Transcript Tissue Level of Organization - Western Washington University

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)
The Tissue Level of Organization
• Group of similar cells
– common embryonic origin
– common function
– bound together by
intercellular substance
What kind of molecules may
make up these intercellular
junctions?
• Histology
– study of tissues
The Origin of Tissues
Differentiate between primary
tissues and embryonic germ
layers.
Morula
Blastula
Gastrula
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?
Define each of
these terms…
List at least on
specialization
from each
embryonic
germ layer.
4 Basic Tissues Types
•
•
•
•
Epithelial
Connective
Muscle
Nervous
Intercellular Junctions
• Tight junctions
• Adherens junctions
• Gap junctions
• Desmosomes
• Hemidesmosomes
What does “hemi” mean?
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?
Gap Junctions
What kinds of materials may
pass between cells through
gap junctions?
In which tissues are gap
junctions common?
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?
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?
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.
Epithelial Tissues and Their
Basement Membrane
What function might the basement membrane serve in the
repair of injury to the epithelium?
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?)
Examples of Simple Squamous
Epithelium
• Surface view of lining
of peritoneal cavity
• Section of intestine
showing serosa
Is this endothelium, mesothelium, or neither?
Classification of Epithelial Tissues
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?
Types of Connective Tissue Fibers
• Collagen (25% of protein in your body)
– tough, resistant to pull, yet pliable
• Elastin (lungs, blood vessels, ear cartilage)
• smaller diameter fibers formed from protein
elastin surrounded by glycoprotein (fibrillin)
• can stretch up to 150% of relaxed length and
return to original shape
• Reticular (spleen and lymph nodes)
– thin, branched fibers that form framework
within organs
– formed from protein collagen
Embryonic Connective Tissue:
Mesenchyme
• Irregularly shaped cells
• In semi-fluid ground substance with reticular
fibers
• Gives rise to all other types of connective tissue
Areolar (loose) Connective Tissue
What happens to
the characteristics
• Black, fine = elastic fibers,
of this tissue if it
• Pink, thick = collagen fibers
becomes
• Purple Nuclei are mostly of fibroblasts dehydrated?
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?
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?
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?
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
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?
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?
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
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?
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
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
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.
Mucus Membranes
E.g. Digestive tract
Name at least two other locations in which you
would find a mucus membrane, and describe their
function.
Serous Membranes
What is the purpose of the
fluid that fills the cavities
created by these doublelayered membranes?
What is mesentery,
and where is it
located?
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?
The Cutaneous Membrane
a.k.a. the skin