Download The Digestive System

The Digestive System
Learning Outcomes
I will…
- describe the parts of the digestive system
- explain how enzymes work in the digestive
system
- explain the different ways food is
processed in the digestive system
(physically and chemically)
Literacy Outcome
I will…
- Create a story about the digestive system
explaining all the key aspects and players
involved
Components of Digestion
There are four components of the digestive process:
1. ingestion - taking nutrients in
2. digestion - breakdown of complex organic
molecules into smaller components by enzymes
3. absorption - transport of nutrients to the cells of the
body
4. egestion - removal of food waste from the body
Ingestion
This stage of digestion includes the oral cavity, salivary
glands, pharynx, esophagus, and stomach
Physical, or mechanical, digestion and chemical
digestion both occur during this stage
Physical: chewing food, churning of stomach
Chemical: enzymes, stomach acid (HCl)
Ingestion
The food enters the oral cavity through the mouth
where food is broken down by the teeth and tongue into
smaller pieces
The food at this stage is referred to as the bolus (ball)
Saliva
The salivary glands then spring into action and begin to
secrete saliva
Saliva contains an enzyme called amylase that breaks
down starches (complex carbs) to simple carbs
(chemical digestion)
Saliva dissolves food particles and allows us to taste
what we are eating
Saliva
How do we taste what we eat?
Magical sensory receptors called taste buds!
These taste buds are connected to nerve cells that relay
the chemical information from the food to you brain
allowing you to say “Hey, that is really sour!”
Saliva
Saliva
It used to be said that there were certain areas of your
tongue that tasted specific things:
Saliva
This is actually not true. There are areas of your tongue
that will have clusters of taste buds that respond to
certain chemicals but they are not isolated to certain
areas of your tongue.
Let’s test it!
Take a candy and put it on the side of your tongue. If
this map was right, you should be tasting sour, not
sweet.
Teeth
The teeth of your mouth are very important in helping to
tear and grind food particles. (mechanical digestion)
The front 8 teeth are known as incisors. They tear at
food.
The teeth to the sides of these are your canines and
also tear at food.
The rest are called your molars and are used to grind up
the food
Esophagus
This is the tube that the bolus travels down before
reaching your stomach
It is covered in very powerful muscles that use a
technique called peristalsis to move the food down the
gastrointestinal tract
Cool fact: peristalsis will move food towards your
stomach even if you are standing on your head!
Stomach
The stomach is where lots of digestive magic happens both chemical and mechanical
Food is stored here and where proteins begin their initial
digestion process
The stomach is covered in muscle, 3 layers in fact.
Stomach
As food enters, the
different muscle layers
contract in different
directions causing the food
to churn and mix with the
HCl aiding in further break
down
Stomach
How does food stay in the stomach while it digests?
There are two very important sphincters.
1. Lower esophageal sphincter (LES)
2. Pyloric sphincter
These ensure the acidic stomach liquid only moves in
certain directions
Stomach
The LES prevents the stomach acid from going back up
into the esophagus while the pyloric sphincter opens to
allow the partially digested food to move on to the small
intestine.
The stomach can hold about 1.5L of food at a time on
average. This amount can expand or shrink depending on
the person and their diet.
Stomach
There are millions of cells on the inside of the stomach
wall that secrete various fluids (gastric juices) that aid
digestion
Gastric fluid includes mucus, hydrochloric acid (HCl),
pepsinogens, and other substances
Stomach
Mucous protects the inner lining of the stomach from the
HCl
HCl kills many harmful substances in the food
Pepsinogen becomes pepsin which is a protein digesting
enzyme
Pepsin
Pepsinogen is activated by HCl turning it into pepsin.
The pepsin breaks down proteins in the food but not the
proteins of the stomach lining because it is protected by
mucus (most of the time)
What can go wrong?
Heartburn - when the LES is weak and stomach acid
refluxes back into the esophagus leading to damage to
the muscle tissue
Peptic ulcers - when the mucus lining of the stomach
breaks down and the HCl and pepsin destroy the cell
membrane
Digestion
As the food moves on, it enters the small intestine through
the pyloric sphincter.
This is where most of the chemical digestion occurs.
Most of the digestion occurs in the duodenum (the first
part of the sm. intestine).
Small Intestine
The small intestine secretes digestive enzymes and
moves the food through using peristalsis (like the
esophagus).
Most of the absorption of nutrients and water occurs
here.
There are long villi along the inner surface of the intestine
and each are covered in smaller microvilli
Small Intestine
These projections have extensive networks of capillaries
(small blood vessels) that take the dissolved nutrients
from the food and transport them around the body.
Specifically transport monosaccharides and amino
acids.
There are also lymph vessels that are called lacteals that
transport the products of fat digestion
Pancreas
The pancreas is a large organ located behind the
stomach
When acids enter the small intestine, a chemical called
prosecretin is converted to secretin
This chemical is absorbed into the bloodstream and taken
to the pancreas where it stimulates the release of
bicarbonate ions
Pancreas
Bicarbonate ions (HCO3-) act as a buffer and are
released from the pancreas into the small intestine to
counteract the acidic gastric fluid that has entered it.
These ions change the pH from 2.5 to about 9.0. This
change in pH inactivates pepsin so the small intestine is
not being degraded.
Pancreas
The pancreas also releases many enzymes to aid
digestion:
Pancreas
Trypsinogen is a protein digesting enzyme and is activated by
enterokinase turning it into trypsin. Trypsin acts on partially digested
proteins
Erepsins complete protein digestion taking the short chain peptides
and turning them into amino acids
Pancreas
Amylase is released continuing digestion of
carbohydrates
Lipases are also released and break down fats
- pancreatic lipase - breaks down fats (saturated and
unsaturated)
- phospholipase - phospholipids
Liver and Gallbladder
Liver makes a fluid called bile
Bile contains bile salts that aid fat digestion
When the stomach is empty, the gallbladder stores the
bile in a concentrated form
Liver and Gallbladder
When fats are in the small intestine, the hormone
cholecystokinin (CCK) is released
CCK is carried to the gallbladder triggering release of bile
salts
These bile salts then break down large fat globules
(mechanical digestion)
Liver and Gallbladder
The liver is also used to break down hemoglobin from
red blood cells - the brown colour of feces comes from
this process
The liver can filter out many substances in the body like
alcohol and send it to the bloodstream to be excreted in
the urine
Problems?
Gallstones: crystals of bile salts can form in the
gallbladder which is very painful and can block the bile
duct
Jaundice: collection of bile pigments in the blood.
Caused by blockage of bile duct
Cirrhosis: chronic inflammation of the liver leading to
scarring and growth of fibrous connective tissue
Large Intestine
Chemical digestion is complete by the time it reaches the
large intestine
The colon stores waste and reabsorbs water from it
Houses bacteria like E. coli to synthesize vitamins B and
K
Cellulose from plant matter provides bulk for the feces
Large Intestine
As material builds up, a signal is sent to the nervous
system through receptors in the intestine wall saying
“Hey! We are full down here, time to make room!” which
prompts a bowel movement.
People that do not eat enough cellulose (fibre) will not
have as many bowel movements leading to buildup of
wastes and toxins in their bodies - can lead to colon
cancer over time
The Magical Story of Digestion
Now to delve into these notes a bit deeper!