6.2: The Blood System

https://s.yimg.com/fz/api/res/1.2/2kG.LrAa1_1YmAd00EZMKw--/YXBwaWQ9c3JjaGRkO2g9NjY5O3E9OTU7dz05MDA-/http://criticalcaredvm.com/wp-content/uploads/2015/03/6-red-blood-cells-sem-susumu-nishinaga.jpg

Understandings Arteries convey blood at high pressure from the ventricles to the tissues of the body.

Arties have muscle cells and elastic fibers in their walls.

The muscle and elastic fibers assist in maintaining pressure between pump cycles.

Blood flows through tissues in capillaries. Capillaries have permeable walls that allow exchange of materials between cells in the tissue and the blood in the capillary.

Veins collect blood at low pressure from the tissues of the body and return it to the atria of the heart.

Valves in veins and the heart ensure circulation of blood by preventing backflow.

There is a separate circulation for the lungs.

The heart beat is initiated by a group of specialized muscle cells in the right atrium called the sinoatrial node.

The sinoatrial node acts as a pacemaker.

The sinoatrial node sends out an electrical signal that stimulates contraction as it is propagated through the walls of the atria and then the walls of the ventricles.

The heart rate can be increased or decreased by impulses brought to the heart through two nerves from the medulla of the brain.

Epinephrine increases the heart rate to prepare for vigorous physical activity.

Applications and Skills A: William Harvey’s discovery of the circulation of the blood with the heart acting as the pump.

A: Pressure changes in the left atrium, left ventricle, and aorta during the cardiac cycle.

A: Causes and consequences of occlusion of the coronary arteries.

S: Identification of blood vessels as arteries, capillaries, or veins from the structure of their walls.

S: Recognition of the chambers and valves of the heart and the blood vessels connected to it in dissected hearts or in diagrams of heart structure.

Blood VesselsThere are three main types of blood vessel:

Arteries carry high pressure blood away from the heart to tissues that need it

Capillaries are very small (< 10 μm diameter) and therefore can penetrate virtually every tissue in the body. Blood moves slowly through them under low pressure providing opportunities for the exchange of substances.

Veins carry the low pressure blood back to the heart using valves to ensure blood flows in the correct direction.

Arteries and veins tend to be large structures; smaller arteries are known as arterioles and correspondingly smaller veins are venules.

Arteries have a relatively thick smooth muscle layer to change the inside diameter of the lumen.

A capillary bed is a network of capillaries that drain into a single venule.

Muscle contracts to decrease the size of the lumen. This causes an increase blood pressure and therefore maintains high blood pressure between the pulses of high pressure blood travelling from the heart.

Elastic fibers stretch to increase the lumen with each pulse of blood. After the pulse of blood passes the fibers recoil decreasing the lumen size and therefore helping to maintain a high blood pressure.

Relatively small lumen maintains high blood pressure.

The structure of arteries

Thick muscular wall and fibrous outer layer help the artery to withstand high pressure

https://commons.wikimedia.org/wiki/File:Blausen_0055_ArteryWallStructure.png

https://commons.wikimedia.org/wiki/File:Capillary_system_CERT.jpg

The structure of capillariesCapillaries are the smallest blood vessels and are adapted for the exchange of substances to and from the blood.

This enables tissues to gain nutrients and molecules such as oxygen and to rid themselves of waste material.

Capillaries also allow substances to enter and leave the organism, e.g. gas exchange of oxygen and carbon dioxide in the lungs.

Wall is one cell thick allows easy diffusion of substances in and out of the capillary due to the short diffusion distance.

Blood travels slowly under low pressure allowing more opportunity for exchange.

Basement membrane is permeable to many substances

The walls and membrane can contain pores to further aid the diffusion of substances

Due the the massive number of capillaries present and the small lumen the surface area available for the exchange of substances is very large.

Image adapted from: https://commons.wikimedia.org/wiki/File:Capillary.svg

The structure of veins

https://commons.wikimedia.org/wiki/File:Venous_valve.svghttp://40.media.tumblr.com/tumblr_m0dwjt3WKQ1qzcf71o1_500.jpg

Veins return blood to the heart for recirculation.

Because of the low pressure valves are required to prevent back-flow of the blood and therefore ensure that the blood moves towards to heart.

Because there is less pressure to resist the walls of the veins are thinner and less elastic than arteries. They also contain less muscle than the arteries.

The large lumen (compared to arteries and the thickness of the wall) means that the blood is under low pressure.

Artery Capillary Vein

Thick walled Wall is 1 cell thick Thin walled

No exchanges All exchanges occur No exchanges

No internal valves No internal valves Internal valves present

Internal pressure high

Internal pressure low

Internal pressure low

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http://www.kscience.co.uk/animations/blood_system.swf

Circuit through blood vessels:- A large artery- Smaller artery branches- An arteriole (small artery)- A capillary bed- A venule (small vein)- A larger vein- Large vein which takes

back to the heart- Begins again

Now try to label this heart: http://sciencelearn.org.nz/Contexts/See-through-Body/Sci-Media/Animation/Label-the-heart

Left atrioventricular valve

Right atrioventricular valve

http://www2.estrellamountain.edu/faculty/farabee/Biobk/heartbeat.gif

http://goo.gl/YeoeJ

adrenalin is also known as epinephrine

WHEN BOTH CHAMBERS ARE AT REST (Diastole) - Atrial pressure is slightly higher (keeps AV valve

open)

- Pressure in aorta is higher than in left ventricle (keeps semilunar valve closed to prevent backflow)

http://goodfoodeating.com/wp-content/uploads/2014/06/Systolic-diastolic-heart-actions.jpg

WHEN ATRIA ARE IN SYSTOLE- Ventricles in diastole

- Pressure produced is not very high since the muscle of the atria are relatively thin.

- Much of the blood has already accumulated passively into the ventricle.

WHEN VENTRICLES ARE IN SYSTOLE- Atria are in diastole

- Pressure in atrium greater than ventricle (causes AV valve to close)

- Pressure in aorta still higher, SL valve remains closed

- Ventricle highly muscular pressure build up

- Pressure in ventricle becomes higher than aorta, SL valve opens, ventricle pumps blood into aorta

- Pressure drops, SL valve closes

Both chambers go back into diastole and the cardiac cycle repeats.

ATHEROSCLEROSIS- Build up of plaque in the arteries

- Arteries become harder, less flexible

- Genetics and eating habits influence plaque build up

http://www.health-choices-for-life.com/images/arterialplaque.jpg

Partial or complete occlusion can lead to a heart attack- Coronary arteries supply oxygen rich blood to cardiac muscle

- Blockage decreases blood supply

- This deprives the muscle of oxygen

- Leads to coronary muscle tissue death

Identify the labeled structures using your understanding of blood vessels.

a

b

https://www.ouhsc.edu/histology/Text%20Sections/Cardiovascular.html

HomeworkVOCAB

Arteries, veins, capillaries, pulmonary arteries, pulmonary veins, atria, ventricles, blood pressure, pulmonary circulation, systemic circulation, cardiac muscle, myogenic muscle contraction, sinoatrial node, atrioventricular node, medulla, cardiac nerve, vagus nerve, myogenic heart rate, epinephrine, adrenal glands, diastole, systole, cardiac cycle, semilunar valve, atrioventricular valve, atherosclerosis, plaque, endothelium, aorta, coronary arteries, occlusion, coronary thrombosis, acute myocardial infarction

Challenge yourself: 1 (pg 279), 2 (pg280)

Nature of Science (pg 283) Summarize how ideas about blood flow have changed over time. How did Harvey come to his conclusion about a closed circulatory system?

Exercises 4-6 (pg 283)