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8/8/2019 Week 11 Digestive System s2 2010
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DIGESTIVE SYSTEM
Week 11
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Functions:
1. Digestion
± Motility ± movement of food through the digestive tract by: Ingestion
Mastication
Degulation ± swallowing
Peristalsis
± Secretion
Exocrine ± water, HCL acid, bicarbonate
Endocrine ± hormones that regulate the digestive system
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2. Absorption
± The process of digested foods transportedacross the wall of the small intestine into the
blood and lymph.
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ANATOMY
Mouth
Pharynx Esophagus
Stomach
Small intestine
Large intestine Rectum
Anus
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Figure 16.1
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Divided into 2 main structur al areas:
Tubular gastrointestinal tract ± approximately
9m long and extends from mouth to anus
Accessory organs ± teeth, tongue, salivary
glands, liver, gallbladder, pancreas
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DIGESTIVE SYSTEM ACTIVITIES
Ingestion of food into the mouth
Movement of food along the digestive tract
Mechanical preparation of food for digestion
Chemical digestion of food
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Absorption of food
Absorption of digested food into the
circulatory and lymphatic system
Elimination of indigestible substances and
waste products from the body by defecation
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The Or al Cavity
Functions of the Tongue ± Mechanical processing of food
± Manipulation to assist chewing and
swallowing
± Sensory analysis (taste, texture)
± Participation in speech
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The Or al Cavity
Salivary Glands
± Three pairs of glands ± Functions of saliva
Lubricates, cleanses oral cavity
Dissolves chemicals
Suppresses bacterial growth
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The Or al Cavity
Teeth
± Participate in mastication of food
± 20 deciduous teeth (³baby teeth´)
± 32 secondary teeth (³adult teeth´)
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Teeth: Structural Components and Dental
Succession
Figure 16-6(c)
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The Pharynx
Functions of the Pharynx
± Common passageway for
food, drink, and air
Digestive MoviePLA Y
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ESOPHAGUS
Portion of the GI tract connecting the
pharynx to the stomach.
Collapsible muscular tube.
Approximately 25cm long.
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Figure 16.8a
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The stomach provides for the physical
breakdown of food that must precede chemicaldigestion.
Initiate digestion of proteins (CHO continues
from mouth but fats not digested here)
Kill bacteria with the strong acidity of gastric juice
STOMACH - Functions
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Functions Continued
Move food into the SI as a pasty material =
chyme. Only substances that can be absorbed and
digested in the stomach are alcohol and
aspirin
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The Small Intestine
Digestion in the Small Intestine
± Most digestion and absorption occurs in the small intestine ± Digestive enzymes and buffers are released by:
Pancreas
Liver
Gall bladder
Approximately 7 metres long
Food takes 4 hours to travel through the small
intestine
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Figure 16.10
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The Large Intestine
Overview of the Large Intestine
± Reabsorbs water and electrolytes
± Compacts feces
± Absorbs vitamins (K, biotin, and B5) made by
bacteria
± Stores faeces before defecation
1.2 metres long
Food takes 12-18 hours to travel through
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OTHER RELATED
STRUCTURES
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Pancreas
Produces pancreatic juice, an exocrinesecretion containing bicarbonate andimportant digestive enzymes that is passed
into the duodenum via the pancreatic duct.
Insulin and glycogen regulator
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The Liver
Functions of the Liver
± Metabolic regulation Store absorbed nutrients, vitamins
Release nutrients as needed
± Hematological regulation
Plasma protein production
Remove old RBCs
± Production of bile
Required for fat breakdown
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The Liver
The Surface
Anatomy of the Liver
Figure 16-14(a)
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The Liver
Figure 16-14(b)
The Surface Anatomy of the Liver
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GALL BLADDER
Stores and concentrates bile
Bile contains:
± Salts, bilirubin, cholesterol and other compounds
Bile is ejected into the duodenum.
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Digestion and Absorption
Processing and Absorption of Nutrients
± Two Steps in Processing M echanical
Chemical
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Digestion and Absorption
Processing and Absorption of Nutrients
± Carbohydrates
Starches are broken down by amylases
± Results in di- and trisaccharides
Enzymes on cell surface split them to monosaccharides
Absorbed by the walls of intestine
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The Digestion and Absorption of Carbohydrates
Figure 16-18(a) (1 of 2)
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Figure 16-18(a) (2 of 2)
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Digestion and Absorption
Processing and Absorption of Fats
± Bile emulsifies fats to small droplets
± Lipase hydrolyzes triglycerides into fatty acids
and monoglycerides
± Lipids diffuse into cells of intestinal wall
± Triglycerides are reformed
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The Digestion and Absorption of Lipids
Figure 16-18(b) (1 of 2)
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Figure 16-18(b) (2 of 2)
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Digestion and Absorption
Processing and Absorption of Nutrients
± Proteins Breakdown starts in stomach
± Pepsin and HCl produce fragments
Breakdown continues in small intestine
± Pancreatic proteases produce small peptides
± Peptidases releases amino acids
Intestinal wall absorbs amino acids into the body
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The Digestion and Absorption of Proteins
Figure 16-18(c) (1 of 2)
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Figure 16-18(c) (2 of 2)
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Digestion and Absorption
Water and Electrolyte Absorption
± About nine liters/day enter the digestive tract Two liters of ingested water
Seven liters of watery secretions
± Ions are absorbed by many mechanisms
Sodium, calcium, chloride, bicarbonate ± All but about 150 ml is absorbed by osmosis, as
water ³follows´ the ions
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Digestion and Absorption
Absorption of Vitamins
± Fat-soluble vitamins combine with lipidsfor absorption
± Water -soluble vitamins diffuse across
the digestive epithelium
Exception: vitamin B12
requires intrinsic factor (from the gastric mucosa) for absorption
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Aging and the Digestive System
Age-Related Changes in the Digestive
System
± Thinner, more fragile epithelium
± Reduced epithelial stem cell division
± Weaker peristaltic contraction Reduced smooth muscle tone
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DIGESTIVE SYSTEMS IMPORTANCE IN
EXERCISE
Helps to digest and store fuel important for
muscle contraction Breaks down food to fuel resynthesis of ATP
( fuel used to power mitochondria)