Blood Flow Through the Heart

Blood Flow Through the Heart

• The heart is a muscular pump circulating blood throughout the body, delivering oxygen and nutrients to tissues, removing waste.
• The heart separates oxygen-poor and oxygen-rich blood, carrying them through different sides.
• Deoxygenated blood (low oxygen) is shown in blue, and oxygenated blood (high oxygen) is shown in red.

Right Side of the Heart (Deoxygenated Blood)

• Deoxygenated blood returns to the heart from the body via the superior and inferior vena cava.
• The blood enters the right atrium.
• The right atrium contracts, forcing blood through the tricuspid valve.
• Blood then flows into the right ventricle.
• The right ventricle contracts, forcing blood through the pulmonary semilunar valve.
• Blood is pumped through the pulmonary artery, which delivers the deoxygenated blood to the lungs for oxygenation.

Left Side of the Heart (Oxygenated Blood)

• Oxygenated blood returns from the lungs via the pulmonary veins.
• Blood enters the left atrium.
• The left atrium contracts, pushing blood through the mitral (bicuspid) valve to the left ventricle.
• The left ventricle, thicker-walled and more powerful, pumps blood through the aortic semilunar valve.
• Blood is distributed to the body via the aorta, branching into smaller arteries that deliver oxygenated blood to the body's tissues.
• Coronary arteries branch off the aorta, providing oxygenated blood to the heart muscle.

Valves in the Heart

• The heart's valves ensure unidirectional blood flow.
• Valves regulate blood flow:
  • Tricuspid valve between right atrium and right ventricle
  • Pulmonary semilunar valve between right ventricle and pulmonary artery
  • Mitral (bicuspid) valve between left atrium and left ventricle
  • Aortic semilunar valve between left ventricle and aorta
• These valves prevent backflow, ensuring continuous blood movement through the heart.

Cardiac Cycle

• The cardiac cycle is a complete heartbeat sequence with two phases:
  • Systole: Contraction of heart chambers (ventricles).
  • Diastole: Relaxation of heart chambers (ventricles).
• These phases are vital for effective blood circulation.

Heart Sounds

• Heart sounds (Lub-Dub) are not the heart pumping; they are caused by the snapping shut of valves.
  • Lub (first sound): Closure of the mitral and tricuspid valves.
  • Dub (second sound): Closure of the aortic and pulmonary valves.
• These sounds indicate cardiac valve function.

Blood Vessels

• Arteries carry blood away from the heart.
• Veins carry blood toward the heart.
• Capillaries are tiny vessels connecting arteries and veins, with thin walls for oxygen, nutrient, and waste exchange.
• Blood consists of plasma, red blood cells, white blood cells, and platelets.

Cardiac Output

• Cardiac output (CO) is the amount of blood ejected by the heart each minute.
• CO is calculated by stroke volume (SV) multiplied by heart rate (HR).
• Stroke volume is the blood volume pumped by each ventricle per beat.
• Heart rate is the beats per minute.
• Normal stroke volume is roughly 70 mL/beat, and normal heart rate is around 75 bpm.
• Cardiac output is about 5.25 liters per minute; the amount of blood passing through the heart per minute is normally 4-6 liters.

Determinants of Cardiac Output

• Four factors influence cardiac output: heart rate, preload, afterload, and contractility.
• Heart rate (HR): The number of beats per minute, affected by chronotropic factors:
  • Positive chronotropes (increase HR): Sympathetic stimulation (adrenaline/epinephrine and noradrenaline/norepinephrine), some drugs (e.g., atropine).
  • Negative chronotropes (decrease HR): Parasympathetic activity (acetylcholine), some drugs (e.g., adenosine).
• Preload: Blood volume in ventricles at end-diastole (end-diastolic volume). Influenced by venous return, blood volume, and atrial contraction.
• Afterload: Resistance ventricles must overcome to pump blood, heightened by hypertension, atherosclerosis, and vasoconstriction.
• Contractility: Force of myocardial contraction for a given preload. Influenced by inotropic factors:
  • Positive inotropes (increase contractility): Sympathetic stimulation (noradrenaline/norepinephrine), some drugs (e.g., dobutamine).
  • Negative inotropes (decrease contractility): Parasympathetic stimulation (acetylcholine), some drugs (e.g., beta blockers, calcium channel blockers).

Heart Anatomy and Function

• The heart is a muscular organ with four chambers: right atrium, right ventricle, left atrium, and left ventricle.
• Valves control blood flow, preventing backflow.
• The left ventricle has thicker walls than the right ventricle because it pumps blood to the entire body.

Additional Information

• Venous return (blood flow back to the heart) relies on gravity and smooth muscle contractions in veins.
• Interruption of blood flow to the heart muscle due to a blocked coronary artery causes a heart attack.

Explore the intricate pathway of blood flow through the heart in this quiz. Learn how deoxygenated blood returns to the heart and how it is pumped to the lungs for oxygenation. Test your understanding of the heart's anatomy and its crucial role in maintaining circulation.