Download Digestive System

Biology 20
Digestive System
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DIGESTIVE SYSTEM

HETEROTROPHIC NUTRITION
 Unable to manufacture food from inorganic
molecules.
 Depend on autotrophs.

AUTOTROPHIC NUTRITION
 Organisms capable of synthesizing organic
molecules from simple inorganic material.
 Types: photosynthesizers and
chemosynthesizers.
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4 Steps of Heterotrophic Nutrition
1) Ingestion
• eating or drinking
• Heterotrophs need:
– Sugars
– Amino Acids
– Fatty Acids
– Glycerol
– Minerals
– Vitamins
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4 Steps of Heterotrophic Nutrition
2) Digestion
• Breakdown of macromolecules into smaller
ones that can be absorbed by the cells
– Mechanical -- chewing
– Chemical -- digestive enzymes
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4 Steps of Heterotrophic Nutrition
3) Absorption
• Nutrients are absorbed into the blood
– Digested monomers
– Water
– Minerals
– Vitamins
4) Egestion
• Elimination of undigested material
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Parts

Organs
•
•
•
•
•
•
•
Mouth
Pharynx
Esophagus
Stomach
Small Intestine
Large Intestine
Rectum

Glands
•
•
•
•
Salivary Glands
Pancreas
Liver
Gall Bladder
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Order of Events
Order of Events
Digestive System
•Overview – Labeling of the
Digestive system!
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Digestive
System
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Mouth

Hard Palate
• hard part of roof of mouth

Soft Palate
• back of roof of mouth

Pharynx
• chamber in throat where
– nasal cavity and mouth meet
– esophagus and trachea meet

Mucus Membranes
• lubricates walls of mouth for easy
passage of food
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Mouth

Purpose
• Mechanical digestion by teeth and tongue
– increases surface area for action by enzymes
– Mixes food thoroughly
• Chemical digestion by enzymes in saliva

Secretions
• Saliva
– 1 to 2 liters per day
– from 3 pairs of glands in the mouth
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Salivary Glands
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Mouth

Composition of Saliva
• Water
– moistens food
• Amylase
– begins STARCH digestion
• Mucin
– lubricant
– binds food together for easier swallow
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Mouth

Control of Salivary Secretions
• Mechanical pressure
– food in the mouth
• Nervous system
– Brain thinking of food in the mouth
– Signal sent to salivary glands from the brain
– Mmmmmmm. Fooooood….
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Order of Events
Pharynx
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Pharynx
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Pharynx
Throat
 Common tube through which both air
and food pass
 Four openings

• Nasal Cavity
• Trachea

Mouth Cavity
Esophagus
Contains a flap of tissue called the
EPIGLOTTIS
• This prevents food from entering the
trachea
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Order of Events
Esophagus


Hollow muscular tube
Connects pharynx to the stomach
What makes the food go to the stomach?

Movement of food by peristalsis
• rhythmic waves of contraction and relaxation of
muscular walls
• food is squeezed through esophagus into stomach
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Peristalsis
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Peristalsis
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Esophagus


Hollow muscular tube
Connects pharynx to the stomach
What makes the food go to the stomach?

Movement of food by peristalsis
• rhythmic waves of contraction and relaxation of
muscular walls
• food is squeezed through esophagus into stomach

Epiglottis shunt food into esophagus during
swallowing
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Esophagus

Structure
• thick walled and muscular
• from pharynx to stomach
• walls contain mucus glands which
secrete mucin
– mucin lubricates food for easy passage
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Order of Events
Stomach
a hollow muscular pouch
 located high in the abdominal cavity,
just under the diaphragm
 The esophagus connects to the
stomach by the cardiac sphincter.
Heartburn

• muscular ring surround esophagus at this
point
• acts like a valve to open and close the
tube
• keeps the food from falling out of your
stomach when standing on your head.
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Stomach
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Stomach

FUNCTIONS
• temporary storage of food
• liquefaction of food
• beginning of protein digestion
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Secretions -- Gastric Juice

Secreted into the stomach cavity by
stomach cells
• churning of the stomach mixes juice with
food

Contains
• Hydrochloric Acid – HCl(aq)
– pH of 1-2
– destroys bacteria present in food
– liquefies food.
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Secretions -- Gastric Juice
• Pepsin
–an enzyme which begins protein digestion
• (proteins broken down into smaller chains)
But aren’t the stomach cells made of protein?
–Pepsin is produced and secreted in an
inactive form called pepsinogen
• which is converted into the active form by the
low pH.
• This protects the cell from self-digestion
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Stomach

stomach lined with mucus coating
• prevents acid and protein digesting
enzymes from damaging wall

when food is liquefied it is called
chyme.

squirted into small intestine through
the pyloric sphincter
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Stomach
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Small Intestine

About 6 meters long
• Three sections
1) Duodenum
• first 25 cm
• digestion
2) Jejunum
• next 2 meters
• absorption
3) Ileum
• next 4 or 5 meters
• absorption
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Small Intestine

FUNCTION
• complete the digestion of food
• absorb the nutrients into the circulatory
system (blood)
• important secretions from the pancreas
and the liver.
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Secretions -- Pancreatic Fluid

Contains
• NaHCO3 – sodium bicarbonate
– raises pH to 8
• Pancreatic Amylase
– an enzyme which continues the digestion of
starch into maltose units
• Lipase
– enzyme digesting lipids into fatty acids & glycerol
• Trypsin and Chymotrypsin
– enzymes which continue protein digestion
– also secreted in inactive forms
– activated by alkaline pH
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Small Intestine

LIVER and GALLBLADDER
• The liver produces bile
– brown fluid
• bile is stored in the gallbladder
• when fats enter the small intestine, the
gallbladder contracts and squirts bile into
the duodenum
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Small Intestine
• bile emulsifies fats
–physically breaks them down into
smaller drops
–Kaboom!!! Blows it up!!!
–greater surface area
for action by lipase
• bile is NOT an enzyme because it
does not cause a chemical change
in fat.
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Small Intestine

All types of foods are acted upon.
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Small Intestine

digestion of disaccharides and
dipeptides is completed by enzymes
produced by the small intestine
• sucrase
– digests sucrose
• maltase
– digests maltose
• lactase
– digests lactose
• aminopeptidase
– breaks down dipeptides into amino acids
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Small Intestine
once all food molecules are at
monomer stage, they are ready to be
absorbed into the circulatory system
 the inside of the S.I. is covered with
millions of tiny finger-like projections
called villi

• each villus is actually covered with
millions of microvilli
• the villi and microvilli increase surface
area for absorbing food molecules into
blood.
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Absorption in the Small Intestine
Digested
Nutrient
Product
Method of
Absorption
Site of
Absorption
Small Intestine
notice that glycerol recombines with 3
fatty acids to form a fat molecule
which enters the lacteal instead of the
capillary
 Why is fat completely digested and
then recombined to form a fat
molecule again?

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Large Intestine
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Large Intestine
Material NOT absorbed by this point
will enter the large intestine through
another sphincter – the ileal-caecal
sphincter
 The caecum is a small pouch at the
beginning of the large intestine.

• contains a small projection called the
appendix
– this is a vestigial organ which functions in
cellulose digestion in some herbivorous
mammals
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Functions of the Large Intestine

absorb water into blood

absorb vitamins and minerals into blood

eliminate undigested material from
digestive tract
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Large Intestine

Some bacteria live in the large
intestine of mammals
• they digest material that we are not able
to digest

a byproduct of this activity results in
the synthesis of vitamins
• Vitamin K
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Rectum & Anus
Rectum & Anus
last section of digestive tract
 rectum is a holding pouch for feces
 feces exits the digestive tract through
a sphincter muscle called the anus.
 rectal veins are found near opening

• if they get inflamed…
– the inside diameter of anus decreases
– passage of feces is difficult and painful
– called hemorrhoids or piles.
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What About Fiber???
 fiber
in the diet serves to retain
water throughout the digestive
tract resulting in soft feces.
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1 = Esophagus
2 = Stomach
3 = Small Intestine
4 = Pancreas
5 = Liver
6 = Large Intestine
7 =Large Intestine
8 =Large Intestine
9 = Large Intestine
10 = Rectum
Biology 20
Control of Digestive Secretions
Saliva

Nervous
• Pavlov
• Sight, smell, presence, or even thought
of food stimulates vagus nerve
• results in the production of saliva
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Gastric Juice
 Nervous
• Stimulation of vagus nerve also
stimulates cells of stomach to begin
producing gastrin
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Gastric Juice

Hormonal
• Gastrin (a hormone) is released from
certain upper stomach cells into the
bloodstream.
• gastrin circulates until it reaches the
lower stomach cells resulting in the
release of gastric juices.
• Once pH falls below 2, gastrin stops
being secreted.
• If pH rises above 2.5 gastrin secretion
begins again.
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Pancreatic Juice

Nervous
• presence of food in mouth and stomach
stimulates pancreatic secretions

Hormonal
• presence of chyme in the S.I. causes the cells of
the duodenum to secrete the hormone secretin
into the blood
• Secretin (a hormone) causes the pancreas to
begin producing pancreatic juice
• Pancreatic Juice will enter the duodenum
through the pancreatic duct.
• when acidic chyme becomes alkaline,
production of secretin stops
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Liver & Gall Bladder
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Bile

Hormonal
• presence of chyme in the S.I. causes the
cells of the duodenum to secrete the
hormone cholesystekinin into the blood.
• This causes the gall bladder to contract,
propelling bile into the duodenum
through the bile duct
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Biology 20
FUNCTIONS OF THE LIVER
Liver
largest organ in the body
 receives blood from 2 supplies

• hepatic artery – oxygen rich blood from
heart
• hepatic portal vein – nutrient rich blood
from intestinal walls

liver acts as a “gatekeeper” between
blood leaving intestines and blood
entering general circulation
• the liver removes excess nutrients
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Liver & Gall Bladder
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Functions of the Liver
1) Digestive Function
• Production of bile which emulsifies fats
2) Regulation of Blood Glucose
• removes excess glucose from blood after meal
and converts it to glycogen
• once glycogen stores are full, it converts extra
glucose into fat which is released from liver into
the blood and stored in adipose tissue
• when blood sugar levels fall, liver converts
glycogen back into glucose and releases it into
blood
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Functions of the Liver
3) Breakdown of Red Blood Cells
• destroys old RBC’s
• the pigment is excreted in bile
• the iron is stored for future RBC’s
4) Synthesis of Plasma Proteins
• manufactures important blood proteins
– fibrinogen
– albumin
– globulin
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Functions of the Liver

Storage
• vitamin B12
• fat-soluble vitamins
• iron

Detoxification
• liver breaks down poisons and non-food
substances in blood
• e.g.: alcohol, caffeine, nicotine, drugs, excess
hormones

Excretory Function
• deamination (breakdown) of excess amino acids
• production of urea
– excreted in urine
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