Blood Vessels

1. Blood Vessels

2. Blood Vessels • There are 100,000 miles of blood vessels. • With the exception of hyaline cartilage (which is avascular), no cell is more than a few cell diameters away from a blood vessel, so they can get oxygen, nutrients, remove waste.

3. Blood Vessels • Arteries get smaller and thinner and are then called arterioles. • Arterioles get smaller and thinner until their lumen is just one red blood cell in diameter. At this point, they are called capillaries, and this is where the oxygen exchange takes place. • Capillaries then get larger as they take waste products away from the cells in the capillary bed and head back to the heart; now they are called venules. • As venules get bigger, they are called veins until they return to the heart.

4. Blood Vessels • From the heart the blood is pumped to the lungs to get more oxygen. • During this trip, they get smaller again until they are capillaries, then they get the oxygen from the lungs and drop off the waste products (carbon dioxide). • Then the blood returns to the heart to get pumped out to the body again. • All blood vessels (except the smallest) look similar.

5. Tunica intima Endothelium Subendothelium Tunica media Smooth muscles Elastic fibers Tunica adventitia Vasa vasorum

6. Structure of Blood Vessels • Composed of three layers (tunics) • Tunica intima • ENDOTHELIUM: simple squamous epithelium. Allows for smooth flow of blood. Similar to endocardium. • SUBENDOTHELIUM: loose connective tissue.

7. Structure of Blood Vessels • Composed of three layers (tunics) • Tunica media • SMOOTH MUSCLE: allows vasoconstriction. Allows blood to be directed to parts of body. • ELASTIC FIBERS: within smooth muscles. Allows for forced vasodilation during heart contraction.

8. Structure of Blood Vessels • Composed of three layers (tunics) • TUNICA ADVENTITIA (TUNICA EXTERNA): dense fibrous connective tissue which thins out to loose connective tissue. • Protects the blood vessel (strong) • Gives vessel strength for shape • Anchors vessel to surrounding tissue; loosens with age. • Lumen – central blood-filled space of a vessel

9. These layers are thick, so they need their own vascular supply: VASA VASORUM(blood vessel for a blood vessel) to supply the oxygen. • The endothelium layer does not need this because it’s in direct contact with the blood, but the subendothelium needs it.

10. Tunica intima Endothelium Subendothelium Tunica media Smooth muscles Elastic fibers Tunica adventitia Vaso vasorum

11. Structure of Arteries, Veins, and Capillaries Figure 19.1a

12. Types of Blood Vessels • Arteries – carry blood away from the heart • It does not matter if it is oxygenated or deoxy blood. If it is leaving the heart, it is an artery. • Capillaries – smallest blood vessels • The site of exchange of molecules between blood and tissue fluid • Veins – carry blood toward the heart • It does not matter if it is oxygenated or deoxy blood. If it is entering the heart, it is a vein.

13. Arteries • ARTERIES carry blood away from the heart. • Arteries have a smaller lumen than veins of similar size. • Arterial walls are thicker than venous walls. • Arteries have more elastin than veins. • Arteries have no valves because the blood pressure in arteries is high enough that there is no backflow of blood.

14. Arteries Two types of large arteries: Elastic Muscular

15. Types of Arteries • Elastic arteries – the largest arteries • Diameters range from 1 - 2.5 cm • Includes the aorta and its major branches • High elastin content dampens surge of blood pressure Figure 19.2a

16. ELASTIC ARTERIES • Largest, closest to heart. • Has to take the full force of the systolic contraction; compensates by expanding a lot. • There of lots of elastic fibers in the tunica intima as well. • Does blood flow during diastole? Yes; elastic arteries return to original size, pumps blood. • This is another pump besides the heart.

17. Muscular Arteries • Muscular (distributing) arteries • Distal to elastic arteries • From 0.3 mm- 1 cm • Includes most of the named arteries • Tunica media is thick Figure 19.2b

18. MUSCULAR ARTERIES • Function is to distribute blood, and help control which regions of the body get blood. • When you are exercising, you want the blood from the GI system to go to muscles. • When your hands are cold, your body is using its blood for something more important. Therefore, the vessels will constrict in the hands. • Dilation is just lack of constriction.

19. ARTERIOLES • These are microscopic; they are the smallest type of artery. • Large ones look like muscular arteries. • Small ones only have two layers: endothelium and tunica media. • One of the characteristics of an arteriole is that when it contracts, the lumen closes completely.

20. Types of Arteries • Arterioles • Smallest arteries • Diameters range from 10 µm to 0.3 mm Figure 19.2c

21. Aneurysm • A sac-like outpouching of an artery • Can rupture at any time; in aorta or brain can cause death within a few seconds. • Symptoms: Swelling or throbbing (asymptomatic in brain) • Some common locations for aneurysms include: • Aorta • Brain • Leg • Intestine (mesenteric artery aneurysm) • Splenic artery aneurysm (can form during pregnancy)

22. Aneurysm • Causes of an aneurysm: • Defect in part of the artery wall • High blood pressure (abdominal aortic aneurysms) • Congenital (present at birth) • Usually not detected except by an angiogram or ultrasound. • Treatment: surgical repair

23. Aneurysm

24. Stroke

25. The Ovation Abdominal Stent Graft System • Aneurysms can be repaired through open surgery or less invasively with endograft repair using a stent graft otherwise known as an endograft. • Endograftsfeature a tube typically made of plastic material that is supported by a metal frame or stent. They are compressed into a delivery catheter, inserted into the femoral artery of the leg and then threaded into position in the weakened portion of the artery where they are released. Once released, the endograft expands against the wall of the aorta to redirect blood flow away from the aneurysm.

26. How to Recognize a Stroke (“STROKE”) • S * Ask the individual to SMILE. • T * Ask the person to TALK and SPEAK A SIMPLE SENTENCE (Coherently; i.e. It is sunny out today) • R * Ask him or her to RAISE BOTH ARMS. • O * Open the mouth and stick out the tongue • K * Keep them comfortable and still • E * Get EMERGENCY help (911)If one side of the body responds differently than the other side, or if they have trouble with the task, call 911.

27. Important: • You don’t have enough blood to go around; you only have 5 liters for 100,000 miles of blood vessels. • At any given time, most blood vessels will be closed (except at lungs). • Are you using your legs now? When your legs run low on oxygen, the vessels there will open up again. • Are you using your brain now? I hope so! The vessels there will be open. • When your leg falls asleep, there is pressure on an artery which stops the blood flow. When the nerves are deprived of oxygen, they tingle.

28. Some clinically significant arteries • Femoral artery: easy to find pulse, but susceptible to injury. • Circle of Willis: loop of arteries around pituitary and optic chiasma. Common area for stroke to cause blindness.

29. Circle of Willis

30. Capillaries • Smallest blood vessels; they are found everywhere • These are the only sites of nutrient, gas exchange, and waste exchange in the cardiovascular system. • Diameter from 8–10 µm • Diameter is similar to an erythrocyte • Red blood cells pass through single file • They only have an endothelium.

31. Capillaries • Site-specific functions of capillaries • In the lungs – oxygen enters blood, carbon dioxide leaves • In the small intestines – receive digested nutrients • In endocrine glands – pick up hormones • In the kidneys – removal of nitrogenous wastes

32. Capillary Permeability • Intercellular clefts – gaps of unjoined membrane • Small molecules can enter and exit • Three types of capillaries • Continuous – most common • Fenestrated (“window”) – have pores • Discontinuous (Sinusoids) – have very large gaps

33. Types of Capillaries • CONTINUOUS CAPILLARIES • FENESTRATED CAPILLARIES • DISCONTINUOUS CAPILLARIES

34. CONTINUOUS CAPILLARIES • All capillaries are made of simple squamous epithelium. • Continuous capillaries are most common, found in all organs of body. • They have intracellular clefts, the function of which is essential for plasma to leak out and bathe each cell with extracellular fluid, which is rich in oxygen and nutrients. • Erythrocytes and platelets don’t fit through, but leukocytes can squeeze through so they can enter and leave the blood vessels as needed.

35. Continuous Capillary Figure 19.4a

36. FENESTRATED CAPILLARIES • These have a lot more leakage because there are more pores (holes). • Found in areas where lots of fluids need to be moved back and forth (synovial membrane, small intestine).

37. Fenestrated Capillary Figure 19.4b

38. DISCONTINUOUS CAPILLARIES (sinusoidal capillaries) • These have very large gaps in the capillary. • Anything can go in and out here, including erythrocytes. • These are found in red bone marrow, where RBCs are made, and they need to enter the circulation by way of the sinusoidal capillaries. • These capillaries are also in the liver and spleen, where red blood cells are destroyed.

39. Sinusoids Figure 19.4c

40. Capillary Beds Figure 19.3a

41. PRE-CAPILLARY SPHINCTER • A small muscle in front of each capillary, controls the flow of blood to individual capillaries. • ARTERIOLES direct the blood flow to the specific tissue. PRE-CAPILLARY SPHINCTERS direct the blood flow to specific cells. • If one cell is starving, the capillary next to it will open. The sphincter opens and closes depending on the needs of individual cells.

42. Capillary Beds Figure 19.3b

43. PRE-CAPILLARY SPHINCTER • There is not enough blood to go around, so blood always flows only to those cells and tissues that need it. • They drop off nutrients, pick up CO2 waste, etc.

44. Veins • Veins take blood TO the heart. Two types: • Venuole: from the capillary to the vein • Vein: takes blood to the heart. • Thinner walls (less pressure here) • Larger lumen (blood moves more slowly) • Skeletal muscle pushes on the vein to move the blood uphill. • Need valves in veins

45. Valves in Veins • How does blood get uphill back to the heart? Veins need valves. • Veins are the only BLOOD vessels that have valves (although LYMPH vessels also have valves). • Valves in veins allow blood to move in only one direction. What pushes the blood? The muscles of the body constrict, squeezing the vessels. This is a type of blood pump.

46. Veins

47. BLOOD PUMPS • The heart • Elastic arteries • Muscles constricting the veins

48. Clinically Significant Veins • Greater Saphenous vein: used for coronary bypass; most likely becomes varicose. • Facial vein: “Danger triangle” infection spreads to meninges in brain. • Renal vein: oxygen poor, and contains the lowest concentration of nitrogen waste.

49. Veins that are rich in oxygen and nutrients • Umbilical vein • Hepatic Portal vein • Pulmonary vein

50. Fun Fact • Shivering increases your body heat by 18 fold. • Moderate walking only increases it by 3 fold.