Transcript The Tissue Level of Organization Chapter 5 What is a Tissue? • The human body is composed of trillions of cells • There are.

The Tissue Level of
Organization
Chapter 5
What is a Tissue?
• The human body is composed of trillions of cells
• There are approximately 200 cell types that
make up the trillions of cells
• These 200 cell types can be further grouped into
4 categories according to their roles – these 4
categories are called tissues
• Tissues are groups of cells that function together
to keep a body alive
Types of Tissues
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•
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•
Epithelial Tissue
Connective Tissue
Muscle Tissue
Neural Tissue
Epithelial Tissue
Consist of 2 sub-categories:
1. Epithelia
2. Glands
Epithelia are layers of epithelial cells that cover the
internal or external surfaces of various organs,
ducts, vessels, etc.
Glands are structures whose cells produce fluid
secretions. They are either attached to epithelia
or made from epithelia
Characteristics of Epithelia
• Cellularity – made up entirely of cells that are closely
bound by tight junctions, gap junctions and desmosomes
• Polarity – One end of the tissue usually faces an
internal or external area of an organ (apical surface) and
the other end is either attached to other tissues or a
basement membrane called a basal lamina (basolateral
surface)
• Avascularity – Epithelia do not contain blood vessels
– they get their oxygen and nutrients from adjacent cells.
• Regeneration – Epithelial cells are constantly lost on
the exposed surface – so they are constantly replaced
by cell division of stem cells
Polarity of Epithelial Cells
POLARITY AND THE
CONTROL OF PERMEABILITY
Apical surfaces of internal
passageways may have
special extensions called
microvilli
What are the Functions of Epithelial Tissue?
• Provide Physical Protection – against
abrasion, dehydration and destruction from
chemical or biological agents
• Control Permeability – some allow substances
to enter / leave or pass through, other epithelial
cells are quite impermeable
• Provide Sensation – large sensory nerve
supply
• Produce Specialized Secretions – These
epithelial cells are called gland cells (Cells of the
thyroid, salivary glands, etc.) They use blood
and interstitial fluid as carriers of the chemicals
they release
Maintaining Epithelia Integrity
I. Intercellular connections
– CAMs (Cell Adhesion Molecules - proteins)
– Intercellular cement (Proteoglycans,
glycosaminoglycans such as Hyaluronan)
– Cell Junctions
• Tight Junctions – prevent passage of fluids and solutes
(e.g. Stomach lumen)
• Gap Junctions – proteins called connexons leave gaps for
passage of various materials
• Desmosomes – CAMs and proteoglycans link adjacent
cell membranes with internal intermediate filaments–
strong, resist stretching and pulling
– Belt Desmosomes, Button Desmosomes and Hemidesmosomes
(Between cell and basal lamina)
Intercellular Junctions, cont’d.
Acantholysis and Desmosomes
Pemphigus
• Pemphigus involves blistering
of the outer (epidermal) layer
of the skin and mucous
membranes. It is an
autoimmune disorder in which
the immune system produces
antibodies against specific
proteins in the skin and
mucous membrane. These
antibodies produce a reaction
that leads to a separation of
epidermal cells (acantholysis).
The antibodies usually develop
against desmosome proteins.
Loss of desmosomes causes
epidermal cells to “Float away”
Maintaining Epithelia Integrity
II. Attachment to the Basal Lamina
Epidermal cells hold each other as well as the basal lamina which
consists of 2 layers:
Lamina lucida – consists of proteins secreted by adjacent cells – acts as a
barrier that restricts movement of proteins
Lamina Densa – contains bundles of proteins that gives the basal lamina
strength
Hemidesmosomes finally attach epithelial cells to the complete basal lamina
Maintaining Epithelia Integrity
III. Epithelial Maintenance and Repair
Stem cells or germinative cells within the
epithelial tissue divide continually, to give
rise to new epithelial cells to replace those
that have died out due to exposure to toxic
chemicals, pathogenic bacteria, abrasions,
etc.
Types of
Epithelial Tissue
(Epithelia)
Simple Squamous
• Thin, single layer of flat cells attached to
basal membrane (lamina)
• Substances pass through very easily
• Forms walls of capillaries, lines other
blood and lymph vessels, lines insides of
certain organs
• Lines alveoli of lungs
• Easily damaged!
Simple Cuboidal
• Single layer of cube-shaped cells attached
to basal membrane
• Covers ovaries, lines tubes and ducts of
kidneys, certain glands such as pancreas,
salivary glands and liver
• Can be used to secrete glandular products
or reabsorb materials such as water (in
kidneys)
Simple Columnar
• Single layer of elongated cells, attached to basal
membrane
• Cells may or may not be ciliated on their apical
surface
• Nonciliated simple columnar epithelia lines the uterus,
parts of the GI tract and
• Can secrete digestive juices
• Because of thickness, they protect underlying tissues
• Ciliated simple columnar epithelia lines the fallopian
tubes, to move eggs
• Some line intestines and have villi and microvilli to
increase surface are for absorption
Pseudostratified Columnar
•Appears stratified,
but is not
•Apical surface of
cells have cilia
•Line respiratory
tract
•Contain special
cells called goblet
cells that secrete
mucous to trap dust
and microorganisms
Stratified Squamous
• Many layers of squamous cells, so relatively
thick
• Cells at apical surface are flattened and buildup
a protein called keratin, which protects them
from water damage, microorganisms, etc. Cell
division occurs in deeper layers where cells are
cuboidal or columnar
• Upper layer of skin (keratinized)- tough, dead
• Oral cavities, throat, esophagus, vagina, anal
canal – all non-keratinized; upper layer cells are
soft, alive.
Stratified Cuboidal
•2 or 3 layers of cuboidal epithelium
•Line the ducts of salivary glands, mammary glands, sweat
glands, etc.
•Also lines immature or developing tubes in the male and female
reproductive systems
Stratified Columnar
• Cells at apical end
tend to be columnar
(elongated) whereas
cells at the basal level
are cuboidal in shape
• Line the vas deferens,
male urethra and
areas of the pharynx
Transitional Epithelium
• Changes in response to
increased tension
• Able to stretch; also
prevents materials in the
urethra from reentering the
tissues
• Lines inside of uterus,
urinary bladder and urethra
• When walls of these organs
expand, the cells appear
cuboidal
• When walls stretch
(distend), the cells appear
flattened
Glandular Epithelium
• Cells specialized to produce and secrete
substances into ducts leading out of the gland
• Glandular cells are actually embedded in and
surrounded by columnar and cuboidal epithelial
cells
• Two types of glands:
– Exocrine: secrete products into ducts that that open
into and internal or external surface (goblet cells,
salivary , sweat glands)
Endocrine: secrete products into blood and other body
fluids (Pituitary, thyroid, pancreas, adrenal, ovaries,
testes, etc.)
Endocrine
Glands
Products secreted into
blood and other body
fluids.
Secretions affect various
organs and tissues all
around body
Exocrine Glands
There are multiple ways of classifying
exocrine glands. By their
1. Structure
2. Method of secretion
3. Products secreted
Exocrine Gland Structure
Exocrine glands contain a glandular portion and a
duct portion, the structures of which can be used
to classify the gland.
• The duct portion may be branched (called
compound), coiled, or unbranched (called
simple).
• The glandular portion may be tubular or alveolar
(acinar). Sometimes both (tubuloacinar)
• If the glandular portion branches, then the gland
is called a branched gland.
Exocrine Gland Methods of Secretion
Exocrine glands are named apocrine, holocrine, or
merocrine glands, based on how their product is
secreted.
• Apocrine glands - a portion of the gland’s cell
body which contains the secretion, is lost during
this type of secretion. (e.g. Mammary glands)
• Holocrine glands - the entire cell disintegrates
to secrete its substance. (e.g. sebaceous glands
of skin)
• Merocrine glands - cells secrete their
substances by exocytosis. Also called "eccrine."
(e.g. salivary, pancreatic, and sweat glands)
Merocrine
Apocrine
Holocrine
Exocytosis
Cell parts break off
Entire cell disintegrates, replaced by mitosis
Apocrine Glands
Holocrine Glands
Sebaceous glands are
found in the skin of
mammals. They secrete an
oily substance called sebum
that is made of fat (lipids)
and the debris of dead fatproducing cells. These
glands exist in humans
throughout the skin except in
the palms of the hands and
soles of the feet. Sebum
acts to protect and
waterproof hair and skin,
and keep them from
becoming dry, brittle, and
cracked. It can also inhibit
the growth of
microorganisms on skin.
Merocrine Glands
Exocrine Glands Products Secreted
• Serous cells secrete proteins, often enzymes
and other materials such as lipids. Examples
include chief cells
• Mucous cells secrete mucous. Examples include
esophageal glands, and pyloric glands.
• Mixed glands secrete both protein and mucus.
Examples include the salivary glands, although
parotid gland is predominantly serous (clear)
and contains amylase, and sublingual gland is
predominantly mucous.
Types of Cells Found in Connective Tissue
• Fibroblasts – make protein fibers
• Chondrocytes – make cartilage
• Macrophages – WBCs that perform phagocytosis,
usually attached to connective fibers, but can roam
around
• Erythrocytes, Leukocytes – O2, CO2 transport;
defense
• Mast Cells – located near blood vessels, prevent
blood clotting by releasing heparin. Also release
histamine that causes inflammatory and allergic
reactions
• Osteocytes –maintain bone tissue
• Adipocytes – Store fat droplets, but look like
fibroblasts at first
Fibroblasts – The most abundant
cells in connective tissue
•
Produce 3 major protein fibers in
connective tissue:
1. Collagenous fibers
2. Elastic fibers
3. Reticular fibers
Collagenous Fibers
• Thick threads of the protein
collagen
• Grouped in long parallel
bundles
• Strong, can resist significant
pulling force
• Make up ligaments (connect
bone to bone) and tendons
(connect muscles to bones)
Tissue with a lot of collagenous
fibers is considered dense
connective tissue – the
opposite is loose connective
tissue
Collagen Abnormalities
Ehlers-Danlos Syndrome
Chondrodysplasia
Not enough collagen, so
elastin is predominant
connective tissue, skin
very stretchy
Stunted growth, deformed
joints – NOT DWARFISM!
•Made up of branching
bundles of microfibrils
of a protein called
elastin (or tropoelastin)
•Weaker than collagen,
but elastic
•They can coil and
recoil
• Accounts for the
elasticity of structures
such the skin, blood
vessels, heart, lungs,
intestines, tendons, and
ligaments
•Tissues with lots of
elastin appear yellow
Elastic Fibers
Elastin is normally no longer made after puberty and aging begins.
Reticular Fibers
• These are also made up of collagen Type III, but are very thin
fibers
• They are highly branched and form delicate, mesh-like
networks in many tissues
• Networks of these fibers make up lymphatic and hemopoietic
tissues such as the thymus, lymph nodes, spleen, and bone
marrow.
Connective Tissue
Categories
1.
2.
3.
4.
5.
6.
7.
8.
Loose connective tissue
Dense connective tissue
Reticular connective tissue
Elastic connective tissue
Adipose tissue
Cartilage
Bone
Blood
Loose Connective Tissue
Found between
muscles, under skin,
under epithelial
tissue
CONTAINS MANY
BLOOD VESSELS –
which supplies blood
to epithelial cells
• Forms thin membranes throughout body,
• Cells are mainly fibroblasts separated by a a gel-like
substance made up of loosely packed collagen and elastin
fibers which the fibroblasts secrete
Dense Connective Tissue
•
•
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Closely packed fibers of elastin and collagen fibers
Only a few cells inside; mainly fibroblasts
Divided into 2 categories
1. Regular dense – very strong, collagen fibers oriented in
one direction
– Binds body part together as in tendons and ligaments
– Poor blood supply – so tissue repair is slow
2. Irregular – more randomly organized collagen fibers
– Has blood supply
– Found in dermis of skin (inner layer) and the tough
capsules that surround many of the organs such as the
kidneys, adrenal glands, nerves, bones, and the covering
of muscles. It provides support and strength.
Regular vs. Irregular Dense Connective Tissue
Adipose Tissue
•Two types of adipose cells are found in fat tissues, white and brown
adipocytes. These adipose cell types vary in their ability to mobilize energy from
stored fat. Brown fat cells are smaller and more efficient at converting fat into
available energy. Brown fat is more typical in infants, being replaced gradually by
white fat as we age. In both cell types fat droplets enlarge to push nuclei and
cytoplasm to the periphery.
Reticular Connective Tissue
• Made up of thin Type III collagenous fibers
(reticular fibers) and another protein called
reticulin
• Supports walls of internal organs and
networks of these fibers make up
lymphatic and hemopoietic tissues such as
the thymus, lymph nodes, spleen, and
bone marrow.
• Contains blood vessels
Elastic Connective Tissue
• Consists of yellow, elastic fibers
• Collagen fibers and fibroblasts can be
found between the elastic fibers
• Found mainly in structures such the skin,
blood vessels, heart, lungs, intestines and
between vertebrae of spinal column
Cartilage
• Rigid, structural model for
developing bones – as children
mature into adults, more and
more cartilage gets replaced by
bone
• The matrix is mainly collagen
fibers embedded in a gel-like
ground substance which is
made of proteins like
chondromucoprotein and
chondroitin sulfate and water
• Chondrocytes lie in the matrix in
small cavities called lacunae
Cartilage, cont’d.
• Cartilage lacks blood supply, but is usually
surrounded by connective tissue called
perichondrium that supplies it with
nutrients
• Cartilage heals slowly and chondrocytes
do not often divide (lack of blood supply)
• 3 Types: Hyaline, Elastic and
Fibrocartilage
Hyaline Cartilage
• Most common
• Glass-like
• Found on ends of bones
– End of nose
– Rings in respiratory
passages (trachea)
– Embryonic skeleton –
template for bone
development
Elastic Cartilage
• More flexible than
hyaline cartilage
because the matrix
contains more elastic
fibers
• Epiglottis and
“skeleton” of external
ear
Elastic Cartilage
in the ear
Fibrocartilage
• Very tough – contains
collagen fibers
• Absorbs shocks and
pressure
• Forms pads in
vertebral discs,
cushions bones in
knees and pelvis
Vertebral Discs
Bone (Osseous Tissue)
• Most rigid connective tissue
• Rigidity due to mineral salts such as
calcium phosphate and calcium carbonate
in its matrix
• Bone also contains collagen
• Contains red marrow which forms blood
cells, stores and releases inorganic salts
Bone Tissue – active, living tissue!
• Consists of concentric layers called
lamellae, around central canals or
Haversian canals
• Each bone unit around a central
canal is called an osteon or
Haversian system
• Each central canal contains blood
vessels
• Chambers called lacunae (lacuna)
contain osteocytes which used to be
bone-making osteoblasts that have
become entrapped in their own
secretions.
• Osteocytes extend their cellular
extensions into the bone matrix
through fine tubes called canaliculi
• The cell extensions form gap
junctions with each other - this way
nutrients can pass from the blood
vessels to all bone cells quickly
Blood
• Various cell types found in a liquid matrix called
plasma
– Erythrocytes (RBCs)
• Transport O2, CO2
• Stay within blood vessels
– Leukocytes (WBCs)
• Fight infection (immune system)
• Can move from blood vessels to connective tissues
– Platelets (Cell fragments)
• Help with clotting
• Most blood cells are produced in hematopoietic
tissue like red marrow
White Blood Cell
Platelets
Red Blood Cells
Muscle Tissue
• Skeletal Muscle (voluntary muscles)
• Smooth Muscle (involuntary muscles)
• Cardiac Muscle
Skeletal Muscle
– Attach bones
– Movement can be controlled by us
– Long and narrow cells (Muscle fiber) containing
myofibrils made of actin and myosin filaments
– The myofibrils have alternating light and dark
striations
– Cells are multinucleated and have many
mitochondria
– Actin and myosin protein filaments in cells slide past
each other in response to nerve impulses and
cause muscle to expand and contract
Skeletal Muscle Dissected
(Plasma membrane of a muscle cell)
(Cytoplasm of a muscle cell)
(Group of Filaments)
(Muscle Cell)
(A bundle of muscle cells)
(Threads of
Myosin and
actin proteins)
Fibrodysplasia Ossificans Progressiva
(FOP).
•A rare genetic disorder that transforms skeletal
muscle into bone.
•Children with FOP look normal at birth except
for a characteristic malformation of the great
toe.
•During the first decade of life, affected children
begin to develop painful swellings that look like
tumors. These swellings seize the skeletal
muscles and transform them into bone.
Smooth Muscle
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•
•
Called smooth because it lacks striations
Cells shorter than skeletal muscle cells
Spindle-shaped
Single, central nucleus
Forms muscles of the digestive tract,
uterus, urinary bladder, blood vessels, etc.
• Cannot be controlled - involuntary
Smooth Muscle Fibers cells)
Cardiac Muscle
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•
Found in heart only
Cells striated and joined end-to-end
Cells form branches
Single-nucleated
Special intercellular junctions between cells
is called an intercalated disc – found only in
cardiac muscle cells
• Involuntary – can even continue to function
without nerve stimulus
Cardiac Muscle
Branching
Nervous Tissue
• Found in brain, spinal cord (CNS) and peripheral
nervous system (PNS)
• Main nerve cells are called neurons
• Highly specialized
• Send impulses to each other, muscles and
glands
• Other supporting nervous tissue is made up of
cells called Neuroglial cells, which support
neurons, provide them with nutrients and help
with cell-to-cell communication
Neurons
Membranes and Organs
• Two or more types of tissues working
together form an organ or membrane
• Epithelial membranes are composed of
epithelial tissue and its underlying
connective tissue
• Epithelial membranes are considered
organs!
END OF CHAPTER
Epithelial Membranes
1. Synovial membrane – line joints, mostly
connective tissue
2. Serous membrane – line inside of body
cavities, reduce friction between body cavity
walls and organs – secrete clear, serous fluid
3. Mucous membrane – Line tubes that open to
outside – nose, throat, anus, urethra, vagina,
penis – secrete mucus
4. Cutaneous membrane – also called skin –
protect body from external elements