🔬General Biology I Unit 40 – The Circulatory System

Overview and Function

• The circulatory system transports oxygen, nutrients, hormones, and waste products throughout the body
• Consists of the heart, blood vessels, and blood working together to maintain homeostasis
• Plays a crucial role in delivering oxygen and nutrients to cells and removing metabolic waste products (carbon dioxide, urea)
• Helps regulate body temperature by distributing heat evenly and facilitating heat loss through the skin
• Assists in the body's immune response by transporting white blood cells and antibodies to sites of infection or injury
• Enables communication between organs and tissues through the transport of hormones and signaling molecules
• Maintains fluid balance within the body by controlling the distribution of water and electrolytes

Anatomy of the Heart

• The heart is a muscular organ about the size of a closed fist located in the chest cavity
• Divided into four chambers: two atria (upper chambers) and two ventricles (lower chambers)
  • Right atrium receives deoxygenated blood from the body via the superior and inferior vena cava
  • Left atrium receives oxygenated blood from the lungs via the pulmonary veins
  • Right ventricle pumps deoxygenated blood to the lungs through the pulmonary artery
  • Left ventricle pumps oxygenated blood to the body through the aorta
• The heart wall consists of three layers: epicardium (outer), myocardium (middle), and endocardium (inner)
• Heart valves ensure unidirectional blood flow and prevent backflow
  • Tricuspid valve between the right atrium and right ventricle
  • Pulmonary valve between the right ventricle and pulmonary artery
  • Mitral valve between the left atrium and left ventricle
  • Aortic valve between the left ventricle and aorta
• The coronary arteries supply the heart muscle with oxygenated blood
• The conduction system of the heart generates and propagates electrical impulses to coordinate heart contractions

Blood Vessels and Circulation

• Blood vessels form a closed network that carries blood throughout the body
• Arteries carry oxygenated blood away from the heart to the body's tissues (except for the pulmonary artery)
  • Arteries have thick, elastic walls to withstand high pressure and pulsatile flow
  • Arterioles are smaller arteries that help regulate blood flow and pressure
• Veins carry deoxygenated blood from the body's tissues back to the heart (except for the pulmonary veins)
  • Veins have thinner walls and larger lumens compared to arteries
  • Venules are smaller veins that collect blood from capillaries
  • Veins contain valves to prevent backflow of blood
• Capillaries are the smallest blood vessels that form a network between arterioles and venules
  • Allow for the exchange of gases, nutrients, and waste products between the blood and tissues
• The circulatory system has two main circuits:
  • Pulmonary circulation carries deoxygenated blood from the heart to the lungs and returns oxygenated blood to the heart
  • Systemic circulation carries oxygenated blood from the heart to the body's tissues and returns deoxygenated blood to the heart

Blood Composition

• Blood is a connective tissue composed of plasma (liquid portion) and formed elements (cells and cell fragments)
• Plasma makes up about 55% of blood volume and consists primarily of water, proteins, electrolytes, nutrients, and waste products
  • Plasma proteins include albumin (maintains osmotic pressure), globulins (antibodies), and fibrinogen (clotting factor)
• Formed elements make up about 45% of blood volume and include:
  • Red blood cells (erythrocytes): transport oxygen and carbon dioxide; contain hemoglobin
  • White blood cells (leukocytes): part of the immune system; defend against infections and foreign substances
    • Granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes)
  • Platelets (thrombocytes): cell fragments involved in blood clotting and wound healing
• Hematocrit is the percentage of blood volume occupied by red blood cells (normally 40-45% in adults)
• Blood typing is based on the presence or absence of specific antigens on red blood cell surfaces (A, B, AB, O and Rh factor)

Cardiovascular Health and Diseases

• Cardiovascular diseases are disorders that affect the heart and blood vessels
• Atherosclerosis is the buildup of plaque in the arteries, leading to narrowing and reduced blood flow
  • Risk factors include high cholesterol, high blood pressure, smoking, obesity, and diabetes
• Coronary artery disease (CAD) occurs when the heart's blood supply is reduced due to atherosclerosis
  • Can lead to angina (chest pain) or myocardial infarction (heart attack)
• Hypertension (high blood pressure) puts extra strain on the heart and blood vessels
  • Can damage the endothelium and contribute to atherosclerosis, heart failure, and stroke
• Heart valve disorders (stenosis, regurgitation) can impair the heart's ability to pump blood effectively
• Arrhythmias are abnormal heart rhythms that can be caused by problems with the heart's conduction system
• Congestive heart failure occurs when the heart cannot pump enough blood to meet the body's needs
• Lifestyle factors that promote cardiovascular health include regular exercise, a balanced diet, stress management, and avoiding smoking

Regulation and Homeostasis

• The cardiovascular system is regulated by neural, hormonal, and local mechanisms to maintain homeostasis
• Autonomic nervous system (sympathetic and parasympathetic) influences heart rate and contractility
  • Sympathetic stimulation increases heart rate and contractility (fight-or-flight response)
  • Parasympathetic stimulation decreases heart rate and contractility (rest-and-digest response)
• Baroreceptors in the aorta and carotid arteries detect changes in blood pressure and send signals to the brain to adjust heart rate and vascular tone
• Hormones such as epinephrine, norepinephrine, and thyroid hormones can affect heart rate and contractility
• The renin-angiotensin-aldosterone system (RAAS) regulates blood pressure and fluid balance
  • Renin (from the kidneys) converts angiotensinogen to angiotensin I
  • Angiotensin-converting enzyme (ACE) converts angiotensin I to angiotensin II, a potent vasoconstrictor
  • Angiotensin II stimulates the release of aldosterone, which promotes sodium and water retention
• Local factors such as nitric oxide and endothelin help regulate vascular tone and blood flow in specific tissues

Lab Work and Experiments

• Measuring blood pressure using a sphygmomanometer and stethoscope
  • Systolic pressure (top number) is the pressure during heart contraction; diastolic pressure (bottom number) is the pressure during heart relaxation
• Electrocardiogram (ECG or EKG) records the electrical activity of the heart
  • Can detect arrhythmias, ischemia, and other abnormalities
• Echocardiogram uses ultrasound to visualize the heart's structure and function
  • Can assess valve function, chamber size, and wall thickness
• Cardiac catheterization involves inserting a catheter into the heart to measure pressures, take samples, or perform procedures (angioplasty, stent placement)
• Blood tests can measure various parameters:
  • Complete blood count (CBC) assesses red blood cells, white blood cells, and platelets
  • Lipid panel measures cholesterol levels (total, LDL, HDL) and triglycerides
  • Cardiac enzymes (troponin, CK-MB) can indicate heart muscle damage
• Heart rate and blood pressure response to exercise can be tested using a stress test or treadmill test

Real-World Applications

• Understanding the circulatory system is crucial for healthcare professionals (physicians, nurses, pharmacists) to diagnose and treat cardiovascular disorders
• Research in cardiovascular physiology leads to the development of new drugs, devices, and therapies
  • Anticoagulants (heparin, warfarin) prevent blood clots
  • Beta-blockers reduce heart rate and blood pressure
  • Statins lower cholesterol levels and reduce the risk of atherosclerosis
  • Pacemakers and implantable cardioverter-defibrillators (ICDs) treat arrhythmias
• Public health initiatives promote cardiovascular health through education and prevention programs
  • Encouraging healthy lifestyles (exercise, diet, stress management)
  • Raising awareness about risk factors (smoking, obesity, hypertension)
• Advances in cardiovascular imaging (CT, MRI, PET) allow for earlier detection and monitoring of heart disease
• Tissue engineering and regenerative medicine aim to develop new treatments for heart failure and other cardiovascular disorders
  • Stem cell therapy to regenerate damaged heart muscle
  • Bioartificial hearts or heart valves to replace diseased ones