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.
4 Steps of Heterotrophic Nutrition
1) ___________________
• eating or drinking
• Heterotrophs need:
– Sugars
– Amino Acids
– Fatty Acids
– Glycerol
– Minerals
– Vitamins
2) ___________________
• Breakdown of macromolecules into smaller ones that can be
absorbed by the cells
• ______________-- chewing
• ______________-- digestive enzymes
Carbs ---------------------------
Fats -----------------------------
Proteins ------------------------
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3) ___________________
• Nutrients are absorbed into the blood
Digested monomers
Water
Minerals
Vitamins
4) ___________________
• Elimination of undigested material
• poo
Parts
ORGANS
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GLANDS
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Labeling of the Digestive System – Know these parts!
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Mouth
• Hard Palate
• hard part of roof of mouth
• Soft Palate
• back of roof of mouth
• ______________
• chamber in throat where:
nasal cavity and mouth meet
esophagus and trachea meet
• Mucus Membranes
• lubricates walls of mouth for easy passage of food
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
 Composition of Saliva
• Water
– moistens food
• Amylase (ptyalin)
– begins STARCH digestion
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• Mucin
– lubricant
– binds food together for easier swallow
 Control of Salivary Secretions
• __________________________
– food in the mouth
• __________________________
– Brain thinking of food in the mouth
– Signal sent to salivary glands from the brain
– Mmmmmmm. Fooooood….
Pharynx
 Throat
 Common tube through which both ________ and ________ pass
 Four openings
• ____________
• ____________
• ____________
• ____________
 Contains a flap of tissue called the _____________________
• This prevents food from entering the trachea
Esophagus
 Hollow muscular tube
 Connects ______________ to the __________________
What makes the food go to the stomach?
 Movement of food by ______________________
• rhythmic waves of contraction and relaxation of muscular walls
• food is squeezed through esophagus into stomach
 Epiglottis and uvula shunt food into esophagus during swallowing
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 Structure
• thick walled and muscular
• from pharynx to stomach
• walls contain mucus glands which secrete mucin
ò mucin lubricates food for easy passage.
Stomach
 A hollow muscular pouch
 Located high in the abdominal cavity, just under the diaphragm
 The esophagus connects to the stomach by the __________________.
Heartburn
• muscular ring surround esophagus at this point
• acts like a valve to _______ and __________ the tube
• keeps the food from falling out of your stomach when standing
on your head
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 FUNCTIONS
• temporary storage of food
• liquefaction of food
• __________________________________
Secretions -- Gastric Juice
 Secreted into the stomach cavity by stomach cells
• churning of the stomach mixes juice with food
 Contains
• ______________________________________
ò pH of 1-2
ò destroys bacteria present in food
ò liquefies food.
• ______________________________________
– 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 ____________________
• which is converted into the active form by the low
pH.
• This protects the cell from self-digestion
– stomach lined with mucus coating
– prevents acid and protein digesting enzymes from
damaging wall
– when food is liquefied it is called ____________.
– squirted into small intestine through the _____________________
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Small Intestine
 About 6 meters long
• Three sections
1) _______________
• first 25 cm
• digestion
2) _______________
• next 2 meters
• absorption
3) _______________
• next 4 or 5 meters
• absorption
FUNCTION
• complete the ______________ of food
• _____________the nutrients into the circulatory system (blood)
• important secretions from the ___________ and the ________
• Secretions -- Pancreatic Fluid
• Contains
• _____________________________
• raises pH to 8
• _____________________________
• an enzyme which continues the digestion of starch into
maltose units
• _____________________________
• enzyme digesting lipids into fatty acids & glycerol
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• _____________________________
• enzymes which continue protein digestion
• also secreted in inactive forms
• activated by alkaline pH
LIVER and GALLBLADDER
• The __________ produces bile
• brown fluid
• bile is stored in the __________________
• when fats enter the small intestine, the ___________ contracts
and squirts bile into the _________________
• bile
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.
• All types of foods are acted upon.
 digestion of
and
is completed by
enzymes produced by the small intestine
• sucrase
– digests _______________
• maltase
– digests _______________
• lactase
– digests _______________
• aminopeptidase
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– breaks down __________________________
 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 _______________
• each villus is actually covered with millions of _____________
• the villi and microvilli increase _________________________
for absorbing food molecules into blood.
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Absorption in the Small Intestine
Digested Nutrient
Product
Method of
Site of Absorption
absorption
 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
 Material NOT absorbed by this point will enter the _____________
through another sphincter – the ilial-caecal sphincter
 The caecum is a small pouch at the beginning of the large intestine.
• contains a small projection called the ______________ this is a
___________ organ which functions in cellulose digestion in
some herbivorous mammals
Functions of the Large Intestine
 absorb __________ into blood
 absorb ___________ and minerals into blood
 eliminate __________________from digestive tract
 Some bacteria live in the large intestine of mammals
ò they digest material that we are not able to digest
 a byproduct of this activity results in the synthesis of vitamins
ò Vitamin K
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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
_________.
 rectal veins are found near opening
ò if they get inflamed…
ò
the inside diameter of anus decreases
ò passage of feces is difficult and painful
ò called
or
.
What About Fiber???
 fiber in the diet serves to __________________throughout the
digestive tract resulting in soft feces.
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1 = ________________
2 = ________________
3 = ________________
4 = ________________
5 = ________________
6 = ________________
7 = ________________
8 = ________________
9 = ________________
10 = _______________
Control of Digestive Secretions
Saliva
 Nervous
• Pavlov
• Sight, smell, presence, or even thought of food stimulates
____________________
• results in the production of ______________
Gastric Juice
 Nervous
• Stimulation of vagus nerve also stimulates cells of stomach to
begin producing _____________
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 Hormonal
• Gastrin (a hormone) is released from certain upper stomach
cells _____________________
• 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.
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
Liver & Gall Bladder
 Hormonal
• Presence of __________ in the S.I. causes the cells of the
______________ to secrete the hormone _____________ into
the blood.
• This causes the gall bladder to ___________, propelling bile
into the duodenum through the ________________.
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FUNCTIONS OF THE LIVER
 largest organ in the body
 receives blood from 2 supplies
•
– oxygen rich blood from heart
•
– 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
1) ____________________________
• Production of bile which emulsifies fats
2) ____________________________
• 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
3) _______________________________
• destroys old RBC’s
• the pigment is excreted in bile
• the iron is stored for future RBC’s
4) _______________________________
• manufactures important blood proteins
– fibrinogen
– albumin
– globulin
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5) _____________________________
• vitamin B12
• fat-soluble vitamins
• iron
6) __________________________
a. liver breaks down poisons and non-food substances in blood
b. e.g.: alcohol, caffeine, nicotine, drugs, excess hormones
7) __________________________
a. deamination (breakdown) of excess amino acids
b. production of urea
i. excreted in urine
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Secretions
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