Download Digestion2

Thursday, January 14th, 2010
DAILY QUIZ #1
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You will need a sheet of lined paper + pen/pencil
Clear off desk
Put up a binder/text between person next to you
Put your NAME & PERIOD at the top of sheet
Daily Quiz #1
1-1
1. a) This nutrient is used in our bodies as a quick
source of energy.
b) Give one food source you can obtain it from.
2. Give one reason for chewing.
3. What is the function of salivary amylase?
4. Give one example of how your body ensures that
a food bolus enters the esophagus.
5. What is the term used to describe the rhythmic
contractions of the esophagus?
Daily Quiz #1
1-2
1. a) This nutrient is used in our bodies as enzymes.
b) Give one food source you can obtain it from.
2. Give one example of mechanical digestion.
3. Why is the phrase “Salivary amylase digests
disaccharides” incorrect?
4. Give one example of how your body ensures that
a food bolus enters the esophagus.
5. What is the term used to describe the rhythmic
contractions of the esophagus?
Daily Quiz #1
1. a) This nutrient is used in our bodies as a
“cushion” for our organs.
b) Give one food source you can obtain it from.
2. Where does chemical digestion FIRST occur?.
3. What does salivary amylase digest?
4. Can you breathe while swallowing? Explain.
5. What is the term used to describe the rhythmic
contractions of the esophagus?
1-4
http://lamscience.shawwebspace.ca
The Digestive System …cont’d
Thursday, January 14th, 2010
Esophagus  Stomach
• Food bolus travels down esophagus
 arrives at cardiac sphincter (muscles
around opening to stomach)  valves
that open when relax & close when
contract
 normally, this sphincter prevents food
from moving up out of stomach, but when
vomiting occurs, a reverse peristaltic wave
causes the sphincter to relax and contents
of stomach are propelled outward
The Stomach
• a thick-walled, J-shaped organ that lies on left side of
the body beneath the diaphragm
• can stretch to hold 2-4L of solids/liquids in an average
adult (baby stomach holds 60 mL, cow stomach holds
300L)
• 2 sphincter muscles:
cardiac (closer to heart)
and pyloric sphincter
( into small intestine)
The Stomach
• 3 layers of muscle contract to churn and mix contents
• pacemaker cells at top
of stomach stimulate
contractions at rate of
3/minute  fuller the
stomach, the more
peristalsis
http://www.mhhe.com/biosci/genbio/espv2
/data/animals/008/index.html
Cells of Stomach Lining
• the mucus lining of the stomach contains inner GASTRIC
GLANDS which produce GASTRIC JUICE .
• 3 types of stomach cells:
Mucus cells – secrete a
protective coat (mucus)
Parietal cells – secrete HCl
(pH 3) to kill bacteria and help
break food down
Peptic cells – secrete
pepsinogen
Protein Breakdown in the Stomach
In the presence of HCl, pepsinogen forms PEPSIN, a
HYDROLYTIC ENZYME that breaks down proteins
into smaller chains of amino acids called peptides.
(Note: peptides are further broken down into
individual amino acids by other enzymes later on)
pepsin
protein + H2O --------> peptides
Think About It
• Why doesn’t the stomach digest itself?
Why Doesn’t the Stomach Digest Itself?
1) Mucus layer prevents HCl from eating through
2) HCl not formed until it crosses the stomach
lining
3) Pepsin could digest protein in stomach cells, but
it is INACTIVE until mixes with HCl
Gastric Ulcers
• Lesions in the stomach lining
– Are caused mainly by the bacterium Heliobacter
pylori
Bacteria
1 µm
Mucus
layer of
stomach
http://www.medicine.uottawa.ca/students/MD/BlockOrientation/
assets/img/gastro/Gastric_Ulcer.jpg
Figure 41.18
Animations + Quizzes
• http://highered.mcgrawhill.com/classware/ala.do?isbn=0072956208&
alaid=ala_996429&showSelfStudyTree=true
Hydrochloric Acid Production… of the Stomach
Ch 41
• http://highered.mcgrawhill.com/classware/ala.do?isbn=0072956208&
alaid=ala_996426&showSelfStudyTree=true
Hormones ad Gastric Secretion Ch 41
Supplementary Articles
 Fat Vaccine
http://www.sciencentral.com/articles/view.php3?language=english&type=
&article_id=218392830
 Fat microbes
http://www.sciencentral.com/articles/view.php3?language=english&type=
&article_id=218392900
 Hunger hormone
http://www.sciencentral.com/articles/view.php3?language=english&type=
&article_id=218392440
 Fat and exercise
http://www.sciencentral.com/articles/view.php3?language=english&type=
&article_id=218392693
The Small Intestine
• Most of digestion (enzymatic hydrolysis of food) and
absorption of nutrients occur in the small intestine.
• About 6 m in length,
tapers from about 3cm in
diameter at the pyloric
sphincter to about 1.5-2 cm
at the ileocecal valve
(where joins large intestine)
The Small Intestine
Made up of 3 major sections:
Duodenum: 25-30 cm long,
receives food from stomach,
receives bile and pancreatic juice
through the common duct about
10 cm along from the stomach 
site of most active enzyme
production and digestion
Jejunum: 1-1.5 m long, has fewer
intestinal glands, more specialized
for absorption.
Ileum: 4-5 m long, produces no
enzymes but does most of the
absorption
The large surface area of the SI (about 300 m2) is the
result of several levels of folding:
The lining of the small intestine is not smooth:
• Circular folds in the submucosa slow the passage of
food and increase the area. They are covered with...
• Villi, millions of microscopic fingerlike projections
which are, in turn, covered with...
• Microvilli, tiny cytoplasmic projections from the
surface of individual columnar epithelial cells.
Circular folds  Villi  Microvilli
20
• The enormous microvillar surface is an adaptation that
greatly increases the rate of nutrient absorption
Microvilli
(brush border)
Vein carrying blood to
hepatic portal vessel
Blood
capillaries
Epithelial
cells
Muscle layers
Villi
Epithelial cells
Large
circular
folds
Lacteal
Key
Nutrient
absorption
Intestinal wall
Villi
Lymph
vessel
Figure 41.23
Structure of a Villus
1. An outer layer of columnar epithelial cells:
- some cells covered in microvilli for absorption
- some are glandular cells
which produce and release
enzymes or mucus into the
intestinal lumen
- some have digestive
enzymes bound to their
outer membrane
Structure of a Villus
2. A layer of blood
capillaries that absorb
the sugars and amino
acids and carry them
back towards the
mesenteric blood
vessels, the hepatic
portal vein and the
liver
Structure of a Villus
3. A small blind-ended
lymph vessel called
the lacteal that
returns fluids and
lipoprotein droplets
to the blood stream
Functions of the Small Intestine
1. Neutralize acidity of stomach contents with
bicarbonate from pancreas
2. Mechanically mix the chyme with pancreatic
juice, bile and intestinal secretions
3. Continue the breakdown of food
4. Absorb simple sugars and amino acids into
the blood by active transport (requires ATP)
Enzymatic Action in the Small Intestine
• The first portion of the small intestine is the duodenum
– Where acid chyme from the stomach mixes with digestive
juices from the pancreas, liver, gallbladder, and intestine itself
Liver
Bile
Gallbladder
Stomach
Acid chyme
Intestinal
juice
Pancreatic juice
Pancreas
Duodenum of
small intestine
Figure 41.19
Accessory Organ - Pancreas
• Produces proteases (protein-digesting enzymes)
that are activated once they enter the
duodenum
- Trypsinogen
 Trypsin
Pancreas
•
•
•
•
Peptidase
Amylase
Lipase
Nuclease
Membrane-bound
enteropeptidase
Inactive
trypsinogen
Other inactive
proteases
Figure 41.20
Lumen of duodenum
Trypsin
Active
proteases
Chemical Breakdown in the SI
• http://highered.mcgrawhill.com/classware/ala.do?isbn=0072956208&
alaid=ala_996426&showSelfStudyTree=true
Enzyme Action and the Hydrolysis of Sucrose
Brooker Ch 41
• Enzymatic digestion is completed as peristalsis
moves the mixture of chyme and digestive
juices along the small intestine
Protein digestion
Carbohydrate digestion
Oral cavity,
pharynx,
esophagus
Polysaccharides
(starch, glycogen)
Fat digestion
Nucleic acid digestion
Disaccharides
(sucrose, lactose)
Salivary amylase
Smaller polysaccharides,
maltose
Stomach
Proteins
Pepsin
Small polypeptides
Lumen of
small intestine
Polysaccharides
Pancreatic amylases
Maltose and other
disaccharides
Polypeptides
Pancreatic trypsin and
chymotrypsin (These proteases
cleave bonds adjacent to certain
amino acids.)
Smaller
polypeptides
DNA, RNA
Pancreatic
nucleases
Nucleotides
Pancreatic carboxypeptidase
Figure 41.21
Small peptides
Disaccharidases
Monosaccharides
Dipeptidases, carboxypeptidase, and aminopeptidase (These
proteases split
off one amino acid at a time, working from opposite ends of a
polypeptide.)
Amino acids
Bile salts
Fat droplets (A coating of
bile salts prevents small droplets from coalescing into
larger globules, increasing
exposure to lipase.)
Pancreatic lipase
Amino acids
Epithelium
of small
intestine
(brush
border)
Fat globules (Insoluble in
water, fats aggregate as
globules.)
Glycerol, fatty
acids, glycerides
Nucleotidases
Nucleosides
Nucleosidases
and
phosphatases
Nitrogenous bases,
sugars, phosphates
What happens to the food we eat?
Supplementary Reading
http://www.whfoods.com/genpage.php?tname
=faq&dbid=16#dig5
Absorption
• Occurs in the jejunum and to a lesser extent in
the ilieum
Absorption
• Amino acids and sugars
– Pass through the epithelium of
the small intestine and enter the
bloodstream
• Glycerol and fatty acids are
absorbed by epithelial cells
– Where they are recombined into
fats within these cells
• These fats are
then mixed with
cholesterol and
coated with
proteins
– Forming small
molecules
called
chylomicrons,
which are
transported
into lacteals
Figure 41.24
Fig. 41.13
Fig. 41.14
Fig. 41.14c
Fig. 41.14d
Fig. 41.14d
Learning Log
• describe how the small intestine is specialized
for chemical & physical digestion & absorption
• describe the structure of the villus, including
microvilli, & explain the functions of the
capillaries & lacteals within it
• relate specific digestive enzymes to their
glandular sources & describe the digestive
reactions they promote