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Digestive system
Primery Purpose of Digestive System
• Breaking down nutrients to the degree to
be absorbed, distributed and used by the
• Scince, dealing with digestive system is
call gastro-enterology.
Functions of digerstive system
• Digestion - mechanical & chemical
• Absorbtion - uptake of digested nutrients into
blood vessels within the wall of digestive tract
• Elimination – of waste substances out of the
Basic anatomy of digestive system
(p.955, fig. 25.1)
The system consists of 2 major subdivisions
• Digestive tract : mouth – pharynx – esophagus
– stomach – small intestine – large intestine
• Accessory organs: salivary glands, liver,
Mouth (pp.958-959)
• Teeth & tongue provied with mechanical
• Salivary glands (parotid is the largest) provide
with chemical digestion
• Salivary amylase digest carbs and salivary
lipase starts digest fats
Pharynx & esophagus
• Pharynx is muscular funnel, connecting mouth
with esophagus.
• Esophagus is 30 cm muscular tube, which
passes thorax, penetrates diaphagm and
enters stomach.
• Stomach is J-shaped muscular organ, which
spreads from esophagus to small intestine.
Stomach (p.966, fig. 25.12)
• Apart from mechanical digestion, stomach
provides with chemical digestion of the following
– Pepsin – digests proteins
– Gatric Lipase – digests 10-15% of fats
• Stomach secrets also hydrocloric acid, which
activates these enzymes .
• Stomach secrets Intrinsic factor, which binds
vit.B12 for its further absorbtion in small
intestine (without vit.B12 hemoglobin can’t be
synthesized, and anemia develops)
Functions of hydrochloric acid
• Activates gastric enzymes
• Destroys connective tissues
• Converts ferric ions into absorbable ferrous
(Fe2+) ions for hemoglobin synthesis
• Destroys many pathogens
Small intestine (p.980, fig.25.24)
• Consists of 3 parts
– Duodenum (lat. “12”) 25 cm length, gets bile &
pancreatic content
– Jejunum (lat. “empty”)– 1.5 m length, major part
of digestion & absorbtion
– Ileum (lat. “twisted”)– 2.5 length, has thinner
walls, rich in lymphatic nodes.
Large intestine (p.991, fig. 25.31)
• It consists of the following parts:
– Ascending colon
– Transverse colon
– Descending colon
– Sigmoid colon
– Rectum
• It function to reabsorb water & NaCl and form
Accessory organs
• Liver (p.975)
• Pancreas (p.977)