Transcript Digestive System

Digestive System
Humans as Heterotrophs
Hetero=another Trophe= nutrition
• As heterotrophs we cannot create carbon, therefore we need to ingest
carbon in our food.
• All of our cells require nutrition for;
1) Growth
2)Repair
3) Maintenance
Functions of the Digestive System
1. Break down of food into nutrients.
2. Nutrients absorbed in the body.
3. Transported throughout the circulatory
system.
Nutrients in the cell can be used as a
source of energy
OR
Used for the synthesis of chemical
compounds
Stages of the Digestive System
1. Ingestion: taking in nutrients,
eating/drinking.
3. Absorption: taking up
of digested molecules
4. Egestion: removal of
waste.
2. Digestion: breaking down complex
molecules into smaller ones.
1. Ingestion
• Ingestion occurs when food enters the mouth.
• It is mechanically broken down by teeth.
Question: Is this a form of digestion?
What’s wrong with
this?
1. Ingestion
 Chewing stimulates the release of saliva from
the salivary organs.
 Saliva contains a mixtures of water, mucus and
enzymes.
1. Ingestion: Amylase
• Enzyme that breaks starch down into simple
sugars.
1. Ingestion:Bolus
• Food that has been chewed and mixed with
saliva becomes a bolus.
 The epiglottis, a flap of skin
directs food down the
esophagus.
1. Ingestion: Peristalsis
• When the bolus has entered the esophagus
muscle contractions called peristalsis move it
towards the stomach.
2. Digestion:Stomach
• Mechanical and chemical digestion occur in
the stomach.
• The stomach is J-shaped, it stores food, and
has a capacity of 1.5 L
2. Digestion: Sphincters
• Food enters and exits the stomach
through sphincters.
• Sphincters are muscles surrounding a
tube-like structure
• The bolus enters the stomach when the
esophageal sphincter relaxes.
2. Digestion: Gastric Juice
• The stomach contains gastric juice secreted by
the stomach lining.
• Gastric juice contains a mixture of:
HCl (hydrochloric acid)
Enzymes
Mucus
2. Digestion: Gastric Juice
• HCL
Breaks down fibres &
Bacteria
• Mucus
Protect stomach lining
from HCL
Why?
• If stomach lining is
destroyed ulcers form.
2. Digestion
• The stomach absorbs:
 Water
 Alcohol
 Some medications (Aspirin)
Chief Cells
• Gastric chief cells found in the
stomach produce pepsin, which
breaks down large proteins into
peptides.
• Replaced every 2-4 days.
Parietal Cells
• Stomach cells found in the glands.
• Secrete gastric acid.
• HCl acid secreted by active
transport in the stomach.
2. Digestion: Chyme
• Chyme travels out of the stomach by the
pyloric sphincter into the small intestine.
• Chyme is a mixture of:
Water
Digested food
Gastric Juices
2. Digestion: Small Intestine
• After the pyloric sphincter
chyme enters the duodenum
• 7m in length, 2.5cm in
diameter.
• Duodenum is first 25cm of the
small intestine.
2. Digestion: Duodenum
• Majority of digestion
occurs here.
• Secretions from
pancreas and
gallbladder enter the
duodenum via a duct.
2.Digestion: Liver
• Has four functions in digestion:
1. Synthesis
2. Breakdown
3. Detoxification
4. Storage
Liver: Synthesis
• Produces bile which breaks
down fats.
• Bile is stored in the
gallbladder
Gallbladder
• Organ
• Stores bile before it is
released in the small
intestine.
• Bile aids in the digestion
of lipids.
Synthesis: Bile
• Bile is an emulsifier (a
compound used to mix
immiscible substances)
• This allows for the
breakdown of fats and for
travel through the digestive
system.
Detoxification
• Removes toxins from the
body including
Alcohol
Chemicals
Storage
• Vitamins and carbohydrates (as glycogen) are stored in the liver.
Pancreas
• Increases the pH of chyme
from 2.5 to 9 due to the
production of sodium
bicarbonate, which is an
alkaline (base)
• Secretes enzymes for
digestion
Lipase (fats)
Trypsin (proteins)
Small Intestine
• Secretes
Maltase (maltose - >
glucose)
Peptidase (protein
breakdown)
• Duodenum (beginning),
Jejunum (middle), Ileum (end).
Overall: Food & Enzymes
• Carbohydrates -> Glucose
(amylase & maltase & lactase)
• Proteins -> Amino Acids
(pepsin & peptidase)
• Fats (triglycerides) -> Fatty Acids & Glycerol
(bile & lipase)
3. Absorption
• The jejunum and ileum contain villi (finger like
projections) which increase the surface area.
• The villi help with absorption of
Glucose
Amino Acids
Fatty Acids
Glycerol
3. Absorption
• Once nutrients are
absorbed through the
villi they enter the
bloodstream and are
dispersed throughout
the body.
Capillaries
• Small blood vessels.
• Transports
monosaccharides,
amino acids, and water
throughout the
bloodstream.
• Are a component of the
stomach, the large, and
small intestine.
Lymphatic Vessels
• Absorb fatty acids and
monoglycerides and
transports them to the
bloodstream.
• Why necessary?
3. Absorption:
Large Intestine
• Water absorption
• Bacteria living in colon
releasing Vitamin K & B,
also absorbed.
Rectum and Anus:
4. Egestion
• The rectum stores and
compacts waste.
• Cellulose aids in the
ejection of material from
the bowels. It is the main
source of our dietary fibre.
• Lack of cellulose in the
diet can lead to colon
cancer.
Digestive System
• The entire process takes 24-36 hours.