When we breathe, what's really going on?

You may think that breathing is a voluntary action, however, your brain disagrees!


Breathing is actually a sensory reaction, which is initiated and controlled by the inspiratory and expiratory centres within the medulla oblongata. (Located in the lower region of the brainstem)


The diaphragm is a key component of the nervous system. It is supplied with spinal nerves from segments c3, c4 and c5. The intercostal musles are supplied by the corresponding thoracic t1 to t12 spinal nerves.
The nerves of the diaphragm lead from the spine, and the brain stem, and run back to collections of neurons in the medulla - whose function is to control unconscious processes such as rate and depth of breathing.


In turn, these are adjoined to a second respiratory centre in the pons (which asists in the rate of movement and breathing). The interaction between these two centres enables automatic breathing, and neurons are both stimulatory and inhibitory.


The areas of the pons are involved in automatic breathing,and if conscious control is excerted, these centres are overpowered by the cerebella cortex. There is a direct link to the respiratory muscles through the relevant motor neurons, coming directly from the motor cortex of the cerebella cortex.

Inbuilt in the pons is a standard rate of breathing, which is variable, allowing connections between the pons and the medulla. The sensors that detect the oxygen and carbon dioxide concentration of blood are located in the aortic arch.


The autonomic control of breathing involves a reflex response...


...There are stretch receptors contained in the walls of the bronchi and bronchioloes which - during inspiration - are stimulated when the lungs inflate.
The receptors are connected to sensory nerves, and they send action potentials along the vagus nerve.

This inhibits the inspiratory centre in the medulla, and makes inspiration stop, and expiration begin. When the lungs deflate, the stretch receptors stop sending action potentials to the inspiratory centre.
At this stage, inhibition stops, and inspiration commences once again.

Also found within the medula are chemoreceptors. These are sensitive to chemical changes in the blood - They are also found in aortic bodies in the aorta, and in the carotid bodies in the carotid arteries carrying blood to the head.
If the chemoreceptors detect a decrease in the PH of the blood, they send a signal to the medulla to send more frequent nerve impulses to the intercostal muscles and diaphragm . This then increases the rate and depth of breathing.

Bibliography:

http://www.nytimes.com/

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www.medical_dictionary.thefreedictionary.com

The constituents of plasma, and their functions

Blood is a specialised tissue which consists of several types of cell suspended in a fluid called plasma. The cellular constituents consist of red blood cells, white blood cells and platelets.
Plasma is the yellow liquid part of blood which surrounds the red blood cells. It contains many dissolved substances , like glucose, salts and amino acids. It also contains plasma proteins, such as blood clotting factors.
About 55% of our blood's total volume is made up of plasma, and about 95% of it consists of water.


Plasma is important because it allows blood to navigate fast moving substances in solution and slow moving thicker substances in suspension.
When the heart pumps blood to cells in the body, plasma brings nourishment to them, and removing waste products.

Some materials which are in transit in the blood are Cabon Dioxide which travels to the lungs, digested food which travels to the liver, and wastes (ie, urea) which travels to the kidneys. Once these materials have reached their destination, they are removed from the blood.
Proteins make up a small percentage of the blood, and are equally divided between serum albumin and a large ariety of serum globulins. Serum albumin is made up in the liver. It binds many small molecules for transport through the blood. It also helps maintain the osmotic pressure of the blood.
The other proteins present are all serum globulins. These iclude:

Alpha globulins - like the proteins which transport thyroxin and retinol.

Beta globulins - such as the iron transporting protein transferring.

Gamma globulins - most antibodies are these. Gamma globulins increase in number following illness.

Bibliography:

http://www.penhealth.com/

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How the structure of a red blood cell relates to it's function

Red blood cells (Erythrocytes) contain haemoglobin, and transport oxygen to the cells, and the majority of Carbon Dioxide back to the lungs. These cells are bioconcave in shape, making them more flexible, and increasing their overall surface area. This aids the uptake of oxygen.

Red blood cells only have a short life span, and live about 120 days, before being ingested by phagoccytic cells in the liver and spleen. They are made in the red bone marrow, and in adults can be produced in the thoracic boes, vertebrae, cranial bone and ends of the femur and humerus bones.

The fascinating thing about red blood cells is that the blood contains approximately 25 trillion, and they have to be replaced at about 3 million per second - that's pretty speedy! The condition Anaemia is the deficiency of red blood cells

The transport of oxygen is assisted by the red blood cells. The pigment haemoglobin binds four oxygen molecules to every one. Oxyhaemoglobin then forms. The oxygen molecules are carried to individual cells in the body tissue, where they are then released. This binding of oxygen is a reversible reaction.

Carbon dioxide diffuses from the tissues into the red blood cells and combines with water to form carbonic acid. This is generally a slow reaction, but it is accelerated in the red blood cell by the presence of the enzyme carbonic anhydrase. Most of the carbon dioxide is carried in the red blood cells rather than the plasma because of this enzyme.

Bibliography:

www.howstuffworks.com

cgpartnership handout, week 24

When we feel our heart beat, whats really going on?

The heart is a muscular pump which pushes blood around the body. It is roughly about the size of a fist, and is madeup of cardiac muscle. The heart is divided ito four chambers:


Right Atrium
Left Atrium

Right Ventricle
Left Ventricle

The heart is also divided into upper and lower compartments by the interventricular septum. The heart tissue is called endocardium , and the muscle is called myocardium. The heart is covered by two layers of fibrous tissue called pericardium.

The heart contains a series of valves which ensure the correct direction of blood flow. The tricuspid valve - which separates the Right Atrium from the Right Ventricle. The pulmonary valve - which separates the Right Ventricle from the pulmonary artery. The bicuspid (or mitral) valve - which separates the Left Atrium from the Left Ventricle, and the aortic valve - which separates the Right Ventricle from the ascending aorta.

There are four main blood routes into and out of the heart, these are:

Vena Cava (Vein)

Pulmonary artery

Aorta (Artery)

Pulmonary Vein

The heart wall structure consists of three layers:

Epicardium - thin outer layer. This gives the surface of the heart a smooth texture.

Endocardium - smooth inner lining, which is continuous with the large blood vessels to which the heart connects.

Myocardium - makes up the bulk of the heart, and is responsible for the pumping action. It is made up of strong cardiac muscle fibres, connected by electrical synapses.

The Cardiac Cycle

The Cardiac cycle describes the complete round of cardiac systole and diastole with the intervals between or commencing with any events in the heart's action to the moment when the same event is repeated.
Systole - contraction (working)
Diastole - ventricular relaxation (resting)

The blood flows from area of high pressure to an area of low pressure, unless the flow is blocked by a valve. The events on the left and right of the heart are the same, but pressures are lower on the right hand side. Contraction of the myocardium generates pressure changes which result in orderly movement of blood.

The Atrial Systole

• The heart is full of blood and ventricles are relaxed.
• Both atria contract, and blood passes down to the ventricles.
• Atrio-Ventricular valves open due to blood pressure.
• 70% of blood flows passively down to the ventricles, so the atria don't have to contract much.

Ventricular Systole

• Atria relax
• Ventricular walls contract, and blood is forced out.
• Pressure of blood forces the Atrio-Ventricular valves to close
• The pressure of blood opens the semi-lunar valves.
• Blood passes into the aorta and pulmonary arteries.

Diastole

• Ventricles relax.
• The pressure in the ventricles falls below that in the artery.
• Blood under high pressure in arteries causes the semi-lunar valve to close.
• During diastole, all heart muscles relax.

Regulation of the Cardiac Cycle:

• Cardiac muscle is myogenic (self exciting).
• The heart's contractions occur spontaneously though frequency can be affected by exercise/danger.
• These affected contractions are coordinated by the sinoatrial (S.A) and Atrio-Ventriuar (A.V) nodes.
• S.A node is located in the upper wall of the right atrium, and is responsible for wave of electrical stimulation that initiates atrial contraction.
• Once the wave reaches the A.V node in the lower right atrium, it's delayed there before being conducted through various structures leading to a contraction of ventricles.
• A delay at the A.V node allows time for all blood in the atria to fill respective ventricles

The bundle of His are the muscle fibres responsible for conducting the waves of electrical activity to the Purkyne fibres.

Purkyne fibres are finer muscle fibers found in the right and left ventricle walls. They carry waves of electrical activity into the muscular walls of the right and left ventricles, causing them to contract simultaneously, from the bottom up.

Click on the following link to see a video of a beating heart. This may help you understand this post more easily:

http://www.youtube.com/watch?v=rguztY8aqpk


Bibliography:

http://www.10b3circulation.wordpress.com/

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