Teamwork

1
Teamwork

• The human body contains about
• 100 trillion cells.
• However, no one cell can carry out all the
  necessary bodily functions by itself. So, cells
  aggregate and form TISSUES
• Tissue ? Collection of cells with a similar
  structure and function.
• The study of tissues is known as histology

2
Tissues

• There are 4 primary tissue types in the human
  body
• Epithelial (covering/lining)
• Connective (support)
• Muscle (movement)
• Nervous (control)
• These tissues differ in the types and functions
  of their cells, and the products of those cells
  and the relative distribution of the two.
• Which picture on this slide corresponds to which
  tissue?

3
Epithelial Tissue

• Covers the surface of the body, lines the body
  cavities, forms the external and internal linings
  of most organs, and constitutes the bulk of most
  glands.
• Functions include
• 1. Protection 4. Absorption
• 2. Secretion 5. Filtration
• 3. Sensory reception
• Its found all over the place!
• On the right we have a section of skin. Where
  would the bulk of the epithelial tissue be found?

4
Characteristics of Epithelia

• Composed almost entirely of sheets of
  close-packed cells very little extracellular
  material.
• Look at the cartoon below (it represents the
  epithelium that lines much of your respiratory
  tract) . Do you see much space between these
  cells? Now look at the actual slide and notice
  the same thing.
• Epithelial cells are often strongly connected
• to adjacent cells via tight junctions and
  desmosomes

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• Tight junctions are protein complexes that
  completely encircle a cell and thus connect it to
  all its neighboring cells and makes it impossible
  for anything to pass btwn them. Common in lining
  of the stomach intestines. (Why here?)
• Desmosomes spot weld that holds cells
  together and enables a tissue to resist
  mechanical stress. Common in the epidermis and
  cervix. (Why these 2 areas?)

6
Characteristics of Epithelia

• Polarity
• Different areas of epithelial cells have
  different structures. (If they have different
  structures, they can have different ___________)
• The area of an epithelial cell adjacent to the
  exterior or to a body cavity is the apical side
  and the opposite area is the basal side.
• In the picture at the top right, what is present
  in the basal portion of the cell thats not in
  the apical portion?
• Always supported by a layer of connective tissue.
• Its known as the basement membrane and is
  labeled by arrows in the pictures at the right.

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More Characteristics of Epithelia

• No blood vessels its avascular.
• Can you pierce your skin with a needle without
  bleeding?
• Has the capacity to regenerate.
• Why is this a good thing?
• Considering the locations of epithelial tissue,
  is it likely to get damaged?

8

• We classify epithelia based on the number of cell
  layers present and the shape of the cells in the
  apical layer.
• If there is only one layer of cells, the
  epithelium is simple. If there is more than one
  layer, the epithelium is stratified.
• There are 3 cell shapes
• Squamous flat, scale-like
• Cuboidal cube-shaped
• Columnar column-shaped

9
Epithelia Types

• You can see that weve got at least 6
• Simple squamous
• Simple cuboidal
• Simple columnar
• Stratified squamous
• Stratified cuboidal
• Stratified columnar
• There are actually 2 other ones that are special
  transitional epithelium and pseudostratified
  columnar epithelium.

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Simple Squamous Epithelium

• Microscopic Appearance
• Single layer of flattened cells, shaped like
  fried eggs with bulge where nucleus is located.
• Nucleus is flattened in the plane of the cell.
• Cytoplasm may be very thin and tough to see.
• In surface view, cells have angular contours and
  nuclei appear round.

Above, the roundish structure is a ball of
capillaries found in the kidneys known as a
glomerulus. The blue arrow indicates the simple
squamous epithelium surrounding it.
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Simple Squamous Epithelium

• Locations
• Air sacs (alveoli) of lungs
• Glomerular capsules of kidneys
• Some kidney tubules
• Lining of heart and all blood vessels
• Here its called the endothelium
• Serous membranes
• External lining of visceral organs
• Here its called the mesothelium

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Endothelium
The blue arrow points directly at the nucleus of
an endothelial cell. What type of cell does the
yellow arrow indicate?
13
Simple Squamous Epithelium

• Functions
• Thinness allows material to rapidly diffuse or be
  transported through the epithelial layer.
• Example ? Gases diffuse across the thin air sac
  epithelium in the lungs.
• Blood traveling to the lungs is high in CO2 and
  low in O2. After gas exchange in the lungs, the
  blood leaving is high in O2 and low in CO2
• Why is thinness an asset in this situation?
• In pneumonia, a build-up of mucus can increase
  the distance that the gases must move. Does this
  make it easier or harder to breathe?

14
Simple Squamous Epithelium

• More Functions
• Blood is filtered through the epithelium of the
  kidney capillaries.
• This begins the process of removing waste
  products from the blood and modifying its ionic
  content.
• Secretion of a lubricating fluid by the
  epithelium making up the serous membranes (well
  talk about them soon).

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Simple Cuboidal Epithelium

• Microscopic Appearance
• Single layer of square or round cells.
• Centrally-placed spherical nuclei.
• Apical layer often has microvilli.
• Microvilli are small extensions of the cell
  membrane that increase the surface area of the
  cell.
• You usually want a cell to have more surface area
  when it is involved with secretion or absorption.
• WHY?

Above, we have a longitudinal section of a kidney
tubule. Notice the almost square-shaped cells .
One cell is highlighted for you in red.
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Simple Cuboidal Epithelium

• Locations
• Liver
• Pancreas
• Thyroid, salivary, and most other glands
• Most kidney tubules
• Bronchioles (small tubes within the lungs)

Cross-Section of a kidney tubule
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Simple Cuboidal Epithelium

• Functions
• Absorption
• Kidney tubules
• Microvilli often present to increase the
  available surface area
• Liver
• Secretion
• Kidney tubules
• Liver
• Pancreas
• Thyroid, salivary, and most other glands

Cross-section of the thyroid gland
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Simple Columnar Epithelium

• Microscopic Appearance
• Single layer of tall, narrow cells.
• Oval or sausage-shaped nuclei, vertically-oriented
  , usually located in the basal half of the cell.
• Secretory vesicles sometimes visible in apical
  portion of the cell.
• Microvilli occasionally present.
• Cilia occasionally present.
• Cilia are hair-like extensions of the cell
  membrane that can move and sweep material across
  the cell surface
• Goblet cells often interspersed.
• Secrete a lubricating mucus

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Simple Columnar Epithelium

• Locations
• Inner lining of stomach, intestines, and rectum.
• Inner lining of gallbladder
• Inner lining of uterus and uterine tubes

Simple columnar epithelium lining the lumen of
the gallbladder.
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Simple Columnar Epithelium

• Functions
• Absorption and secretion
• Columnar cells in small intestine have microvilli
  to increase the available surface area for the
  absorption of nutrients.
• Movement of egg and embryo in uterine tube.
• Hence the presence of cilia.
• Secretion of mucus.
• Lots of goblet cells in the large intestine so as
  to lubricate it and ease the passage of feces.

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Stratified Squamous Epithelium

• Microscopic Appearance
• Multiple cell layers with cells becoming flatter
  and flatter toward surface.
• In keratinized stratified squamous epithelium,
  the apical layers are layers of dead cells
  lacking nuclei and packed with the tough protein
  keratin.
• Nonkeratinized stratified squamous epithelium
  lacks the layers of dead cells at the surface.

This is keratinized stratified squamous
epithelium from the sole of the foot. It extends
the length of the blue line on the left. Notice
the multiple layers of clear, dead, enucleated
cells.
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Stratified Squamous Epithelium

• Location of keratinized version
• Epidermis. Palms and soles of feet are typically
  heavily keratinized.
• Locations of non-keratinized version
• Lining of oral cavity and surface of tongue
• Lining of esophagus
• Lining of vagina and anal canal

Non-keratinized stratified squamous epithelium
What do the regions that contain the
non-keratinized version have in common?
23
Which of these is keratinized and which is
non-keratinized stratified squamous epithelium?
24
Stratified Squamous Epithelium

• Functions
• Protection!
• Keratinized version (a.k.a. dry epithelium)
  protects against mechanical abrasion, water loss,
  and pathogen entry.
• Keratin is very strong, waterproof, and is
  bacteriostatic (prevents bacteria from
  reproducing).
• Non-keratinized version (a.k.a., wet epithelium)
  also protects from mechanical abrasion.
• Eating food, swallowing, sexual intercourse,
  birth, defecation.

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Stratified Cuboidal Epithelium

• Microscopic Appearance
• 2 or more layers of cells.
• Surface layers are square or round (cuboidal).
• Locations
• Some sweat gland ducts.
• Ovarian follicle
• Cells that surround the developing egg

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Stratified Cuboidal Epithelium
To the left, we have an oocyte (egg cell)
surrounded by stratified cuboidal epithelium.
The oocyte is circled in blue

• Functions
• Contributes to sweat secretion.
• Secretion of ovarian hormones (e.g., estrogens)

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Stratified Columnar Epithelium

• Microscopic Appearance
• 2 or more layers of cells.
• Surface cells tall and narrow with basally
  located nuclei.
• Locations
• Rare.
• Small portions of anal canal, pharynx,
  epiglottis, and male urethra.
• Sometimes seen in large ducts of sweat and
  salivary glands.
• Functions
• Often seen where 2 other tissue types meet
• Structural integrity of gland ducts

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Pseudostratified Columnar Epithelium

• Microscopic Appearance
• Looks multi-layered, but its NOT!
• All cells touch the basement membrane.
• In stratified epithelia, only the bottom cell
  layer touches the basement membrane.
• Cells are of varying heights which gives the
  appearance of stratification. Nuclei are at
  several levels.
• Often has goblet cells interspersed.
• Cells often have cilia.

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Pseudostratified Columnar Epithelium

• Locations
• Respiratory tract from nasal cavity to bronchi.
• Ciliated
• Goblet cells
• Portions of male reproductive tract
• Non-ciliated

Ciliated pseudostratified epithelium from the
respiratory tract. Do you see how it appears
that there are multiple layers. Do you see the
cilia (indicated by the arrow)?
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Pseudostratified Columnar Epithelium

• Functions
• In the respiratory tract there are lots of
  mucus-secreting goblet cells.
• The mucus traps dust and bacteria
• Cilia sweep the bacteria-laden mucus up the
  respiratory tract towards the pharynx where it
  can be swallowed.
• Smoking paralyzes cilia smokers have to cough
  violently to expel their mucus. Then they die!

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Here, we have pathogens traveling down the
pharynx trying to attack the surface cells. How
can they be repelled???
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The mucosal cells lining the trachea have
released a flood of mucus, trapping the
pathogens! Now what???
33
The cilia successfully sweep the pathogens up and
away!
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Transitional Epithelium

• Microscopic Appearance
• Somewhat resembles stratified squamous
  epithelium, but the surface cells are rounded and
  often bulge above surface (dome-shaped).
• Typically 5-6 cell layers thick when relaxed and
  2-3 cell layers thick when stretched.
• Cells may be flatter and thinner when epithelium
  is stretched.
• Some cells are binucleate, i.e., they have 2
  nuclei.

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Transitional Epithelia

• Locations
• Predominant epithelium lining the urinary tract
• Found in part of the kidney, the ureters (tubes
  that connect the kidney to the urinary bladder),
  the urinary bladder, and part of the urethra.
• Functions
• Stretches to allow filling of the urinary tract.
• Originally called transitional because it was
  thought to be an intermediate between stratified
  squamous and stratified columnar epithelium.
  This isnt true but the name has persisted.

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Easy Epithelium Review ?
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Glands
Thyroid Gland An endocrine gland

• A gland is a cell or an organ that secretes
  substances for use inside or outside the body.
• Glands are composed predominantly of epithelial
  tissue.
• Glands are broadly classified as
• Endocrine
• Exocrine

An exocrine gland
Stomach Both an exocrine and an endocrine gland
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Exocrine Glands

• Typically secrete material into ducts that lead
  to the body surface or to one of the cavities
  that is continuous with the body surface, i.e.,
  digestive, reproductive, respiratory tract.
• Exo outside and crine secrete.
• Can be multicellular or unicellular.
• Multicellular
• Pancreas, stomach, sweat glands, salivary glands,
  mammary glands, sebaceous glands, etc.
• Unicellular
• Goblet cells.

The parotid gland (a salivary gland)
Goblet Cell
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Endocrine Glands

• Endo within.
• Do not secrete material into ducts.
• Secrete chemical signals called hormones into the
  bloodstream where they travel through the body
  and affect other cells.
• Examples include
• Thyroid, thymus, testes, ovaries, pituitary,
  pineal, adrenal, etc.

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Exocrine Gland Structure

• Exocrine glands are either
• Simple if their ducts do not branch.
• Compound if their ducts do branch.
• Exocrine glands are further classified by the
  shape of their secretory portion as
• Tubular if the secretory portion is the same
  diameter as the duct.
• Alveolar if the secretory portion is like a round
  ball .
• Tubuloalveolar if its a combination of the 2.

Compound
Simple
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Connective Tissue

• Most abundant, widely distributed, and
  histologically variable of the 4 primary tissue
  types.
• Consists of cells that are typically widely
  separated by lots of extracellular material
  referred to as the extracellular matrix.
• In the diagram above, compare the density of
  cells in the epithelial layers and in the
  connective tissue layers. Whats the difference?
• Most cells are not in contact with each other but
  are distributed throughout the extracellular
  matrix.

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Functions of Connective Tissue

1. Binding of organs
2. Support
3. Physical protection
4. Immune protection
5. Movement
6. Storage
7. Heat production
8. Transport

What do you NOT see a lot of in this micrograph
of connective tissue?
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Categories of CT
Loose Connective Tissue

1. Fibrous connective tissue (a.k.a. connective
   tissue proper)
2. Supporting connective tissue
3. Fluid connective tissue

Bone
Blood
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Fibrous Connective Tissue

• Most diverse type of CT.
• Contain extremely conspicuous fibers hence the
  name, fibrous connective tissue.
• The illustration below shows a 3-D model of some
  typical CT fibers, typically made of multiple
  strong filamentous proteins twisted about one
  another.
• Fibrous CT consists of cells, fibers, and
  something called ground substance.
• Of these 3, which you do suppose is typically NOT
  that abundant?

46
Cells of Fibrous CT

• Fibroblasts
• Fibro fat, blast making
• Large, flat cells with tapered ends produce
  fibers and ground substance.
• Inactive ones are known as fibrocytes.
• Macrophages
• Macro large, phage eating
• Large phagocytic cells that wander through
  connective tissue, where they engulf and destroy
  bacteria, other foreign particles, and dead or
  dying cells of our own body.
• They activate the immune system when they
  encounter foreign matter called antigens.
• Derived from white blood cells known as monocytes.

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Cells of Fibrous CT

• Leukocytes
• Leuko white, cyte cell
• White blood cells that crawl out of the
  bloodstream and spend the majority of their time
  in the CT. Many are phagocytes that wander in
  search of pathogens.
• Plasma Cells
• Certain white blood cells differentiate into
  plasma cells when they detect foreign agents.
• Plasma cells produce and secrete antibodies
  (proteins that bind to foreign molecules
  (antigens), thus inactivating them or marking
  them for future destruction.

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Cells of Fibrous CT

• Mast Cells
• Often found in CT adjacent to blood vessels.
• Secrete a chemical called heparin which is an
  anti-coagulant and a chemical called histamine
  which is a vasodilator.
• Adipocytes
• Adipo fat
• Appear in small clusters in some fibroconnective
  tissues.
• If they dominate an area, we call that area
  adipose tissue.
• Contain huge droplets of lipids for storage.

49
Fibers in Fibrous Connective Tissue

1. Collagenous Fibers
2. Reticular Fibers
3. Elastic Fibers

Collagen Fibers as seen with a scanning electron
microscope
50
Collagenous Fibers
Close-up of a single fiber

• Interwoven strands of the protein collagen.
• The most abundant protein in the human body.
• Thick fibers with great tensile strength i.e.,
  its tough to pull them apart.
• In fresh tissue, they have a white appearance, so
  they are sometimes called white fibers.
• In stained slides, they are often pink and they
  usually appear quite wavy.
• Tendons, ligaments, and the deep layer of the
  skin (the dermis) are made primarily of
  collagenous fibers.

Multiple fibers arranged in the extracellular
matrix
51
Reticular Fibers

• A thinner collagen fiber coated with
  glycoproteins.
• Stained black in the adjacent micrograph of the
  liver.
• These fibers can branch extensively and form
  networks or frameworks for certain organs.

52
Elastic Fibers

• Made primarily of a protein called elastin, whose
  coiled structure allows it to stretch and snap
  back like a rubber band.
• Account for the ability of the lungs, arteries,
  and skin to spring back after they are stretched.
• Fresh elastic fibers are yellowish and thus often
  called yellow fibers.

In this slide, A is an elastic fiber what do
you suppose B is?
53
Ground Substance

• Gelatinous material that occupies the space
  between the cells and the fibers in connective
  tissues.

Imagine some lime Jell-o that a not-so-bright
chef decided to make with carrots and grapes.
The carrots are like fibers, the grapes like
cells, and the Jell-o itself is the ground
substance/
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Types of Fibrous Connective Tissue

• 2 types based on the relative abundance of
  fibers.
• Loose Connective Tissue
• Lots of ground substance and cells. Fewer
  fibers.
• Leaves lots of empty space in tissue sections.
• Dense Connective Tissue
• Fibers occupy the most space. Much lower number
  of cells and less ground substance.
• Appears closely packed in tissue sections.

55
Types of Loose CT
1

1. Areolar CT
2. Reticular Tissue
3. Adipose Tissue

2
3
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Areolar CT

• Microscopic
• Appearance
• Loose arrangement of collagenous and elastic
  fibers. Some reticular fibers. (All 3 fiber
  types.)
• Scattered Cells. All 6 types can be present.
• Abundant ground substance.
• Numerous blood vessels. (Highly vascular.)

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Areolar CT

• Locations
• Underlying nearly all epithelia.
• Surrounding blood vessels, nerves, trachea, and
  esophagus.
• Between muscles.
• Within mesenteries, and the visceral layers of
  the pericardium and the pleura.

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Areolar CT

• Functions
• Loosely binds epithelia to deeper tissues.
• Allows passage of nerves and blood vessels
  through other tissues.
• Provides an arena for immune defense.
• Blood vessels provide nutrients and waste removal
  for overlying epithelia.

59
Reticular Tissue

• Microscopic Appearance
• Loose network of reticular fibers and a type of
  fibroblast known as the reticular cell.
• Infiltrated with numerous white blood cells.
• Often appears dark purple or black.
• Locations
• Lymph nodes, spleen, thymus, and bone marrow.

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Reticular Tissue

• Functions
• The branching network of reticular fibers will
  form a scaffold-like framework for lymphatic
  organs.
• Spleen, thymus, and lymph nodes.
• Such a framework is known as a stroma.
• The functional tissue of these organs is known as
  the parenchyma.

61
Adipose Tissue

• Microscopic Appearance
• Dominated by adipocytes large, empty-looking
  cells with thin margins.
• Nucleus usually pressed against the cell membrane
  signet ring appearance.
• Often pale.
• Blood vessels often present.

62
Adipose Tissue

• Locations
• Subcutaneous fat beneath skin.
• Breast.
• Heart surface.
• Cushioning organs
• Kidneys
• Eyes

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Adipose Tissue

• Functions
• Energy storage.
• Thermal insulation.
• Shock absorption
• Protective cushioning for some organs.

64
Types of Dense CT
1

1. Dense regular
2. Dense irregular

2
65
Dense Regular CT

• Microscopic Appearance
• Densely packed, parallel, often wavy collagenous
  fibers.
• Slender fibroblast nuclei compressed between
  bundles of collagenous fibers.
• Scanty open space (little ground substance)
• Scarcity of blood vessels.

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Dense Regular Connective Tissue

• Locations
• Tendons.
• Ligaments.

NOTE the waviness of the fibers. What function
could this structural aspect provide?
67
Dense Regular CT

• Functions
• Ligaments bind bone tightly to other bones.
  Resist stress.
• Tendons attach skeletal muscles to bone and
  transfer muscular tension to bones.

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Dense Irregular CT

• Microscopic Appearance
• Densely packed, collagenous fibers running in
  random directions. Compare this to dense regular
  CT.
• Scanty open space (ground substance).
• Few visible cells.
• Scarcity of blood vessels.

69
Dense Irregular CT

• Locations
• Deeper portion of dermis of skin.
• Capsules around visceral organs such as the
  liver, spleen, and kidneys.
• Fibrous sheaths around cartilages and bones.

70
Dense Irregular CT

• Functions
• Provides a durable, hard to tear structure that
  can withstand stresses placed in unpredictable
  directions.
• Why arent tendons and ligaments made of this
  stuff?

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Supporting Connective Tissue

• They provide the majority of the structural
  support of the human body.
• 2 types
• Cartilage
• Bone.

1
2
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Cartilage

• Supportive CT with a flexible, rubbery matrix.
• Cells called chondroblasts secrete the matrix and
  surround themselves in it until they become
  trapped in little cavities known as lacunae
  (lacuna is Latin for lake).
• Once enclosed in lacunae, cells are called
  chondrocytes.

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Cartilage

• Cartilage is avascular and chondrocytes depend on
  the diffusion of nutrients through the stiff,
  viscous matrix.
• Thus their metabolism and rate of division
  (a.k.a. mitosis) is low and healing of torn
  cartilage is a long process.
• Its avascular b/c chondrocytes produce a
  chemical called antiangiogenesis factor that,
  like its name suggests, prevents the growth of
  blood vessels.
• Based on this, why do you suppose shark cartilage
  has been touted as a possible aid in the fight
  against cancer?
• Cartilage matrix collagenous fibers that range in
  thickness from invisibly fine to conspicuously
  coarse.

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Cartilage
3

• 3 types (classified based on fiber differences)
• Hyaline Cartilage
• Elastic Cartilage
• Fibrocartilage.

1
2
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Hyaline Cartilage

• Microscopic Appearance
• Clear, glassy matrix, often stained light blue or
  pink.
• Hyalos is Greek for glass.
• Fine, dispersed collagenous fibers, not usually
  visible.
• Chondrocytes often in small clusters of 3-4 cells
  within a single lacuna (known as cell nests or
  isogenous groups).
• Covered by a perichondrium a fibrous sheath
  made of dense irregular connective tissue.

76
Hyaline Cartilage

• Locations
• Forms the majority of the fetal skeleton.
• Forms boxlike structure around larynx and
  supportive rings around trachea and bronchi.
• Attaches ribs to the sternum.
• Forms a thin articular cartilage over the ends of
  bones at moveable joints.

Close-up of Hyaline Cartilage. Notice the 2
cells in the single lacuna
77
Hyaline Cartilage

• Functions
• Eases joint movements.
• Keeps airways patent.
• Moves vocal cords.
• Precursor of bone in the fetal skeleton.
• Structural attachment.

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Elastic Cartilage

• Microscopic Appearance
• Elastic fibers form web-like mesh amid lacunae.
• Always covered by a perichondrium.
• Locations
• External ear.
• Epiglottis flap of tissue that covers the
  tracheas when you swallow to prevent food/liquid
  from going down the wrong pipe.
• Eustachian tube connects the ear to the
  nasopharynx.

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Elastic Cartilage

• Functions
• Provides flexible, elastic support.
• What happens when you bend and release your ear?

A Chondrocyte B Matrix w/ black
elastic fibers C -Lacuna
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Fibrocartilage

• Microscopic Appearance
• Parallel collagenous fibers similar to those of
  tendon.
• Rows of chondrocytes in lacunae between
  collagenous fibers.
• Chondrocytes are fewer and smaller and are not in
  isogenous groups.
• Never has a perichondrium.

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Fibrocartilage

• Locations
• Pubic symphysis the anterior joint between the
  2 halves of the pelvic girdle.
• Intervertebral discs that separate the bones of
  the spinal column.
• Menisci (shock-absorbing pads of cartilage) in
  the knee joint.
• At points where tendons insert on bones near
  articular hyaline cartilage.
• Functions
• Resists compression and absorbs shock in some
  joints.
• Often a transitional structure between dense
  connective tissue and hyaline cartilage.
• For example, at some tendon-bone junctions.

82
More Connective Tissues

• Bone is the other supporting connective tissue.
  It will be discussed in detail later.
• Blood is a fluid connective tissue that youll
  examine in AP II.

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Muscle and Nervous Tissue

• Nervous tissue
• Consists of 2 cell types Neurons and glia.
• Detects stimuli, integrates information, and
  transmits signals.
• Muscular tissue
• 3 types skeletal, cardiac, and smooth.
• Specialized to contract and exert forces on other
  tissues.
• Major function is the creation of movement.

84
Body Membranes

• The majority of the bodys structures are lined
  by epithelial membranes.
• Such structures include body cavities, tracts,
  external surfaces of organs, and the external
  surface of the body itself.
• An epithelial membrane is defined as
• A continuous multicellular sheet composed of at
  least 2 primary tissue types An epithelium bound
  to an underlying layer of fibrous connective
  tissue.

85
Epithelial Membranes
Serosa covering the heart

1. Cutaneous membrane
2. Mucous membranes
3. Serous membranes

Mucosa lining the duodenum (1st part of the small
intestine
86
Cutaneous Membrane

• Skin!
• Its an organ system consisting of a keratinized
  squamous epithelium (epidermis) firmly attached
  to a thick layer of dense irregular connective
  tissue (dermis).
• Unlike other epithelial membranes, it is exposed
  to the air and is a dry membrane.

87
Mucous Membranes (a.k.a. Mucosae)

• Line passageways (body cavities) that open to the
  external environment.
• Digestive, respiratory, urinary, and reproductive
  tracts.
• Wet membranes that are bathed by their own
  secretions or, in the case of the urinary tract,
  urine.
• Mucosae have 2 or occasionally 3 layers
• Lining epithelium (simple columnar or
  nonkeratinized stratified squamous) is adjacent
  to the lumen and above the
• Layer of areolar CT called the lamina propria
  which is sometimes above a
• Layer of smooth muscle called the muscularis
  mucosae.

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Mucous Membranes

• Have absorptive, secretory protective
  functions.
• Often covered with mucus secreted by goblet
  cells, multicellular mucous glands, or both.
• Mucus is often involved in trapping foreign
  particles (including bacteria) or providing
  lubrication.
• The presence of mucus does not define a mucous
  membrane however e.g., the mucous membrane
  lining the urinary tract lacks mucus.
• Cells modified for absorption are present in the
  small intestine
• Cells modified for protection are present mainly
  at those positions of the tracts closest to the
  exterior.

Normal stomach mucosa
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Serous Membranes (a.k.a. Serosae)

• Moist membranes found in closed ventral body
  cavities not open to the exterior.
• Line the insides of the peritoneal, pleural, and
  pericardial cavities and line the outer
  surfaces of some of the viscera.
• Consist of a simple squamous epithelium lying
  upon a thin layer of areolar CT.
• Secrete a thin, watery fluid that arises from the
  blood. Its called serous fluid.

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Serosae

• Provide an efficient means of lubricating cavity
  walls and organ exteriors so as to reduce the
  friction associated with movement.
• Why is this essential?
• The serosa lining the pleural cavity and the lung
  exterior are the parietal and visceral pleurae,
  respectively. Those of the heart are the
  parietal and visceral pericardium and those of
  the abdomen are the parietal and visceral
  peritoneum.

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Tissue Repair

• 2 possibilities
• Regeneration ? Replacement of dead or damaged
  cells by the same type of cells as before. Most
  skin injuries heal by regeneration. The liver
  also regenerates quite well.
• Fibrosis ? Replacement of damaged tissue with
  scar tissue, composed mainly of collagen produced
  by fibroblasts. Helps hold an organ together but
  does not restore normal function. Examples
  include severe cuts and burns, the healing of
  muscle injuries, and scarring of the lungs in
  tuberculosis.

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Stages of Healing a Wound to the Skin

1. Severed blood vessels bleed into the cut. Mast
   cells and cells damaged by the cut release
   histamine which dilates blood vessels, increases
   blood flow to the area, and makes capillaries
   more permeable. Blood plasma seeps into the
   wound carrying antibodies, clotting proteins, and
   blood cells.

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• A blood clot forms, loosely knitting the edges of
  the cut together and interfering with the spread
  of pathogens. Scab forms and seals the wound and
  blocks infection. Beneath it, macrophages begin
  to clean up tissue debris.
• New capillaries sprout from nearby vessels and
  grow into the wound. The deeper portions of the
  clot become infiltrated by capillaries and
  fibroblasts and transform into a soft mass called
  granulation tissue. Macrophages remove the blood
  clot while fibroblasts secrete collagenous fibers
  to replace it.

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Stages of Healing a Wound to the Skin

1. Surface epithelial cells around the wound
   multiply and migrate into the wounded area
   beneath the scab. The scab loosens and
   eventually falls off, and the epithelium grows
   thicker. Thus, the epithelium regenerates while
   the underlying connective tissue undergoes
   fibrosis.