Digestion (6.1) Flashcards
Define the alimentary canal
The organs through which food actually passes (eg. oesophagus, stomach, small/large intestine)
Define the accessory organs
The organs that aid in digestion but do not transfer food (eg. salivary glands, pancreas, liver, gall bladder)
What two groups of organs comprise the human digestive system?
The alimentary canal and the accessory organs.
Define mechanical digestion
Where food is physically broken down into smaller fragments by chewing (mouth), peristalsis (oesophagus, stomach and small intestine) and segmentation (the intestines).
Describe peristalsis
Occurs in the oesophagus, stomach and small intestine.Continuous segments of longitudinal smooth muscle rhythmically contracting and relaxing, pushing food along the alimentary canal.
Describe segmentation
Occurs in the intestines.The contraction and relaxation of non-adjacent segments of circular smooth muscle.
Define chemical digestion
Where food is broken down by the action of chemical agents (enzymes, acids and bile).
Describe how stomach acids aid with chemical digestion
The stomach contains gastric glands which release digestive acids that create a low pH (acidic) environment. This denatures proteins/other macromolecules, aiding in digestion as it changes their shape, increasing their surface area for absorption and making it easier to transport.
Describe how bile aids with chemical digestion
The liver produces bile which is stored in the gall bladder and released into the intestines. Bile contains bile salts which break down fats into smaller pieces (emulsification).
Describe how enzymes aid with chemical digestion
Digestive enzymes are secreted predominantly by the pancreas but can also be released by the stomach and salivary gland. Enzymes allow for digestive processes to occur at speeds necessary for survival.
What is absorption?
The process of taking nutrients from the digestive system into the blood.
What are the features of villi?
High SA - microvilliSurrounded by a dense capillary network (rich blood supply)Single layer epithelium (minimal diffusion distance)
What are the methods of absorption?
1) Simple diffusion (hydrophobic nutrients eg. lipids)2) Facilitated diffusion (hydrophilic nutrients eg. fructose)3) Active transport (eg. glucose/amino acids)4) Osmosis (water/ions)The main method of transport is endocytosis. This uses vesicles to pass fluid through the membrane.
Salivary glands
Releases saliva to moisten food. It also contains enzymes to initiate starch breakdown (salivary amylase). (Accessory organ)
Oesophagus
Connects the mouth to the stomach. Food is mixed with saliva and moved in a bolus via peristalsis. (Alimentary canal)