digestive system Flashcards
what does the alimentary canal do?
forms a tube through the centre of the body
food is… from this canal for the purpose that the food can be…
ingested, digested, absorbed, egested
assimilated
what makes up the small intestine?
duodenum and ileum
what makes up the large intestine?
the colon and the anus
what is ingestion?
taking food in through the mouth and swallowing
what is digestion?
breaking down large insoluble molecules in food into smaller pieces and smaller soluble molecules
what is absorption?
the movement of small soluble molecules out of the gut and into the blood by diffusion and active transport
what is egestion?
passing out undigested food through the anus
what is assimilation?
building larger biological molecules from the small soluble molecules, in all cells
what is the first structure in the alimentary canal?
the mouth
where does ingestion take place?
the mouth
what also happens in the mouth?
digestion
what is an example of mechanical digestion in the mouth?
- food is broken up into smaller pieces in the mouth by chewing
- this increases the surface area for enzymes and also prevents discomfort when swallowing
what is an example of chemical digestion in the mouth?
- saliva is released into the mouth by the salivary glands
- makes the food easier to swallow
- contains amylase
what does amylase break down starch to?
starch-> maltose
what happens when amylase reaches the stomach?
amylase works best at a neutral pH so it is denatured when it reaches the stomach and stops working
what happens before swallowing?
the food is shaped into a ball by the tongue and moved towards the back of the mouth
what is the ball of food called?
a bolus
what is the epiglottis and what does it do?
a flap which blocks the food from entering the trachea
what is the oesophagus?
a long tube that connects the mouth to the stomach
what process occurs in the oesophagus?
peristalsis
what is peristalsis?
- two sets of muscles push the food down the oesophagus
- the circular muscles contract behind the bolus pushing it along
- when the longitudinal muscles contract, they make the oesophagus wider and the circular muscles relax
what do the gastric glands in the stomach wall secrete?
the enzyme pepsin
what does pepsin do?
begins the process of digesting proteins into peptides
what are peptides?
shorter chains of amino acids
what does the contraction of the stomach wall cause?
mixing of the contents of the stomach- maximising contact between enzymes and food
what are pepsin’s optimum conditions?
an acidic pH
why are the conditions in the stomach acidic?
the release of hydrochloric acid by the gastric glands
pepsin has a high or low pH?
very low
pepsin is covered in what?
a mucus lining
what does the hydrochloric acid in our stomach do?
kills many bacteria and fungi which may be present in the food we eat
what 2 processes occur in the small intestine?
digestion and absorption
what process happens in the duodenum?
digestion
the duodenum is the final site of what?
chemical digestion
what enzymes does the pancreas make?
trypsin, amylase and lipase
where does the pancreas secrete the enzymes into?
the duodenum
what does trypsin do?
breaks down protein into peptides
what does lipase do?
breaks down lipids into glycerol and 3 fatty acids
what does the duodenum wall also contain?
glands which make enzymes and secretes them into the duodenum
the glands in the duodenum wall make what enzymes?
maltase and peptidase
what does maltase do?
breaks down maltose into glucose
what does peptidase do?
breaks down peptide into amino acids
bile is found where?
in the duodenum
where is bile produced?
in the liver
where is bile stored?
in the gall bladder
where is bile released into and through where?
released into the duodenum through the bile duct
what are the two functions of bile?
1) neutralises the stomach acid- enzymes in the duodenum work best at pH 7-8
2) emulsifies lipids- breaks large droplets into smaller droplets- increasing SA for lipase to digest the fats
what happens once the food has entered the ileum?
digestion is over and absorption begins
what are the finger like projections found in the ileum called?
villi
what does the villi do?
absorb small soluble molecules
how are the small soluble molecules absorbed?
- some by diffusion
- however, some such as glucose are also absorbed by active transport
how is the rate of diffusion in the ileum increased?
- large SA- folding of ileum, villi and microvilli
- short diffusion distance- villi walls are one cell thick
- high concentration gradient- provided by capillary network and lacteals removing absorbed molecules
what is the colon the site for?
all reabsorption of water
where is faeces stored?
in the rectum
where are faeces egested from?
the anus
what is excretion?
the expulsion of faeces from the anus- the removal of undigested food from the body
what is excretion?
the removal of waste substances produced by chemical reactions in the body
what are some examples of excretion?
- carbon dioxide- removed by the lungs
- urea- removed by the kidneys and sweat
where does assimilation occur?
takes place in all cells using the food molecules absorbed to build more complex molecules such as proteins
