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Thursday 22 April 2010

Conditions necessary for effective gaseous exchange

The walls of the alveoli are made up of an extreemly thin, single layer of squamous epithelial cells. The external surface of the alveoli are covered with pulmonary capillaries.
The gaseous exchange occurs when oxygen passes from the alveoli into the capillary blood. Carbon dioxide leaving the blood then enters into the gas filled alveolus. Essentials of Human Anatomy and Physiology (Elaine N. Marieb)

There are a number of necessary conditions that allow effective gaseous exchange. Here is a list of 5 important factors.

1. Temperature: the warmer the conditions are the faster the diffusion rate between the blood and alveoli.

2. A constant ventilation must be in place to maintain a concentration gradient to stop equilibrium.

3. Thin permeable cell walls allow rapid diffusion. Faster gas exchange.

4. A larger surface area to volume ratio, for example if there are lots of alveoli stacked together in the lungs, more gaseous exchange is able to take place.

5. A concentration difference of the gases from one side to the other.



Arteries, Veins and Capillaries

The vascular system is like a road system. As the heart beats, blood is propelled into large arteries leaving the heart and then moves into smaller and smaller arteries until it reaches the arterioles which feed the capillary beds in the tissues. Capillary beds are drained by venules which empty into veins, that eventually empty into great veins that enter into the heart.

Arteries carry oxygenated blood away from the heart to the vital organs and tissues, this means that the arteries walls need to be thicker than veins as they need to be able to expand as the  blood is pumped through them. The walls need to be strong and stretchy as they are continuously under changes in pressure.
Arteries do not have valves (except for the semi-lunar valves of the pulmonary artery and the aorta).

Veins tend to have thinner walls than arteries as the blood flowing through them is deoxygenated and under low pressure. Veins are far from the heart in the circulatory pathway. They tend to have less muscle than arteries and contain valves. The valves throughout the main veins prevent blood flowing in the wrong direction. Veins drain blood from the tissues and return the deoxygenated blood back to the heart.

Capillaries are extremely tiny and narrow. They are found in most organs and tissues of the body. They are supplied with blood from the arterioles and drained by venules. Capillary walls are one cell thick and this enables exchanges of oxygen, carbon dioxide, water and salts etc between blood and the surrounding body tissues.-www.ivy-rose.co.uk



The Nervous System

The nervous system is the bodies fast acting control system. Sensory receptors detect changes in the body and send messages via electrical signals called nerve impulses. The cental nervous system assess the information it receives and responds by activating the appropriate muscles or glands.


The lower brain stem contains the midbrain, pons, and medulla oblongata. The medulla oblongata conducts impulses traveling between the brain and spinal cord. This area also controls involuntary actions like breathing and swallowing. The pons, above the medulla oblongata, links the cerebral cortex and the cerebellum.

Although the heart would be able to contract on its own, the nervous system enables a constant regular beat. The nerves relay messages from the brain and are able to slow down or speed up the heart beat according to its needs.

Plasma

Plasma is approximately 90% water and is the liquid part of blood. The composition of plasma varies continuously as cells remove or add substances to the blood. If the body is receiving a healthy balanced diet, plasma is kept relatively constant.
There are over 100 different substances which dissolve in plasma, these being nutrients, metal ions (salts), respiratory gases, hormones, plasma protiens and various wastes and products of cell metabolism.
Plasma proteins serve a variety of functions. For example, albumin (the most abundent plasma protein) contributes to the osmotic pressure of the blood, which helps to keep water in the blood stream.

Tuesday 6 April 2010

Red Blood Cells

The human body contains more red blood cells than any other cell. A single drop of blood contains millions of red blood cells that are constantly travelling through the body delivering oxygen and removing waste. Each cell has a lifespan of about 120 days so the body is constantly producing new ones to replace the ones that have died or been lost from the body.
Red blood cell are also known as erythrocytes. Each of the cells has a unique appearance, they are thinner in the centre and thicker on the edges. This makes the cell really flexible and allows it to twist and bend around blood vessels. Their small size and strange shape makes them ideally suited for gaseous exchange.
Erythrocytes are red in appearance because they carry a substance called hemoglobin. This combined with oxygen makes the cell become bright red in colour.
Red blood cells contain no nucleus, by having no nucleus the cells are more efficient transporters of oxygen.







If you were to look at a droplet of blood under a microscope you would be able to see smooth disc shaped red blood cells, white blood cells and platelets.