Human Digestion (lesson three) Flashcards
Human Digestion
Humans have a complete digestive system
what is the gastrointestinal tract?
The tube our food is digested through is called the gastrointestinal tract, or GI tract for short
- It is approximately 7-9 meters long
- Its purpose is to ingest, digest, absorb, and egest our food
where does chemical and physical digestion start?
Both chemical and physical digestion of your food starts in the mouth
how does the mouth digest physically?
It is broken down physically by your teeth by tearing and cutting with your incisors and canines and by grinding and crushing with your molars
how does the mouth digest chemically?
It is broken down chemically with your saliva which contains enzymes
what helps digest food in many ways?
your saliva helps digest your food in many ways
Amylase
Amylase is an enzyme which breaks down complex carbohydrates into smaller disaccharides
- It also contains mucus which is a protective lubricant which helps you swallow
bolus
When the food is ready to be swallowed as a moist ball of food it is called a bolus
ingestion (Swallowing Food)
- your tongue pushes the food to the back of your mouth
- It is then pushed into the pharynx and your soft palate is raised to prevent food from entering your nasal passage
- At the same time the epiglottis covers the entrance to your trachea, called the glottis
- This process of taking food into the body by swallowing is called ingestion
Esophagus
Once food is swallowed, it moves into the stomach through the esophagus
- This is a long muscular tube
- As it is stretched by the food, wave-like muscle contractions called peristalsis push the food downwards
- This process takes about 8 seconds
The Stomach
- The food enters the stomach through a circular piece of muscle called the gastroesophageal sphincter
- When this muscle relaxes, food can enter the organ called the stomach
- The stomach can accommodate 2L of food
- Food mixed with gastric juices, now called chyme, exits the stomach through the pyloric sphincter
Digestion in the Stomach
The stomach is also involved in both chemical and physical digestion of your food
- The muscle in the stomach churns and physically breaks down your food
- Digestive enzymes, like pepsin which breaks down proteins, chemically digest your food
where does most of the digestion happen
Most of your digestion happens in the small intestines
The Small Intestine
- ## This is a 7m tube about 2.5 cm in diameter that digests lipids, carbohydrates, and proteins
how many sectors of there of a small intestine?
There are three sections
1. The duodenum
2. The jejunum
3. The ileum
The duodenum
The duodenum, where most enzymes are added
The jejunum
The jejunum, where digestion continues and some nutrients are absorbed
The ileum
The ileum, where most of the nutrients are absorbed
Absorption in the Small Intestine
- The inner surface of the small intestine is folded into many finger-like projections
- These are called villi and microvilli and function to maximize the surface area and absorption by a factor of 500
- The nutrients enter the bloodstream (i.e. are absorbed) through capillary beds in the villi
- This involves absorption in more than one way
- Simple diffusion that follows the concentration gradient (including osmosis)
- Facilitated diffusion through the use of a transport protein
- Active transport (goes against the concentration gradient) that uses transport proteins and ATP (energy molecule)
The Large Intestine
- The large intestine is 1.5 m in length and 7.6 cm in diameter
- It is joined to the small intestines through the cecum where the appendix is also attached
- The colon is the longest part of the large intestine and is made up of the ascending, transverse, descending and sigmoid colon
- The last 20 cm is called the rectum which holds the feces until it can be eliminated, or egested, through the anus
what important role does the large intestine play in?
The large intestine plays an important role in the absorption of:
- Water
- Ions
- Vitamins
Egestion
- Egestion is the removal of waste food materials from the body
- These would include materials like cellulose and fibre (i.e. indigestible materials), which are important as they give us a full feeling for a longer time and reduce overeating
- Nerves in the large intestine detect the movement of food in the rectum and tell us to eject the food by a bowel movement
