Download Student Notes - Circulatory and Respiratory

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THE CIRCULATORY SYSTEM
THE CIRCULATORY SYSTEM
All organisms move substances internally from one place to another. The circulatory system is responsible for the movement of
substances (O2, CO2, nutrients, & wastes) through the body. The human circulatory system has three components: the heart, the blood
vessels, and the blood.
I. THE HEART
The function of the heart is to keep the blood moving constantly in the body. The heart is a large organ made of cardiac muscle
cells that have a high number of mitochondria. Humans have a 4-chambered heart. The heart is divided into a right and left side
with two chambers making up each side. The two sides are divided by a septum.
A. Structure
1. Membranes – There are 3 layers of tissue that surround the heart.
a. Pericardium – Outermost layer; membrane composed of connective tissue that surrounds and protects the heart.
b. Myocardium – Middle layer; cardiac muscle tissue that forms the four chambers of the heart.
c. Endocardium – Innermost membrane that lines the chambers, covers the valves, and continues into the vessels.
Composed of smooth, epithelial tissue to prevent blood clotting.
2. Chambers
a. Atria (atrium =singular) - Upper chambers of the heart that receive blood. Walls are thinner and less elastic than
ventricles.
b. Ventricles – Lower chambers of the heart that pump blood to the lungs and body. Have thick, elastic walls,
especially the left ventricle because it pumps blood out to the body.
3. Valves – Flaps of epithelial tissue reinforced with connective tissue that keep blood flowing in one direction and increase the
pumping efficiency of the heart.
B. Types of Circulation
1. Systemic – The flow of blood from the left side of the heart to the body and back to the heart. The main artery involved is
the aorta; main veins involved are the superior and inferior vena cava.
2. Pulmonary – The flow of blood from the right side of the heart to the lungs and back to the heart. Pulmonary arteries
carry O2 poor blood from the heart to the lungs; pulmonary veins carry O2 rich blood from the lungs to the heart.
3. Coronary – since the heart is a major organ, it needs its own supply of O2 rich blood. This is coronary circulation. The
coronary arteries are the first two branches of the aorta. These arteries branch into capillaries that circulate oxygenated
blood to the myocardium for the heart to use, then the coronary veins return the deoxygenated blood to the right atrium.
C. Pathway of Blood Flow Through the Heart.
Superior/Inferior Vena Cava  Right Atrium Right Ventricle Pulmonary Artery  Lungs  Pulmonary Veins 
Left Atrium  Left Ventricle  Ascending/Descending Aorta
II. THE BLOOD VESSELS
Blood vessels are composed of connective tissue for strength, smooth muscle tissue to facilitate blood flow, and they are lined
with epithelial tissue for smoothness.
Types – There are three types of blood vessels:
A. Arteries – Carry blood Away from the heart. Arteries have thick, elastic walls to withstand the pressure of spurts of blood
from contraction of the heart. Arteries branch into arterioles and then to capillaries. Arteries carry blood
that is high in oxygen and low in carbon dioxide, except for the pulmonary artery.
B. Veins – Carry blood to the heart. Veins have thinner, less elastic walls. They contain valves to keep blood flowing in one
direction. Veins branch into venules which lead to the other side of the capillary bed. Veins carry blood low in oxygen and
high in carbon dioxide except for the pulmonary vein.
C. Capillaries – Network in which O2, glucose, & other nutrients are exchanged with CO2 and other wastes. Capillaries
are only one-cell thick, so red blood cells must flow through one-by-one. This allows time for diffusion.
III. THE BLOOD
Blood is classified as connective tissue with a matrix of plasma. Plasma is the liquid that makes up approximately 55% of
blood. Plasma is 90% water, the other 10% is made up of proteins, ions, vitamin K, lipids, hormones, etc.
A. Erythrocytes (RBC’s)
Function is to deliver O2 to all body cells. Most numerous cells in blood, they are doughnut-shaped cells that lose their
nuclei as they mature in the red marrow. This adaptation allows them to squeeze through tiny capillaries and provides more
area for oxygen transport. Red blood cells contain hemoglobin, and iron-containing protein that binds oxygen.
Erythrocytes circulate every 120 days & are destroyed in the spleen.
B. Leukocytes (WBC’s)
Larger and fewer in number than RBC’s. Their primary function is to fight infection by engulfing pathogens or marking them
for destruction. Some WBC’s are able to leave the blood vessels.
C. Thrombocytes (platelets)
Cell fragments that break off from large cells produced in the red marrow. Like RBC’s, they lack a nucleus, but platelets
are smaller than red blood cells. Platelets begin the clotting process by sticking together to form a plug when they come in
contact with a rough surface. Thrombocytes live about 10 days.
THE HEART
THE RESPIRATORY SYSTEM
The function of the respiratory system is to bring about the exchange of O2 and CO2 . This is called external respiration. Cellular
respiration is the production of ATP from glucose and O2 in the mitochondria of a cell. CO2 and H2O are released as waste products.
External respiration provides the O2 needed for cellular respiration to occur!!!
I. THE RESPIRATORY PASSAGEWAY
A. Airway to the Lungs
Air normally enters the respiratory system through the mouth and nasal passages, which begin the process of filtering,
warming, and moistening the air. From there, the air passes through the pharynx (upper throat) and the larynx. The larynx
contains the vocal cords, bands of connective tissue that tighten and vibrate to create sound when air passes through.
Attached to the larynx is a flap of tissue called the epiglottis. The epiglottis closes when food is swallowed to prevent food from
entering the trachea. After air passes over the larynx, it enters the trachea, a tube supported by bands of cartilage to prevent it
from collapsing when air passes in and out. The trachea divides at its lower end into two tubes called bronchi (singular =
bronchus). The trachea and bronchi are lined with cilia and cells that secrete mucus.
B. Inside the Lungs
Inside each lung, the bronchi narrow as they branch into smaller passageways called bronchioles. The bronchioles end in
millions of tiny sacs called alveoli. The alveoli are the site for the exchange of O2 and CO2. Each alveolus is surrounded by a
capillary to allow O2 to diffuse from the lung to the blood to be delivered to cells for cellular respiration, and CO2 to diffuse from
the blood to the lung to be exhaled.
II. BREATHING
A. Inhalation & Exhalation
The lungs are surrounded by the pleural membrane and hang freely in the thoracic cavity. There are no muscles attached to
the lungs. The muscles involved in breathing are the intercostal muscles, located between the costas and the diaphragm, a
dome-shaped muscle located below (but not attached to!) the lungs.
Breathing occurs as a result of a change in pressure. When the diaphragm contracts, it flattens which increases the volume of
the chest cavity and decreases the pressure. In addition, the intercostal muscles contract, further increasing the volume of the
chest cavity. Air rushes into the lungs. As the diaphragm and intercostal muscles relax, volume of the chest cavity decreases,
and the increased pressure of the lungs help force the air back out.
B. Control of Breathing
Breathing is controlled by the medulla oblongata. Motor neurons stimulate the skeletal muscle of the diaphragm to contract.
The stimulus for breathing is the concentration of CO2 in the blood, which is monitored by the hypothalamus.