Transcript The Digestive System

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
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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.
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SWALLOWING THE BOLUS
Pharynx
*The digestive and respiratory passage connection
*Then the two systems separate
Esophagus
The 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
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WHERE THE MAGIC HAPPENS.
Digestive Physiology
William 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 pitslead 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 Level
The 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
Mucus
A thick layer of mucus covers the stomach wallprotects 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 reflexcauses sphincter to close the opening temporarily
*Done slowly to insure thorough digestion
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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 INTESTINE
Villi
*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
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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
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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 level
BUT 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
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THE LIVER
The largest gland in the body
In 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 veins
HEPATIC 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 veins
IF GLYCOGEN IS DEPLETED….. D:
*liver converts glycerol (from fats)/amino acids into glucose necessitates
deamination (removal of amino groups)
…STILL GOING
Urea
*complex metabolic pathway combines ammonia with carbon dioxideforms urea
*the usual nitrogenous waste product from amino acid breakdown in humans
Bile
*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
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THE LAST STOP ON OUR TOUR, THE GALLBLADDER
Pear-shaped muscular sac attached to the surface of the liver
Approx. 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
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