Transcript Digestive System

Digestive System
What does it do?
Function

To prepare food/nutrients for absorption
What must happen to food before
it can be absorbed?
(What is absorption?)
 (What can easily be absorbed?)


How does a bacteria obtain nutrients from
food?
Digestion

Two types of digestion
– physical/mechanical digestion: breaking the
food into smaller pieces (to increase surface
area)
– Chemical digestion: breaking large molecules
down into smaller molecules (by use of
enzymes)
Is it inside?
GI tract
The digestive system is essentially a tube
that runs through the body
 This ‘tube’ is called the GASTROINTESTINAL (GI) TRACT
 The space inside the GI tract is called the
LUMEN

Accessory organs
Several organs lie adjacent to the GI tract
at different points and secrete substances
which facilitate digestion and/or
absorption
 Salivary glands, liver, gall bladder and
pancreas

Basic terms
Ingestion: food enters the GI tract
 Digestion: food is mechanically and
chemically broken down
 Absorption: nutrients pass through a cell
membrane and enter the body
 Egestion: unabsorbed and waste
materials leave the GI tract

Soft palate
mouth
Parotid gland
Sublingual gland
pharynx
Submaxillary gland
epiglottis
Esophagus
Liver
Stomach
Gall bladder
Pancreas
Bile duct
Pancreatic duct
duodenum
Transverse colon
Small intestine
Descending colon
Large intestine
Ascending colon
caecum
rectum
appendix
anus
The Mouth
Mechanical digestion
 (some chemical)
 Teeth
 Tongue
 Salivary Glands

Teeth
Incisors – flat-edged – cutting
 Canines – triangle – grasping and tearing
 Molars – square – grinding/crushing

Tongue

Used to move food
around the mouth

Forms chewed up
food into BOLUS –
wet ball of food
Salivary Glands
Salivary Glands

Produce saliva which
– Moisten
– Soften
– Lubricate

Saliva also contains amylase which begins
the breakdown of starch
Pharynx and Epiglottis
Pharynx and Epiglottis
Pharynx: joint passage for air and food
where the oral and nasal cavities meet
 Epiglottis: flap of tissue which prevents
food from going down airway

Esophagus
Esophagus
Tube connecting mouth to stomach
 Bolus is propelled to the stomach via
PERISTALSIS
 Peristalsis: wave-like muscular
contractions

Stomach
Stomach

Thick, muscular organ with three layers of
muscle churns food with gastric juices

Cells produce hydrochloric acid, pepsin
and mucus

Small molecules like water, amino acids
and alcohol can be directly absorbed
Gastric Pits
Stomach secretions

Parietal cells produce HYDROCHLORIC
ACID which make the stomach acidic

Chief cells produce PEPSIN which begins
digestion of protein

Other cells produce MUCUS which protect
the stomach lining
CHYME

The mixture of blended up food and acid
is known as CHYME
Small Intestine
Small Intestine
Long, narrow tube 2-3cm in diameter but
approximately 7m long
 Consists of three sections: duodenum,
jejunem and ileum
 Site of chemical digestion and absorption
 Pancreas and Liver add secretions to
chyme

Villi and Microvilli
Villi and Microvilli

Increase surface area for absorption
Secretions in the small intestine

The pancreas and liver add secretions to
the chyme in the duodenum in order to:
– Neutralize the acid
– Continue chemical digestion
– Improve absorption
The Pancreas
Produces BICARBONATE which neutralizes
the stomach acid
 Also produces many DIGESTIVE ENZYMES
which break down food

Digestive Enzymes
Proteases break down protein (Trypsin,
Chymotrypsin, exopeptidases)
 Lipases break down fat
 Amylases break down starch

The Liver and Gall Bladder
The liver produces BILE which is stored in
the gall bladder
 Bile emulsifies fat
 This allows it to be broken down by
lipases and absorbed

Bile
Large Intestine
Large Intestine
Tube 6cm in diameter and 1.5m long
 Primary function is to reabsorb water and
form stool
 Bacteria in the large intestine produce
vitamin K

Large Intestine
Caecum is the ‘dead-end’ that lies below
where the small intestine connects to the
large intestine
 The appendix is the finger-like extension
off of the caecum
 The appendix is theorized to act as a
reservoir for bacteria

Rectum and Anus
Rectum and Anus
The rectum is the area where stool is
stored immediately before egestion
 The anus is the opening
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