Transcript Digestion - Angelfire

Hierarch in Biology
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The living world is organized in a series of
hierarchical levels from less complex to more
complex
Atom
Molecule
Organelle
Cell
Tissue
Organ
Organ system
Digestive System
Cells can perform all the necessary
functions of life
 For nutrition and digestion a single cell
acquires nutrients through diffusion,
osmosis and active transport
 Multicellular organisms require a more
specialized system for digestion
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Role of Digestion
The human body requires six types of
nutrients in order to function
 The organs of the digestive system allow
you to extract useful nutrients from food,
deliver them to your cells and eliminate
wastes
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Basic Structure
The disgestive tract (alimentary canal) is
basically a muscular tube open at both
ends
 The inner surface of tube is continuous
with outer surface of body
 Food enters one end, products of
digestion are absorbed and waste
products are eliminated
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Structure of Wall of Digestive
Tract
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Layers of the gastrointestinal wall are
basically the same throughout
Types of Mucosa Tissue
Steps in Digestion
There are four basic steps in digestion
 Ingestion
 Digestion (mechanical and chemical)
 Absorption
 Elimination
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Ingestion
Digestive tract is approx. 6.5 to 9 m long
 It stores and breaks down organic
molecules into simpler components
 Digestion begins in the mouth where food
is taken in, chewed by the teeth and
formed into a bolus by the tongue
(physical digestion)
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Saliva begins the chemical digestion of
food
 Movement through the esophagus is
regulated by contractions of smooth
muscles called peristalsis
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http://www.westga.edu/~lkral/peristalsis/
Digestion - Stomach
Digestion begins in the stomach
 Gastric fluids (mucus, HCl, and
pepsinogins) aid in digestion
 Mucus provides the stomach with a
protective coating against the effects of
HCl and pepsinogins
 HCl kills harmful substances ingested with
food and converts pepsinogin into its
active form pepsin
 Pepsin is a protein digesting enzyme
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Digestion – Small Intestines
Most digestion occurs in the small
intestine (~7 m in length) within the first 25
– 30 cm (the duodenum)
 Pancreatic fluids are stimulated by the
conversion of secretin from prosecretin in
the small intestine
 Pancreatic enzymes begin the chemical
digestion of lipids, proteins and
carbohydrates
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Absorption (stomach and small
intestines)
The stomach absorbs some water, specific
vitamins, some medicines and alcohol
 Most absorption takes place within the
small intestine
 Long fingerlike tubes (villi) greatly increase
the absorptive surface area
 Cells that make up the lining of each villus
have microvilli which further increase the
surface area
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Each villus contains blood capillaries and
lymph vessels called lacteals
 Some nutrients are absorbed by diffusion
while others are actively transported
 Carbohydrates and amino acids are
absorbed into the capillaries
 Fats are absorbed into the lacteals
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Absorption (large intestine)
Large intestine (~ 1.5 m long) stores
wastes long enough to reabsorb water out
of the wastes
 Large intestine contains bacteria such as
E. coli which are essential to life and use
waste material to synthesize vitamins B
and K
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Elimination
As wastes build up in the large intestine,
receptors in the intestine wall provide
information to the central nervous system
 This results in the prompting of a bowel
movement resulting in the removal of
potentially toxic wastes from the body
 Ingestion of indigestible cellulose (fibre)
increases the occurrence of bowel
movements
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Components of Digestion
System
Accessory Organs in Digestion
Salivary Glands secrete saliva and
mucus which:
 lubricate food
 contain salivary amylase to begin
carbohydrate breakdown
 Dissolves food particles
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Liver
 Liver synthesizes bile
 Bile is a mixture of bile salts, bile acids,
cholesterol, phospholipids, fatty acids
and water
 Liver also extracts absorbed nutrients or
toxins from blood
 decomposes toxins such as hydrogen
peroxide, ammonia and alcohol
 Converts glucose into glycogen
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Gallbladder
Muscular sac that stores and concentrates
bile from liver
 When fat enters duodenum endocrine
cells in duodenum release hormone
cholecystokinin (CCK)
 CCK causes gallbladder to contract and
send bile into duodenum to emulsify fats
and aid in absorption of lipids
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Pancreas
Secretes a number of substances
essential to digestion such as:
 bicarbonate, lipases, carbohydrases and
proteases
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Homeostatsis
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Means the maintenance of a steady internal
state (such as blood pressure, respiration
rate, body temperature and blood sugar
levels)
Negative feedback relates of homeostasis
1. a variable rises above or below a normal
range
2. receptors detect the change and signal
other parts to respond
3. Organs receive the signal and respond
accordingly to return variable to normal