Neuro: 1:00 - 2:00Scribe: Brittney Wise

Monday, April 6, 2009Proof: Laura Adams

Dr. ZehrenStructures of the Cardiovascular SystemPage1 of 14

NOTE: The notes that are found under the slide in the power point have been copied and pasted under each slide in the transcript (they are italicized).

Introduction [S1]:
[S2] General Remarks
[S3]Components of the Cardiovascular System - Includes heart, arteries, vein, and capillaries.
[S4] Pattern of Blood Flow Through Heart - Not going to discuss this right now. He will cover this in the next hour.
[S5] Arteries carry blood away from the heart
Arteries are defined as vessels carrying blood away from the heart. Although they usually carry oxygen/nutrient rich blood, this is not always the case. The pulmonary arteries would be a major exception (shown in blue). Pulmonary arteries carry blood away from the heart but they have unoxygenated blood.
Arteries are said to branch. The lumen/diameter of the vessel gets smaller as you get to the level of the arterioles which leads into the capillary beds.
1. Arteries are defined as vessels carrying blood away from the heart. Arteries progressively branch into smaller and smaller vessels. Note that although most arteries carry O2 rich blood to the tissues of the body, the pulmonary trunk and arteries carry O2 poor blood to the lungs.
[S6] Veins carry blood toward the heart
Veins are defined as vessels carrying unoxygenated blood toward the heart. The pulmonary veins are carrying oxygenated blood back to the heart.
Veins have tributaries not branches and they get larger and larger as they get closer to the heart.
Veins in the limbs are characterized by the presence of valves which ensure that blood only flows to the heart. Other veins, like the hepatic portal vein for example, has no valves in it. So, veins may or may not have valves, it depends on whether or not the venous flow has to work against gravity.
1. Veins are vessels that carry blood toward the heart. Veins have tributaries (not branches). Like the tributary system of a river, small veins unite to form larger veins, which unite to form still larger veins, etc. Althoughmost veins carry O2 poor blood back to the heart, the pulmonary veins (not labelled) are an exception.
[S7] Structure of Blood Vessels
[S8] Distinguishing Arteries from Veins
All blood vessels (with the exception of capillaries) have 3 layers in their walls. If we look at an artery and a vein of about equal diameter we see that each has
Tunica intima (tunica = coat)
the innermost coat and is primarily endothelium
the integrity of this endothelium is important; if it’s torn that will interrupt blood flow and can lead to a clot/thrombus formation
Tunica media (middle layer) is smooth muscle which controls the diameter of the lumen and therefore the blood pressure and the amount of peripheral blood reaching some area
Tunica adventitia (outermost coat) is a connective tissue coat
In this layer there are both vessels and nerves
Many of the vessels that are here are going to the smooth muscle of the tunica media, making these autonomic fibers controlling the tone in that muscle
There are also blood vessels in the tunica adventitia which supply the vessels itself. Unless the vessel has an extremely thin wall like a capillary where it can get its own oxygen and nutrients directly from the blood, vessels need their own blood supply and that is called the vasa vasorum (this is an important term that means vessels of the vessel)
The thickness of the tunica media is the easy way that you can tell arteries and veins apart. Arteries have a thicker tunica media than veins which gives them a much more rigid wall.
Capillaries are the vessels that unite the smallest arteries (arterioles) and the smallest veins (venules).
Capillaries only have a tunica intima, only an endothelial coat, which facilitates the exchange of oxygen and nutrients. The exchange occurs at the level of the capillary beds. They form networks or a capillary bed (shown in the diagram).

1. Arteries and veins have three coats or tunics:

Tunica intima – consists of an endothelium (lining of flattened cells) and a thin layer of connective tissue.

The integrity of the endothelium is essential to normal blood flow; if injured blood cells stick at site of injury and form a clot.

Tunica media – consists of a layer of smooth (involuntary) muscle. Contraction of the smooth muscle regulates the size of the lumen of the vessel and helps determine blood pressure and blood flow.

Tunica adventitia – consists of a layer of connective tissue. Adventitia contains nerves that innervate the smooth muscle and small vessels (vasa vasorum) that supply the cells of the vessel wall which are too far removed from blood in the vessel itself to receive nutrition.

2. The structural difference between arteries and veins is primarily the degree of development of the tunica media. For any given size, the tunica media in an artery is thicker than in a vein. (The more rigid wall of an artery compared to the thinner, more collapsed wall of a vein usually makes it easy to distinguish arteries from veins in the lab.)

3. In addition to arteries and veins, there are capillaries which unite the smallest arteries (arterioles) with the smallest veins (venules). Capillaries form interconnecting networks (capillary beds) where O2 and nutrients leave the blood stream and enter the extracellular spaces to supply tissues, and where CO2 and wastes from the tissues enter the blood stream. Capillaries consist only of the tunica intima in order to allow this interchange to occur.

4. Arteriolesare the most important factor in regulating peripheral blood flow (their tunica media is composed almost entirely of smooth muscle and so they are particularly contractile). If too many arterioles are contracted (or so diseased that they can’t relax), there is an increase in blood pressure; if too many are relaxed, there is a decrease in blood pressure.

5. Can discussion the significance of arteriovenous anastomoses (not shown) at this point. An arteriovenous anastomoses consists of a vessel which directly connects an arteriole w/ a venule. This shunting vessel is equipped w/ a well-developed muscular wall which is capable of completely closing this channel, thereby forcing blood to pass through the capillary bed, or, contrarily, of opening wide and short-circuiting the capillary bed. These anastomoses are functionally useful b/c they provide a means whereby a part of the body can receive the proper amount of blood needed at a particular time (for example, during a meal the anastomoses are closed, allowing increased blood flow to the capillary beds of the GI tract so nutrients can be absorbed, but between meals the anastomoses are open, thus diverting blood to other areas where it may be needed more (eg, muscles).

[S9] Arterial System
[S10] Head and Neck
With regard to the head and neck the chief arteries are the common carotids and the vertebral arteries. Remember that the right common carotid and the right subclavian artery branch off the brachiocephalic artery or trunk which itself comes from the aortic arch.
On the left side the common carotid and subclavian arteries are independent branches that branch directly off the aortic arch.
[S11]Common Carotid Arteries and Vertebral Arteries
If we go and look at the distribution of the internal carotid arteries and vertebral arteries they are mainly involved in supplying the brain.
Both the ICA’s and the vertebral arteries will come together at the base of the brain and form the arterial Circle of Willis and this is what supplies the brain.
ICA - branches off and goes up through the temporal bone of the skull
Vertebral arteries - branch off of the subclavian artery, pass through the transverse foramina of the cervical vertebrae, merge from the uppermost cervical vertebrae, and pass into the skull through the foramen magnum
The ICA has no branches in the neck and the only branch it has that distributes outside the head is the opthalamic artery.
1. The head & neck receives its blood supply primarily from the two common carotid aa and the two vertebral aa.

2. On the right side of the body, the common carotid a. arises from the brachiocephalic trunk (which itself arises from the aortic arch in the thorax). On the left side, the common carotid a. arises independently from the aortic arch.

3. Likewise, the right subclavian a. (which supplies the upper limb) arises from the brachiocephalic trunk whereas the left subclavian a. arises independently from the aortic arch.

[S12] Blood Supply to the Brain – (shared most of its information with slide 11)
1. The brain receives its arterial blood from the two internal carotid arteries (ICA) and the two vertebral arteries.

2. The ICAs arise from the common carotid aa. and have no branches in the neck. The ICAs enter the skull through the carotid canals in the petrous temporal bones.

3. The vertebral arteries arise from the subclavian aa. in the root of the neck. They enter the skull through the foramen magnum.

4. At the base of the brain the ICAs and vertebral arteries are involved in the formation of the arterial circle (of Willis), which supplies the brain.

[S13] External Carotid Artery and It’s Branches (“SALFOPSM”)
This has 8 branches in the neck and gets its name because it supplies to the outside of the skull.
You remember the names of these branches (SALFOPSM). Remember to look at these on your own again.
1. The COMMON CAROTID A. splits into int. and ext. carotid aa. at the superior border of the thyroid cartilage (CV4).

2. The EXT. CAROTID A. distributes primarily to the outside of the skull. It lies anterior to the internal carotid a.

3. The ext. carotid a. has 8 branches . The mnemonic (nonsensical, but perhaps useful) for remembering these branches is S. A. L. F. O. P. S. M. ---

Superior thyroid a.
Ascending pharyngeal a.
Lingual a.
Facial a.
Occipital a.
Posterior auricular a.
Superficial temporal a.
Maxillary a. (Whew !).

These arteries distribute to the areas their names suggest.

[S14] Upper Limb
[S15] Subclavian Artery and It’s Continuation
The chief artery of the upper limb is going to be the subclavian artery (artery shown in blue). The subclavian artery will arch over the 1st rib (it is directly against the rib and can be compressed against it) and past the 1st rib it changes names and becomes the axillary artery.
The axillary artery has numerous branches that we won’t name that supply the axillary or armpit region. It then continues until it reaches the lower border of this muscle, the teres major muscle,and it will change its name again and will become the brachial artery because now it’s in the arm or brachium.
The brachial artery also has many branches and the only one that we will point out is the profunda brachii artery or deep brachial artery. This is a fairly large artery that winds around behind the humorous and supplies the posterior compartment of the arm, the muscles, and so forth. Since it is directly against the bone it can easily be injured if you shatter your humorous at the mid-shaft level.
1. The subclavian a. (BLUE) is the chief artery supplying the upper limb. (x)On the R side it arises from the brachiocephalic trunk; on the left side from the aortic arch.

2. The subclavian a. arches over the 1st rib (on both sides) to become the axillary a., which lies in the axilla (armpit). At the lower border of the teres major m., the axillary a. changes its name to brachial a. (brachium = arm). The brachial a. descends in the arm until it reaches the cubital fossa in front of the elbow, where it divides into radial and ulnar aa.

3. The subclavian a. gives branches to the scapular (shoulder) region; namely the transverse cervical and suprascapular aa. The axillary a. also gives branches to the scapular region; namely the subscapular a. Since these branches of the subclavian and axillary aa. anastomose in the scapular region, they provide a collateral circulation to the upper limb should the main arterial trunk become blocked between the thyrocervical trunk of the subclavian a. and the origin of the subscapular a.

4. The brachial a. gives off several named branches, the largest of which is the profunda brachii a. (= deep brachial a.). This artery supplies the posterior compartment of the arm. (x)The brachial a. also gives off branches involved in the anastomoses around the elbow joint, as mentioned earlier.

[S16] Radial and Ulnar Arteries
The brachial artery will continue down in front of the elbow in the cubital fossa region where it will divide into 2 terminal branches, the radial and the ulnar. The radius is the bone on the lateral side of the forearm and the ulna on the medial side.
Both of these have branches that will supply structures in the forearm.
They both enter the palm of the hand and in the palm of the hand they form 2 arches:
The superficial palmar arch which is formed primarily by the ulnar artery.
The deep palmar arch which is formed primarily from the radial artery.
From these arches precede other arteries that supply the digits.
1. The radial and ulnar arteries are terminal branches of the brachial a. The radial and ulnar aa. descend on the radial (thumb side) and ulnar (little finger side) of the forearm to reach the hand. (x)(Note that the common interosseous a., a branch of the ulnar a., splitting into ant. and post. interosseous aa. which supply the ant. and post. compartments of the forearm.)

2. In the hand, the radial and ulnar aa. anastomose with each other to form the superficial and deep palmar arches. From these arches proceed branches which supply the digits.

[S17] Thorax
[S18] Blood Supply to Thoracic Wall
The thoracic wall itself is supplied by the intercostal arteries. These arteries run between the ribs.
Posterior intercostal arteries mostly come directly off the thoracic aorta as segmental branches that run laterally and supply the tissues of the thoracic wall.
The anterior intercostals arteries arise from the internal thoracic that comes off the subclavian.
The upper intercostal spaces receive their anterior intercostal arteries directly off the internal thoracic.
Lower down in the thorax, the lower intercostal spaces get their anterior intercostal arteries from a branch of the thoracic called the musculophrenic.
What’s important to notice is that these anterior and posterior intercostals arteries anastomose with each other in the intercostal space.
THE BLOOD SUPPLY TO THE THORACIC WALL IS CHIEFLY BY THE ANT. & POST. INTERCOSTAL AA. Most of the POST. INTERCOSTAL AA. arise as direct segmental branches of the descending thoracic aorta. The ANT. INTERCOSTAL AA. to the upper intercostal spaces originate from the int. thoracic a.; those to the lower spaces originate from the musculophrenic a. The ant. and post. intercostal aa. ANASTOMOSE in an intercostal space. This is clinically important (see later slide re: coarctation of aorta).
[S19] Coarctation of Aorta
This is a condition where the aorta is severely constructed just beyond the point where the left subclavian branched off.
It’s a congenital deformity.
You see the severe constriction and you might ask if this is compatible with life and it is. The reason that it is, is because you have collateral circulation, essentially a bypass around that obstruction.
What happens over time is that the subclavian arteries begin to enlarge, the internal thoracic arteries which are branches off the subclavian begin to enlarge, and the anterior and posterior intercostal arteries begin to enlarge; the flow in the anterior intercostals arteries is lateral, away from the sternum (which is a normal pattern of blood flow), but then when they anastomose with the posterior intercostals there is a reverse blood flow in the posterior intercostal arteries.
The posterior intercostals carry the blood back to the aorta distal to where the occlusion is, so there is just a bypass to the point of obstruction allowing the lower part of the body to get adequate blood supply. Over time these intercostal arteries get so large that they can be palpated on the chest wall and the pulsations of those intercostal arteries can be felt and they can also erode the ribs as they get larger.
Eventually this can be corrected surgically but a person can live for a number of years with this condition.
1. In COARCTATION OF THE AORTA, a congenital condition in which the aortic arch is severly constricted, the intercostal aa. may become greatly enlarged and provide for a collateral circulation to the body distal to the point of constriction.

2. This type of coarctation is compatible w/many years of life b/c the collateral circulation carries blood to the thoracic aorta inferior to the stenosis. The collateral vessels may become so large that they cause notable pulsation in the intercostal spaces and erode the adjacent surfaces of the ribs, which is visible in chest x-rays. (COA, 5th ed., p. 175).