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/vasodilation2) Blood Viscosity (thickness): depends on ratio of RBCs to

plasma volume3) 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 muscles2) Baroreceptors: detect changes in pressure in

major arteries 3) Chemoreceptors: monitor blood levels of O2,

CO2, 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+), CO2, and O2

OUTPUT TO EFFECTORS(increased frequency of nerve impulses)Heart: decreased rate

Heart: increased rate and contractility

Blood vessels: vasoconstrictionCardiovascular(CV) center

Vagus nerves(parasympathetic)

Cardiac acceleratornerves (sympathetic)

Vasomotor nerves(sympathetic)

Hormonal Regulation

- Several hormone systems help regulate blood pressure and blood flow1) 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

ReceptorsBaroreceptors in arch of aorta and carotid sinus are stretched less

Control centers

CV center inmedulla 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