Upload
others
View
5
Download
0
Embed Size (px)
Citation preview
Chapter 8: Digestion
Structure and Functions of Digestive OrgansMacronutrients
Digestive Enzymes
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!!
What are steps of Digestion?
Ingestion
Digestion
Absorption
Egestion
Assimilation
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?
How many parts of the digestive system can you name?
Primary Organs:
MouthPharynx
EsophagusStomach
Small IntestineLarge Intestine
Anus
Accessory Organs:
Salivary glandsPancreas
LiverGall Bladder
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
Mouth - Secretions
Salivary Glands - secret up to 2L of saliva a day
Saliva contains: Water - moisten food
Amylase - enzyme which breaks down starches
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
Esophagus
Connects pharynx to stomach by passing through middle of thorax(chest)
Moves food by wave-like contractions and relaxations of muscular walls = PERISTALSIS
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
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
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
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
Ulcers - when gastric fluid goes wrong
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
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
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
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
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
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!)
Large Intestine- Structure
3 main parts: Colon and Rectum
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
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
Hormone Control of Digestion
Secretin - released from small intestine when HCl acid enters from the stomach
Stimulates release of pancreatic secretions
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