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CHAPTER 4
THE TISSUE LEVEL OF
ORGANIZATION
Pictures from Essentials of Anatomy & Physiology, Third Edition
Four Primary Types of Tissue - overview
1. Epithelium
• Tightly packed cells form a barrier between external
environment on outside & inside. (lumens
respiratory & digestive tracts)
• Forms endocrine & exocrine glands
• Forms nails & hair
2. Connective
• Loosely packed
• Space between cells occupied by fluid & protein
fibers secreted from cells
• Collagen is produced in large amts by many (not
all) connective cell types.
3. Muscle
• Often assoc w/ connective tissue
• Cells shorten (contract) in response to voluntary &
involuntary nerve activation
• Contractions: reduce distance between 2 bones, the
circumference of a lumen (capillaries), or the
volume of a chamber (heart).
• Classification based on the type of innervation (dist
of nerves – voluntary or involuntary) and the
visibility by light microscope of microfilaments
(striated or unstriated).
• 3 types: smooth, skeletal, cardiac
4. Nervous
• Send & receives info as electrical potentials
• Specific nerve cells can release hormones and/or act
as a biological clock
• Cells of muscle & nervous tissue can alter their
membrane electrical potential in response to an
electrical, chemical and hormonal stimuli
Epithelial Tissue - characteristics
• Cover an exposed surface
• Cells are bound closely together
• Always have a “free” surface exposed to the
environment or some internal chamber or
passage
• Always attached to the connective tissue below via
basement membrane
• No blood vessels – “avascular”
• Line internal and outside body cavities
Epithelial 4 Functions
1. Protect exposed & internal surfaces from abrasion,
dehydration and damage from chem or biological
agents - skin
2. Controls what leaves or enters body – permeable
or relatively impermeable
3. Specialized cells can detect changes in the
environment & relay this info to the nervous
system - skin
4. Produce specialized secretions: glandular epith
–
Exocrine secretions: released onto body surfaces.
Enzymes entering dig tract, sweat, milk
–
Endocrine secretions: aka hormones, released into
surrounding tissues. Produced in pancreas, thyroid,
pituitary gland
Intercellular Connections
•
To protect other tissues, ET must be attached to one
another by cell junctions. 3 types: Fig. 4-2
1. Tight – prevent water & solutes between cells,
exposed to harsh chem or enzymes (dig tract lining
protect from acids, wastes, dig enzymes)
2. Gap – held together by interlocked membrane prot,
forms a narrow passage, movement of ions (cardiac
& smooth muscle)
1. Desmosomes – thin layer of “protein fibers”, can
be
1. Button - small discs
2. Belt - surround a cell
3. Hemidesmosomes (attach to basement membrane)
•
Very strong - can resist stretching – in skin, dead
cells are shed in sheets
Cell Attachments
Epithelial Surface
• Microvilli – absorption or secretions – digestive &
urinary tracts
• Cilia – to move substances across – respiratory tract
Epithelial Surface
See Fig. 4-3 b
Basement Membrane
• Holds cell to the underlying connective tissues
• Made of protein fibers
• Provides a barrier from underlying tissue into
epithelial tissue
Epithelial Renewal & Repair
• Must continually repair & renew itself because of
exposure to enzymes, bacteria, abrasion, chemicals
• Survive ~ 1-2 days
• Stem or germinative cells – division of these make
new cells, near basement membranes
Classifying Epithelia
• Number of cell layers and shape of cell
• Refer to figures in book
• Layers:
– Simple: 1 cell thick, in contact with basement
membrane protect areas inside the body (line body
cavities, blood vessels), secretion, absorption, gas
exchange – thinness is an advantage
– Stratified: multi cell thick, more protection. Areas
that have mechanical or chemical stress (skin, linings
of mouth)
Epithelial – Cell Shape
• Squamous – thin, flat, large nucleus (look like fried
eggs from the top)
• Cuboidal – squarish, form neat rows, nuclei in
middle
• Columnar – squarish, taller & thinner, nuclei near
basement membrane
• Refer to Figures 4-4 & 4-5 for cell examples
Simple Squamous Epithelium
Simple Cuboidal Epithelium
Simple Columnar Epithelium
Pseudostratified Epithelia
• Looks stratified but all of the cells contact the
basement membrane
• Layered appearance – usually have cilia
Transitional Epithelia
• Withstands considerable stretching, seems to have
many layers
Stratified Squamous Epithelia
• Where there is great mechanical stress
Glandular Epithelia
• Figure 4-6
• Contain gland cells – produce secretion
• Endocrine – discharged into blood, surrounding
tissue or tissue fluids – hormones
• Exocrine – discharge onto internal or external
surface (skin) or into a duct or tube
Glandular Secretion
Connective Tissue
•
Most diverse tissue – never exposed to outside
environment – highly vascular
•
All have 3 basic components:
1. Specialized cells
2. Protein fibers
3. Ground substance – varies in consistency
•
Matrix that surrounds the cells – made of protein
fibers & ground substance
Connective Tissue - Functions:
1. Support, protect (bone)
2. Transport materials (blood, lymph)
3. Store energy reserves (adipose)
4. Defend body (antibodies)
Classifying Connective Tissues
Connective Tissue Proper
Connective Tissue Proper - cell population
• Fibroblasts - most abundant; produce & maintain
connective fibers & ground sub.
• Macrophages - phagocytize damaged cells or
pathogens & release chem. that get the immune
system going; fixed (long time) & free (an infected
area)
• Fat cells (adipose cells or adipocytes) - contains
large drop of lipid (nucleus is squeezed to one side);
# of cells differs depending on the area of body
• Mast cells - small, mobile cells near blood vessels,
cytoplasm is packed w/ vesicles that secrete
chemicals after injury or infection
• WBCs also present - produce antibodies (destroy
pathogens or foreign substances)
Connective Tissue Fibers
• Collagen - most common; unbranched; strong &
flexible; claimed to be "replenished" in skin cream
ads
• Elastic - contains elastin; branched; return to
original length; prevents cheeks from remaining
permanently disfigured when grandmother pinches
them.
• Reticular - least common; branching; form
framework
Ground Sub
• Clear, colorless, maple syrup - slows pathogens
down so phagocytes can catch them
Connective Tissue is Characterized as
1. Loose
2. Adipose (type of loose)
3. Dense
Loose Connective Tissue
• Areolar tissue - little space
• Packing material – fills spaces between organs,
provides cushioning and support to epithelia tissue
beneath skin
• Has all cells & fibers
• Lot blood vessels
Loose Connective Tissue
Adipose
• Type of loose c.t. that is dominated by fat cells
• Provides another source of padding, cushion,
insulation that slows heat loss, storage for energy
• Liposuction – removes unwanted adipose tissue
temporarily
Adipose Tissue (type of loose)
Dense Connective Tissue
• Tough, strong, durable
• Consist mostly of collagen fibers
• Tendons attach muscles to bones
• Ligaments connect bones to bones.
Dense Connective Tissue
Fluid Connective Tissue
• Distinct cells, no fibers
• Blood - RBC (1/2 vol of blood); matrix is plasma
containing WBCs & platelets (blood clotting)
• Extracellular fluid - plasma, interstitial fluid &
lymph.
• Arteries (away from heart) & veins (to heart), water
and solutes move from capillaries to tissues
• Lymph (contain WBCs) carried in lymphatic vessels
next to capillaries in tissues; returned to cardio
system at vein
Fluid Connective Tissue
Cartilage – don’t have to know the 3 types
• Matrix containing cartilage is a firm gel with fibers
• Chondrocytes – only cells that live in the matrix
• Covers bones between joints
• Connects ribs to breastbone
• Forms ear & ear canal
• Between vertebrae in spine
• Pads in knee joint (prevents bone-bone contact,
limits movement, shock absorbers)
• Heals slowly - avascular.
Cartilage (Hyaline)
Cartilage (Elastic)
Cartilage (Fibrocartilage)
Bone
• Osseous tissue – bone cells are “osteocytes”
• Not much ground substance
• Matrix is mainly of hard calcium compounds &
flexible collagen fibers – makes them strong &
resists shattering.
• See Table 4-2 (page 99) for comparison of bone &
cartilage
Bone – more on this later….
Membranes
• At cellular level – lipid bilayer
• At tissue level – form a barrier
• Basement membrane that separates epithelia from
connective tissue
• Epithelia & connective tissue combine to form
membranes that cover & protect other structures &
tissues
Muscle Tissue
• Specialized for contraction
• 3 types
– Skeletal
– Cardiac
– Smooth
• Contraction is the same, organization of their actin
& myosin filaments is different
Skeletal Muscle Tissue
• Contain large, multinucleated cells held together by
collagen & elastic fibers
• Look striped because of the organization of the
actin & myosin fibers
• AKA “striated voluntary muscle” – don’t contract
unless stimulated by nerves
• Cannot divide, however, new muscle fibers are
produced through divisions of stem cells in adult
tissue – partial repairs can occur after an injury
Skeletal Muscle Tissue
Cardiac Muscle Tissue
• Found only in the heart
• Much smaller than skeletal fibers & usually have
only 1 nucleus
• AKA “striated involuntary muscle”
• Do not rely on nerve activity – “pacemaker cells”
establish a regular rate of contraction
Cardiac Muscle Tissue
Smooth Muscle Tissue
• Found in the walls of blood vessels, around hollow
organs (bladder) and in layers around various tracts
(respiratory, circulatory, digestive, reproductive)
• Small, slender, tapering to a point at each end, 1
nucleus
• Actin & myosin are scattered throughout the cells
so there are no striations (stripes)
• AKA “nonstriated involuntary muscle”
• Can divide – regenerate after injury
Smooth Muscle Tissue
Neural Tissue
• Specialized to conduct electrical impulses that
communicate info from one area of the body to
another
• 2 types of cells
– Neurons: transmit info as electrical impulses in their
cell membranes, longest cells in body, most cannot
divide under normal circumstances & therefore have
a very limited ability to repair themselves after injury
– Neuroglia: supporting cells
Neurons
Tissue Injuries & Repair
• Injuries affect several tissues at the same time –
respond together
• Requires 2 processes:
– Inflammation
– Repair or regeneration
Inflammation
• Isolates damaged tissue from healthy tissue –
swelling, warmth, redness, pain
• Damaged cells, tissue parts & pathogens are
cleaned up. Infection – inflammation caused from
pathogens
• Mast cells stimulated – release histamine & heparin
that cause bv to dilate & become more permeable.
Skin becomes red, swollen, pain. Increases delivery
of nutrients, oxygen and phagocytic wbc’s, blood
clotting proteins, speed removal of waste products
and toxins.
Regeneration
• Tissue is replaced or repaired to normal function
• Fibroblasts produce dense collagen fibers (scar
tissue) – over time this usually disappears
• Epithelia, connective tissue – regenerate well
• Smooth, skeletal muscle tissues – regenerate poorly
• Cardiac and neural tissue – cannot regenerate
• Therefore, different patterns of tissue organization
dictate how each organ can regenerate after injury.
Tissues & Aging
• Decrease in the speed and effectiveness of tissue
repair
• Cumulative injuries from health problems or other
damage, inactivity, diet, reduction in estrogens
• Some effects are genetically programmed