Download Bio 20 6.2 6.3 notes

Bio 20 C6.2 – 6.3 The Digestive System p. 217
Clips: 1 = an amazing trip through the digestive system using an internal camera. Don’t watch right before
lunch!!!! 2 = Crash Course: Digestion for more details. 3 = quick review of the digestive tract
 1. https://www.youtube.com/watch?v=_QYwscALNng
 2. https://www.youtube.com/watch?v=s06XzaKqELk&list=PLPNiuLL71mb97pmnYVnNCbj61bZ8-mDo
3.http://www.youtube.com/watch?v=bI3Hoxy0qCc&index=82&list=PLXwnjgs_UWpIyKAZ9yaEUbv8Sz1
AMve45
 Fill in BLM 6.2.1 Digestive System Quiz using info from clips and pg. 217. Note which organs are
accessory organs (3) vs the digestive tract (food actually passes through the tract) – also known as
the GI tract (gastrointestinal tract).
 Check out the length of the digestive system organs on pg. 218! Average total is 8m !!!!
The 7 important Important Secretions Involved in Digestion
1. Saliva
2. Mucus
3. Enzymes
4. Acid
5. Bile
6. Bicarbonate
7. Hormones
 You might want to watch the following clip: http://www.youtube.com/watch?v=-Zyk0H1HmjA
(another review of the digestive tract, functions and secretions)
 Fill out BLM 6.2.2 Important Secretions of the Digestive System using pg. 219 and Table 1 below:
Table 1. How macromolecules are hydrolyzed in the digestive system (Fig. 6.21. pg.225)
Macromolecule
Enzyme
Hydrolysis Product
Sugars
amylases and carbohydrases
Lipids
(bile) and lip_____
Proteins
Nucleic Acids
Pep___, prote______, peptid_____
Nucle_____
nucleosid_______
Digestion Begins in the Mouth
Monosaccharides
p. 218
Secretions of the mouth
1) saliva
2) mucus
3) the enzyme salivary amylase.
Chemical digestion (hydrolysis) starts in the mouth, when an
enzyme in saliva, called salivary amylase, begins to break
down starch into simpler sugars.
Physical digestion also begins in the mouth by teeth chewing,
grinding and tearing – increasing surface area for digestion.
Water and mucus moisten the food. Your tongue rolls food
into a bolus, pushing it to the back of your mouth for
swallowing.
Learning Check!
 Why is physical digestion (mechanical breakdown) of food stuffs important?
 How does this occur in the mouth?

What is amylase?

Chew a cracker. Describe it’s initial flavour. Keep chewing til the flavour becomes sweet.
How long did this take? ____________ . What caused this change?
What is the function of amylase?
 Put your hands on your Adam’s apple (part of your tracheae). What body system does your
Adam’s apple belong to? _____________________________. Now swallow. What does your
Adam’s apple do when you swallow? _______________________. Why?
 What is the function of the epiglottis?
The Esophagus
p. 219
The esophagus is the muscular connector between the
mouth and the stomach.
Peristalsis, a wavelike series of muscular contractions and
relaxations, that moves the bolus to the stomach. The
esophageal sphincter is a ringlike muscular structure that
lets the food into the stomach when it relaxes. When
contracted, it prevents the acidic stomach contents backing
back up into the esophagus (preventing heartburn!).

Describe how food moves through the esophagus to the
stomach. Use the words epiglottis, esophagus, peristalsis,
esophageal sphincter, and stomach in the description.
The Stomach p. 220
The stomach has 3 functions: storage, some digestion, and pushing food into the small intestine. Peristalsis
in the stomach mechanically digests food. The enzyme pepsin in the presence of hydrochloric acid (HCl)
begins chemical digestion of proteins. When empty the stomach is the size of a large sausage with a capacity
of 50 ml. The stomach has folds called rugae that expand to accommodate 2 – 4L of food and mechanically
break down the food!
Secretions of the stomach:
1) mucus
2) pepsin, an enzyme that digests protein
3) hydrochloric acid (HCl) promotes the
digestion of protein. Pepsin works best at
a pH 2.0.
4) hormones
Learning Check!
40 million cells lining the stomach secret 2-3
L of gastric juice each day!
 1. Why does the stomach have folds? What are these folds called?
 2. What is the importance of the pyloric sphincter?
 3.
How does physical digestion occur in the stomach?
 4. What is chyme?
 5. What is gastric juice made of?
 6. What causes the low pH of the stomach environment?
 7. What are the 2 functions of this highly acidic environment?
 8.
What are the 3 reasons the proteins of the stomach cells are not digested by its gastric juices?
a.
b.
c.
 9. Why are few substances absorbed in the stomach? Exceptions: alcohol and aspirin so they get
into our bloodstream much faster than nutrients that are not absorbed until they are digested in
the small intestine.
 10. Read Thought Lab 6.2. “An Accident and an Opportunity” p. 221.
 11. What is the sound of your stomach growling? P. 222 FYI
The Small Intestine
p. 222
 Watch this clip: https://www.youtube.com/watch?v=Iyu6WSdpVQ that shows the digestion of food particles
in the small intestine, where nutrients (except fats)
are absorbed into the blood stream, sent to the liver
where they are processed, stored or rereleased into the
blood stream for use in the body.
 1. Why is small intestine described as small when it is longest part of the digestive tract?
 2. What is main function of small intestine?
 3. What are the 3 regions of the small intestine?
 4. Describe the duodenum and what happens there.
 5. Why is the surface area greatly increased in the small intestine?
 6. Using Fig. 6.17, draw and label small intestine ridges, villi and microvilli to show how the
surface area of the small intestine is greatly increased. Do the calculations in Biology File pg.
223.
 7. Why is there a capillary network in each villi? What does the vein and artery connected to this
network do (see Fig. 6.17 p. 222)?
 8. Why are their lots of mitochondria just below the microvilli (hint: nutrients are actively
transported across the microvilli membranes)?
 9. What happens in the jejunum?
 10. What happens in the ileum?
 11. Why are most of the digestive enzymes secreted into the small intestine rather than into the
stomach?
Accessory Organs: Liver, Gall Bladder and Pancreas
(Parts B, C, H on your Digestive System BLM 6.2.1)
 1. The pancreas delivers about 1L of pancreatic fluid to the duodenum each day composed of
enzymes and bicarbonate (HCO3--, often as NaHCO3). Complete the following table:
Enzymes in Pancreatic Fluid
Enzyme
Trypsin, chymotrypsin
(proteases)
Pancreatic amylase
(carbohydrase)
Lipase
Function
 2 . What is the function of bicarbonate in the pancreatic fluid?
 3. Where are bile salts produced and what is their function in digestion?
 4. What is the function of the gall bladder?
 Use Handouts “ Important Secretions of the Digestive System: Enzymes” and pg. 224 – 228,
BLM 6.2.7 “Absorption of Nutrients” to learn all of the following material. You may want to
draw your own flowchart.
Digestion and Absorption of Carbohydrates
1) Amylases break down the huge carbohydrate polymers starch (from plants) and glycogen (from
animals) into disaccharides: sucrose, maltose, and lactose, primarily in the small intestine (though
a small amount happens initially in the mouth).
2) Carbohydrases (sucrase, maltase, lactase) break the 3 disaccharides into their component
monosaccharides: glucose, fructose and galactose.
3) Monosaccharides are absorbed by active transport into the villi, then into the capillary in the
villi, and then directly to the liver, where all monosaccharides are converted to glucose.
Glucose is then circulated from the liver to where it is needed in the body. Excess glucose is
temporarily stored in the liver and muscle as glycogen til needed, when it is converted back to
glucose for energy use.
Digestion and Absorption of Proteins
1) Proteins are broken into small polypeptides and peptides by pepsin in the stomach.
2) Chymotrypsin and trypsin (proteases released into the small intestine in their inactive
form) are activated and then break down the small polypeptides from the stomach into small peptides.
Peptidases from the small intestine and pancreas complete digestion of peptides into amino
acids.
3) Just like glucose, the amino acids enter the villi by active transport, then into the villi blood
vessel to the liver where they are sent for use to the rest of the body.
1)
2)
3)
4)
Digestion and Absorption of Lipids
Arrival of lipids in the duodenum stimulates secretion of bile which emulsifies lipids into small
fat droplets that can be efficiently attacked by lipases.
Lipases then hydrolyze fats into glycerol and fatty acids.
Glycerol and fatty acids diffuse into villi, then reassemble into triglycerides, are coated with
proteins so they are soluble and can enter the lacteals (lymph vessels).
The lymph system carries the coated triglycerides to the chest area where they are converted back
to glycerol and fatty acids in the blood stream and to body cells that need them.
Learning Check!  Two main differences in the digestion and absorption of fats is how they enter the cells
of the intestinal wall (___________________ ), and what type of vessel they enter (__________________
_______________________) when compared to digestion of carbohydrates and proteins.
Digestion and Absorption of Nucleic Acids
1) DNA and RNA are digested in the small intestine by nucleases to nucleotides. The nucleotides are
broken down by nucleosidases into the 4 bases (A, T , G, C), sugars and phosphates.
2) Just like glucose and amino acids, the bases, sugars and phosphates enter the villi and its
capillaries by active transport.
3)
Hormonal Control of Digestion p. 230
The digestive tract is coordinated by the nervous system and the endocrine (hormonal) system. This control
is important for maintaining internal equilibrium in living systems. Read pg. 230 then using a flow chart
show how the hormone gastrin acts in the stomach in terms of protein digestion and HCl.
1. What do we mean by a negative feedback mechanism? Use the example of gastrin and HCl
pg. 230.
The Large Intestine p. 230
The material that remains in the small intestine after nutrients are absorbed enters the last part of the
digestive system : the large intestine.
1. Why is it called LARGE if it is so much smaller that the small intestine?
2. Does digestion occur in the large intestine?
3. What is the main function of the large intestine?
4. What is absorbed by the large intestine?
5. Billions of anaerobic intestinal bacteria are in the large intestine (colon). What are the two
things they do for us?
6. What is the role of the rectum?
6.3 Health and Digestive System Disorders p. 233
Learning Check: Briefly: define and discuss causes and treatments of the following disorders:
 1. Stomach: ulcers
 2. Inflammatory Bowel Disease: (new treatment may be establishing healthy microflora ecosystem).
a) Ileum (usually): Crohn’s Disease
b) Colon: Colitis
 3. Liver:
a) Hepatitis
b) Cirrhosis
c) Gallstones