Topic 1 - Circulatory System Flashcards
pulmonary circulation
flow of blood to and from lungs
systemic circulation
circulation that supplies blood to the body expect to the lungs
aorta
largest artery in the body - carries blood from the left ventricle to the rest of the body
pulmonary artery
artery carrying oxygen-poor blood from the heart to the lungs
pulmonary veins
delivers oxygen rich blood from lungs to the left atrium
superior vena cava
vein that returns blood to the right atrium of the heart from the upper half of the body
inferior vena cava
carries blood from lower regions of the body to the right atrium
what is the primary function of the heart?
to pump blood throughout the body, supplying oxygen and nutrients to tissues and removing carbon dioxide and other wastes
4 chambers of the heart
r. atrium, r. ventricle, l. atrium, l. ventricle
where does deoxygenated blood enter the heart?
through the superior and inferior vena cava into the right atrium
pathway of deoxygenated blood in heart
r. atrium -> tricuspid valve -> r. ventricle -> pulmonary valve -> pulmonary artery
pathway of oxygenated blood
pulmonary vein -> l. atrium -> mitral (bicuspid) valve -> l. ventricle -> aortic valve -> aorta
which side of the heart handles deoxygenated blood?
right side
which side of the heart handles oxygenated blood?
left side
what are the atrioventricular valves, and where are they located?
tricuspid valve (between the r. atrium and r. ventricle) and the mitral (bicuspid) valve (between the l. atrium and l. ventricle).
what are the semilunar valves, and where are they located?
pulmonary valve (between the r. ventricle and pulmonary artery) and the aortic valve (between the l. ventricle and aorta).
systole
- phase of the heartbeat when the heart muscle contracts and pumps blood
- squeeze during systole
diastole
- phase when the heart muscle relaxes and fills with blood
- dilate (relax and expand to fill with blood)
the function of the coronary arteries?
supply oxygen-rich blood to the heart muscle itself.
what is the role of the sinoatrial (SA) node?
- pacemaker of the heart
- initiates the electrical impulses that set the heart rate
what is an electrocardiogram (ECG or EKG)?
a test that measures the electrical activity of the heart to show how well it is working
arteries and arterioles
- thick muscular wall
- can stretch to control amount of blood flowing
- carries blood away from the heart
- elastic fibers to withstand high blood pressure.
atherosclerosis
- buildup of fatty material/ cholesterol
- cholesterol turns into plaque and arteries come hard, causing high blood pressure
- arteries can rupture or blood clots can form
capillaries
- smallest blood vessel
- gas exchange
- 1 cell thick
one way valves
only allow blood to move towards the heart
skeletal muscle role
muscle contractions push blood in the veins back to the heart
septum
a thick wall of muscle that divides the left and right sides of the heart
atrium
the smaller upper chamber that receives blood returning to the heart
ventricle
the larger v-shaped bottom chamber that pumps blood from the heart
exercise overall effect on heart rate
lowers it
hot tub effect on heart rate
quickens heart rate (harder to remove heat from the body)
cold weather effect on heart rate
slows heart rate (easier to remove heat from body)
if a person has a heart murmur, it means their heart has a weak or malfunctioning valve, usually the mitral or tricuspid valves. How might this affect the blood flow through the heart?
- a heart murmur caused by a weak or malfunctioning mitral or tricuspid valve can lead to improper closure of the valve
- result in blood leaking backward (regurgitation) or restricted blood flow (stenosis)
- reduced efficiency of the heart’s pumping action, increased workload on the heart, and potentially cause symptoms like fatigue, shortness of breath, and fluid buildup in the lungs or other parts of the body
a person is diagnosed with a “hole” in their heart, specifically a small hole between the left and right atrium. How might this affect the blood flow through the heart?
- Increased Blood Flow to the Lungs: - mixed blood increases the volume of blood flowing to the right atrium and subsequently to the right ventricle + the lungs, causing the lungs to receive more blood than normal
- Reduced Efficiency - the mixing of oxygenated and deoxygenated blood reduces the efficiency of the heart’s function in delivering oxygen-rich blood to the body
- Heart Enlargement - over time, the increased workload on the right side of the heart can cause it to enlarge and weaken, potentially leading to heart failure if left untreated
if an Olympic athlete has an increased stroke volume of 100 mL, calculate their cardiac output at rest (50 BPM), with light excise (115 BPM) and with high-intensity exercise (180 BPM). Assume the stroke volume
remains constant.
Given:
Stroke Volume (SV) = 100 mL
Resting Heart Rate (HR) = 50 BPM
Heart Rate with Light Exercise = 115 BPM
Heart Rate with High-Intensity Exercise = 180 BPM
Summary
Cardiac Output at Rest: 5000 mL/min
Cardiac Output with Light Exercise: 11,500 mL/min
Cardiac Output with High-Intensity Exercise: 18 ,000 mL/min
explain why you might expect an Olympic athlete to have a lower resting heart rate than a person with an
inactive lifestyle.
- enhanced cardiovascular efficiency (higher stoke volume, heart does not need to beat as frequently to maintain the same cardiac output)
- Improved Heart Muscle (training leads to hypertrophy (enlargement) of the heart muscle, especially the left ventricle)
3.. Enhanced Oxygen Utilization (Increased Capillary Density & Higher Hemoglobin Levels)
function of the pulmonary valve
to prevent blood from flowing back into the right ventricle
during which phase of the cardiac cycle does the heart muscle contract to pump blood out of the chambers?
k into the right ventricle
systole
purpose of the mitral valve
prevent blood from flowing back into left atrium
what condition results from a blockage in the coronary arteries?
myocardial infarction (heart attack)
arteriole
small artery that joins a larger artery to a capillary
venule
small vein that joins a larger vein to a capillary
varicose veins
abnormally swollen, twisted veins with defective valves; most often seen in the legs
hypertension
abnormally high blood pressure
plasma
pale yellow fluid portion of blood where cells are suspended (55% of blood volume)
white blood cells
blood cells that perform the function of destroying disease-causing agents
platelets
particle that begins the blood clotting process at the site of a wound
red blood cells
- contain hemoglobin and transport oxygen to the body’s cells
- biconcave in shape.
hemoglobin
an iron-containing protein in rd blood cells that binds oxygen
fibrinogen
a protein that forms a plug that seals damaged blood vessels
bone marrow
location in which your blood cells are formed
hemophilia
a blood disorder involving the blood’s reduced ability to clot
plaque
a deposit of fatty material that builds up in your arteries
what is blood pressure measured with
sphygmomanometer
define blood pressure.
blood pressure is the force exerted by the blood against the walls of the blood vessels, especially the arteries, as it is pumped by the heart through the circulatory system.
what are the two components of blood pressure measurements?
systolic pressure (the top number) and diastolic pressure (the bottom number)
what is diastolic pressure?
diastolic pressure is the minimum pressure exerted on the walls of the arteries when the heart relaxes between beats
what unit is blood pressure typically measured in?
blood pressure is typically measured in millimeters of mercury (mmHg)
what is considered normal blood pressure in adults?
normal blood pressure is generally defined as a systolic pressure less than 120 mmHg and a diastolic pressure less than 80 mmHg
what factors can contribute to high blood pressure?
factors such as genetics, lifestyle (including diet, physical activity, and stress levels), age, obesity, smoking, and certain medical conditions can contribute to high blood pressure
Q: How can blood pressure be managed or reduced?
blood pressure can be managed or reduced through lifestyle changes (such as adopting a healthy diet, regular exercise, and stress management), medication, and other interventions recommended by healthcare professionals
what are the potential consequences of untreated hypertension?
untreated hypertension can lead to serious health complications, including heart disease, stroke, kidney disease, and vision loss
describe the difference between systolic and diastolic blood pressure
systolic (maximum pressure during heart contraction) and diastolic (minimum pressure between heartbeats) blood pressure reflect heart function and arterial health
low-density lipoprotein (LDL)
a blood protein that carries cholesterol in the blood from the liver to the rest of the body
- considered bad
high-density lipoprotein (HDL)
a blood protein that carries cholesterol in the blood form the body cells to the liver
- considered good
essential fatty acid
a fatty acid that the body cannot synthesize itself and must be obtained from food
- omega-3 and omega-6
atherosclerosis
a hardening of the arteries due to the accumulation of fatty deposits
coronary heart disease
restricts blood flow through the coronary arteries
angina
chest pain caused by narrowing of vessels that supply blood to the heart tissue
heart attack
the death of heart cells due to a blockage in the coronary arteries that supply oxygenated blood to the heart
stroke
the sudden loss of brain function caused by an interruption in the blood flow to the brain
aneurysm
a widening or bulging of a blood vessel due to a weakening of the vessel wall
blood vessel size that increases blood pressure (hypertension)
vasoconstriction, decreases in diameter of blood vessels
blood vessel size that decreases blood pressure (hypotension)
vasodilation, increases in diameter of blood vessels
lifestyle factors that increase blood pressure
stress, little activity, old age
what happens to systolic and diastolic pressure as people age
both go up (arteries are not as flexible + can develop a layer pf plaque or cholesterol
true or false: both left & righ side pump at the same time
true
true or false: all artieries carry oxygenated blood away from heart
- all arteries carry blood away from heart
- most oxygenated expect pulmonary arteries
true or false: all veins carry deoxygenated blood towards heart
- all veins carry blood towards heart
- most are deoxygenated, expect pulmonary veins
what ensure oxygenated and deoxygenated blood are separated
septum
true or false: atria have thinner walls than ventricles
true
left or right ventricle has thicker, more muscular walls
left ventricle is more muscular (pumping against higher resistance)
explain why it is more dangerous if an artery—rather than a vein—is cut in an accident.
- blood pressure - blood spurts out rapidly and forcefully
- volume of blood loss
contracting and relaxing the
muscles in their lower legs helps prevent fainting
muscle contraction - compressions helps propel blood upwards towards heart - adequate blood flow to heart
the left ventricle pumps out past __________ valve into aorta
semilunar
what is the cardiac cycle?
refers to the sequence of events that occur during one complete heartbeat, including the contraction and relaxation of the heart chambers to pump blood throughout the body
what are the two main phases of the cardiac cycle?
the systole phase, during which the heart contracts and pumps blood, and the diastole phase, during which the heart relaxes and fills with blood.
Q: Describe the events that occur during systole.
during systole, the ventricles contract (ventricular systole), pushing blood out of the heart into the pulmonary artery and aorta. at the same time, the atria are relaxed and filling with blood (atrial diastole).
describe the events that occur during diastole.
during diastole, the ventricles relax (ventricular diastole), allowing them to fill with blood from the atria. at the same time, the atria contract (atrial systole), pushing blood into the ventricles.
what is atrial systole?
atrial systole is the contraction of the atria, which occurs during diastole. It facilitates the filling of the ventricles with blood by pushing blood through the atrioventricular valves (tricuspid and mitral valves) into the ventricles.
what is ventricular diastole?
ventricular diastole is the relaxation of the ventricles, which occurs during diastole. It allows the ventricles to fill with blood from the atria, preparing them for the next contraction (systole)
what is ventricular systole?
ventricular systole is the contraction of the ventricles, which occurs during systole. It forces blood out of the ventricles and into the pulmonary artery and aorta, leading to systemic and pulmonary circulation
what is atrial diastole?
atrial diastole is the relaxation of the atria, which occurs during systole. It allows the atria to fill with blood from the veins (vena cavae and pulmonary veins) in preparation for the next cardiac cycle
what are the three main layers of blood vessel walls?
the tunica intima, tunica media, and tunica externa
describe the tunica intima
tunica intima is the innermost layer of blood vessel walls. it is composed of endothelial cells supported by a thin layer of connective tissue.
what is the function of the tunica intima?
the tunica intima provides a smooth surface for blood flow, helps regulate vascular tone and permeability, and plays a role in preventing blood clot formation (hemostasis).
describe the tunica media
the tunica media is the middle layer of blood vessel walls, consisting of smooth muscle cells and elastic fibers.
Q: What is the function of the tunica media?
the tunica media regulates the diameter of blood vessels (vasoconstriction and vasodilation) and helps maintain blood pressure and blood flow by altering vessel resistance.
describe the tunica externa
the tunica externa, also known as the tunica adventitia, is the outermost layer of blood vessel walls. it is composed of connective tissue, including collagen fibers and elastic fibers.
what is the function of the tunica externa
the tunica externa provides structural support and protection to blood vessels, anchoring them to surrounding tissues and organs. It also contains blood vessels (vasa vasorum) that supply nutrients and oxygen to the vessel wall.
how do the structure and composition of blood vessel walls vary among arteries, veins, and capillaries?
- arteries have thicker tunica media and more elastic fibers to withstand high blood pressure. - veins have thinner walls and contain valves to prevent backflow of blood.
- capillaries have a single layer of endothelial cells, facilitating the exchange of substances between blood and tissues.
cardiac cycle stages
- heart is relaxed, atria fills with blood. AV valves are closed.
- AV valves open, atria contracts to move blood to ventricles (semilunar valves closed)
- AV valves close, ventricles contract to allow blood out to the arteries (aorta & pulmonary artery)
AV valves during systole
closed
AV valves during diastole
open
semilunar valves during systole
open
semilunar valves during diastole
closed
what are the main components of blood?
RBC - erythrocytes
WBC - leukocytes
platelets - thrombocytes
plasma
describe the structure of red blood cells (erythrocytes).
RBCs are biconcave discs without a nucleus. they contain hemoglobin, a protein that binds and transports oxygen.
what is the function of red blood cells (erythrocytes)?
RBCs transport oxygen from the lungs to tissues and organs throughout the body and help remove carbon dioxide for exhalation.
describe the structure of white blood cells (leukocytes).
WBC are larger than red blood cells and have a nucleus
what is the function of white blood cells (leukocytes)?
WBC are part of the immune system and help defend the body against infections and foreign invaders, such as bacteria, viruses, and parasites.
describe the structure of platelets (thrombocytes)
platelets are small, disc-shaped cell fragments without a nucleus
what is the function of platelets (thrombocytes)
platelets play a crucial role in blood clotting (hemostasis) by forming clots to stop bleeding from damaged blood vessels.
what is plasma
plasma is the liquid component of blood, composed of water, proteins, electrolytes, hormones, gases, and waste products.
what is the function of plasma?
plasma transports nutrients, hormones, and waste products throughout the body, maintains blood pH and osmotic balance, and plays a role in immune responses and blood clotting.
buffers in blood
- carbonic acid & hydrogen carbonate that help to buffer excess base or acids and maintain constant pH
- pH over 0.5 in blood can be fatal
describe the process of platelet adhesion.
- platelet hits rough edge of a a ruptured blood vessel, accumulate and release thromboplastin and Ca2+
- thromboplastin and Ca2+ convert into fibrinogen and fibrin
- fibrin is a stretchy net that traps RBCs
sickle cell anemia (affected RBC’s)
abnormally shaped RBC’s do not flow well and can cause a blood clot (mutation in DNA)
anemia (affected RBC’s)
- reduced RBCs or iron
- symptoms: similar to being at high attitude, shortness of breath, low enegry level
CO(g) poisoning (affected RBC’s)
- due to incomplete combustions (cars, furnaces)
- CO(g) competes with oxygen to bind with hemoglobin
- symptoms: shortness of breath, dizziness, nausea
Leukaemia ( (affected WBC’s)
- increase in the number of abnormal WBCs
- can be treated by destroying abnormal cells followed by bone marrow transplant
Abnormally high RBC count
person is in low oxygen environment and trying to compensate
- could be adjusting to high altitude environment
high WBC & platelet count
could have an open wound and trying to fight infection
barrier responses (1st line of defence)
- keeps pathogens out
- skin, sweat, & oil
- hair & cilia
- eyelashes
- stomach acid
- sneezing
- coughing
non-barrier responses (2nd line of defence)
- inflammation of the area
- immune response (antibody production)
inflammatory response
- WBCs leak out of capillaries
- WBCs engulfs pathogens
- WBCs use enzymes to digest the pathogen
- pus forms
immune response happens when
if inflammatory response fails, immune response initiated
septal defect
a condition where the opening between the left and right halves of the heart fails to close before birth, causing excess blood to be pumped to the lungs
pathogen
an agent that causes disease
bateria
microscopic, single celled organism that lacks a nucleus
virus
a non-cellular particle that multiples within the cells of an living organism
fungus
absorbs food in solution directly through cells walls (mold, mushrooms, yeast)
protozoan
a group of microscopic organisms that have a nucleus. Can only divide within a host (ex. parasites, the cause for malaria)
antigen
- protein markers on surface of all cells (including viruses, bacteria, and your own body cells)
- help identify a cell
macrophages
A type of WBC that engulfs a foreign pathogen and displays its antigen
antibody
- proteins produced by WBC’s when a foreign antigen enters the body
- handcuffs (immobilize the invader)
-chemical that only works on bacteria
helper T cells
coordinates the immune response by sending chemical signals to activate other immune cells, such as B cells and T cells
B cells
WBCs that produce anti bodies
memory B cells & memory T cells
remains n the bloodstream after the pathogen is destroyed to keep track of the antigens so the next time the pathogen enters the immune response will be quicker
killer T cells
WBC that attacks and destroys infected body cells
suppressor T cells
signals the system to return to pre-infection state
vaccinations
biological preparation that increases immunity by stimulating production of antibodies
what is immunity?
immunity is the ability of an organism to resist or defend against harmful pathogens, such as bacteria, viruses, and parasites.
describe adaptive immunity
adaptive immunity is a specific immune response that develops after exposure to a pathogen. It involves the activation of lymphocytes (T cells and B cells) and the production of antibodies to target and eliminate specific pathogens.
what is passive immunity?
temporary immunity conferred by the transfer of antibodies from one individual to another. It can occur naturally (e.g., from mother to fetus via placenta or breast milk) or artificially (e.g., through injection of antibodies).
how does the immune system distinguish between self and non-self antigens?
the immune system distinguishes between self and non-self antigens through the recognition of self antigens during development and the elimination or suppression of immune responses against self antigens.
explain the concept of self-tolerance and its importance in preventing autoimmune diseases.
self-tolerance is the ability of the immune system to recognize and tolerate self antigens while mounting immune responses against non-self antigens. it is crucial for preventing autoimmune diseases, where the immune system attacks the body’s own cells and tissues due to a loss of self-tolerance.
cholesterol
a waxy, fat-like substance present in the cell membrane of every body cell and in food from
animal sources
Saturated Fatty Acids
made from long chains of fatty
acids in which all the carbons are connected by single
covalent bonds
Unsaturated Fatty Acids
- made from long chains of
fatty acids in which there is at least one double or triple
bond - monounsaturated - only one double/triple bond
- polyunsaturated - more then one double/triple bond
what lifestyle factors might the doctor ask about regarding the patient’s risk of developing circulatory diseases?
of the patient developing a circulatory disease
A: Exercise habits, diet, smoking status, and stress levels
what problem in a water delivery system can be compared to something stuck in one of the pipes in the human circulatory system?
a blockage or obstruction in a blood vessel, such as a clot or plaque buildup, leading to reduced blood flow and potential loss of blood supply to certain tissues or organs.
what problem in a water delivery system can be compared to a faulty valve in the water pump in the human circulatory system?
malfunctioning heart valves, such as stenosis (narrowing) or regurgitation (leakage), which can disrupt the normal flow of blood within the heart and between its chambers, affecting overall circulatory function.
autoimmune disease
a disorder in which the immune system attacks the body’s own cells, eg. cystic fibrosis, MS, Type 1 diabetes
HIV and immune response
- HIV invades Helper T-cells
- HIV can live in T-cells for days or even years without becoming active
- when it becomes active, helper t-cell’s DNA to reproduce
- when helper t-cell bursts, HIV spreads to other t-cells and repeats the process
how does the body initially respond to HIV infection?
the body mounts an immune response to HIV, producing antibodies and activating cytotoxic T cells to target and destroy infected cells. however, HIV can evade immune responses and establish a chronic infection.
compare how long the body takes to produce antibodies after first exposure to second exposure
- antibodies produced much quicker & more are produced on second exposure
- memory cells recognize the antigens
describe the role of autoantibodies in autoimmune diseases.
autoantibodies are antibodies produced by the immune system that mistakenly target and attack the body’s own cells and tissues. They contribute to the development and progression of autoimmune diseases by causing inflammation and tissue damage.
auto immune diseases treatment
anti-inflammatory or immunosuppressant drugs
fibrin
a thread-like insoluble protein
formed from fibrinogen. the threads of fibrin mesh to form the fabric of a blood clot
list the four components of blood in decreasing order of their relative volume in whole blood (from most
- Plasma
- Red blood cells (erythrocytes)
- White blood cells (leukocytes)
- Platelets (thrombocytes)
explain why an anticoagulant might be useful for treating circulatory system problems.
anticoagulants help prevent the formation of blood clots, which can obstruct blood flow in blood vessels and lead to serious circulatory system problems such as heart attacks, strokes, or pulmonary embolisms.
Burn victims suffer a significant loss of skin tissue and are, therefore, highly susceptible to deadly dehydration. What blood component best addresses this problem?
plasma: contains water, electrolytes, and proteins, which help maintain blood volume and hydration levels in the body
why is it hard for cancer patients receiving radiation treatment to produce platelets?
Radiation treatment can damage the bone marrow, which is responsible for producing blood cells, including platelets. As a result, cancer patients undergoing radiation therapy may experience decreased platelet production, leading to thrombocytopenia (low platelet count) and an increased risk of bleeding. This difficulty in platelet production is compounded by the effects of cancer itself, which can disrupt normal bone marrow function and further impair platelet production.
suggest a reason for the lower volume of white blood cells in a sample of blood even though they are produced at twice the rate of red blood cells.
WBCs (leukocytes) are larger and less numerous than red blood cells (erythrocytes), resulting in a lower overall volume in a blood sample. Additionally, white blood cells are capable of migrating out of the bloodstream and into tissues to perform their immune functions, whereas red blood cells primarily remain within the blood vessels. Therefore, even though white blood cells are produced at a higher rate than red blood cells, a significant portion of them may be residing in tissues rather than circulating in the bloodstream, leading to a lower concentration in a blood sample.
antiseptics
a solution or substance that prevents or inhibits
the growth of microorganisms
Antiviral
chemical that only works on viruses
how does malaria enter the body?
malaria parasites evade immune detection by hiding in liver cells before infecting red blood cells, where they modify surface proteins to avoid immune surveillance.
how does hepatitis C enter the body?
hepatitis C virus enters the body through infected blood, infects liver cells, and evades immune elimination by rapidly mutating surface proteins and suppressing immune responses.
how does tuberculosis enter the body?
tuberculosis bacteria enter the body through inhalation, infect lung cells, and evade immune detection by inhibiting phagolysosome fusion and modulating immune responses.
how does Salmonella enter the body?
salmonella bacteria enter the body through contaminated food or water, invade intestinal cells, and evade immune detection by inhibiting phagocytosis and resisting antimicrobial peptides.
what are the similarities between bacteria and viruses?
both bacteria and viruses are microscopic pathogens that can cause diseases in humans, animals, and plants. They replicate and spread within host organisms and can be transmitted from person to person through various routes.
what are the differences between bacteria and viruses?
bacteria are single-celled organisms with a cell wall, cell membrane, and genetic material (DNA or RNA). They are capable of independent reproduction and metabolism. Viruses, on the other hand, are acellular particles consisting of genetic material (DNA or RNA) surrounded by a protein coat (capsid). They cannot replicate or carry out metabolic functions on their own and rely on host cells for replication.
how do bacteria and viruses differ in size?
bacteria are larger than viruses, ranging in size from 0.2 to 10 micrometers in diameter, whereas viruses are much smaller, typically ranging from 20 to 300 nanometers in size.
how do bacteria and viruses differ in structure?
bacteria are prokaryotic cells with a cell wall, cell membrane, and genetic material contained within a nucleoid region. They may also have flagella or pili for movement and attachment. Viruses are not cells and consist of genetic material (DNA or RNA) enclosed in a protein coat (capsid). Some viruses may also have an outer lipid envelope derived from the host cell membrane.
how do bacteria and viruses differ in replication?
bacteria reproduce by binary fission, a process of asexual reproduction in which one cell divides into two identical daughter cells. Viruses replicate by hijacking host cells and using their cellular machinery to produce new viral particles through either the lytic cycle (resulting in cell lysis and release of viral particles) or the lysogenic cycle (integrating viral DNA into the host genome).
Along what sequence of structures does an anesthetic continue its journey through the circulatory system?
Venule, vein, heart, artery, arteriole
which blood component is responsible for starting the clotting process?
Platelets
heart murmur
- abnormal sound heard during a heartbeat cycle
- valve dysfunction, turbulence in blood flow
- structural defect, septal defects
- anemia, hyperthyroidism, or fever
what is the function of the septum in the heart, and why is it important for cardiac function?
- thick wall that divides right and left sides of the heart
- division ensures that oxygen-rich blood returning from the lungs to the l. atrium does not mix with oxygen-poor blood returning from the body to the r. atrium
elastic fibers
stretch and recoil to accommodate the surge of blood ejected from the heart during systole
