1. Cardiovascular system - Blood Vessels Chapter 13

2. Basic Anatomy of Circulatory routes
Arteries
Arterioles
Capillaries
Venules
Veins
Carry blood towards the heart
Carry blood away from the heart
Connect capillaries to veins
Control blood flow into capillaries & help regulate BP
Allow for “exchange” of O2/CO2, nutrients/wastes

3. Structure of Blood Vessels

4. Arteries & Veins
Both are comprised of 3 layers of tissue - tunica interna, tunica media & tunica externa - surrounding “lumen” through which blood will flow:
All structural difference between arteries & veins primarily due to differences in pressure of blood flowing within
Lumen – larger diameter in veins compared to corresponding artery

5. Arteries & Veins
Tunica Interna – innermost endothelium of simple squamous epithelium + basement membrane
Arteries – have an “internal elastic lamina” of elastic CT to allow for expansion under pressure
Veins – may have “valves” (folds of endothelium + CT) to prevent backflow of blood due to low pressure

6. Arteries & Veins
Tunica Media – middle layer containing smooth muscle (for contractility/vasoconstriction) & elastic CT (for elasticity)
Arteries – have relatively thick tunica media allowing for significant vasoconstriction & elasticity
Veins – relatively thin tunica media therefore no significant constriction/elasticity

7. Arteries & Veins
Tunica Externa (a.k.a. adventitia) – made of collagenous CT
Arteries – thin layer
Veins – thickest layer of vein, trying to support against gravity & low pressure

8. As blood moves through CV system from arteries  veins, pressure within the vessels decreases significantly
Blood also has to move against gravity in many veins
Venous return is aided by:
Continuous heartbeat
Valves
Muscular compression – “milking of veins through skeletal muscle contraction
Respiratory pump – breathing  changes in pressure in abdominal/thoracic cavities

9. Arterioles & Venules
Very small, almost microscopic vessels with only 2 layers of tissue surrounding lumen
Arterioles – endothelium (tunica interna) + very thin layer of smooth muscle cells (tunica media); regulate blood flow to tissues & affect arterial blood pressure
Venules – endothelium (tunica interna) + thin layer of CT (tunica externa)

10. Capillaries
Microscopic, very thin-walled vessels comprised of endothelium with basement membrane
Found in all tissues of the body except for those that are “avascular”
Usually form branching networks (“capillary beds”) within tissues for increased surface area

11. Capillaries Structure of capillaries allows for
filtration - at arterial end due to high “capillary hydrostatic pressure” (CHP)
reabsorption - at venous end due to high “blood osmotic pressure” (BOP)

12. Physiology of Circulation
Primary function of CV system is to maintain adequate blood flow to capillaries of tissues
Under normal circumstances, capillary blood flow is directly related to cardiac output (increased C.O.  increased blood flow, and vice-versa)
Capillary blood flow is also affected by pressure & resistance

13. Physiology of Circulation
Pressure:
“Blood pressure” - the “force” exerted on the wall of a vessel from the blood within; related to the “beating” of the heart
Systolic pressure – pressure within artery when ventricle contracts
Diastolic pressure – pressure remaining within artery when ventricle relaxes
“Circulatory pressure” – the difference in pressures throughout the circulatory system (high pressure in arteries (avg.100mm Hg at aorta)  low pressure in veins (avg. 2mm Hg at IVC))
Blood flow is directly related to circulatory pressure – blood will move from high to low pressure. If arterial blood pressure increases, capillary blood flow will increase, & vice-versa

14. Physiology of Circulation
Resistance
Resistance – any force that opposes movement
Peripheral resistance – refers to resistance of blood flow in arterial side of system; mainly occurs at arterioles
Peripheral resistance primarily due to friction between blood & BV walls
As peripheral resistance increases (ie. with vasoconstriction of arterioles), capillary blood flow decreases (inverse relationship)

15. Circulatory Routes - overview

16. Circulatory Routes – Pulmonary Circuit

17. Circulatory Routes – Systemic circuit
Ascending aorta (gives off coronary arteries)
Aortic arch
Brachiocephalic trunk
Left common carotid artery
Left subclavian artery
Thoracic (descending) aorta
Abdominal aorta
Common iliac arteries
Arterial blood from left ventricle into ascending aorta
Venous return to right atrium through SVC, IVC & coronary sinus