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Digestion and Nutrition

Nutrition and digestion

Brian Berning

on 4 October 2013

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Transcript of Digestion and Nutrition

Nutrition and Digestion
get their food from particles in their surrounding water
live on their food source (or in it) and can eat their way through it.
get their food from sucking liquids from a living host. Those liquids are rich in nutrients (think a mosquito and human blood).
(that's us) get their food from ingesting large pieces of food
ingestion: the act of eating
digestion: breaks down the food into smaller pieces, molecules that can be absorbed for nutrients. digestion includes both mechanical digestion (food is physically broken down into smaller pieces) and chemical breakdown (hydrolysis, the adding of a water molecule).
absorption: absorption of nutrients (occurs in digestive tract)
elimination: getting rid of undigested wastes
The food we eat can usually be classified into proteins, fats and carbohydrates. In digestion, these are broken down into smaller molecules because they are all too large to nourish the cells themselves because they can't pass through the plasma membrane. Animals also need small components to make molecules.
There are different types of digestive compartments. Food vacuoles are the most simple of all digestive compartments, where digestion occurs by phagocytosis.
An alimentary canal includes both a mouth and anus. Food that enters from the mouth will, in most animals pass through the pharynx (throat) and esophagus.
Organisms like cnidarians as well as flatworms have what is called a gastrovascular cavity. The gastrovascular cavity is a simple digestive compartment with the mouth as the only opening.
These organs can churn the food that is digested. The intestines are where absorption actually occurs and where chemical digestion happens. Lastly, the anus eliminates the undigested materials.
Some animals have a crop which is a small organ where food can be softened and stored. The crop is a pouchlike organ. Stomachs and gizzards store food for a period time but are more muscular than the crop.
Another major function of the large intestine is to absorb water from the alimentary canal. As this water is absorbed, the undigested food becomes more solid. The feces are waste products that are made primarily of indigestible plant fibers as well as prokaryotes. Colon bacteria also produce some useful vitamins (vitamin K, B vitamins and biotin) which are absorbed into the bloodstream. Feces are stored in the end part of the colon called the rectum.
The large intestine carries the undigested material. It compacts the feces and reclaims water. The large intestine is also called the colon and is about 1.5 meters in length.
The small and large intestine joins at a T-like junction where a sphincter helps control the path of unabsorbed food. The cecum is an arm of the T junction that is a blind pouch. The appendix is a small projection of the cecum that is basically a mass of white blood cells that makes a small contribution to immunity. The appendix is also very prone to infection called appendicitis. The appendix must be removed but it doesn't have any negative effects on the body.
As with everything, evolution has played a role on digestive systems in vertebrates. The digestive system of vertebrates often correlate to their diet as does the length of the digestive system. For instance, carnivores usually have larger stomachs that are more expandable and herbivores and omnivores usually have longer alimentary canals than carnivores. Ruminants (cattle, sheep, deer) have four chambers of their stomach.
The hepatic portal vein functions in:
transporting nutrients that are absorbed by the intestines straight to the liver
removing extra glucose and converting it to glycogen to store in liver cells
The liver in addition to producing bile, processes nutrient rich blood from the intestines. The liver is located in the middle of the heart and intestines. Capillaries from the intestines lead into veins that lead into the hepatic portal vein.
The liver also make nutrients into new substances. For instance, it synthesizes proteins, plasma proteins (used for blood clotting) and lipoproteins (used for transporting fat). The liver can also modify substances so they are less toxic to the body. It can turn alcohol and drugs into inactive products that are then eliminated through the urine and does this before they are absorbed by the digestive tract and carried throughout the circulatory system. Of course the liver cannot handle excessive use of any toxic substance and damage can result.
Digestion of carbohydrates: begins in the oral cavity and is completed in the small intestine. Pancreatic amylase hydrolyzes the starch.
Digestion of proteins: begins in the stomach and is completed in the small intestine. Trypsin and chymotrypsin break the polypeptides.
Digestion of fats: Are undigested until the duodenum. The bile salts cause the fat globules to be physically broken up and lipase breaks down the fatty acids and glycerol.
Nuceleases hydrolyzes nucleic acid.
Most chemical digestion and nutrient absorption occurs in the small intestine. The pancreas and liver also help with digestion in the small intestine. The pancreas produces pancreatic juice which consists of digestive enzymes and an alkaline solution with a bicarbonate. The bicarbonate is the buffer to neutralize the chyme in the small intestine. The liver produces bile. The bile contains salts that emulsify the fats so that they are more prone to 'attack' by enzymes. The gallbladder stores the bile until it is needed. The duodenum is the first 25cm of the small intestine where chyme is squirted from the stomach mixes with the bile from the gallbladder as well as pancreatic juice and the digestive enzymes secreted by the small intestine.
The lining of the small intestine is about 300m2. The villi are small projections which have projections called microvilli. Villi and microvilli help increase the surface area. Nutrients are absorbed by diffusion and other nutrients are pumped against concentration gradients into epithelial cells
When we feel hungry, we are actually feeling our empty stomach contracting which is that 'pang' of hunger. Chyme is the 'broth' if you will, inside our stomach that is rich with nutrients. So what can go wrong in our digestive system? Both acid reflux and gastric ulcers are common. Acid relux is the backflow of chyme into the esophagus, weirdly referred to as heartburn. Gastric ulcers are open sores that if not treated can lead to an actual hole in the lining which can be deadly.
The stomach stores food and continues in the digestive process. The stomach breaks down more food with the help of acid and enzymes. Our stomach is a very stretchy organ- it can hold up to two whole liters of food and drink. The stomach secretes gastric juice which consists of mucus, enzymes and acid. The pH of gastric juice is about 2. This highly acidic mixture breaks apart the cells in food and also kills bacteria. The interior of the stomach is an extensively folded surface with small pits that lad to tubular gastric glands. Gastric glands secretes compounds of gastric juice.
There are mucus cells, parietal cells and chief cells.
Mucus cells secrete mucus that both lubricates and protects the cells than line the esophagus.
Parietal cells secrete hydrogen and chloride ions the combine in the lumens in the stomach and make hydrochloric acid.
Chief cells secrete pepsinogen which is an inactive form of the enzyme pepsin. The hydrochloric acid converts the pepsinogen to pepsin which in turn activates more pepsinogen.
Peristalsis comes into play as soon as we swallow. Remember, these are muscular, wave-like contractions that move the food from the esophagus to the stomach. The esophagus and trachea are both in the pharynx, but most of the time our esophagus is closed off by a sphincter so that air can flow from our larynx, through the trachea and into the lungs. When we swallow, it triggers a swallowing reflex where the sphincter relaxes and allows the bolus of food to enter into the esophagus. At the same time, the larynx moves upward and tips the epiglottis (a cartilage flap) down covering the larynx. After the bolus of food enters the esophagus, the larynx moves back downward, reversing the action so that the epiglottis tips back up and the trachea is once again open for breathing. The job of the esophagus is to move food from the pharynx to the stomach. The muscles at the top of the esophagus are voluntary, the rest obviously are involuntary.
We can produce more than one liter of saliva per day. Buffers serve in neutralizing food acids which also help in the prevention of tooth decay. Amylase plays a role in hydrolyzing starches. Chewing is an example of mechanical digestion. Our incisors are used in biting, our canine teeth are used in ripping and our molars are used for grinding and crushing the food. The tongue shapes the food into a ball reffered to as a bolus.
As mentioned before, digestion begins inside the oral cavity. Saliva is a major component. Saliva is secreted by the salivary glands and consists of a glycoprotein the functions in protecting the lining of the mouth and also helps lubricates our food for swallowing.
All animals have the same basic nutritional needs.
1. Fuel to power bodily activities
2. Organic molecules to build molecules
3. Essential nutrients that the animal can not make on its own from raw materials
Everything in the body requires energy, and this of course is our friend ATP. Cells typically use carbohydrates and fats as fuel but when a cell is in short supply of these proteins can also be used. Fats are very rich in energy. Kilocalories are the energy content of food and one Kilocalorie = 1000 calories. A Calorie (what we see on nutritional labels) is equal to a Kilocalorie not a calorie (notice the capital C). The metabolic rate is the rate of energy consumption by the body. The basal metabolic rate (BMR) is the number of Kilocalories a resting animal requires to fuel essential processes over a given amount of time.

Essential nutrients are materials that obtained in preassembled form because an animal cannot make these materials from any raw material. Essential nutrients include essential fatty acids, essential amino acids and vitamins and minerals.

Undernourishment is a condition resulting from a diet chronically deficient in calories.

Malnourishment results from the long term absence of one or more essential nutrients.

Essential fatty acids, for instance linoleic acid, are needed to make phospholipids of cell membranes. We need to obtain 8 of the 20 amino acids through food. These are mainly found in animal products. A healthly diet must include both vitamins and minerals. A vitamin is an organic nutrient that we must obtain from our diet in minute amounts. A mineral is a simple inorganic nutrient that is required in small amounts.
Examples of some vitamins:
Many B vitamins act as coenzymes and vitamin C helps produce connective tissue.

Examples of some minerals:
Calcium is important for bones and formations of nerves and muscles. Iron is needed for hemoglobin.

Most minerals and vitamins can be toxic is consumed in excess.
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