SBI3U - Unit 6 - Digestive System

The goal of the digestive system is to process and breakdown food into small enough pieces that are absorbable by the capillaries to provide nutrients for the body to produce energy

Feeding Mechanisms

Filter Feeding - Filters water and digests particles that is extracted from it
Substrate Feeding - An organism lives on the food source and eat their way through the food
Fluid Feeding - Food consumed in liquid forms
Bulk Feeding - Eat large amounts of food swallowed whole or broken down

Steps of the Digestive System

Ingestion - Food is taken into the body
Digestion - Complex food is converted into simpler substances
Absorption - Capillaries absorb nutrients and the circulatory system transports nutrients into tissues
Egestion - Undigested and non-absorbed food is eliminated from the body

Chemical Secretions

Enzymes - Proteins that act as biological catalysts to speed up chemical reactions in cells but do not break down
- Salivary Amylase - An enzyme from the salivary glands in the mouth; it digests carbohydrate polysaccharides such as starch; it turns polysaccharides into disaccharides such as maltose
- Pepsinogen - An inactive enzyme that is converted to pepsin in the presence of HCl
  - Pepsin - An enzyme from the chief cells of the stomach lining that breaks down proteins into smaller peptides and amino acids
- Prochymosin - The precursor to the enzyme chymosin that is converted by proteinases
  - Chymosin - An enzyme from the stomach lining that coagulates milk proteins into insoluble casein proteins that can be digested by pepsin
- Trypsinogen - The inactive form of the enzyme trypsin, which is converted by enterokinase
  - Trypsin - An enzyme that breaks peptide bonds into proteins, and converts polypeptides into individual amino acids
- Enterokinase - An enzyme produced by the lining of the duodenum that turns trypsinogen into trypsin
- Pancreatic Lipase - A digestive enzyme produced by the pancreas that turns triglycerides into fatty acids and glycerol
- Pancreatic Amylase - A digestive enzyme produced by the pancreas that converts starch into maltose
- Erepsin - Protein digesting enzymes called peptidases from the pancreas and ileum
- Maltase - An enzyme from the small intestine that converts maltose into two glucose molecules
- Lactase - An enzyme from the small intestine that converts lactose into glucose and galactose
- Sucrase - An enzyme from the small intestine that converts sucrose into glucose and fructose
Hormones - Chemical messengers that are secreted in the blood and travel throughout the body to their target tissue
- Gastrin - Released into the blood by G-cells in the stomach lining in response to proteins entering the stomach or thinking of food; targets the chief cells to produce pepsinogen, and parietal cells to produce H+ ions to make HCl, and stimulates the release of gastric juices
- Cholecystokinin - A hormone produces in the small intestine lining, triggered by the presence of chyme and HCl in the duodenum; it causes the gall bladder to contract and release bile into the duodenum; it causes the pancreas to release digestive enzymes into the duodenum
- Prosecretin - The unusable form of the hormone secretin that is activated by a low pH
  - Secretin - A hormone from the small intestine that targets the pancreas, which then releases bicarbonate into the duodenum to neutralize stomach acid
Bicarbonate - The compound HCO₃^- from the pancreas that neutralizes stomach acid by increasing the pH of chyme in the duodenum
Hydrochloric Acid - Acid from the parietal cells in the stomach, which helps break down food and kill potentially harmful pathogens
Mucus - Secreted by the stomach lining to protect itself from the acidic environment, and contains a high concentration of bicarbonate
Bile - A substance produced in the liver made of bile salts, phospholipids, cholesterol, and bile pigments that neutralizes chyme and emulsifies fat; it moves through the common bile duct to the gall bladder
Macromolecule - A broad term for any large molecule
Macronutrients - Macromolecules that provide dietary energy to the body and help it maintain it’s structure
- Carbohydrate - Macronutrients made of carbon, hydrogen, and oxygen, which provide materials to build cell membranes
  - It is the most important source of energy in the body
  - Comes from plants
  - Monosaccharide - A single molecule sugar that can be in a ring or chain formation
    - Glucose - The monosaccharide sugar in blood
    - Fructose - The monosaccharide sugar in fruits
    - Galactose - The monosaccharide sugar in dairy
  - Disaccharide - Sugars made of two monosaccharides formed through dehydration synthesis
    - Maltose - A disaccharide sugar in grains made of two glucose molecules
    - Lactose - A disaccharide sugar in dairy products made of glucose and galactose
    - Sucrose - A disaccharide made of fructose and glucose
  - Polysaccharide - Sugars made of long chains of monosaccharides or disaccharides
    - Starch - A polymer of glucose, created when plants convert sugars to starch to serve as energy storage, where it can be converted back into sugar
    - Glycogen - A polymer of glucose found in the liver and muscles, that serves as the energy storage of animals, where is can be converted back into glucose
    - Cellulose - A polymer of glucose that is the main component of cell walls, where it provides structure, not energy
      - Humans cannot digest it, so it helps with digestion and waste elimination
- Lipids - Macronutrients made of only carbon, hydrogen, and oxygen atoms, that provide the body with energy, cushion and insulate organs, and provide materials to build cell membranes
  - They are harder to be broken down, and are insoluble in water
  - Triglycerides - The most common lipid that is used for long term energy storage and made of one glycerol and 3 fatty acids
    - Saturated Triglycerides - Triglycerides with no double bonds, the maximum number of hydrogen, and firmer at room temperature
    - Unsaturated Triglycerides - Triglycerides with some double bonds and liquid at room temperature
  - Phospholipids - Lipids composed of one phosphate group and two fatty acids, which creates a polar hydrophilic head and non-polar hydrophobic tails
  - Cholesterol - A type of lipid that allows the body to make steroid base sex hormones and maintains the fluidity of the cell membrane
- Protein - A macronutrient composed of hydrogen, carbon, oxygen, and nitrogen and sulfur, that does not provide energy, but helps the body carry out its functions
  - Provides structure and support for blood cells, body tissues, and muscles, and aids in muscle movements
  - Can be enzymes, hormones, antibodies, and protein channels
  - All proteins are made of amino acids
  - Proteins are synthesized when mRNA code is read and the amino acids are assembled into a chain called a polypeptide
  - 8 of the necessary amino acids for humans can only be gotten from food
  - Denaturation - When the chemical bonds of a protein are disrupted due to unfavorable conditions, so the protein begins to break down
- Nucleic Acid - Macronutrients that consists of phosphates, sugars, and nitrogenous bases in a double helix shape that contain genetic information, but does not provide energy or structural support

Structures

Mouth - The cavity that contains the teeth and tongue
Teeth - Includes incisors, canines, premolars, and molars to perform mechanical digestion
Tongue - A very strong muscle that pushes food and moves it into the larynx, and has taste buds to distinguish sweet, salty, sour, bitter, and umami
Pharynx - The cavity that connects the mouth to the epiglottis and esophagus; contains the uvula to prevent food from entering the nasopharynx when swallowing
Epiglottis - The flap of tissue that covers the larynx and trachea when swallowing to prevent food from entering
Esophagus - The passage from the pharynx to the stomach made of strong smooth muscle, which push the bolus down to the stomach
Cardiac Sphincter - The muscular sphincter connecting the esophagus and stomach, which prevents stomach acid from damaging the esophagus through acid reflux
Stomach Muscles - The outer layer is the longitudinal muscle layer; the middle layer is the circular muscle layer; the inner layer is the oblique muscle layer; the folds called rugae expand and contract
Pyloric Sphincter - The muscular sphincter that connects the stomach to the duodenum and regulates the flow of chyme out of the stomach
Duodenum - The shortest part of the small intestine that is the main site for digestion and up to 80% of digestion, where bile and pancreatic enzymes enter
Jejunum - The second region of the small intestine where some proteins and carbohydrates are digested, but mostly absorbs nutrients
Ileum - The third part of the small intestine where all remaining digestion occurs, which releases erepsin, and where food is pushed through the ileocecal sphincter into the colon by peristalsis
Liver - The accessory organ that produces bile, converts carbs into fats, produces plasma proteins, detoxifies poison, stores soluble vitamins, creates urea, and breaks down amino acids
Gall Bladder - The accessory organ that stores bile
Appendix-Cecum - A one sided tube that is joined to the right side of the large intestine that serves as a reservoir for good bacteria and helps with the proper removal of waste and pathogens
Ascending Colon - The first part of the colon that pushes food upward
Transverse Colon - The second part of the colon that pushes food across the body
Descending Colon - The third part of the colon that pushes food down into the sigmoid colon
Rectum - Where feces is stored until its signalled to be expelled through the anal sphincters
Anal Sphincter - The inner sphincter made of involuntary smooth muscle and the outer sphincter made of voluntary skeletal muscle
Villi - Finger-like projections of the inner lining of the small intestine, most abundant in the duodenum
- Microvilli - Microscopic projections of the cell membranes of cells

Processes

Mechanical Digestion - Digestion that physically breaks apart food into smaller pieces
- Mechanical Digestion in Mouth - The teeth grind and break apart food; the tongue moves and pushes food
- Mechanical Digestion in Stomach - Muscular, churning contractions break down the bolus into chyme
Chemical Digestion - Digestion that breaks chemical bonds using enzymes
- Chemical Digestion in Mouth - Saliva moistens food and contains salivary amylase, which begins the process of carbohydrate digestion
  - Bolus - Ingested food mixed with saliva and swallowed
- Chemical Digestion in Stomach - Hydrochloric acid and enzymes break down macronutrients
Bile Emulsifying Fat - Bile is made of non-polar substances, which emulsifies fats
Absorption in Villi - The small intestine is structured to maximize the surface area for absorption, and the nutrients are absorbed through the microvilli, then the villi, and then into the capillaries inside of the villi
Absorption in Lacteals - Fatty acids are absorbed into lacteals, the smallest lymph vessels, that brings the fatty acids to the circulatory system through the subclavian vein
Absorption in Large Intestine - Most nutrients and water is reabsorbed from the chyme, and the volume of indigestible matter is reduced by two thirds
Peristalsis - Rhythmic involuntary muscle contractions, such as those in the esophagus and stomach
Symbiotic Bacteria and Vitamins - When human digestive enzymes can’t properly digest certain foods, gut bacteria help break down these foods, and help provide B vitamins and vitamin K, as well as improving immune function
Circulation in Hepatic Portal Vein - The circulatory system carries monosaccharides, amino acids, and glycerol from the small intestine to the liver through the hepatic portal vein; the liver stores, processes, filters, detoxifies, and delivers nutrients to the rest of the body; blood leaves through the hepatic veins to the vena cava
pH in Stomach - The low pH/ high acidity denatures proteins and kills potentially harmful pathogens
Role and Processing of Fibre