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Basic Histology


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Basic Histology Review Notes

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Basic Histology

  1. 1. BASIC HISTOLOGY 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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