Rebel Biology - Nutrition organisms need a variety of nutrients to perform life s activities the most important ones are fats, carbs, proteins vitamins, water, these either provide direct value(fats/carbs/proteins) or they help facilitate the rxns necessary for the extraction of the others(h 2 0 and vitamins) not all nutrients need to be digested in order to be effective some, like fiber, help stimulate the digestive process
There are 4 basic steps to get the nutrients: in order for the nutrients to be effective in helping organisms they first have to be ingested this is basically bringing the food into the organism often involves the mechanical breakdown of food next the food must be chemically broken down into simpler forms by the process of digestion thirdly the simpler nutrients must be absorbed by the cells of the organism finally the waste products(stuff not needed) have to be eliminated Human Digestion the structure of the human digestive sys is very similar in the basics earthworm diff. organs for diff. stages of digestion the food enters the body through the mouth(oral cavity) where mechanical and some chemical digestion takes place then the following path is taken: pharynx esophagus stomach sm.intestine lg. intestine rectum anus
throughout this process there are diff. digestive glands that secrete digestive juices into the alimentary canal these are the salivary glands, liver, and pancreas
The Mouth the teeth and tongue are the important structures that help breakdown and form the food into a bolus(a food mass) the salivary glands also secrete salivary amylase to help breakdown the starch contained in the food when food is sufficiently chewed it passes through the pharynx and down the esophagus The Esophagus this is the tube leading from the pharynx to the stomach the food is passed down the tube by varying waves of muscular contractions that is called peristalsis
muscles in front of the food relaxes and those behind will contract there is also a strong ring of muscles called a sphincter that will open to allow food to pass into the stomach The Stomach this is a thick walled, muscular sac can expand to hold up to 2 liters of materials there are various glands that release enzymes that act on the food to break it down chemically gastric juices come from gastric glands and help to lower the ph(1.5-2.5) of the stomach to help break down proteins in the food pyloric glands secrete mucous to help protect the lining of the stomach from the high ph only partial digestion of food takes places here and food usually passes through in 2-6 hours and liquids move through faster in around 20 mins or less
when the stomach is empty the gastric juices are removed stimulation from 3 main factors will stimulate the release of the juices again: ➀ the though, sight or smell of food ➁ food touching the lining of the stomach ➂ when food stretches the lining of the stomach then the hormone gastrin will help to stimulate the gastric juices when the food is digested enough into a soupy mess called chyme then the pyloric sphincter will open and it will empty into the small intestine or duodenum Small Intestine a coiled tube about 2.5 cm in diameter and 6.5 m long there are 3 basic parts: duodenum(first section) jejunum (middle section) ileum (end section) most chemical digestion takes place here and this is also the site of absorption this is made more efficient by the presence of many tiny finger like projections on the folds called villi
there are also even smaller villi called microvilli the sm int is in constant motion when food is present in it this mvmnt is much similar to the mvmnt of the esophagus this has 4 main effects: ➀ squeeze through the chyme ➁ mix chyme with with dig. juices ➂ break down food mechanically ➃ speed up absorption contrasting with the stomach most of the dig juices in the sm int are generally alkaline which means basic (ph above 7) the chyme mixes with pancreatic juice, intestinal juice and bile to aid the chem dig.
Large Intestine this is 1.5 m long and about 6cm in diameter no digestion occurs here it has already been done right at the juncture of the sm an lg int there in the appendix (on right side of body) the main function of the lg int is the reabsorption of water from food about 3/4 of the water gets taken back in a second function of the lg int is the absorption of the vitamins that get produced by the bacteria that live in it the third function is elimination of the waste products which consist of cellulose, bile, mucous, and worn out cells from the dig sys this material (feces) is stored for a while in the rectum and periodically removed rough the anus