The digestive system discussion

Question

The digestive system discussion is making us aware of the relevance of this body system. What are the main functions of the stomach, small intestine and large intestine?. What digestive problems do you know related to malfunction of these organs?

Answer 1

Functions:

Stomach: digestion and break down of food to smaller, absorb-able particles.

Small intestine: absorption of nutrients

Large intestine: absorption of water.

Problems:

Stomach: stomach ulcer due to production of too much acid;

Small intestine: Celiac disease (inability to tolerate gluten)  

Large intestine: diarrhea due to inability of large intestine to absorb water.  

Answer 2

The stomach is a highly acidic environment due to gastric acid production and secretion which produces a luminal pH range usually between 1 and 2 depending on the species, food intake, time of the day, drug use, and other factors. Combined with digestive enzymes, such an environment is able to break down large molecules (such as from food) to smaller ones so that they can eventually be absorbed from the small intestine. A zymogen called pepsinogen is secreted by chief cells and turns into pepsin under low pH conditions and is a necessity in protein digestion. [3]

The human stomach can produce and secrete about 2.2 to 3 liters of gastric acid per day with basal secretion levels being typically highest in the evening. The stomach can expand to hold between 2-4 liters of food. It is a temporary food storage area, and in the process of digestion, the food goes into the stomach first.

Absorption of vitamin B12 from the small intestine is dependent on conjugation to a glycoprotein called intrinsic factor which is produced by parietal cells of the stomach.

Other functions include absorbing some ions, water, and some lipid soluble compounds such as alcohol, aspirin, and caffeine.

Also, contrary to popular belief, the stomach is not necessary for survival. The esophagus can be connected directly to the small intestine. You only have to chew your food into a thick pulp before swallowing.

The small intestine is where the vast majority of digestion takes place.

Food from the stomach is allowed into the duodenum by a muscle called the pylorus, or pyloric sphincter, and is then pushed through the small intestine by a process of muscular-wavelike contractions called peristalsis.The small intestine is the site where most of the nutrients from ingested food are absorbed and is covered in wrinkles or folds called plicae circulares. These are considered permanent features in the wall of the organ. They are distinct from rugae which are considered non-permanent or temporary allowing for distention and contraction. From the plicae circulares project microscopic finger-like pieces of tissue called villi (Latin for "shaggy hair"). The small intestine is lined with simple columnar epithelial tissue. The epithelial cells also have finger-like projections known as microvilli. The function of the plicae circulares, the villi and the microvilli is to increase the amount of surface area available for secretion of enzymes and absorption of nutrients.The purpose of these wrinkles and projections is to increase surface area for absorption of nutrients. Each villus is covered in microvilli, which increase the surface area manyfold. Each villus contains a lacteal and capillaries. The lacteal absorbs the digested fat into the lymphatic system which will eventually drain into the circulatory system. The capillaries absorb all other digested nutrients.

The surface of the cells on the microvilli are covered with a water layer, which has a number of functions in absorption of nutrients.

Absorption of the majority of nutrients takes place in the jejunum, with the following notable exceptions:

    * Iron is absorbed in the duodenum

    * Vitamin B12 and bile salts are absorbed in the terminal ileum.

    * Water and lipids are absorbed by passive diffusion throughout

    * Sodium is absorbed by active transport and glucose and amino acid co-transport.

    * Fructose is absorbed by facilitated diffusion.

The digested food can now pass into the blood vessels in the wall of the intestine. This process is called absorption. The inner walls of the small intestine have thousands of finger like outgrowths called villi (singular villus). The villi increases the surface area for absorption of the digested food. Each villus has a network of thin and small blood vessels close to its surface. The suface of the villi absorbs the digested food materials. The absorbed substances are transported via the blood vessels to different organs of the body where they are used to build complex substances such as the proteins required by our body. This is called assimilation. The food that remains undigested and unabsorbed passes into the large intestine. The digestion of proteins into peptides and amino acids principally occurs in the stomach but some also occurs in the small intestine. The small intestine is where the most chemical digestion takes place:

    * peptides are degraded into amino acids. Chemical breakdown begins in the stomach and is further broken down in the small intestine. Proteolytic enzymes, trypsin and chymotrypsin, which are secreted by the pancreas cleave proteins into smaller peptides. Carboxypeptidase, which is a pancreatic brush border enzyme, splits one amino acid at a time. Aminopeptidase and dipeptidase free the end amino acid products.

    * lipids (fats) are degraded into fatty acids and glycerol. Pancreatic lipase is secreted here. Pancreatic lipase breaks down triglycerides into free fatty acids and monoglycerides. Pancreatic lipase performs its job with the help of the salts from the bile secreted by the liver and the gall bladder. Bile salts attach to triglycerides which aids in making them easier for pancreatic lipase to access. This occurs because the lipase is water-soluble but the fatty triglycerides are hydrophobic and tend to orient towards each other and away from the watery intestinal surroundings. The bile salts are the "middle man" that holds the triglycerides in the watery surroundings until the lipase can break them into the smaller components that are able to enter the villi for absorption.

    * carbohydrates are degraded into simple sugars (e.g., glucose). In the small intestine pancreatic amylase breaks down carbohydrates into oligosaccharides. Brush border enzymes take over from there. The most important brush border enzymes are dextrinase and glucoamylase which further break down oligosaccharides. Other brush border enzymes are maltase, sucrase and lactase.

The large intestine takes 12-25 hours to finish up the remaining processes of the digestive system. Food is not broken down any further in this stage of digestion. The large intestine simply absorbs vitamins that are created by the bacteria inhabiting the colon. It is also very important in absorbing water and compacting the f***s, it also stores fecal matter in the r****m until eliminated through the a**s. It is also responsible for passing along solid waste.

Problems:

    * Nausea and Vomiting

    * Bloating

    * Constipation

    * Diarrhea

    * Abdominal Pain