The Hearts Function, Cardiac Cycle and Electrical Activity....

The heart is made of cardiac muscle. It is unique as it never gets tired. The heart contains arteries, veins and capillaries. It's function is to pump oxygenated blood around the body, and de-oxygenated blood back to the lungs.

The heart is divided into two halves by the inter-ventricular septum. There are four chambers to the heart, they consist of the atria which are upper chambers; right atrium (RA) and left atrium (LA). The lower half are the right ventricle (RV) and left ventricle (LV).
It is vital that blood flows in the right direction through the heart which is why it is structured in a precise way.
The tricupsid valve separates the right atrium from the right ventricle. The pulmonic/pulmonary valve separates the right ventricle from the pulmonary artery. The mitral (bicuspid) valve separates the left atrium from the left ventricle.
The aortic valve separates the right ventricle from the ascending aorta.

The structure of the heart walls consists of three layers. The epicardium is a thin outer layer giving the hearts surface a smooth slippery texture. The endocardium is the smooth inner lining of the heart and is continuous with the large blood vessels to which the heart connects. The myocardium makes up the bulk of the heart and is responsible for the pumping action. Strong cardiac muscle fibres make up the myocardium and they are connected by electrical synapses which allow muscle action potentials to spread from fibre to fibre.

There are four main routes for the blood in and out of the heart. These are via the vena cava, pulmonary artery, aorta and pulmonary vein.
The route a blood cell takes is round the cardiac cycle. It starts with a cardiac systole, travels round the cycle and ends with a cardiac diastole. When the myocardium contracts it generates pressure changes resulting in orderly movement of blood. This allows blood to flow from high pressure areas to low pressure areas, only being held up by valves.



When the heart is in atrial systole because it is full, it passes the blood to the ventricular diastole. The atrio-ventricular valves open due to blood pressure allowing 70% of the blood to flow passively down to the ventricles so the atria do not have to contract so much. when the heart is in ventricular systole, because the blood has just been passed down, the atria goes back into diastole. The ventricle walls contract and force the blood out.



The distinct heart beat noise 'lub' comes from the pressure of the blood forcing the atrio-ventricular valves to shut. The pressure of the blood then opens the semi-lunar valves passing blood in to the aorta and pulmonary arteries. The ventricles are now relaxed and have lower pressure than the arteries, causing the now high pressure arteries to shut the semi-lunar valve. The valve shutting creates the second distinct heart beat noise 'dub'. During diastole all the muscles in the heart relax. Blood from the vena cava and pulmonary veins enter the atria starting the cycle again.



Cardiac muscle is myogenic meaning it can contract and relax without receiving signals from nerves. This pattern of contractions controls the regular heartbeat.

The process starts in the sino-atrial node (SAN) which is in the. The SAN sets the rhythm of the heartbeat by sending out regular waves of electrical activity to the atrial walls. This causes the right and left atria to contract at the same time. A band of non-conducting collagen tissue prevents the waves of electrical activity from being passed directly from the atria to the ventricles. Instead these waves of electrical activity are transferred from the SAN to the atrioventricular node (AVN). The AVN is responsible for passing the waves of electrical activity to the bundles of His, or AV bundles. There is a slight delay before the AVN reacts, to make sure the ventricles contract after the atria have emptied.

The bundle of His is a group of muscle fibres responsible for conducting the waves of electrical activity to the finer muscle fibres in the right and left ventricle walls called the purkinje fibres. The purkinje fibres carry the waves of electrical activity into the muscular walls of the right and left ventricles, causing them to contract simultaneously from the bottom up.

Bibliography

CG Partnership handout, wk24

www.images.main.uab.ed/healthsys/ei_0018.jpg

Relating the Structure of Arteries, Veins, Arterioles and Capillaries to their Functions..

Arteries carry blood from the heart to the rest of the body. They are thick walled, muscular and have elastic tissue in the walls to cope with the high pressure caused by the heartbeat. The inner lining of endothelium is folded, allowing the artery to expand, helping it to cope with high pressure.

Veins take blood back to the heart and are wider than equivalent arteries, with very little elastic or muscular tissue. Veins contain valves to stop the blood flowing backwards. Blood flow through the veins is helped by contraction of body muscles surrounding them.

Capillaries are the smallest of the blood vessels and are where metabolic exchange occurs. Substances are exchanged between cells and the capillaries. There are networks of cappilaries in tissue which increase the surface area for exchange. Cappilary walls are one cell thick which speeds up diffusion of substances such as glucose and oxygen into and out of cells.

Arterioles have thin muscular walls, generally one or two layers of smooth muscles. They are a blood vessel with a small diameter, and branch out from an artery to a cappilary. Arterioles receive autonomic nervous system innervation and respond to various circulating hormones in order to regualte their diameter.

Bibliography

CG Partnership handout, wk 24

Wikipedia/image

Red Blood Cells - They have Structure and Function

Red Blood Cells are produced in the bone marrow which is closely attached to a macrophage. When it has expelled its nucleus which is ingested by the macrophage, it leaves the bone marrow and becomes know as a reticulocyte. It then goes through another stage and has to lose its organelles. Once this has happened the red blood cell (rbc) has fully matured in to an Erythrocyte.

Structure - An RBC is biconcave in shape and very flexible. It has the ability to move single file through capillaries without breaking.

An RBC is 1/25,000 of an inch in size.

An RBC can last about 120 days in the blood stream. Once it has become old it is injested by the macrophages in the liver and spleen.

Interesting Fact; Men contain more rbc's per cubic millimetre than women. Men - 5,200,000 pcm; Women - 4,600,000 pcm.

Approximately 40-45% of blood is rbc's.

The red colouring of the Erythrocyte (rbc) comes from a substance called Haemoglobin- a simple protein, and iron pigments. When they are exposed to Oxygen their colour becomes bright scarlet.

Function - It is the red blood cells main function to transport oxygen from the lungs to the cells in the body, where needed. The oxygen is diffused in to the haemogloin protein with in the red blood cell. It circulates around the body as oxyhaemoglobin. In turn, as the oxygen is being diffused in to cells, carbon dioxide is diffused from the cell in to the rbc, and in some cases plasma.

Carbon dioxide combines with the water in the rbc to form carbonic acid. Normally a slow reaction, however, this process is accellerated by the enzyme carbonic anhydrase.

Carbonic acid then seperates in to bicarbonate ions and hydrogen ions. Hydrogen ions combine with the haemoglobin, and the bicarbonate ions go in to the plasma. The remaining Co2 is either dissolved in the plasma, or diffused diectly in to the haemoblobin for gaseous exchange with the alveoli.

Bibliography

CG Partnership handout, wk 22, The blood system

CG Partnership handout, wk 24, Blood

www.getwellnatural.com

http://health.howstuffworks.com/blood1.htm

Plasma and its Function

As you can see from this image, Plasma is the yellow liquid part of blood.

Plasma is responsible for transporting the red blood cells (Erythrocytes), white blood cells (Leukocytes) and platelets (Thrombocytes) around the body.

55% of our bloods volume is made up of plasma.

What does Plasma contain?

We already know plasma carries blood cells.
Plasma also contains the following substances;

SUBSTANCE / / ORIGIN / / DESTINATION

Carbon Dioxide (C02) / / Body / / Lungs

Digested Food / / Gut / / Liver/Body

Wastes (e.g. Urea) / / Liver / / Kidneys

Hormones / / Endocrine Glands / / Where needed

PROTEINS

Proteins approximately make up 6-8% of blood and are divided between serum albumin and varied serum globulins.

Serum albumin

• made in the liver


• binds small molecules for transportation


• helps maintain osmotic pressure of blood

Serum globulins

• Alpha globulins - Transport thyroxin and retinol


• Beta globulins - Iron-transporting protein transferring


• Gamma globulins - Antibodies are mostly gamma globulins and become more abundant following infections or immunisations

WHITE BLOOD CELLS

If your body needs defending -
who does it call -
the white blood cell (wbc)

When germ or infection is detected by the wbc, they race to where it is and immediately start attacking it. They have a variety of ways they can attack a germ or infection, they either produce protective antibodies to overpower or surround and devour the bacteria.

Though the wbc are an essential part of our body's defense system, they do only have a short life span. They can live anything from a few day to weeks.

7000 - 25000 wbc can be found in a single drop of blood at any one time.

This number increases if there is a particularly aggressive infection.

PLATELETS

Their sticky and their oh so funny shaped....

...but what do they do?

They are able to sense air from an open wound and are essential in the clotting factor of blood.
As soon as air is sensed they break apart and gather at the wound along with the mineral calcium, vitamin K and the protein fibrinogen to help form a clot.
The reaction of the platelet with fibrinogen forms fibrin, which resembles tiny threads.
The fibrin threads form a mesh that catch the red blood cells, and as it dries it forms a clot or 'scab'.


RED BLOOD CELLS

You will have to read the blog - 'Red blood cells - They have structure and function' for more information...

Bibliography

CG Patnership handout, wk24, Blood

http://www.fi.edu/learn/heart/blood/platelet.html

www.texasheartinstitute.org

Breathing - It's all about the Rhythm, but what is the Nervous System's Role

You may think you are Breathing voluntarily, but your Brain says different!

The Nervous System plays a key role in generating a normal breathing rhythm.

The Diaphram is an integral part of the Pulmonary System, and is supplied with Spinal Nerves via segments c3, c4 and c5 of the Spinal Cord.

The nerves are connected to the Medulla Oblongta, which is a control centre for respiration. It is located in the lower part of the Brain Stem.
There is a second respiratory centre in the Pons, of which the nerves are also connected. This control centre is located above the Medulla Oblongata.

The interaction between these two particular respiratory centres enable automatic breathing.

Autonomic control of breathing is achieved by the respiratory system and the nervous system being conected by stretch receptors, sensory nerves and the vagus nerve.
The vagus is a cranial nerve which starts in the medulla and continues through the body. It conveys sensory information to the brain on how all the bodys organs are performing.

For autonomic control of breathing the bronchi and bronchioles contain stretch receptors in their walls, which are stimulated when the lungs inflate during inspiration. These receptors are connected to the sensory nerves which send action potentials along the vagus nerve to inhibit the inspiratory centre in the medulla.
This makes inspiration stop so expiration can start. When the lungs deflate the stretch receptors stop sending action potentials to the inspiratory centre so inhibition stops, and allows inspiration to start again.



Now for the technical bit....

• The diaphragm and the intercostal muscles can only contract once they have received an action potential from the medulla


• The centres within the medulla which control the basic Breathing Rhythm are connected to the muscles by motor nerves of the autonomic nervous system


• The inspiratory centre stimulates contractions of the diaphragm and external intercostal muscles, and inhibits the expiratory centre


• As soon as inspiration is complete, the inspiration centre centre stops inhibiting the expiration centre


• When the expiratory centre operates it inhibits the inspiratory centre, so the diaphragm and external intercostal muscles relax


• The inhibition means that both the inspiratory and expiratory centres cannot stimulate the lungs at the same time, this results in a basic breathing rhythm being established

Photos sourced from:

www.infovisual.info

www.apsu.edu

Bibliography

CG Partnership handout, wk 24, Structure and function of the respiratory system

CG Partnership handout, wk 22, The Pulmonary system

Wikipedia