ARTERIAL AND VENOUS CIRCULATION
OBJECTIVES OF THIS LECTURE ARE:
- Identify the functional components of the circulatory system and their roles
- Identify the branches of the ascending aorta, aortic arch, descending aorta, and abdominal aorta
- Identify blood supply to the head, neck, thorax, upper extremities, and lower extremities
- Explain the importance of the Artery of Adamkiewicz
- Outline the main vessels of cerebral circulation
- Describe the Circle of Willis
ARTERIAL AND VENOUS CIRCULATION
•Physical characteristics (2 circulations)
–Systemic circulation
–Pulmonary circulation
ARTERIAL AND VENOUS CIRCULATION
Systemic circulation
Supplies all tissue except lungs
AKA greater circulation or peripheral circulation
ARTERIAL AND VENOUS CIRCULATION
Pulmonary circulation
…
ARTERIAL AND VENOUS CIRCULATION
Functional parts of circulation:
Arteries
Arterioles
Capillaries
Venules
Veins
ARTERIES AND ARTERIOLES
Arteries
Transports blood under high pressure to the tissues
This is why arteries Have strong vascular walls
Blood flows at high velocity
ARTERIES AND ARTERIOLES
Arterioles
Last small branch of arterial system
Act as a control conduit through which blood is released into the capillaries
Strong muscular walls
Can vasoconstrict or vasodilate depending on blood flow requirements of each tissue
ARTERIES AND ARTERIOLES
What’s a benefit of Arterioles having Strong muscular walls?
Can vasoconstrict or vasodilate depending on blood flow requirements of each tissue
CAPILLARIES, VENULES & VEINS
Capillaries
Have the most important function of the circulatory system
Which is diffusion of substances back and fort between blood and tissues
Exchanges fluid, nutrients, electrolytes, hormones, etc
CAPILLARIES, VENULES & VEINS
Venules
Collect blood from the capillaries and gradually grow larger into veins
CAPILLARIES, VENULES & VEINS
Veins
Conduits for transport of blood from venules back to heart
Veins are the reservoir of extra blood
(small or large amount based on the needs of the circulation)
CAPILLARIES, VENULES & VEINS
Which characteristics of veins make them reservoir of extra blood?
Thinner walls than arteries
Much more distensible than arteries
ARTERIAL AND VENOUS CIRCULATION
Graphical representation of distribution of blood volume amoung the various component of circulation
Systemic circulation: 84%
(64% of which is in the veins)
Heart and pulmonary circulation: 16%
WALLS OF ARTERIES AND VEINS
Passageway by which blood flows and is present in both arteries and veins is known as
Lumens
WALLS OF ARTERIES AND VEINS
Btw arteries and veins which has smaller lumen?
Arteries
Smaller lumens help arteries maintain higher pressures as blood moves throughout the system
WALLS OF ARTERIES AND VEINS
There three layers to each vessel knowns respectively as:
Tunica externa/adventitia
Tunica media
Tunica intima
WALLS OF ARTERIES AND VEINS
Tunica externa/adventitia
Outermost layer of a blood vessel
(reponsible for maitaining protection and prevents collapse)
Strengthens/Anchors to surrounding tissue
WALLS OF ARTERIES AND VEINS
Tunica media
Middle layer of blood vessel
Responsible for contraction and relaxation or Vasoconstriction and vasodilation
This is normally the thickest layer in arteries
Much ticker in arteries than in veins
WALLS OF ARTERIES AND VEINS
Tunica intima
Thinnest layer
Boundary between blood in the lumen and the wall of vessel
Inner layer of blood vessel
Has innermost lining made up of Endothelial cells (Endothelium)
WALLS OF ARTERIES AND VEINS
Damage to which part of the tunica intima is the reason for clot formation?
Damage to the endothelium is the reason for clot formation
WALLS OF ARTERIES AND VEINS
Why are the lumen of the arteries more rounded that the lumen of the veins?
This is b/c of the thicker walls and smaller diameters in arteries
The thicker walls in arteries are d/t to their close proximity to the heart, and their higher pressure in relation to veins
DIFFERENCE BETWEEN ARTERIES AND VEINS - Arteries
Direction of flow - Pressure - Walls - Lumen - Valves
Direction of flow: Blood away from Heart
Pressure: Higher
Walls: Thicker: Tunica media thicker than tunica externa
Lumen: Smaller
Valves: None
DIFFERENCE BETWEEN ARTERIES AND VEINS - Veins
Direction of flow - Pressure - Walls - Lumen - Valves
Direction of flow: Blood toward heart
Pressure: Lower
Walls: Thinner: tunica externa thicker than tunica media
Lumen: Larger
Valves: Present most commonly in limbs and in veins that are inferior to heart
DIFFERENCE BETWEEN ARTERIES AND VEINS
Btw arteries and veins, which has valves? Why? What the function of these valves?
Veins have valves b/c they are low pressure vessels
Valves ensure unidirectional flow toward the heart and prevent backward flow toward the capillaries
DIFFERENCE BETWEEN ARTERIES AND VEINS
Swollen, twisted veins that you can see just under the skin. They usually occur in the legs, but also can form in other parts of the body
Varicose veins
In pts w/ Varicose veins, blood pools to the lower extremities d/t the pool of gravity. and the increased blood increases the pressure w/in the vein, and promotes the blood accumulation in the vein and ultimately distension, twisting and visibility to the surface of the skin
AORTIC SEGMENTS
The thoracic aorta is divided into three sections:
Ascending aorta
(Portion that leaves the LV)
Transverse aorta
(aka aortic arch)
Descending aorta
(Portion that descends into the thorax)
AORTIC SEGMENTS
When does the Descending aorta becomes the Abdominal aorta?
after in penetrates the diaphragm
This occurs around level T12
ANATOMY OF THE CEREBRAL CIRCULATION
Ascending aorta ascends from the
aortic valve
ANATOMY OF THE CEREBRAL CIRCULATION
Ascending aorta ascends from the aortic valve and banches off into:
Brachiocephalic artery
Left common carotid artery (LCA) branches off directly off the ascending aorta
Left subclavian artery
ANATOMY OF THE CEREBRAL CIRCULATION
What the other name for the Brachiocephalic artery?
Innominate artery
ANATOMY OF THE CEREBRAL CIRCULATION
What does the Brachiocephalic artery (Innominate) branches off into?
Right subclavian artery
Right common carotid artery
Right common carotid artery bifurcates with right subclavian
Left common carotid arises from aortic arch
ANATOMY OF THE CEREBRAL CIRCULATION
Which carotid Artery provides Blood supply to neck, face, and base of skull?
External Carotid Artery
(Will not be discussed for this lecture)
ANATOMY OF THE CEREBRAL CIRCULATION
Internal Carotid Artery divides into which arteries?
Middle cerebral artery
Anterior cerebral artery
ANATOMY OF THE CEREBRAL CIRCULATION
Which artery provides Arterial blood supply to the brain?
Internal carotid artery
Provides 80% of cerebral blood flow
ANATOMY OF THE CEREBRAL CIRCULATION
Which artery provides Arterial blood supply to the lateral aspect of cerebrum?
Middle cerebral artery
ANATOMY OF THE CEREBRAL CIRCULATION
Which artery provides Arterial blood supply to the Frontal lobe and medial aspect of cerebral hemispheres?
Anterior cerebral artery
ANATOMY OF THE CEREBRAL CIRCULATION
The Internal Carotid Arteries provides 80% of CBF. Where does the remaining 20% comes from?
Vertebral arteries (2)
Arise from subclavian arteries to form basilar artery
Then give rise to the Posterior cerebral artery
ANATOMY OF THE CEREBRAL CIRCULATION
Which vascular structure is considered Cornerstone of inflow of blood to brain
Circle of Willis
Hexagonal ring shaped that lies in the subarachnoid space and circles the pituitary gland
ANATOMY OF THE CEREBRAL CIRCULATION
The Three paired arteries originate from the circle of Willis to perfuse brain are:
Anterior cerebral arteries
Middle cerebral arteries
Posterior cerebral arteries
ANATOMY OF THE CEREBRAL CIRCULATION
communicating arteries that complete the circle of Willis are known as:
Anterior and posterior communicating arteries,
AKA Willsians channels
CIRCLE OF WILLIS
In what % of the population is the Circle of Willis Abnormal or incomplete
in majority of patients
(50-80%)
W/ complete occlusion of a major vessel, infarction can occur if collateral flow is not adequate
CIRCLE OF WILLIS
Under normal circumstances when there is no occlusion, blood flow btw the anterior-posterior or side-to-side or left-to-right circulations does not mix
In the event of an occlusion, the Circle of Willis can act as a shunt btw either anterior-posterior, or Willisian channels, increase collateral flow in an effort to maintain pressure
Collateral flow can also occur through the extrenal carotid arteries
The Willisian channels become important during periods of vessel occlusion of one of the carotid arteries
Collateral circulation from the Willisian channels allows cross filling of the cerebral vessels to maintain blood flow
THORACIC AORTA
The Thoracic aorta is also known as:
Descending aorta
THORACIC AORTA
What’s the thoracic aorta span?
Begins at T4 and extends to T12
THORACIC AORTA
Where does the thoracic aorta begins in reference the the vertebral column?
begins left of the vertebral column
but approaches midline as it descends into the chest
THORACIC AORTA
Arterial Branches of the thoracic aorta include:
Bronchial arteries
Mediastinal arteries
Oesophageal arteries
Pericardial arteries
Superior phrenic arteries
Intercostal and subcostal arteries
ABDOMINAL AORTA
Thoracic aorta becomes abdominal aorta once it passes through
Diaphragm
Ends above pelvis, dividing into iliac arteries
ABDOMINAL AORTA
Major branches of abdominal aorta include:
Inferior phrenic (T12) => inferior aspect of the diaphragm
Celiac trunk (T12) => organs of upper abdomen
Superior mesenteric artery (L1) =>Jejunum, ileum and transverse colon
Inferior mesenteric artery (L3) => transverse, descending, sigmoid colon and rectum
Renal arteries (L1-2) => kidneys
ABDOMINAL AORTA
Where does the abdominal aorta terminates?
Common illiac arteries (L4)
Which branches into internal and external iliacs
Internal iliacs => pelvic structures
External iliacs => legs
BLOOD SUPPLY TO SPINAL CORD
How does the Spinal cord receives its blood supply?
about 25% from two posterior arteries and
about 75% from one anterior spinal artery
BLOOD SUPPLY TO SPINAL CORD
Thoracic portion of anterior spinal artery supplied by
2-3 anterior radicular arteries
The larger radicular artery is the Artery of Adamkiewicz
Artery of Adamkiewicz, also known as the Great Radicular Artery
BLOOD SUPPLY TO SPINAL CORD
Artery of Adamkiewicz rpovides blood supply to:
Major blood supply to lower 2/3 of spinal cord
Provides major blood supply to lumbar and sacral cord
BLOOD SUPPLY TO SPINAL CORD
Variations on the origin of the Artery of Adamkiewicz. Where does is originate in most people?
In 75% of people, originates on the left side of the aorta between T9 and T12 vertebral segments
Segmental supplier of Adamkiewicz varies, (T5-L5)
LOWER EXTREMITY ARTERIAL CIRCULATION
At what vertebral level does the common iliac artery divides to become the internal and external iliacs?
L4
LOWER EXTREMITY ARTERIAL CIRCULATION
Internal iliac artery provides blood supply to:
Pelvic structures
Internal iliac artery => anterior and posterior trunks
Anterior trunk => obturator artery, vesical artery (men) and vaginal artery (females)
Posterior trunk => posterior pelvic wall, gluteal region
LOWER EXTREMITY ARTERIAL CIRCULATION
External iliac artery provides blood supply to:
Lower extremities
External iliac artery => femoral and deep femoral artery => popliteal artery –> dorsal artery