T1L14: Principles of the Cardiorespiratory System

Question 1

Blood vessels

Answer 1

• Different structural and functional characteristics depending on their function
• Oxygenated blood: Arteries, Arterioles, Capillaries
Deoxygenated: Veins and venules

Question 2

Arteries

Answer 2

• Carry blood under high pressure away from the heart
• Arteries have a luminal diameter
Arteries are classified according to contents of tunica: elastic and muscular

Question 3

Microstructure of blood vessels

Answer 3

• Tunica intima - mainly endothelium
• Tunica media - muscular
• Tunica adventitia - CT coat
Difference in size and thickness

Question 4

Endothelium

Answer 4

• Endothelium is a specialised part of tunica intima - squamous epithelial cells
• Endothelial cells are bound together by junctional complexes
Endothelial cells secrete clotting factors and factors which maintain tone of vascular smooth muscle

Question 5

Endothelium-clinical considerations

Answer 5

• Thrombosis: blood clots easily (thrombus) and stray blood clot (embolism)
Atherosclerosis: Lesions to endothelium plaques form increase vessel lumen

Question 6

Elastic arteries

Answer 6

• Elastic arteries are the major conducting vessels - aorta and common carotid
• Tunica media is broad and has a high amount of elastin sheets
• Function: accommodates surges in blood
Continue to push blood downstream to medium arteries

Question 7

Muscular arteries

Answer 7

• Main distributing branches
• Tunica media compromised predominantly of smooth muscle
• Control blood flow by constricting
Have pulsatile contractions to propel blood

Question 8

Arterioles

Answer 8

• Arterioles are microscopic - ≤0.3 mm Ø :
○ intima – thin (endothelium & elastic lamina)
○ media – smooth muscle
○ adventitia – CT merges
distribute blood to capillaries – regulate flow to capillary bed (affects blood pressure)

Question 9

Capillaries

Answer 9

• Continuous 
		○  uninterupted lining  
		○  common: e.g. skin, smooth 
		○  muscle, lungs 
	• Fenestrated
		○  numerous pores ↑ exchange   
		○  e.g. renal glomeruli,  
		○  endocrine glands   
Function: transfer of : oxygen / carbon dioxide, nutrients, hormones, immunologically competent cells, phagocytic cells

Question 10

Venules

Answer 10

• Venules are the smallest veins, they drain capillary beds
	• Post capillary venules 
		○  - union of several capillaries  
		○  - some metabolite exchange 
	• Collecting venules
		○  - progressive ↑ Ø , ↑ muscle  
		○  - passive collecting system
 - no elastin

Question 11

Veins

Answer 11

• Veins are returning low oxygen blood to the heart
• Because of low pressure the walls of the tunica media are thinner
• Medium veins drain venous plexus e.g. cephalic vein
• Large veins have a well developed tunica adventitia e.g. vena cava
Where veins have to work against gravity e.g. limbs valves are common

Question 12

Portal system

Answer 12

• Venous blood that is high in products of digestion needs filtering
• Veins from: spleen, stomach, intestines drain into liver via hepatic portal vein
Filtered by liver and blood drains into hepatic veins and into IVC to be returned to heart

Question 13

Associations between arteries and veins

Answer 13

• Vessels run in close relations - often neurovascular bundles and CT
Pairs of veins surround artery - venae comitantes

Question 14

Anastomoses

Answer 14

• Uniting arteries eg vertebral arteries
• Creates uninterrupted circulation
• Especially in limbs around joints
Clinically in accident ligation, disease anastomoses provide collateral circulation

Question 15

End arteries

Answer 15

• Some arteries have no anastomosis
• Occlusion -> necrosis
○ Blindness = occultation of central artery retinal
Myocardial infarction = coronary artery poor anastomosis

Question 16

venae comitantes

Answer 16

Pairs of veins surround artery