CVS S1 - Introduction to CVS + Anatomy of CVS + DR Work Flashcards Preview

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Flashcards in CVS S1 - Introduction to CVS + Anatomy of CVS + DR Work Deck (60):

Where does exchange of substances between the blood and tissues occur?



What is the major mechanism of substance exchange between the blood and tissues?

Diffusion (98%)


Diffusion is affected by what 3 factors?

Area available for exchange

Diffusion resistance

Concentration gradient


How is area for exchange of substances through capillaries determined?

Determined by 'Capillary density' - Capillaries per unit volume


Where is capillary density highest?

Are all capillaries always perfused?

In tissues with the highest metabolic activity



What is meant by diffusion resistance and how is it determined?

The difficulty of movement through the barrier formed by the capillaries

Determined by:

The nature of the barrier and the nature of the molecules that are diffusing

The distance over which the diffusion occurs
i.e.'Path length'


What effect does concentration gradient between the blood and tissues have on diffusion?

Larger concentration gradient means a greater rate of diffusion, the opposite is also true


How is concentration gradient between blood and tissues determined?

Gradient depends on concentration of substances in blood

Which is in turn affected by the rate of flow, unless blood is supplied at an adequate rate the gradient will dissipate


How much blood must the cardiovascular system supply to the body as a whole?

between 5 and 25L of blood per minute

5L at rest

Up to 25L in strenuous conditions


What is the minimum and maximum rate of blood flow (per minute) to the following organs/systems?


Brain, 0.75L - 0.75L

Heart, 0.3L - 1.2L

Kidneys, 1.2L - 1.2L

Gut, 1.4L - 2.4L

Muscle, 1.0L - 16.0L

Skin, 0.2L - 2.5L

Other, 0.2L - 0.2L


What is meant by 'Perfusion rate'?

Rate of blood flow


Apart from the brain, where else must the cardiovascular system maintain a contant perfusion of?

Heart Muscle


What are the 4 main functional components of the cardiovascular system?

A Pump (The heart)

Distribution vessels (Arteries)

Flow Control



What is meant by 'Flow control' in terms of the cardiovacsular system?

How is this control achieved?

Flow control is the control of cardiac output, so that it might be distributed appropriately

Flow is restricted in parts of the body that are easy to perfuse, driving blood to areas that are not so easy to perfuse

This is achieved with resistance vessels, namely arterioles and pre-capillary sphincters


What is meant by 'Capacitance' in terms of the cardiovascular system?

Capacitance is the ability to cope with changes in cardiac output

This is a store of blood that can be called on to cope with temporary imbalance in the amount of blood returning to the heart and the required cardiac output.

This store is the veins


How is the blood distributed between:

Arteries and arterioles
Heart and lungs

What is the total blood volume?

Arteries and arterioles - 0.55L (11%)

Capillaries - 0.25L (5%)

Heart and lungs - 0.85L (17%)

Veins - 3.35L (67%)

Total volume of ~5L


Where is the heart located in the body?

The middle mediastinum


What is the pericardium?

Describe its location and function

A fibroserous sac surrounding the heart and the roots of the great vessels

It is made up of 2 serious membranes, the visceral (lies against the heart) and the parietal layer

The space between is filled with serous fluid, allowing relatively frictionless motion of the heart


What relationship do the phrenic nerves have with the heart?

Phrenic nerves are responsible for innervation of the pericardium


What is pericarditis?

What is the major problem associated with pericarditis?

Inflammation of the pericardium

Commonly due to infection or post infarct

Accumulation of fluid in the pericardium (pericardial effusion) can lead to cardiac tamponade.

Cardiac tamponade is a condition in which there is so much fluid in the pericardium it restricts inflow of blood into the heart.

This can be rapidly fatal


What are the major vessels entering and leaving the heart?


Inferior and superior vena cavae to the right atrium

Pulmonary enter the left atrium


Pulmonary artery from the right ventricle

Aorta from the left ventricle


Where do the coronary arteries originate from?

The right and left aortic sinus found branching from the ascending aorta


Describe briefly the course of the Right coronary artery and list the major branches.

Originates from right aortic sinus

Passes anteriorly between the right auricle and the pulmonary trunk

Passes through the coronary sulcus between the right ventricle and atrium until it reaches the base of the heart


Right marginal branch
Posterior interventricular artery


Describe briefly the course of the Left coronary artery and list the major branches

Originates from the left aortic sinus

Passes between the pulmonary trunk and the left auricle before entering the coronary sulcus

While still posterior to the pulmonary trunk, it divides.

Divisions are:

Anterior interventricular branch - Descends towards apex

Circumflex branch - Courses towards the left through the coronary sulcus, gives off the left marginal branch


Where is the coronary sinus found and what are its major tributaries?

Found inferior to the left atrium

Tributaries are the great, middle, small and posterior cardiac veins


Where is the great cardiac vein found?

Originates from the apex

Travels up the anterior interventricular sulcus as the 'anterior interventricular vein'

Upon reaching the coronary sulcus the great cardiac vein turns to the left and continues on in the coronary sulcus until it reaches the coronary sinus


What is the function of arteries?

Carry blood away from the heart to the capillary beds


Outline the progression in types of artery from the heart to the capillary beds


Large elastic arteries

Medium muscular arteries





What is the basic structure of an artery or vein?

Tunica intima - Next to lumen
Tunica media
Tunica adventitia - Outer layer


Describe in detail the structure of Elastic arteries

Tunica intima:

Endothelial cells have long axis parallel with long axis of artery

Narrow sub endothelium of connective tissue and discontinuous elastic lamina

Tunica Media:

40-70 fenestrated elastic membranes (elastin) with smooth muscle cells and collagen between these lamellae

Thin external elastic lamina may be present

Tunica adventitia:

Layer of fibroelastic connective tissue
Vasa vasorum (Lymphatic vessels and nerve fibres)


What is the function of elastic arteries?

Expand slightly during systole


Describe in detail the structure of muscular arteries

Tunica intima:
- Endothelium with thick internal elastic lamina

Tunica media:
- 40 layers of smooth muscle connected by gap junctions for coordinated contraction
- Prominent external elastic lamina with fenestrations

Tunica adventitia:
- Thin layer of fibroelastic connective tissue
- Contains vasa vasorum (not very prominent)
- Also contains lymphatic vessels and (unmyelinated) nerve fibres


What are the vasa vasorum?

Why might an artery contain vasa vasorum?

Smaller blood vessels contained within the tunica adventitia of an artery

Diffusion of nutrients through the endothelium is not sufficient to supply the tissues of the vessel


What is the function of the unmyelinated nerves in the tunica adventitia of a muscular artery?

Nerve endings release noradrenaline (sympathetic nerve fibres)

Diffuses through fenestration in the tunica media's external elastic lamina and into the superficial tunica media

Creates a depolarisation of the smooth muscle cells which propagates to all muscle cells via gap junctions causing vasocontriction


As muscular arteries diminish in diameter, what happens to their structure?

Number of smooth muscle layers in the tunica media decreases


How do arterioles differ from muscular arteries in terms of size and their tunica media?

Arterioles are less than 0.1mm diameter, arteries are larger than 0.1mm diameter

Arterioles have 1-3 layers of smooth muscle cells in the tunica media


Would you ever find arterioles with thin internal elastic lamina?

Yes, but only those of larger diameter


What are the main features of small arterioles?

No internal or external elastic lamina

Tunica media is composed of a single smooth muscle cell encircling the endothelial cells

Tunica adventitia is scant


By what percentage can arterioles perform sustained dilation or contraction?

Why is this useful?

Give an example of this process

Most arterioles can dilate up to 60-100% resting diameter

Or can constrict up to 40%

This directs blood to where it might be needed

During strenuous physical activity, arterioles in the gut will constrict to allow greater blood flow to the skeletal muscles


What are meta-arterioles and how do they differ from arterioles?

Meta-arterioles supply blood to capillary beds

Their smooth muscle layer is not continuous

Instead, smooth muscle cells are spaced apart and each encircles the endothelium of a capillary arising from the meta-arteriole (pre-capillary sphincter)


What is the function of smooth muscle cells in meta-arterioles?

Function as pre-capillary sphincters

Allow the arterioles and meta-arterioles to serve as flow regulators for the capillary beds

They control whether a capillary bed is perfused or bypassed


Describe the structure of capillaries

Made up of a single layer of endothelium and a basement membrane

7-10um in diameter


How much of the total blood volume is contained within capillaries?

What is the total exchange surface area of all capillary beds in the body?


Estimated 600m2


What features of capillary structure aid in exchange of substances through the capillary wall?

Narrow lumen is almost completely filled by an RBC, minimising the diffusion path length

As velocity is inversely proportional to cross sectional area, velocity is very low in capillaries compared to the rest of the vasculature, this allows more time for exchange


What are the three types of capillary?



Describe the structure of continuous capillaries

Endothelium with basement membrane

Pericytes form a branching network around the outer surface


What are pericytes?

What processes are they involved in?

Cells capable of dividing into smooth muscle cells or fibroblasts

Divide during angiogenesis, wound healing or tumour growth


How does the structure of fenestrated capillaries vary from continuous capillaries?

Pores (fenestrations) in the endothelium


Describe the structure of sinusoidal capillaries

Fenestrated endothelium with large holes

Discontinuous basal lamina (basement membrane)

Associated pericytes

Some do not have tight junctions and are called 'discontinuous sinusoidal capillaries'

Generally larger in diameter than continuous or fenestrated capillaries


What does the unique structure od sinusoidal capillaries allow for?

Where are sinusoidal capillaries normally found and why?

Allows RBCs and WBCs to pass through the capillary wall

Normally found in the liver and spleen, where greater amount of movement of materials is necessary


List the progression of vascular structures that the blood passes through from the capillaries to the heart (in order)


Post-capillary venules



Large veins



How does the structure of veins differ from that of arteries?

Thinner wall with more connective tissue and less elastic fibres or smooth muscle

Lumen wider and irregular (than accompanying arteries)

Paired semilunar valves that prevent retrograde travel of blood


Describe the structure of post-capillary venules

Structure much like capillaries (endothelium and associated pericytes)

Generally more permeable than capillaries

10-30um diameter

No valves as in larger venules/veins


What do the structural features of a post-capillary venule allow for?

How is this relevant to inflammatory response?

Because pressure is lower (larger diameter) than in capillaries fluid tend to drain into them

Except in inflammatory response where fluid and leukocytes emigrate out (these venules are the preferred location for leukocyte emigration)


How will low blood pressure affect veins?

Veins may collapse if blood pressure isn't maintained


What apart from blood pressure determines blood flow in veins?

Moving blood towards the heart:
- 'Muscle pump' action of the lower limb
- Pressure factors in the abdominal and thoracic cavities

Preventing retrograde flow:
- Valves


In what diameter range will muscle fibres begin appearing in venules?

50um - 1mm


How do the superficial veins of the legs differ from other small or medium sized arteries?

Why is this difference necessary?

Most small/medium arteries have a well defined tunica adventitia

In superficial veins of the leg, there is a well defined muscular wall

This may be to resist distension by gravity


Give some examples of large veins

Vena Cavae
Internal jugular


How do large veins differ from small/medium veins?

Have well developed longitudinal smooth muscle in the tunica adventitia in addition to the circularly arranged smooth muscle in the tunica media