Digestive System
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Transcript of Digestive System
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Digestive System
http://www.youtube.com/watch?v=0gY-zXsUYgs
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Humans as HeterotrophsHetero=another Trophe= nutrition
As heterotrophs we cannot convert carbon therefore we ingest carbon in our food.
All of our cells require nutrition for;1)Growth2)Repair 3)Maintenance
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Functions of the Digestive System
1. Break down of food into nutrients.
2. Nutrients absorbed in the body. 3. Transported throughout the
circulatory system. Nutrients in the cell can be used as a source of energy OR Used for the synthesis of
chemical compounds
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Stages of the Digestive System
1. Ingestion
2. Digestion
3. Absorption
4. Egestion
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1. Ingestion
Ingestion occurs when food enters the mouth.
It is mechanically broken down by teeth
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1. Ingestion: Cont.
Chewing stimulates the release of saliva from the salivary organs.
Saliva contains a mixtures of water, mucus and enzymes.
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1. Ingestion: Amylase
Enzyme that breaks starch down into simple sugars.
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1. Ingestion: Bolus
Food that has been chewed and mixed with saliva becomes a bolus.
The epiglottis, a flap of skin directs food down the esophagus.
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1. Ingestion: Peristalsis
When the bolus has entered the esophagus muscle contractions (peristalsis) move it towards the stomach.
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2. Digestion:
Stomach
Digestion occurs initially in the stomach.
The stomach is J-shaped, it stores food, and has a capacity of 1.5 L
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2. Digestion: Sphincters
Food enters and exits the stomach through sphincters.
Sphincters are muscles surrounding a tube-like structure
The bolus enters the stomach when the cardiac sphincter relaxes.
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2. Digestion: Gastric Juice
The stomach contains gastric juice secreted by the stomach lining.
Gastric juice contains a mixture of:HCL (hydrochloric acid) EnzymesMucus
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2. Digestion: Gastric Juice
HCLBreaks down
fibres & BacteriaMucus
Protect stomach lining from HCL
If stomach lining is destroyed ulcers form.
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2. Digestion
The stomach absorbs: Water Alcohol Some medications (Aspirin)
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2. Digestion: Chyme
Chyme travels out of the stomach by the pyloric sphincter into the small intestine.
Chyme is a mixture of: Water Digested food Gastric Juices
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2. Digestion: Small Intestine
After the pyloric sphincter chime enters the duodenum
Duodenum is first 25cm of the small intestine.
7m in length, 2.5m in diameter.
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2. Digestion: Duodenum
Majority of digestion occurs here.
Secretions from pancreas and duodenum enter via a duct.
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2.Digestion: Liver
Has four functions in digestion:1. Synthesis2. Breakdown3. Detoxification4. Storage
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Synthesis
Produces bile which breaks down fats. Bile is stored in the gallbladder
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1. Synthesis: Bile
Bile is an emulsifier (a compound used to mix immiscible substances)
This allows for the breakdown of fats and for travel through the digestive system.
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1. Synthesis: Gallstones
Gallstones occur when too much bile or concentrated bile is produced in the gallbladder.
The bile will crystalize into gallstones blocking the gallbladder.
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2. Breakdown
Process of removing Nitrogen group from Amino Acids to create urea.
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2. Breakdown: Jaundice
When there is a blockage of the gallbladder Jaundice can occur (yellowing of the skin).
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3. Detoxification
Removes toxins from the body includingAlcoholChemicals
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4. StorageVitamins and carbohydrates are stored in the liver.
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Pancreas
Increases the pH of chyme from 2.5 to 9 due to the production of sodium bicarbonate.
Secretes enzymes for digestionLipase (fats)Trypsin (proteins)
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Small Intestine Secretes
Maltase (maltose - > glucose)
Peptidase (protein breakdown)
Duodenum (beginning), Jejunum (middle), Ileum (end).
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Food & Enzymes
Carbohydrates -> Glucose (amylase & maltase)
Proteins -> Amino Acids (pepsin & peptidase)
Fats (triglycerides) -> Fatty Acids & Glycerol
(bile & lipase)
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3. Absorption
The jejunum and ileum contain villi (finger like projections) which increase the surface area.
The villi help with absorption ofGlucoseAmino AcidsFatty AcidsGlycerol
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3. Absorption
Once nutrient are absorbed through the villi they enter the blood stream and are dispersed throughout the body
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3. Absorption: Large Intestine
Water absorptionBacteria living in colon releasing Vitamin K & B, also absorbed.
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4. Egestion
Cellulose aids in the ejection of material from the bowels.
Lack of cellulose in the diet can lead to colon cancer.
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Digestive System
The entire process takes 24-36 hours.
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Homeostasis
The ability of the body to regulate according to the fluctuating internal and external environment
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Digestion & Homeostasis
Nervous and hormonal system aid digestion before we eat.
Seeing, smelling and tasting food stimulates production of gastric secretions.
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Digestion & Homeostasis Cont.
Swallowing stimulate the production of gastric juices.
Gastrin (hormone) stimulates the release of gastric juice before food arrives.
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Digestion
Speed of Digestion:Large meals with digest quickly due to strong stomach contractions and faster emptying.
Fatty meals slow down digestion due to a hormone response from the small intestine.
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Homeostasis
Receptors in the body sense:Blood Sugar levelsBody TOxygen level
Disruption in homeostasis -> Signal to brain for correction
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Homeostasis: Blood Sugar
Blood SugarConcentration crucial to well beingToo low body shuts down (coma)
Eating increases blood sugar (glucose)
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Homeostasis: Blood Sugar
Body releases insulin from pancreas to bring glucose inside cells.
Extra glucose taken by liver cells and convert to glycogen and stored.
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Homeostasis: Blood Sugar
Decrease in blood sugar pancreas will be activate to release glucagon
Glucagon (hormone) will convert glycogen (in liver), back to glucose, which will be released into the blood.
normal glucose
normal glucose
high glucose
food
low glucose
insulin release (pancrea
s)
cells take up excess glucose, liver makes glycogen
glucagon
release (pancre
as)
glycogen release
as glucose (liver)
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