HUMAN ANATOMY

LECTURE FOUR

TISSUES

(Part 2)

CONNECTIVE TISSUE

• Characterized by cells separated by an extracellular matrix (protein fibers and ground substance)

• Variety of Functions:- encloses organs as a capsule and separates tissues/organs

into layers- connects tissues together (tendons and ligaments)-support and movement (bones)- storage (fat)- cushioning and insulation (fat)- transportation (blood)- protection (blood, immune system, bones)

CONNECTIVE TISSUE CELLSFibroblasts – always present, most common

- secrete hyaluronan (like cement) and proteins for

the matrix

Adipose or Fat Cells (adipocytes) – common in some tissues

(skin) and rare in others (cartilage)

Mast Cells – common beneath membranes, along small blood

vessels

- release heparin, histamine, and proteolytic enzymes (cause inflammation in response to injury)

White Blood Cells – move between blood vessels and

connective tissue

- respond to injury or infection

Macrophages – provide protection by phagocytosis of

pathogens or damaged cells

(i) Fixed – stay in connective tissue

(ii) Wandering – move through connective tissue

Undifferentiated Mesenchyme (stem cells) – have

potential to differentiate into various adult cells

Melanocytes – synthesize and store melanin

- common in the eye and dermis of skin

EXTRACELLULAR MATRIX PROTEIN FIBERS

Composed of three types:• Collagen - like strong ropes, flexible, inelastic (STRENGTH)• Reticular - fine, short collagen fibers (SUPPORT)

- strong but flexible because of branching - fill spaces between tissues and organs

• Elastic – contain elastin (protein), branched and wavy structure - ability to recoil after being stretched (ELASTIC)

EXTRACELLULAR MATRIX GROUND SUBSTANCE

Dense material containing cells and protein fibers:• Hyaluronic acid - polysaccharide

- good lubricant

• Proteoglycans - protein and polysaccharide

- protein attaches to hyaluronic acid and traps

large amounts of water

• Adhesive Molecules – holds proteoglycan aggregates

together

CONNECTIVE TISSUE TERMINOLOGY

Related word stems:

-blasts: create the matrix ie: osteoblast

-cytes: maintain the matrix ie: fibrocyte

-clasts: break the matrix down ie: chondroclast

Fibro… = fibrous connective tissue cells

Chondro… = cartilage cells

Osteo… = bone cells

TYPES OF CONNECTIVE TISSUEBased on physical properties:

(1) Loose (areolar) - loosely arranged collagenous fibers

(2) Dense - fibers in thick bundles that nearly fill all the

extracellular space

- dense regular, dense irregular

(3) Supporting Connective Tissue – cartilage (hyaline,

fibrocartilage, elastic), bone

(4) Fluid Connective Tissue - blood

• Loosely woven fibers with many cells• Fill spaces between and within organs• Surround nerves and blood vessels

(1) LOOSE CONNECTIVE TISSUE

Areolar Tissue

• Loose packing material between organs and tissues – STROMA

• Attaches skin to underlying tissue

• Provides padding, separation of skin from underlying movement

• Supports blood vessels and nerves

• Contains collagen, reticular, elastic fibers and all cells types

Adipose Tissue

• Contains adipocytes (fat cells) with very few fibers or matrix

• Protection, padding, insulation around organs

Yellow (white) - most common with wide distribution

- small ring of cytoplasm surrounding

single large lipid droplet, nucleus

flattened and eccentric

- white at birth, yellows with age

Brown - found in specific areas: axillae, neck, near kidneys

- highly vascularized

Reticular Tissue

• Network of reticular fibers

• Creates supportive stroma for organs (liver and spleen)

(2) DENSE CONNECTIVE TISSUE

• Made up mainly of fibers (mostly collagen)• Few cells (fibroblasts) with little matrix

Dense Regular

• Mainly collagen fibers• Fibers all aligned in same

direction (parallel)• Very strong, able to withstand

great pulling forces in direction of fiber orientation

- tendons (muscle to bone)

- ligaments (bone to bone)

- aponeurosis (muscle to

muscle or several bones)

Dense Irregular• Fibers arranged randomly• Add strength to areas that

are stressed in different directions ie: innermost layers of dermis, scars, capsules of organs, joint cavities

Dense Regular Elastic• Regular, orderly arrangement of fibers• Collagen fibers for strength• Elastin fibers for stretching and recoiling• Found in vocal cords - nuchal ligament

Dense Irregular Elastic • Bundles and sheets of collagenous and elastic

fibers oriented in multiple directions• Strong yet elastic• Found in walls of arteries

(3) SUPPORTING CONNECTIVE TISSUE

• Provide strong framework for supporting the body

• Includes: cartilage and bone

Cartilage• Composed of chondrocytes (cells) in a firm gel matrix

(protein fiber, ground substance and fluid)- fibers are collagen and sometimes elastin- ground substance of proteoglycans and hyaluronic acid complexed together to trap water

• Spaces around chondocytes are called lacunae• Avascular with no nerve supply – heals slowly• Perichondrium – dense irregular connective tissue

surrounding cartilage. - has fibrous layer and inner cellular layer - fibroblasts can differentiate into chondroblasts (healing and

growth)

• 3 types of cartilage:

(i) Hyaline Cartilage

• Most common type • Closely packed collagen fibers in proteoglycan matrix - tough but

flexible • Smooth, covers ends of bones and joints (can withstand repeated

compression), sternum, ribcage, nasal passage, respiratory tract, embryo skeleton

• Involved in growth that increases bone length

(ii) Fibrocartilage• Bundles of interwoven collagen fibers (more fibers than

ground substance)

• Slightly compressible and very tough, withstands pulling and tearing

• Found where great pressure applied to joints: knee, jaw, between vertebrae of spine, around tendons

• Areas like the knee contain both types of cartilage - hyaline covers bony surface, fibrocartilage prevent contact between bones

(iii) Elastic Cartilage

• Contains mainly elastic fibers, some collagen

• Rigid but flexible - recoils back when stretched

• Forms flap (pinnae) of external ear, epiglottis, auditory tube

Bone• Hard connective tissue composed of living cells (osteocytes) in

lacunae (spaces) within a mineralized matrix• Very small amount of ground substance• Matrix composed of 2/3 calcium salts (calcium, phosphate) and

1/3 collagen fibers - gives strength and rigidity: allows bone to support and protect other tissues and organs

• Surrounded by periosteum – connects to tendons and ligaments

• Two types of bone:– Cancellous or spongy bone– Compact bone

Cancellous Bone • Spaces inbetween – like a sponge

• Ends of bones and inside bones

Compact Bone• Bone arranged in concentric circular layers around a central

canal containing a blood vessel

• Found on outside of bones

(4) FLUID CONNECTIVE TISSUE Blood

• Liquid matrix (plasma) lacking fibers• Contains formed elements (RBC’s, WBC’s, platelets)• Flows through vessels

Hemopoietic Tissue• Forms blood cells

• Found in bone marrow

• Types of bone marrow:

Red - hemopoietic tissue surrounded by framework of

reticular fibers. Produces red and white blood cells.

Yellow – yellow adipose tissue• As children grow, yellow replaces much of red marrow

MUSCLE TISSUE• Characteristics:

- muscle cells contain specialized contractile proteins (actin and myosin)

- contracts or shortens with force - moves the body and pumps blood

• Types:Skeletal - attaches to skeleton and enables body movement

- striated (striped) and voluntaryCardiac - heart muscle

- striated and involuntarySmooth - forms walls of organs, around skin and eyes

- unstriated and involuntary – controlled by nervous system

NERVOUS TISSUE

• Form spinal cord, brain, neurons

• Responsible for coordinating and controlling bodily activities

• Neurons (nerve cells) – have ability to produce electrical signals (action potentials)

• Neuroglia – support cells that nourish, protect, insulate neurons

MEDICAL CONDITIONSMarfan’s Syndrome • abnormal fibrillin causes connective tissue to loose

strength and elasticity• weakened cardiovascular system - possible bursting of

major arteriesOsteoporosis • reduction in bone strength, related to exercise, calcium,

ageAging • tissues thin, become fragile, bones become brittleMalignant Melanoma • malignant skin tumors originate from melanocytes

(pigment producing cells) due to genetics, sun exposure• abnormal mole formation• malignant cells migrate to other areas of the body

SOMETHING TO THINK ABOUT

• In tendons, collagen fibers are orientated parallel to the length of the tendon. In the skin, collagen fibers are orientated in many directions. What are the functional advantages of the fiber arrangements in tendons and in the skin?

• A man was suspected of a gruesome murder in which an object was used to repeatedly stabbed and cut the victim. The police found a towel with blood and some tissue on it in the man’s apartment. He claimed he scraped his hand in a fall on the stairs. After examining the towel, a piece of tissue with rigid but clear matrix and lacunae was identified. Explain why the man’s story is very unlikely.

• Explain why it is advisable to suture large wounds.