1. Blood Vessels

2. Circulation All blood is constantly moving along the circulatory system The most vital nutrient which is used most quickly is oxygen, so blood is usually divided into oxygenated and deoxygenated blood in graphs – Realistically even “deoxygenated” blood usually still has about 25- 50% oxygen load

3. Road Analogy If cells are houses and must receive service via streets, the largest blood vessels are freeways Note that like a freeway, major blood vessels such as arteries and veins do NOT deliver oxygen or nutrients but rather move blood quickly to different parts of the body Almost all nutrient and waste exchange happens in small, leaky blood vessels called capillaries

4. Arteries and Veins Arteries move blood away from the heart Arteries in the body have high pressure and are bright red from the oxygen content Veins move blood towards the heart and have very low pressure – Deoxygenated blood is NOT blue, but it is dark, and the vein coverings make it appear blue

5. Blood Vessel Sizes Main arteries lead directly away from the heart before branching into arterioles Arterioles branch further to become capillaries, then rejoin to become venules Venules combine to form veins – Many veins have valves to prevent backflow since there is so little blood pressure – Blood is moved through veins by muscle movement, which is why stretching feels good

6. Capillaries All tissues (except cartilage, epidermis and the lens of the eye) have capillaries that blood flows into from the arteries Capillaries are very thin and leaky so nutrients can diffuse out of the blood into the surrounding tissues Also allows wastes to diffuse into the blood

7. Anatomy of Blood Vessels Major blood vessels (arteries and veins) have smooth muscle and coverings – Smooth muscle helps squeeze blood through and constricts when the blood vessel is damaged All blood vessels have a smooth inner lining called endothelium which reduces friction/turbulence The inner space of a vessel is called the lumen

8. Blood Flow Regulation When a blood vessel increases in diameter it is said to vasodilate – Increases blood flow to an area – Provides additional nutrients, helps be more active and also helps heal damaged tissue When a blood vessel decreases in diameter it is said to vasoconstrict – Cuts off blood supply to ensure more blood goes elsewhere, or to prevent bleeding

9. Variable Flow Capillaries can also be opened and closed to change blood flow to different organs – Blood flow to skin = “flush” to help cooling – Blood flow to muscles = adrenaline rush – Blood flow to digestive system = food coma Much of this is accomplished with smooth muscles around the start of the capillaries, called precapillary sphincters

10. Blood Pressure Blood pressure decreases as the blood travels through arteries, capillaries, and veins – The more viscous the blood (from more RBCs) the faster the pressure drops The blood pressure at the start of the capillary squeezes plasma into the tissues (this is called capillary blood pressure) – The lower pressure at the other end of the capillary sucks fluid back in, which is called blood colloid osmotic pressure

11. Blood Volume Two hormones work against each other to balance blood pressure: – Aldosterone (secreted by adrenal cortex) causes sodium retention and therefore water retention – ANP (atrial natriuretic peptide) is secreted by the atria of the heart and promote excretion of salt and water by the kidneys – Question: what does ADH do? Note that the heart literally asks the kidneys to pee more when it gets overworked

12. Obesity and Blood Pressure Clearly junk food is “unhealthy” but why exactly? – Extra calories are stored as excess body fat, increasing blood volume – Extra cholesterol above what’s needed can form plaques that can block blood vessels – Extra sodium increases blood volume and water retention These factors may, as a pattern, lead to obesity, which is strongly correlated with heart disease

13. Hooray cheerful weekend! Next week is the exam week! Don’t forget the online quiz!!!!1