Download Rebel Biology - Nutrition organisms need a variety of nutrients to

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(H20 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
lg. intestine
stomach
rectum
sm.intestine
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