Sesh 8: Muscle And The CVS Flashcards
What muscle is striated?
Skeletal and cardiac
What types of muscle contain myoglobin?
Skeletal and cardiac.
What colour are slow and fast twitch skeletal muscle fibres?
- Slow=red
- Fast=white
What connective tissue layer covers muscle fascicles?
Perimysium.
What layer covers individual muscle fibres?
Endomysium
What band in the sarcomere contains only actin filaments?
I band
Why does disuse atrophy of muscle occur?
Innervating the muscle less, so producing less protein and reduces fibre diameter.
What is bound to myosin when in the high energy configuration?
ADP + Pi
What is bound to myosin when in the low-energy configuration?
ATP
What is released from myosin during the power stroke?
ADP + Pi
Why does muscle rigor/rigor mortis occur?
Lack of ATP means myosin head cannot detach from actin, so cross bridges stay bound, leading to muscle stiffness.
What is a common marker for cardiac ischaemia?
Troponin I….levels not necessarily proportional to level of damage.
What is a marker for ALL muscle injury/necrosis?
Creatine kinase….levels ARE proportional to infarct size.
Outline the steps in excitation-contraction coupling.
- Impulse along motoneurone reaches NMJ
- V-gated Ca channels open, increasing intracellular [Ca], and causing ACh exocytosis
- ACh binds nAChR’s on sarcolemma
- Na enters muscle cell, causing local depol of sarcolemma
- V-gated Na channels open, causing an action potential that spreads down the t-tubules
- Voltage sensing dihydropyridine R’s in t-tubules change conformation, which open adjacent Ryanodine R’s on the SR
- Ca is released from the SR, and binds to troponin C
- Tropomyosin conformation is changed, exposing actin binding sites and allowing cross bridges to form
What’s the difference between fibrillation and fasciculation?
Fibrillation= unintended contraction of individual muscle cells
Fasciculation=unintended contraction of whole muscle fascicles
Instead of Z bands, what do cardiac muscle cells have?
Intercalated discs
What is the function of intercalated discs between cardiac muscle cells?
Electrical and mechanical coupling to allow myocardium to act as a functional syncytium.
What type of junctions within the intercalated disc allow electrical and mechanical coupling of cardiac muscle cells?
- Electrical=gap junctions
- Mechanical=adherens junctions
What is the primary cause of ANP and BNP release?
Atrial and ventricular distension e.g. In congestive HF
Where is ANP released from?
Atrial myocytes
Where is BNP released from?
Ventricular myocytes, but first identified from brain.
What fibres pass impulses from the AVN to the ventricles?
Purkinje fibres
How are Purkinje fibres modified for their function?
- Lots of glycogen
- Sparse myofilaments
- Lots of gap junctions
What are myoepithelial cells?
Modified smooth muscle, stellate cells, that form a basketwork around secretory units of some exocrine glands to aid secretion.
What are myofibroblasts?
Specialised smooth muscle cells that aid produce a collagenous matrix and contract, to aid wound healing.
What is the orientation of the outer and inner smooth muscle layers of the GIT?
- Outer=longitudinal
- Inner=circular
How can skeletal muscle repair itself?
-Satellite cell mitosis–> hyperplasia
-Satellite cells fuse with myocytes–> hypertrophy
(Skel muscle cells can’t divide as have multiple nuclei).
What happens following myocardial damage?
- Cardiomyocytes can’t regenerate
- Fibroblasts invade and lay down scar tissue
How can smooth muscle repair itself?
-Hyerplasia and hypertrophy of smooth muscle cells
How much of blood is plasma, and how much is red blood cells (in L)?
- Plasma-3L
- RBCs-2L
Where is most blood distributed?
65% within peripheral veins
What % of total blood volume is within capillaries?
5%
What is haemostasis?
A balance of pro-coagulant and anti-coagulant processes.
What vessels does the aortic arch branch into?
- Brachiocephalic trunk
- L common carotid artery
- L subclavian artery
What does the brachiocephalic trunk branch into?
- R common carotid artery
- R subclavian artery
What are the innominate veins formed from?
Union of internal jugular and subclavian veins.
What does the ascending aorta branch into?
R+L coronary arteries.
What is the purpose of papillary muscles?
Attach to AV valves via chordae tendinae, and contract to prevent inversion of AV valves in systole.
What is an end artery?
A terminal artery supplying all/most blood to a body part without significant collateral circulation.
What is the only absolute end artery?
Central retinal artery.
Name 4 functional end arteries.
- Coronary
- Splenic
- Cerebral
- Renal
On what side of the heart is the mitral valve?
Left atrioventricular valve.
What is the difference between damage to the left and right side of the heart?
- L-sided damage–>myocardial infarction
- R-sided damage–> electrical problems
Where is the SAN?
Right atrium of the heart.
Describe the path of electrical impulses of the heart from the SAN to ventricles.
- SAN
- AVN (0.1 sec delay)
- Bundle of His
- L+R bundle branches
- Purkinje fibres
Elastic arteries are known as _________ vessels.
Capacitor (pressure reservoirs)
What makes up the tunica media of the aorta?
- Elastin lamellae
- Smooth muscle cells (that produce elastin, collagen and matrix)
What is the commonest site of aneurysm, and why?
Infrarenal abdominal aorta, because the junction of the supra-and infrarenal aorta naturally contains less elastin fibres.
What is in the tunica media of muscular arteries?
- 40 layers of smooth muscle cells connected via gap junctions…contract–>vasoconstriction
- external elastic lamina
What are vasa vasorum?
Microvasculature supplying the vessel wall, found in the tunica adventitia of muscular arteries.
Arterioles and metarterioles are known as ___________ vessels.
Resistance
What forms a pre-capillary sphincter?
Smooth muscle cells of metarterioles, that encircle the endothelium of a capillary
What is the purpose of vascular shunting?
Blood redistribution e.g. Reduce GIT bloodflow during exercise
Which vessel has the slowest blood velocity?
Capillaries, to allow time for exchange.
Why does fluid flow into post-capillary venules from the capillaries?
The pressure inside them is lower than in capillaries
How are the walls of veins different to arteries?
- Thinner
- More connective tissue
- Less muscle/elastic fibres (except superficial veins in legs-muscular walls to resist distension caused by gravity)
Veins are known as __________ vessels.
Capacitance (can increase vol without big pressure increase)
What is primarily responsible for the return of blood from deep leg veins?
Calf muscle pump.
Thoracic pump=secondary mechanism
What vessel do the coronary veins drain into?
The coronary sinus at the posterior of the right atrium.
What’s the capillary hydrostatic pressure, blood colloidal osmotic pressure and net filtration pressure at the arterial end of capillaries?
- Cap hydrostatic=35mmHg
- Blood colloidal=25mmHg
- Filtration pressure=10mmHg
What’s the capillary hydrostatic pressure, blood colloidal osmotic pressure and net filtration pressure at the venous end of capillaries?
- Cap hydr=15mmHg
- Blood colloidal=25mmHg
- Filtration= -10mmHg
What is the Frank Starling Law of the heart?
As end diastolic volume (stretch) increases, stroke volume (force of contraction) increases due to more overlap of myofilaments allowing more cross bridges to form…until reach optimal, past which increased stretch reduces myofilament overlap and SV e.g LV dysfunction
Name 2 classes of drugs that aim to reduce end diastolic volume.
- Anti-hypertensives
2. Diuretics
What is paroxysmal nocturnal dyspnoea?
An attack of breathlessness when lying flat at night.
What is ‘fixed mottling of the dead leg’ caused by?
Obstruction of bloodflow to the lower limb–>ischaemia–>cell death as Na/K pump can’t function–>release of K as cells lyse
