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BASIC HISTOLOGY
Histology – study of tissues
Tissues – group of cells with similar functions and morphology
Fundamental or Basic Tissues of the Human Body:
Epithelial
Connective
Muscular
Nervous
EPITHELIAL TISSUE:
I - Characteristics:
Formed by epithelial cells
Cells are close together or packed together.
Cells are extremely cohesive and relatively strong force is necessary to separate them.
Provided with a basement membrane / basal lamina on their basal surface.
Avascular tissue.
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:
Protection – covering and lining surfaces of the body ex. Epidermis
Absorption – lining epithelium of intestines
Secretion – glands
Excretion – lining epithelium of tubules of kidney
Filtration – lining epithelium of kidneys
Lubrication – glands secreting mucus ( goblet cells, Brunner’s gland, esophageal glands)
Sensory receptors – neuroepithelium
III – Classification:
Covering / Surface Epithelium – membranous layers that cover the external surfaces or line the cavities of the body
Glandular Epithelium
COVERING / SURFACE EPITHELIUM:
Subtypes:
According to the number of cell layers:
Simple – lined by single layer of cells
According to cell shape:
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
simple cuboidal – single layer of cuboidal cells
ex. Tubules of kidneys
Thyroid follicles
Covering of Ovary
Pigment epithelium of Retina
simple columnar – single layer of columnar cells
ex. Lining epithelium of Intestines and Gall bladder
Lining epithelium of Uterus and Oviducts
Stratified – lined by several layer of columnar cells
well adapted for protection purposes
According to cell shape:
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
Stratified cuboidal
Ex. Ducts of sweat glands
Developing ovarian follicles
Stratified columnar
Ex. Parts of male urethra
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
Transitional –
Modification of stratified epithelium
The number of cells varies with the functional state of the organ
Also called as Uroepithelium.
Ex. Lining epithelium of excretory passages of the Urinary system
GLANDULAR EPITHELIUM:
Classification:
According to number of cells
Unicellular gland – single secreting cell; Goblet cell of the lining of respiratory and intestinal tracts
Multicellular gland
According to manner of secretion
Exocrine gland – provided with ducts
Ex. Gastric glands, Salivary glands
Endocrine gland – “ductless gland”
Ex. Pituitary gland, Thyroid gland
According to fate of secretion
Apocrine gland – partial destruction of secretory cells
Ex. Mammary gland
Holocrine gland – total destruction of secretory cells
Ex. Sebaceous gland
Merocrine gland – no destruction
Ex. Sweat gland
According to type of secretion
Serous gland – thin and watery secretion
Ex. Sweat gland
Mucous gland – thick and viscous
Ex. Sebaceous gland
Mixed gland – Muco-serous secretion
Ex. Sublingual and Submaxillary glands
Cytogenic gland – secretion produces cells
Ex. Testis and Ovary
According to morphology
Simple –
Simple tubular –simple epithelium lined tubules w/c open to the surface; entire tubule in a straight course
Ex. Intestinal glands
Simple coiled tubular – deeper portion of the tubule is coiled or convoluted
Ex. Sweat glands
Simple branched tubular – deeper portion of the tubule divides into tube-like structures
Ex. Uterine glands
Simple branched alveolar / acinar – made up of numerous sac-like structures
Ex. Sebaceous glands
Compound –
Compound tubular – Cardiac glands of stomach
Brunner’s glands
Compound alveolar – Mammary glands
Compound tubulo-alveolar – Salivary glands
Esophageal glands
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:
Cells are relatively few and far apart.
With abundant intercellular substance containing tissue fluid, ground matrix ( extracellular matrix ) and intercellular fibers.
Very vascular.
Derived from mesoderm.
II: Functions:
Connect, bind and support organs and tissues of the body
Protection
Fat storage and insulator
Hematopoetic functions
Immunity
Repair
III: Connective tissue cells: Categorized as:
Fixed cells – permanent
Fibroblasts – principal cells responsible for the synthesis of fibers and ground matrix ; stellate shaped with multiple processes
Mesenchymal cells – known as pluripotential cells
Fat / Adipose cells – characteristic “signet ring” appearance
Reticular cells
Wandering cells – transient
Plasma cells – ovoid cells with eccentric nucleus and intensely basophilic, “cartwheel or spokeswheel appearance of nucleus”
Mast cells – w/ cytoplasmic granules containing heparin & histamine
WBC’s
IV: Connective tissue fibers:
Collagen
Elastic
Reticular
Colorless to white
Yellow
Argyrophilic reacts with silver stains
Elastic and have greater strenght
Slender, refractile fibers
Very slender forming delicate net like patterns
Most abundant and widely distributed
Walls of blood vessels and organs capable of distention
Hematopoetic and lymphoid organs
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:
Fibrous
Collagenous
Elastic
Reticular
Adipose
Mucous
Bone / Osseous
Cartilage
Myeloid
Blood
Lymphatics
A. Fibrous Connective Tissue – depending on the type of fiber that predominates, it is divided into:
Collagenous – collagen fiber predominates
Depending on the amount of collagen fiber – subdivided into:
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
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
Elastic – elastic fiber predominates
Ex. Walls of visceral organs and blood vessels, Yellow ligaments of the vertebral column, suspensory ligament of the penis
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:
Storage of fat
Insulation against heat loss
Mechanical support
2 Types of Adipose Tissues:
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
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
Functions:
Mainly for support of fleshy structures
Performs protection of vital organs
Serves as attachment of muscles, tendons and ligaments
Contributes shape to the body
Acts as levers by which movement of the body is performed
Composition:
Organic – main component is Collagen ( type I ) 95%; responsible for elasticity of bones
Inorganic – in the form of salts, CaPO4 – responsible for the hardness of bones
Bone cells:
Osteocytes – mature bone cells
Osteoblasts – bone forming cells; responsible for the synthesis of the organic components of bone matrix
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 )
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
Periosteum-outer covering, dense irregular connective tissue,
Sharpey’s fibers – bind periosteum to bones
Endosteum-inner covering, lined by single layer of flat cells
VII. Classification as to Structure:
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
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:
Haversian canal
Concentric lamellae
Osteocytes
Canaliculi
Volkmann’s canal – communication between haversian canals or haversian system / osteon.
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
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.
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:
Plasma: 55% of the total quantity
Formed primarily by water; contains plasma proteins like albumin, globulin and fibrinogen.
Slightly alkaline fluid.
Formed elements: 45 % of the total quantity
Red blood cells / Erythrocytes
non nucleated
biconcave disc, average diameter 7.5 um
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
Source of Monocyte formation
Platelets / Thrombocytes
Non – nucleated, biconvex discs avemeter diameter
of 2 to 3 um
Liberates thromboplastin which is important in
blood coagulation
Lymphatics
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