NOTES ON TISSUES EPITHELIAL TISSUES, CONNECTIVE, MUSCLE AND NERVOUS TISSUES INCLUDING CLASSIFICATIONS OF THE TISSUES

1. MR.AMADI.K.O

2. • Tissues - collections of similar cells and the substances
surrounding them
• Tissue classification based on structure of cells, composition
of noncellular extracellular matrix, and cell function
 Major types of adult tissues
 Epithelial
 Connective
 Muscle
 Nervous
 Histology: Microscopic Study of Tissues
 Biopsy: removal of tissues for diagnostic purposes
 Autopsy: examination of organs of a dead body to
determine cause of death

3.  3 major germ layers that form the embryonic disc (source of stem cells)
 Endoderm
 Inner layer
 Forms lining of digestive tract and derivatives
 Mesoderm
 Middle layer
 Forms tissues as such muscle, bone, blood vessels
 Ectoderm
 Outer layer
 Forms skin and neuroectoderm

4.  Cellularity - Consists almost
entirely of cells
 Covers body surfaces, lines
hollow organs, and forms
glands
 Outside surface of the body
 Lining of digestive, respiratory
and urogenital systems
 Heart and blood vessels
 Linings of many body cavities
 Polarity - Has apical, basal, and
lateral surfaces
 Rests on a basement membrane
 Specialized cell contacts bind
adjacent cells together
 Avascular - no blood vessels
 Regenerative -Replaces lost
cells by cell division

5.  Protecting underlying structures; e.g.,
epithelium lining the mouth
 Acting as barriers; e.g., skin
 Permitting the passage of substances; e.g.,
cells lining air sacs in lungs and nephrons in
kidney
 Secreting substances; e.g., pancreatic cells
 Absorbing substances; e.g., lining of
stomach and small intestine

6. Figure 4.1

7.  Number of layers of cells
 Simple- one layer of cells. Each extends from
basement membrane to the free surface
 Stratified- more than one layer.
 Pseudostratified- tissue appears to be stratified,
but all cells contact basement membrane so it is
in fact simple
 Shape of cells
 Squamous- flat, scale-like
 Cuboidal- about equal in height and width
 Columnar- taller than wide

9. Figure 4.3a

10. Figure 4.3b

11. Figure 4.3c

12. Figure 4.3d

13.  Contain two or more layers of cells
 Regenerate from below
 Major role is protection
 Are named according to the shape of cells at
apical layer

14.  Description
 Many layers of cells – squamous in shape
 Deeper layers of cells appear cuboidal or columnar
 Thickest epithelial tissue – adapted for protection

15.  Specific types
 Keratinized – contain the protective protein keratin
 Surface cells are dead and full of keratin
 Non-keratinized – forms moist lining of body
openings

16.  Function – Protects underlying tissues in areas
subject to abrasion
 Location
 Keratinized – forms epidermis
 Non-keratinized – forms lining of esophagus, mouth,
and vagina

17. Figure 4.3e

18.  It is a rare type of epithelial tissues composed
of column shaped cells arranged in multiple
layers

20. STRATIFIED CUBOIDAL EPITHELIUM
 Thin, stratified epithelium which usually consists of only
two or three layers of cuboidal or low columnar cells.
 Not involved in significant absorptive or secretory activity
PRESENT IN:
Ducts of sweat glands
Large ducts of exocrine glands
Anorectal junction

22.  FUNCTION:
 Absorption
 Secretion

23.  Photomicrograph

24. Figure 4.3h

25.  A gland is one or more cells that makes and secretes
an aqueous fluid
 Two types of glands formed by infolding of
epithelium:
 Endocrine: no contact with exterior of body; ductless; produce
hormones (pituitary, thyroid, adrenals, pancreas)
 Exocrine: open to exterior of body via ducts (sweat, oil)
 Exocrine glands classified either by structure or by
the method of secretion
 Classified by structure
 Unicellular: goblet cells
 Multicellular: sweat, oil, pituitary, adrenal

26.  Classified on the basis of types
of ducts or mode of secretion
 Types of ducts
 Simple: ducts with few
branches
 Compound: ducts with
many branches
 If ducts end in tubules or
sac-like structures: acini.
Pancreas
 If ducts end in simple sacs:
alveoli. Lungs

27.  Tight junctions
 Desmosomes
 Gap junctions

28. • Integral proteins of adjacent
cells fuse together
• Completely encircle the cell
and form an adhesion belt.
• Form an impermeable
junction.
• Common near apical region

29.  Desmosomes – two disc-like plaques connected
across intercellular space
 Plaques of adjoining cells are joined by proteins
called cadherins
 Proteins interdigitate into extracellular space
 Intermediate filaments insert into plaques from
cytoplasmic side

30. Figure 3.5b
Linker proteins extend
from plaque like teeth of
a zipper.
Intermediate filaments
extend across width of
cell.
• Common in superficial layers of skin; skin
peels after a sunburn
• Reduces chance of tearing, twisting, stretching

31. • Connexon proteins are trans-
membrane proteins.
• Present in electrically excitable
tissues (heart, smooth muscle)

32.  Noncellular supporting sheet between the
epithelium and the connective tissue deep to it
 Consists of proteins secreted by the epithelial
cells
 Functions:
 Acts as a selective filter, determining which
molecules from capillaries enter the epithelium
 Acts as scaffolding along which regenerating
epithelial cells can migrate
 Basal lamina and reticular layers of the
underlying connective tissue deep to it form
the basement membrane

33.  Apical surface features
 Microvilli – finger-like extensions of plasma
membrane
 Abundant in epithelia of small intestine and kidney
 Maximize surface area across which small molecules
enter or leave
 Cilia – whip-like, highly motile extensions of apical
surface membranes
 Movement of cilia – in coordinated waves

34.  Most diverse and abundant tissue
 Main classes
 Connective tissue proper
 Cartilage
 Bone tissue
 Blood
 Characteristics
 Mesenchyme as their common tissue of origin
(mesenchyme derived from mesoderm)
 Varying degrees of vascularity
 Nonliving extracellular matrix, consisting of ground
substance and fibers
 Cells are not as abundant nor as tightly packed
together as in epithelium

35. Figure 4.5

36.  Enclose organs as a capsule and separate
organs into layers. Areolar
 Connect tissues to one another. Tendons
and ligaments.
 Support and movement. Bones.
 Storage. Fat.
 Insulation. Fat.
 Transport. Blood.
 Protection. Bone, cells of the immune
system.

37.  Ground substance – unstructured material
that fills the space between cells
 Fibers – collagen, elastic, or reticular
 Cells – fibroblasts, chondroblasts, osteoblasts,
hematopoietic stem cells, and others

38.  Fibroblasts - secrete the proteins needed for fiber
synthesis and components of the extracellular matrix
 Adipose or fat cells (adipocytes). Common in some
tissues (dermis of skin); rare in some (cartilage)
 Mast cells. Common beneath membranes; along small
blood vessels. Can release heparin, histamine, and
proteolytic enzymes in response to injury.
 Leukocytes (WBC’s). Respond to injury or infection
 Macrophages. Derived from monocytes (a WBC).
Phagocytic; provide protection
 Chondroblasts - form cartilage
 Osteoblasts - form bone
 Hematopoietic stem cells - form blood cells
 Undifferentiated mesenchyme (stem cells). Have
potential to differentiate into adult cell types.

39.  ECM has 3 major components
1. Protein fibers 2. Ground substance 3. Fluid
 Protein fibers
 Collagen fibers. Composed of the protein collagen.
Strong, flexible, inelastic; great tensile strength (i.e.
resist stretch). Perfect for tendons, ligaments
 Elastic fibers. Contain molecules of protein elastin
that resemble coiled springs. Returns to its original
shape after stretching or compression. Perfect for
lungs, large blood vessels
 Reticular fibers. Formed from fine collagenous fibers;
form branching networks (stroma). Fill spaces
between tissues and organs.

40.  Interstitial (tissue) fluid within which are one or more
of the molecules listed below: ( Can be fluid,
semifluid, gelatinous or calcified.)
 Hyaluronic acid: a polysaccharide. Very slippery;
serves as a good lubricant for joints. Common in
most connective tissues.
 Proteoglycans: protein and polysaccharide
complex. Polysaccharides called glyocosaminoglycans
(chondroitin sulfate, dermatan sulphate, keratan
sulfate). Protein part attaches to hyaluronic acid.
Able to trap large amounts of water.
 Adhesive molecules: hold proteoglycan aggregates
together. Chondronectin in cartilage, osteonectin in
bone, fibronectin in fibrous connective tissue.
 Functions as a molecular sieve through which
nutrients diffuse between blood capillaries and cells

41.  Mesenchyme: source of
all adult connective
tissue.
 Derived from mesoderm
 Delicate collagen fibers
embedded in semifluid
matrix
 Mucus: found only in the
umbilical cord. Wharton’s
jelly.

42. Figure 4.12b

43. Figure 4.12c

44. Figure 4.12d

45. Figure 4.12e

46. Figure 4.12f

47.  Bundles and sheets of collagenous and elastic fibers
oriented in multiple directions
 In walls of elastic arteries (aorta), lungs, vocal
ligaments
 Strong, yet elastic; allows for recoil of tissue after
being stretched

48.  Consists of a large network of collagen & elastic fibres
firmly embedded in chondroitin sulfate.
 Composed of chondrocytes (cells) which occur in
surrounded spaces called lacunae.
 Type of cartilage determined by components of the
matrix.
 Firm consistency.
 Ground substance: Proteoglycans and hyaluronic acid
complexed together trap large amounts of water
(microscopic sponges). Allows tissue to spring back after
being compressed.
 Avascular and no nerve supply. Heals slowly.
 Perichondrium. Covering of Dense irregular connective
tissue that surrounds cartilage. Fibroblasts of
perichondrium can differentiate into chondroblasts
(cartilage-forming cells)
 Types of cartilage
 Hyaline
 Fibrocartilage

49. Figure 4.12g

50. Figure 4.12h

51. Figure 4.12i

52.  Bone tissue
 Cartilage, joints and bones make up the skeletal
system.
 Bones store calcium & phosphorous, house the
red bone marrow& yellow marrow.
 Bones are organs composed of several
connective tissue eg bone(osseus) tissue,
periosteum, red & yellow marrow and
endosteum.
 Bone is classified as either compact or spongy
depending on the arrangement ECM.
 Compact bone basic unit is an osteon or
haversian system and have four parts.

53.  Lamellae – concentric rings of ECM that consist
of mineral salts which give bones its hardness
& collagen fibre for strength.
 Responsible for compact nature.
 Lacunae – small spaces between lamellae that
contain mature bone cells. Osteocytes.
 Canaliculi – projections from the lacunae.
Canals containing processes of osteocytes.
Provide nutrients and routes of excretion.
 A central (haversian) canal – contain blood
vessels and nerves.
 Spongy bone lacks osteon- consists of columns
of bones called trabeculae. Which contain
lamellae, osteocytes laculae & canaliculi.

54. Figure 4.12j

55. Figure 4.12k

56.  Characteristics
 Cells are referred to as muscle fibers or myocytes
 Contracts or shortens with force when stimulated
 Moves entire body and pumps blood
 Types
 Skeletal: attached to bones
 Cardiac: muscle of the heart.
 Smooth: muscle associated with tubular structures
and with the skin. Nonstriated and involuntary.

57. Figure 4.14a

58. Figure 4.14b

59. Figure 4.14c

60. Special characteristics of neurons
 Longevity – can live and function for a lifetime
 Do not divide (amitotic) – fetal neurons lose their
ability to undergo mitosis; neural stem cells are an
exception
 High metabolic rate – require abundant oxygen
and glucose

61. Parts of the Neuron
Cell Body. Aka Soma or Perikaryon
Contains usual organelles plus
other structures
Nissl bodies = chromatophilic
substance = rough E.R: primary
site of protein synthesis
Cytoskeleton of neurofilaments
and neurotubules
No centrioles (hence its amitotic
nature)
Major biosynthetic center
Most neuronal cell bodies
Located within CNS
Ganglia - clusters of cell bodies
that lie along nerves in PNS
Tapers to form axon hillock

62. Figure 4.15

66.  Nerves - bundles of axons wrapped in
connective tissue
 If only sensory axons, called sensory nerves
 If only motor axons, called motor nerves
 If both sensory and motor axons, called mixed nerves
 Connective Tissue Coverings
 Endoneurium – layer of delicate connective tissue
surrounding the axon
 Nerve fascicles – groups of axons bound into bundles
 Perineurium – connective tissue wrapping
surrounding a nerve fascicle
 Epineurium – whole nerve is surrounded by tough
fibrous sheath

67.  Note the similarity of
a nerve to a muscle
1. Just as a muscle is a
collection of muscle
fibers, a nerve is a
collection of nerve
fibers (axons).
2. Each is broken up in
smaller units known
as fascicles

68.  Cells divide more slowly
 Collagen fibers become more irregular in structure, though
they may increase in number
 Tendons and ligaments become less flexible and more fragile
 Elastic fibers fragment, bind to calcium ions, and become
less elastic
 Arterial walls and elastic ligaments become less elastic
 Changes in collagen and elastin result in
 Atherosclerosis and reduced blood supply to tissues
 Wrinkling of the skin
 Increased tendency for bones to break
 Rate of blood cell synthesis declines in the elderly
 Injuries don’t heal as readily