Week 3 Notes
Week 3 Notes BSC 216
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This 8 page Class Notes was uploaded by Austin Miller on Monday January 18, 2016. The Class Notes belongs to BSC 216 at University of Alabama - Tuscaloosa taught by Austin Hicks/Jason Pienaar in Winter 2016. Since its upload, it has received 17 views. For similar materials see Human Anatomy & Physiology II in Biological Sciences at University of Alabama - Tuscaloosa.
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Date Created: 01/18/16
VESSELS & CIRCULATION Blood Vessels: Arteries are the efferent pathways that carries blood away from the heart and branches out along the way Veins are the afferent pathways that carry blood back to the heart and converge along the way The only vessels that come in close contacts to tissues and exchange gas and nutrients are capillaries. Capillaries take the oxygen rich blood from the arteries, use what they need, and send the rest through the veins and back to the heart Structure of Blood Vessels: 1. Tunica intima (interna): a. Innermost tunic b. Direct contact with the blood c. Endothelium= squamous epithelial tissue d. Endothelium is slippery so it can minimize friction for the blood e. Internal elastic lamina is for distensibility 2. Tunica media: a. Middle tunic b. Circular smooth muscle along with elastin c. Controlled by sympathetic nervous system d. Vasoconstriction: smooth muscle contracts and lumen diameter is reduced e. Vasodilation: smooth muscle relaxes and lumen diameter increases f. Helps control blood pressure with it’s extensibility 3. Tunica externa (adventitia): a. Outermost tunic b. Collagen fibers responsible for protection and anchoring c. Possesses nerve fibers, lymphatic vessels d. Vasa vasorum is the network of tiny vessels that nourish the tunica externa and media Structure of Arteries: 1. Elastic arteries: thick-walled, near heart (aorta + branches) a. Lumen has the largest diameter of all arteries b. High in elastin content; present in all three tunics c. Elastin content allows expansion and retraction in response to blood from heart d. Will be directly off heart (aorta) to deal with the high pressure of blood being pumped from the ventricles 2. Muscular arteries: deliver blood to organs, these are most of our arteries a. Thickest tunica media of all vessels; intermediate lumen diameter b. More smooth muscle, less elastin in tunica media than elastic arteries c. Better at vasoconstriction (moving blood) 3. Arterioles: deliver blood to capillary beds within tissues a. Lumen has smallest diameter of all arteries b. Tunica media mostly smooth muscle; few elastin fibers 2 Structure of Veins: 1. Venules: result from convergence of capillaries a. Endothelium plus some surrounding connective tissue b. Highly porous (fluid and WBC’s freely move across walls) c. Larger venules have smooth muscle layers (tunica media) and thin tunica externa 2. Veins: result from the convergence of venules a. 3 tunics b. Walls thinner and lumens larger than arteries c. Very little smooth muscle in tunica media d. Thick tunica externa with thick collagen fibers and elastic fibers e. Blood pressure lower in veins but the large lumens provide little resistance to blood flow to return it to the heart f. Venous valves are extensions of the tunica intima (similar in structure to the semilunar valves of the heart) 3 Blood distribution in Cardiovascular System: Circulatory Routes: 4 As far as circulatory routes go, we see three different options in our body. 1. Simple Pathway- a. This pathway only sees one, single capillary bed and will travel from the heart arteries arterioles capillaries venules and finally veins before retuning back to the heart b. This is the simplest, and most common pathway! 2. Portal System- a. Blood flows through two consecutive capillary networks before returning to the heart i. Between hypothalamus and anterior pituitary ii. In kidneys iii. Between intestines and liver 3. Arteriovenous anastomosis (shunt)- a. Artery flows directly into veins, bypassing capillaries i. In our fingers and toes to reduce heat loss (but can lead to frostbite) b. Venous anastomosis is the most common anastomosis where one vein empties directly into another. This is why vein blockage is less serious than arterial blockage. c. Arterial anastomosis is where two arteries merge and provide collateral (alternative) routes of blood supply to the desired tissue. This is in coronary circulation and around joints 5 (a) Simplest pathway (1 capillary bed) (c) Arteriovenou s anastomosis (shunt) (d) Venous (e) Arterial anastomose anastomose s s Basic Terms of Circulation Physiology: Blood flow- volume of blood flowing through a vessel, organ, or entire circulation in a goven period o For entire vascular system cardiac output = 5-6 L/min Blood flow (F) ~ BP gradient (P)/Resistance (R) o This is the same as saying the greater the pressure difference between two points, the greater the flow. o The greater the resistance, the less the flow. 6 Pressure gradient (P) = Cardiac output (CO) x Peripheral Resistance (PR) o Cardiac output (CO) = stroke volume x heart rate o Stoke colume is the volume of blood expelled from the heart with each ventricular contraction aka how much blood is leaving the heart (b) Portal sure is the force per unit area exerted system by blood on a vessel wall (mmHg) and typically refers to arterial blood pressure in aorta and its (2 capillary beds)nches. We would NOT want to measure this in the veins since the venous bp is much lower. Blood flows from high to low pressure. Peripheral Resistance Vessel radius: most powerful influence on blood flow o The only significant way of controlling peripheral resistance o Vasomotion- change in vessel radius Vasoconstriction- by muscular effort that results in smooth muscle contraction Vasodilation- by relaxation of the smooth muscle o Vessel radius affects blood velocity o Laminar flow- flows in layers, with the center flowing the fastest o Blood flow (F) is proportional to the fourth power of the radius (r) Arterioles can constrict to one-third of fully relaxed radius If r = 3mm, F = 81 mm/sec; If r = 1 mm, F = 1 mm/sec 7 8