digestive system - st leonard's college
TRANSCRIPT
• The function of the system
• The structure and function of each organ
• Specialized cells/tissues in each organ
DIGESTIVE SYSTEM
YEAR 8 BODY SYSTEMS
Let’s think about digestion!
Do you know which organs make up our digestive system?
Do you know the pathway that food takes on
its way through?
Do you know what the purpose of
digestion is?
Umm…? Umm…?
Structures of the digestive system
Digestive System
Large intestine
Mouth
Oesophagus
Rectum
Small
intestine
Stomach
Pancreas
Salivary glands
Liver
Gall bladder
We’re needed too!
Mouth
Oesophagus
Stomach Small intestine
Large intestine
Rectum /Anus
Pathway through the digestive system
Salivary glands
Liver
Gall bladder
Don’t forget
us! Pancreas
Purpose of the digestive system
To break down large food molecules that we have consumed into smaller molecules
The smaller molecules are needed so that:
1) We can get them through the lining of the intestine and into our blood stream
2) We can use them to build our own larger molecules
Fun facts about the digestive system
We eat about 500kg of food per year.
We produce 1.7L of saliva each day.
In the mouth, food is either cooled or warmed to a more suitable temperature.
The oesophagus is approximately 25cm long.
Muscles contract in waves to move the food down the oesophagus. This means that food would get to a person's stomach, even if they were standing on their head.
Fun facts about the digestive system
In an average person, it takes 8 seconds for food to travel down the food pipe, 3-5 hours in small intestine and 3-4 days in the large intestine.
The human body takes 6hrs to digest a high fat meal and takes 2hrs for a carbohydrate meal.
Every day 11.5L of digested food, liquids and digestive juices flow through the digestive system, but only 100mls is lost in faeces.
The digestive system Anus
Appendix
Gall bladder
Large intestine
Liver
Mouth
Oesophagus
Pancreas
Rectum
Salivary glands
Small intestine
Stomach
Can you label this diagram?
The digestive system
Oesophagus
Gall bladder
Small intestine
Stomach
Pancreas
Large intestine
Salivary glands Mouth
Liver
Rectum Anus
Appendix
Let’s start at the very beginning…
What do we need to begin digestion?
o Mandible (jaw)
o Teeth
─ These structures facilitate mechanical digestion.
─ The food is physically broken into smaller pieces by our teeth which are attached and moved by to our jaw.
Saliva
Tongue
Taste buds
Let’s start at the very beginning…
Saliva begins the process of chemical digestion, as well as providing moisture that will help your food begin to break down.
Chemical digestion involves enzymes. These are special chemicals that help chemical reactions occur at a faster rate.
Saliva contains salivary amylase – an enzyme that helps the larger carbohydrate molecules (eg. starch) break down into smaller sugars (eg. maltose).
Let’s start at the very beginning…
Maltose
Starch
Starch Starch
Salivary amylase
Starch Maltose
Does temperature affect enzymes? Investigation 4.10
Copy and complete the results table on p152 into your books.
Complete the activity.
Answer the discussion questions on p152 below the task.
The oesophagus
Food is now chewed and moisturized by saliva and is pushed back by the tongue.
We swallow, and the food goes into the oesophageus.
The muscles that surround this tube contract to push the food into the stomach.
These contractions are called peristalsis and they are powerful enough to allow us to swallow even if lying down — or upside down.
The stomach
A temporary food storage area.
It can expand to hold 2-4Ls of food.
Muscle movements in the stomach wall mix the food with gastric juice.
Gastric juice contains enzymes which help to break down proteins.
The stomach also contains dilute hydrochloric acid, which kills germs and provides a suitable environment for protein digestion.
o eg. the enzyme pepsin for protein breakdown works best in very acidic conditions
The small intestine
A tube about 6m long.
Food moves through it by peristalsis.
It makes more enzymes to complete digestion.
Here, nutrients are absorbed into your bloodstream.
The blood then carries the nutrients to all of the cells of your body, where they will be used to make our own large molecules.
The pancreas, liver and gall bladder are all connected to the small intestine.
The small intestine ...zoomed in!
The small intestine is lined by tiny finger-like projections called villi.
The outer layer of cells lining each villi (called epithelial cells) are covered in similar structures called microvilli
The small intestine ...zoomed in!
Why do you think that the small
intestine needs the villi and microvilli?
They increase the surface area across which the
small intestine can absorb nutrients.
It means that the organ can do its job faster and
more efficiently.
The pancreas
Makes pancreatic juice, which is basic or alkaline so it neutralises the stomach acid.
The pancreas also makes enzymes that break down proteins, fats and carbohydrates.
Gastric juice (HCl in stomach) Pancreatic juice
The liver
The largest internal organ.
It makes bile, which breaks down fats
It also controls blood sugar
It destroys poisons and toxins – like alcohol!
It also stores vitamin A, vitamin D and iron.
The liver
The gall bladder
Bile made in the liver is stored here.
The bile is used to break up fats into droplets small enough to be transported to the rest of the body.
This bile can sometimes form stones and cause severe pain. In this case, the individual would need to reduce their intake of fat, and possibly have to have their gall bladder removed.
The large intestine
The large intestine is also known as the colon.
Undigested material passes into the large intestine and moves along by peristalsis.
The large intestine absorbs water, salts, vitamins and any remaining sugars so that they can be reused by the body.
The colon sits in an upside-down U-shape across your belly
The appendix
This organ is attached to the large intestine.
It used to be involved in digesting woody stems and other plant materials back in the day...
But now it plays no part in digestion in humans.
However, it is believed to play a role in fighting some diseases.
The rectum and anus
Rectum:
o The final part of the large intestine.
o This is where the faeces are stored.
Anus:
o The faeces pass through here when you go to the toilet.
What can go wrong?
Heartburn
Inflammatory bowel disease
Irritable bowel syndrome
Appendicitis
Constipation
Crohn’s disease
Diverticulosis
Gallstones
Haemorrhoids
Pancreatitis
Peptic ulcer
Answer the
following
worksheet
Watch the video on the next slide (also on eBook) and answer the worksheet
SQ8 p153 Q1, 5, 6, 8
SQ8 p157
Q1, 2, 4, 11
SQ8 Student workbook: Worksheet 4.6
What do you do now?
