Topic 6.1: Digestion and Absorption Flashcards
What are two major groups of organs which comprise the human digestive system?
alimetary canal and accessory organs
Define alimentary canal
The alimentary canal consists of organs through which food actually passes (oesophagus, stomach, small & large intestine)
Define accessory organs
The accessory organs aid in digestion but do not actually transfer food (salivary glands, pancreas, liver, gall bladder)
Is the esophagus part of the alimetary canal or accessory organs?
alimetary canal
Is the stomach part of the alimetary canal or accessory organs?
alimetary canal
Is the small intestine part of the alimetary canal or accessory organs?
alimetary canal
Is the salivary glands part of the alimetary canal or accessory organs?
accessory organs
Is the pancreas part of the alimetary canal or accessory organs?
accessory organs
Is the liver part of the alimetary canal or accessory organs?
accessory organs
Is the gall bladder part of the alimetary canal or accessory organs?
accessory organs
Is the large intestine part of the alimetary canal or accessory organs?
alimetary canal
What is the structure and function of the oesophagus?
A hollow tube connecting the oral cavity to the stomach (separated from the trachea by the epiglottis)
• Food is mixed with saliva and then is moved in a bolus via the action of peristalsis
What is the structure and function of the stomach?
A temporary storage tank where food is mixed by churning and protein digestion begins
• It is lined by gastric pits that release digestive juices, which create an acidic environment (pH ~2)
What is the structure and function of the small intestine?
A long, highly folded tube where usable food substances (nutrients) are absorbed
• Consists of three sections – the duodenum, jejunum and ileum
What is the structure and function of the large intestine?
The final section of the alimentary canal, where water and dissolved minerals (i.e. ions) are absorbed
• Consists of the ascending / transverse / descending / sigmoidal colon, as well as the rectum
What is the structure and function of the salivary glands?
Release saliva to moisten food and contains enzymes (e.g. amylase) to initiate starch breakdown
• Salivary glands include the parotid gland, submandibular gland and sublingual gland
What is the structure and function of the pancreas?
Produces a broad spectrum of enzymes that are released into the small intestine via the duodenum
• Also secretes certain hormones (insulin, glucagon), which regulate blood sugar concentrations
What is the structure and function of the liver?
Takes the raw materials absorbed by the small intestine and uses them to make key chemicals
• Its role includes detoxification, storage, metabolism, bile production and haemoglobin breakdown
What is the structure and function of the gall bladder?
The gall bladder stores the bile produced by the liver (bile salts are used to emulsify fats)
• Bile stored in the gall bladder is released into the small intestine via the common bile duct
What is the first step of mechanical digestion?
Food is initially broken down in the mouth by the grinding action of teeth (chewing or mastication)
After Food is initially broken down in the mouth by the grinding action of teeth (chewing or mastication), what is the next step of mechanical digestion?
The tongue pushes the food towards the back of the throat, where it travels down the esophagus as a bolus
After The tongue pushes the food towards the back of the throat, where it travels down the esophagus as a bolus, what is the next step of mechanical digestion?
The epiglottis prevents the bolus from entering the trachea, while the uvula prevents the bolus from entering the nasal cavity
After The epiglottis prevents the bolus from entering the trachea, while the uvula prevents the bolus from entering the nasal cavity, what is the next step of mechanical digestion?
The stomach lining contains muscles which physically squeeze and mix the food with strong digestive juices (‘churning’)
After The stomach lining contains muscles which physically squeeze and mix the food with strong digestive juices (‘churning’), what is the next step of mechanical digestion?
Food is digested within the stomach for several hours and is turned into a creamy paste called chyme
After Food is digested within the stomach for several hours and is turned into a creamy paste called chyme, what is the next step of mechanical digestion?
Eventually the chyme enters the small intestine (duodenum) where absorption will occur
After Eventually the chyme enters the small intestine (duodenum) where absorption will occur, what is the last step of mechanical digestion?
Segmentation contractions move chyme in both directions, allowing for a greater mixing of food with digestive juices
What is segmentation (digestion)?
Segmentation involves the contraction and relaxation of non-adjacent segments of circular smooth muscle in the intestines
What is the first step of chemical digestion?
The stomach contains gastric glands which release digestive acids to create a low pH environment (pH ~2)
After The stomach contains gastric glands which release digestive acids to create a low pH environment (pH ~2), what is the next step of chemical digestion?
The acidic environment functions to denature proteins and other macromolecules, aiding in their overall digestion
After The acidic environment functions to denature proteins and other macromolecules, aiding in their overall digestion, what is the next step of chemical digestion?
The stomach epithelium contains a mucous membrane which prevents the acids from damaging the gastric lining
After The stomach epithelium contains a mucous membrane which prevents the acids from damaging the gastric lining, what is the next step of chemical digestion?
The pancreas releases alkaline compounds (e.g. bicarbonate ions), which neutralise the acids as they enter the intestine
After The pancreas releases alkaline compounds (e.g. bicarbonate ions), which neutralise the acids as they enter the intestine , what is the next step of chemical digestion?
The liver produces a fluid called bile which is stored and concentrated within the gall bladder prior to release into the intestine
After The liver produces a fluid called bile which is stored and concentrated within the gall bladder prior to release into the intestine, what is the next step of chemical digestion?
Bile contains bile salts which interact with fat globules and divide them into smaller droplets (emulsification)
After Bile contains bile salts which interact with fat globules and divide them into smaller droplets (emulsification), what is the next step of chemical digestion?
The emulsification of fats increases the total surface area available for enzyme activity (lipase)
After The emulsification of fats increases the total surface area available for enzyme activity (lipase), what is the last step of chemical digestion?
Enzymes are biological catalysts which speed up the rate of a chemical reaction (i.e. digestion) by lowering activation energy
Enzymes allow digestive processes to therefore occur at body temperatures and at sufficient speeds for survival requirements
Enzymes are specific for a substrate and so can allow digestion of certain molecules to occur independently in distinct locations
What are the four main tissue layers of the small intestine from outside to center?
serosa, muscle layer, submucosa, mucosa
Define serosa (small intestine)
Serosa – a protective outer covering composed of a layer of cells reinforced by fibrous connective tissue
Define muscle layer (small intestine)
Muscle layer – outer layer of longitudinal muscle (peristalsis) and inner layer of circular muscle (segmentation)
Define submucosa (small intestine)
Submucosa – composed of connective tissue separating the muscle layer from the innermost mucosa
Define mucosa (small intestine)
Mucosa – a highly folded inner layer which absorbs material through its surface epithelium from the intestinal lumen
What is the function of villi in the small intestine?
Villi increase the surface area of epithelium over which absorption is carried out
• Villi absorb monomers formed by digestion as well as mineral ions and vitamins
