chapter 8: digestion - weeblymisspawlick.weebly.com/uploads/7/2/2/2/72226221/... · 2019-09-29 ·...
TRANSCRIPT
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Chapter 8: Digestion
Structure and Functions of Digestive OrgansMacronutrients
Digestive Enzymes
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What organisms need Digestion?Heterotrophs - rely on ingestion of organic molecules for production of energy
- consumers!!
Autotrophs - able to produce organic molecules themselves
- plants/producers!!
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What are steps of Digestion?
Ingestion
Digestion
Absorption
Egestion
Assimilation
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What are types of Digestion?
Digestion is both mechanical and chemical
Mechanical - chewing, mashing, softening, mixing ect
Chemical - acids and enzymes
How do we turn foods into energy?
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How many parts of the digestive system can you name?
Primary Organs:
MouthPharynx
EsophagusStomach
Small IntestineLarge Intestine
Anus
Accessory Organs:
Salivary glandsPancreas
LiverGall Bladder
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Mouth - Function
Teeth and Tongue - chewing and mixing of food
Saliva - softens food and contains enzymes
Food is formed into a ball
“bolus” to be swallowed
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Mouth - Secretions
Salivary Glands - secret up to 2L of saliva a day
Saliva contains: Water - moisten food
Amylase - enzyme which breaks down starches
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Pharynx
Area at back of mouth
- sorts food/liquids into the esophagus
- keeps food/liquid out of airways (nasal cavity and trachea)
Sorting is controlled by
a flap = EPIGLOTTIS
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Esophagus
Connects pharynx to stomach by passing through middle of thorax(chest)
Moves food by wave-like contractions and relaxations of muscular walls = PERISTALSIS
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Stomach - structure
J- shaped muscular pouch
Connected to esophagus by the LOWER ESOPHAGEAL SPHINCTER(LES)
small intestine by the PYLORIC SPHINCTER
Sphincters are ring-like muscles which contract to close the opening and relax to open.
They control movement of food through the parts of the digestive system
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Stomach - functionStrong muscular contractions mix food with secretions to break-down molecules (mechanical and chemical digestion)
Gastric folds allow the stomach to stretch and move food along
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Stomach - secretions
Gastric Fluid: up to 500mL can be produced during a meal
Hydrochloric Acid (HCl) -
creates acidic environment in the stomach (pH 1-2)
kills pathogens (bacteria, fungus) in food
Begins chemical digestion of proteins by denaturation
Activates pepsinogen into pepsin
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Stomach - secretions
Pepsin - protein-digesting enzyme
is secreted as pepsinogen (inactive-form) and activated into pepsin by a low pH (HCl acid)
*This a safety measure to protect cells from having their proteins digested!
Mucus - lubricates food material
lines stomach to protect tissue from HCL and pepsin
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Ulcers - when gastric fluid goes wrong
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Small Intestine - function/strucureComplete the digestion of food by mixing with secretions from liver and pancreas (chemical digestion)
Begin absorption of nutrients into the bloodstream
Up to 7m in length
Divided into 3 sections:
DuodenumJejunumIleum
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Small Intestine- structure
The inside of the small intestine is covered with millions of tiny finger-like projections called villi- each villus has an outer layer of of microvilli- The villi and microvilli increase surface area for
absorbing nutrients into the blood
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Small intestine - Pancreas
The pancreas secretes Sodium Bicarbonate and many digestive enzymes into the small intestine.
Sodium Bicarbonate - neutralizes the acidic stomach contents when they enter the small intestine
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Small intestine - Pancreas
Amylase - breakdown of carbohydrate molecules
Lipase - breakdown lipids (fats) into fatty acids and glycerol
Trypsinogen and Ereprsin - breakdown proteins into amino acids
Trypsingoen(inactive form) is converted to trypsin (active form) by enterokinases in the small intestine
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Small intestine - Liver/Gall Bladder
The liver:
- Stores glycogen (form of glucose) and vitamins- Detoxifies harmful substances in the body
- Ex. alcohol, urea, hemoglobin
- Produces Bile which is stored in the Gallbladder until released into the small intestine through the bile duct
Bile contains:
Bile salts - emulsifies fat into small droplets
Pigments - gives feces their brown colour
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Small intestine - Liver/Gall Bladder
Bile salts break down fat into smaller pieces by emulsification which is a type of physical digestion, NOT chemical digestion! (no chemical bonds are broken!)
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Large Intestine- Structure
3 main parts: Colon and Rectum
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Large Intestine - Function
2 parts: Colon and Rectum
Colon - resorbs water and some minerals/vitamins
indigestible material (such as fibre) accumulates and adds bulk for easier passing
Rectum - final storage site of waste materials
has sensory nerves to control bowel movements
material exits through the anus
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Hormone Control of Digestion
Hormones are chemicals secreted into the blood stream to deliver a “message”
Gastrin - released from stomach when it extends with food
stimulates secretion of HCl acid by stomach
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Hormone Control of Digestion
Secretin - released from small intestine when HCl acid enters from the stomach
Stimulates release of pancreatic secretions
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Hormone Control of Digestion
Enterogastrone and Cholecystokinin(CCK)
- both released from small intestine in presence of high fat
Enterogastrone slows down intestinal movement to allow more time for digestion
CCK stimulates release of bile from gall bladder