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 - microvilli
Surrounded 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)
Liver
Used for detoxification. Stores vitamins. Produces and secretes bile which helps in the absorption/emulsification of fats.
(Accessory organ)
Gall bladder
Stores the bile produced by the liver. Releases it into the small intestine.
(Accessory organ)
Stomach
Stores food (between 3-10 hours). Begins protein digestion.
(Alimentary canal)
Pancreas
Produces enzymes which are released into the small intestine. Secretes hormones (insulin/glucagon) to regulate the concentration of blood sugar.
(Accessory organ)
Small intestine
A long folded tube where nutrients are absorbed. Composed of three regions: duodenum, jejunum and ileum. Lined with smooth muscle for peristalsis and segmentation.
(Alimentary canal)
Large intestine
The final section of the Alimentary canal. Water and dissolved minerals are absorbed here. Faeces pass through to the rectum.
How is starch digested in the small intestine?
(Amylose - linear chains, amylopectin - branched chains)
The digestion of starch is initiated by salivary amylase in the mouth and then continued by pancreatic amylase in the small intestine. Amylase breaks down amylose into maltose and amylopectin into dextrin. Maltose and dextrin are digested by the maltase enzyme which is fixed to the epithelial lining of the small intestine. The hydrolysis of maltose and dextrin produces glucose monomers.
Glucose can be hydrolysed to produce ATP or stored as glycogen.
Define surfactants
Substances that allow oil and water to mix/emulsify.
What is assimilation?
The process of carrying absorbed nutrients to various cells to produce energy.
What enzyme does the salivary glands produce?
Salivary amylase for digestion of starch (starch -> maltose)
What enzymes do the stomach produce?
The stomach contains gastric glands which produce stomach acids that aid in chemical digestion. The stomach also produces proteases (protein -> polypeptides).
What enzymes do the pancreas produce?
Pancreatic amylase (starch -> maltose)
Lipase (triglycerides -> fatty acids)
Endopeptidase (peptides -> amino acids)
Nuclease (DNA/RNA -> nucleosides)
