Session 8: Cardiovascular System Flashcards
What is the function of the CVS?
To circulate and transport nutrients, oxygen, carbon dioxide, hormones and blood cells to and from the cells of the body
What are the three essential components of the CVS?
Heart
Blood
Blood vessels
What is the pulmonary circulation?
The portion of the CVS which carries deoxygenated blood away from the heart, to the lungs, and returns oxygenated blood back to the heart
What is the systemic circulation?
The part of the CVS which carries oxygenated blood away from the heart to the body, and returns deoxygenated blood back to the heart
What is the meaning of a “closed” CVS?
Blood never leaves the network of arteries, veins and capillaries
Red blood cells are also known as what?
Erythrocytes
What is the structure of RBCs?
How is this beneficial?
Concave
It means they can pass through the capillaries and remain largely unharmed
How much circulating blood does an average adult have?
5 litres
Of the 5 litres of circulating blood, how much is RBCs?
2 litres
How much of the 5 litres of circulating blood is plasma?
3 litres
Where does the majority of our blood lie?
In our peripheral veins (65%)
What percentage of our circulating blood is found in our capillaries?
5%
Even though capillaries contain the smallest percentage of circulating blood, what makes them ideal for substance exchange?
Their massive surface area
What are the three layers of the walls of arteries and veins?
Tunica intima (next to the lumen) Tunica media (intermediate) Tunica adventitia (outer layer)
The tunica intima (the inner most layer) of arteries, consists of what three layers?
Endothelium
Subendothelial layer
Thick internal elastic lamina
The tunica media (the intermediate layer) of arteries, consists of what main feature? Which are connected by what?
40 layers of smooth muscle cells
Connected by gap junctions
They also have a prominent external elastic lamina
Why are the smooth muscle cells in the tunica media of arteries connected by gap junctions?
So that they can coordinate their contraction
What is the tunica adventitia (the outer layer) of muscular arteries, made up of?
Thin layer of fibroelastic connective tissue containing vasa vasorum (network of small blood vessels), lymphatic vessels and nerve fibres
What are vasa vasorum?
A network of small blood vessels that supply the walls of large blood vessels
What are arterioles?
Arteries with a diameter of less than 0.1mm
What is the difference in the tunica media of arteries compared to arterioles?
Arteries have 40 layers of smooth muscle in their tunica media, arterioles have 1-3 layers of smooth muscle in their tunica media
The tunica intima of arterioles is made up of what layers?
Endothelial cells
Very thin layer of subendothelial connective tissue
The tunica media of arterioles is made up of what?
A single layer of smooth muscle
The tunica adventita of arterioles is made up of what?
Layers of fibroblasts
What are metarterioles?
What is their function?
A blood vessel that links arterioles and capillaries
Supply blood to the capillary bed
What do metarterioles have instead of a continuous tunica media?
Individual smooth muscle cells that are spaced apart and form individual precapillary sphincters
What is the function of the precapillary sphincters of metarterioles?
To control blood flow through arterioles and metarterioles into the capillary bed
Is it possible to by-pass the capillary bed?
Yes, from metarteriole through a thoroughfare channel to the postcapillary venule
What is the function of the lymphatic capillaries at the capillary bed?
Drain away excess extracellular fluid and return it to the blood
At what junctions do the lymphatic capillaries drain excess extracellular fluid into the blood?
The internal jugular vein (Left lymphatics)
The subclavian vein (Right lymphatics)
What happens when precapillary sphincters are closed?
This is known as what?
The blood flow through capillaries is greatly reduced
Peripheral vasoconstriction
Most arterioles can dilate to ____% - ____% of their resting diameter
60-100%
Most arterioles can maintain up to a ___% constriction for a long time
40%
The ability of arterioles to constrict and dilate allows what?
Blood to be directed to where it may be most needed
During strenuous physical exertion, blood flow to skeletal muscles will be increased or reduced? How?
Increased
Through dilation of arterioles
During strenuous physical exertion, blood flow to the intestines will be reduced or increased? How?
Reduced
Through constriction of arterioles
After ingestion of a large meal, what will happen to blood flow to skeletal muscle and to the intestines? How?
Blood flow to skeletal muscle is reduced through constriction of the arterioles
Blood flow to the intestines is increased through dilated of the arterioles
True or false: Passing RBCs fill virtually the entire capillary lumen
True, this minimises the diffusion path to adjacent tissues
At what velocity does blood pass through the capillaries at its lowest?
0.3 mm/s
The capillary is made up of what layers?
A single layer of endothelium
Basement membrane
What are pericytes?
Contractile cells that wrap around the outer surface of the endothelium of capillaries and venules
Pericytes are capable of dividing into what?
Muscle cells or fibroblasts
During what processes would pericytes need to divide and differentiate?
Angiogenesis
Tumour growth
Wound healing
Which vessels of the CVS are responsible for resistance?
Arterioles and metarterioles
Which vessels of the CVS are muscular/ distributing arteries?
Medium arteries
Which vessels of the CVS are exchange vessels?
Capillaries
Which vessels of the CVS are elastic/ conducting arteries?
Large arteries
What are postcapillary venules?
Venules that receive blood from capillaries
Are postcapillary venules more or less permeable than capillaries?
More permeable
What are postcapillary venule walls made up of?
Endothelial lining with associated pericytes
How does the pressure inside postcapillary venules compare to the pressure in capillaries and surrounding tisssue?
This causes what?
The pressure is lower
Therefore, fluid tends to drain into them
Under what conditions would fluid not be drawn into postcapillary venules from capillaries/surrounding tissue?
What happens under these conditions?
During an inflammatory response
Fluid and leukocytes emigrate from postcapillaries to capillaries and surrounding tissue
What are the walls of venules made up of?
Endothelium associated with pericytes or thin smooth muscle cells to form a very thin wall
When compared to arteries, veins have:
- what size diameter?
- what thickness of walls?
- how much connective tissue, elastic and muscle fibres?
Veins have:
- a larger diameter
- a thinner wall
- more connective tissue
- fewer elastic fibres
- fewer muscle fibres
Describe the thickness of each of the layers of small/medium sized veins
Tunica intima = thin
Tunica media= 2-3 layers of smooth muscle
Tunica adventitia= well-developed
Large veins have a diameter of what size?
> 10mm
Describe the thickness of each of the layers of large veins
Tunica intima= thicker than small/medium veins
Tunica media=not prominent compared to small/medium veins
Tunica adventitia= well-developed
Where would you find an exception to veins not having a well-defined muscular wall?
What is a possible reason for this?
In the superficial veins of the legs
To resist distension caused by gravity
Veins are described as capacitance vessels. What is capacitance?
The ability of a blood vessel to increase the volume of blood it holds without a large increase in pressure
Capacitance is _________ ____________ to elasticity
Inversely proportional
What features of veins allows them to stretch a great deal?
They are thin
They are non-elastic
How does venous blood get from the legs back to the heart in a standing human?
The calf muscle pump
True or false: All veins have valves
False, only veins of the lower limbs, the upper limbs and heart have valves
There are no valves in the intraabdominal, intrathoracic or neck veins
Apart from the calve muscle pump and valves, what other mechanism helps to return blood back to the heart from the lower limbs?
The thoracic pump: when we breathe in, the intrathoracic pressure becomes negative and have a sucking affect, attracting blood to rush to the right atrium
Calf muscle pump failure leads to what?
Venous hypertension and venous insufficiency which can lead to venous ulcers
Gravity in the upright human body can cause a _________ gradient of venous pressures
Vertical
Where does the apex of the heart lie?
In the 5th intercostal space
What is the pericardium?
The membrane surrounding the heart that is filled with a small amount of fluid to prevent friction
Which side of the heart is thicker, left or right?
Why?
Left side of the heart is thicker than the right side
Because it has to pump blood around the entire body
What muscles are responsible for stopping the mitral valve from flopping backwards?
Papillary muscles
Which valve in particular is more prone to problems and why?
Mitral valve
Because it is dealing with a much higher pressure
What is the Frank-Starling Law?
The stroke volume of the heart increases in response to an increase in ventricular end-diastolic volume (volume of blood filling the heart)
What is the stroke volume of the heart?
The amount of blood that is pumped from the left ventricle per contraction
The Frank-Starling curve is generally proportional up to a point, what happens at this point when the curve beings to drop off?
The response to an excessive after load which causes pressure overload and LV dysfunction ???
Why does Left Ventricular Failure lead to pulmonary oedema?
Causes blood to accumulate in the pulmonary veins which leads to very high blood pressure, forcing some of the fluid out from the blood into the alveoli
Why is left ventricular failure worse when lying flat?
When stood up gravity would move some of the fluid down to the lower limbs, but when lying flat, the fluid goes to the lungs
What is paroxysmal nocturnal dyspnoea?
Attacks of shortness of breath and coughing generally occurring at night
What is orthopnea?
Shortness of breath that occurs when lying flat
What is left ventricular hypertrophy?
Thickening of the myocardium of the left ventricle
Left ventricular hypertrophy leads to what?
Reduced cardiac output
What happens to plasma Bran Natriuretic Peptide (BNP) in heart failure?
BNP levels increase markedly in left ventricular dysfunction. The level in heart failure correlates with symptom severity
Right ventricle failure can lead to __________ oedema
Peripheral
What is aortic valve stenosis?
Narrowing of the aortic valve
Systemic hypertension leads to ___________ ___________ of large arteries. The media gets _________ and the lumen gets _________ _______.
hypertrophic remodelling
thicker
more narrow
Hyperplasia of what leads to hypertrophy of the bladder?
Prostate
What is TURP?
Transurethral Resection of the Prostate
Name 5 causes of muscle atrophy
Muscle inactivity
Malnutrition
Cancer
Organ failure: Congestive cardiac failure, COPD, renal failure
Neurogenic disease: motor neurone disease, spinal cord injury
Name four diseases caused by smooth muscle dysfunction
Asthma
IBS
Primary hypertension
Detrusor instability
Name three indicators of muscle injury/necrosis and which muscle they indicate injury in
Creatine kinase (all muscle) Myoglobinuria (skeletal muscle) Troponin I (cardiac muscle)
What is myoglobinuria? What is it a sign of?
Presence of myoglobin in the urine
Sign of skeletal muscle injury
What is the significance of “fixed” mottling of the skin?
It implies irreversibility in limb ischaemia
Why does an ischaemic limb with “fixed” mottling need to be amputated as a matter of emergency?
Potassium inside cells leaves due to the pumps not working in dead cells, and the cell swelling and breaking down. Increases potassium levels in the blood will lead to heart arrhythmia and eventually asystolly- cardiac arrest
