Histology

1
Histology

• Study of Tissues
• Epithelial Tissue
• Connective Tissue
• Nervous and Muscular Tissue
• Intercellular Junctions, Glands and Membranes
• Tissue Growth, Development, Death and Repair

2
The Study of Tissues

• 200 Different cell types
• Four primary tissue classes
• epithelial tissue
• connective tissue
• muscular tissue
• nervous tissue
• Histology (microscopic anatomy)
• study of tissues organ formation
• Organ structure with discrete boundaries
• composed of 2 or more tissue types

3
Features of Tissue Classes

• Tissue similar cells and cell products
• arose from same region of embryo
• Differences between tissue classes
• types and functions of cells
• characteristics of matrix (extracellular
  material)
• fibrous proteins
• ground substance
• clear gels (ECF, tissue fluid, interstitial
  fluid, tissue gel)
• rubbery or stony in cartilage or bone
• space occupied by cells versus matrix
• connective tissue cells are widely separated
• little matrix between epithelial and muscle cells

4
Tissue Techniques and Sectioning

• Preparation of histological specimens
• fixative prevents decay (formalin)
• sliced into thin sections 1 or 2 cells thick
• mounted on slides and colored with histological
  stain
• stains bind to different cellular components
• Sectioning reduces 3-dimensional structure to
  2-dimensional slice

5
Sectioning Solid Objects

• Sectioning a cell with a centrally located
  nucleus
• Some slices miss the cell nucleus
• In some the nucleus is smaller

6
Sectioning Hollow Structures

• Cross section of blood vessel, gut, or other
  tubular organ.
• Longitudinal section of a sweat gland. Notice
  what a single slice could look like.

7
Types of Tissue Sections

• Longitudinal section
• tissue cut along longest direction of organ
• Cross section
• tissue cut perpendicular to length of organ
• Oblique section
• tissue cut at angle between cross and
  longitudinal section

8
Epithelial Tissue

• Layers of closely adhering cells
• Flat sheet with upper surface exposed to the
  environment or an internal body cavity
• No blood vessels
• underlying connective tissue supplies oxygen
• Rests on basement membrane
• thin layer of collagen and adhesive proteins
• anchors epithelium to connective tissue

9
Simple Versus Stratified Epithelia

• Stratified epithelium
• contains more than one layer
• named by shape of apical cells

• Simple epithelium
• contains one layer of cells
• named by shape of cells

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Simple Squamous Epithelium

• Single row of flat cells
• Permits diffusion of substances
• Secretes serous fluid
• Alveoli, glomeruli, endothelium, and serosa

11
Simple Cuboidal Epithelium

• Single row cube-shaped cells with microvilli
• Absorption and secretion, mucus production
• Liver, thyroid, mammary and salivary glands,
  bronchioles, and kidney tubules

12
Simple Columnar Epithelium

• Single row tall, narrow cells
• oval nuclei in basal half of cell
• Absorption and secretion mucus secretion
• Lining of GI tract, uterus, kidney and uterine
  tubes

13
Pseudostratified Epithelium

• Single row of cells some not reaching free
  surface
• nuclei give layer stratified look
• Secretes and propels respiratory mucus

14
Stratified Epithelia

• More than one layer of cells
• Named for shape of surface cells
• exception is transitional epithelium
• Deepest cells on basement membrane
• Variations
• keratinized epithelium has surface layer of dead
  cells
• nonkeratinized epithelium lacks the layer of dead
  cells

15
Keratinized Stratified Squamous

• Multilayered epithelium covered with dead
  squamous cells, packed with keratin
• epidermal layer of skin
• Retards water loss and barrier to organisms

16
Nonkeratinized Stratified Squamous

• Multilayered surface epithelium forming moist,
  slippery layer
• Tongue, oral mucosa, esophagus and vagina

17
Stratified Cuboidal Epithelium

• Two or more cell layers surface cells square
• Secretes sweat produces sperm and hormones
• Sweat gland ducts ovarian follicles and
  seminiferous tubules

18
Transitional Epithelium

• Multilayered epithelium surface cells that change
  from round to flat when stretched
• allows for filling of urinary tract
• ureter and bladder

19
Connective Tissue

• Widely spaced cells separated by fibers and
  ground substance
• Most abundant and variable tissue type
• Functions
• connects organs
• gives support and protection (physical and
  immune)
• stores energy and produces heat
• movement and transport of materials

20
Cells of Connective Tissue

• Fibroblasts produce fibers and ground substance
• Macrophages phagocytize foreign material and
  activate immune system
• arise from monocytes (WBCs)
• Neutrophils wander in search of bacteria
• Plasma cells synthesize antibodies
• arise from WBCs
• Mast cells secrete
• heparin inhibits clotting
• histamine that dilates blood vessels
• Adipocytes store triglycerides

21
Fibers of Connective Tissue

• Collagen fibers (white fibers)
• tough, stretch resistant, yet flexible
• tendons, ligaments and deep layer of the skin
• Reticular fibers
• thin, collagen fibers coated with glycoprotein
• framework in spleen, lymph nodes, marrow
• Elastic fibers (yellow fibers)
• thin branching fibers of elastin protein
• stretch and recoil like rubberband (elasticity)
• skin, lungs and arteries stretch and recoil

22
Connective Tissue Ground Substance

• Gelatinous material between cells
• absorbs compressive forces
• Consists of 3 classes of large molecules
• glycosaminoglycans chondroitin sulfate
• disaccharides that attract sodium and hold water
• role in regulating water and electrolyte balance
• Proteoglycan (bottlebrush-shaped molecule)
• create bonds with cells or extracellular
  macromolecules
• adhesive glycoproteins
• protein-carbohydrate complexes bind cell membrane
  to collagen outside the cells

23
Fibrous Connective Tissue Types

• Loose connective tissue
• gel-like ground substance between cells
• types
• areolar
• reticular
• adipose
• Dense connective tissue
• fibers fill spaces between cells
• types vary in fiber orientation
• dense regular connective tissue
• dense irregular connective tissue

24
Areolar Tissue

• Loose arrangement of fibers and cells in
  abundant ground substance
• Underlies all epithelia, between muscles,
  passageways for nerves and blood vessels

25
Reticular Tissue

• Loose network of reticular fibers and cells
• Forms supportive stroma (framework) for lymphatic
  organs
• Found in lymph nodes, spleen, thymus and bone
  marrow

26
Adipose Tissue

• Empty-looking cells with thin margins nucleus
  pressed against cell membrane
• Energy storage, insulation, cushioning
• subcutaneous fat and organ packing
• brown fat (hibernating animals) produces heat

27
Dense Regular Connective Tissue

• Densely, packed, parallel collagen fibers
• compressed fibroblast nuclei
• Tendons and ligaments hold bones together and
  attach muscles to bones

28
Dense Irregular Connective Tissue

• Densely packed, randomly arranged, collagen
  fibers and few visible cells
• withstands stresses applied in different
  directions
• deeper layer of skin capsules around organs

29
Cartilage

• Supportive connective tissue with rubbery matrix
• Chondroblasts produce matrix
• called chondrocytes once surrounded
• No blood vessels
• diffusion brings nutrients and removes wastes
• heals slowly
• Types of cartilage vary with fiber types
• hyaline, fibrocartilage and elastic cartilage

30
Hyaline Cartilage

• Rubbery matrix dispersed collagen fibers
  clustered chondrocytes in lacunae
• supports airway, eases joint movements
• Ends of bones at movable joints sternal ends of
  ribs supportive material in larynx, trachea,
  bronchi and fetal skeleton

31
Elastic Cartilage

• Hyaline cartilage with elastic fibers
• Provides flexible, elastic support
• external ear and epiglottis

32
Fibrocartilage

• Hyaline cartilage with extensive collagen fibers
  (never has perichondrium)
• Resists compression and absorbs shock
• pubic symphysis, meniscus and intervertebral discs

33
Bone

• Spongy bone - spongy in appearance
• delicate struts of bone
• covered by compact bone
• found in heads of long bones
• Compact bone - solid in appearance
• more complex arrangement
• cells and matrix surround vertically oriented
  blood vessels in long bones

34
Bone Tissue (compact bone)

• Calcified matrix in lamellae around central canal
• Osteocytes in lacunae between lamellae
• Skeletal support leverage for muscles mineral
  storage

35
Blood

• Variety of cells and cell fragments some with
  nuclei and some without
• Nonnucleated pale pink cells or nucleated white
  blood cells
• Found in heart and blood vessels

36
Nerve Tissue

• Large cells with long cell processes
• surrounded by smaller glial cells lacking
  processes
• Internal communication between cells
• in brain, spinal cord, nerves and ganglia

37
Muscle Tissue

• Elongated cells stimulated to contract
• Exert physical force on other tissues
• move limbs
• push blood through a vessel
• expel urine
• Source of body heat
• 3 histological types of muscle
• skeletal, cardiac and smooth

38
Skeletal Muscle

• Long, cylindrical, unbranched cells with
  striations and multiple peripheral nuclei
• movement, facial expression, posture, breathing,
  speech, swallowing and excretion

39
Cardiac Muscle

• Short branched cells with striations and
  intercalated discs
• one central nuclei per cell
• Pumping of blood by cardiac (heart) muscle

40
Smooth Muscle

• Short fusiform cells nonstriated with only one
  central nucleus
• sheets of muscle in viscera iris hair follicles
  and sphincters
• swallowing, GI tract functions, labor
  contractions, control of airflow, erection of
  hairs and control of pupil

41
Intercellular Junctions

• All cells (except blood) anchored to each other
  or their matrix by intercellular junctions

42
Tight Junctions

• Encircle the cell joining it to surrounding cells
• zipperlike complementary grooves and ridges
• Prevents passage between cells
• GI and urinary tracts

43
Desmosomes

• Patch between cells holding them together
• cells spanned by filaments terminating on protein
  plaque
• cytoplasmic intermediate filaments also attach to
  plaque
• Uterus, heart and epidermis

44
Gap Junctions

• Ring of transmembrane proteins form a
  water-filled channel
• small solutes pass directly from cell to cell
• in embryos, cardiac and smooth muscle

45
Endocrine and Exocrine Glands

• Secrete substances
• composed of epithelial tissue
• Exocrine glands connect to surface with a duct
  (epithelial tube)
• Endocrine glands secrete (hormones) directly into
  bloodstream
• Mixed organs do both
• liver, gonads, pancreas
• Unicellular glands endo or exocrine
• goblet or intrinsic cells of stomach wall

46
Exocrine Gland Structure

• Stroma capsule and septa divide gland into
  lobes and lobules
• Parenchyma cells that secrete
• Acinus cluster of cells surrounding the duct
  draining those cells

47
Types of Exocrine Glands

• Simple glands - unbranched duct
• Compound glands - branched duct
• Shape of gland
• acinar - secretory cells form dilated sac
• tubuloacinar - both tube and sacs

48
Types of Secretions

• Serous glands
• produce thin, watery secretions
• sweat, milk, tears and digestive juices
• Mucous glands
• produce mucin that absorbs water to form a sticky
  secretion called mucus
• Mixed glands contain both cell types
• Cytogenic glands release whole cells
• sperm and egg cells

49
Holocrine Gland

• Secretory cells disintegrate to deliver their
  accumulated product
• oil-producing glands of the scalp

50
Merocrine and Apocrine Secretion

• Merocrine glands release their product by
  exocytosis
• tears, gastric glands, pancreas, etc.
• Apocrine glands are merocrine glands with
  confusing appearance (apical cytoplasm not lost)
• mammary and armpit sweat glands

51
Mucous Membranes

• Epithelium, lamina propria and muscularis mucosae
• Lines passageways that open to the exterior
  reproductive, respiratory, urinary and digestive
• Mucous (movement of cilia) trap and remove
  foreign particles and bacteria from internal body
  surfaces

52
Membrane Types

• Cutaneous membrane skin
• stratified squamous epithelium over connective
  tissue
• relatively dry layer serves protective function
• Synovial membrane lines joint cavities
• connective tissue layer only, secretes synovial
  fluid
• Serous membrane (serosa) internal membrane
• simple squamous epithelium over areolar tissue,
  produces serous fluid
• covers organs and lines walls of body cavities

53
Tissue Growth

• Hyperplasia tissue growth through cell
  multiplication
• Hypertrophy enlargement of preexisting cells
• muscle grow through exercise
• Neoplasia growth of a tumor (benign or
  malignant) through growth of abnormal tissue

54
Tissue Repair

• Regeneration
• replacement of damaged cells with original cells
• skin injuries and liver regenerate
• Fibrosis
• replacement of damaged cells with scar tissue
• function is not restored
• healing muscle injuries, scarring of lung tissue
  in TB or healing of severe cuts and burns of the
  skin
• keloid is healing with excessive fibrosis (raised
  shiny scars)

55
Wound Healing of a Laceration

• Damaged vessels leak blood
• Damaged cells and mast cells leak histamine
• dilates blood vessels
• increases blood flow
• increases capillary permeability
• Plasma carries antibodies, clotting factors and
  WBCs into wound

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Wound Healing of a Laceration

• Clot forms
• Scab forms on surface
• Macrophages start to clean up debris

57
Wound Healing of a Laceration

• New capillaries grow into wound
• Fibroblasts deposit new collagen to replace old
  material
• Fibroblastic phase begins in 3-4 days and lasts
  up to 2 weeks

58
Wound Healing of a Laceration

• Epithelial cells multiply and spread beneath scab
• Scab falls off
• Epithelium thickens
• Connective tissue forms only scar tissue
  (fibrosis)
• Remodeling phase may last 2 years