Blood Vessels and Circulation

2 Some embryology first  There are at first six pairs of aortic arches  In fish these are connected to the gills  They undergo a transformation in mammals  Birds use the right arch of the fourth pair  Mammals use the left arch of the fourth pair

3 Ventral (anterior) view Full set of arches develops, but not all present at the same time; (before transformation) Transformation : 4 th through 7 th weeks: some persist, some atrophy

4 Right common carotid a Right subclavian a Brachiocephalic trunk th arches become: Left side: aortic arch Right side: brachiocephalic trunk

5 What the aortic arches become… Right common carotid a Right subclavian a Brachiocephalic trunk

6 What the aortic arches become… Right common carotid a Right subclavian a Brachiocephalic trunk

7 What the aortic arches become… Right common carotid a Right subclavian a Brachiocephalic trunk

8 What the aortic arches become… Right common carotid a Right subclavian a Brachiocephalic trunk

9 What the aortic arches become… Right common carotid a Right subclavian a Brachiocephalic trunk

10 What the aortic arches become… Right common carotid a Right subclavian a Brachiocephalic trunk

11 3 Major types of blood vessels  Body  RA  RV  Lungs  LA  LV  Boby 1.Arteries 2.Capillaries 3.Veins Arteries carry blood away from the heart -”branch,” “diverge” or “fork” Veins carry blood toward the heart -”join”, “merge,” “converge”

12 General characteristics of vessels  Three layers (except for the smallest) 1.Tunica intima - AKA intima 2.Tunica media – smooth muscle 3.Tunica externa - AKA adventitia  Lumen is the central blood filled space

13  Intima is endothelium (simple squamous epithelium)  Tunica media: layers of circular smooth muscles  Lamina (layers) of elastin and collagen internal and external  Thicker in arteries than veins (maintain blood pressure) Smooth muscle contraction: - vasoconstriction Smooth muscle relaxation: - vasodilation

14  Adventitia (t. externa) – longitudinally running collagen and elastin for strength and recoil

15 “muscular” middle sized artery

16 Arteries  Carry blood away from the heart  From biggest to smallest, these are the categories: 1. Elastic 2. Muscular 3. Arterioles (then these to capillaries)  Pressure diminishes along the route 1.Elastic arteries: act as conduits  cm diameter  Expand with surge of blood from heart contraction  Recoil from heart relaxation, which aids movement of blood  Elastin is thick in media: dampens the surge of blood pressure  Aorta and its branches

17 Arteries continued 2. Muscular arteries: act as distributing arteries  Middle sized.3mm-1cm  Changes diameter to differentially regulate flow to organs as needed  Internal as well as external elastic lamina  Most of what we see as “arteries”  From these we measure blood pressure Tunica media larger in proportion to the lumen, thus “muscular”

18 Arteries continued 3. Arterioles  Smallest:.3mm-10um  Only larger ones have all 3 layers  Send blood into capillaries Tunica media has only a few layers of smooth muscle cells

19 Capillaries Heart  arteries  capillaries  veins  heart  Capillaries are smallest blood vessel  8-10um  Just big enough for a single file of erythrocytes (RBCs)  Composed of:  single layer of endothelial cells surrounded by a membrane  General Function  Oxygen and nutrient delivery to tissues  CO2 and nitrogenous waste (protein break-down product) removal

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Types of Capillaries 1.Continuous – has virtually no “gaps” open in its walls (e.g., blood-brain barrier) 2.Fenestrated – numerous “pores” in the endothelium (e.g., intestinal lining, kidneys, endocrine glands) 3.Sinusoids – modified “leaky” capillaries (e.g., liver, spleen, bone marrow)

Continuous Capillaries Figure 19.3a

Fenestrated Capillaries Figure 19.3b

Sinusoids Figure 19.3c

Capillary Beds  A microcirculation of interwoven networks of capillaries, consisting of:  Vascular shunts – thoroughfare channel connecting an arteriole directly with a venule  True capillaries – 10 to 100 per capillary bed, capillaries branch off and return to the thoroughfare channel

Capillary Beds

Blood Flow Through Capillary Beds  Precapillary sphincter  Cuff of smooth muscle that surrounds each true capillary  Regulates blood flow into the capillary  Blood flow is regulated by vasomotor nerves and local chemical conditions

Capillary Beds

30 Veins  From smallest to large: Capillaries  venules  veins  heart  Veins are larger than arteries  Tunica externa is thicker  But…blood pressure is lowered at capillaries, so the walls of veins are much thinner  There is less elastin

31 Special features of veins  Valves  Prevent backflow  Most abundant in legs (where blood has to travel against gravity)  Muscular contraction  Aids the return of blood to heart in conjunction with valves

32 Exercise helps circulation (because muscles contract and squeeze blood back to the heart)

33 Vascular anastomoses (shunts)  Alternative pathways or connections between blood vessels  Protect organs from being supplied by just one route  Poor anastomoses & therefore vulnerable: central artery of retina, kidneys, spleen, bone diaphyses

34 Angiogram

35 Major Arteries

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37 Systemic Veins  3 major vessels enter Right Atrium:  SVC (superior vena cava)  IVC (inferior vena cava)  Coronary sinus  Many veins are very superficial (unlike arteries)  Venous plexuses (networks of anastomoses and parallel veins) are very common  Head and hepatic portal systems are unusual

38 Vein overview Note that unlike the arteries, the veins have a brachiocephalic on the right and left sides

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40 Leg veins  Names similar to arteries  Femoral becomes external iliac after crossing under inguinal ligament  External iliac joins with internal iliac to form common iliac vein _________used for grafting in coronary artery bypass grafts: is the longest vein in the body

41 Vascular System ( Blood vessels of the body)  Two circulations  Systemic  Pulmonary  Arteries and veins usually run together  Often nerves run with them  Sometimes the systems do not have bilateral symmetry  In head and limbs, most are bilaterally symmetrical

42 Pulmonary Circulation  Pulmonary trunk branches  Right and left pulmonary arteries  Division into lobar arteries  3 on right  2 on left  Smaller and smaller arterioles, into capillaries surrounding alveoli  Gas exchange  Pulmonary system pressure is only 1/6 of systemic blood pressure

43 Pulmonary Circulation  After gas exchange blood enters venules  Larger and larger into Superior and Inferior Pulmonary veins  Four Pulmonary Veins empty into left atrium

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45 In lungs

46 Systemic Circulation  Oxygenated blood to body  Leaves LV through Ascending Aorta  Only branches are the 2 coronary arteries to the heart  Aortic Arch has three arteries branching from it: 1.Brachiocephalic trunk, has 2 branches:  Right common carotid a.  Right subclavian a. 2.Left common carotid a. 3.Left subclavian a. Ligamentum arteriosum connecting to pulmonary a. remember aortic arches…

47  Hepatic portal system  Picks up digested nutrients from stomach & intestines and delivers them to liver for processing and storage  Storage of nutrients  Detoxification of toxins, drugs, etc.  Two capillary beds  Route: artery to capillaries of gut to hepatic portal vein to liver’s capillaries to hepatic vein to IVC Tributaries of hepatic portal vein: - superior mesenteric vein -splenic vein -inferior mesenteric vein

48 Assignment - Some Diseases  Atherosclerotic cardiovascular disease  Cerebrovascular disease  Coronary artery disease (CAD)  Peripheral vascular disease (PVD)  Affecting veins  Chronic venous insufficiency  Deep venous thrombosis (DVT)  Aneurysms  Portal hypertension  Hypertension