Cardiovascular System: Arteries and Blood Flow

• Blood is responsible for transporting gases, hormones, and cells.
• Blood circulates through arteries, arterioles, capillaries, venules, and veins.

Arteries

• These carry blood away from the heart, typically oxygenated, except for the pulmonary artery.
• Oxygen binding to heme (iron) on red blood cells creates the red color of blood; different substances binding to heme can change the color.
• Arteries are thick vessels that carry oxygenated blood away from the heart to tissues; each organ receives blood from at least one artery.
• Arteries need thicker walls due to the high pressure exerted on them, which include:
  • Tunica Externa: tough outer layer of connective tissue.
  • Tunica Media: thickest layer, composed of smooth muscle and elastic fibers (elastin)
  • Tunica Interna/Intima: smooth endothelium lining the vessel's interior.
• A basement membrane separates the cells of the artery from the connective tissue.
• The change in artery diameter due to the heart's pumping action can be felt as a pulse.
• Major artery blood flow is pulsatile, and pulsations determine heartbeat.
• Systolic pressure is the peak pressure in an artery, associated with ventricular contraction or depolarization.
• During ventricular relaxation, elastic fibers return to their original position, releasing stored potential energy, which is measured as diastolic pressure.
• Arterial wall pressure remains constant, allowing continuous blood flow.
• Smooth muscle in the Tunica Media constricts or relaxes, changing artery diameter through vasoconstriction and vasodilation.

Arterioles

• Smaller versions of arteries that receive blood from the arteries.
• The arterial wall is similar to that of the artery.
• The ANS (Autonomic Nervous System) controls the arteriolar diameter.
• Vasoconstriction decreases blood flow to tissues, while vasodilation increases it.
• Vasodilation causes blushing; more blood is diverted to surface capillaries to release heat.
• Vasoconstriction causes paleness.
• During inflammation, vasodilation increases blood flow, resulting in widened capillaries and increased secretion of fluids and antimicrobial chemicals.
• Arterioles only vasodilate when blood flow is needed in capillaries.

Capillaries

• Connect arterioles to venules.
• The wall consists of a single layer of endothelium covered by a basement membrane.
• The narrowest vessels are around 10 micrometers, allowing only one red blood cell to pass at a time.
• Nutrients and oxygen are exchanged for minerals and vitamins.
• The endothelium is coated with a gel-like membrane for permeability and nutrient-rich plasma.
• Waste is picked up by the plasma and transported away from the tissue.

Venules and Veins

• These carry blood to the heart, usually deoxygenated, except for pulmonary veins
• Blood from capillaries flows into venules then into veins.
• Veins have significantly reduced pressure.
• Valves in veins prevent backflow of blood.
• Veins have thinner smooth muscle layers than arteries due to lower pressure.
• Most body parts have at least one vein to return blood to the heart.
• The hepatic portal vein carries blood from the stomach and intestines to the liver for filtration, retaining its classification as a vein due to low pressure and thin walls.
• Valves open when blood flows toward the heart and close to prevent backflow, ensuring unidirectional movement.
• Skeletal muscles aid blood flow by squeezing veins to open valves and promote forward movement.
• Veins act as a blood reservoir, holding up to 65% of the body’s blood (85% in sedentary individuals).
• Nerve impulses can cause vasoconstriction, increasing fluid pressure and driving more blood to the heart during stress.

Varicose Veins

• Enlarged, bulging veins caused by blood pooling in one-way valves, often damaging them and causing backflow, reducing blood flow to the heart.
• Occur in surface veins due to daily pressure and compression.
• Common causes include prolonged standing, restricted movement, and atherosclerosis.

Atherosclerosis

• Deposits of cholesterol on the arterial wall narrow the lumen, inhibiting blood flow, depositions of minerals and calcium can form plaque.
• Plaque breaking off can damage the arterial wall, triggering blood clotting and potentially blocking the artery, which may result in a heart attack.
• LDLs form atheroma (fatty tissue) on the endothelium, causing cells to signal phagocytes to engulf them.
• Phagocytes become foamy and fat, initiating a pro-inflammatory response and increasing plaque buildup.
• Smooth cells from the Medica Media migrate to the top of the plaque, forming a hard layer and a bump within the artery.
• Anoxia, or lack of blood, due to blockage in a coronary artery causes the heart to beat faster.
• Increased heart rate pressure can rupture the plaque buildup cap and cause a blood clot.
• Angina or initial pain occurs, critical heart failure can occur as the entire coronary artery is blocked.
• Common causes include high LDL levels, chronic high glucose, high blood pressure, trans-fat consumption, and arterial wall infection.

Aneurysm

• Bulge that forms due to a weakened arterial wall, caused by atherosclerosis.
• Rupturing the thin wall can lead to less oxygen, internal bleeding, and less nutrients being delivered to tissue resulting in cell death.
• Types include saccular and fusiform aneurysms.
• Aneurysms in the brain can cause a stroke.

The Heart

• Muscular organ that pumps blood in the body, consisting of two parallel pumps separated by the septum.
• The right side receives deoxygenated blood, and the left side receives oxygenated blood.
• The heart pumps blood to the:
  • Pulmonary system which takes deoxygenated blood via the pulmonary trunk to the lungs to exchange carbon dioxide for oxygen, then the pulmonary veins to the left side of the heart.
  • Systemic circuit where the left side pumps oxygenated blood into the aorta and the rest of the body.
• The left ventricle is larger to pump blood with more force.
• The aorta ascends and splits into five branches that include:
  • The aortic root which supplies blood to coronary arteries.
  • The descending aorta supplies blood to lower body.
  • The rightmost branch to the right arm and brain.
  • The middle branch to the left brain.
  • The leftmost branch to the left arm.
• The heart has four chambers, two thin-walled atria and two thick-walled ventricles, separated by the septum.
• Blood Flow through the heart is as follows:
  • Deoxygenated blood enters the superior and inferior Vena Cava, which dumps into the right atrium and pumps through the tricuspid valve into the right ventricle.
  • Blood is pumped through the pulmonary valve into the pulmonary trunk, deposits carbon dioxide in the lungs exchanging it oxygen.
  • Oxygenated blood dumps into the left atrium through the left and right pulmonary veins.
  • Blood is pumped into the left ventricle through the bicuspid valve.
  • Blood is pumped into the aorta through the aortic valve and to the rest of the body.

Heart Rhythm

• Cardiac muscle generates its action potential and contracts independently without external influence, called myogenic.
• The SA and AV nodes, Bundle of HIS, and Purkinje fibers send, transmit, and receive electrical signals that tell the cardiac muscle when to contract due to myogenic trait.
• The SA node is the heart's pacemaker, usually around 70 bpm and located at the top of the right atrium.
• Coronary heart disease can affect bpm.
• The AV node delays impulses preventing simultaneous contraction of all four chambers.
• The SA node sends electrical signals through the Bundle of HIS to Purkinje fibers, causing ventricular depolarization.
• Depolarization occurs when the heart cell membrane causes contraction of surrounding heart cells.
• Branched cardiac muscle facilitates depolarization spread.
• The SA node has the highest spontaneous contraction rate, with extensive membranes aiding depolarization spread.
• If the SA node fails, the AV node maintains heart rhythm at 60 bpm, but if the AV node fails, the Bundle of HIS cannot generate the cardiac output required.
• An electric pacemaker is placed under the skin, where electrodes placed on the heart initiate contraction and set the pace for the heart when the nodes fail.
• The sympathetic nervous system increases heart rate during stress, while the parasympathetic nervous system returns it to normal using the autonomic nervous system.
• Epinephrine secreted by the adrenal gland mediates heart rate and blood sugar during stress.
• Epinephrine is also used for anaphylactic shock caused by allergies.

Heart Medications

• Foxglove contains digitalis, which strengthens heart contractions.
• Treats heart congestion, where fluid buildup in extremities is due to a weakened heart.
• Nitroglycerin prevents heart attacks by reducing blood pressure and vasodilating arteries.
• Beta Blockers prevent cells from receiving epinephrine by blocking their receiving cells.
  • Beta 1 Blockers block receptors on cardiac muscle preventing increased heart rate and blood pressure
  • Beta 2 Blockers block receptors in blood vessels and bronchioles

Blood Flow

• Heart Rate (bpm): Number of beats per minute.
• Stroke Volume (L/beat): Amount of blood pumped per beat.
• Cardiac Output (L/min): Amount of blood pumped from the heart per minute, calculated as Heart Rate x Stroke Volume.
• Athletes generally have a lower heart rate with a higher stroke volume.
• Blood Pressure, measured with a sphygmomanometer, depends on cardiac output and arterial resistance (elastic fibers).

ECG/EKG(Electrocardiogram)

• Tracks and reports the electrical activity of the heart, reflecting contraction and relaxation activity.
• The initial P wave represents atrial depolarization (systole) and contraction, where AV valves are open and semi-lunar valves are closed.
• The PR interval represents a delay to electrical impulse caused by the AV node where ventricles fill.
• The QRS complex includes:
  • Atrial repolarization (diastole) occurs during ventricular depolarization while blood dumps into the atria.
  • The Q dip represents the septum depolarization as electrical signals pass through the Bundle of HIS to Purkinje fibers.
  • The first half of the R wave represents when electrical signals pass the Bundle of HIS.
    • AV valves close and semi-lunar valves open, and prepares for ventricular contraction.
    • Closing of the AV valves causes the initial and louder “lub” sound of the heartbeat.
  • The second part of the R wave represents the depolarization of the ventricles as the electrical signal reaches both left and right Purkinje fibers.
    • AV valves are closed to prevent backflow.
    • Semi-lunar valves are open.
  • The S dip is to represent the final and complete ventricular depolarization.
• The ST segment represents ventricular contraction (systole), with no electric signal after ventricular depolarization in the QRS complex.
• The T wave is ventricular repolarization (diastole).
  • Semi-lunar valves close causing the “dub” sound, the second and weaker sound of the heartbeat.

Regulation of Blood Pressure

• Receptors in the aorta and carotid artery monitor blood pressure.
• The aorta senses high blood pressure and carotid arteries sense low blood pressure.
• High blood pressure stimulates the medulla oblongata to engage the parasympathetic nervous system, causing vasodilation and reduced heart rate and stroke volume.
• Low blood pressure engages the sympathetic system until receptors in the aorta are activated.
• Blood pressure is measured in systolic and diastolic pressure.
  • Normal blood pressure is 120/80, systolic should be 100-130 mmHg, and diastolic should be around 60-80 mmHg.

Hypertension

• Sustained high blood pressure can weaken blood vessels, leading to increased connective tissue, reduced elasticity, and arterial wall hardening.
• Causes include diet, obesity, smoking, alcohol, stress, age, and genetics.

Thermoregulation

• Body temperature should be at a constant 37 degrees.
• Excess exercise or heat causes the hypothalamus to engage sweat glands and dilate surface blood vessels.
• Cold temperatures cause the hypothalamus to constrict surface blood vessels and cause hair follicles to stand up.
• Shivering.

Explore the structure and function of arteries within the circulatory system, including the role of elastic fibers and blood flow dynamics. Understand the significance of arterial wall integrity and how blood color indicates health status. Learn about arteriole responses during exercise.