Specialised Cardiovascular Elements

Question 1

What is collateral circulation?

Answer 1

Distributing arteries give off branches before terminating in tissues and these connect with others to form a collateral network. This is so if one artery is damaged, the collaterals can supply sufficient blood to the supporting tissue

Question 2

What is anatomical end artery?

Answer 2

This is where one single artery supplies blood to a specific tissue with no collateral circulation. Occlusion of this vessel results in tissue death known as infarction. These rarely occur

Question 3

What is functional end artery?

Answer 3

This is where an artery supplying blood to a specific tissue has insufficient collateral circulation to compensate for arterial blockage which results in tissue death. Examples of this are the coronary, cerebral, and retinal vascular beds

Question 4

What is retina mirabilia?

Answer 4

This is when major arteries split abruptly into multiple parallel vessels = creating a network of blood vessels. Some retina mirabilia, the network reunites as seen in the brain in some species. This may act as a countercurrent heat exchanges, reducing pressure in arteries or allowing exchange of molecules between the arterial and venous system

Question 5

What is arteriovenous anastomoses?

Answer 5

These allow blood vessels to be shunted directly from arterioles to venules, bypassing the capillary bed. AVAs are important for thermoregulation in structures such as the skin, horse hoof, rabbit ear and dog tongue

Question 6

What is vasa vasorum?

Answer 6

This is a fine network of vessels supplying the walls of blood vessels. It is located outside the tunica media and adjacent to the external elastic lamina

Question 7

What is vasa vasorum?

Answer 7

It is a fine network of vessels supplying the walls of major blood vessels. It is located on the outside of the tunica media and adjacent to the external elastic lamina

Question 8

What are the portal systems?

Answer 8

Veins connecting two capillary beds is a portal system. Examples include:

• hepatic portal system which carries nutrients from capillary bed of the gut and liver
• hypothalami-hypophyseal portal system which transports hypothalamic releasing factors to pituitary capillary beds

Question 9

what is alternative venous drainage?

Answer 9

some tissues drain by two venous routes

Question 9

what is alternative venous drainage?

Answer 9

some tissues drain by two venous routes

Question 10

what are veins without valves?

Answer 10

• normally large veins have valves to maintain unidirectional unidirectional blood flow
• some specially adapted large veins lack valves

Question 11

what is bronchial circulation?

Answer 11

• in pig, carnivores and sometimes ruminant, some blood from bronchi drains via bronchial veins to azygous vein which enters right atrium
• reminding bronchial blood and all of it in the horse returns to the heart via oxygenated pulmonary vein to left atrium

Question 12

what is coronary circulation?

Answer 12

• coronary arteries are forest branches of aorta
• left + right coronary arteries do not form collateral circulations + are functional end arteries supplying myocardial capillary bed
• in general = left coronary artery supplies left chambers of heart and right coronary artery supplies right chambers
• there is species variation
• venous drainage from myocardial capillary bed is primarily by great coronary vein which enters right atrium at coronary sinus
• small coronary veins = Thebesian veins also open directly into all four chambers