Chapter 8: Digestion Structure and Functions of Digestive Organs Macronutrients 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: Mouth Pharynx Esophagus Stomach Small Intestine Large Intestine Anus Accessory Organs: Salivary glands Pancreas Liver Gall 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 - function Strong 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/strucure Complete 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: Duodenum Jejunum Ileum
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