Transcript Digestion and Alimentary Canal NH

The Digestion
System
An 8m tube, from mouth
to anus.
Why Digest?
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Most nutrients are too large and insoluble
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Physical breakdown increases s.a
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Chemical breakdown increases solubility
Digestive System
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Alimentary canal- mouth to anus
 Functions
 Movement
 Secretion
 Digestion
 Absorption
 Assimilation
 Egestion
 Nutrient production (by bacteria)
II. Digestion Products:
Proteins
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Carbo-
hydrates
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Lipids
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Amino acids subunits
Muscle,enzymes,Hb
Last use for food
Simple sugar (glucose)
Quick energy food
1st used
Fatty acids & glycerol
Long term food,
insulation,protection
2nd used for food
Be able to draw the gut:
GI Tract
Food
Bolus
Chyme
“Waste”
Mouth
Esophagus
Stomach
Duodenum
Ileum
Jejunum
Cecum
Ascending colon
Transverse colon
Descending colon
Sigmoid colon
What do you think actually happens?
Complete the cartoon strip on the board using diagrams
I 1) Mouth:
Mechanically
breaks up food
Chemically digests
 Carbohydrates
 Basic pH
 Enzyme amylase
from salivary
glands
Wets & forms
“bolus”
Digestion and the Mouth
Cooking
 Mastication
 Saliva
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Enzymes to help breakdown simple sugars
 Mucus to lubricate the food for easier
swallowing
 Lysozyme to kill bacteria
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Tongue
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Taste receptors
 (Flavor is enhanced with the olfactory cells)
 Enzymes to help breakdown fatty acids
Epiglottis
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Movement
http://www.lionden.com/peristalsis.htm
2. Stomach
Mechanically churns
Stores food
Chemically digests
 Proteins
 Acid pH
 Enzyme
Pepsinsinogen and
rennin
 Stretch receptors
initiate gastric
hormone
Mucus Lining prevents
digestion of itself !
What stimulates acid production?
Stimulated by
Animation of acid production
 Gastrin- activates HCl, pancreas, and small
intestine
 Stomach distention
 Histamine
 Thoughts of food (nerve input)
 Food itself
Prevents autodigestion
 Stop secretion when pH is ~2
 Thick mucus layer
Gastrin
Originated from the pyloric region of the
stomach and upper duodenum
 Stimulated by food, thoughts of food
 Stimulates flow of stomach enzymes and
HCl
 Stimulates contraction of cardiac sphincter
 Slows gastric emptying
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The Liver and bile
Liver involved in storage of
vitamins & minerals, glycogen.
 Detoxifies chemicals like alcohol.
 Controls protein levels
(deamination) to make uric acid
 Controls salt levels
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Bile is a mixture of unwanted
cholestrols (emulsifiers),
bicarbonate ions, excess salts and
pygments like haem.
The Pancreas
Bicarbonate ions: HCO3- neutralises acids
 Amylase: starch to maltose
 Trypsin: proteins to polypeptides
 Phospholipase: phospholipids to P.lipids, f.a
 Lipase: lipids to glycerol & f.a.
 Pancreatic Juice pH 8
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Secretin
Originated from the duodenum, jejunum
 Stimulated by the presence of acidic chyme
and the presence of peptones in the
duodenum
 Stimulates the secretion of bicarbonate
 Slows gastric emptying
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Explain the structural features of
exocrine gland cells.
Exocrine glands – secrete into a duct.
Endocrine….? (ductless)
Describe the common structures
H.3.1Draw and label a diagram showing a transverse section
of the ileum as seen under a light microscope.
3. Small Intestine
Absorption
of food
Digestion of
 Lipids (fats)
 Carbos
 Trypsinogen
activated by HCl
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Lipase & Amylase
from the pancreas
Immobilised enzymes
on epithelium
Digestion in Small Intestines
Absorption
 Folds, villi, microvilli expand
absorptive surface
 Most nutrients absorbed here
 Fat-soluble nutrients go into
lymph
 Other nutrients into blood
Explain the structural features of villi including
microvilli, mitochondria, pinocytotic vesicles
and tight junctions.
H.2.5 Outline the role of membrane-bound enzymes on the
surface of epithelial cells in the small intestine in digestion
Immobilised enzymes in the plasma
membrane
They are…….
Overview of Absorption
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Absorptive mechanisms
 Passive diffusion • Facilitated diffusion • Active transport
Absorption from Large Intestines
Large intestine = 1.5m long (caecum, colon,
rectum). No digestion
 Site of water, salt, vitamin absorption (leaving a
mass in a semi-solid state). Vitamin K by bacteria.
 Almost everything of nutritional value has been
utilized by time it reaches the large intestines -leaving only waste (cellulose, pectins, pentosans,
other)
 Feces contains some water, dead mucosal cells,
bacteria, non-absorbed remains of digestion
(inorganic matter and lipid)
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9. Appendix: vestigial organ
Cows and their bacteria…
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Without intestinal symbiotic bacteria, humans
wouldn’t be able to digest many fibrous foods or
get many essential vitamins.
H.2.6 Outline the reasons for cellulose not
being digested in the alimentary canal
Major component of the plant cell wall
 Do not possess cellulase enzymes
 No not have bacteria/protozoan in the gut
which produces cellulase (herbivores do)
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Good consequence??
 Fibre!
 To maintain peristalsis
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The Gastrointestinal Tract-Recap
Objective 6.1.3
Enzyme
Amylase
Protease
Lipase
Example of enzyme
Salivary amylase
Pepsin
Pancreatic lipase
Source
Saliva
Stomach
Pancreas
Substrate
Starch
Protein
Triglycerides (fats or oils)
Products
Maltose (needs to be further
broken down)
Small polypeptides (chain of
amino acids)
Fatty Acids and Glycerol
Optimum pH
pH7 (7.2)
2
7–8
Control of Digestion by the Nervous System
Nutrition and GI Disorders
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Constipation
 Hard, dry, infrequent
stools
 Reduced by high fiber,
fluid intake, exercise
Diarrhea
 Loose, watery,
frequent stools
 Symptom of
diseases/infections
 Can cause dehydration
Diverticulosis
 Pouches along colon
 High fiber diet reduces
formation
Ulcers
Helicobacter pylori
 Heavy use of aspirin
 Excessive acid production in the stomach
 Symptoms
 Pain 2 hours after eating
 Treatment
 Antibiotics
 Antacid
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Heartburn
Gastroesophageal reflux disease
 Gnawing pain in the upper chest
 Acid from the stomach to the esophagus
 Treatment
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Smaller meals
 Less fatty meals
 Stop smoking
 Do not lie down after eating
 Avoid offending foods
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Constipation
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Slows movement of fecal matter
Increases fluid reabsorption; hardening
of the feces
Causes:
 Results from ignoring normal urge
 Antacids, calcium and iron
supplements
Treatment
 Plenty of dietary fiber and fluids
 Laxatives
Quiz
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True or false is stress the cause of stomach ulcers?
What is the name of the organism that causes ulcers?
Why does the HCl and pepsin have no effect on the
organism?
Why can it survive where it lives?
How does the immune system respond and what are the
consequences of this?
What effect does the organism have on the gastric acid?
What is the consequence of this?
A very bad infection of the bacteria could lead to what?
Quiz Answers
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Stress does not cause stomach ulcers
Helicobacter Pylori
The bacteria lives in the mucus on the surface of the epithelial cells.
pH is higher and no enzyme can get to it
The immune system responds by white blood cells
Accumulation of WBCs can damage tissue and cause and ulcer
The bacteria decreases the amount of gastric acid
More chance of ulcers with less acidity
Very bad infection of the bacteria could lead to cancer