Cardiac Cycle, Blood Pressure, Blood velocity, and Blood Vessel cross-sectional area

Heartbeat Control: Intrinsic nodal tissue within the heart controls normal heartbeat Sino atrial node initiates impulse conducted into both atria simultaneously, they contract = atrial systole, blood forced into ventricles. ventricles are relaxed (diastole) and fill with blood. Impulse moves to atrioventricular node (AVN) (location?) conducted through septum to Bundle of HIS

impulse carried from Bundle of HIs through the walls of ventricles by Purkinje fibers causes ventricular systole, forcing blood out of ventricles into the pulmonary trunk and aorta. Atria are in diastole and filling with blood Complete 1st page notes

Animation of cardiac cycle Watch video at 1:30

Modification of the Normal Heartbeat -modification =speeding up or slowing down -stimulation by nerve impulses or hormones -autonomic nervous system or endocrine system = extrinsic control of heartbeat

Autonomic regulation of heartbeat: Nervous system two divisions: sympathetic and parasympathetic Stimulus: hypotension (low blood pressure) Receptor: cardiovascular centre of the medulla oblongata Effector: sympathetic division of autonomic nervous system Response: increase heart rate/stronger heartbeat/increased b.p.

Autonomic regulation of heartbeat: Nervous system Stimulus:Hypertension/ high blood Receptor: cardiovascular center of medulla oblongata Effector:parasympathetic division of autonomic nervous system Response: decreased heart rate/ weaker heartbeat/decrease in blood pressure

Hormonal Regulation of Heartbeat/endocrine system Stimulus: low blood pressure/ hypotension Receptor: cardiovascular center of the medulla oblongata Effector: sympathetic division of autonomic nervous system signals adrenal medulla to release adrenaline and noradrenaline Heart: increase heart rate/ stronger heartbeat/increase blood pressure

Blood Pressure, Velocity, Blood vessel cross-sectional area Blood pressure= force of blood on walls of blood vessels b.p. highest in arteries and lowest in veins b.p.in arteries oscillates in response to ventricular systole and diastole

Blood velocity -decreases and reaches lowest level in capillaries -blood velocity= speed at which blood moves through the blood vessels - blood velocity oscillates in arteries in response to systole and diastole of ventricles -decreases and reaches lowest level in capillaries -increases once again in venules and veins

Blood vessel cross-sectional area total cross-sectional area of all blood vessels of a particular type arteries and veins, individually, have a large cross-sectional area but low total c.s.area due to relatively small number capillaries have small c.s. area individually but a high total due to large numbers. c.s. area highest in capillaries and lowest in arteries and veins.

So what? -blood pressure and blood velocity oscillate in arteries due to systole and diastole - b.p and b.v. decrease due to increasing c.s area and increasing friction btwn. blood vessel walls and blood. -low b.v allows time for exchange btwn. blood and tissues/cells -blood pressure in venules and veins is low due to distance from heart -blood velocity increase in venules and veins due to: *contraction of skeletal muscles *decrease in cross-sectional area *expansion of thoracic cavity/decreases pressure on vessels going back to heart.

How is blood pressure measured? Measured using a sphygmomanometer in mm of Hg systolic=ventricle walls contracting diastolic=ventricle walls relaxing measured at brachial artery above elbow, stethoscope on inner arm pump cuff until no sounds are heard first sounds heard are systolic b.p. reduce pressure on cuff until no sounds heard = diastolic average = 120/80 mm varies depending on activity/anxiety

Homeostatic mechanisms homeostasis is maintained by vasodilation of peripheral blood vessels, increases heat loss, , cools body, decreases b.p. vasoconstriction reduces heat loss, aids in maintaining core temp. and raises b.p. increase heart rate= more Oxygen to cells= increase in b.p.

Hypertension- what is it? how does body respond? abnormally high b.p. contributing factors: excessive saturated fat/ cholesterol leads to artherosclerosis (fatty deposits in the arteries restrict blood flow)

Hypertension factors 2. excessive salt in diet, increases blood osmotic pressure draws water into blood and increases b.p. 3. Nicotine causes vasoconstriction and increases b.p. 4. genetic factors predispose people to high b.p. 5. diabetes and kidney disease may lead to hypertension #1-4 = life-style choices

Hypotension: what is it? Abnormally prolonged low b.p. Contributing factors: excessive blood loss-> decreases b.p. decreased cardiac output = less blood forced through the system leaky heart valves-> backflow-> less blood through system

Modification of normal heartbeat