Viewing All Flashcards for Histo Block 2
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Avascular tissue with a dense intercellular matrix rich in proteoglycans in which
chondrocytes and chondroblasts thrive. It gets its nutrition by diffusion, allowed by the softness of
its matrix.Functions
·
Mechanical
shock absorber to a certain extent.
·
Smooth-surfaced allows joint functions.
May act as model for bone.
You see these in
Lacunae, which is latin for "lake".
·
Big round
cell, 10–50 µm in diameter·
Clear
layer of matrix surrounds the cells (proteoglycans and few collagen)
This clear matrix of collagen and Proteoglycans is what they produceChondronectin, fibronectin and anchorin keep cells attached to the matrix
·
Groups of
up to eight cells chondrocyte (isogenous
groups (L. equal origin) These isogenous groups come from ONE progenitor
cell an go through interstitial growth.
Chondronectin, fibronectin and anchorin
·
Perichondrium
surrounds almost all cartilages. Its outer
layer is made of fibroblasts and type
I collagen. The inner layer has
chondroblasts.
Stimulated by
Growth hormone,
thyroxine, testosterone
Dampened by
Cortisone, hydrocortisone,
estradiol
Stimulated by
Growth hormone,
thyroxine, testosterone
Dampened by
Cortisone, hydrocortisone,
estradiol
Hyaline, fibrous, and elastic.
Hyaline. ·
Most common type, its colour varies from bluish to white.
·
Type II collagen (this collagen is actually quite specific for
cartilage)
·
It is nourished
by the perichondrium or the synovial fluid (articular cartilage).
Elastic
cartilage
Primary protein is
Elastin.
·
Type II collagen plus elastic fibres, which confer a yellowish appearance to it.
o
Auricle of
the ear, auditory tubes, epiglottis, cuneiform cartilage of the larynx
Fibrous
cartilag
Can be relaxed by
relastin, such as during labor and the pubic symphysis. Only type that has Type
I cartilage.
·
Very strong and resilient, it shares characteristics
of both dense connective tissue and
hyaline cartilage.
·
It lacks of perichondrium and is highly
specialized.
·
Type I collagen creates a frame of fibres that accommodate the
chondrocytes.
Pubic symphysis, intervertebral disks, menisci
Highly
specialized cartilaginous
structure Medial (more likely to be injured) and lateral (important due to its
species specificity) Usually in injury you'll also injure the ACL or PCL,
and since the outer third is vascularized, it heals faster than the inner
two thirds. These three groups are called the "unhappy triad". Pivotal
in knee stabilization Outer
third vascularized Two
cell types:
o
Fibrochondrocyte – receives this name since, while being a chondrocyte, it can synthesize type I collagen. It also synthesizes type II, III and VI collagens
o
Fibroblast-like cells – outer third, secretes type I collagen, may have a sensory component
O
Fibrochondrocyte – receives this name since, while being a chondrocyte, it can synthesize type I collagen. It also synthesizes type II, III and VI collagens
Diarthroses and
synovial joints mean the same thing, they allow movement.
Diarthroses
Synovial joint
Synarthroses
Synostosis – Bones joined with bone.
Synchondrosis – Bones joined with cartilage.
Syndesmosis – Bones joined with connective tissue.
Articular cartilage
Hyaline cartilage with collagen fibres distributed in
regard of mechanical stress May be fibrous where shearing forces predominate (margins of glenoid fossa of the
shoulder, acetabulum of hip joint). It lacks of perichondrium (cells replaced by mitosis of the deeper
layers).
Thin vascular membrane with two layers: The intimal layer along with the
underlying subintimal layer is what keeps the synovial fluid locked in the
joint under compression and prevents it from leaking. The intimal cells are
made of fibroblasts and macrophages. The fibroblasts produce hyaluronan and lubricin
to lubricate the joints and the macrophages keep it clean of unwanted material.
Subintimal layer: Adipose and connective tissue, blood
vessels Intimal layer: One to three layers of cells (synovial
cells or synoviocytes)
Two cells types (or
two cell stages)
Type A: 25 % intensely phagocytic, motile. They are macrophages. Type B: 75 % Not
totally clear lineage and functions. Myofibroblast-like cells; secrete collagen, fibronectin, hyaluronic acid. Seems to be
responsible for the production and
absorption of the synovial fluid, which implies that it works on the blood/synovial
fluid exchanges (blood-joint
barrier).
Type B synoviocyte.
Colourless, transparent, viscous fluid, Slightly alkaline Composition varies from
joint to joint Rich in hyaluronic acid Nutritious and lubricant properties: Both articular cartilage and menisci
depend.
Type B: 75 % Not totally
clear lineage and functions. Myofibroblast-like
cells; secrete collagen, fibronectin,
hyaluronic acid. Seems to be responsible for the production and absorption of the synovial fluid,
·
Structural: Main structural provider of the body; attachment for muscles.
·
Protection: Protects organs.
·
Storage: Main depot of calcium and phosphorus.
·
Sanctuary: Postnatal hematopoiesis (hosts the red bone marrow).
Produced by the osteoblasts
Organic components
·
Type I collagen (30% of bone weight, 95% of total organic
components)
·
Type V
collagen (1.5%)
·
Also
traces of type III, X and XI collagen
·
Proteoglycans:
chondroitin 6 sulfate, keratan sulfate
·
Glycoproteins:
sialoproteins, osteocalcin, osteopontin (these bind to the integrins of bone
cells)
·
Glycosaminoglycans
Inorganic components
·
Hydroxyapatite (60%), crystals mostly made of calcium and
phosphorus
·
Water
·
Mononuclear cells
·
Differentiation
from precursors induced by bone
morphogenic protein (BMP) and transforming
growth factor beta
·
Found on
the bone surface,
·
Produce
the extracellular matrix (osteoid)
that later will get calcified.
·
It has an alkaline phosphatase activity (pivotal
for matrix calcification)
·
Secrete macrophage colony stimulating factor
(M-CSF), the receptor for activation of the nuclear
factor Kappa (RANKL), plus osteopontin
(will anchor osteoclast),
osteonecting (joins osteocytes with matrix) and sialoprotein (links osteoblasts to matrix)
·
Gap junctions between themselves and with osteocytes.
As soon as it gets surrounded by matrix, the osteoblast
becomes an osteocyte.
·
Differentiation
from precursors induced by bone
morphogenic protein (BMP) and transforming
growth factor beta
·
Produce
the extracellular matrix (osteoid)
that later will get calcified.
·
Secrete macrophage colony stimulating factor
(M-CSF), the receptor for activation of the nuclear
factor Kappa (RANKL), plus osteopontin
(will anchor osteoclast),
osteonecting (joins osteocytes with matrix) and sialoprotein (links osteoblasts to matrix)
As soon as it gets surrounded by matrix, the osteoblast becomes an osteocyte.
·
Mature form of osteoblasts
·
25 years
life-span
·
Communicate
with each other and with blood vessels using filopodial processes placed inside the canaliculi
·
One per lacuna (no more mitosis or secretion).
·
Large polarized motile cells with 5-100 or more nuclei (average 10-15)·
When they
get active, they secrete the “degrading
environment” and excavate the Howship’s
lacuna
·
Their precursor
is called mononuclear osteoclast
(committed macrophage).
o
Stimulation
with M-CSF promotes mitosis.
o
RANKL binds to it and promote fusion.
o
Osteoprotegerin (OPG) might interfere with RANKL to modulate
differentiation.
Receptors to calcitonin
(but not to parathyroid hormone), colony
stimulating factor 1 receptor, and nuclear
factor Kappa B (RANK
O
Stimulation
with M-CSF promotes mitosis.
o
RANKL binds to it and promote fusion.
Osteoprotegerin
(OPG) might interfere with RANKL to modulate
differentiation
This
is trying to go from elevated Calcium levels to normal levels. The bone is the
major deposit of Calcium in the body. The levels of Ca need to be closely
regulated. When the level is high, you store it in bone. The parafollicular cells detect the
high calcium levels. As a result, they secrete a hormone known as calcitonin. Osteoblasts have calcitonin receptors and that
stimulates them to make a bed of osteotic
bed (osteoid), which needs the 3
components you see above. The collagen and glycosaminoglycans create the framework for alkaline phosphatse to lay down hydroxylapatite. This creates bone
which lowers Calcium levels.
This
is to elevate low calcium levels. This time chief cells of the parathyroid
glands detects the low levels and releases parathyroid hormone. This doesn’t
directly activate the osteoclasts, but first the osteoblast. The osteoblast will secret collagenase which destroys
collagen obviously. This destroys the limiting membrane which protected the
calcified material, and now the osteoclasts will begin to target the crystals of hydroxylapatite, and this releases
the phosphorus and the calcium. As a result, the osteoclasts start dissolving bone and now the Calcium levels go
high, and that activates the mechanism to deal with high calcium levels which
responds by forming collagen which replenishes the limiting membrane.
·
Nutrition and cellular reservoir,
·
Outer
layer of collagen fibres and fibroblasts.
·
Inner
layers with osteoprogenitor cells (easily
differentiate into osteoblasts)
·
There are
also Sharpey’s fibres, which are
collagen fibres that go into the bone and are actually embedded within the
calcified matrix.
·
Found
lining the marrow cavity,
·
Single layer of osteoprogenitor cells and connective tissue
The osteoprogenitor
cells respond mostly to the oxygen concentration. When is high they differentiate into osteoblasts. When low, they
differentiate into chondroblasts. That
is why when blood vessels appear close
to cartilage models, they decay and get replaced by bone.
Primary and secondary bone
In the prenatal life, primary bone appears. It is less strong and well organized,
and most gets replaced by secondary bone
(though it persists in tendon insertions, tooth sockets and suture lines in the
calvaria). Secondary bone is the
usual phenotype we describe as bone.
While both primary and
secondary bone can be compact and cancellous, the classic descriptions of the latter correspond to secondary bone.
Compact: Based in the Haversian system. Its components are illustrated in the image
Volkmann canals, also known as perforating holes, are microscopic structures found in compact bone. They run within the osteonsperpendicular to the Haversian canals, interconnecting the latter with each other and the periosteum. They usually run at obtuse angles to the Haversian canals and contain anastomosing vessels between Haversian capillaries. The Volkmann canals also carry small arteries throughout the bone.
Cancellous (spongy) bone: Based in the trabecula. Main responsible for the mechanical efficiency of the bone.
Bone density and architecture
correlate with the magnitude and direction of the applied load. This means that the mechanical stress is the main morphogenetic influence on bone, and
induces a positive (reinforcement) and
negative (resorption) selection of trabeculae.
Mesenchymal tissue differentiates
into osteoblasts. It is quicker, although less efficient. It is mainly mechanically
induced.
Flat bones of the head Portions of the pelvis Growth of short bones Thickening of large bones
The mesenchymal tissue differentiates
into chondroblasts that create a model. When these cells die, the model is occupied by osteoblasts. It is slower, more efficient. This process is mainly genetically induced.
All large bones
Epiphyseal
plate: Here the endochondral
ossification is organized to replace the cartilage with bone. The layers
of such plate are:
1. Resting
zone: Chondrocytes resting,
lack of mitotic activity.
2. Proliferative
zone: Chondrocytes
proliferating, mitoses are abundant.
3. Hypertrophic
zone: The chondrocytes start
to grow.
4. Calcified
cartilage zone: As the matrix
gets calcified, the chondrocytes die (not as consequence, as far as research
has shown).
5. Ossification
zone: The calcified matrix is
used by the osteoblast as a site to proliferate and create more matrix.
Fracture healing
Bone can only be deposited on a solid base, since mineralization is sensitive to strain.
The natural course of fracture healing with or without a cast (secondary repair):
1. Stabilization of the fractured bone fragments
by callus formation and
fibrocartilage differentiation.
2. Restoration of continuity and bone union by ossification.
3. Substitution of useless areas and partial
correction of misalignment by remodeling.
4. Functional
adaptation.
If surgical fixation is used, intramembranous ossification occurs
instead (primary repair).
Plasma = serum + proteins (blood cloth factors + albumin + antibodies)
Biconcave disk shaped, the shape is maintained mainly by
spectrin. It lacks of nucleus and organelles when it is fully mature. This non-motile
cell is always inside the circulatory system for 120 days. Everyday up to 1
percent of the erythrocytic pool is replaced.
7
micrometres in diameter
Its shape allows easy
and thorough gas saturation as each haemoglobin molecule must be at a critical distance from the membrane.
120 days
Its shape allows easy
and thorough gas saturation as each haemoglobin molecule must be at a critical distance from the membrane.
Integral membrane proteins. Part of the cell membrane, and they face both
the interior and exterior of the cell. Divided into two families: glycophorins and the band 3 protein. The extracellular
portions of these proteins and their corresponding glycocalix components are
responsible for the blood group antigens.
One member of the glycophorin family, Glycophorin
C, is a site for anchoring the
underlying cytoskeletal network. Band
3 protein does the same.
Peripheral membrane proteins. At inner surface of the cell membrane and are
organized in a agonal lattice
network, made of spectrin tertramers,
actin, band 4.1 protein, adducin, band
4.9 protein and tropomyosin. The lattice is anchored to the membrane through the actions of ankyrin (which interacts for that purpose with band 4.2 protein) to the band 3 protein.
Some diseases of these proteins create abnormal RBCs: mutation in the spectrin gene creates
hereditary spherocytosis
(spherical erythrocytes). A deficiency
in band 4.1 protein creates hereditary elliptocytosis, with elliptic erythrocytes. Aside of the
saturation problems these cells face, they also struggle going through the
smallest capillaries and spleen macrophages.
Gas exchange follows diffusion paths: from more concentrated to less concentrated: Arrives to the lung with
low oxygen and high carbon dioxide, and leaves the lung with high oxygen and
low carbon dioxide levels.
1.
Reticulocytes (~ 1 %): Retained strings of rRNA (polysomes), require
a special stain to become apparent (methylene blue, brilliant cresyl blue,
purified azure B, or “reticulocyte stain”).
Howell Jolly bodies: Retained portions of
DNA after the nucleus is expelled
1.
Nucleated erythrocytes: Called ortochromatic erythroblasts or
normoblasts if found in the bone marrow.
6,000 to 10,000 per microlitre.
Divided into granulocytes (neutrophils,
eosinophils, basophils) and agranulocytes
(lymphocytes, monocytes)
Leukocyte granules: Azurophilic and specific. Azurophilic are lysosomes, and the specific are different for each granular leukocyte type.
Neutrophils (polymorphonuclear
leukocytes)
·
60-70 % of leukocytes in blood,
12-15 µm in diameter
·
Nucleus: irregular, with 2 – 5 lobes (most have three lobes)
O
Azurophilic – Contains myeloperoxidase,
defensins (defend the body against a variety of bacteria, fungi, and viruses),
lysozyme (enzyme that degrades bacterial peptidoglycans), azurocidin
(antibacterial activity and antifungal activity against Candida albicans),
bacterial permeability–increasing protein (BPI) (antibacterial activity against
some gram-negative bacteria), enzymes.
o
Specific – Apolactoferrin (binds iron depriving bacteria from it), lysozyme,
collagenase.
o
Tertiary – One type contains metalloproteinases (as gelatinases and collagenases
that facilitate the travel of the neutrophil through connective tissue). The
other type contains phosphatases, and is sometimes called phosphasome.
o
Secretory vesicles – Alkaline phosphatase
60-70 % of leukocytes
Juvenile neutrophils (bands)
·
0.6 % of leukocytes
·
Sausage
shaped (non-lobulated) nucleus
·
Their
number increase in acute bacterial
infectious diseases. When their number is increased, the report might
indicate a "shift to the left".
Marginal pool
Under normal conditions, 90 % of the neutrophils are in the bone marrow,
2 – 3 % are circulating and the rest are in the tissues. Of that 2 – 3 %, one
half circulates, the other lives along
the margins of the smallest blood vessels (particularly at the spleen and
the liver). They quickly enter into the circulation in response of acute stress
(demargination).
2-4 % of leukocytes, they increase in number usually linked to allergic processes (they dampen host’s
response) and parasitic processes (phagocytic
activity)
·
Nucleus: 2 lobes
·
They can recirculate (leave the blood stream and
get back into it).
·
In its azurophilic granules it just has the usual lysosomal enzymes.
·
antiparasitic activity
Major basic protein (MBP) [makes the crystal itself] Eosinophyl cationic protein (ECP) Eosinophil peroxidase (EPO) Eosinophil-derived neurotoxin (EDN) [at the granule matrix]
·
~ 0.5 – 1% of leukocytes in blood
·
12-15 µm
in diameter
·
Nucleus: Irregular lobes
·
Azurophilic granules: Lysosomes.
·
Basophilic granules with heparin, histamine, heparan sulfate and leukotrienes.
·
Unknown precursor, they may complement
the function of mast cells
·
~ 30 % of leukocytes in blood
·
6-8 µm (small), 9-15 µm (medium) and 16-30 µm (large)
·
B, T and N subclasses
·
Nucleus: round or with one indentation
·
Scant and basophilic cytoplasm
·
No granules or azurophilic ones (NK)
·
Scant and basophilic cytoplasm·
No granules or azurophilic ones (NK)
Differentiated in the equivalents of the bursa of Fabricius, they make ~
15 % of the lymphocyte population. They may differentiate into plasma cells or remain as B memory cells once they get exposed to
an antigen.
They differentiate at the thymus,
and account for ~ 80 % of the total
lymphocytes. Further classified into helper, suppressor and cytotoxic classes.
These ones lack of markers
and account for ~ 5 % of the lymphocytes.
Many are natural killer cells and
some might be stem cells (not actual lymphocytes of course, but lymphocytes look-alikes).
NK cells
·
Precursor
of the macrophage
~ 5 % of
leukocytes
·
12-20 µm
in diameter
·
Nucleus: kidney-shaped
·
Cytoplasm:
basophilic
·
No
granules or very fine azurophilic ones; vesicles
·
Half-life in blood: 12 to 24 h
·
Precursor
of the macrophage
These little cells (300,000 per
microlitre, 2-4 µm in diameter, the smaller
are older and the larger younger) are fragments of the megakaryocytic cytoplasm. Each megakaryocyte produces 1000 – 1500 platelets. One third of the
total number are sequestered in the spleen, and the mean life span is 9-12 days (after then they are removed
by the spleen).
If necessary,
platelet production can be increased up
to eight times
300,000 per microlitre
Are fragments of the megakaryocytic cytoplasm.
Two cytoplasmic regions:
Hyalomere: Peripheral, light blue stained Granulomere: Central, with purple granules: Delta granules with serotonin; Lambda granules are lysosomes; Alpha granules have fibrinogen
The serotonin content of the platelets correlate
with the brain serotonin levels, hence
providing a non-invasive method to assess the dynamics of that
neurotransmitter in the CNS.
Collagen exposure is followed by platelet adherence.
Subsequently, thrombin will attract
other platelets and the network of fibrin
will entrap them, creating a haemostatic
plug.
Erythropoiesis Leukopoiesis Thrombopoiesis
Yolk sac: First week
Hepatic (& splenic)
phase: From 3rd to 7th
month (matter of debate)
Bone marrow phase: Starts at 5th - 7th month
After the 10th
birthday, hemopoiesis is confined to the ribs, sternum, pelvis and the proximal epiphysis of the femur and
the humerus.
Yellow
Adipose tissue
Non-functional
Can be replaced by
red marrow if needed
Red
Hemopoietic tissue
Interspersed
adipocytes
·
Stroma: Reticular cells (currently known as adventitial cells) and the reticular fibres they create.
94)
It is made mainly by hemopoietic cells.
·
Hematopoietic cords: Haemopoietic cells and macrophages organize
themselves in these loose cords.
·
Sinusoidal capillaries: Surround the cords and being so open allow an
easy exchange of substances and cells.
·
Stroma: Reticular cells (currently known as adventitial cells) and the reticular fibres they create.
·
Other
cells: Adipocytes, osteoclasts,
osteoblasts, macrophages, plasma cells.
·
There is not a barrier or any other protective
mechanism, so it is very exposed to
noxious influence.
·
Microenvironmental conditions: Certain conditions of the extracellular
matrix.
·
Growth
factors: Hemopoietins (colony
stimulating factors CSF, growth factors).
Stem cells
Able to produce all the subsets of hemopoietic cells
·
Stem cells
lack of morphological unique
characteristics, but they may look like large lymphocytes (granular, maybe)
CFUs
Cells only capable of producing one
particular subset of blood cells are known as colony forming units (CFU)
PPSC (pluripotential stem cell) gives raise to the CFU-Ly (colony forming unit – lymphoid)
from which lymphocytes develop; and to the CFU-GEMM
(colony forming unit – granulocytic,
erythrocytic, monocytic and megakaryocytic)
from which granulocites (neutrophils, basophils, eosinophils), erythrocytes,
monocytes and megakaryocytes (they produce platelets) develop, respectively.
CFU-GEMM includes:
Burst Forming Unit-erythroid (BFU-E)
becomes the CFU-E for the erythroid
lineage
CFU-Eo for the eosinophilic lineage
CFU-Ba for the basophilic lineage
CFU-GM (granulocyte-monocyte) which differentiates
into:
CFU-G for the neutrophilic lineage
CFU-M for the monocyte-macrophage lineage
CFU-Meg for the megakaryocyte lineage
Erythropoiesis: Colonies made of cells with round nuclei; cytoplasm becomes
more homogeneous.
1.
What
characterizes the granulocytopoietic colonies?
Thrombocytopoiesis:
Big cells, with multilobulated nuclei
7 days
~ 7 days from proerythroblast to reticulocyte. It is stimulated by erythropoietin, and requires vitamins (B12, B6, C, E, folic acid, riboflavin,
pantothenic acid, thiamin) and metals (iron, cobalt, manganese) plus aminoacids
Proerythroblast Basophilic
erythroblast (prior and
during this stage the peak of rRNA
formation is reached, and haemoglobin
synthesis starts) Polychromatophilic
erythroblast Ortochromatic
erythroblast (sometimes wrongly
called nucleated erythrocyte,
it is the last nucleated cell of
the lineage and the earliest that
can circulate). Reticulocyte
Erythrocyte
Basophilic
erythroblast (prior and
during this stage the peak of rRNA
formation is reached, and haemoglobin
synthesis starts)
Ortochromatic
erythroblast (sometimes wrongly
called nucleated erythrocyte,
it is the last nucleated cell of
the lineage and the earliest that
can circulate).
Myeloblast Promyelocyte Myelocyte
(specific granules appear, so
at this stage the differentiation
of the eosinophilic, basophilic and neutrophilic colonies start) Metamyelocyte Band Mature
granulocyte
Notice that the myelocyte stage is not only the end of the mitotic phase of
granulocytopoiesis, but also the stage in which specific granules appear and hence the three granulocyte lineages can be distinguished.
Myelocyte stage
14 days
Megakaryoblasts, megakaryocytes.
And up to 64n
Platelets are released from the megakaryocyte cytoplasmic fragmentation.
·
the one at
the upper third of the esophagus and
at the oropharynx.
Muscle fibre
Lacks of gap junctions
·
Myofibrils: Arrangement of sarcomeres. They require desmin and plectin to
get properly organized and stabilized.
·
Myofibrils: Arrangement of sarcomeres. They require desmin and plectin to
get properly organized and stabilized.
Desmin and plectin
·
Myofilament: Thick (myosin II, myomesin,
titin and C protein) and thin (F-actin, tropomyosin, troponin and
associated proteins) ones
The molecule myostatin restricts the size of the muscle fibres
Organization of the skeletal muscle
Endomysium: Surrounds the muscle fibre. Perimysium: Surrounds bundles of muscle fibres.
Epimysium: Surrounds several bundles
, between
two Z lines
·
Darker bands (A bands); H band is a pale central band of the
A band where filaments do not overlap (there tropomodulin caps the minus-end of F-actin to prevent its unwanted
growth)
·
The M line is a lighter zone at the centre
of the H band, and it contains the lateral connections between adjacent thick
filaments linked by myomesin
Lighter bands (I bands) are bisected
by a dark line (Z line).
Nebulin (aligns the actin filament at its core, it’s
anchored to the Z line with its carboxy terminal while its amino terminal ends
in the A band)myosin filament we have titin,
which also anchors the latter to the Z line (similar to what nebulin does with the actin filament)
Peripherally such Z discs are anchored to the
sarcolemma by vinculin and dystrophin in regions called costameres.
· Sarcoplasmic
reticulum (smooth endoplasmic
reticulum) sequesters calcium bound to calsequestrin
· Transverse
(T) tubules system
(invaginations of the cell membrane). They spread the depolarization impulse,
and exist at the level of the A-I
junction.
Triad: Expanded cisternae of the sarcoplasmic reticulum of each side
adjacent to each T tubule.
Troponin and tropomyosin are
intimately related with the actin
molecule and are fundamental for contraction
O
Troponin T: tail of the molecule, anchors the troponin complex to tropomyosin
o
Troponin C: has the binding site for calcium
(calmodulin-like?)
o
Troponin I: binds to actin to inhibit
the interaction between actin and myosin
1.
Binding of calcium to troponin forces
tropomyosin to move, exposing
the myosin-binding sites of the
actin molecule.
2.
Myosin head binds to actin and ATP breaks into
ADP; such energy is used the
myosin head.
3.
The actin filament slides over the myosin
one.
4.
The process repeats.
Nerve-motor unit
1.
One motor neuron fibre.
2.
Any number of muscle fibres.
The smaller the number of fibres
innervated by the motor neuron fibre, the higher the precision and delicacy of movement.
134)
Neuromuscular junction
Acetylcholine is released from the motor neuron into the
synaptic space, and it binds with the receptor
at the muscle fibre inducing membrane
deporalization.
Excess of
acetylcholine is hydrolyzed by cholinesterase.
The depolarization
is internalized via the T tubule inducing the sarcoplasmic reticulum to release calcium.
Propioceptors that maintain the posture and help to coordinate the activity of opposing
muscle groups. They are made of:
Connective tissue Fluid-filled space Thick and thin fibres (intrafusal fibres)
Sensory
(stretch sensitive) nerve fibres
Sensory nerves that penetrate the connective tissue sheath encapsulating
bundles of collagen fibres (continuous with those that make the myotendinous junction). They detect tensional differences in tendons.
Highly specialized system, with collagen
fibres deeply intertwined with the muscle fibres (the collagen fibres insert into infoldings of the plasmalemma
of the muscle fibres).
Types of muscle fibres
Type
I
Type
IIa
Type
IIb
Slow
twitch fatigue resistant
Fast
twitch fatigue resistant
Fast
twitch fatigue prone
Very rich
in mitochondria
Many
mitochondria but also glycogen
Lesser
amount of mitochondria
Rich in
myoglobin (red)
Less
myoglobin (light red)
Scant
myoglobin (light pink)
Continuous
low tension contraction
Continuous
high tension contraction
Short
term high tension contraction
Oxidative
phosphorylation of fatty acids
Oxidative
phosphorylation of fatty acids plus glycolysis
Glycolysis
predominates over mitochondrial activity
↑↑↑ succinate dehydrogenase
↑↑ succinate dehydrogenase
↑ succinate dehydrogenase
Hikers, marathoners,
triathletes
Middle distance
swimmers, 400-800 m
spinters, hockey players, wrestlers, martial arts
Weight-lifters,
short-distance sprinters
Myoglobin is similar to hemoglobin in the sense that binds oxygen, but acts only
within the muscle fibre
·
Mononuclear (some cells binucleated) striated
trouser-shaped cells 15 µm diameter and 85-100 µm in length.·
Intercalated disks with gap junctions
·
Defined sarcomere.
·
Fatty acids are the major fuel of cardiac muscle.
Keeps noticeable amounts of lipofuscin
in the cytoplasm.
·
80 % of the cell volume is occupied by mitochondria.
·
Fatty acids are the major fuel of cardiac muscle.
Granules, 0.2-0.4 µm in diameter, more abundant in
the juxtanuclear area of the cells of the right
atrium, contain the high-molecular weight precursor of the atrial natriuretic factor and brain natriuretic factor.
Intercalated disks
Limit between two continuous cardiac cells, with a straight line or
step-like pattern, which has junctional complexes (gap junctions and others).
·
Transverse portion: Fascia adherentes and desmosomes plus hemi-Z
lines.
·
Lateral portion: Gap junctions (connexons made by connexins)
145)
Tubular system
·
At the
level of the Z line and not as regular as in skeletal muscle.
·
The T tubules are larger and more numerous.
·
Diads: One T tubule and one sacoplasmic reticulum cisterna
·
From small (20 µm) in small blood vessels to large (up to 500 µm) in the pregnant
uterus.
·
Mononuclear cells,
·
Rudimentary sarcoplasmic reticulum,
·
Absence of T tubules (caveoli instead)
·
Presence
of gap junctions.
·
Lattice-like
pattern arrangement of actin-myosin
complexes
·
Dense bodies (cytoplasmic and membrane-related) are the equivalent to the Z line, which means actin is anchored there.
·
Mitochondrial
content is highly variable but overall
low.
·
Absence of T tubules (caveoli instead)
·
Dense bodies (cytoplasmic and membrane-related) are the equivalent to the Z line, which means actin is anchored there.
Smooth muscle patterns
Syncytial
Multiunit smooth muscles
Syncytial contraction
Abundant gap junctions
Poor nerve supply
Large sheets in hollow viscera
Precise and graded contraction
Rich innervation
Few gap junctions
Iris of the eye
The nerve supply in syncytial smooth tissue has regulatory but not excitatory
functions. In the multiunit type of
smooth muscle, the sympathetic and parasympathetic divisions of the autonomous nervous system hold control
of the muscle activation.