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Digestive system class notes

THE DIGESTIVE SYSTEM

Digestive system class notes

The digestive system is made up of the alimentary canal and the associated organs
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The alimentary canal is a tube leading from the mouth to the anus
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It is long and greatly folded to increase the surface area for digestion and
absorption of food
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Digestion refers to the breakdown of complex food substances into simple soluble
molecules that can be absorbed into the body
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DIGESTION IN THE MOUTH
There are three pairs of salivary glands involved:
1
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Sub-mandibular salivary gland; found under the jaw
3
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Saliva is a mixture of water, mucus and an enzyme called salivary amylase
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The
enzyme (salivary amylase) digests the starch to maltose
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The soft palate is raised to open the gullet and close the nasal
cavity
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THE OESOPHAGUS
The food then passes down into the oesophagus
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The wave of muscle contraction is
known as peristalsis
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The stomach wall is made up of thick circular and longitudinal muscle layers
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The mixing is referred to as churning and it results in the formation of a
fluid called chime
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Gastric juice contains enzymes, hydrochloric acid and mucus
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Pepsin; breaks down proteins into peptides
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Rennin; coagulates the milk protein caseinogen to casein
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3
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; activates the inactive form of the enzyme pepsin and
rennin
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4
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DIGESTION IN THE DUODENUM
The duodenum is the first part of the small intestine where most of the digestion
takes place
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ii
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The gall bladder releases the bile into the duodenum
through the bile duct
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It secretes
hormones and digestive juices
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Secretin stimulates
the liver to secrete bile and the pancreas to secrete mineral salt
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The pancreatic juice contains three digestive enzymes:
i
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iii
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Pancreatic amylase; speeds up the breakdown of the remaining starch into
maltose
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Pancreatic lipase; digests lipids into fatty acids and glycerol
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Emulsification is the breakdown of lipids into small fat droplets
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Is highly coiled to fit the limited abdominal space
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The inner walls contain secretory cells, some of which
produce mucus, others produce intestinal juice or succus entericus
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The juice contains enzymes that carry out digestive functions as follows:
i
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iii
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v
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Sucrase; speeds up breakdown of the sucrose into glucose and fructose
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Peptidase; breaks down peptides into amino acids
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The process of digestion is completed in the ileum
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ABSORPTION

Digestive system class notes

This is the process by which the soluble products of the digestion diffuse into the
cellular lining of the villi
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Absorption of the alcohol,
water soluble vitamins B and C and water soluble salts takes place in the stomach
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The ileum is adapted to its function as follows:
i
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iii
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It is highly coiled in order to slow down movement of food thus allowing
more time for digestion and absorption to take place
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The ileum is narrow so as to bring digested food into close contact with the
walls for easier absorption
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Digestive system class notes

v
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The presence of the thin epithelial layer of cells through which digested food
diffuses
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Amino acids and glucose molecules pass through the epithelium of the villi and the
capillary walls into the blood stream by a combination of diffusion and active
transport
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The incorporation of these products of digestion into cell metabolism is
known as assimilation
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ii
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Glucose; is oxidized to release chemical energy during respiration and the
rest is stored as fats underneath the skin
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Amino acids; used in the synthesis of proteins for general body growth and
repair of worn out tissues in the body
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EGESTION
The indigestible and undigested food substances reach the large intestines by
peristalsis
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The remaining semi-solid waste
material is the passed to the rectum where it is stored temporarily and eventually
eliminated from the body as faeces through the anus

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