THE D

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THE DIGESTIVE SYSTEM

Let’s get these gastric juices going…

DIGESTIVE TRACTS

Surprisingly, not all animals have digestive tracks within them

*sponges use food vacuoles

*hydras use gastrovascular cavity/food vacuoles

Overview:

*Food is digested into small molecules so that they can cross the plasma membrane

*Contributes to homeostasis (sustains life in the cells)

The tract:

1) Ingests the yummy food

2) Breaks the delicious food into nutrient molecules for transport across the plasma membrane

3) Absorbs the nutrient molecules

4) Gets rid of undigestible remains from your meal

THE PA

RTS A

ND THEIR

FUNCTI

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TH

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SI T

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N S

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AN OVER LO

OK

http://www.bing.com/images/search?q=The+digestive+system&qpvt=The+digestive+system&FORM=IGRE#view=detail&id=4B17D215EE910AF52F9A39BB8655C5183554E16C&selectedIndex=2

FROM THE FIRST BITE...

Your Lovely Mouth(AKA the oral cavity)

Palate

*roof of the mouth, separates from nasal cavity

*anterior hard palate

*posterior soft palate

*Uvula (the thing that you can touch that will make you vomit) is a posterior extension of the soft palate

The Cheeks and the Lips hold in the food while you chew it and while your saliva mixes with it, gross right?

FROM THE FIRST BITE…Salivary Glands*Send their “juices” through ducts that go to the mouth

*Saliva has the enzyme salivary amylase that starts the starch digestion process (more on this later)

Tongue*Touch and pressure receptors (think of skin)

*Taste buds: stimulated by a food’s chemical composition

-mostly on tongue/surface of the mouth

*Structure: striated muscle and a mucous membrane mixes your chewed food

DID YOU KNOW….this mixture is called a bolus which is the food/mucous combo that you swallow, YUM.

FROM T

HE FR

IST

BITE

http://www.bing.com/images/search?q=The+digestive+system&qpvt=The+digestive+system&FORM=IGRE#view=detail&id=4B17D215EE910AF52F9A39BB8655C5183554E16C&selectedIndex=2

SWALLOWING THE BOLUS

Pharynx*The digestive and respiratory passage connection

*Then the two systems separate

EsophagusThe next stop on our journey through the digestive system…

*tubular structure (approx. 25 cm length)

Sphincters: muscles encircling the tubes and act as valves

-tubes close when the contract, open when relax

-lower gastroesophageal sphincter located where esophagus meets the stomach

-heartburn (contents escape esophagus )

SWALLOWING THE BOLUS

When you swallow the bolus, the soft palate (rear portion of the roof of the mouth) moves back to close the nasopharynx

Epiglottis*a flap of tissue

*covers the glottis (trachea opening)

Bolus can then move through the pharynx/esophagus because the air passages are closed

Peristalsis[Gk. peri (around), and stalis (compression)]

*starts when food enters the Esophagus

*rhythmical contraction

*moves contents along

SWALL

OWIN

G THE

BOLUS

http://www.bing.com/images/search?q=epiglottis&qs=ds&form=QBIR#view=detail&id=446EC46B6B8DAEFD7A9442B21F3225D7DD7F0174&selectedIndex=1

THE S

TOMACH

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WHERE THE MAGIC HAPPENS.

Digestive PhysiologyWilliam Beaumont…proceed into excerpt from book (pg. 638)

- there’s more to the stomach than meets the eye

- JK, before him they didn’t really know

- He’s important, just sayin

WHERE THE MAGIC HAPPENS.

A thick-walled, J-Shape organ on the left side of the body under the diaphragm

Rugae:*Deep folds, disappear when stomach fills (approx. 1 L)

Epithelial Lining*Millions of gastric pitslead into gastric glands-which

produce gastric juice

- I don’t know about you but the fact that they call its “juice” is just…gross.

Fun fact from our glorious text book:

“SO MUCH HYDROCHLORIC ACID IS SECRETED BY THE GASTRIC GLANDS THAT THE AVERAGE STOMACH pH LEVEL IS A 2.”

WHERE THE MAGIC HAPPENS.

pH LevelThe high acidity does a good job at killing off the bacteria and

microorganisms that might be in your food

The pH level also stops activity of the salivary amylase

MucusA thick layer of mucus covers the stomach wallprotects it

from enzymatic activity

-Ulcers (more later)

WHERE THE MAGIC HAPPENS.

Chyme*When your food mixes with gastric juice

*….a luscious….thick….creamy consistency, YUM.

Sphincter*Muscle that surrounds a tube and closes /opens the tube by

contracting/relaxing

*There is another one of these present in a narrow opening at the base of the stomach

*When it opens, a little bit of chyme passes onto the small intestine sets off a neural reflexcauses sphincter to close the opening temporarily

*Done slowly to insure thorough digestion

WHERE T

HE MAGIC

HAPPENS.

http://www.bing.com/images/search?q=the+stomach&qpvt=the+stomach&FORM=IGRE#view=detail&id=FC176575584D0367B65E39C7DCCD9F6D9E6C76BA&selectedIndex=57

THE VERY LONG, SMALL INTESTINE

Named for it’s small diameter

Averages about 6 meters in length, that’s right….roughly 18 feet of small intestines all up in your body.

Slightly basic pH (pancreatic juice contains sodium bicarbonate which neutralizes chyme)

Most enzymatic digestion is present in the small intestine (more later)

Duodenum*first 25 cm

*connects the stomach to the small intestine

*a duct brings bile from the liver/gallbladder/pancreatic juice into the small intestine

Bile*emulsifies fat (causes fat droplets to disperse in water)

THE VERY LONG, SMALL INTESTINEVilli*fingerlike projections

*soft, velvety appearance (I kid you not this is the books description)

*A villus (sing.) has an outer layer of columnar epithelial cells, these each have microscopic extensions (microvilli- contain enzymes and increase surface area)

*This fuzziness: AKA fuzzy border AKA the brush border

*Specialized for absorption

*Food molecules pass through a layer of cells in the Villi

*Nutrients absorbed into vessels of a villus (contain blood capillaries/lymphatic capillary)

*Sugars/amino acids enter blood capillaries

*Glycerol/fatty acids enter epithelial cells, they are joined/packaged as lipoprotein droplets, which enter the lacteal (a lymphatic capillary)

*The food molecules are assimilated to become part of the body tissue

http://ibguides.com/biology/notes/digestion

THE

VERY LO

NG, SMALL

INTE

STINE

http://www.bing.com/images/search?q=the+small+intestines&FORM=HDRSC2#view=detail&id=66AB74442AF209DC1AC762FAC9CE4400DD3BCCC0&selectedIndex=2

THE SHORT, LARGE INTESTINE

Approx. 1.5 meters in length….

ABSORBS WATER, SALTS, AND SOME VITAMINS

Stores undigestible material until it is “eliminated” at the anus

No digestion takes place here

THE SHORT, LARGE INTESTINE

Cecum*lies below the junction with the small intestine

*”blind end” of the large intestine

*Herbivores have a very large cecum compared to that of carnivores

*Has a small projection called the vermiform appendix

Appendix (synonymous with the cecum) *Fights infections

*Appendicitis-appendix gets infected and filled with fluid that it has the possibility of bursting, if it isn't removed before the bursting it can cause peritonitis (infection in the abdominal lining)

THE SHORT, LARGE INTESTINE

1.5 L of water enter the digestive tract daily

95% of this water is absorbed by the small intestine

The remaining 5% is mostly absorbed by the colon (AKA the large intestine)

If the water isn't reabsorbed it leads to diarrhea…which is not fun…

Large population of bacteria for the Large intestine

*E. coli for example

*breaks down undigestible material

*produce some vitamins

THE SHORT, LARGE INTESTINE

Digestive wastes (feces) eventually leave the body through the anus

Anus*feces are 75% water, 25% solid mater…most of the time

*1/3 of the solid matter is made up of intestinal bacteria

-remainder: undigested plant material, fats, wastes, inorganic material, mucus, and dead cells from the intestinal lining

FACT OF THE DAY

*The color of feces is the result of bilirubin breakdown and the presence of oxidized iron. The foul odor is the result of bacterial action

THE

SHORT, L

ARGE

INTE

STINE

http://www.bing.com/images/search?q=the+small+intestines&FORM=HDRSC2#view=detail&id=66AB74442AF209DC1AC762FAC9CE4400DD3BCCC0&selectedIndex=2

THE T

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