Circulatory System

Circulation and Respiration Each breath brings oxygen rich air into your body Your cells need that oxygen Your heart delivers oxygen to your cells Working together, your circulatory and respiratory systems supply cells throughout the body with the nutrients and oxygen that they need to stay alive!

Function The circulatory system transports substances including oxygen, nutrients and wastes to and from cells responding to changing demands by diffusion (from high to low concentration along concentration gradient).

Structure Humans have a closed circulatory system. Blood is pumped through a system of vessels (In an open system, blood flows in vessels and sinuses/gills) Sometimes the circulatory system is also called the “cardiovascular system” because: Cardio = heart Vascular = vessels The human circulatory system consists of: The heart A series of blood vessels Blood that flows through them

The Heart Located near the center of your chest A hollow organ about the size of your fist composed of cardiac muscle. Enclosed in a protective sac of tissue called the pericardium Inside there are two thin layers of epithelial and connective tissue Contractions of the myocardium, a thick cardiac muscle, pump blood through the circulatory system The heart contracts about 72 times a minute Each contraction pumps about 70 mL of blood

Septum, or wall, separates the right side from the left side preventing mixing of oxygen-rich blood and oxygen-poor blood Flaps of connective tissue called valves divide each side into 2 chambers: totaling 4 chambers Upper chambers receive blood = atrium Lower chambers pump blood out of heart = ventricle Heart

Types of Circulation Pulmonary circulation = from right side of the heart to lungs where carbon dioxide leaves the blood and oxygen is absorbed Systemic circulation = from left side of the heart to organs Coronary circulation = through heart tissue

Pulmonary Circulation The right side of the heart pumps blood from the heart to the lungs In the lungs, carbon dioxide leaves the blood while oxygen is absorbed. The oxygen-rich blood goes into the left side of the heart

Systemic Circulation The oxygen-rich blood from the left side of the heart is pumped to the rest of the body Oxygen-poor blood returns to the right side of the heart This blood is oxygen-poor because the cells absorbed the oxygen and released carbon dioxide into the blood The oxygen-poor blood is ready for another trip to the lungs to get oxygen again

Figure 37-2 The Circulatory System Section 37-1 Capillaries of head and arms Capillaries of abdominal organs and legs Inferior vena cava Pulmonary vein Capillaries of right lung Superior vena cava Aorta Pulmonary artery Capillaries of left lung

Blood Flow through the heart Blood leaves the heart in arteries, and blood returns to heart in veins. Oxygenated blood returns from the lungs through the pulmonary veins to the left atrium. Oxygenated blood is pumped from the left atrium through the mitral valve to the left ventricle. Oxygenated blood leaves the left ventricle through the aortic valve to the aorta, which is the largest artery of your body. The aorta branches into various arteries pumping blood through your body. Deoxygenated blood returns from the top of your body through the superior vena cava and from the bottom of your body through the inferior vena cava to the right atrium. Deoxygenated blood is pumped from the right atrium through the tricuspid valve to the right ventricle. Deoxygenated blood leaves the right ventricle through the pulmonary valve to the pulmonary arteries. The pulmonary arteries pump blood to the lungs to absorb oxygen and release carbon dioxide. Heart circulation animation: http://www.nhlbi.nih.gov/health/dci/Diseases/hhw/hhw_pumping.html

The Path of Blood

Valves Blood enters into the atria of the heart, separated from the ventricles by valves, preventing back-flow of blood keeping the blood flowing in one direction When the atria contract, the valves open and blood flows into the ventricles When the ventricles contract, the valves close preventing blood from flowing back into the atria and blood flows out of the heart At the exits of the ventricles, there are valves that prevent blood from flowing back into the heart The “lub-dup” sound of your heart is caused by the closing of the heart’s valves. The “lub” is when the ventricles contract and blood being forced against the artioventricular or A-V (tricuspid or mitral) valves. The “dup” is the blood being forced against the semilunar (aortic or pulmonary) valves.

Figure 37-3 The Structures of the Heart Section 37-1 Inferior Vena Cava Vein that brings oxygen-poor blood from the lower part of the body to the right atrium Tricuspid Valve Prevents blood from flowing back into the right atrium after it has entered the right ventricle Pulmonary Valve Prevents blood from flowing back into the right ventricle after it has entered the pulmonary artery Pulmonary Veins Bring oxygen-rich blood from each of the lungs to the left atrium Superior Vena Cava Large vein that brings oxygen-poor blood from the upper part of the body to the right atrium Aorta Brings oxygen-rich blood from the left ventricle to the rest of the body Pulmonary Arteries Bring oxygen-poor blood to the lungs Aortic Valve Prevents blood from flowing back into the left ventricle after it has entered the aorta Mitral Valve Prevents blood from flowing back into the left atrium after it has entered the left ventricle Left Atrium Right Atrium Left Ventricle Septum Right Ventricle

Heartbeat There are two muscle contractions in the heart: The atria The ventricles Each contraction begins in a small group of cardiac muscle cells in the right atrium that stimulate the rest of the muscle cells = sinoatrial node (SA node) Since the sinoatrial node sets the pace for the heart it is also called “the pacemaker” The impulse spreads from the pacemaker through fibers in the atria to the atrioventricular node (AV node) and through fibers in the ventricles When the atria contract, blood flows into the ventricles When the ventricle contract, blood flows out of the heart

Blood vessels Blood circulates in one direction and it is moved by the pumping of the heart As blood flows through the circulatory system, it moves through three types of blood vessels: Arteries Capillaries Veins

Arteries Large vessels that carry blood away from the heart to tissues of the body Except for the pulmonary arteries, all arteries carry oxygen-rich blood. Arteries have thick walls of elastic connective tissue, contractible smooth muscle, and epithelial cells that help them withstand the powerful pressure produced when the heart contracts and pushes blood into the arteries.

Capillaries The smallest of the blood vessels connecting arteries and veins Walls are one cell thick allowing for easier diffusion of nutrients and oxygen from capillaries to body cells and wastes and carbon dioxide from body cells to capillaries

Veins Return blood to the heart Veins have walls of connective tissue and smooth muscle Large veins contain valves that keep blood flowing towards the heart Many veins are located near skeletal muscles, so when the muscles contract, they help force blood through the veins, even against gravity Exercise helps prevent accumulation of blood in limbs and stretching veins out of shape

Blood Pressure The heart produces pressure when it contracts. The force of blood on the arteries’ walls = blood pressure Blood pressure decreases when the heart relaxes, but there must always be some pressure to keep the blood flowing Doctors measure blood pressure with a sphygmomanometer recording two numbers Systolic pressure = force felt in arteries when ventricles contract Diastolic pressure = force of blood felt in arteries when ventricles relax Average adult’s blood pressure = 120/80

High Blood Pressure Also known as Hypertension Forces heart to work harder, which may weaken or damage the heart muscle and vessels More likely to develop heart disease and increased risk of heart attack and stroke

Heart Attack A medical emergency Coronary arteries (supplying heart blood) bring oxygen and nutrients to the heart muscle itself Blockage of coronary artery may damage or kill part of heart muscle (myocardium) due to lack of oxygen = heart attack Symptoms include: chest pain/pressure, feeling of heartburn/indigestion, sudden dizziness, or brief loss of consciousness

Stroke Blood clots may break free from vessels and get stuck in a blood vessel leading to a part of the brain = stroke Brain cells relying on that vessel may begin to die from lack of oxygen and brain function in that region may be lost Strokes can also occur when a weakened artery in the brain burst, flooding the area with blood

Prevention Exercise – increases respiratory system’s efficiency Cardiovascular diseases are easy to prevent: Exercise – increases respiratory system’s efficiency Weight control – reduces body fat and stress Sensible diet – low in saturated fat reduces risk of heart disease Not smoking – reduces risk of heart disease