Circulatory System Review
Circulatory System Overview
The circulatory system is responsible for the transportation of nutrients, gases, hormones, and waste products throughout the body, ensuring that essential substances reach tissues while waste products are effectively removed.
Types of Circulatory Systems
Gastrovascular Cavities
Internal cavity that serves both digestion and circulation of nutrients.
Found in organisms such as cnidarians and flatworms.
Circulatory Systems
An internal transport system consisting of circulatory fluid, a network of vessels, and a muscular pump.
Open Circulatory Systems
The circulatory fluid is pumped into open-ended vessels.
The fluid flows freely among the organs and tissues.
This fluid is referred to as hemolymph since it does not differ from interstitial fluid.
Common in most mollusks and all arthropods.
Closed Circulatory Systems
The circulatory fluid remains contained within vessels.
The primary circulatory fluid is blood.
Examples include annelids, nematodes, and chordates.
Routes of Circulation in Vertebrates
Single Circulation
Involves a single pathway through the heart where deoxygenated blood is pumped from the heart to the gills, and oxygenated blood flows back to the rest of the body before returning to the heart.
Double Circulation
Comprises two circuits through the heart:
Pulmonary Circuit: Carries deoxygenated blood from the heart to the lungs and oxygenated blood back to the heart.
Systemic Circuit: Transports oxygenated blood from the heart to the tissues and deoxygenated blood back to the heart.
Three-Chambered Heart
Characteristics include:
Deoxygenated blood enters the right side of the heart.
Oxygenated blood enters the left side.
There is some mixing of blood types before exiting the heart.
Found in amphibians and most reptiles.
Four-Chambered Heart
Key features:
Deoxygenated blood is transported on the right side.
Oxygenated blood is contained on the left side.
Complete separation of oxygenated and deoxygenated blood.
Present in crocodilians, birds, and mammals.
Anatomy of the Human Circulatory System
Blood: The primary circulatory fluid.
Blood Vessels: Structures that carry blood throughout the body.
Heart: The muscular organ responsible for pumping blood.
Composition of Blood
Formed Elements of Blood
Erythrocytes:
Red blood cells that transport oxygen.
Notably lack a nucleus.
Leucocytes:
White blood cells that are crucial for the immune system.
Platelets:
Responsible for forming blood clots.
Plasma
The liquid component that serves as a matrix for blood.
Constituents of Plasma
Water: Major component.
Ions (e.g., sodium, calcium, potassium, magnesium, chloride, bicarbonate): Help maintain osmotic balance and pH.
Plasma Proteins: Include albumin, fibrinogen, immunoglobulins (antibodies), and apolipoproteins.
Substances Transported by Blood
Nutrients such as glucose, fatty acids, and vitamins.
Waste products from metabolism.
Respiratory gases (O2 and CO2).
Hormones.
Major Functions of Plasma
Acts as a solvent for transporting various substances.
Maintains osmotic balance and pH buffering.
Plays a role in defense and lipid transport.
Formation of Blood Clots
Initial Response
Upon injury, platelets adhere to the damaged tissue.
Platelets secrete chemicals to enhance stickiness, attracting more platelets to aggregate into a clump.
Amplification through Clotting Factors
Clotting factors from plasma and platelets further amplify the clumping process via positive feedback.
Enzymes convert fibrinogen in plasma to fibrin, a protein that helps reinforce the clot.
Healing Process
Platelets contract to bring the torn edges of the vessel closer.
They release chemicals that stimulate cell division, aiding in healing.
Types of Blood Vessels
Arteries
Carry blood away from the heart.
Composed of:
Epithelial tissue lining the inside.
Smooth muscle for contraction and dilation.
Elastic connective tissue for expansion and recoil.
Arterioles
Smaller branches of arteries that regulate flow through smooth muscle in response to hormonal and nervous system signals.
Veins
Designed to carry blood toward the heart.
Structure includes:
Epithelial tissue.
Smooth muscle (less than in arteries).
Elastic connective tissue.
Venules
Smaller veins that converge to form larger veins.
Blood Transport in Veins
Blood return is aided by skeletal muscle contractions.
Veins contain valves that prevent backflow.
Capillaries
Microscopic blood vessels connecting arterioles and venules.
Feature a single layer of epithelial cells.
Leaky with pores allowing exchange of materials.
Exchange of Materials Between Blood and Interstitial Fluid
Some materials diffuse from blood in capillaries to surrounding interstitial fluid.
Certain substances are transported out via exocytosis.
White blood cells exit through the pores in capillary walls.
Regulation of Exchange
Blood pressure forces fluids out of capillaries, while osmotic pressure pulls fluid back in due to higher solute concentration in blood compared to interstitial fluid.
Typically, blood pressure exceeds osmotic pressure, leading to excess fluid loss, which is returned via lymphatic vessels.
Control of Blood Flow Through Capillaries
Blood may not consistently flow through all capillary beds.
Following a meal, capillary flow in the digestive system increases, whereas it decreases during exercise.
Precapillary Sphincters
Control blood flow into capillary beds.
When relaxed, blood flows into capillaries; when contracted, blood bypasses them.
The contraction and relaxation of these sphincters are regulated by hormonal and nervous system signals.
Structure of the Heart
Chambers
The human heart consists of four chambers:
Atria (2 atria): Blood enters the heart here.
Ventricles (2 ventricles): Responsible for pumping blood out; they have thicker, more muscular walls than atria.
Valves
Valves control blood flow through the heart:
Atrioventricular Valves (AV valves): Located between atria and ventricles.
Semilunar Valves: Situated between ventricles and arteries.
Septum
A muscular wall that separates the right and left sides of the heart.
This separation ensures that oxygenated and deoxygenated blood do not mix:
The right side carries deoxygenated blood, while the left carries oxygenated blood.
Double Circulation
Circulatory Pathways
Pulmonary Circuit: Transports deoxygenated blood to the lungs and back.
Systemic Circuit: Moves oxygenated blood through arteries to capillary beds and returns deoxygenated blood via veins to the heart.
Path of Blood Through the Heart
Deoxygenated blood enters through the superior and inferior vena cava into the right atrium.
Blood passes through the right atrioventricular valve (tricuspid) into the right ventricle.
From the right ventricle, blood flows through the pulmonary semilunar valve into the 2 pulmonary arteries to the lungs for gas exchange (CO2 exchanged for O2).
Oxygenated blood returns via the 4 pulmonary veins into the left atrium.
Blood then enters the left AV valve (bicuspid or mitral valve) into the left ventricle.
Finally, blood exits through the aortic semilunar valve into the aorta for distribution to the body.
Heartbeat
Cardiac Cycle
The complete filling and pumping of blood through the heart, consisting of two phases:
Diastole: The relaxation phase when chambers fill with blood.
Systole: The contraction phase when blood is pumped out.
Phases of the Cardiac Cycle
Atrial and Ventricular Diastole: Both chambers are relaxed. Blood flows into atria and ventricles; AV valves are open while semilunar valves are closed.
Atrial Systole: Atria contract, pumping blood into ventricles. Ventricles fill up completely, AV valves remain open, semilunar valves stay closed.
Ventricular Systole: Ventricles contract, pumping blood out of the heart. AV valves close to prevent backflow, and semilunar valves open to allow blood out.
Heart Sounds
Lub-Dup Sound:
"Lub" corresponds to blood against closed AV valves.
"Dup" corresponds to blood against closed semilunar valves.
Heart Murmurs: Can produce a hissing sound due to blood flowing backward through a defective valve, which may arise from congenital defects or infections and may require surgical repair or replacement.
Control of Heartbeat
Mechanisms of Heartbeat Control
Heartbeat is regulated by specialized cardiac muscle regions:
Sinoatrial Node (SA Node): Known as the pacemaker, it generates electrical signals that stimulate atrial contraction.
Atrioventricular Node (AV Node): Receives signals simultaneously with the atria. It delays the signal by 0.1 seconds, ensuring atria contract before ventricles.
Specialized (Perkinje) Fibers: Transmit signals to the ventricles, resulting in their contraction and ejection of blood from the heart.
Heart Rate
Defined as the number of times the heart beats per minute, typically averaging around 72 beats per minute.
The pulse represents the wave of blood propagated through arteries upon each heartbeat.
Blood Pressure
Measurement
There are two primary pressure readings:
Systolic Pressure: Higher number, indicating pressure during ventricular contraction.
Diastolic Pressure: Lower number, representing pressure during ventricular diastole.
Normal blood pressure is considered to be 120/80 mmHg.
Cardiovascular Disease
Types of Conditions
Anemia
Characterized by a low red blood cell count or insufficient hemoglobin which results in less oxygen transport, leading to weakness and increased infection susceptibility. Could be caused by significant blood loss, mineral deficiencies, cancers, or genetic disorders.
Hypertension
Refers to high blood pressure caused by reduced vessel elasticity or artery blockage. Increases the workload of the heart, can lead to disease, stroke, or kidney failure.
Low Blood Pressure
Insufficient blood supply to body parts resulting in inadequate oxygen transport. May arise due to endocrine disorders, malnutrition, or internal bleeding.
Atherosclerosis
Involves plaque buildup (soft masses and fatty tissues) in the arterial lining which disturbs blood flow. Plaque can rupture, forming clots.
Stroke
Occurs when a cranial arteriole bursts or is obstructed, leading to part of the brain dying due to oxygen deprivation, resulting in neurological issues.
Angina Pectoris
Caused by partial blockage of coronary arteries, resulting in chest pains. Treatment may involve nitroglycerin to dilate the artery.
Myocardial Infarction (Heart Attack)
Occurs when a coronary artery is entirely blocked, causing part of the heart muscle to die due to oxygen deprivation, leading to scar tissue formation which does not contract.
Prevention and Treatment: Includes use of Aspirin to reduce inflammation, angioplasty with stents, and bypass surgery utilizing vessels from the leg to replace blocked arteries.
Atrial Fibrillation (A-Fib)
Characterized by irregular or rapid atrial contractions, resulting in blood clots formation within the heart, which may provoke stroke and heart failure.
Ventricular Fibrillation
Defined by uncontrolled contractions of the ventricles. Defibrillation, which involves delivering a strong electrical current, can help to restore normal rhythms. Additionally, artificial pacemakers may be implanted to regulate heartbeat.
Congestive Heart Failure
A condition in which the heart muscle fails to pump sufficient blood, preventing adequate delivery of oxygen to tissues. Symptoms include fluid build-up leading to shortness of breath and fatigue.
Factors Affecting Cardiovascular Health
Lifestyle Choices
Smoking
Nicotine action causes arterioles to constrict, elevating blood pressure, thus increasing risks for hypertension, heart attacks, and strokes.
Drug Abuse
Substances such as cocaine and amphetamines can induce irregular heart rhythms, heart attacks, and strokes.
Alcohol
Heavy consumption can harm organs, including the heart; however, moderate drinking (2-4 drinks/week for men, 1-3 for women) does not significantly elevate risks.
Weight Gain
Results in the heart pumping blood to more tissue, leading to increased blood pressure and higher risk of hypertension and atherosclerosis.
Healthy Diet
Adopting a diet low in cholesterol and saturated fats contributes to reducing the risk of atherosclerosis.
Exercise
Aids in weight control, stress management, hypertension regulation, and enhances heart capacity, allowing the heart to pump more efficiently and at a lower rate.