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.
Egestion
All undigested materials are transported through the colon where most water
and mineral salts are absorbed.
Amino acids & glucose are absorbed into blood capillaries of the villi in the small
intestine
Capillaries join together to form large venules to form the hepatic portal vein
transports amino acids and glucose to the liver
Glucose and amino acids flow through hepatic vein to the heart
The liver converts excess glucose to glycogen and stores it
Excess amino acids are deaminated by the liver to form urea (waste product) and
are removed from the body
& glucose absorbed into blood capillaries of villi
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The undigested material is temporarily stored in the rectum until it is excreted
through the anus. The undigested waste is then referred to as faeces.
homeostasis
the ability of an organism to maintain stability of internal
conditions (e.g. temperature, chemical balance) despite
changes in its environment
negative
feedback
mechanisms
mechanisms in the human body that detect changes or
imbalances in the internal conditions and restore homeostasis
blood glucose
amount of glucose in the blood
insulin
a hormone made in the pancreas and released into the blood to
help convert glucose to glycogen to reduce blood glucose
glucagon
a hormone made by the pancreas that raises blood glucose
levels by converting stored glycogen to glucose
glycogen
form in which glucose is stored in the liver and cells
The following is a general sequence of events in a negative feedback mechanism:
Step 1: An imbalance is detected
Step 2: A control centre is stimulated
Step 3: Control centre responds
Step 4: Message is sent to target organ/s
Step 5: The target organ responds
Step 6: It opposes / reverses the imbalance
Step 7: Balance is restored.
Diabetes mellitus
Diabetes mellitus is a disorder characterised by high blood glucose levels resulting in
increased fatigue (tiredness), dehydration and lack of energy
Types of diabetes mellitus
Type 1 diabetes
Cause: Usually an inherited disorder or
a loss of insulin-producing cells in the
pancreas
Treatment: Lifelong disorder that
requires daily injections of insulin and
specially adapted diet
Type 2 diabetes
Cause: Insulin resistance where body
does not produce or react to insulin,
usually as a result of poor lifestyle
choices
Treatment: Maintaining a balanced diet,
regular exercise and medication
Balanced diet
A balanced diet is required to maintain good health. A balanced diet should consist
of all the necessary nutrients in their correct quantities. Carbohydrates and fats
provide the body with energy, protein is used for building and repair of cells and
vitamins and minerals for maintenance of immune system and bodily processes. The
amount of nutrients required is dependent on age, gender and level of activity. For
example, growing children need more protein to build and repair cells; active
Different diets
■vegan
■vegetarian
■halaal
■kosher
vegan
Do not eat any animal products such as meat, eggs and milk
vegetarian
Do not eat meat but do eat dairy products and eggs.
halaal
Followers of Islamic faith do not consume pork, alcohol, carnivorous
animals or any food that comes into contact with carnivorous
animals. The slaughter of animals must follow strict rules
kosher
Followers of Jewish faith do not eat pork, shellfish, fish without fins or
scales, no predatory birds etc.
Malnutrition
Malnutrition occurs when a person does not follow a balanced diet.
This can lead to a number of different disorders or diseases
■kwashiorkor
■marasmus
■anorexia
nervosa
■bulimia
■coronary
heart disease
■diabetes
■obesity
