tissuestissues. no single cell… although there are trillions of cells in the human body, there are...

TissuesTissuesTissuesTissues

No single cell…• Although there are trillions of cells in

the human body, there are only about 200 different types of cells

• Cells types combine to form tissues.– Collections of specialized cells and cell

products that perform a limited number of functions.

– Histology is the study of tissues

4 basic tissue types• Epithelia

– Cover exposed surfaces – Line internal passages and chambers– Produce Glandular secretions

• Connective– Fill internal spaces– Provide structural support– Store Energy

4 basic tissue types con’t.

• Muscle– Contracts to produce active

movement

• Neural– Conducts electrical impulses– Carries information

From the outside in…• Epithelial tissue

– Epithelia (singular: epithelium) -- covers internal and external surfaces

– Glands – secreting cells derived from epithelia

Key characteristics of Epithelia

• Bound closely together• A free (apical) surface is exposed to the

environment or internal space• Attached to other cells by basement

membrane• Avascular

– No blood vessels; cell must obtain nutrients across basement membrane

• Continually regenerated due to damage or loss

Functions of Epithelia• Provide physical protection

– Against abrasion, dehydration or destructive agents

• Control permeability• Provide sensation

– Helps relay info to the nervous system

• Produce specialized secretions– Individual cells are called gland cells– Entire tissues are called glandular epithelium

A note about secretions…

• If the secretions are discharged onto the surface of the epithelium, they are called exocrine– Ex. Milk, sweat, digestive enzymes

• If the secretions are released into the surrounding tissue fluid and blood, they are called endocrine– These are hormones; chemical

messengers

Epithelial Surface• AKA Apical Surface• Can have specialized structures

– Microvilli• Small finger-like projections of the cell surface• Help increase surface area for absorption and

secretion of materials• Found in the digestive and urinary tracts

– Cilia• Short hair like structures• Found in the respiratory tract• Helps move mucus trapped irritants

Classifying epithelia• Can be simple or stratified

– Simple = 1 layer of cells– Stratified = multiple layers

• 3 shapes– Squamous – flat like a fried egg– Cuboidal – like little hexagonol boxes– Columnar – like the cuboidal but taller

Pictures of epithelia• Look at the hand outs of pages 94-

96 for the different types of epithelia, both simple and stratified.

Connective TissuesConnective TissuesConnective TissuesConnective Tissues

Connective Tissues• The most diverse tissues of the body• Made of 3 different components

– Specialized Cells– Protein Fibers– Fluid known as Ground Substance

• The protein fibers and ground substance combine to make up the matrix that surrounds the cells

Connective Tissues• Never exposed to the outside

environment although they are throughout the body

• Highly vascularized• Contain receptors to pain,

pressure, temperature, and other sensations

Special differences between epithelia and connective

tissues• Epithelial tissues are composed

mainly of cells• Connective tissues has a majority

of its volume consisting of the extra-cellular matrix

Main uses of connective tissues

• Support & Protection– Help to establish a bony structural

framework

• Transport Materials– Fluid connective tissues are very

efficient at moving dissolved materials throughout the body

Main uses of connective tissues

• Storage of Energy Reserves– Adipose cells store energy until

needed

• Defense of the Body– Respond to invaders of the body and

produce antibodies

3 Major types of Connective Tissue

• Connective Tissue Proper– Ex. Tissue under the skin, fat,

tendons and ligaments– Has many types of cells and fibers in

a syrupy ground substance


• Fluid Connective Tissue– Ex. Blood and Lymph– Has a distinctive cell population in a

watery ground substance with dissolved proteins


• Supporting Connective Tissue– Ex. Cartilage and Bone– Less diverse cell population than CTP

but has a matrix of dense ground substance and closely packed fibers

– Bone is fiberous but calcified to provide rigidity and strength

Lets look at the players…

Connective Tissue Proper

• Major Cell Types– Fibroblasts– Macrophages– Fat cells (adipocytes)– Mast Cells

• Also can include stem cells and cells that produce antibodies


• Connective Tissue Fibers– Collagen – long, straight, and

unbranched strong and flexible– Elastic – Contain the protein elastin,

they are branched and wavy– Reticular – Least common and form a

woven branching framework


• Ground Substance– Should be clear and colorless– Consistency of maple syrup

• Density helps slow bacteria and makes it easier for macrophages to consume them


• Classified as either Loose or Dense• Loose

– Areolar• Least differentiated, contains all of the

cells of CTP• Forms a layer that separates skin from

underlying muscle– Why you can pinch skin without distorting the

muscle


• Loose con’t.– Adipose Tissue (Fat)

• Very similar to Areolar Tissue, just has a majority of adipocytes

• Found under the skin on the sides, buttocks and breasts


• Dense Connective Tissue– Mainly collagen fibers– Tendons – connect skeletal muscle to

bone– Ligaments – Connect bone to bone

Fluid Connective Tissue• Blood

– Watery matrix called plasma– Mostly Red Blood Cells (RBC’s)– Some White Blood Cell– Platelets

How Fluid Connective Tissues Work Together

• Plasma is in constant motion in the blood vessels due to contractions of the heart

• When it gets to capillaries, solutes will dissolve into interstitial fluid (fluid surrounding body cells)

• As interstitial fluid enters lymphatic vessels, lymph forms– Combines cells of the immune system to monitor the body

Supporting Connective Tissue

• Cartilage– Firm gel matrix containing only

chondrocytes– Avascular – why it is difficult to repair– Separated from other tissues by the

perichondrium

3 types of Cartilage• Hyaline

– Tough by flexible, connects ribs to sternum, covers bone surfaces in joints

• Elastic– Very resilient and flexible, found in the outer ear

flap and epiglottis

• Fibrocartilage– Very little ground substance, mostly collagen fibers– Found between vertebrae, connecting bones in the

pelvis

• Bones will be covered in the skeletal unit!

tissuestissues. no single cell… although there are trillions of cells in the human body, there are...

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