HUMAN NUTRITION

* NUTRITION--the life activities by which organisms obtain and process nutrients for energy, growth, repair, and regulation
* humans are heterotrophs--they have to get there food from somewhere, they cannot make their own

* humans need food; which can be described as either nutrients or roughage

NUTRIENTS:
* carbohydrates, lipids, protiens, vitamins, minerals, and water* complex carbos
*
carbos, lipids, and proteins MUST be digested; vitamins, minerals, and water can be absorbed without digestion

ROUGHAGE:
* complex carbos that cannot be broken down but is necessary for the digestive system to work; also known as fiber

* the human digestive system is responsible for:

1) taking in food--ingestion

2) breaking it down mechanically and chemically (hydrolysis)--digestion

3) absorbing the nutrients in food OR

4) egesting the parts of your food which is indigestible--egestion


* the human digestive system (also called the alimentary canal) is a one-way gastrointestinal (gastro=stomach) tract with 2 openings

* food is moved in the correct direction by slow muscle contractions called peristalsis


Human Nutrition

a nice review of the digestive system...once open, choose the digestive system
the importance of vitamins
what is fiber and why is it important?
FOOD SCIENCE see how calories and grams of fat are determined in a sample of food

STRUCTURES OF THE HUMAN DIGESTIVE SYSTEM

It is important to be able to identify and explain the role of every part of this system!


1) oral cavity (mouth)--
* ingestion of food occurs here; contains teeth, tongue, and openings of the salivary glands

A) teeth--

* used to break down food mechanically (mechanical digestion) to increase surface area for digestive enzymes (chemical digestion)

B) tongue--

* moves food around mouth so that teeth work more effectively, helps mix food with saliva, and moves food to the back of the mouth for swallowing

C) salivary glands--

*secretes saliva into digestive system which contains the hydrolytic (the breakdown with water--digestive) enzyme AMYLASE, which digests starch
*chemical digestion of carbohydrates begins in the mouth

2) esophagus--
* when you swallow, food goes into this small tube (about 10 inches--25 centimeters--long)
* mucus is secreted to lubricate the food to slide easier
* peristaltic action (peristalsis) moves the food towards the stomach

A) epiglottis--

* when you swallow, a small flap of tissue closes off your windpipe (trachea) so that food will not go down into the lungs
* this momentarily stops breathing!

3) stomach--
* a thick-walled, muscular sac (organ) whose main job is to liquefy and further digest food
* the lining of the stomach contains gastric glands which secrete gastric juices which contain:

a) gastric protease
b) hydrochloric (HCl) acid
c) mucus
d) water

* gastric protease is an enzyme which begins the digestion of proteins
* the hydrochloric acid lowers the pH of the stomach, not to break down food, but to provide the optimum (best) pH for the gastric protease to work!
* the mucus protects the stomach walls from being eaten away
* the water is used for chemical digestion (hydrolysis)

* the stomach also stores the food for a while; liquids can pass through the stomach in 20 minutes or less while solids can remain in the stomach for 2-6 hours

BOTH MECHANICAL AND CHEMICAL DIGESTION OCCUR IN THE STOMACH!

stomach walls churn food up (MECHANICAL)

hydrolytic enzymes digest food (CHEMICAL)

4) small intestine--
* partially digested food then enters the small intestine
* it is a long tube (just over 20 feet--6.5 meters--long in an average human) where a major portion of food is digested
* intestinal glands line the intestinal walls and secrete lipase, intestinal protease, and maltase to complete chemical digestion of food
* food is digested with the help of accessory organs (food never goes to these places to be digested)

A) liver--

* produces bile and sends it to the gall bladder
* bile is not an enzyme; however it does break down big globs of fat to smaller globblets--called EMULSIFICATION

B) gall bladder--

* slowly secretes bile into the small intestine

C) pancreas--

* secretes enzymes into the small intestine such as intestinal amylase, lipase, and intestinal protease

5) large intestine--
* takes the undigested food and absorbs most of the water and any vitamins not yet absorbed
* solidifies the liquid wastes into solid feces (includes undigested and indigestible material--roughage--bacteria, bile, mucus, and worn out cells from the digestive tract)
* strong peristaltic action forces feces out the anus


A) rectum--

* where solid wastes are temporarily stored
B) appendix--

* has no known function, however, an inflammation of this organ (appendicitis) can be life threatening if it ruptures

C) anus--

* opening in the human body through which feces (solid wastes) are removed

 

Human Nutrition

a nice review of all the digestive organs
this is a longer clip, but it does a great job in reviewing all the important aspects of the human digestive system

REVIEW OF CHEMICAL DIGESTION

hydrolysis = using water to split

* hydrolysis is the splitting of large soluble molecules with the addition of water
* in organisms, this process if regulated by hydrolytic enzymes
* remember, the first part of the enzyme's name tells you what the enzyme works on! (except amylase--starch)

starch + water -----with amylase----> maltose

maltose + water -----with maltase----> 2 glucose

polypeptide + water ------with protease----> amino acids

lipid + water ----with lipase---> 3 fatty acids + glycerol


ABSORPTION OF DIGESTED MATERIAL

* food is absorbed by the body in the small intestine, after it has been digested

* the intestinal wall is lined with millions of villi which increase the surface area for absorption
* in each individual villi (shown below), there are capillaries (very small blood vessels) and other small ducts (pipes) of the lymphatic system called lacteals

HERE'S HOW NUTRIENTS ARE ABSORBED...

I. CARBOHYDRATES--

* glucose (a monosaccharide) is absorbed into the bloodstream by the capillaries
* there, it is sent to the liver to be stored temporarily as glycogen (a polysaccharide--animal starch)
* when the body needs more glucose, it switches the glycogen back and releases the glucose back into the bloodstream for energy

II. PROTEINS--

* amino acids are also absorbed into the bloodstream by the capillaries
* amino acids are stored in the liver until they are needed

* there are 20 different amino acids that humans need to make up proteins
* 8 of them must be obtained from the diet; these are the essential amino acids

III. LIPIDS--

* (the building blocks of lipids) fatty acids and glycerol are absorbed into the lacteals and are passed along in the lymph (which is other fluid--besides blood!)
* they enter the bloodstream through this other set of pipes
* remember, fats are used for high energy storage and to build up cell membranes
* there are 2 main types of fats (lipids)

SATURATED FATS--solids at room temperature (ex. grease, lard); contain lots of hydrogen (H) in their structure; too much in the diet has been linked to cardiovascular disease
POLYUNSATURATED FATS--liquids at room temperature (ex. oils); contain less hydrogen (H) in their structure than the saturated fats; does not appear to be linked to cardiovascular disease

 

Human Nutrition

FOOD SCIENCE see how calories and grams of fat are determined in a sample of food
what are complementary proteins?

MALFUNCTIONS OF THE DIGESTIVE SYSTEM

1) Ulcers--
* an erosion (open sore) of the surface of the digestive tract
* can be caused by smoking, stress, worry, or bad diet

2) Appendicitis--
* when the appendix becomes inflamed
* can be life threatening if it ruptures

3) Gallstones--
* when cholesterol deposits (build-ups) harden in the gall bladder
* affects the secretion of bile into the small intestine which causes great pain

4) Constipation--
* a condition in which the large intestine is emptied with great difficulty
* too much water has been absorbed from the wastes
* and/or not enough roughage (fiber) was present to push material through

5) Diarrhea--
* a gastrointestinal disturbance of some kind which results in:

a) decreased water absorption
b) increased peristaltic action

* diarrhea results in increased, multiple, watery feces
* can result in severe dehydration

Human Nutrition