5.1: cells are organized into tissues

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Chapter 05Lecture Outline

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5.1: Cells are Organized into Tissues

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• In complex organisms, cells are organized into tissues

• Tissues: Groups of similar cells with a common function

• The study of tissues is called histology.

• There are 4 major types of tissues in the body:

1. Epithelial tissue

2. Connective tissue

3. Muscle tissue

4. Nervous tissue

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4 Major Tissue Types

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Intercellular Junctions

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• Tight junctions:• Membranes between cells

merge and fuse• Located among cells that form

linings, sheetlike layers• Blood-brain barrier

• Desmosomes:• Form “spot welds” between cells• Structural reinforcement• Located among outer skin cells

• Gap junctions:• Tubular channels between cells• Molecules can move between cells• Located in cardiac muscle cells

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Intercellular Junctions

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Nanotechnology Meets the Blood-Brain Barrier

• Nanotechnology helps with drug delivery across the blood-brain barrier

• Blood-brain barrier selects which chemicals are allowed to cross; protects from toxins & chemical fluctuations

• Nanotechnology uses structures smaller than 100 nm in at least 1 direction, to help medications cross the barrier

• Example: Anesthetics or chemotherapeutics are combined with liposomes (phospholipid bubbles) to mask portion of drug that cannot cross the barrier

• Example: Insulin can be inhaled in nanoparticles, instead of being injected

From Science to Technology 5.1

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5.2: Epithelial Tissue

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General Characteristics:

• Covers organs and body surface

• Lines cavities and hollow organs

• Makes up glands

• Have a free surface on outside, and basement membrane on inside

• Usually lack blood vessels; nutrients diffuse from underlying connective tissue

• Cells readily divide; injuries heal rapidly

• Cells are tightly packed

• Classified according to cell shape and number of cell layers

• Shapes: squamous (flat), cuboidal (cube-shaped), columnar (tall)

• Layers: simple (one layer of cells), stratified (2 or more layer of cells), or

pseudostratified (appears layered, but is not)

Simple squamous:• Single layer of thin, flat cells• Substances pass easily through• Thin & delicate, can be damaged• Found in diffusion & filtration sites• Lines air sacs (alveoli) & capillaries• Lines blood & lymphatic vessels

Simple cuboidal:• Single layer of cube-shaped cells• Secretion and absorption• Lines kidney tubules, thyroid

follicles• Covers ovaries• Lines ducts of some glands

Epithelial Tissue Types

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Simple Squamous Epithelium

Simple squamous epithelium

Loose connective

tissue

Squamous cell

Nucleus of squamous

cell

Simple Cuboidal Epithelium

Simple cuboidal epithelium

Lumen of tubule

Cuboidal cell

Nucleus of cuboidal cell

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Simple columnar:

• Single layer of elongated cells• Nuclei usually at same level,

near basement membrane• Sometimes have cilia• Sometimes have microvilli• Sometimes have goblet cells

(secrete mucus)• Secretion and absorption• Lines uterus, stomach, intestines

Pseudostratified columnar:• Single layer, but appears layered• Nuclei at 2 or more levels• Cells vary in shape• Often has cilia, goblet cells• Protection from infection• Lines respiratory passageways


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Simple Columnar Epithelium (Ciliated)

Simple columnar epithelium (ciliated)

Simple columnar cell (ciliated) Lumen of uterine tube

Lamina propria

Basement membrane

Cilia

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Simple Columnar Epithelium (nonciliated)

Simple columnar epithelium

Goblet cell

Simple columnar cell Lumen of jejenum Microvilli (brush border) Lamina propria

Pseudostratified Columnar EpitheliumLumen of trachea

Pseudostratified columnar epithelium

Cilia

Lamina propria

Columnar epithelial cell (ciliated)

Nucleus of basal cell

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Stratified squamous: • Many cell layers; thick• Protective layer• Outermost cells are flat• Deeper cells are cuboidal• New cells form, push older cells

toward free surface• Outer layer of skin (keratinized)• Lines oral cavity, vagina, anal canal

Stratified cuboidal: • 2-3 layers of cube-shaped cells• More protection than 1 layer• Lines ducts of mammary, sweat,

& salivary glands, and pancreas


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Stratified Squamous Epithelium (Keratinized)

Epidermis(Stratified squamous epithelium)

Dermis

Stratum basaleStratum spinosum

Stratum granulosum

Stratum corneum

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Stratified Squamous Epithelium (Nonkeratinized)

Stratified squamous epithelium

(nonkeratinized)

Lamina propria

Squamous cell

Stratified Cuboidal EpitheliumStratified cuboidal Cuboidal cell

Lumen of parotid duct Venule

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Stratified columnar:• Top layer of elongated cells • Cube-shaped cells in

deeper layers• Lines part of male urethra,

ducts of exocrine glands

Transitional (uroepithelium):• Many cell layers• Cube-shaped and elongated

cells• Changes shape with increased

tension; stretches• Line urinary bladder, ureters,

and part of urethra


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Stratified Columnar Epithelium

Lumen of spongy urethra

Stratified columnar epithelium

Lamina propria

Columnar cell

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Transitional Epithelium

Luminal cells Blood capillary

Lumen of bladder

Transitional epithelium

Lamina propria

Transitional EpitheliumLM: High Magnification

Mucosa of ureter

Transitional epithelium of

ureter

Cross‐section of ureter

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Transitional Epithelium of Urinary BladderLM: High Magnification

Transitional epithelium of bladder

Lamina propria of bladder Submucosa of bladder

Detrusor muscle

• Glandular Epithelium: Composed of cells that produce and secrete substances into ducts or body fluids

• There are 2 types of glands:• Endocrine glands secrete into tissue fluid or blood• Exocrine glands secrete into ducts that open onto surface

2 structural types of exocrine glands:• Unicellular:

Composed of one cell, such as a goblet cell (secretes mucus)• Multicellular:

• Composed of many cells• Sweat glands, salivary glands, etc.• Simple or compound

Glandular Epithelium

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Simple: duct does not branchCompound: duct branches before it reaches secretory portionTubular: consist of epithelial-lined tubesAlveolar: terminal portions form saclike dilations

Structural Types of Exocrine Glands

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Types of Exocrine Glands

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Merocrine Glands:

Secrete fluid products by exocytosis; salivary & sweat glands, pancreas

Apocrine Glands:

Lose small part of cell during secretion; mammary & ceruminous glands

Holocrine Glands:

Release entire cells filled with product; sebaceous glands

Types of Glandular Secretion

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Summary of Epithelial Tissues

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5.3: Connective Tissues

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General characteristics:• Most abundant tissue type• Cells are farther apart than epithelial cells; contain matrix between cells• Many functions:

• Bind structures together• Provide support and protection• Serve as frameworks• Fill spaces• Store fat• Produce blood cells• Protect against infections• Help repair tissue damage

• Extracellular matrix consists of protein fibers and ground substance; consistency varies from fluid to semisolid to solid

• Most have good blood supply, and are well-nourished, but vascularity varies among tissue types

• Most cells can divide

The Body’s Glue: The Extracellular Matrix

• Functions of normal extracellular matrix (ECM): - scaffolding that organizes & anchors cells into tissues- relays chemical signals that control cell division and differentiation, tissue repair, cell migration

• Cancer: Can convert fibroblasts into myofibroblasts, which take on characteristics of cancer cells; also loosens fibroblast connections, allowing migration of converted fibroblasts and spreading cancer

• Liver Fibrosis: Collagen deposition increases, and ECM now exceeds its normal 3% of organ. Damaging agents evoke normal inflammatory response, but if it continues too long, it can block connection between liver cells and blood, perhaps leading to cirrhosis.

• Heart Failure and Atherosclerosis: Some forms involve excess collagen deposition, which can stiffen the heart or block blood flow

Clinical Application 5.1

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Fibroblasts:• Most common fixed cell

• Large star-shaped cell

• Secrete fibers into extracellular

matrix

Macrophages (Histiocytes):• Usually attached to fibers, but

can detach and wander

• Conduct phagocytosis

• Defend against infection

Major Cell Types of Connective Tissue

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Mast Cells:• Large, fixed cells• Release heparin to prevent

blood clotting• Release histamine, which causes

inflammatory response

Major Cell Types of Connective Tissue

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Fibroblasts produce 3 types of fibers in connective tissue:Collagen Fibers:• Thick threads of collagen, the body’s main structural protein• Great tensile strength and flexible, slightly elastic• Found in ligaments and tendons

Elastic (Yellow) Fibers:• Composed of elastin protein; branching• Can stretch and return to original shape• Not as strong as collagen fibers• Found in vocal cords, respiratory air

passages

Reticular Fibers:• Thin, branching fibers of collagen• Form delicate, supporting networks• Found in spleen, liver

Connective Tissue Fibers

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Components of Connective Tissue

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Abnormalities of Collagen

• Collagen makes up >60% of the protein in bone and cartilage, and a large percentage of dry weight of skin, tendons, ligaments

• Has a very precise structure, and is vulnerable to disruption

• Examples:- Chondrodysplasia: Collagen chains are asymmetric and too wide, causing stunted growth and deformed joints

- Marfan syndrome: Deficiency of the protein fibrillin; leads to long limbs, spindly fingers, sunken chest, weak aorta,dislocation of the lens of the eye

Clinical Application 5.2

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Connective tissues can be classified in 2 major categories:

Connective Tissue Proper:

• Loose connective tissues:

- Areolar

- Adipose

- Reticular

• Dense connective tissues:

- Dense Regular

- Dense Irregular

- Elastic

Specialized connective tissues:

• Cartilage

• Bone

• Blood

Categories of Connective Tissue

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Areolar Connective Tissue: • Forms thin, delicate membranes• Cells are mainly fibroblasts• Gel-like ground substance• Collagenous & elastic fibers• In subcutaneous layer • Beneath most epithelia, where

it nourishes nearby epithelial cells

Adipose Tissue:• Adipocytes store fat• Push their nuclei to one side• Crowd out other cell types• Cushions and insulates• Beneath skin (subcutaneous layer)• Behind eyeballs• Around kidneys and heart• Spaces between muscles

Connective Tissue Types

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Areolar Connective

Tissue

Capillary Endothelial cell of capillary

Mast cell with granules

Nucleus of fibroblasts

Ground substance

Collagen fibers

Elastic fibers

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Adipose Connective Tissue

Adipocytes

Nuclei of adipocytes

Lipid inclusions of adipocytes

Capillaries

Reticular Connective Tissue:• Composed of thin reticular fibers

• Supports walls of internal organs

• Walls of liver, spleen

Dense Regular Connective Tissue:• Closely packed collagenous fibers

• Fine network of elastic fibers

• Most cells are fibroblasts

• Very strong, withstands pulling

• Binds body parts together

• Tendons, ligaments, dermis

• Poor blood supply; slow to heal


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Reticular Connective Tissue

Reticular fibers Ground substance

Leukocytes Macrophages

Dense Regular Connective Tissue

Collagen fibers Ground substance Nuclei of fibroblasts

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Dense Irregular Connective Tissue:• Randomly organized, thick,

interwoven collagenous fibers• Can withstand tension exerted • from different directions• Dermis of skin • Around skeletal muscles

Elastic Connective Tissue:• Abundant yellow elastic fibers• Some collagenous fibers• Fibroblasts• Attachments between bones

of spinal column• Walls of hollow organs, such

as large arteries, airways• Parts of heart• Elastic quality, stretches


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Dense Irregular Connective

Tissue

Collagen fibers Ground substance Nuclei of fibroblasts

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Elastic Connective Tissue

Elastic lamellae

Nuclei of fibroblasts

Nuclei of smooth muscle cells

Tunica intima of elastic artery

Tunica media of elastic artery

Lumen of elastic artery

Endothelium of elastic artery

Internal elastic lamella

Cartilage: • A rigid, specialized connective tissue

• Support, framework, attachments

• Protection of underlying tissue

• Models for developing bone

• Matrix contains collagen in gel-like ground substance

• Chondrocytes (cartilage cells) in lacunae (chambers), surrounded by matrix

• Lacks blood supply; heals slowly

• Covered by perichondrium (connective tissue), which provides some nutrients to the cartilage

• 3 types of cartilage: Hyaline, Elastic, and Fibrocartilage


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Hyaline cartilage:• Most common type

• Fine collagen fibers

• Ends of bones in joints

• Nose, respiratory

passages

• Embryonic skeleton

Elastic cartilage:• Flexible, due to elastic

fibers in matrix

• External ear, larynx


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Fibrocartilage:

• Very tough, due to many collagenous fibers

• Shock absorber

• Intervertebral discs

• Pads of knee and pelvic girdle


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Hyaline CartilageChondrocytes

Extracellular matrix

Perichondrium

Lacunae

Nuclei of chondrocytes

Elastic CartilageChondrocytes

Elastic fibers

Ground substance

Lacunae


Perichondrium

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FibrocartilageChondrocytes

Collagen fibers

Ground substance

Lacunae


• Bone (Osseous Tissue):• Most rigid connective tissue

• Solid matrix, composed of mineral (Ca) salts & collagen

• Supports structures

• Protects vital structures

• Produces blood cells

• Stores & releases Ca, P

• Attachment sites for muscles

• Forms skeleton

• Contain osteocytes (bone cells) in lacunae

• 2 types: compact and spongy


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Compact Bone

Osteon

Central Canal Osteocytes in lacuna

Cement line

Interstitial lamellae

Spongy Bone

Marrow cavity Trabeculae

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Compact Bone:• Osteoblasts deposit matrix in lamellae (layers)• Lamellae occur in rings around central canals• Osteocytes + matrix + central canal form cylindrical units called osteons• Osteons are cemented together to form compact bone• Central canals contain blood vessels; bone is well-nourished, heals more

quickly than cartilage


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Blood:• Cells suspended in fluid matrix called plasma

• Red blood cells transport gases

• White blood cells defend again infection

• Platelets help in blood clotting

• Transports substances around body


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Fluid Connective TissueBlood

Erythrocytes

Neutrophils

Platelets

Connective Tissues

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5.4: Types of Membranes

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• Membranes are sheets of cells

• Epithelial membranes are composed of epithelial and connective tissue; cover body surfaces and line cavities

• 3 types of epithelial membranes:

1. Serous membranes:

- Line body cavities that do not open to outside of body

- Inner linings of thorax and abdomen; covers organs

- Simple squamous epithelium + areolar connective tissue

- Secrete serous fluid for lubrication, reducing friction

2. Mucous membranes:

- Line cavities and tubes that open to the outside of body

- Lining of digestive, respiratory, urinary, and reproductive tracts

- Epithelium + areolar connective tissue

- Goblet cells secrete mucus

3. Cutaneous membrane:

- Covers body surface

- Commonly called skin

- Part of integumentary system

Synovial membranes:

- Different from epithelial membranes

- Composed entirely of connective tissue

- Line joint cavities

Types of Membranes

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5.5: Muscle Tissues

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General Characteristics:• Muscle cells are also called muscle fibers

• Contractile; can shorten and thicken

• 3 types of muscle tissue: skeletal, cardiac, and smooth

Skeletal muscle tissue:• Attached to bones

• Striated

• Voluntary

• Multinucleated cells

• Long cylindrical cells

• Stimulated by nerve

cells

Skeletal Muscle Nuclei

A band

I band

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Smooth Muscle Low Magnification

Longitudinal smooth muscle fiber

Smooth muscle fiber

Transverse smooth muscle fiber

Smooth MuscleHigh Magnification Smooth muscle fiber

Nuclei of smooth muscle fiber

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Cardiac Muscle

Branched cardiac cell Intercalated disc Nuclei of cardiac cell

Smooth muscle tissue:• Non-striated

• Spindle-shaped fibers

• Walls of hollow organs

• Walls of blood vessels

• Involuntary

Cardiac muscle tissue:• Only in wall of heart

• Branching cells

• Involuntary

• Striated

• Intercalated discs

Muscle Tissues

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5.6: Nervous Tissue

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Nervous tissues:• Found in brain, spinal cord, peripheral nerves

• Main cells are neurons, which are specialized for communication, via conduction of nerve impulses (sensory reception, motor control)

• Neurons coordinate, integrate, and regulate body functions

• Neuroglia support and nourish neurons

Nervous TissueNeuron

Dendrites

Axon

Nucleus of neuron

Nucleolus of neuron

Nissl substance

Nuclei of glial cells

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Tissue Engineering: Building a Replacement Bladder

• Donor organs are in short supply

• Tissue Engineering is showing promise for organ replacement, by growing cells or extracellular matrix from a person’s own cells or matrix, on a synthetic scaffold.

• No rejection by immune system

• Has already been used to provide skin, cartilage, bone, blood vessels

• Urinary bladders are being replaced by growing tissue donated by the patient

• Patient’s bladder tissue contains progenitor cells for smooth muscle and uroepithelium, which are used to grow a new bladder on a synthetic dome

• After implant, synthetic scaffold degenerates over time, leaving new bladder in place

From Science to Technology 5.2

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Muscle and Nervous Tissues

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5.1: cells are organized into tissues

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