Histology: The Study of Tissues

1
Chapter 4

• Histology The Study of Tissues

2
Tissue Level of Organization

• The classification of tissue types is based on
  the structure of cells the composition of
  noncellular substance surrounding cells
  (extracellular matrix) and the functions of the
  cells.

3
Tissues and Histology

• Tissue Level of Organization
• Epithelial
• Connective
• Muscle
• Nervous
• Histology Microscopic Study of Tissues

4
Epithelium Characteristics

• Consists almost entirely of cells
• Covers body surfaces and forms glands
• Has free and basal surface
• Avascular
• Undergoes mitosis

5
Functions of Epithelia

• Protecting underlying structures
• Acting as barriers
• Permitting the passage of substances
• Secreting substances
• Absorbing substances

6
Types of Epithelium

• Types of epithelium is based on the shape of the
  epithelial cells
• Squamous cells are flat or scale-like
• Cuboidal cells are cube-shaped about as wide
  as they are tall
• Columnar cells are taller tan they are wide.

7
Classification of Epithelium

• Simple
• Squamous, cuboidal, columnar
• Consists of a single layer of cells with each
  extending from the basement membrane to the free
  surface
• Stratified
• Squamous, cuboidal, columnar
• Consists of more than one layer of cells, only
  one of which is attached to the basement membrane.

8
Classification of Epithelium

• Pseudostratified
• Columnar
• Special type of simple epithelium
• It appears to be stratified but it is not (false
  psuedo)
• Consists of one layer of cells, with all the
  cells attached to the basement membrane.

9
Classification of Epithelium

• Transitional
• Cuboidal to columnar when not stretched and
  squamouslike when stretched

10
Simple Squamous Epithelium

• Consists of a single layer of cells, with each
  cell extending from the basement membrane to the
  free surface.
• The nuclei appear as bumps when viewed as a cross
  section because the cells are so flat

11
Simple Squamous Epithelium

• Function diffusion, filtration, some protection
  against friction, secretion and absorption
• Locationlining of blood and lymphatic vessels
  (endothelium) and small ducts, alveoli of the
  lungs, loop of Henle in kidney tubules, lining of
  serous membranes (mesothelium) and inner surface
  of the eardrum.

12
Types of Epithelium
13
Simple Cuboidal Epithelium

• Cuboidal cells are cube-shape about as wide as
  they are tall.
• Single layer of cube-shaped cells, some cells
  have microvilli or cilia.

14
Simple Cuboidal Epithelium

• Function active transport and facilitated
  diffusion result in secretion and absorption by
  cells of the kidney tubules, secretion by cells
  of glands and choroid plexus, movement of
  particles embedded in mucus out of the terminal
  bronchioles by ciliated cells.

15
Simple Cuboidal Epithelium

• Location kidney tubules, glands and their
  ducts, choroid plexus of the brain, lining of
  terminal bronchioles of the lungs, and surface of
  the ovaries

16
Types of Epithelium
17
Simple Columnar Epithelium

• Single layer of tall, narrow cells. Some cells
  have cilia (in bronchioles of lungs, auditory
  tubes, uterine tubes and uterus) or microvilli
  (intestines).

18
Simple Columnar Epithelium

• Function movement of particles out of the
  bronchioles of the lungs by ciliated cells. It
  is partially responsible for the movement of the
  oocyte through the uterine tubes by ciliated
  cells. Secretion by cells of the gland, the
  stomach and the intestine. Absorption by cells
  of the intestine.

19
Simple Columnar Epithelium

• Location Glands and some ducts, bronchioles of
  lungs, auditory tubes, uterus, uterine tubes,
  stomach intestines, gallbladder, bile ducts and
  ventricles of the brain.

20
Types of Epithelium
21
Stratified Squamous Epithelium

• Consists of more than one layer of cells, only
  one of which is attached to the basement membrane
• Cells are cubodial in shape in the basal layer
  and progressively flatten toward the surface.

22
Stratified Squamous Epithelium

• The epithelium can be moist or keratinized
• In most the surface cells retain a nucleus and
  cytoplasm.
• In keratinized stratified epithelium, the
  cytoplasm of cells at the surface is replaced by
  keratin, and the cells are dead

23
Stratified Squamous Epithelium

• Function protection against abrasion and
  infection.
• Location moist-mouth, throat, larynx,
  esophagus, anus, vagina, inferior urethra, and
  cornea.
• Keratinized - skin

24
Types of Epithelium
25
Stratified Cuboidal Epithelium

• Multiple layers of somewhat cube-shaped cells.
• Function secretion, absorption and protection
  against infection.
• Location sweat gland ducts, ovarian follicular
  cells, and salivary gland ducts.

26
Types of Epithelium
27
Stratified Columnar Epithelium

• Multiple layers of cells, with tall, thin cells
  resting on layers of more cubodial cells. The
  cells are ciliated in the larynx
• Function protection and secretion
• Location mammary gland duct, larynx and a
  portion of the male urethra.

28
Types of Epithelium
29
Pseudostratified Columnar Epithelium

• Single layer of cells some cells are tall and
  thin and reach the free surface and other do not.
  The nuclei of these cells are at different
  levels and appear stratified. The cells are
  almost always ciliated and are associated with
  goblet cells that secrete mucus onto the free
  surface.

30
Pseudostratified Columnar Epithelium

• Function synthesize and secrete mucus onto the
  free surface and move mucus (or fluid) that
  contains foreign particles over the surface of
  the free surface and from passages.
• Location lining of nasal cavity, nasal sinuses,
  auditory tubes, pharynx, trachea and bronchi of
  the lungs.

31
Types of Epithelium
32
Transitional Epithelium

• Stratified cells that appear cubodial when the
  organ or tube is not stretched an squamous when
  the organ or tube is stretched by fluid.

33
Transitional Epithelium

• Function accommodates fluctuations in the
  volume of fluid in an organ or tube. Protection
  against the caustic effects of urine.
• Location lining of the urinary bladder, ureter,
  and superior urethra.

34
Types of Epithelium
35
Cell Connections

• Functions
• Bind cells together
• Form permeability layer
• Intercellular communication
• Types
• Desmosomes
• Tight
• Gap

36
Exocrine Glands

• Unicellular
• Goblet cells

37
Multicellular Exocrine Glands
38
Exocrine Glands and Secretion Types

• Merocrine
• Sweat glands
• Apocrine
• Mammary glands
• Holocrine
• Sebaceous glands

39
Connective Tissue

• Abundant
• Consists of cell separated by extracellular
  matrix
• Diverse
• Performs variety of important functions

40
Connective Tissue Cells

• Specialized cells produce the extracellular
  matrix
• Suffixes
• -blasts create the matrix
• -cytes maintain the matrix
• -clasts break the matrix down for remodeling

41
Connective Tissue Cells

• Adipose or fat cells
• Mast cells that contain heparin and histamine
• White blood cells that respond to injury or
  infection
• Macrophages that phagocytize or provide
  protection
• Stem cells

42
Extracellular Matrix

• Components
• Protein fibers
• Collagen which is most common protein in body
• Reticular fill spaces between tissues and organs
• Elastic returns to its original shape after
  distension or compression
• Ground substance
• Shapeless background
• Fluid

43
Connective Tissue Categories

• Adult
• Loose
• Dense
• Connective tissue with special properties
• Cartilage
• Bone
• Blood

44
Functions of Connective Tissue

• Difficult to describe general properties of CT in
  the same way as epithelial tissue. 
• CT is so much more diverse. 
• Some of the characteristics may not fit all of
  the CT types perfectly-- but they will fit most
  of them.

45
Functions of Connective Tissue

• Connective tissues are typically
  well-vascularized
• They can usually reproduce well (to recover from
  injury) 
• Exception   They need a good number of cells to
  help with this, and dense connective tissue has
  only sparse numbers of cells. they have a lot of
  noncellular material, called extracellular matrix
  material (or just matrix).

46
Extracellular Matrix

• The space between cells can be called the
  extracellular space/material or the intercellular
  space/material. 
• "Extra-" means outside of, while "inter-" means
  between. We will use the term extracellular space
  to prevent other confusion
• That's because intercellular is easily confused
  with another term we will be using 
  intracellular.  "Intra-" means within, and we
  will use intracellular to discuss what is inside
  the cell

47
Extracellular Matrix

• To the right, the extracellular space is all in
  pink.  
• The space is filled with material.  If the
  material is only liquid, the tissue as a whole
  will be loose.  An example of that is in blood.  
• If the material in the extracellular space has
  some tough strands (called fibers) of protein in
  it, that gives the entire tissue a stronger
  consistency (because the cells are now sitting in
  a mesh of fibers).

48
Ground Substance

• This is the liquid portion of the extracellular
  matrix. 
• It is never entirely watery, but more gel-like. 
• A thin ground substance is seen in blood.   The
  ground substance is not just water, but it is
  also filled with many dissolved solute particles.

49
Extracellular Matrix Fibers

• The number, properties, and alignment of fibers
  in the extracellular matrix will help determine
  the properties of the connective tissue.  There
  are three main types of connective tissue
  fibers.  Two are made out of a protein called
  collagen, while the third is made out of a
  protein called elastin. 

50
Extracellular Matrix Fibers

• Collagen is a protein that forms a long strand. 
  If many of these strands are put together the
  large resultant bundle can be quite strong.  If
  only a few of these strands are intertwined, the
  small resultant bundle is only somewhat strong. 
  Collagen is has greater properties of strength
  than of elasticity. 
• Elastin, on the other hand, is not so strong,
  but has elastic properties.

51
Extracellular Matrix Fibers

• Reticular fibers  Thin bundles of collagen. 
• They are very short, thin fibers that branch to
  form a network and appear different
  microscopically from other collagen fibers.
• Not as strong as most collagen fibers.

52
Extracellular Matrix Fibers

• Elastic fibers  stretchy branching bundles of
  elastin.  Also called yellow fibers, because they
  tend to look yellower than collagen bundles do. 

53
Extracellular Matrix Fibers

• All of these types of extracellular matrix fibers
  can run together in different ways

54
Extracellular Matrix Fibers

• as a mixture of fiber types mainly of one fiber
  type
•                              OR
• loosely piled, with no one orientation
• densely piled, with no one orientation
• densely piled, all having the same orientation

55
Connective Tissue Cell Types

• There are three main cell types in connective
  tissue.  These three cell types may appear in
  most of the types of connective tissue.  There
  are also cell types that are specific for certain
  connective tissues (and are only found there).

56
The three main cell types are

• Fibroblasts
• macrophages
• mast cells

57
fibroblasts

• these important cells are the ones that lay down
  the extracellular matrix fibers! 
• They tend to be elongate in appearance

58
macrophages

• These cells are large and are derived from blood
  cells.  
• A certain white blood cell can leave the blood
  and enter tissue, and is then called a
  macrophage. 
• This cell is a scavenger in our connective
  tissues.  It chews up foreign particles in the
  tissue by phagocytosis, protecting and cleaning
  out our bodies.

59
mast cells

• these cells communicate chemically with our
  blood.
• They signal our blood by releasing heparin and
  histamine, telling our blood when it should clot
  or allow inflammation of certain tissues. 
• That means that these cells help begin a repair
  process, when needed, in tissue.

60
Other cells that you may find in specific
connective tissues are

• osteocytes-- only found in bone
• chondrocytes-- only found in cartilage (or
  developing bone)
• adipocytes-- only found in adipose tissue for
  storing fat

61
Other cells that you may find in specific
connective tissues are

• blood cells-- found only in blood (unless you are
  injured)
• 5. reticulocytes-- found only in reticular
  connective tissue.  Call them fibroblasts.

62
If a connective tissue has plenty of cells within
it, it is better at recovering after injury.  For
example, if the skin is cut, and the dermis is
thus cut, the mast cells will, of course, help
get blood in the area to fill the hole left by
the cut and then will also get the blood to begin
clotting.  After that, however, we need to
replace the clot with more dermis.
63
This is possible because the fibroblasts in the
remaining dermis begin dividing and secreting
more fibers for the matrix.  As the fibroblasts
make more dermal connective tissue, the
macrophages start removing the clot.  And,
voila!  The repair is done.
64
If, however, a connective tissue has few cells
(and/or blood supply is limited), it is more
difficult to repair that connective tissue.  An
example of this is in tendons and ligaments.  It
is difficult to repair tendons and ligaments
after injury-- the healing time is much longer
than for a broken bone
65
Specific Types of Connective Tissue

• Loose connective tissue
• Dense connective tissue
• Cartilage
• Bone

66
Loose connective tissue

• It binds the skin to the underlying organs and
  fills spaces between muscles.
• This is composed of a mixture of collagenous and
  elastic fibers within the ground substance. 
• Fibroblasts, macrophages, and mast cells can be
  found within it.

67
Loose Connective Tissue

• Also known as areolar tissue
• Loose packing material of most organs and tissues
• Attaches skin to underlying tissues
• Contains collagen, reticular, elastic fibers and
  variety of cells

68
Dense Connective Tissue

• Dense regular
• Has abundant collagen fibers
• Tendons Connect muscles to bones
• Ligaments Connect bones to bones
• Dense regular elastic
• Ligaments in vocal folds
• Dense irregular
• Scars
• Dense irregular collagenous
• Forms most of skin dermis
• Dense irregular elastic
• In walls of elastic arteries

69
Dense connective tissue

• This tissue is made up of A LOT of fibers.  If it
  is regular dense connective tissue, it is mainly
  made up of parallel collagenous fibers.
• There is very little room for vascularization.
•   This is the type of tissue that makes up
  tendons and ligaments.

70
Dense Regular Connective Tissue
71
If it is irregular dense connective tissue, it is
found making up the dermis of your skin.  It has
a lot of collagenous and elastic fibers The
fibers are not oriented in parallel bundles they
are randomly arranged.
72
Dense Irregular Connective Tissue
73
Cartilage

• Composed of chondrocytes located in spaces called
  lacunae
• Next to bone firmest structure in body
• Types of cartilage
• Hyaline
• Fibrocartilage
• Elastic

74
Cartilage

• This tissue contains chondrocytes, and the
  extracellular matrix material was secreted by
  them. 
• They secrete a dense matrix, so dense that after
  they secrete it they end up stuck inside of it.
• There are different types of cartilage, each
  having its own appearance and elastic qualities.

75
Hyaline Cartilage

• Found in areas for strong support and some
  flexibility
• Rib cage and cartilage in trachea and bronchi
• Forms most of skeleton before replaced by bone in
  embryo
• Involved in growth that increases bone length

76
Fibrocartilage

• Slightly compressible and very tough
• Found in areas of body where a great deal of
  pressure is applied to joints
• Knee, jaw, between vertebrae

77
Elastic Cartilage

• Rigid but elastic properties
• External ears, epiglottis

78
Connective Tissue with Special Properties

• Adipose tissue
• Consists of adipocytes
• Types
• Yellow (white)
• most abundant, white at birth and yellows with
  age
• Brown
• found only in specific areas of body as axillae,
  neck and near kidneys
• Reticular tissue
• Forms framework of lymphatic tissue
• Characterized by network of fibers and cells

79
Adipose Tissue
80
Reticular Tissue
81
Bone

• Hard connective tissue that consists of living
  cells and mineralized matrix
• Has an Organic and inorganic portion
• Types
• Cancellous or spongy bone
• Has spaces between trabeculae (plates of bones)
• Compact bone
• More solid (almost no space)
• Many thin layers

82
Bone

• This tissue contains osteocytes, which are mature
  bone cells.  These cells also end up stuck inside
  the dense extracellular matrix that we think of
  as bone.  Because bones extracellular matrix is
  so dense, much more so than others, diffusion of
  nutrients through it is very difficult. 

83
Therefore, osteocytes do not use diffusion to get
their nutrients.  Instead, they extend tiny
little processes to communicate with each other
and with the blood the development of these
processes makes tiny little holes in the matrix,
and these holes are called canaliculi.
84
Cancellous Bone

• Location In the interior of the bones of the
  skull, vertebrae, sternum and pelvis, also found
  in the ends of long bones.
• Structure latticelike network of scaffolding
  characterized by trabeculae with large space
  between them filled with hemopoietic tissue. The
  osteocytes are located within lancunae in the
  trabeculae.

85
Cancellous Bone

• Function Acts as a scaffolding to provide
  strength and support without the greater weight
  of compact bone.

86
Compact Bone

• Location Outer portions of all bones and the
  shafts of long bones
• Structure Hard, bony matrix predominates. Many
  osteocytes are located within lancunae that are
  distributed in a circular fashion around the
  central canals.

87
Compact Bone

• Function Provides great strength and support.
  Forms a solid outer shell on bones that keeps
  them from being easily broken or punctured.

88
Bone
89
Blood

• Matrix between the cells is liquid. Blood cells
  are free to move around
• Hemopoietic tissue
• Forms blood cells
• Found in bone marrow
• Yellow
• Red

90
Blood

• Location within the blood vessels. Produced by
  hemopoietic tissues. White blood cells
  frequently leave the vessels and enter the
  interstitial spaces.
• Structure Blood cells and a fluid matrix.

91
Blood

• Function Transport oxygen, carbon dioxide,
  hormones, nutrients, waste products, ad other
  substances. Protects the body from infections
  and is involved in temperature regulation.

92
Bone Marrow

• Location within marrow cavities of bone. Two
  types yellow marrow (mostly adipose tissue) in
  the shafts of long bones and Red marrow
  (hemopoietic or blood-forming tissue) in the ends
  of the long bones and in short, flat and
  irregularly shaped bones

93
Bone Marrow

• Structure Reticular framework with numerous
  blood-forming cells (red marrow)
• Function Production of new blood cells (red
  marrow) lipid-storage (yellow marrow)

94
Bone Marrow
95
Muscle Tissue

• Characteristics
• Contracts or shortens with force
• Moves entire body and pumps blood
• Types
• Skeletal
• Striated and voluntary
• Cardiac
• Striated and involuntary
• Smooth
• Nonstriated and involuntary

96
Skeletal Muscle
97
Cardiac Muscle
98
Smooth Muscle
99
Nervous Tissue

• Found in brain, spinal cord and nerves
• Ability to produce action potentials
• Cells
• Nerve cells or neurons
• Consist of dendrites, cell body, axons
• Consist of multipolar, bipolar, unipolar
• Neuroglia or support cells

100
Neurons
101
Neuroglia
102
Membranes

• Mucous
• Line cavities that open to the outside of body
• Secrete mucus
• Serous
• Line cavities not open to exterior
• Pericardial, pleural, peritoneal
• Synovial
• Line freely movable joints
• Produce fluid rich in hyaluronic acid

103
Inflammation

• Response when tissues damaged or with an immune
  response
• Manifestations
• Redness, heat, swelling, pain, disturbance of
  function
• Mediators
• Include histamine, kinins, prostaglandins,
  leukotrienes
• Stimulate pain receptor and increase blood vessel
  permeability

104
Tissue Repair

• Substitution of viable cells for dead cells
• Skin repair
• Primary union Edges of wound close together
• Wound fills with blood
• Clot forms
• Scab
• Pus
• Granulation tissue
• Scar
• Secondary union Edges of wound not close
• Clot may not close gap
• Inflammatory response greater
• Wound contraction occurs leading to greater
  scarring

105
Tissue Repair
106
Tissues and Aging

• Cells divide more slowly in older than younger
  people
• Tendons and ligaments become less flexible and
  more fragile
• Arterial walls become less elastic
• Rate of blood cell synthesis declines in elderly
• Injuries are harder to heal in elderly