Download 6.1 Digestion

Digestion
From food to poo
Crash Course VIDEO:
http://www.youtube.com/watch?v=s06XzaKqELk
Small
molecules
Pieces
of food
Mechanical
digestion
Chemical digestion
Nutrient
(enzymatic hydrolysis) molecules
enter body
cells
Undigested
material
Food
INGESTION
DIGESTION
ABSORPTION
ELIMINATION
IB Learning Objective
• Explain why digestion of large food molecules is
essential
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The Need for Digestion
Two reasons for the digestion of food:
1. Change food into useable forms:
–
Food that humans eat contain
substances made by other organisms.
Manu of which are not suitable for
human tissue.
–
Thus the must be broken down and
changed into useful forms
–
Example:
Proteıns amıno acıds dıfferent proteıns
The Need for Digestion
Two reasons for the digestion of food:
2. Food molecules may be too big to be
absorbed:
–
Food molecules are absorb by the villi in
our small intestines.
–
Thus food molecules must be broken
down into small enough molecules that
they can be absorbed by:
•
Simple diffusion,
•
facilitated diffusion
•
or active transport.
IB LEARNING OBJECTIVE
• State the source, substrate, products and
optimum pH conditions for one amylase, one
protease and one lipase
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Three types of food molecules that must be
digested
1. Starch
2. Proteins
3. Triglycerides (Fats and Oils)
Enzymes of digestion
Amylase
Protease
Lipase
Example Salivary
of enzyme Amylase
Pepsin
Pancreatic
Lipase
Source
Wall of stomach Pancreas
Salivary
glands
Substrate Starch
Proteins
Triglyerides
(fats and oils)
Products
Maltose
Small Peptides
Fatty Acid and
glycerol
Optimum
pH
pH 7
pH 1.5
pH 7
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
IB Learning Objective
• Explain the need for enzymes in digestions
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Enzymes essential to digestion of food molecules
• Digestions of food molecules will happen naturally
at body temperature BUT very slowly
• Thus, ENZYMES are essential to speed up the
process.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
IB Learning Objective
• Outline the reasons for cellulose not being
digested in the alimentary canal.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Summary of digestion
• Some molecules cannot be digested (example:
Cellulose)
• The enzyme cellulase digest cellulose, but
humans lack the gene that codes for this enzyme.
• Undigested cellulose is an important part of
dietary fibre, which has beneficial effects on the
digestive system.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
IB LEARNING OBJECTIVE
•
Draw and Label a diagram of the digestive system. This diagram
should include the following structures and clearly show the
interconnections between these structures:
–
Mouth
–
Esophagus
–
Stomach
–
Small intestines
–
Large intestines
–
Anus
–
Liver,
–
Pancreas
–
Gall bladder
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Parts of the Digestive System
Mouth
Pharynx
Salivary
glands
Esophagus
Liver
Gallbladder
Stomach
Pancreas
Large intestine
Small intestine
Rectum
Sequence of digestion
– Food is digested as it
passes along the
alimentary canal from
mouth to anus.
– Food enters mouth,
moves into the
esophagus, the
stomach, next small
intestine, then large
intestine, and finally
anus.
Video Of Digestions
• http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2
6/animation__organs_of_digestion.html
• http://www.youtube.com/watch?v=bNMsNHqxszc
• FUNNY VIDEO:
http://www.youtube.com/watch?v=jsVgi8hoFFc
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Summary of digestion
• Longitudinal and circular muscle fibers along
the walls of the alimentary canal contract and
relax squeezing the food and breaking up large
solid lumps.
• Digestive juices release by salivary glands,
stomach and pancreas contain enzymes which
help break food molecules
LE 41-15b
Salivary
glands
Mouth
Esophagus
Gallbladder
Liver
Pancreas
Stomach
Small
intestines
Large
intestines
Rectum
Anus
A schematic diagram of the
human digestive system
IB LEARNING OBJECTIVE
• Outline the function of the stomach
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The Stomach Summary
• The Stomach
• Food from the esophagus empties into the
stomach.
• The stomach continues mechanical and
chemical digestion.
• Alternating contractions of three smooth
muscle layers churn food.
Stomach
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Function of Stomach Summary
– Mechanical Digestion
• The stomach contracts to churn fluids and
food, gradually producing a mixture known
as chyme.
• After 1–2 hours, the pyloric valve between
the stomach and small intestine opens and
chyme flows into the small intestine.
The Stomach Summary
– Chemical Digestion
• The stomach lining has millions of gastric
glands that release substances into the
stomach.
– Some glands produce mucus, which
lubricates and protects the stomach wall.
– Other glands produce hydrochloric
acid, which makes the stomach contents
very acidic.
– Other glands produce pepsin, an
enzyme that digests protein.
Interior surface of stomach
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Function of Stomach
• Before food reaches the stomach, gastric juices
are being secreted, as a result of a involuntary
reflex action.
• When food enters the stomach more gastric
juices are released.
Function of Stomach
• When food enters the stomach a hormone gastrin
is released.
• Gastrin signals for the stomach to increase the
amount of hydrochloric acid (HCl) in the
stomach
• The pH of the stomach is about 3 (very acidic)
when food enters
Function of Stomach
• Bacteria which could cause food poisoning, are
most killed by acid conditions.
Enzymes released by stomach.
• Enzyme released by stomach is pepsin.
• Pepsin functions has an optimum pH of 1.5 (very
acid).
• Pepsin digests proteins.
Pepsin vs. Pepsinogen
• Since pepsin digests proteins, it could be harmful
to the cell of the glands that secrete them.
• They are therefore secreted as an inactive precursors called Pepsinogen.
• Pepsinogen is an inactive form of pepsin.
• Pepsinogen becomes pepsin when it is released
in the hydrochloric acid (HCl) of the stomach
LE 41-17
Structure of stomach
Esophagus
Cardiac orifice
Stomach
5 µm
Pyloric sphincter
Interior surface of stomach
Small
intestine
Folds of
epithelial
tissue
Epithelium
Pepsinogen
Gastric gland
Pepsin
(active enzyme)
HCl
Pepsinogen and HCl
are secreted into the
lumen of the stomach.
HCl converts
pepsinogen to pepsin.
Pepsin then activates
more pepsinogen,
starting a chain
reaction. Pepsin
begins the chemical
digestion of proteins.
Mucus cells
Chief cells
Parietal cells
Chief cell
Parietal cell
IB LEARNING OBJECTIVE
• Outline the function of the small intestine
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Function of the Small Intestine
• The small intestine is the longest section of the
alimentary canal
• It is the major organ of digestion and absorption
LE 41-19
Liver
Bile
Gallbladder
Stomach
Acid chyme
Intestinal
juice
Pancreas
Duodenum of
small intestine
The Small Intestine
• As chyme from the stomach is pushed
through the pyloric valve, it enters the
duodenum.
• The duodenum is the first of three parts of
the small intestine, and is where most
digestive enzymes enter the intestine.
The Small Intestine
• Accessory Structures of Digestion
Liver
Bile duct
Gallbladder
Pancreas
Duodenum
Pancreatic
duct
To rest of small
intestine
The Small Intestine
– Accessory Structures of Digestion
• Just behind the stomach is the pancreas.
The Small Intestine
• During digestion, the pancreas:
• produces enzymes that break down
carbohydrates, proteins, lipids, and
nucleic acids.
Enzymes of the Pancreas
• Amylase – completes breakdown of
starches into maltose
• Protease – completes the breakdown of
small polypeptides (proteins) to amino acids
• Lipase – converts fat to glycerol and fatty
acids
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Pancreas
• Pancreas also produces sodium
bicarbonate, a base that neutralizes
stomach acid so that these enzymes can be
effective.
• Sodium bicarbonate is released into the
duodenum of the small intestine right after
chyme enters it from the stomach.
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LIVER
• Assisting the pancreas is the liver, which
produces bile.
• Bile dissolves and disperses droplets of
fat in fatty foods. This process is called
emulsification
• Emulsification increases surface area
of lipid droplets
• This enables enzymes (lipase) to
break down smaller fat molecules.
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Liver – Bile -- Digestion of Lipids
• Bile is stored in the gallbladder.
– and released into the small intestines.
– Lipid molecules tend to bond together
and are only accessible to lipase
(enzyme) at the lipid–water interface/
boundary.
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Parts of the small intestines
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Absorption in the Small Intestine
• The small intestine is
adapted for the
absorption of nutrients.
• Most absorption occurs in
the ileum of the small
intestine
IB LEARNING OBJECTIVE
• Explain the structure of the villus is related to its
role in absorption and transport of products of
digestions
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Absorption in the ileum of the Small Intestine
• The folded
surfaces of the
ileum are covered
with fingerlike
projections called
villi.
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Ileum
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Absorption in the Small Intestine
• The Small Intestine
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Relationship between structure of villus and its
function
• Villi increase surface area over view food is
absorbed
• An epithelium consists of only one layer of cells,
which is all that food have to pass through in order
to be absorbed
• Protrusions of exposed plasma memebrance of
the epithelium called microvilli, increase surface
area for absorption.
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Absorption in the Small Intestine
• The Small Intestine
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Relationship between structure of villus and
its function
• Cell surfaces of villi have more
projections called microvilli.
• These provide an enormous surface
area for the absorption of nutrient
molecules.
• Slow, wavelike contractions of
smooth muscles move the chyme
along this surface.
Relationship between structure of villus and its
function
• Protein channels and pumps in
microvilli allow for rapid absorption of
food by facilitated diffusion and active
transport
• A lot of mitochondria in epithelium
cell need for ATP in active transport.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Relationship between structure of villus and its
function
• Blood capillaries inside villus
are very close to epithelium
so the distance for diffusion of
food is very small.
• A lacteal (lymph vessel) in
the centre of villus carries fat
away after digestion.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Relationship between structure of villus and its
function
• There are many pinocytic vesicles near the
microvilli.
• Pinocytic vesicles are formed by endocytosis
• Each vesicles are formed from plasma
membrane and so contain both:
– Protein channels for facilitated diffusion
– Protein pumps for active transport
• Digested food can be absorbed from vesicles into
the cytoplasm of cells
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Small Intestine
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Ileum of the small intestines
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IB LEARNING OBJECTIVE
• Outline the function of the large intestine
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Large Intestine
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The Large Intestine
• The Large Intestine
• When the chyme leaves the small intestine,
it enters the large intestine, or colon.
• The large intestine removes water from the
chyme.
• Water is absorbed quickly, leaving
undigested materials behind.
• Concentrated waste material passes
through the rectum and is eliminated from
the body.
• The colon houses strains of the bacterium
Escherichia coli, some of which produce vitamins