Digestive System Flashcards
The digestive system
The digestive system is responsible for breaking down complex molecules into their
simplest forms to be absorbed into the body to sustain life
mouth
cavity
The mouth cavity consists of many parts:
Teeth which break down and grind food
Tongue which mixes food and is used for swallowing of food
Hard and soft palate which forms the roof of the mouth
Salivary glands release saliva which contains enzymes (called
carbohydrases) to chemically break down carbohydrates
pharynx &
oesophagus
After food is swallowed (now called the bolus), it moves into the
pharynx which is the tube used to take in food and air
The food moves down to the larynx where the epiglottis (a
cartilage flap) stops food from going into the trachea
Food goes down the oesophagus
The oesophagus pushes food down to the stomach by peristalsis
stomach
The stomach is a muscular sac with thick walls
It churns the food and mixes it with gastric juice (hydrochloric acid
– HCl) and enzymes (this mixture is called chyme)
The stomach has two sphincters (a ring of muscles to close a
tube) to keep both openings to the stomach closed while food is
being digested
liver & gall
bladder
Liver cells produce bile which is stored in the gall bladder until
being released into the duodenum of the small intestine
Bile has a number of functions in digestion:
o Bile emulsifies large fat globules into small fat droplets which
aids digestion
o It neutralises the acidic fluid (chyme) which comes from the
stomach
o It promotes peristalsis in the small intestine
o It acts as an antiseptic which prevents decay of food
particles in the small intestine
pancreas
Secretes pancreatic juices which digest carbohydrates, proteins
and lipids in the small intestine (exocrine gland).
Also neutralises chyme from the stomach
Controls blood glucose levels in the body (endocrine gland)
small
intestine
The small intestine in humans is 6 m long and divided into three
regions: duodenum; jejunum and ileum
Duodenum is the first portion which receives bile from the liver
and pancreatic juices from the pancreas
Jejunum is the middle portion which secretes intestinal juices
Duodenum is the final portion which is the region of most
absorption in the small intestine
The small intestine has transverse folds and microscopic villi
which greatly increases the surface area for absorption
colon
The colon (also called the large intestine) is divided into three
regions: ascending colon, transverse colon and descending colon
Most water and mineral salts are absorbed in the colon
The descending colon leads to the rectum followed by the anus
where undigested food is egested
There are five steps in the digestive process
■Ingestion
■Digestion
■Absorption
■Assimilation
■Egestion
mastication
to chew food
enzyme
a protein that acts as a catalyst to regulate or speed up most
biochemical reactions in living cells
emulsion
a fine dispersion of minute droplets of one liquid (e.g. fats &
oils) in another in which it is not soluble or miscible
protease
a group of enzymes that catalyses the breakdown of proteins
into amino acids
carbohydrase
a group of enzymes that catalyses the breakdown of
carbohydrates into simple sugars
lipase
a group of enzymes that catalyses the breakdown of lipids
(fats and oils) into glycerol and fatty acids
lacteal
a lymph capillary in the villi of the small intestine where fats
are absorbed
deamination
removal of an amino group from amino acids
metabolism
the chemical processes that occur within a living organism in
order to maintain life
Mechanical digestion
Mechanical digestion is the physical breakdown of large food particles into
smaller particles.
Mechanical digestion (no enzymes)
Mechanical digestion is the physical breakdown of large food particles into
smaller particles.
Physical digestion does not alter the chemical structure of the compounds but
it increases the surface area.
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Physical digestion occurs during mastication, churning in the stomach and
during peristalsis.
Food is moved through the digestive system by the rhythmic contraction and
relaxation of circular muscles along the alimentary canal (Figure 5). This
process is called peristalsis.
Peristalsis is a reflex action and is triggered by the presence of the food in the
alimentary canal.
Chemical digestion
Chemical digestion is the breaking down of large food compounds into smaller food
compounds using digestive enzymes
Assimilation
Assimilation is the incorporation of absorbed nutrients into the cells of the
body
Assimilation
Assimilation is the incorporation of absorbed nutrients into the cells of the
body. The body cells absorb the required nutrients which are necessary for
the building and maintenance of compounds.
For example, muscle cells will absorb amino acids to be converted to proteins
and glucose will be absorbed by cells to provide energy.
The liver plays a vital role in the assimilation of nutrients.
The liver is responsible for the metabolism of glucose, deamination of amino
acids, the breakdown of alcohol, drugs and hormones.