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Bio 20 - Teacher: The Digestive System

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Meaghan McKenzie

on 23 June 2013

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Transcript of Bio 20 - Teacher: The Digestive System

The Digestive System
The Mouth.
Physical Digestion
Teeth: chewing, mashing, cutting

Tongue: mixing

Saliva: secreted by salivary glands. Moistens food and helps break it up, and assists swallowing.

All three increase the surface area of substrate (food)
Chemical Digestion
The bolus passes through the ESOPHAGEAL SPHINCTER (band of muscle) into....
Physical Digestion
3 layers of stomach muscle squeeze, churn, and mix food.

this helps to break the food up further as well as mix it with the gastric juice.
Chemical Digestion
Stomach secretes GASTRIC JUICE, which contains:

Hydrochloric acid (HCl):
starts to break down proteins.
pH 1-3 kills most bacteria ingested with food.
Enzyme that breaks proteins down into smaller polypeptides.

Secreted in inactive form.

Activated by low pH of gastric juice.
The Esophagus
Bolus is propelled using PERISTALSIS - a wave-like contraction of the muscle
The journey begins at...
The chewed up food is now called a BOLUS

After sufficient chewing, it travels through....
the EPIGLOTTIS keeps food from going down your wind pipe (larynx/trachea)
Animation: http://www.getbodysmart.com/ap/respiratorysystem/larynx/epiglottis/tutorial.html
Enzyme in saliva that breaks down starch (in food) into simple sugars (disaccharides)
The Small Intestine
SEGMENTATION: contraction of segments of the muscles - sloshes chyme back and forth, helps mix chyme with enzymes.
A muscular, sac-like organ
Functions: store, digest, and push food into small intestine.
A muscular tube that connects the mouth and stomach.
The stomach is prevented from digesting itself by secreting:
protective mucus.
very little HCl until food is present.
an inactive form of pepsin.
Chemical Digestion
Physical Digestion
Muscular tube made of 3 parts: Duodenum, jejunum, ileum.

Longest part of the digestive tract (small only in diameter).

Peristalsis pushes food along the intestine.

Main function: finish digestion and absorb nutrients.
The Large Intestine
Accesory Organs
The Liver
The Pancreas
The Gallbladder
Intestinal fluid, containing water and enzymes, is secreted (mostly) in the jejunum.
CARBOHYDRASES: enzyme that breaks down polysaccharides and disaccharides into monosaccharides.

PEPTIDASES: enzyme that breaks down small peptides into amino acids.

NUCLEOSIDASES: enzyme that breaks down nucleotides into bases, sugars, and phosphates.
The inner lining of the small intestine has circular ridges about 1.3cm high.

These ridges are covered in bristle-like projections, called VILLI, which give the ridges a "velvety appearance"

The surface cells of the villi have microscopic bristles, called MICROVILLI

These 3 structures increase the SURFACE AREA of the small intestine 54 000 times!
Each villi contains a capillary network and lymph vessels

Nutrients are absorbed by the cells of the villi and are carried to the rest of the body via the blood and lymph

Absorption of water and nutrients occurs in the whole intestine, but mainly in the jejunum and ileum
Vital role in digestion, but not physically part of the digestive tract
Secretes PANCREATIC FLUID into the duodenum. This fluid contains:

BICARBONATE: neutralizes HCl from stomach, gives chyme a pH 8.

ENZYMES: are mostly inactive until they are activated by intestinal enzymes.
TRYPSIN and CHYMOTRYPSIN: break down small peptides into smaller peptides.

PANCREATIC AMYLASE: breaks down starch into disaccharides. Likes neutral pH.

LIPASE: breaks down lipids into fatty acids and glycerol.

NUCLEASE: breaks nucleic acids into nucleotides and components.
help the digestion of lipids by pancreatic lipase by EMULSIFYING fat droplets into very small drops, increasing the surface area for the enzyme to work on.
The largest organ in the human body - 1.5 kg

Secretes BILE, a fluid that contains bile salts and pigments, into the duodenum.
Stores bile from the liver in between meals.

The arrival of fat-containing chyme in the duodenum causes the gallbladder to contract.

A common bile duct is shared by the liver and the gallbladder.
After 4-6 hours, any remaining undigested chyme travels to...
Shorter than the small intestine, but larger in diameter.
Functions: Absorption and elimination of feces.
the main portion of the large intestine, absorbs water and salts.

4 parts: ascending, transverse, descending, and sigmoid.
Peristalsis moves undigested food along the colon and into the rectum

Undigested food + colon bacteria = FECES
has 3 folds that enable it to retain feces while passing gas.

Opening to anus controlled by 2 sphincters: One is involuntary (controlled by nervous system). The other is voluntary.
Animation of Hormone Secretion: http://www.mcgrawhill.ca/school/applets/abbio/ch06/gastric_three_phases_of.swf
Source: stomach

Stimulus: entry of food into stomach.

Target: stomach
*recall: Hormones travel through bloodstream from their place of origin to their targets.
Secretin, CCK (Cholescystokinin) and GIP (Gastric Inhibitory Peptide)
Source: Duodenum

Stimulus: Entry of acidic chyme (Secretin)/ fatty chyme (CCK, GIP) into duodenum.
Target: pancreas
Stimulus: release more bicarbonate to neutralize acidic chyme.
Bile Pigments:
waste products from the breakdown of red blood cells - do not take part in digestion.

further breakdown of undigested food

produce vitamins B-12 and K, and some amino acids
Target: Stomach

Response: Decreased stomach contractions and secretions - reduces the amount of chyme entering the small intestine.
Response: increase acid and pepsin secretion.

Inhibition: lowered pH inhibits further secretion.
And in 20-40 hrs, the food that entered your body will leave it through the anal canal in the form of feces.
Functions: begins chemical and physical digestion of food.
Historical Discoveries
Dr. Beaumont and
Alexis St. Martin - 1825
Ivan Pavlov - 1890
Barry J. Marshall and J. Robin Warren - 1984
Dr. Beaumont studied the digestion of different types of food through a hole to St. Martin's stomach.

TODAY: Holes to stomachs are still used to observe digestion and digestive problems and diseases. They are, however, using cows and not humans!
Discovered that the bacteria Helicobacter pylori were the cause of gastric inflammation, and gastric and duodenal ulcers.

Proved their theory by drinking a culture of the bacteria to show they caused ulcers.

Were able to treat patients using antibiotics and bismuth (found in pepto-bismol).

In 2005, the doctors won a Nobel Prize for their discovery!
Studied the effect of the nervous system on body functions, specifically salivation.

Observed that dogs drooled in the presence of food, and was able to train them to drool in response to other stimuli (e.g. sound, light).

Importance: explored relationship between the nervous system and bodily functions.
The liquidy food is now called CHYME.
After 2-3 hrs it passes through the PYLORIC SPHINCTER into the...
The Stomach
Target: pancreas and gallbladder

Stimulus: increased pancreatic secretions and gallbladder contractions

In the LIVER:
monosaccharides other than glucose are converted into glucose
glucose is stored as glycogen
amino acids undergo modification
Monosaccharides and amino acids are absorbed into the bloodstream, which takes them to the liver.

Triglycerides are absorboed into the lymph vessels.
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