Download smooth muscle

組織學
Historlogy
台北醫學大學/解剖學科
教授：邱瑞珍
分機號碼：3261
電子郵件信箱：rueijen@tmu.edu.tw
1
Muscle Tissue
台北醫學大學/解剖學科
教授：邱瑞珍
分機號碼：3261
電子郵件信箱：rueijen@tmu.edu.tw
2
學習目的
• The morphological and functional
characters of skeletal, cardiac and
smooth muscles.
3
參考資料
• Junqueira's Basic Histology, twelfth
edition, text and atlas, Anthony L.
Mescher, McGraw-Hill Companies
4
Summary
I. Skeletal muscle
1. nuclei: multi-nucleation, peripherally
located
2. Myofibrils：myosin (thick)
filaments, actin (thin) filaments
3. striation:
dark band – A band (anisotropic); H
band; M-line light band – I band
(isotropic); Z-line sarcomere
4. Sarcoplasm :mitochondria, Golgi
complex, glycogen, lipid droplets &
myoglobin sarcoplasmic reticulum
5. Sarcolemma transverse (T) tubules –
located at A-I junctiontriad→triad
II. Cardiac muscle
1. nucleus: one or two, centrally located
2. myofibrils: similar to skeletal muscle
3. sarcoplasm: abundant, numerous
mitochondria and lipid droplets,
sarcoplasmic reticulum
4. sarcolemma: T- tubule located at Zline, intercalated disc – desmosome + gap
junction
Heart wall: epicardium, myocardium &
endocardium
Purkinje fiber: specialized cardiac muscle
cells
conduct impulses
III. Smooth muscle
•nucleus: one, centrally located
•myofibrils: less orderly arranged, no
striation, with dense body
•sarcoplasm: various organelles, poor
sarcoplasmic reticulum
4.sarcolemma: no T-tubule, caveolae or
5
vesicles (Ca2+), gap junction
Muscle tissue:
differentiated cell property:
contractility
microfilaments & associated proteins
Æ generate forces
drive movement within organs
& body
Nearly all muscle cells:
from mesoderm
differentiate by cell lengthening with
synthesis of myofibrillar proteins
6
3 types of muscle tissue:
morphologic & functional characteristics
structure adapted to physiologic role
Skeletal muscle:
bundles of very long, cylindrical
multinucleated cells
show cross-striations
contraction: quick, forceful,
under voluntary control
interaction of thin actin
filament & thick myosin
filament
sliding
7
Cardiac muscle:
also cross-striations
elongated, branched cells
lie parallel to each other
end-to-end contact
intercalated disks
only in cardiac muscle
contraction:
involuntary, vigorous,
rhythmic
8
Smooth muscle:
collections of fusiform cells
not show striations
contraction:
slow, not subject to voluntary control
9
Cytoplasm of muscle cells:
Sarcoplasm
Smooth ER:
Sarcoplasmic reticulum
Cell membrane:
Sarcolemma
10
SKELETAL MUSCLE
Consist of muscle fibers:
long, cylindrical multinucleated cells
diameter : 10-100µm
Multinucleation:
fusion of embryonic mesenchymal cells
myoblasts
Long oval nuclei:
found at peripheral of cell
under cell membrane
11
Organization
Epimysium :
an external sheath of dense connective tissue
surrounding entire muscle
Perimysium :
surrounding fascicles (bundles) within muscle
Endomysium :
surrounded each muscle cell
basal lamina
12
Connective tissue:
transmit mechanical forces
Blood vessels:
penetrate the muscle
within connective tissue
form a rich capillary network
in endomysium
lymphatic vessels & larger blood vessels:
other layers
Muscle-tendon:
myotendinous junctions
13
Muscle fibers
Longitudinally sectioned:
cross-striations: light & dark bands
Dark bands : A bands
Light bands : I bands
Within I band: Z line
Sarcomere: Z line to Z line
2.5 µm long in resting muscle
14
Sarcoplasm: little rER or free ribosome
filled with long cylindrical filamentous bundles
called myofibrils
parallel to long axis of fiber
Myofibrils : 1-2 µm
consist of end to end sarcomeres
pattern of transverse striations
A & I banding pattern:
regular arrangement of myofilaments
thin & thick
15
Thick myofilament :
1.6μm long, 15nm wide
occupy A band: central portion of sarcomere
Thin myofilament:
run between & parallel to thick filaments
one end attached to Z line
1.0μm long, 8nm wide
I band:
portions of thin filaments
not overlap the thick filaments
A band:
composed mainly thick
overlapping portions
of thin
16
A band: a lighter zone in center
H zone
only rod-like portions of myosin molecule
no thin filaments
Bisecting H zone:
M line
lateral connection of thick
major protein:
myomesin
myosin-binding protein
hold thick
creatine kinase
supply energy
17
Thin & thick: overlap within A band
A cross section:
each thick filament surrounded by 6 thin
a hexagon
18
Thin filaments:
composed of
F-actin
associated with tropomyosin
long fine polymer
also troponin
globular complex of 3 subunits
Thick filaments:
consist primarily myosin
Myosin + actin:
55% of total protein of striated muscle
19
F-actin:
long filamentous polymers
containing 2 strands of globular
(G-actin) monomers
5.6 nm in diameter
twisted around each other:
double helical formation
each G-actin: a binding site for myosin
anchored on Z line: α-actinin
20
Each tropomyosin subunit:
a long, thin molecule: 40nm long
containing 2 polypeptide chains
assemble to form a long polymer
located in groove between actin strands
Troponin:
complex of 3 subunits
TnT: attach to tropomyosin
TnC: bind calcium ions
TnI: inhibit actin-myosin interaction
21
Myosin :
much larger complex:
molecule weight ~500kDa
2 heavy chains, 2 pairs of light chains
Heavy chain:
thin, rod-like molecules
150 nm long, 2-3 nm thick
made of 2 heavy chains
twisted as myosin tails
small globular projections: heads
ATP binding site
enzymatic capacity to hydrolysis ATP
binding actin
22
4 light chains:
associated with head
Several hundred myosin molecules:
arranged within each thick filament
rodlike portions overlapping
globular heads: directed toward either end
Crossbridges:
between thin & thick
formed by head of thick
& part of rod portion
involved in conversion
chemical energy
Æ mechanical energy
23
Sarcoplasmic Reticulum &
Transverse Tubule System
In muscle:
sER: specialized for Ca2+ ion sequestration
depolarization Æ release Ca2+
Surface-initiated depolarization signals
Æ diffusion to sER
In large muscle cells:
diffusion of depolarization
Æ peripheral earlier than central
Uniform contraction:
transverse (T) tubules
24
T tubules :
fingerlike invaginations of sarcolemma
Form a complex network of tubules
Encircle every myofibil
Near A-I band boundaries of each sarcomere
Adjacent to opposite side of each T tubule:
expanded terminal cisternae of
sarcoplasmic reticulum
2 cisternae + a T tubule : triad
At triad:
depolarization Æ
sarcolemma Æ T tubules
Æ sarcoplasmic reticulum
25
Mechanism of Contraction
Resting sarcomeres:
thick & thin partially overlapping
During contraction:
thick & thin not change their length
Contraction :
increase amount of overlap between filaments
sliding of thin & thick
induced by an action potential produced
at synapse
26
27
If no ATP available:
actin-myosin complex become stable
rigor motis occur after death
During contraction:
I band decrease in size
H band diminishes in width
sarcomere, whole cell (fiber) greatly shorten
28
Muscle Fiber Types
The most available forms of energy:
ATP & phosphocreatine
energy-rich phosphate compounds
Chemical energy also stored in glycogen particles
0.5-1% muscle weight
Muscle tissue obtains energy:
Aerobic metabolism of fatty acids & glucose
fatty acid Æ acetate Æ citric acid cycle
Æ ATP
Short-term exercise:
Anaerobic metabolism of glucose (from glycogen)
produce lactate
oxygen debt
29
Skeletal muscles: 3 types
physiological, biochemical, histochemical
characteristics
•Type I (slow, red oxidative) fibers
contain many mitochondria
abundant myoglobin
a protein with iron groups
bind O2, produce a dark red color
energy from aerobic oxidative
phosphorylation of fatty acids
adapted for slow, continuous
contraction
over prolonged periods
30
•Type IIa (fast, intermediate oxidative-glycolytic)
fibers
many mitochondria
much myoglobin, also glycogen
both oxidative metabolism &
anaerobic glycolysis
intermediate between other types
both in color & energy metabolism
adapted for rapid contractions &
short bursts of activity
31
•Type IIb (fast, white glycolytic) fibers
fewer mitochondria
less myoglobin
abundant glycogen
pale in color
depend largely on glycolysis for energy
fatigue quickly
typically small muscles
Differentiation of muscle
Æ red, white, intermediate
controlled by frequency of impulses from
motor innervation
Simple denervation of muscle:
fiber atrophy & paralysis
32
CARDIAC MUSCLE
During embryonic development:
mesodermal cells align into chainlike arrays
Cardiac muscle cells:
complex junctions between processes
Cells: branch & bind to cells in adjacent fibers
Cardiac muscle cells:
15μm in diameter, 85-100 μm in length
cross-striated banding
pale-staining 1 or 2 nuclei
centrally located
endomysium:
rich capillary network
33
Intercalated discs
Interface between adjacent muscle cells
many junctional complex
Desmosomes, fasciae adherens:
bind cardiac cells
Gap junction:
act as electrical synapses
allow cells of cardiac muscle
act as a multinucleated syncytium
contraction signals passing in a
wave from cell to cell
34
Contractile proteins: same as skeletal muscle
T- tubules: more numerous & larger
Sarcoplasmic reticulum: less well developed
Contain numerous mitochondria:
40% or more of cytoplasmic volume
need for continuous aerobic metabolism
occupy 2% volume of skeletal muscle
Fatty acids:
major fuel of heart
store as triglycerides
Glycogen particles: also present
Lipofuscin pigment granules:
often found near the nuclei
35
SMOOTH MUSCLE
Smooth muscle fibers:
elongated, tapering, nonstriated cells
each enclosed by a thin basal lamina
& a fine network of reticular fibers
Connective tissue:
combine force generated by each fibers
Æ a concerted action
Smooth muscle cells:
range in length:
20μm in small blood vessels
~500 μm in pregnant uterus
single nucleus in center
Contract: border scalloped
nucleus distorted
36
A rudimentary sarcoplasmic reticulum: present
No T tubules
Thin & thick myofilaments :
crisscross obliquely through the cell
forming a latticelike network
Sliding filament mechanism
Intermediate filaments:
desmin: major protein in all smooth muscle
vimentin: additional component in vascular
Both & F-actin insert into dense bodies
37
Dense body:
membrane-associated or cytoplasmic
contain α-actinin
functionally similar to Z discs
Attachment of thin & intermediate filaments:
help transmit contractile force Æ other cells
& surrounding network of reticular fibers
Not under voluntary control
Regulated by autonomic nerves, hormones,
local conditions
1.Multiunit smooth muscle
contract independently
2.Unitary smooth muscle
gap junctions :
38
(X) contract independently
In addition to contractile activity:
smooth muscle cells also synthesize
collagen, elastin, proteoglycans,
ECM components
normally synthesized by fibroblasts
39
REGENERATION OF MUSCLE TISSUE
Skeletal muscles :
(X) mitotic activity
limited regeneration
sparse mesenchymal satellite cells
muscle injury or other stimuli
Cardiac muscles:
lack satellite cells: no regenerative capacity
damage : fibrobalsts proliferation Æ
myocardial scar
Smooth muscle :
more active regenerative response
(V) mitotic activity
40