Basic Histology Review Notes

1. BASIC HISTOLOGY
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Histology – study of tissues
Tissues – group of cells with similar functions and morphology
Fundamental or Basic Tissues of the Human Body:
A. Epithelial
B. Connective
C. Muscular
D. Nervous
EPITHELIAL TISSUE:
I - Characteristics:
A. Formed by epithelial cells
B. Cells are close together or packed together.
C. Cells are extremely cohesive and relatively strong force is necessary to
separate them.
D. Provided with a basement membrane / basal lamina on their basal surface.
E. Avascular tissue.
F. Maybe derived from 3 germ layers:
Ex. Ectoderm – epidermis of skin; epithelium of cornea
Mesoderm – lining epithelium of kidneys, male & female reproductive
tracts
Endoderm – lining epithelium of gastrointestinal tract
II - Functions:
A. Protection – covering and lining surfaces of the body ex. Epidermis
B. Absorption – lining epithelium of intestines
C. Secretion – glands
D. Excretion – lining epithelium of tubules of kidney
E. Filtration – lining epithelium of kidneys
F. Lubrication – glands secreting mucus ( goblet cells, Brunner’s gland,
esophageal glands)
G. Sensory receptors – neuroepithelium
III – Classification:
A. Covering / Surface Epithelium – membranous layers that cover the external
surfaces or line the cavities of the body

2. B. Glandular Epithelium
COVERING / SURFACE EPITHELIUM:
Subtypes:
A. According to the number of cell layers:
1. Simple – lined by single layer of cells
According to cell shape:
a. simple squamous – single layer of flat cells
ex. Endothelium of blood vessels
Mesothelium of body cavities
Thin loop of Henle in kidneys
Parietal layer of Bowman’s capsule
- well adapted for exhange and filtration functions
b. simple cuboidal – single layer of cuboidal cells
ex. Tubules of kidneys
Thyroid follicles
Covering of Ovary
Pigment epithelium of Retina
c. simple columnar – single layer of columnar cells
ex. Lining epithelium of Intestines and Gall bladder
Lining epithelium of Uterus and Oviducts
2. Stratified – lined by several layer of columnar cells
- well adapted for protection purposes
According to cell shape:
b. Stratified squamous
1. Stratified squamous keratinized / cornified
Ex. Epidermis of skin
2. Stratified squamous non-keratinized / non-cornified
Ex. Lining epithelium of Esophagus, Mouth , Anal canal,
Vagina
c. Stratified cuboidal
Ex. Ducts of sweat glands
Developing ovarian follicles
d. Stratified columnar
Ex. Parts of male urethra

3. 3. Pseudostratified -
a. Modification of simple epithelium.
b. All cells are in contact with the basal lamina but not all of them reach
the apical surface.
c. Cell shapes are variable.
d. False stratification
ex. Respiratory epithelium – Pseudostratified columnar epithelium
with Goblet cells
4. Transitional –
a. Modification of stratified epithelium
b. The number of cells varies with the functional state of the
organ
c. Also called as Uroepithelium.
Ex. Lining epithelium of excretory passages of the Urinary
system
GLANDULAR EPITHELIUM:
Classification:
A. According to number of cells
1. Unicellular gland – single secreting cell; Goblet cell of the lining of
respiratory and intestinal tracts
2. Multicellular gland
B. According to manner of secretion
1. Exocrine gland – provided with ducts
Ex. Gastric glands, Salivary glands
2. Endocrine gland – “ductless gland”
Ex. Pituitary gland, Thyroid gland
C. According to fate of secretion
1. Apocrine gland – partial destruction of secretory cells
Ex. Mammary gland
2. Holocrine gland – total destruction of secretory cells
Ex. Sebaceous gland
3. Merocrine gland – no destruction
Ex. Sweat gland

4. D. According to type of secretion
1. Serous gland – thin and watery secretion
Ex. Sweat gland
2. Mucous gland – thick and viscous
Ex. Sebaceous gland
3. Mixed gland – Muco-serous secretion
Ex. Sublingual and Submaxillary glands
4. Cytogenic gland – secretion produces cells
Ex. Testis and Ovary
E. According to morphology
1. Simple –
a. Simple tubular –simple epithelium lined tubules w/c open to the
surface; entire tubule in a straight course
Ex. Intestinal glands
b. Simple coiled tubular – deeper portion of the tubule is coiled or
convoluted
Ex. Sweat glands
c. Simple branched tubular – deeper portion of the tubule divides
into tube-like structures
Ex. Uterine glands
d. Simple branched alveolar / acinar – made up of numerous sac-
like structures
Ex. Sebaceous glands
2. Compound –
a. Compound tubular – Cardiac glands of stomach
Brunner’s glands
b. Compound alveolar – Mammary glands
c. Compound tubulo-alveolar – Salivary glands
Esophageal glands

5. JUNCTIONAL COMPLEXES – structures that provides for cell attachment
4 Types:
1. Macula adherens / Desmosomes – found in the stratified epithelia of mouth,
esophagus, vagina and skin.
2. Zonula adherens / Intermediate junction / Fascia adherens – found in intercalated
disc of cardiac muscles
3. Zonula occludens / Tight junction – found in epithelia of urinary bladder & GIT
4. Nexus or Gap junction – found in epithelial, muscular and nervous tissues
CONNECTIVE TISSUE:
I: Characteristics:
A. Cells are relatively few and far apart.
B. With abundant intercellular substance containing tissue fluid, ground matrix
( extracellular matrix ) and intercellular fibers.
C. Very vascular.
D. Derived from mesoderm.
II: Functions:
A. Connect, bind and support organs and tissues of the body
B. Protection
C. Fat storage and insulator
D. Hematopoetic functions
E. Immunity
F. Repair
III: Connective tissue cells: Categorized as:
A. Fixed cells – permanent
1. Fibroblasts – principal cells responsible for the synthesis of fibers and
ground matrix ; stellate shaped with multiple processes
2. Mesenchymal cells – known as pluripotential cells
3. Fat / Adipose cells – characteristic “signet ring” appearance
4. Reticular cells
B. Wandering cells – transient
1. Plasma cells – ovoid cells with eccentric nucleus and intensely basophilic,
“cartwheel or spokeswheel appearance of nucleus”

6. 2. Mast cells – w/ cytoplasmic granules containing heparin & histamine
3. WBC’s
IV: Connective tissue fibers:
Collagen Elastic Reticular
Colorless to white Yellow Argyrophilic reacts with
silver stains
Elastic and have greater Slender, refractile fibers Very slender forming
strenght delicate net like patterns
Most abundant and widely Walls of blood vessels and Hematopoetic and
distributed organs capable of lymphoid organs
distention
Types of Collagen fibers and their distribution:
Type I: Most abundant and widely distributed
Dermis, bone, tendon, dentine, Fascia, Sclera of Eyeball, Capsules of
Organs, Fibrous cartilage
Type II: Hyaline and Elastic cartilages
Type III: Smooth muscles, Hematopoetic and Lymphoid organs ( liver & spleen)
Type IV: Basement membranes
Type V: Fetal membranes
V: Classification of Connective tissue:
A. Fibrous
1. Collagenous
2. Elastic
3. Reticular
B. Adipose
C. Mucous
D. Bone / Osseous
E. Cartilage
F. Myeloid
G. Blood

7. H. Lymphatics
A. Fibrous Connective Tissue – depending on the type of fiber that predominates, it is
divided into:
1. Collagenous – collagen fiber predominates
Depending on the amount of collagen fiber – subdivided into:
a. Loose – also called as “Areolar tissue”- with numerous
potential spaces which can be distended by fluid, blood or pus;
found in the papillary layer of dermis, hypodermis, serosal
linings of the peritoneal and pleural cavities, pia mater of spinal
cord, endomysium of muscles, endoneurium of nerves
b. Dense – close packing of its fibers; occur in the form of bands,
sheets, cords or bundles
b.1 – Dense, irregular – fibers are randomly oriented
ex. Reticular layer of dermis, submucosa of esophagus,
capsules of organs, periosteum, perichondrium
b. 2 – Dense, regular – fibers are oriented in one direction
only, giving it great tensile strength
ex. Tendons, ligaments, aponeurosis
2. Elastic – elastic fiber predominates
Ex. Walls of visceral organs and blood vessels, Yellow
ligaments of the vertebral column, suspensory ligament of the penis
3. Reticular – reticular fiber predominates; forms the supporting
framework of bone marrow and most of the lymphoid and hematopoietic
organs
B. Adipose tissue – special type of connective tissue wherein adipose cell predominates.
Characteristic “signet ring appearance”
Functions:
1. Storage of fat
2. Insulation against heat loss
3. Mechanical support

8. 2 Types of Adipose Tissues:
A. Yellow / White / Unilocular – forms the main bulk of fats in the body. It is
the adult or mature form; contains a single large fat droplet
B. Brown / Multilocular – fetal or immature form; with multiple lipid
droplets
C. Mucous Connective tissue – abundance of ground matrix composed mainly of
hyaluronic acid; jelly-like consistency containing collagen fibers and few elastic or
reticular fibers; Wharton’s jelly of the umbilical cord.
D. Bone / Osseous tissue - specialized type of connective tissue wherein the intercellular
matrix is infiltrated with Calcium salts
I. Functions:
a. Mainly for support of fleshy structures
b. Performs protection of vital organs
c. Serves as attachment of muscles, tendons and ligaments
d. Contributes shape to the body
e. Acts as levers by which movement of the body is performed
II. Composition:
a. Organic – main component is Collagen ( type I ) 95%;
responsible for elasticity of bones
b. Inorganic – in the form of salts, CaPO4 – responsible for the
hardness of bones
III. Bone cells:
a. Osteocytes – mature bone cells
b. Osteoblasts – bone forming cells; responsible for the synthesis
of the organic components of bone matrix
c. Osteoclasts – multinucleated giant cells involved in bone
resorption
Parathyroid gland secretes PTH which stimulates Osteoclasts
to release Ca from bone ( to increase Ca blood level )

9. IV. Bone development:
a. Intramembranous – derived from mesenchyme; bones referred
as membrane bones
ex. Flat bones of skull, maxilla, mandible
b. Intracartilagenous / Endochondral – derived from hyaline
cartilage
ex. Bones at the base of skull, vertebral column, pelvis,
extremities
V. BoneGrowth:
a. Appositional- increase in circumference of bones
b. Interstitial – increase in length of bones
VI. Bone Coverings
a. Periosteum-outer covering, dense irregular connective tissue,
Sharpey’s fibers – bind periosteum to bones
b. Endosteum-inner covering, lined by single layer of flat cells
VII. Classification as to Structure:
a. Spongy – made up of bony processes called trabeculae giving it a
porous appearance; found in the epiphysis and metaphysic of long
bones, diploe of flat bones and in the medullary cavities
b. Compact – more solid, found in the diaphysis of long bones and
plates of flat bones; unit structure of a compact bone is called as
Osteon or Haversian system.
Components of Haversian System:
1. Haversian canal
2. Concentric lamellae
3. Osteocytes
4. Canaliculi
Volkmann’s canal – communication between haversian canals or
haversian system / osteon.

10. E. Cartilage:
I. Characteristics:
a. Chondrocyte / Cartilage cell is the characteristic cell
b. Firm, pliable type of connective tissue – the intercellular matrix
has a rigid consistency but less resistant to pressure than bone
c. Provided with fibers – collagen and elastin.
d. Avascular tissue.
e. Covered with Perichondrium – dense, irregular connective tissue
II. Functions:
a. Support to soft tissues.
b. Provide a sliding area for joints.
c. Essential for growth of bones.
III. Types: Based on the types of fibers present.
a. Hyaline – most common and widely distributed; with moderate
amount of collagen fibers; found in the costal cartilages of ribs,
thyroid and cricoid cartilages of larynx, cartilaginous rings of
trachea and bronchi, and articular cartilages.
b. Elastic – contains collagenous fibers plus large number of elastic
fibers; most flexible type; found in the auricles of the external ear,
in the walls of the external auditory canal, Eustachian tube,
epiglottic, corniculate and cuneiform cartilages of the larynx.
c. Fibrous – Also called as fibrocartilage, intermediate tissue
between dense connective tissue and cartilage; contains large
large amounts of collagen fibers; found in the intervertebral
discs and pubis symphysis
F. Myeloid – referred also as bone marrow, located in the medullary canals of long
bones and medullary cavities of spongy bones.
I. Types:
a. Red bone marrow – also called as hematogenous or active bone
marrow. In newborns, all the bone marrow is red type. In adults,
it is found in flat bones ( sternum, ribs, clavicle ), bones of pelvis,
diploe of skull bones, in vertebrae and in proximal epiphysis of
femur and humerus. Main function is for production of blood
cells.
b.Yellow bone marrow – In adults, most of the bone marrow is
this type. This type contains great amounts of adipose cells. Main
function is for storage of fats.

11. G. Blood
I. Characteristics:
a. Specialized connective tissue consisting of formed elements and a fluid
intercellular plasma.
b. Total quantity constitutes about 8 % of total body weight.
II. Components:
a. Plasma: 55% of the total quantity
Formed primarily by water; contains plasma
proteins like albumin, globulin and fibrinogen.
Slightly alkaline fluid.
b. Formed elements: 45 % of the total quantity
1. Red blood cells / Erythrocytes
- non nucleated
- biconcave disc, average diameter 7.5 um
2. White blood cells / Leucocytes
2.1 Granular
- Neutrophils / Polymorphonuclears
55 to 65 % of the total count
Nucleus consists of 3 to 5 sausage masses
of chromatin
Granules contain lyzosomal enzymes which
has anti-bacterial activity
First line of defense against infection
- Eosinophils
1 to 3 %
Nucleus is usually bilobed and its cytoplasm
contains coarse acidophilic granules
Increase in parasitic and allergic infections
- Basophils
0.5 to 1 %
Nucleus may assume a S, U or J shaped and
its cytoplasm contains larger basophilic
granules with histamine and heparin.
2.2 Agranular
- Lymphocytes
25 to 35 %
With large spherical nucleus slightly indented
on one side and thin cytoplasm
Increase in viral infections
- Monocytes
2 to 8 %
Largest WBC
Nucleus is kidney shaped and cytoplasm has
a grayish blue tint

12. Source of Monocyte formation
3. Platelets / Thrombocytes
Non – nucleated, biconvex discs avemeter diameter
of 2 to 3 um
Liberates thromboplastin which is important in
blood coagulation
H. Lymphatics