Download Histology Review Guide

Histology Review Guide
Four main types of tissues
Epithelial
Connective
Muscle
Nerve
Epithelial
Covering, lining, and glandular tissue
General characteristics
Cell walls are touching (vary in how tightly they are joined)
Apical and basal surfaces
Basement membrane
Supported by connective tissue
Avascular (epithelial tissue depends on diffusion of nutrients from connective tissue
below)
Innervated
Regenerates well
Organized by number of layers
Simple – one layer
Stratified – several layers (stratified is named for the top layer)
And epithelial tissues are organized by shape
Squamous
Cuboidal
Columnar
Squamous – “scaly” flattened cells
Simple squamous are found in the alveoli of the lungs and in the filtering structures of
kidneys
Stratified squamous covers the body and extends into body openings
Provides protection from abrasion externally as the outer layer of skin.
Internally, stratified squamous protects openings to the outside of the respiratory,
digestive, and urogenital systems. Examples are the nasal passages and the esophagus.
Cuboidal
Simple cuboidal in kidney tubules (filtration)
In endocrine glands – secretes directly into the blood stream (hormones)
Pseudostratified ciliated columnar
Pseudostratified ciliated columnar lines the bronchi and brings mucus and bacteria
trapped in the mucus up to be swallowed. Nearby goblet cells secrete the mucus.
Columnar
Simple lines digestive tract
Columnar may have microvilli or cilia
Goblet cells are associated with simple columnar cells and secrete mucus in intestinal and
respiratory passages
Connective tissue
Cells are separated by non-living matrix secreted by the cells ( blood cells do not secrete
the matrix of blood, the plasma)
Matrix includes protein fibers, for example, collagen and elastic fibers. Matrix includes
proteins such as GAGs. GAGs are stored with water so the water content of matrix is
generally high. Chondroitin sulfate is one example of a GAG.
Connective tissue cells that are mitotic (actively dividing) and secreting matrix have the
suffix – “blast”.
Fibroblasts form connective tissue proper – areolar, adipose, dense, reticular and
elastic connective tissue. i.e. all connective tissue types except blood, cartilage, and bone.
Chondroblasts form cartilage
Osteoblasts form bone
When these “blast” cells mature and division slows
- cyte is added instead of blast
- Fibrocytes, chondrocytes, and osteocytes are mature cells that are no longer
dividing and secreting matrix.
Adipose
Highly vascularized
Very little matrix
Each cell contains a large drop of triglycerides
18 – 50% of body weight within normal weight ranges
Brown adipose tissue uses energy to make heat instead of ATP
Brown adipose is found only in young babies and replaces shivering.
Areolar or loose connective tissue
Remember epithelial cells are avascular and receive nutrients by diffusion. Areolar
connective tissue is the connective tissue bonded to the basement membrane of epithelial
tissue. Areolar is found under the skin and mucus membrane and around organs. Areolar
holds large amounts of fluid – as large a volume as the blood. Most cell types obtain
nutrients and release wastes into the fluid of areolar connective tissue. The matrix of
areolar connective tissue includes collagen and elastic fibers loosely associated in a
viscous matrix. Areolar houses cells of the immune system – i.e. macrophages that “eat”
bacteria and mast c
ells that secrete histamines. Histamines increase permeability of
capillaries.
Dense irregular in the dermis of the skin gives skin its flexibility
Dense regular – found in ligaments and tendons consists mainly of regular, wavy rows
of collagen and very little matrix. Dense regular can stretch, but resists twisting.
Elastic connective tissue proper is widely distributed in arteries and lungs and allows
them to expand and contract.
Cartilage
Avascular and not innervated
Hyaline – most common type of cartilage - nose, connects ribs to sternum, and between
joints, growing ends of bones in children
Slow recovery from injury
Elastic cartilage
Ears and epiglottis are high in elastic tissue. The epiglottis blocks the trachea as food
passes.
Fibrocartilage
Fibrocartilage has high compressive and tensile strength and is found in weight-bearing
areas of the body such as the intervertebral discs and the menisci which are cartilages of
the knee joint.
Bone
Vascular
Osteoblasts secrete the matrix. Osteocytes are in a pool of fluid called a lacuna.
Then bone salts such as calcium phosphate are deposited
Osteons are concentric layers of matrix surrounding a blood vessel
Blood
Blood is connective tissue because it arises from the same embryonic tissues as
connective tissue
Blood cells do not secrete the matrix (plasma) surrounding the cells
Nervous Tissue
Neurons
Cell body contains the nucleus and organelles
Dendrites bring nerve signals toward the cell body
Axons bring nerve signals away from the cell body
Muscle
Skeletal muscle has striations and flattened, multiple nuclei. Skeletal muscle is
voluntary
Cardiac muscle has striations, is branching and has intercalated discs
Intercalated discs of cardiac muscle contain gap junctions that speed
communication and desmosome junctions that reinforce cardiac muscle cells
Smooth muscle cells spindle-shaped are spindle-shaped and form sheets of tissue
Cardiac and smooth muscle are involuntary
Tissue repair
When epithelial tissue is torn
As platelets are attracted to the injury and attract other platelets, a clot forms.
Mast cells release histamines that increase permeability of capillaries and increase flow
of blood, immune cells, and clotting factors to the damaged tissues.
The first tissue to regenerate is called granulation tissue. In granulation tissue, tiny nubs
of regenerating capillaries cause this tissue to bleed easily.
Fibroblasts multiply and migrate to the injured site and secrete collagen. Fibroblasts are
contractile and pull injured tissues together. Fibroblasts secrete growth factors for
regeneration of other cells.
Damaged tissues produce new cells
New cells may replace fibrocytes as they die and are absorbed
Or fibrocytes may form scar tissue
Tissues vary in their ability to regenerate.
Best regeneration –
Epithelial
Bone
Not as good
Smooth muscle and ligaments and tendons
Poor
Skeletal muscle and cartilage
Very poor to no regeneration
Cardiac and nerve
Where cells cannot regenerate and in severe wounds, scar tissue forms from fibroblasts
Scar tissue can cause adhesions of organs after abdominal surgery and interfere with
movement of intestines, of joints, of the heart
In the case of non-regenerating tissues such as cardiac muscle, non-functional scar tissue
replaces functional tissues.