Digestivesystem / Cardio-respiratory System Assignment
Digestive system/Cardio-respiratory System Assignment
Normally, as food moves along the digestive tract, digestive juices and enzymes digest and absorb calories and nutrients. After we chew and swallow our food, it moves down the oesophagus to the stomach, where a strong acid continues the digestive process. The stomach is a sack-like portion of the digestive tract. Its inner surface is highly convoluted, enabling it to fold up when empty and open out like an expanding balloon as it fills with food. Thus while the human stomach has a volume of only about 50ml when empty, it may expand to contain 2 - 4 litres of food when full.
Gastric bypass surgery promotes weight loss by closing off parts of the stomach to make it much smaller. To perform the surgery, doctors create a small pouch at the top of the stomach where food enters from the oesophagus. Initially, the pouch holds about 1 ounce of food and later expands to 2-3 ounces. The lower outlet of the pouch usually has a diameter of only about 3/4 inch. This small outlet delays the emptying of food from the pouch and causes a feeling of fullness.
http://www.upmc.edu/NewsBureau/medsurg1/gastric_bypass_study.htm
With this surgery, a section of the upper stomach is stapled to form a gastric pouch. Then, a portion of the upper intestine called a Roux limb is attached to the pouch. Food goes into the gastric pouch and through the Roux limb, bypassing the rest of the stomach. This bypass reduces the amount of calories and nutrients the body can absorb.
Most patients will then lose weight quickly and continue to do so for 18-24 months. There will usually be a dramatic improvement in virtually every medical problem associated with obesity - high cholesterol, high blood pressure, type 2 diabetes, sleep apnea, arthritis etc. Although there can be complications with the surgery itself and follow-up surgery is sometimes needed. Some patients develop gallstones during substantial weight-loss, and also nutritional deficiencies such as anaemia and osteoporosis. But the benefits usually outweigh the costs and most patients can expect to greatly increase their life expectancy.
http://www.niddk.nih.gov/health/nutrit/pubs/gastric/gastricsurgery.htm
Hunger is best described as the primary physiological drive to find and eat food. This state is driven by several different internal forces that all work together to extinguish the need for food and put the body in a state of satiety, meaning the desire to eat ceases.
The hypothalamus is a part of the brain that plays a particularly important role in feeding behaviours, this is because it actually regulates satiety. In many studies where specific nerve cells in the hypothalamus were destroyed, satiety either increased or decreased causing either obesity or weight loss. It is thought that various brain cells can be destroyed, either by specific chemicals, surgery, and certain forms of cancer.
Nutrients in the blood are probably the biggest contributors to the control of satiety. After we eat and digest a meal, the amino acids, glucose, and fatty acids are all absorbed into the blood stream. This absorption causes a state of satiety and hunger decreases. Within a few hours after we eat, the concentration of these nutrients falls as they are used for fuel. As the available nutrient concentration in the blood falls, the satiety level decreases and hunger signals begin to start once again.
It is also thought that neurotransmitter production of histamine and serotonin may also control hunger. Studies have shown that when subjects were deprived of calories or sufficient protein, histamine production increased causing an increase in the synthesis of the amino acid histidine, thus a significant decrease in hunger and food intake is experienced.
Changes in serotonin production have also been linked to satiety controls. Various nutrients, especially carbohydrates, increase serotonin production. High levels of this neurotransmitter cause increased synthesis of the amino acid tryptophan, which appears to calm one's mood, induce sleepiness, and decrease the desire to eat more carbohydrates.
Many different hormones, drugs and hormone like compounds have been shown to influence feeding patterns. For instance, after a meal, blood concentrations of cholecystokinin, secretin, gastrin, glucagon and a few other hormones increase. These hormonal increases have been shown to increase satiety.
Endorphins, cortisol, and insulin all lead to decreased satiety or increased hunger. The significant presence of cortisol in those genetically prone to obesity may be a big problem. Insulin however, is a double edge sword. High insulin levels increase liver metabolism of nutrients. In this case it promotes satiety. However, as insulin does its job by ridding the blood of nutrients, it then causes hunger to return.
Obesity has become an epidemic on a global scale and poses one of the greatest threats to human health and well being as the 21st century approaches. The World ...
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Endorphins, cortisol, and insulin all lead to decreased satiety or increased hunger. The significant presence of cortisol in those genetically prone to obesity may be a big problem. Insulin however, is a double edge sword. High insulin levels increase liver metabolism of nutrients. In this case it promotes satiety. However, as insulin does its job by ridding the blood of nutrients, it then causes hunger to return.
Obesity has become an epidemic on a global scale and poses one of the greatest threats to human health and well being as the 21st century approaches. The World Health Organisation has declared that obesity is a disease of pandemic significance, which threatens the developing world as well as developed countries.
There is an evolutionary benefit conferred on people who are able to store fat. In olden times when food was scarce, it was fatter people - those who were able to store fat - who would survive illness and scarcity. Obesity would be rare in those times since periodic shortages made it impossible for weight to be gained progressively. However, although we live in the 20th century our bodies are still "in the caves" so to speak, because culture has galloped ahead of our biological response to culture. This means that our bodies have not adapted to an environment in which there is plenty of food.
The average fresh vegetables in our diet in the 1930's, weight for weight, contained 50% more minerals than it does in the 1990's. This is a major and significant change in diet. The hectic lives people live today mean more and more people don't have time to cook a healthy meal when they get home from work, and they rely more on fast food and microwave meals, which are both high in fat and salt content. People are much more stressed these days and a lot of people turn to calorie rich foods to console themselves.
Although there have never been as many members of gym's and health clubs as there are now, there is still less people getting regular exercise than there were in the past. Labouring jobs (ie mining & farming etc) are increasingly being done by machines - a lot of people now have jobs in the 'information society'. Where they take a few steps in the morning to the car, a few steps (or maybe even take the lift) into the office, and then sit at a computer for 8 hours a day! Washing clothes is done automatically by a machine, TV channels are changed over by remote control, and even shopping can now be done over the internet. As a result there's now very little need for anyone to ever take more than a few steps.
The trend toward greater numbers of heavier children is largely due to two factors: a diet that is high in calories and includes more fats and sweets, and a lifestyle that is not physically active. Children in the past have come home from school and then gone straight out to play with their friends and so got plenty of exercise. It is more common now for children to get home and turn on the TV, or the games console, and in very recent times; go on the internet, or the world wide web and send e-mails. An increase in mobile phones mean children can now sit at home and talk to their friends rather than go out and see them.
A more insidious factor is also being blamed for the rise in overweight children. American and British children are exposed to around 10 food commercials for every hour of television that they watch. Most of the commercials are bright and jazzy and sell fast food, soft drinks, sweets and sugar-sweetened breakfast cereal. Childhood obesity rates are highest in countries where advertising on children's TV is least regulated - in Australia, USA and England. Sweden and Norway maintain a virtual ban on advertising to children, and have consistently low levels of childhood obesity.
http://www.jr2.ox.ac.uk/bandolier/booth/hliving/ObTV.html
Evidence from Sims - Vermont state prison experiment, clearly shows that body weight is clearly a problem of biology rather than behaviour. Body mass it seems is fixed and resistant to change over the short term. Sims concluded that the body was remarkably well equipped to balance energy intake and output, and to reach an energy equilibrium, or homeostasis, at which it felt naturally comfortable. Most of the prisoners found it extremely difficult to put on weight and a lot of the subjects dropped out of the study early on, as they became increasingly reluctant to over-eat. This shows that the body feels uncomfortable at gaining excessive weight above the point at which it feels naturally comfortable. After the required 200 days, all the prisoners except two, shed the excess weight easily and returned to the weight they were before the experiment had begun, both had in fact found it the least difficult to put the weight on in the first instance. It was later discovered that both men had a family history of obesity. The prisoners with obesity in their background were, it seemed, genetically inclined to reach homeostasis at a higher weight, than the other participants; the high-calorie diet only helped manifest their genetic proclivity.
Other evidence linking genetics with body weight regulation, has been found in adopted twin studies. The body mass index (BMI) of identical twins separated at birth and raised apart, usually correlated nicely with that of their biological parents, rather than with that of their adopted parents. This strongly suggests that genetics, not psychology, play the larger role in human obesity.
Leptin it seems has evolved to prevent the body from starving. A dramatic decline in fat cells, where leptin is manufactured, triggers the body into a starvation response. Automatically the need to eat arises to eat, to protect itself from dying. This could have evolved at a time when food was sometimes scarce, the body would then build up it's fat supplies in case there were harsh times ahead.
It has been speculated that television viewing is one of the most easily modifiable causes of obesity among children. Television viewing may reduce energy expenditure, that is reduce the amount of energy a child would usually burn up while partaking in other activities, such as playing sports. It has been shown that even reading expends more energy than watching TV (thought to be because of an increase in brain activity).
An increase in TV viewing has also been shown to increase dietary energy intake, that is an increase in the amount of calories a child consumes per day compared to a child who watches less TV. A study by researchers at the University at Buffalo, USA, found the incidence of obesity was highest among children who watched four or more hours of television a day and lowest among children watching an hour or less a day. The study also found the incidence of obesity increased by 2% for every additional hour of television watched (Dietz, 1985).
'Calorie density' refers to the number of calories per unit weight of food. Foods that are said to be calorie-dense are usually high in saturated fats, sugar and salt products. They often lack antioxidants and are generally low in nourishment. Examples of this type of food would be French fries and mayonnaise. Alcoholic beverages are also high in calorific value and provide almost no nutrients. Pure fat is 9 calories per gram, as opposed to only 4 calories per gram for carbohydrates and protein. Predictably, fruits and vegetables provide nutrient dense, calorie-lean nourishment.
The ratio between the total weight of the food in grams and the total number of calories can be very useful in helping to visualise calorie density. Simply divide the total number of calories by the total grams of food.
http://slimmingpartner.com/CalorieDensity.htm
The intestinal surface is made larger for more absorption of nutrients by various structures: The villi are finger like projections. The surface of each villus has microvilli, which increase the surface area as hairlike projections. The small intestine has a surface area of 300 m2, about 600 times more than a plain tube of the same size.
Each villus has an arteriole, a venule and a lymph duct (lacteal). After passing through the epithelium, the fat enters the lacteal and goes into the lymph system, which drains into the venous system.
http://meds.queensu.ca/medicine/physiol/undergrad/phase2/phase2e/nutrients.htm
The mechanisms of absorption of water-soluble, and fat-soluble products are rather different. Water-soluble products pass through the plasma membranes of the epithelial cells of the villi by means of transport proteins, their transport maybe passive, by facilitated diffusion, or by active transport.
The characteristic structure and organisation of the liver enables it to perform vital roles in regulating, synthesising, storing, secreting, transforming, and breaking down many different substances in the body. In addition, the liver's ability to regenerate lost tissue helps maintain these functions, even in the face of moderate damage.
Blood cholesterol is produced by the liver and is essential for maintaining cells and hormones - without a certain amount, the body would cease to function properly. Cholesterol is a very important chemical building block in the body's manufacture of a variety of hormones, cellular structural components and bile. As a fat it will not dissolve in the blood, which is predominantly water based, and so to be carried in the bloodstream cholesterol is bound to a variety of different proteins.
There are two types of cholesterol: high-density lipoproteins (HDL) or "good" cholesterol, and low-density lipoproteins (LDL) or "bad" cholesterol. HDL in the blood carries cholesterol from other parts of the body back to the liver, which leads to its removal. This keeps cholesterol from building up on artery walls. The more HDL cholesterol you have in your blood, the better. If you have too much LDL in your blood, the excess will deposit on your artery walls, causing the damaging build up that can lead to heart disease and/or maybe a heart attack.
http://www.americanheart.org/presenter.jhtml?identifier=4488
Atherosclerosis comes from the Greek words athero (meaning gruel or paste) and sclerosis (hardness). It's the name of the process in which deposits of fatty substances, cholesterol, cellular waste products, calcium and other substances build up in the inner lining of an artery. This build up is called plaque. Plaques can grow large enough to significantly reduce the blood's flow through an artery. But most of the damage occurs when they become fragile and rupture. Plaques that rupture cause blood clots to form that can block blood flow or break off and travel to another part of the body. If either happens and blocks a blood vessel that feeds the heart, it causes a heart attack. If it blocks a blood vessel that feeds the brain, it causes a stroke.
Atherosclerosis is a slow, complex disease that typically starts in childhood and often progresses when people grow older. In some people it progresses rapidly, even in their third decade. Many scientists think it begins with damage to the innermost layer of the artery. This layer is called the endothelium. Causes of damage to the arterial wall include:
* Elevated levels of cholesterol and triglyceride in the blood.
* High blood pressure
* Tobacco smoke
* Diabetes
Tobacco smoke greatly worsens atherosclerosis and speeds its growth in the coronary arteries, the aorta and arteries in the legs. Because of the damage to the endothelium, fats, cholesterol, platelets, cellular waste products, calcium and other substances are deposited in the artery wall. These may stimulate artery wall cells to produce other substances that result in further buildup of cells. These cells and surrounding material thicken the endothelium significantly. The artery's diameter shrinks and blood flow decreases, reducing the oxygen supply. Often a blood clot forms near this plaque and blocks the artery, stopping the blood flow.
http://www.americanheart.org/presenter.jhtml?identifier
Foods that are high in protein, ie meat, egg yolks, and internal animal organs (liver, brain, etc) can also be high in fat & so should be eaten sparingly. Moderate amounts of protein (lean meat and poultry, beans and lentils and textured vegetable protein food like quorne) for example are OK, because they contain very little, if any fat.
We know that some aspects of our diet promote the development of atheroma i.e. diets high in saturated fats. We also know that there are some foods, which help to protect the heart.
A healthy diet, would be one that is:
* Low in saturated fats (animal or dairy produce);
* High in fruit and vegetables - Eating between 5 to 9 portions per day;
* High in fibre (whole grain cereals and whole grain varieties of bread, rice and pasta);
* Moderate amounts of carbohydrates (bread, potatoes, rice and pasta);
* Moderate amounts of protein (lean meat and poultry, beans and lentils and textured vegetable protein food like quorne).
http://website.lineone.net/~salisburyheart/risk.htm
The importance of maternal nutrition and the consequences of low birth weight are only now being recognised. Studies by David Barker and his team at the University of Southampton General Hospital UK, have shown that low birth weight is associated with an increased risk of hypertension, non insulin dependent diabetes and endocrine disorders. The study published in the British Medical Journal found that men with low weight at birth had high death rates due to coronary heart disease. The explanation offered by the researchers for such high death rates is that coronary heart disease and its biological risk factors such as hypertension, non insulin dependent diabetes mellitus, abnormalities in lipid metabolism and blood coagulation are associated with low birth weight. The hypothesis as to how these diseases occur, is that, the inadequate nutrition for the growing foetus forces it to make changes and adaptations in organ structure which later lead to coronary heart disease. The study suggests that a mother's health should be improved before and during birth for the long-standing welfare of the child.
British Medical Journal 1 (Volume 315, No. 7114)
The pancreas is a soft, greyish-pink, lobulated gland. It is approximately 12-15cm long and is located deeply on the posterior abdominal wall, near the liver and small intestine. It produces insulin and secretes it into the bloodstream to regulate blood sugar and help the body use sugar as a fuel to move muscles, make new cells and promote healing. If a person's pancreas stops producing insulin, then the person develops diabetes, a serious disease that can damage the eyes, nerves, the kidney and small blood vessels.
Late onset diabetes, also known as 'type 2' diabetes, is a heterogeneous disease that is caused both by genetic & environmental factors. The disease is characterised by chronic hyperglycaemia, owing to a combination of insulin resistance and changed insulin secretion. As a result there is insufficient insulin action to keep the blood glucose level within normal limits.
A low volume-density of blood vessels in the pancreas could make a rat susceptible to late onset diabetes. This is because the blood vessels may struggle to get enough insulin into them, and then around the body, to control the blood sugar level.
http://www.umassmed.edu/diabeteshandbook/chap01.htm
Regular physical activity can help increase lung capacity and strengthen all muscles in the body, including the heart. This will help improve circulation and also help the body use oxygen more efficiently. Being active can control weight by helping to burn off extra pounds, build lean muscle mass and reduce body fat. It also helps build and maintain healthy bones and joints. Other benefits include, helping to control blood pressure, lessening a diabetic's need for insulin, and boosting the levels of "good" HDL-cholesterol, which can help stop the build-up of fatty deposits in the coronary arteries, therefore reducing the risk of coronary heart disease.
http://www.suttersantarosa.org/education/exheart.html
REFERENCES
British Medical Journal 1 (Volume 315, No. 7114)
http://www.americanheart.org/presenter.jhtml?identifier=4488
http://www.jr2.ox.ac.uk/bandolier/booth/hliving/ObTV.html
http://medweb.bham.ac.uk/http/depts/path/Teaching/foundat/athero/athero4.htm
http://www.suttersantarosa.org/education/exheart.html
http://slimmingpartner.com/CalorieDensity.htm
http://www.umassmed.edu/diabeteshandbook/chap01.htm
http://www.upmc.edu/NewsBureau/medsurg1/gastric_bypass_study.htm
http://website.lineone.net/~salisburyheart/risk.htm
RCAT class notes 2003
