The Human Digestive Tract 


The Mouth

• salivary glands (parotid, sublingual, submaxillary) - produces saliva

--->lubricate food ---> dissolves food particles ---> allows us to taste food --->contains amylase (enzyme)

breaks down starch---> disaccharide = chemical digestion • teeth are important for mechanical

digestion

Teethdifferent shapes have different

functions. incisors-cut the food. canines (or cuspids)-tear and shred

food premolars (or bicuspids)- tear, crush,

and grind the food. molars -crush and grind food

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The Esophagus- mucin is secreted by cells (lubricate

path) - lined with circular & longitudinal muscles - work together to push food down peristalsis - wave like muscular contraction

that moves food

• If you found a skull of an unknown animal, what could you examine so that you could hypothesize about its diet? Explain with an example.

• Infer how food reaches an astronaut’s stomach when s/he is floating in zero gravity.

• Your friend is convinced that digestion begins in the stomach. Is this true or false? Explain and include two facts to support your answer.

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The Stomachesophogeal (cardiac) sphincter found before

stomach - thickened muscular ring - controls movement of food in & out of stomach

The Stomach- J-shaped with lots of ridges

(rugae) to allow for expansion - gastric juices contain mucus,

hydrochloric acid, & pepsin • mucus - protects stomach

lining • HCl - kills harmful substances

(pH1-3) - activates pepsin • pepsin - enzyme that cuts

proteins into shorter chains of aa (polypeptides)

The Stomach 


- muscle layers ---> work to mechanically by churning to breakdown food into:

chyme - thick liquid found in stomach

The Stomach- pyloric sphincter found at end of stomach - controls movement of food out of stomach into

sm intestine

Small Intestine

- 6-7 m long - muscles moves food along (peristalsis) - primary functions: chemically breakdown chyme

& absorb nutrients - a lot of surface area is needed!

Small Intestine• how does the intestine increase surface area for

absorption of nutrients? - folds in intestine covered by villi (finger-like extensions) - microvilli on villi - capillaries in villi absorb nutrients

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3 sections of small intestine:

1. duodenum - chemical breakdown is primary - pancreas & gall bladder empty enzymes

to breakdown 2. jejunum - breaks down proteins &

carbohydrates 3. ileum - absorbs remaining nutrients - pushes undigested material along

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The Large Intestinecaecum - first section - appendix is attached to it --> role:

Bacteria replacement!

Watch this video about the latest research on gut bacteria (microbes).

The Large Intestine (cont’d)colon - water is absorbed - bacteria (E. coli) help to break down material ---> produce vitamin B-12 & K - final result is feces - feces passes through rectum & anal canal by peristalsis anal sphincter - allows for control of elimination

Katie Couric’s first husband died of colon cancer. He was too embarrassed to have a colonoscopy when he first had symptoms (eg., rectal bleeding). Katie wanted to encourage people to get a colonoscopy before it was too late so she had the procedure on TV!! Let’s take a look!

As you watch, notice how the inside of the large intestine looks.

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Colonoscopy

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The Pancreas

• secrete enzymes into the small intestines. • act on carbohydrates (amylase), fats (lipase),

and peptides (proteases) • secretes a basic solution (bicarbonate) to

neutralize chyme (---> making it slightly basic)

The Liver & Gall Bladder


Liver

The Liver & Gall Bladder


Liver • continuously makes bile - speeds up fat digestion

- bile emulsifies fat = physical digestion - smaller droplets of fat chemically broken down by

lipases

The Liver & Gall Bladder


Other important functions of the liver include: - breaks down old RBC - storage of excess chemicals from blood

eg. sugar, vitamins A, D, E, K - breaks down amino acids for storage of

- detoxifies poisons and drugs (including alcohol)

gall bladder - stores bile

1. Read 411 - 415, 418 2. Complete pg 419 #1, 6, 7, 8, 10, 12

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Classwork/Homework

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