tubular Compound tubulo-alveolar

Salivary Glands

Mucous acini

Serous acini

Active transport Merocrine Apocrine Holocrine Endocrine

Mode of Secretion

Connective TissueFatFat cells

TandenFibroblasts

BoneOsteocytes

Connective Tissue

• Is one of the 4 basic tissues of the body.• Structurally it is made up of cells and large

amount of intercellular space containing extracellular matrix.

• Matrix is the dominating component of this tissue.• It forms framework, connecting, supporting and

packing tissue of the body.• It also plays a dynamic role in the development,

growth and homeostasis of other tissue types.

Loose connective tissue

Dense connective tissue

Connective Tissue

Fibroblasts

Extracellular matrix

Mammary Glands

Epithelial tissue

Composition

• Cells• Extracellular matrix

Types of Cells in Loose Connective Tissue

1. Residents:FibroblastsMacrophagesReticular cells Mesenchymal cells

2. Visitants:Mast cellsPlasma cellsLeukocytesFat cellsMelanocytes

Loose Connective Tissue

Elastic fibers

Capillary

Neutrophil

Plasma cell

Fibroblast

Collagen fibers

Macrophage

Adipocyte

Mast cell

Lymphocyte

Fibroblast (Ultrastructure)Nucleus

Rough ER

Collagen

Extracellular matrix

Collagen Producing Cells

1. Fibroblast-More than one type of collagen2. Chondroblast- Type II collagen3. Osteoblast-Type I4. Reticular cell- Type III5. Smooth muscle-Type I & III

Extracellular Matrix• Extracellular matrix (Fibers & Ground substance) is synthesized and

secreted mainly by the fibroblasts & the fibers are assembled in the extracellular space.

• FibersPrime function is support & plays strengthing role in

• Ground substanceFunctions are1. Acts as a molecular sieve & stops the spread of noxious substances2. Plays very important role in cellular nutrition & waste removal3. Plays a vital role in aging. Its amount diminishes with age and

wrinkles start appearing.

Fiberous Components

Connective tissue fibers are long, slender protein polymersthat are present in variable proportions in different types ofconnective tissue. In many cases the predominant fiber type is responsible forconferring specific properties on the tissue.• Collagen Fibers:• Elastic Fibers:• Reticular Fibers:

Collagen FibersCollagen Fibers:

Most abundant protein in the body.Synthesis & assembly:Collagen types-Type I- most abundant & occurs in loose and dense connective tissue & bone.Type II- occurs in cartilage.Type III- occurs in hematopoitic tissues.Type IV- occurs in basal laminae & does not form fibers or fibrils.Type V- in placental basement membranes & blood vessels.Type X- around hypertrophic, degenerating chondrocytes of the growth plate where bone formation is to occur.

Synthesis of Collagen

Fibroblast

Procollagen (Triple-helical units)

Procollagen peptidaseTropocollagen

Collagen fibril

Collagen fiber

Extracellular

Intracellular

Collagen’s main amino acids

Glycine (34%)

Proline (12%)

Hydroxyproline (10%)

Ground SubstanceProteoglycans:

They are made up of a core protein to which glycosoaminoglycans (GAGs) are attached. GAGs are polysacharides that contain aminosugars.GAGs-Chondroitin sulphate, Dermatan sulphate, Keratan sulphate & Heparin sulphate.Hyaluronic acid is a GAG but do not form proteoglycans.Matrix viscosity and rigidity are determined by the amount and types of GAGs, their association with the core protein to form proteoglycans, GAG-fiber association, and GAG-GAG associations.

Glycoproteins:Fibronectin-mediates the attachment of cells to the extracellular matrix.Laminin-a component of basal laminae that mediates the attachment of epithelial cells.

Tissue fluids:Salts:

Connective Tissue TypesA. Connective Tissue Proper:

1. Loose connective tissue2. Dense connective tissue

a) Dense regular connective tissueb) Dense irregular connective tissue

B. Reticular connective tissue:C. Elastic connective tissue:D. Mucous connective tissue:

Connective Tissue ProperA. Connective Tissue Proper:

1. Loose connective tissue (lamina propria)2. Dense connective tissue

a) Dense regular connective tissue (Tendon, ligament)b) Dense irregular connective tissue (Dermis, organ capsule)

Loose CT Dense CT

Elastic Connective tissue

Elastic fibers consist of an amorphous protein called elastin and numerous protein microfibrils embedded in it.Diameter range 0.1-10um.Elastic fibers are collected in thick, wavy, parallel bundles & seperated by loose collagenous tissue with fibroblasts.Ground substance is sparse.Elastic connective tissue provides flexible support.Predominates in the ligamentum flava of the vertebral column & the suspensory ligament of the penis.

Reticular Connective TissueThese fibers look very similar to collagen but are thinner than them (0.1-1.5um).More highly glycosylated.Form delicate silver-staining network instead of thick bundles.Composed mainly of type III collagen and some glycoprotein.These fibers are covered by long processes of the reticular cells.There is very little ground substance.Reticular connective tissue supports motile cells & filters body fluids.It is found mainly in hematopoietic tissue (bone marrow, spleen and lymph nodes).

Reticular fibers

Lymphocyte

Reticular cell Nu

Reticular cells

Lymph Node

Reticular Connective Tissue

Mesenchyme

Mesenchyme is embryonic connective tissue.Its stellate and fusiform cells (mesenchymal cells) are derived from mesoderm.They give rise to all the connective tissue of of the body.These are multipotential cells and persist in adults to give rise to new generations of connectivetissue cells especially during wound healing, bone repair and tissue fibrosis.

Mesenchymal Tissue (Embryo)Neural tube

Mesenchyme

Somite

Notochord

Neural tube

Extracellular matrix

Mesenchymal cells

Histophysiology A. Functions:

1. Support.2. Defense.

a) Physicalb) Immunologic

3. Repair.4. Storage.5. Transport

B. Edema:C. Hormonal Effects:D. Nutritional Factors:E. Collagen Renewal:

Special Types of Connective Tissues

• Adipose tissue• Blood & lymph• Cartilage• Bone

Blood

White Blood Cells (Granulocytes)

Neutrophil Eosinophil Basophils

Functions:-

Neutrophils act as first line of defense in infections.

Eosinophils respond to allergic states & parasitic infection

Basophils release heparin & histamine

Defense SystemINNATE DEFENSES (Do not require immunization)

Physical barriers

Chemical barriers

Soluble factors

(Skin, mucous membranes)

(Low pH, Mucous)

(Lysosomes, Interferons, Acute phase proteins, Complements)

Facilitates

CELLS (Macrophages, Granulocytes)

Fast response

Limited Flexibility

Non-specific

No memory

Facilitate

ADAPTIVE DEFENSES (Requires immunization)

Directly kill infected cells

T lymphocytes

B lymphocytes

Cytotoxic

Help

Delayed response

Highly flexible

Highly specific

Memory, lasting immunity

ANTIBODIES

Mast Cells

Functions:-

Produce heparin, an anticoagulant

Produce histamine to render blood vessels permeable

Mast cells

Monocytes

Nucleus

Cytoplasm

RBC

Nucleus

Cytoplasm

Phagocytized RBC Nucleus

B Lymphocytes deliver antibodies-mediated immune response

T lymphocytes deliver cell-mediated immune response

Natural killer cells kill tumor & nonself cells

LYMPHOCYTES

Plasma Cells

Plasma cells produce antibodies to fight the infections

Immunoglobulins IgG, IgA, IgM, IgE & IgD

Plasma cells

Lymphocyte

Functions:-

Phagocytose, process & present antigens to lymphocytes

Act as scavengers etc.

Macrophage

Macrophage

Unilocular Adipose Tissue

Adipocytes

Nucleus

Multilocular Adipose Tissue

Cartilage

Perichondrium

Chondroblasts

Chondrocytes

Lacuna

Cartilage matrix

Isogenous group

of chondrocytes

Primary Bone

Periosteum

Osteoblasts

Osteocytes

Bone matrix

Bone trabecula

Nervous Tissue

CerebellumCortical neurons

Spinal cordMotor neurons

Spinal ganglionSensory neurons

Divisions of the Nervous System

• Central Nervous System (CNS)• Peripheral Nervous System (PNS)• Autonomic Nervous System (ANS)

Nervous System

General Features• Two Classes of Cells:

1. Neurons2. Supporting cells

• Impulse Conduction:• Synapses:• Divisions of the Nervous System:• Embryonic Development of Nervous Tissue:• Aging and Repair:• Meninges:• Blood-Brain barrier:

Cells of the Nervous Tissue

Two Classes of Cells:1. Neurons.2. Supporting, neuroglial or glial cells.

Neurons

• Cell Body• Dendrites• Axon• Classification of Neurons

Neuron

Neuromuscular Junction

Skeletal muscles

Motor end plateAxon

NeuronBlood capillary

Glial cells

Dendrites

Nissl bodies

Axon hillock

Nucleus

Nucleolus

Myelinated axons

Neuron (Cell body)• Cell Body:-It is also called soma or perikaryon-It is the synthetic & trophic center of cell -It can receive signals from axons of other neurons through synaptic contacts on its cell membrane and relay them to its axon-Nucleus usually large, central, spherical and euchromatic-Nucleus with prominent nucleolus-Cytoplasm contains many organelles like mitochondia, lysosomes etc.-Cytoplasm has abundant free polyribosomes & rough endoplasmic reticulum, appears as basophilic purplish-blue clumps called Nissl bodies-Well developed Golgi to pack & often glycosylates neurotransmitters in neurosecretory, or synaptic vesicles-Abundant neurotubules (microtubules) & neurofilaments (intermediate filaments) in soma, dendrites & axon

Neuron (Dendrites)• Dendrites:

-Extensions of cell body, specialized to increase the surface area for incoming signals-Synaptic contacts are made on them-Some synaptic sites on them look like sharp projections called dendritic spines gemmules-Proximal ends has some Nissl bodies

Neuron (Axon)• Axon:

-One axon per neuron, its cytoplasm called axoplasm & its plasma membrane, the axolemma.-A complex cell process (uniform diameter) carries impulses away from the soma.-The part of the cell body where axon exits the soma is called the axon hillock and it lacks Nissl bodies.-Axon can be myelinated or unmyelinated.-Myelin sheath in CNS is provided by the oligodendrocyte , while in PNS by the Schwann cell-Axon diameter & myelin thickness determines the speed of nerve impulse. Internode (Myelin –covered) & Node (without myelin) -Some axons have branches called collaterals.-Terminal branching of axon is called terminal arborization.-Each branch ends as a bulb-like sac called terminal bouton, each bouton contains many mitochondria & neurosecretory vesicles. Specialized region of plasma membrane of bouton that take part in the formation of synapse is called as presynaptic membrane.

Nerve (Myelinated axons)

Perineurium

Endoneurium

Nodes of Ranvier

Axon

Myelin

Axon

Myelinated Axon (E.M.)

Node of Ranvier

Neurilemma

Myelin

Axoplasm

Synapses (Chemical)Synapses are specialized junctions by which a stimulus is transmitted from a neuron to its target cell.1. Presynaptic Membrane:This is part of plasma membrane of terminal bouton.2. Synaptic Cleft:Fluid-filled space between pre and post synaptic membranes.3. Postsynaptic Membrane:This is part of plasma membrane of the target cell. It is thickerthan presynaptic membrane due to the presence of receptors forneurotransmitters. When enough receptors are occupied, hydrophilic channels open, resulting in depolarization of thepostsynaptic membrane. Neurontransmitter like acetylcholinethat remains in the synaptic cleft is degraded by acetylcholinesterase.This removal of extra acetylcholine allows postsynaptic mambrane to reestablish its resting potential and prevents continuous firing of the postsynaptic neuron in response to a single stimulus.

Types of Synapses

• Axodendritic (Between an axon & a dendrite)

• Axosomatic (Between an axon & a cell body)

• Dendrodendritic (Between dendrites)• Axoaxonic (Between axons)

Neuron (Types)• Based upon Configuration of cell processeses:

Multipolar (Motor neurons of spinal cord)Bipolar (Retina, olfactry mucosa)Unipolar(Photoreceptors, rods & cones of retina)Pseudounipolar (Sensory neurons of dorsal root ganglia)

• Based upon Cell size:Golgi type I (Motor neurons of spinal cord)Golgi type II (Interneurons of spinal cord)

• Based upon FunctionMotor neurons (Multipolar neurons of ventral horn etc.)Sensory neurons (Pseudounipolar neurons of dorsal root ganglia)Interneurons (Golgi type II neurons)

• Based upon Neurotransmitter releasedCholinergic neurons (Most somatic motor neurons)Adrenergic & noradrenergic neurons (Postganglionic sympathatic neurons)Dopaminergic (Some neurons of hypothalamus)GABAergic (Some neurons of the brain)

Types of Neurons

Unipolar Bipolar Pseudounipolar Multipolar

Supporting Cells

• Provide structural and functional support to neurons.

• Take part in the formation of blood-brain barrier, thus monitoring the passage of materials from blood to neurons.

Supporting cells of CNS

1. Astrocytes:- (Blood-Brain Barrier) a) Protoplasmic astrocytesb) Fibrous astrocytes

2. Oligodendrocytes:- (Myelin to axons in CNS)

3. Ependymal cells:- (Produce the CSF)

4. Microglial cells:- (Macrophages of the nervous system)

Supporting Cells of PNS

1. Schwann cells:A Schwann cell may envelop segments of several unmyelinated axons or provide a segment of a single myelinated axon with its myelin sheath. Each mylinated axon segment (internode) is wrapped around by layers of a Schwann cell process with most of its cytoplasm squeezed out. This multilayered Schwann cell plasma membrane (mainly of phospholipids) is called myelin. The gaps between myelin sheath segments are the nodes of Ranvier.

2. Satellite cells:Each neuron outside the CNS is surrounded by a single layer of cells, called satellite cells.

Aging and Repair

• A neuron is a terminally differentiated cell.• And is incapable of undergoing mitosis.• Aging neurons accumulate more of lipofuscin

pigment.• Neurons lost through injury or surgery cannot be

replaced.• If the cell body remains intact, the injured axon can

regenerate itself.• If stimulated by injury, supporting cells, unlike

neurons, can divide.

Blood-Brain Barrier

• Components of the barrier:1. Endothelial cells of continuous type

capillaries (Tight junctions)2. Basal lamina3. Cytoplasmic processes of astrocytes.

Blood-brain Barrier

Peripheral nerve

Perineurium

Endoneurium

Myelinated axons

Peripheral Nerve (Fascicle)

Response of Nerve Tissue to InjuryA. Damage to the Cell Body:

A neuron is a terminally differentiated cell & is unable to divide. So damaged or dead neurons can’t be replaced.

B. Damage to the Axon:1. Degenaration:- Distal to the site of injury, axon & myelin degenerate. Within 2-3 days, they are removed & these clear endoneurial channels are occupied by Schwann cells. Proximal to the site of injury, retrograde degeneration of axon goes up to 2 internodes, then injured axon is sealed. Cell body also undergoes changes in response to the injury. The Nissl bodies disappear (chromatolysis) & nucleus moves to the periphery. (2 Weeks)2. Regeneration:- Begins at 3rd week, Nissl bodies reappear, protein synthesis starts. Axon’s proximal stump gives off a number of small processes called neurites. One of these enters and grows in an endoneurial channel and synaptic contacts are remade with the target cell. The target cell or organ deprived of innervation often atrophy.

Cell body

Nissl bodies

Axon

Schwann cells

Motor end plate

Muscle Before injury 2 weeks 3 weeks 3 months No healing

A B C D ENerve Injury & Recovery

Muscle TissueCardiac muscle

Skeletal muscle

Visceral muscle

Basic Properties of Muscle Tissue

1. Excitability- ability to respond to a stimulus

2. Conductivity- ability to propagate a limited response

3. Contractility- ability to shorten

4. Relaxability- ability to relax (return to original shape after contraction)

Nucleus

IC Disc

Cardiomyocyte in Longitudinal Section

Cardiomyocyte Purkinje CellIn Cross Section

Nucleus

Myofibrils

EndomysiumCapillary

Smooth Muscle

Skeletal Muscle

Endomysium

Cardiomyocytes

Nucleus

Cardiomyocyte (Long. Section)

Cardiomyocytes

Nucleus

Myofibrils

Endomysium

Capillaries

Cardiomyocytes (Cross section)

Comparison Of Types Of Muscles

Location

Cell size/shape

Nuclei

Striations Z lines

T tubules & Sarcoplasmic reticulum

Cell junctions

Muscles of skeleton

Long; cylindrical

Many; peripherally located

Yes Yes

Triads at A-I junctions

None

Heart

Short, branched

Single; centrally located

Yes Yes

Diads at Z line

Intercalated disks (Adherens, occludens & nexi)

Visceral organs

Variable, fusiform

Single: central

No Dense bodies

Caveolae replace T tubules; sparse

Nexi (Gapjunctions)

Property Skeletal Muscle Cardiac Muscle Smooth Muscle

EM of Cardiac muscle (IC disc)

Macula adherens

Gap junction

Fascia adherens

EM of Skeletal muscle