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BLOCK C > Histology > Flashcards

Histology Flashcards

1
Q

Subdivisions of muscle

A

Muscle >muscle fibers(cell) >myofibrils >sarcomeres

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2
Q

Embryological layer origin of muscle tissue

A

Mesodermal.

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3
Q

Describe muscle fibers of skeletal striated muscle

A

Multinucleated cells
Nuclei in the perphery
Banding pattern.
Striated.

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4
Q

Describe muscle fibers of cardiac muscle

A

1 nucleus in the center
Largest amount of capillaries per sq meter.
Contains intercalated disks.
Striated

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5
Q

Describe muscle fibers of smooth muscle

A

A lot of actin.
No myofibrils: only myofilaments (actin)
Centrally located nuclei
Cells uniformely shaped. Myofibrils not seen in cross section.

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6
Q

Type of contraction in each muscle

A

Skeletal: quick, forceful, voluntary
Cardiac: involuntary, rigorous, rhythmic
Smooth: slow, involuntary

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7
Q

Which types of muscles undergo hypertrophy vs hyperplasia?

A

Hypertrophy: striated skeletal and cardiac

Hyperplasia: smooth muscle (eg. endometrium)

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8
Q

Most abundant type of muscle

A

Skeletal striated muscle.

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9
Q

Distinguish between endomysium, perimysium and epimysium in the skeletal striated muscle.

A

Epimysium: periphery of muscle
Perimysium: separate bundles of muscle fibers (septa). Contain gap junction.
Endomysium: separation of individual muscle fibres.

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10
Q

What is a junctional complex in the striated skeletal muscle?

A

Skeletal muscle has fingerlike projections at its end containing actin inserting into connective tissue. This is also called musculotendinous junction.

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11
Q

Name for a bundle of muscle fibers

A

Fascicle

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12
Q

Describe the sarcomere of the striated muscle cell

A

The Z lines delimit the sarcomere (contains alpha-actinin to bind to actin molecules)
- Thin actin filaments of from Z line and penetrate into A band, but not until middle.
- Thin myosin filaments start in the middle (H band) and extend towards the Z line.

A band: thick and thin filaments. In the middle: H band is only myosin, since actin does not reach the middle. M line is in the middle of the H band and is where myosin originates (contains creatine kinase).

I band: only actin filaments, contains Z line from which actin protrudes.

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13
Q

3 subunits of troponin binding to actin

A

TnI: inhibition of the actin-myosin interaction
TnC: binding of Ca2+
TnT: anchoring to tropomyosin

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14
Q

Mechanism of striated skeletal muscle contraction

A

The AP is transmitted to the cell via the T Tubule (triad). AP causes the depolarization of the SR, which now releases Ca2+.

  1. Ca2+ influx from the SR.
  2. Ca2+ binds to TnC of troponin
  3. Myosin can now bind to actin because the tropomyosin moves away upon Ca2+ binding.
  4. Myosin head bending causes sliding of the thin filament over the gthick filament.
  5. Ca2+ is removed by the SR through the ATPase calcium pump.
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15
Q

What happens to different bands of the sarcomere when there is contraction?

A
  1. H band becomes shorter because thin filaments are displaced towards the center.
  2. Sarcomere becomes shorter.
  3. I band becomes shorter.

Thick and thin filaments do not change in length

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16
Q

Name 3 other less important proteins that bind to skeletal muscle fibers

A

Tropomodulin, titin (supports myosin), nebulin (stabilizes actin)

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17
Q

What enzyme does the M line contain?

A

Creatine kinase

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18
Q

Where does the AP travel inside the skeletal muscle fiber? Where is this structure lcoated?

A

Inside the t-tubule, which is an invagination of the sarcolemma.

T tubule is located between 2 adjacent cisternae. Located at the A-I junction.

AKA triads.

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19
Q

What structure allows calcium to be pumped back into the SR for muscle relaxation?

A

Calcium ATPase. Located at the membrane of the SR.

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20
Q

ID A, I and Z bands on this image

A
21
Q

True or False: the perimysium surrounds the fascicle.

A

True. Fascile = bundle of muscle cells.
Then, inside, the endomysium surrounds individual muscle cells, which in turn contain myofibrils.

22
Q

What is the terminal bouton?

A

AKA neuromuscular junction or motor end plate.
This is where the myelinated motor nerves branch out within the perimysium and endomysium, and lose their myelin sheath. 1 Nerve can innervate several muscle cells.

23
Q

Describe the neuromuscular junction to transmit AP

A

The basement membrane of the muscle cell is continuous with the BM of the axon.

The post-synaptic membrane is folded and very irregular.

Axon releases ACh onto ACh Receptors. Na+ flows into the cell and K+ flows out, creating depolarization. There are T tubules that are continuous with the sarcolemma and go deep into sarcoplasm.

24
Q

What is myasthenia gravis?

A

An autoimmune disease due to presence of auto-Abs against acetylcholine receptor. No muscle contraction.

25
Q

3 walls of the heart

A

Epicardium (periphery, visceral serous pericardium)
Myocardium (flesh, main part)
Endocardium

26
Q

2 layers of the pericardium, and subdivision of the serous layer.

A

External layer: fibrous pericardium
Internal layer: serous pericardium

Internal serous pericardium: parietal serous pericardium (in contact with fibrous) and visceral serous, AKA epicardium.

27
Q

Are intercalated disks features of only cardiac muscles?

A

Yes. They contain gap junctions and are very important for the AP propagation through the heart.

Intercalated disks separate two adjacent cardiac myocytes.

28
Q

3 zones making up the intercalated disk

A
  1. Zonula adherens (transverse)
  2. Macula adherens (transverse)
  3. Gap junction (lateral)
29
Q

What are gap junctions made up of?

A

Coupled connexons.
Each connexon is made up of 6 connexins, which together create a half-channel. The half-channel is connected to that of the next cell, which creates a gate through which Ca2+ can flow.

30
Q

Where are triads and diads located on cardiac muscle cells?

A

At the Z line (opposed to skeletal muscle cells, where they were located at the A-I junction)

31
Q

Are there gap junctions in smooth muscle?

A

Yes.

32
Q

Appearance of contracted smooth muscle

A

Skewed appearance.

33
Q

Process of contraction in smooth muscle

A
  1. Ca2+ influx
  2. Ca2+ activates myosin light chain kinase such that the heavy chains can now bind actin.

Myosin phosphatase is what causes relaxation upon decreased Ca2+ levels.

34
Q

What are dense bodies in smooth muscle cells?

A

Located on plasma membrane, rich in alpha-actinin and dystrophin. “Z line”. This is from where the actin filaments emerge.

35
Q

3 muscle disorders and what causes them

A
  1. Ehlers-Danlos syndrome. Mutation in smooth muscle fibers. Affects CT.
  2. Myasthenia gravis. Abs destroy ACh-receptpros so no more APs and muscle excitability.
  3. Muscular dystrophy. Mutation in dystrophin and laminin genes.
36
Q

What is a vasa vasorum?

A

A vessel within the vessel

37
Q

What is IELM in a vessel?

A

internal elastic limited membrane.
Present in the muscular artery, like a sleeve, sometimes fenestrated.

38
Q

3 main histological layers of blood vessels

A

Intima (Endothelium, Sub-endothelial layer)
Media (elastic membranes and/or smooth muscle cells)
Adventitia (CT, vasa vasorum)

39
Q

Condition for a vessel to be considered an artery in histology vs condition to be considered arteriole

A

If there are >4 layers of smooth muscle cells in the media.

< 2 : arteriole.

40
Q

What causes varicose veins?

A

Dysfunction of the valves in the veins. Due to high blood pressure in superficial veins.

41
Q

Is there IELM in the media of veins? What about adventitia and vasa vasorum?

A

No IELM.
There can be vasa vasorum in large veins.
Adventitia is very prominent.

42
Q

How are smooth muscle cells organized despite their intrinsic disorganization?

A

Thanks to lamellae: smooth muscle cells are short and their extremities attach to adjacent lamellae. These contribute to solidity and resilience of the wall.

43
Q

How much times greater than the volume of the aorta is the volume of the capillaries?

A

800x greater

44
Q

Classification of capillaries according to permeability

A
  1. Permeable: fenestrated or sinusoids.
  2. Impermeable/continuous
45
Q

Is there a BM in lymphatic vessels?

A

No

46
Q

What causes vasoconstriction and what causes vasodilation in smooth muscle cells?

A

Vasoconstriction: endothelin binding to receptor causing Ca2+ increase.

Vasodilation: NO, promoting conversion from GTP to cGMP leading to vasodilation.

47
Q

How is fibrin formed?

A

Thrombin acts on fibrinogen to convert it to fibrin.

48
Q

Metabolic functions of the endothelium (2)

A
  1. Conversion of Angiotensin I to II
  2. Inactivation of Bradykinin and of serotonin, prostalgandins, NE, etc

BLOCK C (7 decks)

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