Chapter 16.2: Blood Flow Through Blood Vessels

Resistance -Vascular Resistance: the opposition to blood flow due to friction between blood and blood vessel walls -↑ resistance = ↑ blood pressure -Affected by three factors: 1)Size of lumen: changes from vasoconstriction/vasodilation 2)Blood Viscosity (thickness): depends on ratio of RBCs to plasma volume 3)Total Blood Vessel Length: longer vessels have more resistance

Regulation of Blood Flow/Blood Pressure -Controlled by multiple negative feedback systems -Body can adjust heart rate, blood volume, and vascular resistance - Produces either sudden or long-term changes

The Cardiovascular Center -Located in the medulla oblongata of the brain -Regulates heart rate -Controls neural and hormonal negative feedback systems -Receives input from three sensory receptors: 1)Proprioreceptors: monitor movements of joints and muscles 2)Baroreceptors: detect changes in pressure in major arteries 3)Chemoreceptors: monitor blood levels of O 2, CO 2, and pH -Located in carotid and aortic bodies

CV Center Output -Flows along sympathetic and parasympathetic nervous system -↑ sympathetic = ↑ heart rate and ↑ vasoconstriction -↑ parasympathetic = ↓ heart rate and ↓ vasoconstriction INPUT TO CARDIOVASCULAR CENTER (nerve impulses) From proprioceptors: monitor joint movements From baroreceptors: monitor blood pressure From chemoreceptors: monitor blood acidity (H + ), CO 2, and O 2 OUTPUT TO EFFECTORS (increased frequency of nerve impulses) Heart: decreased rate Heart: increased rate and contractility Blood vessels: vasoconstriction Cardiovascular (CV) center Vagus nerves (parasympathetic) Cardiac accelerator nerves (sympathetic) Vasomotor nerves (sympathetic)

Hormonal Regulation -Several hormone systems help regulate blood pressure and blood flow 1)Aniogtensin II causes vasoconstriction in response to drop in blood volume - Aldosterone stimulates reabsorption of water by kidneys 2) Epinephrine/Norepinephrine increase cardiac output and vasoconstriction 3)Antidiuretic Hormone (ADH) causes vasoconstriction in response to dehyrdration 4)Atrial Natriuretic Peptide (ANP) lowers blood pressure by causing vasodilation and promoting loss of salt and water in urine

Some stimulus disrupts homeostasis by Blood pressure Receptors Baroreceptors in arch of aorta and carotid sinus are stretched less Control centers CV center in medulla oblongata Effectors Increased heart rate lead to increased cardiac output (CO) Constriction of blood vessels increases systemic vascular resistance (SVR) Increased sympathetic, decreased parasympathetic stimulation Return to homeostasis when increased cardiac output and increased vascular resistance bring blood pressure back to normal Decreasing Decreased rate of nerve impulses Increased secretion of epinephrine and norepinephrine from adrenal medulla Input Output Increased BP