DIGESTIVE SYSTEM IN HUMANS
2.2.2.2 Digestive system in humans
Why a person can swallow something while
standing on their head - Once food enters the esophagus a
series of wave-like muscular contractions in the walls of the esophagus
(peristalsis) start and the food is pushed towards the stomach and other parts
of the alimentary canal
Metabolism
- All of the chemical and
physical processes necessary for life
Anabolism
- The chemical reactions of
metabolism that build up complex substances from simple
materials, they require
energy which comes from catabolism
Catabolism - A
chemical reaction of metabolism which breaks down complex substances into
simple ones and release energy
Biological
importance of saliva - Contains
the digestive enzyme salivary amylase which digests starch to
maltose, lubricates food
for easier swallowing
Importance of bile - Salts in
bile break down fats through emulsification, reacts with fat soluble vitamins (A,D,E,K) to make them water soluble,
salts in bile neutralize HCl
Autolysis - Refers to the destruction of a cell through the action of its own
enzymes i.e. self digestion Lipase - An
enzyme which digests fats and oils
Catalysts - Substances
that increase the speed of a chemical reaction and are used up in the reaction
i.e. enzymes
Deanimation
- The breakdown of unwanted
amino acids in the liver by removal of nitrogen containing part
of the nucleus
Distase
- An enzyme which digests
stored starch in seeds
Emulsification
- Breakdown of fats into
droplets
Protease
- An enzyme which digests
protein
Trypsin
- An enzyme produced by the
pancreas which digests proteins converting them to amino acids
Enzymes
which digest protein cannot digest starch because different enzymes can only
break down specific types of substrates
Absorption
- The movement of digested
(soluble) food through the walls of the alimentary canal into the
blood stream
Amylase
- A type of enzyme which
digests carbohydrates,
Alimentary
Canal (Gut) - A tube running
from the mouth to the anus inside which digestion and absorption
take place
Assimilation
- Utilization of digested
food to build cells in the body
Bile - A
greenish-yellow liquid made in the liver which is passed into the duodenum
where its function is to aid in the
digestion of fats
Cecum - A part of the intestine at the junction between
the ileum and colon, serves no function in man but is
used for digestion of
cellulose in herbivores
Chyme - The
semi-fluid mass of partly digested food expelled by the stomach into the
duodenum Cilium - An organelle found
in eukaryotic cells which help to move nutrients or other cells along in the
organism
Digestion
- The process by which food
is made soluble by the action of digestive juices (enzymes)
Dormancy
- A resting, inactive
condition in which metabolism almost stops
Duodenum - The part of the alimentary canal
between the stomach and the
ileum Esophagus - The tube through
which food passes
from the mouth to the
stomach
Fatty
Acids - Chemical
components released when
fats are broken down during
digestion Fermentation - The
breakdown of sugar by
organisms such as yeast and bacteria which takes
place under anaerobic
condition
Gastrointestinal
Tract - Refers to the
stomach and
intestines
Gall
Bladder - A small bladder
inside the liver where
bile is stored
Glycogen
- A carbohydrate similar to
starch. It is stored in the liver
and muscles of mammals and then is converted into glucose as the body requires
energy for metabolism
Hepatic Portal Vein - Vessel in which blood containing absorbed food is carried from the intestine to the
liver
Lacteal
- Part of the lymphatic
system which extends through the
centre of the villus. Its purpose is to absorb digested fat from the ileum
Larynx -
The voice box
Mucus - A
sticky fluid produced by goblets cells
Pepsin - An enzyme produced by the stomach which
begins the digestion of
proteins
Peristalsis
- A wave-like contraction of
the tubular organs such as the alimentary
canal (gut) which propels the contents of the tube in one direction
Pharynx - An area at the back of the mouth immediately above the trachea and
esophagus Rectum - The last part of
the alimentary canal
Saliva -
Fluids produced and
released into the mouth by three pairs of salivary glands in response to food.
Contains the enzyme
salivary amylase, mucin and minerals. Saliva is alkaline so the pH will be
lowered Sphincter - A ring of muscle
found in the walls of tubular organs such as the alimentary canal whose
contraction slows or stops
movements of substances through the tube Stomach
- A bag like organ at the end of the esophagus
Trachea
- The wind pipe
Villi - Minute
finger-like structures on the inner surfaces of the duodenum and ileum. These
occur in the millions greatly
increasing the surface area available for absorption
Liver - Detoxifies poisonous substances in the body such
as alcohol, performs deamination to break down amino acids and form urea
Functions of the liver - Helps regulate blood sugar
levels, stores fat to prevent starvation,
deamination, storing vitamin A and D, stores iron from broken down
erythrocytes (red blood cells)
Ileum - The region of the alimentary canal between the
duodenum and colon where digestion is completed
and absorption takes place, small intestine. It
also secretes intestinal juice
Intestinal
Juice (Succus Entericus) - Juice
containing proteins which help to break down food substance
as it passed through the
ileum
Contents and roles of intestinal juice - Mucus, mineral salts, enzymes Mucus - Helps to lubricate the
intestinal wall and prevents autolysis
Mineral Salts - Produced in order to
neutralize the acid chyme from the stomach and to provide a more suitable pH for the action of enzymes
in the intestine
Enzymes
- Protease, enterokinase,
nucleotidase, carbohydrase
Protease
- Convert peptides into
smaller peptides and amino acids and hydrolyses dipeptides into
amino acids
Enterokinase
- A non-digestive enzyme
which activates the trypsinogen produced by the pancreas
Nucleotidase
- Converts nucleotides into
sugars, organic bases and phosphoric acid
Carbohydrases
- Amylase, maltase, lactase,
sucrase
Amylase
- Completes the hydrolysis of
starch to maltose
Maltase - Hydrolyses maltose into glucose
Lactase
- Hydrolyses lactose (the
sugar in milk) into glucose and galactose
Sucrase - Hydrolyses sucrose into glucose and fructose
Factors affecting the absorption of digested
food in the ileum - Being well supplied with blood capillaries
to ensure digested food substances are absorbed into the blood, must have a
thin epithelial lining which is permeable to molecules like glucose which will
increase the rate of diffusion of the digested food substances, the epithelial
cells must be rich in mitochondria to provide energy for their activities since
the absorption of some nutrients must be forced since absorption is taken
against their concentration gradient, must possess a large surface area for
absorption
Efficient absorption in the ileum through a
large surface area is achieved in the following ways - It is long (almost 6m in humans), its walls are folded to provide large
internal projections, the folds themselves have numerous villi, the epithelial
cells lining the villi are covered with minute projections called microvilli
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