The Digestive System

Nutrients to energy

Steps

z Digestion:

ylarge molecules broken down to small molecules

yenzymes

yoccurs outside cells

z Absorption:

ydigested material is absorbed through the bloodstream

z Assimilation:

yabsorbed nutrients are used by cells for growth and maintenance

Types of nutrients

zOrganic: carbohydrates, fats, proteins

ycarbohydrates and fats supply energy

yproteins supply tissue building

zInorganic: water, minerals, and vitamins

carbohydrates

zNearly half of the food we eat

z“fuel foods”

ybread, potatoes, milk, sugar, fruit

zcarbohydrates break down into glucose

proteins

zAmino acids are converted into energy

zthe body can’t store protein therefore what is not used is decomposed

Nutrient absorption

z Fats:

yfat from the gut - fat to the blood - adipose tissue

z Carbohydrates:

yenters all cells

yif it enters fat cells it will be converted to fat

ysome enter liver and skeletal muscle and is converted to glycogen

z Amino acids:

yenters all cells and is converted to protein

yenters liver and is converted to glycogen

yeventually is converted to urea

Glucose absorption

zGlycogen - glucose (liver) - blood glucose

zprotein - amino acids - glucose - blood glucose

zadipose - fat in blood - carbon dioxide and energy (except in brain)

zprotein - amino acids (liver) - glucose - blood glucose - all CHO, fat, glycogen supplies used up

Control of absorption

zHORMONES:

yINSULIN: STIMULATES ENTRY OF GLUCOSE INTO CELLS

yGLUCOGON: REVERSES EFFECT OF INSULIN

Anatomy

zDigestive tract is 24-26 feet long!

zMouth, pharynx, esophagus, stomach, small intestine (17’), large intestine, rectum, anus

Mouth

zProduces 1-1.5 liters of saliva a day

zcontrolled by nueral reflex not hormones

zfunctions:

ymoistens food

ysecretes enzyme salivary amylase

Stomach

zContains: water, hydrogen ions, enzymes, proteins

zcontrolled by hormones

zbasically a container for food

Small intestine

zMost of digestion occurs here

zOther organs that help the small intestine:

ypancreas: source of water, carbonate, enzymes

ygall bladder: stores bile salts

yliver: produces bile salts

ypurpose of bile: breaks up fat so water and enzymes can break it up better