Tissues
Chapter 4

Tissue - groups of cells with similar structure
and function.
Four principle human tissue types:
epithelium (covering)
connective (support)
muscle (movement)
nervous (control)
Histology: study of tissues
A fertilized egg called a zygote will rapidly
divide into a blastocyst.
By week 3: three layered embryo (gastrulation)
- ectoderm: “outer skin”, epidermis and
nervous system
- mesoderm: skeletal, muscular and
circulatory systems
- endoderm: “inner skin” linings of the
digestive and respiratory
tracts
Epithelial: sheet of cells that covers body
surfaces and lines inside of body
cavities.
Glandular epithelium: glands
Functions:
- protection
- absorption
- filtration
- excretion
- secretion
- sensory reception
- gas exchange

Characteristics of epithelial tissue:
- Cellularity: composed of closely packed cells
- Specialized contacts: tight junctions and
desmosomes bind these closely packed cells
- Polarity: apical surface:
- free surface exposed
basal surface:
- lower surface attachment
- Basement membrane: basal lamina (filtering) +
reticular lamina (collagen protein fibers).
Together they help resist tearing and stretching of
epithelium
-
-
Avascularity: epithelial tissue does not have a blood
supply.
Regeneration: replace lost tissue via cell division

Epithelium classification:
All epithelial tissue has two names:
1st: number of cell layers
2nd: shape of cells
Number of cell layers:
Simple: single layer (absorption and filtration)
Stratified: multiple layers (protection)
Pseudostratified: artificial/false layers
Shape of cells:
Squamous: flat and scale like
Cuboidal: cube shaped
Columnar: column shaped
Transitional: varies
1) Simple Squamous Epithelium:
a.
Description: single layer of flattened cells
with a disc-shaped central nuclei and sparse
cytoplasm.
b. Function: allows passage of materials by
diffusion and filtration in sites where
protection is not important. Also secretes
lubricant.
c.
Locations: Kidney glomeruli, air sacs of
lungs, capillaries, linings of heart and
lymphatic system.
2) Simple cuboidal epithelium
a.
Description: single layer of cube-like cells
with large spherical centrally located
nuclei.
b. Function: secretion and absorption
c.
Locations: Kidney tubules, ducts and
secretory portions of glands, ovary surface
3) Simple columnar epithelium
a.
Description: single layer of tall cells with
round to oval nuclei; some cells bear cilia;
may contain goblet cells that produce
mucus.
b. Function: absorption; secretion of mucus
and enzymes; cilia propel substances.
c.
Location: non-ciliated type lines digestive
tract, gallbladder, and ducts from glands;
ciliated type lines small bronchi, uterine
tubes, and uterus.
4)
a.
b.
c.
Pseudostratified columnar epithelium
Description: single layer of cells of
differing
heights so that nuclei are a differing levels; may
contain goblet cells and bear cilia. All cells
contact the basement membrane but not the free
surface (only the tallest cells). Nuclei are at
different levels giving the false appearance
Function: secretion, propulsion by ciliary
action.
Location: non-ciliated type lines male
reproductive ducts; ciliated type lines much of
respiratory tract.
5) Stratified squamous epithelium
a.
Description: thick layers of flattened cells;
often keratinized layer and a mitotic layer.
b. Function: protects underlying tissues in
areas subject to abrasion
c.
Location: non-keratinized type lines the
mouth and vagina; keratinized type forms
the epidermis of skin.
6) Transitional epithelium
a.
Description: resembles both stratified
squamous and stratified cuboidal. Basal
cells are cuboidal or columnar; surface
cells are dome shaped.
b. Function: stretches readily and permits
distension.
c.
Location: Lines uterus, bladder, and
urethra
7)
a.
b.
Glandular epithelium
Endocrine glands: “ductless” glands that
produce hormones.
Exocrine glands: glands possessing ducts
Merocrine: secrete products by exocytosis.
pancreas and sweat glands
Holocrine: accumulate products until the
cell ruptures. Sebaceous “oil”
glands
 Connective tissue: most abundant tissue in
human body.
- binding and support (ligaments)
- protection (bone)
- insulation (adipose)
- transportation (blood)
- absorb shock
- immunity
Ground substance: unstructured material that
fills the space between cells and contains the
fibers.

Classification of connective tissues
I- Embryonic connective tissue
- mesenchyme (all connective tissue
derived)
- mucous connective tissue (Wharton’s
jelly found in fetus)
II- Mature connective tissue
A. Loose connective tissue
- areolar tissue
- adipose tissue
- reticular connective tissue
B. Dense connective tissue
- dense regular connective tissue
- dense irregular connective tissue
- elastic connective tissue
C. Cartilage
- hyaline cartilage
- fibrocartilage
- elastic cartilage
D. Bone (osseous) tissue
E. Blood (vascular) tissue
Blast cells are active cells that secrete both fibers and
ground substance (matrix). Cyte cells are mature
cells that maintain (repair or regenerate) matrix.
Examples of connective tissue cell types are as
follows:
Connective tissue proper - fibroblasts/fibrocytes
Cartilage - chondroblast/chondrocyte
Blood - hemocytoblast/hemocyte
- Hematopoietic stem cells: blood producing cells
Bone - osteoblast/osteocyte

Loose connective tissue- loosely woven fibers
Areolar: Most widely distributed connective
tissue in the body
- binds body parts
- wraps around small blood vessels
and nerves.
- binds skin to underlying structures
- composed mainly of fibroblasts
- forms lamina propria in mucous
membranes
Adipose: primarily made of adipocytes.
- storage of triglycerides
- nucleus is pushed to the side
- insulator
- reduces heat loss through skin.
- energy reserve
- subcutaneous, around kidneys,
omentum (over intestines), behind
eyeball (orbital fat)
Omentum
Reticular: composed of reticular fibers
- forms stroma (internal framework) in
organs; mainly lymphoid
- spleen
- lymph nodes
- bone marrow
- supports white blood cells
- binds smooth muscle cells together.

Dense regular connective tissue
- fibrous connective tissue
- bundles of collagen fibers with fibroblasts
strongest and most abundant.
- high tensile strength fibrous
protein
- collagen molecules are
secreted in the extracellular
spaces and fibers are
spontaneously formed;
called white fibers
- tendons: muscle to bone
- aponeuroses : sheet like tendons (muscles to
other muscle/bones)
- ligaments : bone to bone. Contain more
elastin fibers so they have a
better ability to stretch.
Tendon

Dense irregular connective tissue: contains
collagen fibers that have an irregular pattern.
- seen in sheets
- tensions are exerted in various
directions
- dermis of skin
- periosteum of bone
- heart valves

Cartilage: ability to endure great stress.
- contains dense network of collagen and
elastic fibers embedded in chondroitin
sulfate.
- chondrocytes are located in spaces called
lacunae.
- has no blood supply
- no nerves
Hyaline cartilage: called gristle. Most abundant
type of cartilage
- located: ends of long bones (articular
cartilage)
- nose
- trachea
- bronchi
- ends of ribs
- flexibility
- movement of joints
- support
Fibrocartilage: chondrocytes scattered among
collagen.
- pubic symphysis
- intervertebral discs
- menisci of the knee.
- support and fusion
- absorb compressive shock
Elastic cartilage: Similar to hyaline cartilage,
more elastic fibers present (stretching)
- pinna of ear
- epiglottis
- vocal cords
- walls of artery

Bone (osseous) tissue: Support, protection,
storage, blood forming tissues.
- calcified matrix with many collagen fibers
- lie in “little lakes” called lacunae.
- blood cell formation (hematopoiesis)
- well vascularized
- mature cells called osteocytes

Muscle tissue:
1- Skeletal muscle tissue (striated): Long slender and
multinucleated; many mitochondria. Voluntary.
Attached to muscle (bone movers)
2- Smooth muscle tissue (no striations): central
nucleus. Involuntary. Located in walls of hollow
organs; GI tract, blood vessels.
3- Cardiac muscle tissue (striated): heart muscle
(myocardium). Contains intercalated discs (electrical
connectors). Autorhythmicity. Involuntary control
Skeletal Muscle
Smooth Muscle
Cardiac Muscle

Nervous tissue: basic cell is neuron.
- generate and conduct nerve impulses
- brain, spinal cord and nerves
- dendrites, cell body and axon

Blood (connective) tissue:
- develops from mesenchyme
- soluble proteins in plasma will clot blood
and from visible fibers
- Transport gases, nutrients and waste
products