Question

a)_Discuss the factors affecting gas exchange in the lungs

38-Upper Digestive Tract

a)_Discuss the stomach and include one usual abnormal finding

Answer 1

Answer :

a) Gas exchange is the delivery of oxygen from the lungs to the bloodstream, and the elimination of the carbon dioxide from the bloodstream to the lungs. It occurs in the lungs between the alveoli and a network of tiny blood vessels and capillaries, which are located in the walls of the alveoli.

The thickness of the membrane :

The thickness of the respiratory membrane occasionally increases-for instance, as a results of edema, fluid in the intersticial space of the membrane and in the alveoli-so that the respiratory gases must then diffuse not only through the membrane but also through this fluid. Also some pulmonary diseases cause fibrosis of the lungs , which can increases the thickness of some portions of the respiratory membrane. Because the rate of the diffusion through the membrane is inversely proportional to the thickness of membrane, any factor that increases the thickness to more than 2 to 3 times normal can interfere significantly with normal respiratory exchange of gases.

The surface area of the membrane :

The surface area of the respiratory membrane can be greatly decreased by many conditions. For instance, removal of an entire lung decreases the total surface area to one half normal.Also, in emphysema, many of the alveoli coalesce, with dissolution of many alveolar walls. Therefore, the new alveolar chambers are much larger than the original alveoli, but the total surface area of the respiratory membrane is often decreased as much as fivefold because of loss of the alveolar walls. When the total surface of the area decreased to about one third to one fourth normal, exchange of gases through the membrane is impeded to a significant degree, even under resting conditions, and during competitivesports and other strenous exercise , even the slightest decrease in surface area of the lungs can be a serious detriment to espiratory exchange of gases.

The diffusion coefficient of the gas in the substance of the membrane :

The diffusion coefficient for transfer for each gas through the respiratory membrane depends on the gas's solubility in the membrane and inversly, on the squre root of gas's molecular weight. The rate of diffusion in the respiratory membrane is almost exactly the same as that in water, therefore , for a given pressure difference, carbondioxide diffuses about 20 times as rapidly as oxygen. Oxygen diffuses about twicw as rapidly as nitrogen.

The partial pressure differencec of the gas between the two side of the membrane :

The pressure differance across the respiratory membrane is the differance between the partial pressure of the gas in the alveoli and the partial pressure of the gas in the pulmonary capillary blood. The partial pressure repressents a messure of the total number of molecule of a particular gas striking a unit area of the alveolar surface of the membrane in unit time, and the pressure of the gas in the blood repressents the number of molecules that attempt to escape from the blood in the opposite direction. Therefore, the difference between these two pressure is a messure of the net tendency for the gas molecules to move through the membrane. When the partial pressure of a gas in the alveoli is greater than the pressure of the gas in the blood, as is true for oxygen, net diffusion from the alveoli into the blood occurss; When the pressure of the gas in the blood is greater than the partial pressure in the alveoli, as is true for carbon dioxide, net diffusion from the blood into the alveoli occurs.

38. a) Upper digestive tract :

Stomach :

The stomach is a muscular organ located on the left side of the upper abdomen. The stomach receives food from the oesophagus. As food reaches the end of the oesophagus, it enters the stomach through a muscular valve called the lower oesophageal sphincture. The stomach secretes acids enzymes that digest foodd. Ridges of muscle tissue called rugae line the stomach. The stomach muscles contract periodically , churning food to enhance digestion. The pyloric sphincture is a muscular valve that opens to allow food to pass from the stomach to the small intestine.

Usual abnormal findings:

One of the usual abnormal finding of the stomach is stomach pain or abdominal pain, that is pain from inside the abdomen or the outer muscle wall, ranging from mild and temporary to severe. Abdominal pain can have causes that are no due to underlying disease. Examples include constipation, wind, overeating stress or muscle strain.

Abdominal pain is common and often inconsequential. Acute and severe abdominal pain,however, is almost always symptom of intra-abdominal disease.it may be the sole indicatorof the need for surgery and must be attended to swiftly: gangrene and perforation of the gut can occur <6 hours from onset of symptoms in certain conditions (eg, interruption of the intestinal blood supply due to a strangulating obstruction or an arterial embolus). Abdominal pain is of particular concern i patients who are very young or very old and those who have HIV infection or are taking immunosuppresents (including corticosteroids).