Tissues Pt.2 Flashcards
(34 cards)
Bone
bone is connective tissue
Hard, calcified CT
2 meanings:
Osseous tissue
(2 types = spongy bone & compact)
OR
Organ, named bone = more than just osseous tissue)
General features of bone as an organ
typical long bone
Typical Long Bone
2 types = spongy
(trabecular / cancellous - strength with reduction in weight) + compact
Organ = other tissue
types: epithelium,
nervous and other types of CT
Functions: support, protection; attachment site for muscles (levers);
marrow = blood formation; electrolyte balance; pH balance;
detoxification (repository)
Diaphysis - growing through
Epiphysis - growing upon
Epi = in addition, upon
bone cell (4)
Deposition = osteoblasts
(lay down bone tissue - non-mitotic)
Maintenance = osteocytes
Remodelling = osteoclasts
(multinucleate cells, bone macrophages)
Macrophage = large eater
Bone = cells + matrix
Organic (1/3) = collagen fibres +
protein & carbohydrate complexes
Collagen = resistance to twisting and
bending forces (bone is brittle in its absence - shatter)
(Osteogenesis imperfecta = brittle bone disease)
Inorganic (2/3) = calcium salts (mainly
calcium phosphate salts)
Bone loses rigidity in its absence
(Rickets & Osteomalacia - soft bones)
epiphyseal line
mature, represents bony joint
osteocytes and canaliculi
Osteocytes nourished via diffusion
- facilitated by gap junctions between cells.
Cell processes travel through small canals called canalicili.
epiphyseal plate
epiphyseal plate = growing
compact bone
Units of bone structure = osteon
= concentric rings of bone
Outer bone
- circumferential lamellae
Blood vessels
- central artery & vein.
muscle, stuff to know!!
must be able to describe the characteristics, function and location of different types of muscle
overview of muscle
3 types: skeletal, cardiac and smooth.
All forms are:
- Excitable
- Extensible - able to stretch between contractions
- Elastic - recoil
- Contractile
- Highly cellular
- Well vascularised
- All contain large numbers of the myofilaments required for contraction.
The 3 types of muscle differ in terms of:
- Where they are found
- Structure of their cells
- How they are activated to contract
Main functions relate to:
* Movement
* Stabilisation (e.g. around joints)
* Maintenance of posture
* Generating heat (skeletal muscle - shivering during cold stress)
* Blood glucose regulation (absorb, store & use glucose)
skeletal muscle (voluntary and striated)
Striated = cross-striations across the muscles cells.
Control is largely voluntary but reflex (involuntary) movements are also possible.
Most is attached to bone - movement
of appendicular and axial skeleton.
BUT
Visceral striated muscle = morphologically identical to skeletal
muscle but restricted to soft tissues.
Examples: tongue, pharynx, upper part of the esophagus, lumbar part of the diagram (speech, swallowing &
breathing).
Contraction = rapid BUT skeletal muscle tires quickly and
requires rest to recover.
Refractory period = 1-2 milliseconds.
(RP = time between when muscle is stimulated to contract and how long before it can be stimulated again).
A named muscle is a discrete organ - contains many muscle fibres (cells), lots of connective tissue, which carries blood vessels and nerves.
Terminology:
Myo = muscle
Myofibre* = muscle cell
Sarco = flesh
Sarcolemma = cell membrane (lemma = husk)
Sarcoplasm = cytoplasm
Sarcoplasmic reticulum = SER (reticulum = little net) - calcium storage
muscle fibre
Long protein cords = myofibrils
- Lots of mitochondria - packed into spaces between myofibrils
- Abundance of glycogen stored as granules called glycosomes (= glycogen bodies)
- Each myofibril = a bundle of parallel
protein microfilaments = myofilaments
3 types of myofilaments:
* Thick filaments = myosin
* Thin filaments = actin AND
* Elastic filaments
Individual skeletal muscle cells are cylindrical.
Typical muscle cell is about 100 umetres in diameter (may be as great as 500 metres) and from 3 - 30cms long (but can be up to 1m).
Due to their length skeletal muscle cells are termed myofibres (muscle fibres).
Multinucleated cells = fusion of cells called myoblasts during
embryonic development.
Each myoblast contributes its nucleus.
Syncitium: syn = together; -cytium = cells.
Functionally acting together as one cell.
Nuclei are positioned against the cell membrane = peripherally placed.
Some myoblasts remain as unspecialised satellite cells - role in regeneration of damaged skeletal muscle.
BUT
Limited possibility for repair - in adults, skeletal muscle cells are not able to replicate.
need to know about striations
- An individual muscle cell contains lots of myofibrils.
- Each myofibril is made up of hundreds of sarcomeres arranged end to end.
- Sarcomeres = contractile units of the muscle fibre.
- Muscle contraction occurs because actin and myosin filaments slide over each other = shortening of the sarcomere = sliding filament theory.
- Shortening of hundreds of end
to end sarcomere = shortening
of entire muscle.
Motor Neurons & Motor Units
- Skeletal muscles are innervated by nerve fibres that arise from the brain stem and the spinal cord.
- If the nerve fibres are damaged, skeletal muscle cannot contract.
- Each nerve fibre branches out to supply multiple muscle fibres.
- Each individual muscle fibre (cell) receives its nerve supply from the terminal branching of a nerve.
(Electrically insulated due to amount of surrounding connective tissue)
- All muscle fibres innervated by the terminal branchings of a single nerve behave as a functional unit.
- One nerve fibre + all the muscle fibres it
innervates = motor unit.
Motor units
~200 muscle fibres are innervated by each motor neuron
BUT the structure of motor units relates to their function.
Fine control = 1 motor neuron + 3-6
muscle fibres (cells) = small motor units.
Examples = muscles of eye movement & hand.
Strength = 1 motor neuron + up to 1000 muscle fibres (cells) = large motor units.
Examples = postural and locomotor
muscles (back & lower limbs).
Multiple motor units in each muscle = some able to rest & recover while some are active
= differential rates of fatigue in a muscle units allow for sustained muscle function.
cardiac muscle (involuntary and striated)
Cardiac muscle = heart only
Starts beating by week 4 of embryological development and never stops until you die
Cells are called cardiomyocytes (cardiocytes).
Cardiocytes:
- are shorter than skeletal muscle (50-100 umetres and thicker relative to their their size (10-20 umetres).
- can contract without nervous stimulation = autorhythmic BUT moderated by autonomic nervous control (sympathetic & parasympathetic)
- contain a single nucleus
- are branched cells
- are rich in glycogen (energy store)
- exhibit specialised junctions with each other = intercalated discs
- exhibit a low level of cell division (1%) but insufficient to repair damage. No satellite
cells. Damage = scarring.
Intercalated discs (2 parts):
Intercalated discs (2 parts):
- Mechanical junctions = desmosomes = tissue integrity: keeps cells firmly bound to each other.
- Electrical junctions = gap junctions; allows each cardiocyte to directly stimulate adjoining cells.
- Cardiac muscle acts as a syncytium (= all cells acting as one)
- Electrical barrier between atria (thin walled chambers) and ventricles (thicker walled) of the heart.
- Atria contact together; ventricles contract together.
- Cardiac muscle refractory period = 250 milliseconds - allow?) for full ejection of blood from chambers before refilling.
TEM - note the following:
Presence of sarcomere (same contractile units as skeletal muscle); abundant mitochondria; intercalated discs (electron dense) = desmosomes + gap junctions
smooth muscle (involuntary and non-striated)
= visceral muscle (viscera = internal organs)
Found in the walls of organs, usually layered - depends on location
Like cardiac muscle is auto-rhythmic so can contract independent of nervous stimuli
Responds to multiple stimuli - chemicals, hormones, pH, CO2, 02, temperature, stretch.
Specialised for slow, prolonged contraction
mitochondria in cardiac muscle
- Mitochondria in cardiac muscle are larger and more abundant compared to skeletal muscle.
- Mitochondria occupy ~ 25% of the cell in cardiac muscle
(skeletal muscle mitochondria ~ 2%)
smooth muscle cells
Smooth muscle cells:
- can secrete connective tissue matrix (well developed RER and Golgi) - collagen, reticular fibres & elastin (depends on location).
- are capable of cell division to maintain or increase their numbers.
Gap junctions are produced according to need (e.g. uterus during pregnancy)
