The Heart + Circulatory System - Chp 26

Why do we need a circulatory system?

larger organisms need a circulatory system to supply all of their cells with the materials that are needed

Describe an open circulatory system:

• blood is not always in enclosed vessels
• blood is pumped into open-ended vessels
• blood flows around the cells of the animal's body
• blood flows back into the heart through ostia (openings in the heart's wall

Example of an organism with an open circulatory system:

snail, spider

Describe a closed circulatory system:

• blood remains closed in a continuous system of blood vessels
• materials are exchanged between the blood + cells through thin walls of the smallest blood vessels

Example of an organism with a closed circulatory system:

humans

What is the closed circulatory system composed of?

blood, heart + blood vessels

What are the benefits of a closed circulatory system?

• blood can be pumped around the body faster
• nutrients and oxygen get pumped around faster which allows animals to be more active
• allows for the increase of decrease of blood flow (pressure)

What are the 3 types of blood vessels?

arteries, veins + capillaries

Describe the function of an artery:

• carries blood away from the heart
• arteries are divided into smaller blood vessels called arterioles
• blood is under high pressure which causes the artery to slightly expand (pulse)
• carries mostly oxygenated blood

Describe the structure of an artery

• collagen on the outside, is a tough layer of inelastic protein which prevents the walls from over expanding
• thick layer of smooth muscle and elastic fibres
• single layer of living cells called endothelium surround the lumen
• narrow lumen
• no valves

Describe the function of veins:

• carries blood to the heart
• divide into smaller veins called venules
• blood is under low pressure
• carry mostly deoxygenated blood

Describe the structure of veins:

• collagen on the outside, is a tough layer of inelastic protein which prevents the walls from over expanding
• thin layer of smooth muscle and elastic fibres
• single layer of living cells called endothelium surround the lumen
• large lumen
• contains valves

Describe the function of capillaries:

• tiny vessels that link the arteries and veins
• allow the diffusion of substances from bloodstream to cells around the body
• carry both oxygenated and deoxygenated blood

Describe the structure of capillaries:

one layer of endothelium cells

Where is the heart located?

between the two lungs in the chest, in the thoracic cavity, behind the sternum, inside rib cage and above diaphragm

What muscle is the heart made from?

cardiac muscle, very slow to fatigue, under unvoluntary control

What membrane surround the heart + what is its function?

• a double membrane sac called the pericardium
• pericardial fluid is found between the membranes
• reduces friction when the heart beats

Septum

divides the heart into two sides

Atria

• the two upper chambers of the heart, they pump blood to the lower chambers of the heart (ventricles)
• only pump blood a short distance, they have thin walls

Ventricles

• the two lower chambers of the heart, they pump blood out of the heart
• the left ventricle wall is thicker as it pumps the blood around the body
• the right ventricle wall is thinner as it only pumps blood to the lungs

Valves

separate the atria + ventricles, they prevent the backflow of blood

Chordae Tendineae

connective tissue that hold the valves in place

Papillary muscle

attach to the chordae tendineae to prevent the valvles collapsing when they contract

Tricuspid valve

found on the right side of the heart between the atrium and ventricle, 3 cuspids
tricuspid -> right

Bicuspid valve

found on the left side of the heart between the atrium and ventricle

Semilunar valves

Allow one-way flow of blood from the lower half of the bocy back to the heart

Inferior vena cava

carries deoxygenated blood from the lower half of the body back to the heart

Superior vena cava

carries deoxygenated blood from the upper half of the body back to the heart

Pulmonary artery

carries deoxygenated blood away from the right side of the heart to the lungs to excrete carbon dioxide and absorb more oxygen

Aorta

largest artery in the body carrying oxygenated blood away from the left side of the heart to all the major organs of the body (except the lungs)

Pulmonary vein

carries oxygenated blood towards the right hand side of the heart from the lungs

Coronary arteries

bring oxygenated blood from the base of the aorta to the heart muscle

Coronary veins

return deoxygenated blood directly to the right atrium

Heart attack

• blockage of the coronary arteries is a common cause of heart attacks
• can cause pain called angina

Heart - diagram

Blood flow in the heart

• Deoxygenated blood enters the right atrium from the superior vena cava and inferior vena cava
• Right atrium contracts and forces the blood through the tricuspid valves into the right ventricle, the vena cava closes to prevent the backflow of blood
• When the right ventricle contracts the tricuspid valves close, the force of contraction pushes the blood out of the heart through the semilunar valves in the pulmonary arterty to the lungs
• In the lungs, gaseous exchange takes place
• Left atrium contracts and forces blood through the bicuspid valves into the left ventricle
• When the left ventricle contracts the bicuspid valves close, the force of contraction pushes the blooc out of the heart through the semilunar valves into the aorta, to the rest of the body
• In the cells, the O₂ is used in respiration and CO₂ is made
• When both ventricles relax the semilunar valves close
• This process on both sides of the heart occurs at the exact same time

What are the 2 circulatory systems in the human body?

• pulmonary system pumps blood from the heart →lung →heart
• systemic system pumps blood from heart →body tissues →heart

Double circulation

Blood passes through the heart at least twice
before reaching the same point again
eg humans
heart→lung→heart→body

Single circulation

Blood is pumped from the heart around the body
and back to the heart again in a single circuit
eg earthworm
heart→body→heart→body

Advantages of double circulation

• Separates oxygenated and deoxygenated blood.
• Ensures there is enough blood pressure to pump
  blood all around the body

Disadvantages of single circulation

Can only exert low pressure around most of the body

Portal system

a blood pathway that begins and ends in capillaries, do not connect directly to the heart

Example of a portal system

hepatic portal vein in humans connects the stomach and intestines to the liver

Adaptations of capillaries

• 1 cell thick, substances can easily diffuse through
• numerous meaning greater surface area for diffusion
• fully permeable endothelial cells, substances can easily pass through

Heart sound

• lub dub
• sound made by the closing of the valves
• 1st close of the bicuspid and tricuspid valves
• 2nd close of the semilunar valves

Heartbeat

alternating contractions (systole) and relaxation (diastole) of the muscle of the heart

Systole

heart muscle contraction

Diastole

heart muscle relaxing

What controls the rate of the heartbeat?

a small bundle of specialised tissues called the pacemaker

Cardiac cycle

• The atria and ventricles are both in diastole, blood enters the atria and all valves are closed.
• The heartbeat is initiated by the sino- atrial node
• SA node sends out an electrical impulse causing atrial systole, the tricuspid and bicuspid valves open to allow this blood to flow into the ventricles, the vena cava and
  pulmonary vein closes to stop the blood entering the atria.
• Blood is now in the ventricles, all valves remain closed, atrial systole
• The electrical impulses from the SA node now stimulate the artrio- ventricular node which is found above the Tricuspid Valve.
• The AV node sends an impulse down special muscle fibers found in the Septum called bundle of Hiss and
  into the purkinje fibers in the wall of the ventricles.
• This causes ventricular systole, the semilunar valves open and tricuspid/bicuspid valves close.
• The blood is forced out of the heart through the aorta and pulmonary artery
• The heart relaxes (diastole). Cycle repeats.