The digestive system Flashcards
What is the gastrointestinal tract
The gastrointestinal tract is a 9m muscular tube from mouth to anus
What are the layers of the gastrointestinal tract
The mucosa- highly folded inner layer of mucus producing tissue
The submucosa- The layer below the mucosa which is the location of glands involved in digestion
The muscularis- the muscular smooth muscle layer that contracts in waves to propel food along the tract
The serosa- the protective outer layer
What are the types of digestion
Mechanical digestion is chewing and churning food to break it down into smaller pieces
Chemical digestion is where enzymes break food into smaller molecules that can be absorbed
What are carbohydrates
Carbohydrates are long polysaccharide chains made of glucose. Found in starch and sugars eg bread, pasta potato
What are fats
Most fats are triglycerides which are made of glycerol and three fatty acids. Found in fatty meat and dairy
What are proteins
Proteins are polypeptide chains of amino acids. Found in lean meats, beans and nuts
Explain the first stage of digestion
Detect to swallow
- Food is detected by olfaction
- The sublingual, submandibular and parotid salivary glands secrete saliva.
- Food is masticated by the teeth
- Salivary amylase breaks starch into maltose
- A bolus is formed which is swallowed to the oesophagus
What is ptyalism
Ptyalism is an overproduction of saliva which is common in pregnancy
Explain the second stage of digestion
stomach
- Food enters the stomach through the lower oesophageal sphincter which prevents reflux
- The food is broken down by parietal cells which produce HCl, which the stomach is protected from due to the mucous produced by mucous cells
- Chief cells produce pepsin which digests the proteins into polypeptides
- Food is churned for 1-2 hours to form chyme
- chyme leaves through the pyloric sphincter
Why do pregnant women suffer with heartburn
In pregnancy the abdominal organs compress the stomach causing gastric juice to enter to oesophagus
Explain the third stage of digestion
duodenum
- Food enters the duodenum and Bile made in the liver is released by the gallbladder
- Bile salts digest fat into fat droplets and bile pigment breakdown into bilirubin and biliverdin
- Pancreatic juice is released by pancreatic ducts
- The Bicarbonate ions neutralise the HCL
- Pancreatic amylase breaks starch into maltose
- Pancreatic lipase digests fat into fatty acids & glycerol
- Trypsin breaks polypeptides into peptides
What complications can bile cause
Bile can settle in the gallbladder as biliary sludge and cause gallstones which enter to bile duct
Bile can also become stuck in the bile duct and cause bilirubin to leak into the blood and cause jaundice
Explain the fourth stage of digestion
Illeum
- Food enters the ileum and glucose and amino acids are absorbed by the villi
- Intestinal lipase breaks fats into fatty acids and glycerol
- Intestinal peptidase breaks peptides into amino acids
- Maltase breaks maltose into glucose
- Lacteal is a lymphatic vessel which absorbs the products of digestion in the illeum
Explain the fifth stage of digestion
the colon
- Food passes through the ascending, transverse, descending and sigmoid colon where water and electrolytes are absorbed
- Microorganisms in the colon synthesise vitamin K which is needed for blood clotting
Why are babies given vitamin k
Babies are given vitamin K as they have a sterile gut with no microorganisms to produce it
