Physiology
Objective
Describe the structure and function of the cardiovascular system.
Trace the flow of blood through the heart, lungs, and body.
Understand the physiological importance of blood pressure, cardiac output, and vascular resistance.
Recognize how the cardiovascular system supports cellular and systemic homeostasis.
Overview
The cardiovascular system is a closed-loop system responsible for the circulation of blood, which delivers oxygen, nutrients, hormones, and removes waste products from the body's tissues. It consists of three main components:
The Heart – A muscular organ that pumps blood throughout the body.
Blood Vessels – A network of arteries, veins, and capillaries.
Blood – A fluid connective tissue that carries essential substances to and from cells.
Heart Structure and Chambers
Right Atrium: Receives deoxygenated blood from the systemic circulation.
Right Ventricle: Pumps blood to the lungs via the pulmonary arteries.
Left Atrium: Receives oxygenated blood from the lungs.
Left Ventricle: Pumps oxygenated blood into systemic circulation via the aorta.
Blood Vessels: The Body’s Highway System
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Structure: Thick, elastic walls
Function: Carry blood way from the heart under high pressure
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Structure: Smooth muscle
Function: Regulate resistance and blood flow
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Structure: Thick walls, elastic
Function: Exchange of gases, nutrients, waste
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Structure: Thin walls, valves
Function: Return blood to heart, blood reservoirs
How Blood Moves
CIRCULATION
Blood circulates in two loops:
Pulmonary Circuit: Heart → Lungs → Heart (picks up oxygen)
Systemic Circuit: Heart → Body → Heart (delivers oxygen)
CYCLES
The cardiac cycle is one full heartbeat: filling, pumping, and relaxing.
Phases:
Diastole: heart relaxes and fills with blood
Systole: heart contracts and pumps blood out
How Your Body Controls the System
Autonomic Nervous System
Your brain controls your heart automatically:
Sympathetic (fight or flight): speeds up the heart, increases pressure
Parasympathetic (rest and digest): slows things down
Blood Pressure
Pressure comes from how much blood your heart pumps and how wide/narrow your blood vessels are.
Blood pressure is the force that blood exerts on the walls of the arteries as it flows through them. It’s highest in the arteries, particularly in the aorta, and decreases as it moves through smaller vessels.
High blood pressure (hypertension) can damage arteries, leading to conditions like atherosclerosis (plaque buildup in arteries), which increases the risk of heart attack or stroke.
Low blood pressure (hypotension) can lead to dizziness, fainting, and inadequate oxygen supply to organs.
Dissect the distinctive pathway and functions involved in the process of blood pressure
Normal Blood Pressure
Normal Range:
Systolic: Less than 120 mmHg
Diastolic: Less than 80 mmHg
Normal BP: 120/80 mmHg or lower.
Why Blood Pressure Matters
Normal Blood Pressure:
Ensures that blood is circulating efficiently to deliver oxygen and nutrients to organs and tissues.
Helps the heart work at a normal pace, without excessive strain.
High Blood Pressure (Hypertension):
Increases the risk of heart disease, stroke, kidney disease, and other complications.
Often called the “silent killer” because it doesn’t have obvious symptoms but can cause long-term damage to the heart and blood vessels.
Low Blood Pressure (Hypotension):
May cause dizziness, fainting, and shock in severe cases.
Can be caused by dehydration, heart problems, or blood loss, leading to inadequate oxygen delivery to the organs
Blood
Blood is a fluid tissue that circulates throughout the body, transporting essential substances like oxygen, nutrients, and waste products. It’s made up of cells and plasma, and plays a crucial role in maintaining homeostasis, fighting infections, and regulating body temperature.
Blood is made up of four components
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What it is: Plasma is the liquid portion of the blood and is primarily made up of water (about 90%), proteins, hormones, nutrients, and waste products. It acts as a medium for transporting these substances throughout the body.
Key Functions:
Transports nutrients (e.g., glucose, amino acids) and waste products (e.g., urea) to and from cells.
Regulates body temperature by distributing heat
Maintains blood pressure and volume by helping in osmotic regulation.
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What they are: These are disc-shaped cells that carry oxygen from the lungs to tissues and carbon dioxide from tissues to the lungs. Red blood cells (RBCs) contain the protein hemoglobin, which binds to oxygen.
Key Functions:
Oxygen transport: Hemoglobin binds to oxygen in the lungs and releases it to tissues in need.
Carbon dioxide transport: They also help carry carbon dioxide back to the lungs to be exhaled.
Lifespan: RBCs live for about 120 days, after which they are broken down in the spleen and liver.
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What they are: White blood cells are part of the immune system and are responsible for fighting infections. Unlike red blood cells, they have a nucleus and can move out of blood vessels into tissues to attack foreign invaders.
Key Functions:
Defense against infections: They destroy harmful pathogens like bacteria, viruses, and fungi.
Immune response: Leukocytes produce antibodies to recognize and neutralize harmful substances.
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What they are: Platelets are small, disc-shaped cell fragments that play a crucial role in blood clotting.
Key Functions:
Blood clotting: When a blood vessel is injured, platelets aggregate at the site, releasing substances that form a clot to stop bleeding. This involves fibrinogen turning into fibrin to form a clot mesh.
Lifespan: Platelets last for about 7-10 days before being removed by the spleen.
Oxygen and Carbon Dioxide Transport in Blood
The main role of blood is the transport of gases like oxygen (O₂) and carbon dioxide (CO₂).
Oxygen Transport: RBCs contain hemoglobin, a protein that binds to oxygen molecules in the lungs. Each hemoglobin molecule can carry up to four molecules of oxygen. Oxygen is then transported to tissues for cellular respiration.
Carbon Dioxide Transport: When tissues produce carbon dioxide as a waste product, it enters the bloodstream. Around 70% of CO₂ is carried as bicarbonate ions in the plasma, about 20% binds to hemoglobin, and the rest dissolves directly in plasma
Examine the different structures and processes involved in the bodily gas transfer
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What is it:
Hypertension occurs when the force of blood against the walls of the arteries is consistently too high. It develops gradually and often goes unnoticed because there are usually no symptoms.Why It’s a Problem:
If left untreated, high blood pressure can lead to serious complications such as heart disease, stroke, kidney failure, and damage to the arteries. Over time, the constant pressure damages the walls of the arteries, causing them to become stiff and narrow, which makes the heart work harder.
Hypertension increases the risk of developing atherosclerosis and aneurysms (weakened areas of the artery wall that can burst)
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What is it:
Atherosclerosis is a condition where plaque (a combination of fat, cholesterol, calcium, and other substances) builds up in the arteries, causing them to narrow and stiffen. This plaque buildup can begin as early as childhood but typically develops over decades. In its early stages, atherosclerosis doesn’t present noticeable symptoms. However, as the plaque hardens, blood flow becomes restricted.
Why is it a problem:
The narrowing of arteries limits the flow of oxygen-rich blood to vital organs and tissues. This can cause chest pain (angina), shortness of breath, or, in severe cases, lead to a heart attack or stroke if the plaque ruptures and forms a blood clot.
Atherosclerosis is one of the leading causes of cardiovascular disease and is often referred to as the "silent killer" because it develops slowly and silently over time without noticeable symptoms.
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What is it:
Anemia is a condition in which the body lacks enough healthy red blood cells or hemoglobin to carry adequate oxygen to the tissues. Hemoglobin is the protein in red blood cells that binds to oxygen and transports it throughout the body. Anemia can be caused by a variety of factors including iron deficiency, vitamin B12 deficiency, chronic disease, blood loss, or genetic disorders like sickle cell anemia.
Why is it a problem:
With insufficient red blood cells, the body’s organs and tissues receive less oxygen, leading to fatigue, weakness, dizziness, and shortness of breath. The heart must pump harder to deliver oxygen to the body, which can lead to heart failure in severe cases. If left untreated, anemia can weaken the heart over time, especially if the underlying cause, such as blood loss, is not addressed. Anemia can be diagnosed with a blood test and is often treated by addressing the root cause, such as taking iron supplements or managing an underlying health condition.
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What is it:
Hemophilia is a genetic disorder where the blood doesn’t clot properly due to a deficiency in clotting factors, which are proteins in the blood that help stop bleeding. People with hemophilia may bleed longer than usual after an injury or even experience spontaneous internal bleeding. It is most commonly inherited and occurs more often in males.
Why is a problem?
Without sufficient clotting factors, individuals with hemophilia are at risk of excessive bleeding, even from minor cuts or bruises. Internal bleeding, especially in the joints and muscles, can lead to pain and permanent joint damage over time. In severe cases, uncontrolled bleeding into the brain or abdominal organs can be life-threatening
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What is it?
A stroke occurs when blood flow to a part of the brain is disrupted, either by a blocked artery (ischemic stroke) or by a ruptured blood vessel (hemorrhagic stroke). In ischemic stroke, a clot blocks the blood flow, while in hemorrhagic stroke, a blood vessel breaks, leading to bleeding in or around the brain. Both types of strokes result in brain cells being deprived of oxygen, which can lead to permanent brain damage
Why it is a problem
The effects of a stroke depend on the area of the brain affected, but they can include paralysis, difficulty speaking or understanding speech, vision problems, and changes in behavior or cognition. Stroke is one of the leading causes of disability and death worldwide, and it requires immediate medical attention to restore blood flow to the brain and minimize damage. Quick treatment can improve recovery outcomes, but long-term rehabilitation is often needed to regain function. Risk factors for stroke include hypertension, atherosclerosis, smoking, and diabetes.
Clinical Conditions of the Circulatory System
Forces against the walls of the arteries in Hypertension
Plaque accumulation in the arteries (Atherosclerosis)
Insufficiency in healthy blood cells (Anemia)
Review with a Story
Imagine blood as a delivery truck:
The heart is the engine that keeps it moving.
The arteries are highways going out.
The capillaries are local roads where deliveries happen.
The veins are roads back to the warehouse (the heart).
If any road is blocked, or the engine fails, deliveries (oxygen/nutrients) stop—and the whole system suffers.
Key Takeaways
Blood Vessels: Arteries carry oxygen-rich blood away from the heart, while veins return oxygen-poor blood back. Capillaries allow nutrient exchange between blood and tissues.
Blood Pressure: Normal blood pressure is around 120/80 mmHg. High blood pressure (hypertension) strains the heart and damages vessels.
Blood Composition: Blood is made up of plasma, red blood cells, white blood cells, and platelets. Each has a unique function, like oxygen transport and immune defense.
Clinical Conditions: Conditions like hypertension, atherosclerosis, and anemia affect circulation and can lead to serious health problems if not managed.
Prevention & Management: Regular check-ups, healthy lifestyle choices, and managing chronic conditions are the key to maintaining a healthy circulatory system.