The Tissue Level of The Tissue Level of OrganizationOrganization

Chapter 5

What is a Tissue?

• The human body is composed of trillions of cells • There are approximately 200 cell types that

make up the trillions of cells• These 200 cell types can be further grouped into

4 categories according to their roles – these 4 categories are called tissues

• Tissues are groups of cells that function together to keep a body alive

Types of Tissues

• Epithelial Tissue

• Connective Tissue

• Muscle Tissue

• Neural Tissue

Epithelial Tissue

Consist of 2 sub-categories:1. Epithelia2. Glands

Epithelia are layers of epithelial cells that cover the internal or external surfaces of various organs, ducts, vessels, etc.

Glands are structures whose cells produce fluid secretions. They are either attached to epithelia or made from epithelia

Characteristics of EpitheliaCharacteristics of Epithelia

• CellularityCellularity – made up entirely of cells that are closely – made up entirely of cells that are closely bound by tight junctions, gap junctions and desmosomesbound by tight junctions, gap junctions and desmosomes

• PolarityPolarity – One end of the tissue usually faces an – One end of the tissue usually faces an internal or external area of an organ internal or external area of an organ (apical surface)(apical surface) and and the other end is either attached to other tissues or a the other end is either attached to other tissues or a basement membrane called a basal lamina basement membrane called a basal lamina (basolateral (basolateral surface)surface)

• AvascularityAvascularity – Epithelia – Epithelia do not contain blood vesselsdo not contain blood vessels – they get their oxygen and nutrients from adjacent cells.– they get their oxygen and nutrients from adjacent cells.

• RegenerationRegeneration – Epithelial cells are constantly lost on – Epithelial cells are constantly lost on the exposed surface – so they are constantly replaced the exposed surface – so they are constantly replaced by cell division of stem cellsby cell division of stem cells

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Apical surfaces of internal passageways may have special extensions called microvilli

What are the Functions of Epithelial Tissue?

• Provide Physical Protection – against abrasion, dehydration and destruction from chemical or biological agents

• Control Permeability – some allow substances to enter / leave or pass through, other epithelial cells are quite impermeable

• Provide Sensation – large sensory nerve supply

• Produce Specialized Secretions – These epithelial cells are called gland cells (Cells of the thyroid, salivary glands, etc.) They use blood and interstitial fluid as carriers of the chemicals they release

Maintaining Epithelia IntegrityI. Intercellular connections

– CAMs (Cell Adhesion Molecules - proteins)– Intercellular cement (Proteoglycans,

glycosaminoglycans such as Hyaluronan)– Cell Junctions

• Tight Junctions – prevent passage of fluids and solutes (e.g. Stomach lumen)

• Gap Junctions – proteins called connexons leave gaps for passage of various materials

• Desmosomes – CAMs and proteoglycans link adjacent cell membranes with internal intermediate filaments– strong, resist stretching and pulling

– Belt Desmosomes, Button Desmosomes and Hemidesmosomes (Between cell and basal lamina)

Intercellular Junctions, cont’d.

Acantholysis and Desmosomes

• Pemphigus involves blistering of the outer (epidermal) layer of the skin and mucous membranes. It is an autoimmune disorder in which the immune system produces antibodies against specific proteins in the skin and mucous membrane. These antibodies produce a reaction that leads to a separation of epidermal cells (acantholysis). The antibodies usually develop against desmosome proteins. Loss of desmosomes causes epidermal cells to “Float away”

Pemphigus

Maintaining Epithelia Integrity

II. Attachment to the Basal LaminaEpidermal cells hold each other as well as the basal lamina

which consists of 2 layers: Lamina lucida – consists of proteins secreted by adjacent cells – acts as a barrier that restricts movement of proteinsLamina Densa – contains bundles of proteins that gives the basal lamina strength

Hemidesmosomes finally attach epithelial cells to the complete basal lamina

Maintaining Epithelia Integrity

III. Epithelial Maintenance and Repair

Stem cells or germinative cells within the epithelial tissue divide continually, to give rise to new epithelial cells to replace those that have died out due to exposure to toxic chemicals, pathogenic bacteria, abrasions, etc.

Types of Epithelial Tissue

(Epithelia)

Simple Squamous

• Thin, single layer of flat cells attached to basal membrane (lamina)

• Substances pass through very easily

• Forms walls of capillaries, lines other blood and lymph vessels, lines insides of certain organs

• Lines alveoli of lungs

• Easily damaged!

Simple Cuboidal

• Single layer of cube-shaped cells attached to basal membrane

• Covers ovaries, lines tubes and ducts of kidneys, certain glands such as pancreas, salivary glands and liver

• Can be used to secrete glandular products or reabsorb materials such as water (in kidneys)

Simple Columnar

• Single layer of elongated cells, attached to basal membrane

• Cells may or may not be ciliated on their apical surface

• Nonciliated simple columnar epithelia lines the uterus, parts of the GI tract and

• Can secrete digestive juices• Because of thickness, they protect underlying tissues• Ciliated simple columnar epithelia lines the fallopian

tubes, to move eggs• Some line intestines and have villi and microvilli to

increase surface are for absorption

Pseudostratified Columnar•Appears stratified, but is not•Apical surface of cells have cilia•Line respiratory tract•Contain special cells called goblet cells that secrete mucous to trap dust and microorganisms

• Many layers of squamous cells, so relatively thick

• Cells at apical surface are flattened and buildup a protein called keratin, which protects them from water damage, microorganisms, etc. Cell division occurs in deeper layers where cells are cuboidal or columnar

• Upper layer of skin (keratinized)- tough, dead

• Oral cavities, throat, esophagus, vagina, anal canal – all non-keratinized; upper layer cells are soft, alive.

Stratified Squamous

Stratified Cuboidal

•2 or 3 layers of cuboidal epithelium•Line the ducts of salivary glands, mammary glands, sweat glands, etc.•Also lines immature or developing tubes in the male and female reproductive systems

Stratified Columnar

• Cells at apical end tend to be columnar (elongated) whereas cells at the basal level are cuboidal in shape

• Line the vas deferens, male urethra and areas of the pharynx

Transitional Epithelium

• Changes in response to increased tension

• Able to stretch; also prevents materials in the urethra from reentering the tissues

• Lines inside of uterus, urinary bladder and urethra

• When walls of these organs expand, the cells appear cuboidal

• When walls stretch (distend), the cells appear flattened

Glandular Epithelium

• Cells specialized to produce and secrete substances into ducts leading out of the gland

• Glandular cells are actually embedded in and surrounded by columnar and cuboidal epithelial cells

• Two types of glands: – Exocrine: secrete products into ducts that that open

into and internal or external surface (goblet cells, salivary , sweat glands)

Endocrine: secrete products into blood and other body fluids (Pituitary, thyroid, pancreas, adrenal, ovaries, testes, etc.)

Endocrine Glands

Products secreted into blood and other body fluids.

Secretions affect various organs and tissues all around body

Exocrine Glands

There are multiple ways of classifying exocrine glands. By their

1. Structure

2. Method of secretion

3. Products secreted

Exocrine Gland StructureExocrine Gland Structure

Exocrine glands contain a glandular portion and a Exocrine glands contain a glandular portion and a duct portion, the structures of which can be used duct portion, the structures of which can be used to classify the gland. to classify the gland.

• The duct portion may be branched (called The duct portion may be branched (called compoundcompound), coiled, or unbranched (called ), coiled, or unbranched (called simplesimple).).

• The glandular portion may be tubular or alveolar The glandular portion may be tubular or alveolar (acinar). Sometimes both (tubuloacinar)(acinar). Sometimes both (tubuloacinar)

• If the glandular portion branches, then the gland If the glandular portion branches, then the gland is called a branched gland. is called a branched gland.

Exocrine Gland Methods of Secretion

Exocrine glands are named apocrine, holocrine, or merocrine glands, based on how their product is secreted.

• Apocrine glands - a portion of the gland’s cell body which contains the secretion, is lost during this type of secretion. (e.g. Mammary glands)

• Holocrine glands - the entire cell disintegrates to secrete its substance. (e.g. sebaceous glands of skin)

• Merocrine glands - cells secrete their substances by exocytosis. Also called "eccrine." (e.g. salivary, pancreatic, and sweat glands)

Merocrine

Apocrine

Holocrine

Exocytosis

Cell parts break off

Entire cell disintegrates, replaced by mitosis

Apocrine Glands

Holocrine GlandsSebaceous glands are found in the skin of mammals. They secrete an oily substance called sebum that is made of fat (lipids) and the debris of dead fat-producing cells. These glands exist in humans throughout the skin except in the palms of the hands and soles of the feet. Sebum acts to protect and waterproof hair and skin, and keep them from becoming dry, brittle, and cracked. It can also inhibit the growth of microorganisms on skin.

Merocrine Glands

Exocrine Glands Products Secreted

• Serous cells secrete proteins, often enzymes and other materials such as lipids. Examples include chief cells

• Mucous cells secrete mucous. Examples include esophageal glands, and pyloric glands.

• Mixed glands secrete both protein and mucus. Examples include the salivary glands, although parotid gland is predominantly serous (clear) and contains amylase, and sublingual gland is predominantly mucous.

Types of Cells Found in Connective Tissue

• Fibroblasts – make protein fibers • Chondrocytes – make cartilage• Macrophages – WBCs that perform phagocytosis,

usually attached to connective fibers, but can roam around

• Erythrocytes, Leukocytes – O2, CO2 transport; defense

• Mast Cells – located near blood vessels, prevent blood clotting by releasing heparin. Also release histamine that causes inflammatory and allergic reactions

• Osteocytes –maintain bone tissue• Adipocytes – Store fat droplets, but look like

fibroblasts at first

Fibroblasts – The most abundant cells in connective tissue

• Produce 3 major protein fibers in connective tissue:

1. Collagenous fibers

2. Elastic fibers

3. Reticular fibers

Collagenous Fibers• Thick threads of the protein

collagen• Grouped in long parallel

bundles• Strong, can resist significant

pulling force• Make up ligaments (connect

bone to bone) and tendons (connect muscles to bones)

Tissue with a lot of collagenous fibers is considered dense connective tissue – the opposite is loose connective tissue

Collagen Abnormalities

Ehlers-Danlos Syndrome

Not enough collagen, so elastin is predominant connective tissue, skin very stretchy

Chondrodysplasia

Stunted growth, deformed joints – NOT DWARFISM!

Elastic Fibers•Made up of branching bundles of microfibrils of a protein called elastin (or tropoelastin) •Weaker than collagen, but elastic•They can coil and recoil• Accounts for the elasticity of structures such the skin, blood vessels, heart, lungs, intestines, tendons, and ligaments•Tissues with lots of elastin appear yellow

Elastin is normally no longer made after puberty and aging begins.

Reticular Fibers• These are also made up of collagen Type III, but are very thin fibers • They are highly branched and form delicate, mesh-like networks in many tissues• Networks of these fibers make up lymphatic and hemopoietic tissues such as the

thymus, lymph nodes, spleen, and bone marrow.

Connective Tissue

Categories

1. Loose connective tissue2. Dense connective tissue3. Reticular connective tissue4. Elastic connective tissue5. Adipose tissue6. Cartilage7. Bone8. Blood

Loose Connective Tissue

• Forms thin membranes throughout body, • Cells are mainly fibroblasts separated by a a gel-like

substance made up of loosely packed collagen and elastin fibers which the fibroblasts secrete

Found between muscles, under skin,under epithelial tissueCONTAINS MANY BLOOD VESSELS – which supplies blood to epithelial cells

Dense Connective Tissue• Closely packed fibers of elastin and collagen fibers• Only a few cells inside; mainly fibroblasts• Divided into 2 categories

1. Regular dense – very strong, collagen fibers oriented in one direction

– Binds body part together as in tendons and ligaments– Poor blood supply – so tissue repair is slow

2. Irregular – more randomly organized collagen fibers– Has blood supply– Found in dermis of skin (inner layer) and the tough

capsules that surround many of the organs such as the kidneys, adrenal glands, nerves, bones, and the covering of muscles. It provides support and strength.

Regular vs. Irregular Dense Connective Tissue

Adipose Tissue

•Two types of adipose cells are found in fat tissues, white and brown adipocytes.  These adipose cell types vary in their ability to mobilize energy from stored fat.  Brown fat cells are smaller and more efficient at converting fat into available energy.  Brown fat is more typical in infants, being replaced gradually by white fat as we age.  In both cell types fat droplets enlarge to push nuclei and cytoplasm to the periphery.

Reticular Connective Tissue

• Made up of thin Type III collagenous fibers (reticular fibers) and another protein called reticulin

• Supports walls of internal organs and networks of these fibers make up lymphatic and hemopoietic tissues such as the thymus, lymph nodes, spleen, and bone marrow.

• Contains blood vessels

Elastic Connective Tissue

• Consists of yellow, elastic fibers

• Collagen fibers and fibroblasts can be found between the elastic fibers

• Found mainly in structures such the skin, blood vessels, heart, lungs, intestines and between vertebrae of spinal column

Cartilage• Rigid, structural model for

developing bones – as children mature into adults, more and more cartilage gets replaced by bone

• The matrix is mainly collagen fibers embedded in a gel-like ground substance which is made of proteins like chondromucoprotein and chondroitin sulfate and water

• Chondrocytes lie in the matrix in small cavities called lacunae

Cartilage, cont’d.

• Cartilage lacks blood supply, but is usually surrounded by connective tissue called perichondrium that supplies it with nutrients

• Cartilage heals slowly and chondrocytes do not often divide (lack of blood supply)

• 3 Types: Hyaline, Elastic and Fibrocartilage

Hyaline Cartilage

• Most common• Glass-like• Found on ends of bones

– End of nose– Rings in respiratory

passages (trachea)– Embryonic skeleton –

template for bone development

Elastic Cartilage

• More flexible than hyaline cartilage because the matrix contains more elastic fibers

• Epiglottis and “skeleton” of external ear

Elastic Cartilage in the ear

Fibrocartilage

• Very tough – contains collagen fibers

• Absorbs shocks and pressure

• Forms pads in vertebral discs, cushions bones in knees and pelvis

Vertebral Discs

Bone (Osseous Tissue)

• Most rigid connective tissue

• Rigidity due to mineral salts such as calcium phosphate and calcium carbonate in its matrix

• Bone also contains collagen

• Contains red marrow which forms blood cells, stores and releases inorganic salts

Bone Tissue – active, living tissue!

• Consists of concentric layers called lamellae, around central canals or Haversian canals

• Each bone unit around a central canal is called an osteon or Haversian system

• Each central canal contains blood vessels

• Chambers called lacunae (lacuna) contain osteocytes which used to be bone-making osteoblasts that have become entrapped in their own secretions.

• Osteocytes extend their cellular extensions into the bone matrix through fine tubes called canaliculi

• The cell extensions form gap junctions with each other - this way nutrients can pass from the blood vessels to all bone cells quickly

Blood• Various cell types found in a liquid matrix called

plasma

– Erythrocytes (RBCs)• Transport O2, CO2• Stay within blood vessels

– Leukocytes (WBCs)• Fight infection (immune system)• Can move from blood vessels to connective tissues

– Platelets (Cell fragments)• Help with clotting

• Most blood cells are produced in hematopoietic tissue like red marrow

Platelets

White Blood Cell

Red Blood Cells

Muscle Tissue

• Skeletal Muscle (voluntary muscles)

• Smooth Muscle (involuntary muscles)

• Cardiac Muscle

Skeletal Muscle– Attach bones– Movement can be controlled by us– Long and narrow cells (Muscle fiber) containing

myofibrils made of actin and myosin filaments– The myofibrils have alternating light and dark

striations– Cells are multinucleated and have many

mitochondria– Actin and myosin protein filaments in cells slide past

each other in response to nerve impulses and cause muscle to expand and contract

Skeletal Muscle Dissected

(A bundle of muscle cells)

(Muscle Cell)

(Cytoplasm of a muscle cell)(Plasma membrane of a muscle cell)

(Group of Filaments)

(Threads of Myosin and actin proteins)

Fibrodysplasia Ossificans Progressiva (FOP).

•A rare genetic disorder that transforms skeletal muscle into bone. •Children with FOP look normal at birth except for a characteristic malformation of the great toe. •During the first decade of life, affected children begin to develop painful swellings that look like tumors. These swellings seize the skeletal muscles and transform them into bone.

Smooth Muscle

• Called smooth because it lacks striations

• Cells shorter than skeletal muscle cells

• Spindle-shaped

• Single, central nucleus

• Forms muscles of the digestive tract, uterus, urinary bladder, blood vessels, etc.

• Cannot be controlled - involuntary

Smooth Muscle Fibers cells)

Cardiac MuscleCardiac Muscle

• Found in heart onlyFound in heart only• Cells striated and joined end-to-endCells striated and joined end-to-end• Cells form branchesCells form branches• Single-nucleatedSingle-nucleated• Special intercellular junctions between cells Special intercellular junctions between cells

is called an intercalated disc – found only in is called an intercalated disc – found only in cardiac muscle cellscardiac muscle cells

• Involuntary – can even continue to function Involuntary – can even continue to function without nerve stimuluswithout nerve stimulus

Cardiac Muscle

Branching

Nervous TissueNervous Tissue

• Found in brain, spinal cord (CNS) and peripheral Found in brain, spinal cord (CNS) and peripheral nervous system (PNS)nervous system (PNS)

• Main nerve cells are called neuronsMain nerve cells are called neurons• Highly specializedHighly specialized• Send impulses to each other, muscles and Send impulses to each other, muscles and

glandsglands• Other supporting nervous tissue is made up of Other supporting nervous tissue is made up of

cells called Neuroglial cells, which support cells called Neuroglial cells, which support neurons, provide them with nutrients and help neurons, provide them with nutrients and help with cell-to-cell communicationwith cell-to-cell communication

Neurons

Membranes and Organs

• Two or more types of tissues working together form an organ or membrane

• Epithelial membranes are composed of epithelial tissue and its underlying connective tissue

• Epithelial membranes are considered organs!

END OF CHAPTER

Epithelial Membranes

1. Synovial membrane – line joints, mostly connective tissue

2. Serous membrane – line inside of body cavities, reduce friction between body cavity walls and organs – secrete clear, serous fluid

3. Mucous membrane – Line tubes that open to outside – nose, throat, anus, urethra, vagina, penis – secrete mucus

4. Cutaneous membrane – also called skin – protect body from external elements