1. Chapter 5
Histology
Copyright (c) The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

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

3. 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

4. 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

5. Embryonic Tissues Embryo begins as single cell 3 Primary germ layers
divides into many cells and layers (strata)
3 Primary germ layers
ectoderm (outer)
forms epidermis and nervous system
endoderm (inner)
forms mucous membrane lining GI tract and respiratory system and digestive glands
mesoderm (middle) becomes mesenchyme
wispy collagen fibers and fibroblasts in gel matrix
gives rise to muscle, bone, blood

7. 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

8. Sectioning Solid Objects
Sectioning a cell with a centrally located nucleus
Some slices miss the cell nucleus
In some the nucleus is smaller

9. 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.

10. 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

11. Four primary tissue classes
Epithelial tissue
Connective tissue
Muscular tissue
Nervous tissue

12. 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

13. 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

14. Simple Squamous Epithelium
Single row of flat cells
Permits diffusion of substances
Secretes serous fluid
Alveoli, glomeruli, endothelium, and serosa

15. 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

16. 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

17. Pseudostratified Epithelium
Single row of cells some not reaching free surface
nuclei give layer stratified look
Secretes and propels respiratory mucus

18. 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

19. Keratinized Stratified Squamous
Multilayered epithelium covered with dead squamous cells, packed with keratin
epidermal layer of skin
Retards water loss and barrier to organisms

20. Nonkeratinized Stratified Squamous
Multilayered surface epithelium forming moist, slippery layer
Tongue, oral mucosa, esophagus and vagina

21. 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

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

23. Four Types of Connective Tissue
1. Fibrous
Loose
Dense
2. Cartilage
3. Bone
Spongy
Compact
4. Blood

24. 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

25. 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

26. 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 and lymph nodes
Elastic fibers (yellow fibers)
thin branching fibers of elastin protein
stretch and recoil like rubberband (elasticity)
skin, lungs and arteries stretch and recoil

27. 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

28. 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

29. Loose Connective: Areolar Tissue
Loose arrangement of fibers and cells in abundant ground substance
Underlies all epithelia, between muscles, passageways for nerves and blood vessels

30. Loose Connective: 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

31. Loose Connective: 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

32. Dense Regular Connective Tissue
Densely, packed, parallel collagen fibers
compressed fibroblast nuclei
Tendons and ligaments hold bones together and attach muscles to bones

33. 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

34. Connective: 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

35. 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

36. Elastic Cartilage Hyaline cartilage with elastic fibers
Provides flexible, elastic support
external ear and epiglottis

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

40. Connective: 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

41. Compact Bone

42. Bone Tissue (compact bone)
Calcified matrix in lamellae around central canal
Osteocytes in lacunae between lamellae
Skeletal support; leverage for muscles; mineral storage

43. Connective: 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

44. 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

45. 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

46. Skeletal Muscle
Long, cylindrical, unbranched cells with striations and multiple peripheral nuclei
movement, facial expression, posture, breathing, speech, swallowing and excretion

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

48. 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

49. Intercellular Junctions
All cells (except blood) anchored to each other or their matrix by intercellular junctions

50. Tight Junctions Encircle the cell joining it to surrounding cells
zipperlike complementary grooves and ridges
Prevents passage between cells
GI and urinary tracts

52. 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

54. 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

56. Glands
A gland is a cell or organ that secretes substances in the body or releases them for elimination.
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

57. 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

58. 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

59. Types of Secretions Serous glands Mucous 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

60. Holocrine Gland
Secretory cells disintegrate to deliver their accumulated product
oil-producing glands of the scalp

61. 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

62. 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

63. 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

64. Membranes
Cutaneous Membrane
Serous Membrane
Synovial Membrane

65. 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

66. Changes in Tissue Types
Tissues can change types
Differentiation
unspecialized tissues of embryo become specialized mature types
mesenchyme to muscle
Metaplasia
changing from one type of mature tissue to another
simple cuboidal tissue before puberty changes to stratified squamous after puberty

67. Stem Cells Undifferentiated cells with developmental plasticity
Embryonic stem cells
totipotent (any cell type possible)
source = cells of very early embryo
Pluripotent (tissue types only possible)
source = cells of inner cell mass of embryo
Adult stem cells (undifferentiated cells in tissues of adults)
multipotent (bone marrow producing several blood cell types)
unipotent (only epidermal cells produced)

68. Tissue Shrinkage and Death
Atrophy = loss of cell size or number
disuse atrophy from lack of use (leg in a cast)
Necrosis = pathological death of tissue
gangrene - insufficient blood supply
gas gangrene - anaerobic bacterial infection
infarction - death of tissue from lack of blood
decubitus ulcer - bed sore or pressure sore
Apoptosis = programmed cell death
cells shrink and are phagocytized (no inflammation)

69. Tissue Repair Regeneration Fibrosis
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)

70. Tissue Engineering Production of tissues and organs in the lab
framework of collagen or biodegradable polyester fibers
seeded with human cells
grown in “bioreactor” (inside of mouse)
supplies nutrients and oxygen to growing tissue
Skin grafts already available
research in progress on heart valves, coronary arteries, bone, liver, tendons

71. 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

72. Wound Healing of a Laceration
Clot forms
Scab forms on surface
Macrophages start to clean up debris

73. 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

74. 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