Tissues Pt.2

Question 1

Bone

Answer 1

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

Question 2

typical long bone

Answer 2

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

Question 2

bone cell (4)

Answer 2

Deposition = osteoblasts

(lay down bone tissue - non-mitotic)

Maintenance = osteocytes

Remodelling = osteoclasts

(multinucleate cells, bone macrophages)

Macrophage = large eater

Answer 3

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)

Question 3

epiphyseal line

Answer 3

mature, represents bony joint

Question 4

osteocytes and canaliculi

Answer 4

Osteocytes nourished via diffusion

• facilitated by gap junctions between cells.

Cell processes travel through small canals called canalicili.

Question 4

epiphyseal plate

Answer 4

epiphyseal plate = growing

Question 5

compact bone

Answer 5

Units of bone structure = osteon

= concentric rings of bone

Outer bone

• circumferential lamellae

Blood vessels
- central artery & vein.

Question 6

muscle, stuff to know!!

Answer 6

must be able to describe the characteristics, function and location of different types of muscle

Question 7

overview of muscle

Answer 7

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)

Question 7

skeletal muscle (voluntary and striated)

Answer 7

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).

Answer 8

A named muscle is a discrete organ - contains many muscle fibres (cells), lots of connective tissue, which carries blood vessels and nerves.

Answer 8

Terminology:

Myo = muscle

Myofibre* = muscle cell

Sarco = flesh

Sarcolemma = cell membrane (lemma = husk)

Sarcoplasm = cytoplasm

Sarcoplasmic reticulum = SER (reticulum = little net) - calcium storage

Question 9

muscle fibre

Answer 9

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

Answer 9

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.

Question 10

need to know about striations

Answer 10

• 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.

Question 10

Motor Neurons & Motor Units

Answer 10

• 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.

Question 10

Motor units

Answer 10

~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.

Question 11

cardiac muscle (involuntary and striated)

Answer 11

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.

Question 12

Intercalated discs (2 parts):

Answer 12

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.

Answer 12

TEM - note the following:

Presence of sarcomere (same contractile units as skeletal muscle); abundant mitochondria; intercalated discs (electron dense) = desmosomes + gap junctions

Question 13

smooth muscle (involuntary and non-striated)

Answer 13

= 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

Question 13

mitochondria in cardiac muscle

Answer 13

• 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%)

Question 14

smooth muscle cells

Answer 14

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)

Answer 14

Cells are fusiform in shape (wide middle with tapered ends). Range in length: 20 umetres = small blood vessels;

200 umetres = intestinal wall; 500 umetres = wall of uterus during pregnancy

Non-striated appearance because contractile elements are not arranged in regular repeating units as is the case for skeletal and cardiac muscles

Dense bodies are analogous to the Z lines in striated muscle (Z lines demarcate sarcomeres).
They anchor the thin (actin filaments).

Nuclei can have a corkscrew appearance in contracted SM

Question 14

how do smooth muscle cells communicate

Answer 14

they communicate via gap junctions (can act like a syncytium)

Question 14

comparing muscle types in histological sections

Answer 14

Histological characteristics of the 3 muscle types differ according to:

• Presence or absence of striations
• Cell shape (cylindrical, branching, fusiform)
• Cell length (long vs short)
• Number of nuclei in a cell (one vs several)
• Position of nuclei (peripheral vs central)
• Intercalated discs (present vs absent)

Question 15

muscle in cross section

Answer 15

Increase in the size of skeletal and cardiac muscle occurs via hypertrophy

(hyper = over; trophy = nourishment)
Increases in smooth muscle occurs via hypertrophy and hyperplasia
(-plasia = formation)

Answer 16

Objective: Describe the characteristics, function and location of the different types of muscle.

Example Exam Question: Compare and contrast the structural features of cardiac and smooth muscle.

Compare = what do they have in common?

Single, centrally placed nucleus;
Same contractile elements (actin and myosin);

Both have gap junctions;

Both are short relative to skeletal muscle

Contrast = how do they differ?
Intercalated discs in CM; dense bodies in SM

Different cell shape (cardiac = branched; smooth = fusiform);
CM is striated; SM is not;

Not relevant to this question = involuntary; each behaves as a syncytium.

Question 17

shape of smooth muscles

Answer 17

Cells are fusiform in shape (wide middle with tapered ends). Range in length: 20 metres = small blood vessels;

200 metres = intestinal wall; 500 metres = wall of uterus during pregnancy

Non-striated appearance because contractile elements are not arranged in regular repeating units as is the case for skeletal and cardiac muscles

Dense bodies are analogous to the Z lines in striated muscle (< lines demarcate sarcomeres).

They anchor the thin (actin) filaments.

They also anchor smooth muscle cells to each other.

Question 17

smooth muscle

Answer 17

= 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, COz, 02, temperature, stretch.

Specialised for slow, prolonged contraction

Question 18

Histological characteristics of the 3 muscle types differ according to:

Answer 18

• Presence or absence of striations
• Cell shape (cylindrical, branching, fusiform)
• Cell length (long vs short)
• Number of nuclei in a cell (one vs several)
• Position of nuclei (peripheral vs central)
• Intercalated discs (present vs absent)

Question 18

smooth muscle cell communication

Answer 18

smooth muscle cells communicatre via a gap junction (can act like a syncytium)

Question 18

muscle in cross-section

Answer 18

Increase in the size of skeletal and cardiac muscle occurs via hypertrophy

(hyper = over; trophy = nourishment)

Increases in smooth muscle occurs via hypertrophy and hyperplasia
(-plasia = formation)

cardiac is single nucleus, centrally placed, striated, involuntary with intercalated disks, branched shape.

smooth is single nucleus, centrally placed, non-striated, involuntary without intercalated disks, fusiform shape.