L5 Blood Vessels

Question 1

What is the general structure of blood vessels?

Answer 1

Tunica intima the innermost and thinnest layer that lines the lumen. It is composed of a single layer of endothelium which is in contact with the blood and a thin layer of subendothelial connective tissue. This is surrounded by the internal elastic lamina, a layer of circulatory arranged elastic fibres.

Tunica media - The middle layer is the muscular component of the vessel wall and thickest in arteries. Smooth muscle cells are arranged in circular and spiral layers which are supported by elastic fibres and collagen. The smooth muscle cells and elastic fibres are embedded in a Ground substance rich in proteoglycans. Proteoglycans are proteins bound to sugars. It is separated from the tunica adventitia using the external elastic lamina.

Tunica adventitia (tunica externa) Outermost layer comprised entirely of connective tissue - collagen and fibroblasts. It is the thickest layer in veins

Question 2

What is ground substance?

Answer 2

Ground substance is an amorphous gel-like substance in the extracellular space that contains all components of the extracellular matrix (ECM) except for fibrous materials such as collagen and elastin. It is rich in proteoglycans which are proteins bound to sugars.

Question 3

What is the diameter of elastic arteries?

Answer 3

1-2 cm - they maintains pressure of around 80 mmHg

Question 4

What is the diameter of muscular arteries?

Answer 4

10 microns

Question 5

What is the Nervi vasorum?

Answer 5

Sympathetic nerves in the vessels that innervate the vessel.

Question 6

What is the role of the endothelium?

Answer 6

• It is critically involved in exchange and how blood flow is regulated through chemical mediators such as endothelin. These can result in hypertension if produced in excess or an unregulated way.
  
  • Endothelium is also involved in preventing blood clots.
    Endothelium is continuous throughout the circulatory system, even in the chambers of the heart
• Endothelial cells secrete substances that have an effect on vasoconstrictor tone and vascular permeability. They also play a role in blood clotting and the growth of new cells.

Question 7

How is blood able to travel in the correct direction in veins?

Answer 7

• Skeletal-muscle contraction system - This helps contract the veins. activate the muscle, venous return and helps you stand up for longer
  
  • Pressure of the artery next to the vein
    
    • Act of breathing in, helps lower intrathoracic pressure and draw blood back into the heart

Question 8

What are differences between arteries and vein?

Answer 8

Arteries generally appear rounded with thick walls and small lumens. Veins have thin walls with large lumens and so generally appear flattened.

The tunica intima of arteries has endothelium usually appears wavy due to construction of smooth muscle. The internal elastic membrane is present in lager vessels. In veins the endothelium appears smooth - the internal elastic membrane is absent.

The tunica media in arteries is normally the thickest layer. The smooth muscle cells and elastic fibres predominate. External elastic membrane is present in larger vessels. In veins this is the thinnest layer, smooth muscle cells and collagenous fibres predominate and nervi vasorum and vasa vasorum present. The External elastic membrane is absent.

The tunica external is normally thinner than the media in arteries (except in largest arteries). In veins this is the thickest layers. In both vessels The collagenous and elastic fibres, Nervi vasorum and vasa vasorum are present. .

Question 9

What are different types of capillaries?

Answer 9

Continuous capillaries - most common type. Forms the basis of the BBB and found in most vascularised tissues. Water and ions can pass across these vessels and small molecules can pass over areas that are incomplete known as intracellular crests. The BBB is impenetrable.

Fenestration capillaries: Found in special sites like SI where you absorbed nutrients, kidneys to filter the blood and endocrine organs e.g. pituitary that releases thyroxine or growth hormone into the blood..

Sinusoid: Least common and so found in very specialised sites. Liver (for albumin for example), spleen, lymph nodes. Allows the passage of large molecules like plasma proteins or cells.

Question 10

What are the different types of flow in blood vessel?

Answer 10

In capillaries types of flow:

• Frictionless flow - if the blood vessel did not exert any resistance on the blood. Occurs in very few situations on earth. This is the Ideal situation.
• Laminar flow - what we should have in blood vessels. Most efficient way of blood flow. As you progress to the centre of the lumen, blood flow is faster. This is silent. Blood flows in layers that do not flow over each other. At the walls of the vessels, there is almost no flow.
• Turbulent flow is noisy. This is a contributing factor to thrombosis. Compress the artery creating turbulent blood flow and so can measure blood pressure. There is mixing fo the layers which each travelling in different directions.

Question 11

What are the different components of Virchow’s Triad?

Answer 11

Stasis, Vessel wall injury and Hypercoagulability.

Question 12

What is systolic pressure?

Answer 12

Theblood pressurewhen the heart is contracting. It is specifically the maximumarterial pressureduring contraction of the left ventricle of the heart.

Question 13

What is diastolic pressure?

Answer 13

Thediastolic pressureis specifically the minimumarterial pressureduring relaxation and dilatation of the ventricles of the heart when the ventricles fill withblood.

Question 14

What is mean arterial pressure?

Answer 14

This is the average pressure in the arteries and so average force of the blood in the vessels over the tissues. Statistical concept. It however but can be approximated by taking the diastolic pressure and 33% of the systolic pressure. A normal value is between 70-110 , but must be over 60. Less than 60, not reflects inadequate perfusion of the tissues leading to ischaemia and hypoxia.

Question 15

What is pulse pressure?

Answer 15

This is the difference between the systolic pressure and diastolic pressure. This should be 25% of the systolic pressure at least.
A high or wide pulse pressure occurs during exercise. Hypertension can be represented by a sustained high pulse pressure. Lower than 25% that is described lower or narrow. This occurs in heart failure aortic stenosis or lost a lot of blood

Question 16

What is hypertension?

Answer 16

In people aged 18 years or olderhypertensionisdefinedas either a systolic or a diastolic blood pressure measurement consistently higher than an accepted normalvalue(this is above 129 or 139 mmHg systolic, 89 mmHg diastolic depending on the guideline).

Question 17

What is hypotension?

Answer 17

Hypotensionis a decrease in systemic blood pressure below accepted lowvalues. It may be absolute with changes in systolic blood pressure to less than 90 mm Hg or mean arterial pressure of less than 65 mm Hg. It may be relative to a decrease in diastolic blood pressure to less than 40 mm Hg.

Question 18

What factors affect blood flow?

Answer 18

• Cardiac output
• Compliance
• Volume
• Viscosity of the blood
• Blood vessel length and calibre

Question 19

What is Poiseuislle’s law and what can we deduce about blood flow using the equation?

Answer 19

Flow is proportional to the pressure difference across the tube, radius to the power of four and inversely proportional to the viscosity and length of the tube.

Radius - This is the most important. The radius of the blood vessel can change really quickly, within seconds in response to neuro and chemical that trigger vasocontraction and dilation. Affective as flow is proportional to radius to the power of 4. iscosity of blood does not change very quickly - only with too polycythaemia, anaemia and conditions that affect plasma proteins such as liver failure. T

Question 20

Which vessels are the resistance vessels?

Answer 20

Arterioles due to the biggest change in pressure.

Question 21

what are features of the coronary system?

Answer 21

• There are Phasic changes in the coronary circulatory system - opposite to all other vascular beds. Blood flow cannot happen through capillaries in systole. In diastole, the blood flow is high in the coronary arteries. The coronary arteries fill in diastole.
  
  • The intramyocardial pressure - when the heart contracts it spirals up and all the muscles goes up in one direction to force the blood into the aorta. There is a gradient of pressure within myocardium itself and it is at its highest closest to the chamber. It is less high as you go towards the outsides of the heart. This means the resistance is greatest in the vessels in the subendocardial region. There are more vessels in the subendocardial region than there are further out. This however does mean this area susceptible to ischaemia. If the blood pressure decreases you can get a subendocardial myocardial infract due to the pressure differences.

Question 22

How does auto regulation occur in the coronary system?

Answer 22

Local metabolism or autoregulation is the most important thing to keep blood flowing. The chemical signals work at the level of precapillary sphincters to open or close capillaries depending on where blood is needed. Open a sphincter allowing blood in when there is an increase lactic acid or other metabolic by-products, acidosis, hypoxia, hypercapnia, hyperthermia in order to increase blood flow. The converse will cause blood flow to divert by closing the sphincters. These mechanisms are found elsewhere however are proportionally more important in the coronary.

Question 23

What is bronchial circulation?

Answer 23

Blood supply to the lungs from the systemic circulation. These are branches that come of the descending part of the thoracic aorta.

Question 24

What is the result of increase resistance through the pulmonary circuit?

Answer 24

The pulmonary circulation operates at a lower pressure. The arteries and arterioles here are less muscular compared to elsewhere. Local metabolic control is very important - much of this is regulated by oxygen levels. Anything that increases resistance through the pulmonary circulation such as lung disease or pulmonary hypertension will increase the work of the heart and cause right ventricular hypertrophy. The right side of the heart is larger leading to right heart failure. Patients then have wake up at night and sit up at night and produced pink sputum.

Question 25

What is the circle of Willis?

Answer 25

The Circle of Willis is a continuous circulation that comes form the carotids and vertebral arteries. Blockage in one of the arteries affects areas of the brain and leads to different symptoms of stroke.

Question 26

Give age-related changes to the vasculature.

Answer 26

• Fibrous thickening of the intima
  
  • Fibrous sand scarring of media
  • Accumulation of ground substance
  • Myxoid degeneration - this accumulates in the wall of the artery and makes it more susceptible to injury
  • Fragmentation of elastic intima

Question 27

What is arteriosclerosis?

Answer 27

The thickening and hardening of the walls of the arteries, occurring typically in old age. Arteries are inflamed or injured due to smoking, diabetes, high glucose or high lipids. They become less compliant leading to an Increase resistance and blood pressure, leading to more turbulent more blood flow and more vessel wall stresses. All of this leads to more injury and more disease. The inflammation will spread weakening the wall and scars the wall leaving it sclerotic. Circulating triglycerides accumulate and become trapped within the wall, producing a plaque once cells and platelets have come and formed a clot.

Question 28

What is dissection?

Answer 28

Blood trapes between layers of intima, media and adventitia. Blood flow is forced apart. False lumen, forcing layers of blood flow apart and there is a flap between the two.

Question 29

What is an aneurysm? What is the difference between a true and false aneurysm?

Answer 29

An is a localised permanent abnormal dilation of arteries.
True aneurysm - affects all 3 layers of the arteries
False - blood is within the layers and budges out

Question 30

What is an AAA?

Answer 30

Abdominal aortic aneurysm (AAA) - usually happens below the kidneys. Typically happens in older white males with CV risk factors such as high blood pressure and cholesterol. Very important and so get a screening program on 65.

Question 31

What are risk factors for an AAA?

Answer 31

• Age
  
  • Sex
  • Family History
  • Smoking
  • Hypertension
    
    • Hyperlipidaemia