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HISTOLOGY & EMBRIOLOGY II > LECTURE 7 (Cardiac and Smooth Muscle) > Flashcards

LECTURE 7 (Cardiac and Smooth Muscle) Flashcards

1
Q

Describe the embryonic development of Cardiac Muscle

A

Mesenchymal cells around the primitive heart tube align into CHAINLIKE ARRAYS -> Cells within one fiber branch and join with cells in adjacent fibers -> Heart consists of cells INTERWOVEN in SPIRALING layers that provide for a characteristic wave of contraction that wrings out of the heart ventricles

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2
Q

Describe the structure of Cardiac Muscle

A
  • Striated
  • One nucleus that is centrally located
  • ENDOMYSIUM containing rich capillary network surrounds cells
  • PERIMYSIUM separates bundles and layers of muscle fibers
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3
Q

Describe the transverse lines that cross the fibers in cardiac muscle

A
  • INTERCALATED DISCS which cross the fibers at irregular intervals where the myocardial cells join
  • Transverse & Longitudinal regions
  • TRANSVERSE REGIONS = composed of DESMOSOMES and FASCIA ADHERENS JUNCTIONS which provide strong intercellular adhesion during the cells’ constant contractile activity
  • LONGITUDINAL REGIONS = filled with GAP JUNCTIONS that act as electrical synapses
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4
Q

What is present in Cardiac and Skeletal muscle cells?

A
  • Mitochondria (40%)
  • Fatty acids (stored as triglycerides in small lipid droplets)
  • Glycogen granules
  • Perinuclear lipofuscin pigment granules
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5
Q

What is the difference between T-tubules in ventricular muscle fibers and atrial muscle fibers?

A

VENTRICULAR
- well-developed
- large lumens
- penetrate the sarcoplasm in the vicinity of the myofibrils’ Z discs

ATRIAL
- smaller/entirely absent

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6
Q

Sarcoplasmic reticulum is less well-organised in cardiac compared to skeletal muscle fibers (TRUE/FALSE)

A

TRUE

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7
Q

What differentiates the T-tubules in cardiac cells than in skeletal muscle fibers?

A

Cardiac cells have DYADS instead of TRIADS

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8
Q

What can Cardiac muscle fiber contraction be described as?

A

Intrinsic and spontaneous

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9
Q

What is the difference between contraction in cardiac muscle and skeletal muscle?

A

CARDIAC MUSCLE
- continuous contraction
- initiated, regulated and coordinated locally by nodes of unique myocardial fibers

SKELETAL MUSCLE
- contraction of individual myocardial fibers is all-or-none
- Rate of contraction is modified by autonomic innervation at the nodes of conducting cells (SYMPATHETIC = accelerates, PARASYMPATHETIC = decreases )

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10
Q

What are the properties of secretory granules in cardiac muscle?

A
  • Found near atrial muscle nuclei
  • Associated with small Golgi complexes
  • Release the peptide hormone ATRIAL NATRIURETIC FACTOR (ANF) which acts on target cells in the kidney to affect Na+ excretion and water balance
    [contractile cells of the heart’s atria thus also serve an endocrine function]
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11
Q

Where are the Purkinje fibres/Purkinje cardiomyocytes located?

A

Sub-endocardium

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12
Q

What is the function of Purkinje Fibres?

A

Important in the electrical stimulation of the heart -> To allow contraction of the ventricle muscle, these fibres need to stimulate the myocardium in a synchronised manner

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13
Q

What are the properties of Purkinje fibres?

A
  • Larger than cardiac muscle cells
  • Fewer myofibrils, lots of glycogen and mitochondria and no T-tubules
  • Connected by DESMOSOMES and GAP JUNCTIONS but not INTERCALATED DISCS
  • Specialised conducting fibres
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14
Q

Where do Purkinje fibres extend to?

A
  • Interventricular septum
  • Papillary muscles
  • Up the lateral walls of the ventricles
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15
Q

What is the most common injury sustained by cardiac muscle?

A

ISCHAEMIA

[tissue damage due to lack of oxygen when coronary arteries are occluded by heart disease]

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16
Q

Lacking muscle ___________ cells, adult mammalian cardiac muscle has little potential to regenerate after injury

A

Satellite

17
Q

What causes myocardial ischaemia?

A

Occurs when blood flow to the heart muscle is obstructed by a partial or complete blockage of a coronary artery by a buildup of plaques (ATHEROSCLEROSIS) -> If plaques rupture, you can have a heart attack (MYOCARDIAL INFARCTION)

18
Q

Describe the development of atherosclerosis

A

Too many CHOLESTEROL particles in blood -> Cholesterol may accumulate on ARTERY WALLS -> PLAQUE may form and the deposits may narrow or block your arteries -> Plaque can burst causing a BLOOD CLOT

19
Q

What is smooth muscle specialised for?

A

Slow, steady contraction under the influence of autonomic nerves and various hormones

20
Q

Describe the fibers of smooth muscle

A

Elongated, tapering and unstriated cells with elongated nuclei which are enclosed by an external lamina and a network of type I and type III collagen fibers comprising the ENDOMYSIUM

21
Q

Where is the nuclei in smooth muscle cells located?

A

Centrally at the cell’s widest part

22
Q

How do the filaments of smooth muscle differ in appearance to other muscle?

A

Filaments of smooth muscle are arranged differently and appear less organised

23
Q

Describe Smooth Muscle

A
  • Linked by numerous gap junctions
  • Borders of the cell become scalloped and nucleus becomes distorted when smooth muscle contracts
  • Concentrated near the nucleus are mitochondria, polyribosomes, RER and vesicles of Golgi apparatus
  • Cell surface are small plasmalemma invaginations
24
Q

Do smooth muscles contain T-tubules?

A

NO

The T-tubules’ function is unnecessary in these smaller, tapering cells with many gap junctions

25
Q

Do smooth muscles contain Sarcoplasmic reticulum?

A

YES

26
Q

What differentiates smooth muscle cells to skeletal muscle cells?

A
  • Myofibrillar arrays of actin and myosin organised differently from striated muscle
  • Myosin filaments have a LESS REGULAR ARRANGEMENT among the thin filaments and FEWER CROSSBRIDGES than in striated muscle
  • Actin filaments not associated with troponin and tropomyosin, using instead CALMODULIN and MLCK to produce contraction
27
Q

What is the role of Dense bodies in smooth muscle cells?

A

Serve as points for transmitting the contractile force not only within the cells but also between adjacent cells

28
Q

__________ muscle is not under voluntary motor control and its fibers lack well-defined neuromuscular junctions

A

Smooth

29
Q

What is contraction in smooth muscle cells stimulated by?

A

Autonomic nerves

[in gastrointestinal tract, smooth muscle is also controlled by various PARACRINE SECRETIONS and in the uterus by OXYTOCIN from the PITUITARY GLAND]

30
Q

Describe the innervation of smooth muscle

A

Axons of autonomic nerves passing through smooth muscle have VARICOSITIES that lie in close contact with muscle fibres -> SYNAPTIC VESICLES in varicosities release NEUROTRANSMITTER which diffuses and binds receptors in sarcolemma of numerous cells -> Stimulation is propagated to more DISTANT FIBRES via GAP JUNCTIONS that allow cells to contract SYNCHRONOUSLY or in a COORDINATED MANNER

31
Q

Describe Leiomyomas

A

Benign tumours that develop from smooth muscle fibres and are usually unproblematic. The tumours occur anywhere in the body where smooth muscle is found (e.g skin, eyes, bladder and gastrointestinal and respiratory tracts)

Also occur in the UTERUS WALL where they are called FIBROIDS -> become large to produce PAINFUL PRESSURE and UNEXPECTED BLEEDING

32
Q

How can skeletal muscle cells display limited regeneration?

A

MESENCHYMAL SATELLITE CELLS lying inside the external lamina of each muscle fiber reserve myoblasts which persist after muscle differentiation -> After injury, the quiescent satellite cells become ACTIVATED, PROLIFERATING and FUSING to form new skeletal muscle fibers

33
Q

What happens after major traumatic injuries?

A

Scarring and excessive connective tissue growth interferes with skeletal muscle regeneration

34
Q

Describe muscle regeneration in Cardiac muscle

A

Lacks SATELLITE CELLS and shows very little regenerative capacity beyond early childhood -> Defects/damage to heart muscle are replaced by proliferating fibroblasts and growth of connective tissue -> Form myocardial scars

35
Q

Describe muscle regeneration in Smooth muscle

A

Capable of a more ACTIVE REGENERATIVE RESPONSE -> After injury, smooth muscle cells undergo MITOSIS and REPLACE DAMAGED TISSUE

36
Q

What is the capacity for regeneration in Skeletal, Cardiac and Smooth muscle cells?

A

SKELETAL = Limited, involving satellite cells mainly
CARDIAC = Very poor
SMOOTH = Good, involving mitotic activity of muscle cells

HISTOLOGY & EMBRIOLOGY II (13 decks)

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