Download 1Digestive System

Digestive System
http://www.youtube.com/watch?v=0gY-zXsUYgs
 As heterotrophs we cannot convert carbon
therefore we ingest carbon in our food.
Humans as
Heterotrophs
Hetero=another
Trophe= nutrition
 All of our cells require nutrition for;
1) Growth
2) Repair
3) Maintenance
1. Break down of food into nutrients.
2. Nutrients absorbed in the body.
Functions of
the Digestive
System
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
2. Digestion
3. Absorption
4. Egestion
 Ingestion occurs when food enters the mouth.
 It is mechanically broken down by teeth
1. Ingestion
 Chewing stimulates the release of saliva from
the salivary organs.
1. Ingestion:
Cont.
 Saliva contains a mixtures of water, mucus and
enzymes.
 Enzyme that breaks starch down into simple
sugars.
1. Ingestion:
Amylase
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.
 When the bolus has entered the esophagus
muscle contractions (peristalsis) move it
towards the stomach.
1. Ingestion:
Peristalsis
 Digestion occurs initially in the stomach.
2. Digestion:
Stomach
 The stomach is J-shaped, it stores food, and
has a capacity of 1.5 L
 Food enters and exits the stomach through
sphincters.
 Sphincters are muscles surrounding a tube-like
structure
2. Digestion:
Sphincters
 The bolus enters the stomach when the cardiac
sphincter relaxes.
 The stomach contains gastric juice secreted by
the stomach lining.
 Gastric juice contains a mixture of:
HCL (hydrochloric acid)
2. Digestion:
Gastric Juice
Enzymes
Mucus
 HCL
 Breaks down fibres &
Bacteria
2. Digestion:
Gastric Juice
 Mucus
Protect stomach lining
from HCL
 If stomach lining is
destroyed ulcers form.
Heliobacter
pylori
 The stomach absorbs:
 Water
 Alcohol
2. Digestion
 Some medications (Aspirin)
 Chyme travels out of the stomach by the
pyloric sphincter into the small intestine.
 Chyme is a mixture of:
 Water
 Digested food
2. Digestion:
Chyme
 Gastric Juices
2. Digestion:
Small
Intestine
 After the pyloric sphincter
chime enters the duodenum
 Duodenum is first 25cm of the
small intestine.
 7m in length, 2.5m in
diameter.
2. Digestion:
Duodenum
 Majority of digestion
occurs here.
 Secretions from
pancreas and duodenum
enter via a duct.
 Has four functions in digestion:
1. Synthesis
2. Breakdown
2.Digestion:
Liver
3. Detoxification
4. Storage
 Produces bile which breaks down fats.
 Bile is stored in the gallbladder
Synthesis
1. 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.
 Gallstones occur when too much bile or
concentrated bile is produced in the
gallbladder.
1. Synthesis:
Gallstones
 The bile will crystalize into gallstones blocking
the gallbladder.
2. Breakdown
 Process of removing
Nitrogen group from
Amino Acids to create
urea.
 When there is a blockage of the
gallbladder Jaundice can occur (yellowing
of the skin).
2. Breakdown:
Jaundice
 Removes toxins from the body including
Alcohol
Chemicals
3. Detoxification
4. Storage
 Vitamins and carbohydrates are stored in the liver.
 Increases the pH of chyme
from 2.5 to 9 due to the
production of sodium
bicarbonate.
Pancreas
 Secretes enzymes for
digestion
Lipase (fats)
Trypsin (proteins)
Small Intestine
 Secretes
Maltase (maltose - > glucose)
Peptidase (protein
breakdown)
 Duodenum (beginning),
Jejunum (middle), Ileum (end).
 Carbohydrates -> Glucose
(amylase & maltase)
Food &
Enzymes
 Proteins -> Amino Acids
(pepsin & peptidase)
 Fats (triglycerides) -> Fatty Acids & Glycerol
(bile & lipase)
 The jejunum and ileum contain villi (finger like
projections) which increase the surface area.
 The villi help with absorption of
3. Absorption
Glucose
Amino Acids
Fatty Acids
Glycerol
 Once nutrient are absorbed through the villi
they enter the blood stream and are dispersed
throughout the body
3. Absorption
Digestive System
3. Absorption:
Large Intestine
 Water absorption
 Bacteria living in colon
releasing Vitamin K & B,
also absorbed.
4. Egestion
 Cellulose aids in the
ejection of material from
the bowels.
 Lack of cellulose in the diet
can lead to colon cancer.
Digestive
System
 The entire process takes 24-36 hours.
Homeostasis
 The ability of the body
to regulate according
to the fluctuating
internal and external
environment
Digestion &
Homeostasis
 Nervous and
hormonal system aid
digestion before we
eat.
 Seeing, smelling and
tasting food
stimulates
production of gastric
secretions.
 Swallowing stimulate the production of gastric
juices.
 Gastrin (hormone) stimulates the release of gastric
juice before food arrives.
Digestion &
Homeostasis
Cont.
Speed of Digestion:
Digestion
 Large meals with digest quickly due to strong
stomach contractions and faster emptying.
 Fatty meals slow down digestion due to a
hormone response from the small intestine.
 Receptors in the body sense:
Blood Sugar levels
Homeostasis
Body T
Oxygen level
 Disruption in homeostasis -> Signal to brain for
correction
 Blood Sugar
Concentration crucial to well being
Too low body shuts down (coma)
 Eating increases blood sugar (glucose)
Homeostasis:
Blood Sugar
 Body releases insulin from pancreas to bring
glucose inside cells.
 Extra glucose taken by liver cells and convert to
glycogen and stored.
Homeostasis:
Blood Sugar
food
Homeostasis:
Blood Sugar
 Decrease in blood
sugar pancreas will be
activate to release
glucagon
 Glucagon (hormone)
will convert glycogen
(in liver), back to
glucose, which will be
released into the
blood.
insulin
release
(pancreas)
cells take up excess
glucose, liver makes
glycogen
high
glucose
normal
glucose
normal
glucose
low glucose
glycogen
release
as glucose
(liver)
glucagon
release
(pancrea
s)