Chapter 21 Test Answers – Flashcards

This would imply that the vessels are passive. In reality, blood vessels are living organs that can actively participate in controlling blood flow and regulating passage of materials into and out of blood.

Heart --> arteries --> arterioles --> capillaries --> venules --> veins --> heart

Small arteries that connect to capillaries.

Small veins that connect to capillaries.

any vessel that blood flows through prior to flowing through capillaries. These always carry blood away from the heart. The blood in arteries tends to be at relatively high pressure. In the systemic circulation, the blood in arteries is oxygenated (red). Ventricles pump blood into large elastic arteries that branch repeatedly to form many progressively smaller arteries. As they become smaller they transition from having a large amount of elastic tissue and a smaller amount of smooth muscle tissue to having a smaller amount of elastic tissue and a larger amount of smooth muscle tissue. Arteries are classified as 1.) elastic arteries 2.) Muscular arteries 3.) arterioles.

Any vessel that blood flows through after flowing through capillaries. These carry blood toward the heart. THe blood in veins tends to be at relatively low pressure. In the systemic circulation, the blood in the veins is deoxygenated (blue). Classified as 1.) Venules 2.) Small veins 3.) medium or large veins.

‐A capillary = a vessel that is narrow and that has a thin wall ‐The capillary is the only place in the vascular system where materials flow between blood and tissues.

The pulmonary vessels and the systemic vessels.

Transport blood from the right ventricle, through the lungs and back to the left atrium.

Transport blood through all parts of the body from the left ventricle and back to the right atrium.

1.) Carrie blood 2.) Exchange of nutrients, waste products, and gases within tissues. 3.) Transport substances (hormones, parts of the immune system, molecules for coagulation etc.) 4.) Helps to regulate blood pressure. 5.) Directs blood flow to tissues.

They both consist of 3 layers.

1.) Inner- Tunica intima 2.) Middle- Tunica media 3.) Outer - Tunica adventitia

Inner layer = Tunica intima ‐Inner lining = endothelium: (the endothelium is continuous with the endocardium of the heart) A simple squamous epithelium on a thin basement membrane ‐Underneath the endothelium = a layer of connective tissue (called lamina propria, don't learn this term) ‐Finally, a layer of elastic fibers = the internal elastic membrane (fenestrated layer) seperates the inner layer from the middle layer.

Middle layer = Tunica media ‐This layer is mostly made up of smooth muscle cells arranged circularly around the blood vessel allows the vessel to dilate/constrict ‐Contraction of muscle vasoconstriction (narrowing of vessel diameter) ‐Relaxation of muscle vasodilation (expansion of vessel diameter) ‐vasoconstriction and vasodilation of arteries and veins is an important tool for cardiovascular regulation, regulating the amount of blood flowing through them. ‐The tunica media also has a layer of elastic fibers = the external elastic membrane ‐This is thicker & stronger than the elastic layer found in the tunica intima -Seperates the tunica media from the tunica adventitia. ‐The tunica media is especially thick in large arteries

Outer layer = Tunica adventitia, which is a layer of tough connective tissue. Connective layer is dense near the tunica media and loose connective tissue that merges with the connective tissue surrounding the blood vessel. ‐Note that nerves run in the adventitia ‐2 functions: (1) The vessels sense pain when disrupted; (2) Axons of the sympathetic nervous system run here innervate the muscles in the tunica media ‐Note that no parasympathetic fibers run in vessels!

The layers are continuous with the three layers of the heart. Anteries and veins merge directly with the heart.

Unlike arteries and veins, capillaries only have one layer = a thin layer of endothelium with a basement membrane OUtside of the basement membrane is a layer of loose connective tissue that merges with the connective tissue surrounding the capillary. -Along the length of the capillary are precapillary cells, closely associated with the endothelial tissue. They are between the basement membrane, and the endothelial cells. They are fibroblasts, macrophages, or undifferentiated smooth muscle cells. ‐Also note how thin they are, about the diameter of an RBC or less! RBCs often have to bend to get through Most capillaries are fenestrated = they have spaces in the endothelium that allow water & small molecules to flow ‐Cells and large molecules (such as albumin, RBCs, large water soluble molecules like proteins) are generally prevented from flowing -Some capillaries are not fenestrated these are in muscle, and nervous tissue and other locations.

Capillaries form extensive vascular networks between arterioles and venules ‐These networks penetrate through all tissues no cell in the body is more than a few cell diameters away from a capillary! ‐These capillary networks are the site of exchange of materials (O2, CO2, nutrients, etc) between blood and tissues.

One important component of capillary networks = precapillary sphincters = smooth muscle rings that are found at the entry points of the capillary network ‐These sphincters allow the body to regulate the amount of blood flowing through different parts of the capillary network ‐When the sphincters dilate increase blood flow to that part of the network ‐When the sphincters constrict decrease ‐They are critical for allowing the body to regulate the flow of blood to different tissues

Different tissues have different density of capillary networks ‐More metabolically‐active tissues have more dense capillary networks ‐The body can create more extensive capillary networks in tissues that receive a lot of training - e.g., the skeletal muscles of athletes develop large and extensive capillary networks ‐Skin has an especially dense capillary network used in thermoregulation ‐Increased blood flow to skin Decreased body temp, and vice‐versa

Arterioles supply blood to the capillary network. Arterioles --> metarterioles (vessels with isolated smooth muscle cells along their walls) --> Thoroughfare channel (a vessel that extends from a metarteriole to a venule). Blood frow from the metarteriole to the throughfare channel is controlled by precapillary sphincters (smooth muscle cells located at the origin of the branches.) Blood flows from the throughfare channel to the venules.

Arterial capillaries are the ends of capillaries closest to the arterioles. Venous capillaries are the capillaries closest to the venules.

Allow blood to flow from the arterioles to small veins without passing through capillaries.

an arteriovenous anastomesis the consists of arterioles with abundent smooth muscle in their wall. They are present in large numbers in the soles of feet, the palm of hands, the terminal phalanges and nail beds. Function to help regulate temp. When body temp decrease they constrict less blood flows through them, body temp increases dialate more blood flows through them.

The histology of arteries and veins can be predicted by the pressure of the blood that flows in them: ‐Arteries experience blood at high pressure, which is pulsatile because of the beating of the heart The blood puts a lot of force on the vessel walls ‐Veins experience blood at low pressures because the pressure is lost as blood flows through capillaries low force on the vessel walls The differences in force on the vessel walls lead to some big differences in structure ‐Compared to veins, arteries have thicker muscle and elastic membranes ‐The largest arteries = elastic arteries = have elastic fibers throughout the tunica media ‐Veins have thinner walls with relatively few elastic fibers -Another difference= venous valves.

Venous valves One problem faced by veins = the blood pressure isn't high enough to bring blood back to the heart, especially in the lower limbs The body has devised an anatomical solution to this problem = veins have valves that prevent blood from flowing away from the heart ‐The valves are infoldings of the tunica media. The valves keep blood from flowing backwards and to keep the blood flowing forwards the body acts as a pump.

‐As muscles contract, they squeeze veins that pass through or near them forces blood to flow through the veins ‐Since the valves only allow blood to flow toward the heart, this squeezing pumps blood toward the heart

Some people develop dilation of their veins the valves no longer work veins become even more dilated because of back‐flowing blood ‐This condition is called varicose veins ‐It is often partially hereditary; other risks include prolonged standing and obesity ‐Is often painful, can have serious complications such as blood clotting in large veins risk for embolus (clot breaking off and traveling to other parts of the body)

Artery has thicker walls in comparison with a vein. The promanent layer in the artery is the tunica media (smooth muscle) The predominante layer in the vein is the tunica adventitia. Tunica media is thinner than in the artery.

Largest in diameter, aka conducting arteries. High bp, more elastic tissue and less amount of smooth muscle in walls.

Medium and small sized arteries. Walls are thick, tunica media is well developed. Aka distributing arteries, the smooth muscle cells allow them the partially regulate blood supply to different parts of the body by constricting or dialating.

Most blood vessel walls are innervated by unmylinated sympathetic nerves. Nerve fibers branch to form plexuses in the tunica adventitia, and the neurotransmitters go along the smooth muscle cells of the tunica media. Sympathetic innervation cause vessels to constrict. (Parasympathetic innervates the penis and clitoris and cause the blood vessels to dialate.) Between the smooth muscles are gap junctions so stimulations of a few muscle cells cause contstriction in a relatively large segement of the blood vessel.

Arterial disease is the major cause of myocardial infarction and stroke, and thus it is the major disease process that leads to death in the US

As we age, our arteries undergo a natural "hardening" process called arteriosclerosis ‐This involves a loss of the elastic and muscle components of the tunica media and an increase in dense connective tissue ‐A number of different processes lead to this result; a certain amount is inevitable during aging ‐Regardless of the cause, the end result is that arteries become less flexible and less able to dilate/constrict ‐As a result, the heart must work harder to pump blood into stiff arteries ‐Also impairs the body's ability to regulate blood flow

Atherosclerosis The most dangerous form of arteriosclerosis is atherosclerosis ‐This is the deposition of fatty material within the wall of the artery - the fatty deposit is called a plaque ‐There are also white blood cells within plaques the plaque is partially a result of the immune response. ‐This is the most common cause of myocardial infarction Risk factors: Many factors predispose a person to the formation of atherosclerotic plaques: Major risk factors: (1) High cholesterol; (2) Male sex; (3) Hypertension; (4) Tobacco use; (5) Diabetes; (6) Genetics (family history of the disease) Treatment: There are drugs that reduce cholesterol called statins that can minimize or even reverse plaques ‐However, the most effective way to prevent & treat atherosclerosis is through diet and exercise! - These can also lead to a reversal of atherosclerotic plaques.

Pulmonary circulation is the system of blood vessels that carries blood from the right ventricle of the heart to the lungs and back to the left atrium of the heart. The pulmonary trunk carries blood from the heart --> the right and left pulmonary arteries (goes to each lung, gas exchange occurs) ‐Note that these are truly arteries, but they carry deoxygenated blood! ‐They carry blood away from the heart, and they experience relatively high pressures, though not nearly as high as those seen in the systemic circulation ‐Normal systolic pulmonary pressure = 25 mmHg Veins: There are four pulmonary veins (two from each lung) that carry oxygenated blood back to the heart (left atrium).

The systemic arteries carry oxygenated blood from the heart to the body.

One concept that's important to understand about systemic arteries: Many places in the body have anastomoses, these are arterial structures where arteries flow together to offer alternate routes of blood flow to certain regions of the body ‐Makes the blood supply somewhat resistant to the loss of an individual artery because blood can flow 'backwards' from other paths = corollary circulation.

The aorta is the largest‐diameter artery in the body. All arteries of the systemic circulation are derived either directly or indirectly from the aorta.

(1) Ascending aorta; (2) Aortic arch; (3) Descending aorta

Only two branches come off this portion of the aorta = the R and L coronary arteries

This portion of the aorta arches posteriorly & left to posterior body wall just to the left of the spine The aortic arch has three major branches: (1) 1st branch = the brachiocephalic trunk ‐This quickly divides Becomes right subclavian (runs under clavicle to right upper limb) and right common carotid (to head) (2) 2nd branch = Left common carotid (to head) (3) 3rd branch = Left subclavian (under clavicle to left upper limb)

Descends through the thorax and abdomen to the left of the spine gives off all branches to structures in the thorax and abdomen. ‐The regions of the descending aorta are often named separately: the thoracic aorta and the abdominal aorta. At the inferior region of the pelvis, the descending aorta branches into the common iliac arteries.

In both the thorax and the abdomen, there are two types of branches off the descending aorta: (1) Parietal branches = paired branches that come off the side of the aorta ‐One pair comes off at each vertebral level ‐These supply the structures of the body wall (muscles and bones mostly) ‐In the thorax, parietal branches are called intercostal arteries ("intercostal" = between ribs) ‐In the abdomen, parietal branches are called lumbar arteries (2) Visceral branches = Sometimes paired, sometimes unpaired; come off near the anterior center of the aorta ‐These supply the organs of the thorax & abdomen ‐They are especially large & numerous in the abdomen At the inferior region of the pelvis, the descending aorta branches into the common iliac arteries. ‐These then branch into the internal iliac (supplies pelvic organs) and the external iliac (goes to lower limb)

The head and neck are supplied by two primary arteries: (1) The common carotids, which supply both the brain and other head structures (2) The vertebral arteries, which supply only the brain

‐On the R, this is a branch off of the brachiocephalic artery ‐On the L, this branches directly off the aortic arch The common carotid runs up the neck branches to form external carotid & internal carotid ‐External carotid = provides blood to all head structures except for the brain ‐Internal carotid = one of two arteries providing blood supply to the brain.

The carotid body: In the wall of the internal carotid artery, just after the branch from the common carotid, lives a sensory structure called the carotid body, this is a chemoreceptor organ: Senses levels of several blood chemicals including O2, CO2, and pH ‐Information from the carotid sinus is used to trigger important heart and blood vessel reflexes.

This is the second blood supply to the brain ‐It runs through the transverse foramina of cervical vertebrae on its way to the brain

Sources: The blood supply to the brain comes from two pairs of arteries: (1) R and L internal carotid enter the skull at the base of the brain near the hypothalamus (2) R and L vertebral These merge at the base of the pons to become a single artery = the basilar artery ‐The basilar artery runs along the brainstem provides the main blood supply to brainstem & cerebellum = vital structures!!

Cerebral arterial circle: At the base of the brain, around the region of the hypothalamus, the R and L internal carotids and the basilar arteries join form the cerebral arterial circle (AKA Circle of Willis) ‐This is an example of an arterial anastomosis: It's a circle of relatively large vessels Blood can flow in any direction Helps compensate if one component of the blood supply is reduced ‐However, complete loss of one component of the circle cannot be adequately compensated by others brain damage will occur due to lack of blood supply

Branches from the cerebral arterial circle: The cerebral arterial circle gives rise to 3 arteries that supply the cerebrum: (1) The anterior cerebral artery (2) The middle cerebral artery (3) The posterior cerebral artery ‐Each of these supplies corresponding regions of the cerebrum

The major blood supply to the upper limb comes via one artery with three names: (1) Inside the thorax, the artery is the subclavian artery, running deep to the clavicle, as its name suggests (2) As the artery passes the clavicle and enters the shoulder region, it becomes the axillary artery ‐It runs in the axilla (armpit) (3) As the artery passes into the arm, it becomes the brachial artery supplies the arm

Branches of subclavian & axillary arteries: Note that on their way to the arm, the subclavian and axillary arteries give off branches that supply blood to the shoulder and back Ones to know: (1) Internal thoracic artery, AKA internal mammary (from subclavian): Supplies the anterior thoracic wall ‐Main importance = clinical: This artery is the first choice for use in coronary bypass surgery ‐The artery is disconnected from the thoracic wall reconnected to a blocked coronary artery (2) Subscapular artery (from axillary): This is the largest branch of the axillary supplies muscles of the scapula

Distal arteries Blood to the distal arm comes in via the brachial artery ‐Note that there are also small collaterals, e.g. the deep brachial artery, that also bring blood down from proximal arteries ‐These provide some back‐up in case the brachial is lost, but they are pretty small - see the next slide for a more anatomically accurate view of the size of these collaterals. After the brachial artery passes the elbow, it divides into the two major arteries supplying the distal upper limb: (1) The radial artery = on the thumb side (lateral) (2) The ulnar artery = on the pinkie side (medial)

The key thing to know about the arterial supply of the hand = the radial and ulnar arteries supply separate channels of blood to the hand, but there are extensive anastomoses in this blood supply lots of redundancy There are two primary anastomoses in the hand: (1) The deep palmar arch; (2) The superficial palmar arch ‐These arches are large arteries that carry blood across the hand and allow easy flow from one side to the other ‐Very helpful in case of loss of one branch along the way lots of collateral paths for blood to flow

the descending aorta gives off parietal and visceral branches. We'll focus on the visceral branches of the abdominal aorta since these are the most complex and important. I'll discuss the visceral arteries in two groups: (1) The arteries that are unpaired; (2) The arteries that are found in pairs.

3 unpaired visceral branches The unpaired visceral branches of the abdominal aorta all supply digestive organs. (1) Celiac trunk: Emerges from the aorta just after it passes through the diaphragm ‐It gives off three branches: (a) The left gastric artery supplies stomach (b) The splenic artery supplies the spleen (c) The common hepatic artery supplies the liver with oxygenated blood (see "Hepatic portal system" for another supply of blood to the liver) (2) Superior mesenteric artery = the main blood supply to (i) pancreas, (ii) small intestine, (iii) proximal colon (3) Inferior mesenteric artery = the main blood supply to the distal colon.

The arteries of both small & large intestines form vast anastomoses called arcades ‐These arteries run in the peritoneal membrane

3 paired visceral branches: (1) Renal arteries; (2) Suprarenal arteries; (3) Gonadal arteries The gonadal arteries are interesting because they originate fairly high but then run down into the pelvis to supply the ovaries or testes ‐This reflects the development of the gonads, which start off near the kidneys and then descend down during fetal development.

When it reaches the pelvis, the abdominal aorta branches forms the L and R common iliac arteries Each of these then branches to form two arteries: (1) Internal iliac artery = supplies the organs of the pelvis (2) External iliac arteries = supplies the lower limb

Proximal arteries: The proximal arteries of the lower limb show a similar continuum as in the upper limb: External iliac artery becomes the femoral artery in the thigh becomes the popliteal artery as it passes through the popliteal space (behind the knee).

The femoral artery, where it originates at the top‐medial portion of the thigh, runs fairly close to the surface provides an easy point to feel a pulse. ‐This pulse is particularly important because it's requires the lowest blood pressure ‐When the heart is not pumping well, some other pulses will be lost, even though the heart may still be partially functioning ‐But the femoral pulse is the last to go; so if you can't feel a femoral pulse, the heart is not pumping at all!

Distal arteries: The popliteal artery branches into an anterior branch & posterior branch: Anterior branch = the anterior tibial artery; Posterior branch = the posterior tibial artery These then supply the foot ‐Note that there are no arterial arches in the foot! The arterial supply of the foot is more susceptible to blockage

1.) Coronary sinus (returns blood from the walls of the heart. 2.) Superior vena cava (returning blood from the head, neck, throax, and upper limbs. 3.) Inferior vena cava (returing blood from the abdomen, pelvis, and lower limbs.)

In general, the pattern of veins follows the arteries; however they are quite a bit more variable from person to person

As with arteries, the veins divide up anatomically by whether or not they serve the brain

the dural venous sinuses = spaces within the dura that drain blood out of the brain ‐These venous sinuses merge to form the internal jugular vein. The venous sinuses are spaces within the dura mater surrounding the brain.

Blood from the head outside the brain drains into the external jugular vein The internal and external jugulars travel separately down the neck merge near the heart drain into the SVC

Like the arteries, the veins that drain the thoracic wall are called intercostal veins and the veins that drain the abdominal wall are called lumbar veins These drain into a large vein running along the posterior body wall to the R of the spine = the azygous vein The azygous vein then drains into the SVC

Merger of iliacs: The external iliac vein (from the leg) and the internal iliac vein (from the pelvis) merge to form the common iliac vein ‐The R and L common iliac veins then merge form the inferior limit of the inferior vena cava (IVC) Joining of visceral veins: The IVC is then joined by the following veins: (i) Gonadal; (ii) Renal; (iii) Suprarenal; (4) Hepatic ‐Notice no digestive organs here! 2 things to note: (1) The abdominal organs have separate venous drainage from the body wall (2) The digestive organs do not drain directly into the IVC;

One of the most important concepts of venous anatomy = blood from digestive organs does not directly enter the venous system ‐Instead, it all drains through a separate venous system = the hepatic portal system All the blood from digestive organs flows through the liver Why does blood pass through the liver? Answer = the liver does extensive filtering of the blood ‐Removes toxins ‐Stores excess nutrients, supplies nutrients that are deficient in the blood ‐Adds the many proteins that are synthesized by the liver - Example? A = Clotting factors After passage through the liver, the blood enters the hepatic vein, which IVC

(1) The deep veins of the leg are large‐caliber = can store large amounts of blood ‐Two consequences: (a) Gravity can large amounts of blood being 'stuck' in the leg veins ‐The body has mechanisms to help prevent this, but they can malfunction (b) The deep veins are the most common site of life‐threatening blood clots = deep venous thrombosis (DVT) ‐The biggest risk = clot can break off travel to lungs serious lung injury or death = pulmonary embolus (PE) (2) The veins of the leg are generally very redundant with lots of collateral channels for drainage ‐So: The leg veins provide a good source of vessels to use for bypass elsewhere in the body ‐e.g.: Coronary bypass surgery: The 2nd best option = take a leg vein to replace the blocked portion (3) The great saphenous vein = the longest vein in the body.

the goal of the cardiovascular system is to maintain blood flow through capillaries

relatively slowly - needs to have time for exchange to occur

The flow rate is nearly identical.

Capillaries have a higher resistance! •Pressure (P) = Flow (F) x Resistance (R) ‐Rearranged: F = P/R ‐So: increased resistance decreased flow

they have a smaller diameter ‐In fact, the equation relating resistance (R) to diameter (D) is R = 1/D4 ‐And we know that F = P/R ‐So: F = P x D^4 ...hence, as D drops, flow drops very quickly!! ‐This is why blood flows so slowly through capillaries!

The effect of vessel diameter on blood flow isn't only relevant to capillaries...in fact: The relationship F = PxD4 is the key factor used by the body to control where blood flows. ‐All arteries and veins have smooth muscle that can alter their diameter; Which layer? A = tunica media ‐All capillary networks have precapillary sphincters that can narrow the entryway to the network ‐When one vessel constricts, it severely reduces blood flow to downstream vessels shunts blood to other parts of the vascular system

see the importance of vessel diameter in maintaining flow. ‐But there's another factor in the equation = pressure (P) ‐Without pressure, there is no flow, regardless of the diameter of vessels The pressure on the blood is generated by the heart. ‐But the blood undergoes a long journey around the body after leaving the heart, and it cannot flow unless the pressure is maintained during that journey. So what happens to the pressure as blood flows around the body? ‐To get a feel for the answer, consider water flowing through a sprinkler system. ‐As fluid passes through vessels, the pressure drops. ‐Greater resistance greater pressure drop. As blood flows around the body, blood pressure drops.

Arteries: Pressure drops slowly because D is large low resistance Page 10 of 14 ‐Note that the pressure in arteries is pulsatile because arteries basically carry the pressure that is generated by the heart, and the pressure generated by the heart is, of course, pulsatile (2) Capillaries: Pressure drops rapidly due to the very small vessel diameter = high resistance ‐Note that the pulsatile nature of the pressure is lost in the capillaries (3) Veins: Pressure is low, but doesn't drop much more because vessel diameter is high (=low resistance)

Hypertension (back to Slide 39) Let's imagine that something caused the arterial diameter to become narrower higher resistance ‐e.g.: During systole, when blood pressure is high, arteries usually stretch somewhat ‐However, arteriosclerosis = "hardening of the arteries" less flexible arteries don't expand What happens to the blood pressure curve? Answer = pressure drops faster in the arterial system MM: Draw it ‐But then pressure is lower at the capillaries because F = P x D4 ‐Would mean a potentially severe loss of blood flow to capillaries very dangerous! The body can compensate for this by increasing the pressure generated by the heart MM: Draw a higher pressure curve ‐But notice that now the overall pressure in the arterial system is higher! ‐This is the condition called hypertension: Excess resistance in the arterial system that causes the heart to generate more pressure If this is just a short‐term condition, say when you're really stressed and your sympathetic NS is activated, your system can handle it fine. ‐But chronically, this can lead to two types of consequences: (Slide 40 hypertension_heart, hypertension_retina) (1) The heart can restructure itself by growing new muscle tissue = hypertrophy ‐This actually makes the heart much less efficient - it requires more oxygen, and has a smaller stroke volume ‐Reduces exercise tolerance, increased risk of myocardial infarction (2) Arteries suffer damage from the sustained high pressures ‐Greatly increased risk of hemorrhagic stroke ("hemorrhagic" = bleeding) = the bursting of an artery ‐Most susceptible organs = kidneys, retinas, brain ‐Also tends to cause arteries to become stiffer positive feedback