The Tissue Level of Organization

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The Tissue Level of Organization

• "It is not birth, marriage, or death, but
  gastrulation, which is truly the most important
  time in your life."
•             Lewis Wolpert (1986)

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The Tissue Level of Organization

• Group of similar cells
• common embryonic origin
• common function
• bound together by intercellular substance
• Histology
• study of tissues

What kind of molecules may make up these
intercellular junctions?
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The Origin of Tissues
Differentiate between primary tissues and
embryonic germ layers.
Morula
Blastula
Gastrula
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Gastrulation in birds and mammals
from LIFE The Science of Biology, Purves et al,
1998
Does this process result in a change in the shape
of the embryo? Does it change the number of
embyronic germ layers?
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Define each of these terms List at least on
specialization from each embryonic germ layer.
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4 Basic Tissues Types

• Epithelial
• Connective
• Muscle
• Nervous

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Intercellular Junctions

• Tight junctions
• Adherens junctions
• Gap junctions
• Desmosomes
• Hemidesmosomes

What does hemi mean?
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Tight Junctions
This type of intercellular junction is common in
transport epithelia.

• Why do you think tight junctions are located
  nearer the luminal cell border rather than the
  basolateral border?
• Describe the structure and function of the apical
  cell border for these cells that line the
  intestine.
• Where are transport epithelia found?

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Gap Junctions
What kinds of materials may pass between cells
through gap junctions? In which tissues are gap
junctions common?
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Desmosomes

• Give at least two examples of tissues containing
  desmosomes.
• Where else would you expect to find keratin, and
  for what purpose?
• What analogy would you use to describe the
  structure of a desmosome?
• What function does this structural feature
  provide for the tissue?

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Hemidesmosomes

• Half of a desmosome!
• Connect cells to extracellular material
• basement membrane
• Which tissues are connected to a basement
  membrane, and would therefore possess
  hemidesmosomes?

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Epithelial Tissue -- General Features

• Cover surfaces, line cavities and form glands
• Name one multicellular gland formed by epithelial
  tissue.
• Differentiate between endocrine, exocrine and
  heterocrine glands.
• Attached to underlying connective tissue by a
  basement membrane
• Avascular---without blood vessels
• nutrients diffuse in from blood vessels in
  underlying connective tissue
• What does this mean for especially thick
  epithelia?
• Good nerve supply
• Rapid cell division responsive to environmental
  stresses
• Named according to the shape and arrangement of
  cells
• List the general functions of epithelial tissues.

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Epithelial Tissues and Their Basement Membrane
What function might the basement membrane serve
in the repair of injury to the epithelium?
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Simple Squamous Epithelium

• Single layer of flat cells
• lines blood vessels (endothelium), closed body
  cavities (mesothelium)
• very thin --- controls diffusion, osmosis and
  filtration
• What is the primary function of this tissue
  (protection or transport)? (Hint What is its
  function as an endothelium,as mesothelium?)

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Examples of Simple Squamous Epithelium

• Section of intestine showing serosa

• Surface view of lining of peritoneal cavity

Is this endothelium, mesothelium, or neither?
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Classification of Epithelial Tissues
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Connective Tissues

• Cells rarely touch due to usually large amount of
  intercellular material (extracellular matrix)
• Matrix(fibers ground substance) secreted by
  cells
• Consistency varies from liquid or gel to solid
• Function is to support, connect, protect and
  insulate
• Good nerve blood supply except cartilage
  tendons

Areolar c.t.
What are the three major cell types often found
in connective tissues, and what are their
functions?
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Types of Connective Tissue Fibers

• Collagen (25 of protein in your body)
• tough, resistant to pull, yet pliable
• Elastin (lungs, blood vessels, ear cartilage)
• Reticular (spleen and lymph nodes)
• thin, branched fibers that form framework within
  organs
• formed from protein collagen

• smaller diameter fibers formed from protein
  elastin surrounded by glycoprotein (fibrillin)
• can stretch up to 150 of relaxed length and
  return to original shape

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Embryonic Connective TissueMesenchyme

• Irregularly shaped cells
• In semi-fluid ground substance with reticular
  fibers
• Gives rise to all other types of connective tissue

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Areolar (loose) Connective Tissue
What happens to the characteristics of this
tissue if it becomes dehydrated?

• Black, fine elastic fibers,
• Pink, thick collagen fibers
• Purple Nuclei are mostly of fibroblasts

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Adipose Tissue

• Peripheral nuclei due to large fat storage
  droplet
• Deeper layer of skin, organ padding, yellow
  marrow
• Reduces heat loss, energy storage, protection

Why are these cells sometimes called signet
ring cells?
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Dense Regular Connective Tissue

• Collagen fibers in parallel bundles with
  fibroblasts between bundles of collagen fibers
• White, tough and pliable when unstained (forms
  tendons)
• Also known as white fibrous connective tissue
• Do you see many blood vessels in this tissue?
  Implication?

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Dense Irregular Connective Tissue

• Collagen fibers are irregularly arranged
  (interwoven)
• Tissue can resist tension from any direction
• Very tough tissue -- white of eyeball, dermis of
  skin

a.k.a. ??
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Hyaline Cartilage

• Chondrocytes sit in spaces called lacunae
• No blood vessels or nerves so repair is very slow
  
• Matrix may or may not contain fibers
• What would you call the cells that form this
  tissue?

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Compact Bone

• Osteon lamellae (rings) of mineralized matrix
• calcium phosphate---give it its hardness
  (________________)
• interwoven collagen fibers (and other proteins)
  provide strength and flexibility (______________)
• Osteocytes in spaces (lacunae) in between
  lamellae
• Canaliculi (tiny canals) connect cell to cell
• Central canal contains blood vessels, nerves a
  lymphatic vessel

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Blood

• Connective tissue with a liquid matrix the
  plasma
• Formed elements red blood cells (erythrocytes),
  white blood cells (leukocytes) and cell fragments
  called platelets
• Provide clotting, immune functions, carry
  nutrients, wastes, etc.
• What are the functions of each of the formed
  elements? Where are the formed elements
  manufactured?

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Muscle

• Cells that shorten due to the chemical and
  physical interaction between myofilaments
• Actin and Myosin
• Compare and contrast this feature of muscle
  tissue cells with other cells not specialized for
  contraction.
• Types of muscle
• skeletal muscle
• cardiac muscle
• smooth muscle
• Compare the functions of the three types of
  muscle tissue.
• How is contraction in each of these tissues
  controlled?

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Skeletal Muscle

• Cells are large long cylinders with many
  peripheral nuclei
• How did these cells become multinucleate?
• Visible light and dark banding (looks striated)
• What structure(s) within these cells account for
  the striations?
• Voluntary (conscious) control

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Cardiac Muscle

• Cells are branched cylinders with one central
  nuclei, striated
• Involuntary
• If so, then why are there nerves that innervate
  the heart?
• Attached to and communicate with each other at
  intercalated discs
• What type(s) of intercellular junctions are
  present at intercalated discs?

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Smooth Muscle

• Spindle shaped cells with a single central nuclei
  
• Walls of hollow organs (blood vessels, GI tract,
  bladder), often arranged in sheets or layers
  (visceral smooth muscle)
• Waves of contraction that propel the contents of
  the intestine or ureter are called
  _____________________.
• Involuntary, and non-striated

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Nerve Tissue

• Cell types -- neurons and neuroglia (supporting
  cells more later)
• Functional classification motor, sensory, and
  interneurons
• Structural classification unipolar, bipolar,
  multipolar
• long cell processes conduct nerve signals
• dendrite --- signal travels towards the cell body
  
• axon ---- signal travels away from cell body

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Membranes as Organs

• Epithelial layer sitting on a thin layer of
  connective tissue (the lamina propria near
  layer)
• Types of membranes
• mucous membrane
• serous membrane
• synovial membrane
• cutaneous membrane (skin)
• Describe one location where each is found, the
  principle cells/tissues and intercellular
  junctions (if important), the secretion(s), and
  the function(s) for each type of membrane.

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Mucus Membranes
E.g. Digestive tract
Name at least two other locations in which you
would find a mucus membrane, and describe their
function.
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Serous Membranes
What is the purpose of the fluid that fills the
cavities created by these double-layered
membranes?
What is mesentery, and where is it located?
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Synovial Membranes
Do you recognize this joint? Name the bones in
this figure. What other features can you
identify? What is the purpose of the patella?
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The Cutaneous Membrane

• a.k.a. the skin