THE DIGESTIV

E SYSTEM

F R O M TH E F

I RS T B

I TE O

F FO O D T

O I T’ S

J OU R N E Y T

O

T H E FI N

I SH L

I NE

THE DIGESTIVE SYSTEM

Let’s get these gastric juices going…

DIGESTIVE TRACTSSurprisingly, 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 food2) Breaks the delicious food into nutrient molecules for transport across the

plasma membrane3) Absorbs the nutrient molecules4) Gets rid of undigestible remains from your meal

THE PA

RTS AND TH

EIR

FUNCTIO

NS

T H E NE C E S S I T

I ES A

N D TH E N S

O M E

AN OVER LO

OK

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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 THE F

RIST

BITE

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SWALLOWING THE BOLUS Pharynx*The digestive and respiratory passage connection*Then the two systems separateEsophagusThe 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 nasopharynxEpiglottis*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

SWALLO

WING THE

BOLUS

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THE STO

MACH

I T’ S

GO O D S

I DE A

N D I T’ S

BA D S

I DE

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 foodThe 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.

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THE VERY LONG, SMALL INTESTINENamed for it’s small diameterAverages 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

intestineBile*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 V

ERY LO

NG, SMALL

INTESTIN

E

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THE SHORT, LARGE INTESTINEApprox. 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 appendixAppendix (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 daily95% of this water is absorbed by the small intestineThe 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

anusAnus*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,

LARGE

INTESTINE

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THE TH

REE ACCESSORY

ORGANS

T H E PA N C R E A S , L

I VE R , A

N D GA L L B L A D D E R

THAT THING HENOK/MATTHEW ALREADY TALKED ABOUT

THE PANCREAS*deep inside the abdominal cavity*rests on the posterior abdominal wall*endocrine and exocrine function*Endocrine gland: secretes insulin/glucagon hormones that

maintain normal blood glucose levelBUT WE WANT TO FOCUS ON THE EXOCRINE FUNCTION*Pancreatic cells make pancreatic juice (has sodium

bicarbonate/digestive enzymes)*Pancreatic amylase digests starch/trypsin digests

protein/lipase digests fat

THAT

THING

HENOK/MATT

HEW ALREADY

TALKED ABOUT

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THE LIVERThe largest gland in the bodyIn the upper right section of the abdominal cavity under the diaphragm Approx. 100,000 lobules serve as structural/functional units Triads*between lobules*has a bile duct that takes bile away from the liver

- a branch of the heptic artery, brings Oxygen rich blood to the liver-a branch of the heptic portal vein also which transports nutrients from the intestines

*central veins of lobules enter a hepatic vein*blood goes frOm the intestines to the liver by the hepatic portal vein and

from the liver to the inferior vena cava via the hepatic veinsHEPATIC VEINS ARE IMPORTANT.

THE LIVER“In some ways, the liver acts as the gatekeeper to the blood.”

When blood moves through those special, important veins previously mentioned, it removes poisonous substances/detoxifies them

Removes and stores iron, Vitamins A, B12, D, E, and K

Makes plasma proteins and helps to regulate the quantity of cholesterol in the blood

BUT WAIT, THERE’S STILL MORE….Maintains blood glucose level at 100mg/100ml (0.1%), even

though we still eat often...and a lot*When insulin is there: excess glucose in blood is removed and

stored in the liver as glycogen*between meals, glycogen breaks down into glucose which can

then enter the hepatic veinsIF GLYCOGEN IS DEPLETED….. D: *liver converts glycerol (from fats)/amino acids into glucose

necessitates deamination (removal of amino groups)

…STILL GOINGUrea*complex metabolic pathway combines ammonia with carbon

dioxideforms urea*the usual nitrogenous waste product from amino acid breakdown in

humansBile*The Liver produces this*A pleasing…yellow green color…

-contains the pigment bilirubin (Like your feces!) *contains bile salts

-from cholesterol (emulsify fat in the small intestine) -emulsification leads to droplets that make a larger surface area to be acted on by a digestive enzyme from the pancreas

THE LIV

ER

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THE LAST STOP ON OUR TOUR, THE GALLBLADDER

Pear-shaped muscular sac attached to the surface of the liverApprox. 1000 ml of bile are produced by the liver each day, any

excess is stored in this lovely organ*Water is reabsorbed

-bile becomes a thick…..mucus like….delicious, material*When needed, bile leaves the gallbladder and moves onto the

duodenum via the common bile duct*Cholesterol content in the bile can come out of solution and form

crystals-if they grow, they form gallstones-the passage of those stones may block the common bile duct-could then cause obstructive jaundice-then it must be removed

THE LA

ST STO

P ON OUR

TOUR, TH

E GALLBLADDER

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THANK YO

U FOR RISKING

YOUR APPE

TITE

Sincerel

y, yo

ur diges

tive s

ystem

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