5.1 Digestion Flashcards
What is the difference between digestion and absorption?
Digestion involves the mechanical and chemical breakdown of food, extraction of nutrients and breakdown of macronutrients.
Absorption is the transfer of nutrients from the lumen of the small intestine to blood or lymphatic capillaries surrounding the digestive tract.
what process of digestion happens in the mouth?
Salivary glands secrete saliva (starch digesting enzymes) and chewing (mastication) breaks down food
What is the epiglottis?
It is a flap in the throat that prevents food from entering the windpipe
What happens to food after swallowing?
The food (bolus) heads into the oesophagus where the oseophageal sphincter controls passage from oesophagus to the stomach
What is the role of the stomach in the GI tract?
The stomach adds juices and grinds the bolus into chyme (semi liquid)
What is the role of the pyloric sphinter?
It regulates the flow of chyme into the small intestine
Where does small intestine receive digestive juices from?
Gall bladder and pancreas
What are the three segments of the small intestine?
duodenum
jejunum
ileum
Where does food continue from the large intestine?
The large intestine (colon) begins at the ileocaecal valve and undigested residues continue through to the rectum (forming stool) and excreted through the anus
What are five aspects of muscular (mechanical) digestion)?
- Chewing (mastication)
- Peristalsis
- Stomach action
- Segmentation
- Sphincter contractions
What structures contribute to mastication?
- The human jaw is one of the most powerful muscles in the body
- Tooth enamel is the hardest substance produced by the body
- The tongue is a conglomeration of eight different muscles, which makes it the body’s most flexible muscle
- Several glands (including sublingual, submandibular and parotid) secrete saliva to help dissolve food and provide particles in solution to react with taste buds
What does peristalsis mean?
It is the way food is moved down the intestine and the oesophagus, through GI tract
Squeezing and pushing food through mechanism
How does muscles allow for peristalsis?
How does stomach action assist in digestion?
What is segmentation?
What are the four sphincters in the GI tract?
- Oesophageal sphincter
- Pyloric sphincter
- Ilocaecal valve
- two sphincters of the anus
How does the oesophagus muscles and diaphragm work together to act as a sphincter muscle?
What is ghrelin?
A hormone secreted by stomach cells which tells the brain when its hungry or full
What stimulates ghrelin release?
Empty stomach stimulates ghrelin release
Where are ghrelin receptors found?
hypothalamus
What stops ghrelin release?
A full stomach
What are the other roles of ghrelin?
- Glucose and energy homeostasis
- Cardio protection
- Muscle atrophy
What six places does chemical breakdown of food happen?
Salivary glands
Gastric glands
Pancreas
Liver
Gall bladder
Intestinal glands
How does chemical breakdown of food happen by salivary glands?
How does chemical breakdown of food happen by gastric glands?
How does chemical breakdown of food happen by the pancreas?
How does the chemical breakdown of food happen by the liver?
How does the chemical breakdown of food happen by the gall bladder?
How does the chemical breakdown of food happen by intestinal glands?
What are the broad functions of each part of the small intestine?
- duodenum is the place where most digestion occurs
- Jejunum is the place where most absorption of nutrients occurs
- ileum is where absorption of some important nutrients occurs (vitamins b12, A, D, E and K)
What does the duodenum do?
- Delivery of chyme/HCl
- Liver/gallbladder delivers bile
- Pancrease delivers pancreatic juice (enzymes)
- Brush border enyzme
What is the role of microvilli and the brush border?
Brush border enzymes sit on top of the brush border and microvilli act like bristles on a brush to get in contact with food
How does the pH of the GI tract vary?
Gastric juice secretes very acidic HCl, pancreatic juice secretes sodium biocarbonate and bile is also slightly alkaline
What is the purpose of gastric juice in the stomach?
Gastric juice contains HCl. The strong acidity is to prevent bacterial growth and aid protein digestion. Stomach cells secrete mucus to guard against acid, enzymes and disease causing bacteria
Why does pancreas secrete sodium bicarbonate?
Pancreatic juice contains sodium bicarbonate, which is alkaline and this helps to neutralise the acidic chyme that enters the duodenum. From this point on chyme remains at neutral or slightly alkaline pH
In the mouth how are carbohydrates, fibre, fat and proteins borken down?
In the stomach how are carbohydrates, proteins and fat broken down?
In the small intestine how are carbohydrates, fat protein and vitamins and minerals broken down?
How are fluids/minerals, and fibre broken down in the large intestine?
Which molecules go where when being absorbed in the small intestine?
- Water soluble nutrients and small products of fat digestion are released to the bloodstream
- Fat soluble vitamins and alrger fats form chlyomicrons and are released to the lymphatic system
What direction does blood normally travel?
Where does blood leaving the digestive system go instead?
- Instead, the blood leaving the digestive system goes by way of vein, not to the heart, but to the liver.
- heart, arteries, capiliaries (intestines), portal vein, liver, capillaries (liver), hepatic vein, heart
What does the hepatic portal vein do?
It collects blood from the GI tract and delivers it to the capillaries of the liver
What is the role of the liver in digestion?
It removes toxic substances and might cause harm and prepares waste products for excretion.
Liver is susceptible to poisons, viruses (hepatitis), drugs (ie. alcohol and barbituates), toxins and contaminants (ie. pesticide residues, mercury)
What is the pathway of blood circulation in the liver?
What is the role of the lymphatic system in digestion?
- Mucosal cells bundle large fatty acids and fat soluble vitamins (lipids) into chlyomicrons because they are insoluble and will not enter capillaries
- Chlyomicrons are released into the lacteals within the villi
- Chylomicrons bypass the liver and enter the circulatory system in the right lymphatic duct and thoracic duct (near the heart)
What are the three components of the lymphatic system?
Lymph, lymphatic vessels, lymphatic tissues and organs
What are the funcitons of the lymphatic system?
What factors influence the health of the GI tract?
- Age, diseases and diet can affect function.
- Estimated 10 trillion (1012) microbes (bacteria, viruses, protozoa and other microganisms) live in GI tract.
- Flora or microflora assist digesting some fibre and protein.
What is the difference between probiotics and prebiotics?
Probiotics are bacteria found in the foods such as yoghurt, that can be beneficial to health.
Prebiotics are certain chemical compounds, not absorbed but used as food by intestinal bacteria.
What health factors does the gastrointestinal microbiome influence?
What three hormones are the main ones in regulating GI tract?
Gastrin
Secretin
Cholecystokinin
What is the main role of gastrin?
What is the main role of secretin?
What is the main role of cholecystokinin?
