The Circulatory System

• The circulatory system's main objective is to analyze the structure and functions of the systems of the human body.
• Specific areas of focus include major organs (heart, blood vessels), structure, function, heart-rate, stroke volume, cardiac output, and blood pressure.
• Four systems connected for movement: nervous, muscular, skeletal, and circulatory.
• The nervous system sends signals to the muscular system for contraction.
• The muscular system contracts and pulls on bones in the skeletal system for movement.
• Muscles require fuel to contract.
• The circulatory system transports oxygen and nutrients for energy throughout the body.
• The circulatory system consists of the heart, blood, and blood vessels (arteries, veins, capillaries).
• The heart pumps blood through a network of vessels to circulate substances throughout the body.
• Transports oxygen, nutrients and food to cells
• Removes carbon dioxide and waste from cells
• Carries hormones

Blood Functions

• White blood cells prevent infection by fighting diseases, bacteria, viruses and protects against blood loss by forming clots
• Blood helps maintain temperature and pH to ensure homeostasis (balance in the body)
• Body temperature is regulated by dilating or constricting blood vessels.
• Cells and tissues require a pH of 7.4 to function optimally.
• Blood plasma helps regulate pH levels.
• Blood is a specialized fluid tissue for the circulatory system's functions.
• Plasma is the liquid part of blood, containing red and white cells, and platelets.
• Red blood cells (Erythrocytes) carry oxygen using hemoglobin, produced in bone marrow with 5 million per drop
• Hemoglobin, an iron-rich protein, gives red cells their color and transports oxygen.
• Plasma carries blood cells, digested food (glucose), hormones, and waste (CO2, urea).
• Plasma is composed of 90% water, 8% proteins, and 2% salts.
• White blood cells/leukocytes and platelets make up 1% of blood composition.
• Some white blood cells produce antibodies that destroy viruses.
• Other white blood cells destroy germs and can leave blood vessels to reach infections.
• Platelets are cell fragments that stick together and form clots to stop bleeding.

The Heart

• The heart is a muscular pump flowing blood; a cardiac muscle that contracts continuously without tiring
• The heart is an involuntary muscle that beats over 100,000 times per day.
• At rest, the heart pumps 5-7 liters of blood per minute, taking about 20 seconds for the blood to move around the body
• Consists of two muscular pumps
• The heart is located behind the thoracic cage (ribs and sternum) in the cardiac notch of the lungs,the size of a clenched fist.
• Trained athletes can experience cardiac hypertrophy (enlargement of the heart).

Heart Wall Layers

• Endocardium (inner layer): Allows uninterrupted blood flow.
• Myocardium (middle layer): Composed of cardiac muscle.
• Epicardium/pericardium (outer layer): Reduces friction and maintains heart shape.
• Coronary arteries cover the exterior of the heart and feed the muscle with blood e.g blockage leads to attacks and hypertension

Heart Chambers

• Has four chambers: two atria and two ventricles.
• Atria: Two smaller chambers at the top of the heart, the right atrium receives deoxygenated blood, the left atrium receives oxygenated blood.
• Ventricles: Two larger chambers at the bottom of the heart.
• Ventricle walls are thicker than atria.
• Atria contract to move blood into ventricles.
• The right ventricle wall is thinner than the left ventricle.
• Right ventricle: Pumps blood to the lungs (low resistance, spongy tissue).
• Left ventricle: Pumps blood to the body and determines how much blood is distributed.
• Septum: Thin muscular wall dividing the left and right sides of the heart.

Valves and Blood Vessels

• The circulatory system is closed, with blood flowing inside vessels, and blood clots seal cuts to limit blood loss.
• Valves prevents back-flow of blood and ensures unidirectional flow.
• Atrioventricular valves: Located between the atria and ventricles, pushed open by blood flow from the atria.
  • Tricuspid valve: Located between the right atrium and right ventricle.
  • Bicuspid (Mitral) valve: Located between the left atrium and left ventricle.
• Semilunar valves: Located between the heart and arteries.
  • Aortic valve: Located between the left ventricle and the aorta.
  • Pulmonary valve: Located between the right ventricle and the pulmonary artery.
• Blood vessels transport blood; arteries, veins, and capillaries.
• Endothelium lines arteries, veins, and capillaries (single layer of squamous cells).
• Walls of arteries and veins are composed of smooth muscle tissue and fibre secreting cells.

Arteries vs Veins

• Arteries carry blood at high pressure, delivering blood to tissues and stretch and recoil.
• As arteries leave the heart, they branch into smaller arterioles then capillaries.
  • Pulmonary artery carries blood to the lungs.
  • The Aorta is the main artery carrying blood to all parts of the body.
• Veins accommodate blood volume and return it to the heart at low pressure.
• Capillaries join with Veinules which connect to become veins
  • Pulmonary vein carries blood from the lungs.
  • Vena Cava carries deoxygenated blood to the heart.
• Smooth Muscle: involuntary muscle that look smooth under a microscope.
• These muscles are in walls of hollow organs like blood vessels and gut walls
• Short cells contract in length and width, causing vessels to narrow and move substances along.
• The heart has two sides (left and right) separated by a septum for double circulation.
• Pulmonary circulation is a short loop from the heart to the lungs (right side).
• Systemic circulation sends blood from the heart to the body (left side).

Cardiac Cycle

• The cardiac cycle involves cardiac contraction and blood transportation during heartbeat.
• Heartbeat: one complete cycle of contraction
• Heart rate: the number of heartbeats per minute (pulse).
• The heart pumps blood by contracting the atria followed by the ventricles.
• Filling with blood is called diastole phase
• Emptying of blood is called systole phase.
• The ventricles contract, while the atrioventricular valves close.
• Blood flows into the heart when it is relaxed.
• The right atrium fills with deoxygenated blood from the vena cava veins.
• The left atrium fills with oxygenated blood from the pulmonary veins.

Cardiac Dynamics

• The atria contract (atrial systole), pumping blood through the atrioventricular valves.
• The semi lunar valves remain closed.
• The right atrium pushes blood into the right ventricle, and the left atrium pushes blood to the left ventricle.
• The blood is forced from heart through semilunar valves and into arteries
• The ventricles pump blood through the semilunar valves into the pulmonary artery, and the left ventricle pumps blood through the semilunar valves (aorta valve) to the body.
• During exercise: muscles produce more carbon dioxide and need more oxygen, so increased blood flow occurs.
• Heart beats faster/stronger.
• Blood redirects away from other organs to the stomach etc.
• Cardiac Output: The amount of blood ejected from the heart in one minute.
• Cardiac Output = stroke volume X heart rate (Q = S.V. X H.R.)
• Stroke volume: amount of blood heart pumps each ventricle during one contraction.
• Heart rate: the number of beats per minute.
• A person's average resting stroke volume is 75ml per beat, with a heart rate of 72 bpm resulting in a cardiac output of 5.4 L/min.
• Aerobic training can increase muscle size (hypertrophies).
• Ventricles stretch further and contract harder, increasing both resting and maximal stroke volumes.
• Maximum heart rate is estimated at 220 minus a person's age.
• Heart rate plateaus when a person reaches maximum heart rate.

Cardiac calculations

• 12-year-old students: a fit student has a cardiac output of 31.2 L, while an unfit has 24.5 L.
• Cardiac Output: stroke volume X heart rate (Q = S.V. X H.R.)
• Heart Rate calculation: 220 - age = 208
• Fit student: heart rate = 208 and stroke volume = 150
• Unfit student: heart rate = 208 and stroke volume = 117.7