Chapter 4
The Tissue Level of Organization
Group of similar cells
common embryonic origin
common function
Histology
study of tissues
Pathologist
looks for tissue changes that indicate disease
4 Basic Tissues (1)
Epithelial Tissue
covers surfaces because cells are in contact
lines hollow organs, cavities and ducts
forms glands when cells sink under the surface
Connective Tissue
material found between cells
supports and binds structures together
stores energy as fat
provides immunity to disease
4 Basic Tissues (2)
Muscle Tissue
cells shorten in length producing movement
Nerve Tissue
cells that conduct electrical signals
detects changes inside and outside the body
responds with nerve impulses
Origin of Tissues
Primary germ layers within the embryo
endoderm
mesoderm
ectoderm
Tissue derivations
epithelium from all 3 germ layers
connective tissue & muscle from mesoderm
nerve tissue from ectoderm
Biopsy
Removal of living tissue for microscopic examination
surgery
needle biopsy
Useful for diagnosis, especially cancer
Tissue preserved, sectioned and stained before microscopic
viewing
Cell Junctions
Tight junctions
Adherens junctions
Gap junctions
Desmosomes
Hemidesmosomes
Tight Junctions
Watertight seal between cells
Plasma membranes fused with a strip of proteins
Common between cells that line GI and bladder
Adherens Junctions
Holds epithelial cells together
Structural components
plaque = dense layer of proteins inside the cell membrane
microfilaments extend into cytoplasm
Desmosomes
Resists cellular separation and cell disruption
Cellular support of cardiac muscle
Hemidesmosomes
Half a desmosome
Connect cells to extracellular material
basement membrane
Gap Junctions
Tiny space between plasma membranes of 2 cells
Crossed by protein channels called connexons forming fluid
filled tunnels
Cell communication with ions & small molecules
Muscle and nerve impulses spread from cell to cell
heart and smooth muscle of gut
Epithelial Tissue
-- General Features
Closely packed cells forming continuous sheets
Cells sit on basement membrane
Apical (upper) free surface
Avascular---without blood vessels
nutrients diffuse in from underlying connective tissue
Good nerve supply
Rapid cell division
Covering / lining versus glandular types
Basement Membrane
Basal lamina
from epithelial cells
collagen fibers
Reticular lamina
secreted by connective tissue cells
reticular fibers
holds cells to connective tissue
guide for cell migration during development
Types of Epithelium
Covering and lining epithelium
epidermis of skin
lining of blood vessels and ducts
lining respiratory, reproductive, urinary & GI tract
Glandular epithelium
secreting portion of glands
thyroid, adrenal, and sweat glands
Classification of Epithelium
Classified by
arrangement of cells into layers
simple = one cell layer thick
stratified = many cell layers thick
pseudostratified = single layer of cells where all cells
don’t reach apical surface
nuclei at found at different levels so it looks multilayered
Classified by shape of surface cells
squamous =flat
cuboidal = cube-shaped
columnar = tall column
transitional = shape varies with tissue stretching
Simple Squamous
Epithelium
Single layer of flat cells
lines blood
vessels (endothelium), body cavities (mesothelium)
very thin --- controls diffusion, osmosis and filtration
nuclei centrally located
Cells in direct contact with each other
Examples of Simple Squamous
Surface view of lining of peritoneal cavity
Section of intestinal showing serosa
Simple Cuboidal Epithelium
Single layer of cube-shaped cells viewed from the side
Nuclei round and centrally located
Lines tubes of kidney
Absorption or secretion
Example of Simple Cuboidal
Sectional view of kidney tubules
Nonciliated Simple Columnar
Single layer rectangular cells
Unicellular glands =goblet cells secrete mucus
lubricate GI, respiratory, reproductive and urinary systems
Microvilli = fingerlike cytoplasmic projections
for absorption in GI tract (stomach to anus)
Ex. Nonciliated
Simple Columnar
Section from small intestine
Ciliated Simple Columnar Epithelium
Single layer rectangular cells with cilia
Mucus from goblet cells moved along by cilia
found in respiratory system and uterine tubes
Ex. Ciliated Simple Columnar
Section of uterine tube
Stratified Squamous Epithelium
Several cell layers thick
Surface cells flat
Keratinized = surface cells dead and filled with keratin
skin (epidermis)
Nonkeratinized = no
keratin in moist living cells at surface
mouth, vagina
Example of Stratified Squamous
Section of vagina
Papanicolaou Smear (Pap smear)
Collect sloughed off cells of uterus and vaginal walls
Detect cellular changes (precancerous cells)
Annually for women over 18 or if sexually active
Stratified Cuboidal Epithelium
Multilayered
Surface cells cuboidal
rare (only found in
sweat gland ducts & male urethra)
Stratified Columnar Epithelium
Multilayered
Surface cells columnar
Rare (very large ducts & part of male urethra)
Transitional
Epithelium
Multilayered
Surface cells varying in shape from round to flat if
stretched
Lines hollow organs that expand from within (urinary
bladder)
Pseudostratified
Columnar
Single cell layer
All cells attach to basement membrane but not all reach free
surface
Nuclei at varying depths
Respiratory system, male urethra & epididymis
Glandular Epithelium
Derived from epithelial cells that sank below the surface
during development
Exocrine glands
cells that secrete---sweat, ear wax, saliva, digestive
enzymes onto free surface of epithelial layer
connected to the surface by tubes (ducts)
unicellular
glands or multicellular glands
Endocrine glands
secrete hormones into
the bloodstream
hormones help maintain homeostasis
Structural Classification of Exocrine Glands
Unicellular are single-celled glands
goblet cells
Multicellular glands
branched (compound) or unbranched (simple)
tubular or acinar (flask-like) shape
Methods of
Glandular Secretion
Merocrine -- most glands
cells release their products by exocytosis---saliva,
digestive enzymes & sweat
Apocrine
smelly sweat & milk
upper part of cell possibly pinches off & dies
(perhaps--see EM data)
Holocrine -- oil gland
whole cells die & rupture to release their products
Connective Tissues
Cells rarely touch due to extracellular matrix
Matrix(fibers & ground substance secreted by cells
Consistency varies from liquid, gel to solid
Does not occur on free surface
Good nerve & blood supply except cartilage & tendons
Cell Types
Blast type cells = retain ability to divide & produce
matrix (fibroblasts, chondroblasts, & osteoblasts)
Cyte type cells = mature cell that can not divide or produce
matrix (chondrocytes & osteocytes)
Macrophages develop from monocytes
engulf bacteria & debris by phagocytosis
Plasma cells develop from B lymphocytes
produce antibodies that fight against foreign substances
Mast cells produce histamine that dilate small BV
Adipocytes (fat cells) store fat
Connective Tissue
Ground Substance
Supports the cells and fibers
Helps determine the consistency of the matrix
fluid, gel or solid
Contains many large molecules
hyaluronic acid is thick, viscous and slippery
condroitin sulfate is jellylike substance providing support
adhesion proteins (fibronectin) binds collagen fibers to
ground substance
Types of Connective Tissue Fibers
Collagen (25% of
protein in your body)
tough, resistant to pull,
yet pliable
formed from the protein collagen
Elastin (lungs,
blood vessels, ear cartilage)
smaller diameter fibers formed from protein elastin
surrounded by glycoprotein (fibrillin)
can stretch up to 150% of relaxed length and return to
original shape
Reticular (spleen and lymph nodes)
thin, branched fibers that form framework of organs
formed from protein collagen
Marfan Syndrome
Inherited disorder of fibrillin gene
Abnormal development of elastic fibers
Tendency to be tall with very long legs, arms, fingers and
toes
Life-threatening weakening of aorta may lead to rupture
Mature Connective Tissue
Loose connective tissue
Dense connective tissue
Cartilage
Bone
Blood
Lymph
Loose Connective Tissues
Loosely woven fibers throughout tissues
Types of loose connective tissue
areolar connective tissue
adipose tissue
reticular tissue
Areolar Connective Tissue
Cell types = fibroblasts, plasma cells, macrophages, mast
cells and a few white blood cells
All 3 types of fibers present
Gelatinous ground substance
Areolar Connective Tissue
Black = elastic fibers,
Pink = collagen fibers
Nuclei are mostly fibroblasts
Adipose Tissue
Peripheral nuclei due to large fat storage droplet
Deeper layer of skin, organ padding, yellow marrow
Reduces heat loss, energy storage, protection
Brown fat found in infants has more blood vessels and
mitochondria and responsible for heat generation
Liposuction or Suction Lipectomy
Suctioning removal of subcutaneous fat for body contouring
Dangers include fat emboli, infection, injury to internal
organs and excessive pain
Reticular Connective Tissue
Network of fibers & cells that produce framework of
organ
Holds organ together (liver, spleen, lymph nodes, bone
marrow)
Cartilage
Network of fibers in rubbery ground substance
Resilient and can endure more stress than loose or dense
connective tissue
Types of cartilage
hyaline cartilage
fibrocartilage
elastic cartilage
Hyaline Cartilage
Bluish-shiny white rubbery substance
Chondrocytes sit in spaces called lacunae
No blood vessels or nerves so repair is very slow
Reduces friction at joints as articular cartilage
Fibrocartilage
Many more collagen fibers causes rigidity & stiffness
Strongest type of cartilage (intervertebral discs)
Elastic Cartilage
Elastic fibers help maintain shape after deformations
Ear, nose, vocal cartilages
Growth & Repair of Cartilage
Grows and repairs slowly because is avascular
Interstitial growth
chondrocytes divide and form new matrix
occurs in childhood and adolescence
Appositional growth
chondroblasts secrete matrix onto surface
produces increase in width
Bone (Osseous) Tissue
Spongy bone
sponge-like with spaces and trabeculae
trabeculae = struts
of bone surrounded by red bone marrow
no osteons (cellular
organization)
Compact bone
solid, dense bone
basic unit of structure is osteon (haversian system)
Protects, provides for movement, stores minerals, site of blood
cell formation
Compact Bone
Osteon = lamellae
(rings) of mineralized matrix
calcium &
phosphate---give it its hardness
interwoven collagen
fibers provide strength
Osteocytes in spaces (lacunae) in between lamellae
Canaliculi (tiny canals) connect cell to cell
Blood
Connective tissue with a liquid matrix = the plasma
Cell types = red blood cells (erythrocytes), white blood
cells (leukocytes) and cell fragments called platelets
Provide clotting, immune functions, carry O2 and CO2
Lymph
Interstitial fluid being transported in lymphatic vessels
Contains less protein than plasma
Move cells and substances (lipids) from one part of the body
to another
Membranes
Epithelial layer sitting on a thin layer of connective
tissue (lamina propria)
Types of membranes
mucous membrane
serous membrane
synovial membrane
cutaneous membrane (skin)
Mucous Membranes
Lines a body cavity that opens to the outside
mouth, vagina, anus
etc
Epithelial cells form a barrier to microbes
Tight junctions between cells
Mucous is secreted from underlying glands to keep surface
moist
Serous Membranes
Simple squamous cells overlying loose CT layer
Squamous cells secrete slippery fluid
Lines a body cavity that does not open to the outside such
as chest or abdominal cavity
Examples
pleura, peritoneum and pericardium
membrane on walls of cavity = parietal layer
membrane over organs in cavity = visceral layer
Synovial Membranes
Line joint cavities of all freely movable joints
No epithelial cells---just special cells that secrete
slippery fluid
Muscle
Cells that shorten
Provide us with motion, posture and heat
Types of muscle
skeletal muscle
cardiac muscle
smooth muscle
Skeletal Muscle
Cells are long cylinders with many peripheral nuclei
Visible light and
dark banding (looks striated)
Voluntary or
conscious control
Cardiac Muscle
Cells are branched
cylinders with one central nuclei
Involuntary and
striated
Attached to and communicate with each other by intercalated
discs and desmosomes
Smooth Muscle
Spindle shaped cells with a single central nuclei
Walls of hollow organs (blood vessels, GI tract, bladder)
Involuntary and nonstriated
Nerve Tissue
Cell types -- nerve
cells and neuroglial (supporting) cells
Nerve cell structure
nucleus & long
cell processes conduct nerve signals
dendrite --- signal travels
towards the cell body
axon ---- signal travels away from cell body
Tissue Engineering
New tissues grown in the laboratory (skin & cartilage)
Scaffolding of cartilage fibers is substrate for cell growth
in culture
Research in progress
insulin-producing cells (pancreas)
dopamine-producing cells (brain)
bone, tendon, heart valves, intestines & bone marrow
Tissue Repair: Restoring Homeostasis
Worn-out, damaged tissue must be replaced
Fibrosis = replacement with stromal connective tissue cells
(scar formation)
Regeneration = replacement with original cell types
(parenchymal cells)
some cell types can divide (liver & endothelium)
some tissues contain stem cells that can divide
bone marrow, epithelium of gut & skin
some cell types can not divide & are not replaced
muscle and nervous tissue
Important Clinical Terminology
Regeneration versus fibrosis
Granulation tissue
very actively growing connective tissue
Adhesions
abnormal joining of tissue
occurs after surgery or inflammation
Conditions Affecting Tissue Repair
Nutrition
adequate protein for structural components
vitamin C production of collagen and new blood vessels
Proper blood circulation
delivers O2 & nutrients & removes fluids &
bacteria
With aging
collagen fibers
change in quality
elastin fibers fragment and abnormally bond to calcium
cell division and protein synthesis are slowed
Sjogren’s Syndrome
Autoimmune disorder producing exocrine gland inflammation
Dryness of mouth and eyes
20 % of older adults show some signs
Systemic Lupus Erythematosus (SLE)
Autoimmune disorder -- causes unknown
Chronic inflammation of connective tissue
Nonwhite women during childbearing years
Females 9:1 (1 in 2000 individuals)
Painful joints, ulcers, loss of hair, fever
Life-threatening if inflammation occurs in major organs ---
liver, kidney, heart, brain, etc.