UNIT 2: From Food to Fuel: How the Human Body Utilizes Food
Introduction to the Digestive System PART ONE
Systems of the Body
The Digestive System Also referred to as alimentary system, the gut, gastrointestinal system (GI) or GI tract. Is basically a long tub that runs from the mouth to the rectum. The space inside the GI tract (referred to as the lumen) is technically outside the body.
Digestive System Components Brain Mouth Esophagus Stomach Small intestines Large intestines (colon) Rectum (anus) Mouth
Accessory organs to the GI system Brain Teeth Tongue Salivary glands Gall bladder Pancreas Liver
Mouth 14. Esophageal Valve Esophagus Liver Stomach 15. Duodenum (small intestines) Ascending Colon (large intestines) ileocaecal valve Appendix Pyloric sphincter Transverse Colon (large intestines) Jejunum (small intestines) Descending Colon (large intestines) Rectum Ileum (small intestines
Major Functions of the GI System Turn food into molecules (from nutrients) that the body can use for energy, growth, repair, maintenance and regulation of body processes Regulation of the body s metabolism A protective barrier from harmful infections and foreign substances that come in with food and through the mouth
Features of the GI System Muscular: muscles move food through the lumen (peristalsis) Immunity: 70% of the body s immune system is within and around the digestive system Neurological: has more nerve endings than the spine; more neurotransmitters than the brain; connected to the brain by the vagus nerve (enteric nervous system)
Features of the GI System Endocrine: secretes hormones and is regulated by hormones Cardiovascular: beneficial bacteria in the gut control blood cholesterol and fats levels Metabolic: the beneficial bacteria in the digestive system regulate the body s metabolism (chemical and physical processes that occur that keep the body functioning)
Importance of Healthy Diet When healthy and receiving the nutrients needed, the one-cell-thick lining of the GI tract repairs and replaces itself every 3-5 days. When nutrition is not optimal, this process is hindered which results in a GI lining that does not digest and absorb nutrients OR protect the body from invasions of harmful bacteria, yeasts, viruses and undigested food
The Digestive Process Eating ingestion of food through the mouth Involves teeth, tongue, parotid & salivary glands Digestion mechanical and chemical breakdown of food Occurs in mouth, stomach & small intestines Secretion water, acid, buffers and enzymes released from the walls of the GI into the lumen Lubricates, adjusts ph levels, triggers enzymes (protein substances that drive chemical reactions taking place in the body
The Digestive Process Mixing/propulsion muscles contract throughout the GI to move through the digestive tract (peristalsis) Absorption molecules from digested food move through the epithelial cell lining of the small intestines into the blood stream then the liver OR directly to the lymph system where they are processed before delivered to the body cells for use.
The Digestive Process Assimilation fuel and nutrients enter the cells from the bloodstream (not part of digestive process but the ultimate goal) Takes place inside the body Elimination excretion of wastes that include indigestible food components, waste products, bacteria, shed cells from intestinal lining and unabsorbed food
ANSWER THESE QUESTIONS 1. What is digestion? 2. Name and explain all 7 steps of the digestive process. 3. Explain what having a gut feeling means. 4. Why is the gut considered our second brain? 5. Explain what peristalsis is in your own words.
Anatomy of the Digestive System PART TWO
Where does digestion really start?
Brain Thinking about food Hearing about food Seeing food Smelling food Tasting food Triggers responses that prepare the body to receive food
Mouth Teeth and tongue (Mechanical digestion) Salivary glands produce saliva and enzymes (chemical digestion)
Esophagus Tube from the mouth to the stomach Peristalsis moves the food along Food passes into the stomach through the esophageal sphincter (keeps food from coming back up into esophagus) which opens as food is moved along by peristalsis)
Stomach Crushes and mixes food into chyme Beginning of chemical protein digestion Food is in the stomach for 2-4 hours (carbohydrates stay shortest time, fats longest) Gastric juices secreted (enzymes, hydrochloric acid, hormones and intrinsic factor)
Small Intestine 15-20 feet long; flattened out would be the size of a tennis court. Food completely digested and absorbed Lining is covered with villi and microvilli which are covered by the one-cell-thick epithelial layer. Three sections: duodenum, jejunum and ileum Each section absorbs certain nutrients
Small Intestines
Lumen, Villi, Microvilli, Epithelial Layer (Brush border) Epithelial cells (blood vessels) (Lymph vessel) Crypt (gland)
GI Mucosa Inner lining of the intestines Large mucous membrane Digested food molecules are absorbed through it Is the centre of the immune system (first line of defence against infections)
Leaky Gut The cells in the single cell layer of the GI mucosa are tightly held together when healthy When unhealthy, the space between the cells becomes loose and allow undigested food, toxins and harmful bacteria to enter the body
Leaky Gut Is associated with a wide range health problems including allergies, obesity, poor nervous system function, acne and bowel diseases Stems from a poor diet, stress and even medications
How to avoid Consume a whole foods diet Avoid refined foods Manage stress Don t abuse medications
Pancreas Functions: Aid digestion by secreting enzymes into the digestive system Produces insulin and glucagon, hormones that regulate blood sugar
Liver Performs over 500 functions! Processes all the nutrients received from food and makes them useable by the body Produces bile, a digestive juice that allows fats to be digested Makes hormones that regulate body processes Filters toxins brought in from food (detoxify) Stores glycogen (glucose), vitamins and minerals from food for later use Is part of the immune system (filters bacteria)
The Liver The liver is the most complex of all the body organs. While it protects you from toxins and bacteria and regulates your entire body systems, it can be abused and damaged by poor diet. Refined foods full of chemicals and excessive alcohol consumption put stress on the liver. When this happens, the liver does not perform its functions very well which leads to illness. Keeping your liver healthy by eating quality, whole foods is the best step you can take towards wellness.
Gallbladder Function is to store bile produced by the liver Bile emulsifies fats in the small intestine so they can be acted on by enzymes and digested.
The Appendix Finger-like sac that extends off the beginning of the colon. Part of the lymph system Important in immune health during first decade of life
Large Intestine or Colon Ileocaecal valve separates from small intestines 3-5 feet long Functions are: Absorb water and remaining nutrients from chyme Form stool (feces)
Large Intestine or Colon Three main parts Ascending colon Transverse colon Descending colon Rectum stores stool(poop) before eliminated Bacteria that resides in the colon produce vitamins and fatty acids that nourish the body in which they reside A healthy colon protects against leaky gut and disease. Stool that is in the colon too long allows toxic substances to be reabsorbed and cause illness
REVIEW QUESTIONS 1. What are the 3 sections of the small intestines? 2. What is the GI mucosa and why is it so important? 3. Explain what a leaky gut is and how it occurs. What are preventative measures? 4. Why is the liver so important? 5. What happens when a person abuses their liver?
Digestion and Absorption Process PART THREE
Digestion Physical Mastication (Chewing and mixing) (teeth and tongue) Crushing (muscles in stomach and small intestine) Peristalsis (waves of muscular contractions that move food through GI)
Digestion Chemical Enzymes (proteins that speed up chemical reactions) break down macronutrients into smaller, absorbable compound Hydrochloric acid in the stomach sterilizes food and starts to break down proteins Bicarbonate adjusts the ph of digesting food so other chemicals can do their work Bile in the small intestines makes fats digestible Mucus lubricates food for passage through GI
The Brain Digestion starts here with the smell, sound and sight of food causing saliva, stomach juices, enzymes and hormones beginning to flow in preparation of receiving food
Only when a person is relaxed and focused on eating does the GI received signals from the brain for the digestion process. Therefore, food is digested better and made available for the body to use. This is the reason why it is important sit down and just eat instead of doing other activities at the same time.
Mouth Chewing increases surface area of food so enzymes can act on it Saliva, containing enzymes, is secreted from glands in the mouth to soften and dissolve food Chemical digestion of carbohydrates and fats begins with the secretion of the enzymes amylase and lipase. Taking time to properly chew food to a soft mush allows the rest of digestive tract to most effectively finish the job.
Esophagus Food chewed to a soft lump is called a bolus The bolus is voluntarily swallowed pass the epiglottis and down the esophagus Peristalsis (muscle waves) move the bolus to the esophageal sphincter and into the stomach.
Stomach Chops, liquefies and churns food to a soupy liquid called chyme Gastric juices containing water, hydrochloric acid, mucus, enzymes (pepsin and lipase) and hormones (gastrin) and intrinsic factor are secreted and begin to digest proteins and fats. Hydrochloric acid sterilizes food and break down proteins. Intrinsic Factor needed to absorb vitamin B12 Alcohol, water and salts are absorbed directly from the stomach into the bloodstream
Stomach Food is in the stomach 2-4 hours (less for carbohydrate meal, more for fat, protein and fibre) When healthy, lining is coated with thick mucus which protects it from hydrochloric acid damage A whole foods diet supports stomach function and health. Refined foods diminishes stomach health by depleting it of essential nutrients AND requiring it to digest damaged proteins and fats which stresses the lining.
Stomach When chyme is ready to leave the stomach, peristalsis causes the pyloric valve to open and allow the chyme to slowly enter the small intestines. Food is only minimally digested in the stomach
Small Intestines Where food is completely digested and absorbed Intestinal wall has 2 functions: Allow nutrients to pass into the bloodstream/lymph Block foreign substances (chemicals, bacteria, undigested food molecules)
Small Intestines DIGESTION Secretions from the pancreas, gallbladder and the small intestine s own glands work on the chyme to break it down into absorbable nutrients (proteins: amino acids; carbohydrates: sugars and fats: fatty acids) Secretions also release vitamins and minerals so they can be absorbed The secretions include: bicarbonate, enzymes, hormones and bile
Small Intestines ABSORPTION Each part of the small intestine absorbs certain nutrients Nutrients pass through the one-cell thick epithelial layer that lines the microvilli and enters the blood stream (a few fatty acids, sugars, proteins, vitamins and minerals) or lymph system (most fatty acids)
Small Intestines
Small Intestines When the mucosal lining is damaged due to poor lifestyle choices (ex. Poor diet or over-use of medications) the small intestine can not adequately fulfill its functions and disease eventually results. A diet of whole foods supports the function of the small intestines and the mucosal lining. A refined foods diet does not provide the nutrients necessary to support small intestines function and damages the mucosal lining. This leaves the individual open to disease-causing substances.
Small Intestines When the chyme has completed its 3-10 hour journey through the small intestine, it passes through ileocaecal valve, the connection to the large intestine.
Large Intestines (Colon) Functions of the colon are: No further digestion To absorb water and the few remaining nutrients from the chyme Form stool Beneficial bacteria located here digest some of the fibre from food to produce vitamins and beneficial fatty acids that are needed by the body.
Transverse Colon: Stool begins to form Descending Colon: Passage of well-formed stool to the rectum Ascending Colon: Absorption of water/last nutrients Rectum: Storage of stool until bowel movement
Large Intestines (Colon) A whole foods diet that is rich in fiber from vegetables and whole grains supports the function of the colon by providing fiber for: beneficial bacteria to use (insoluble form) bulk to help move stool through the colon at an optimal rate (insoluble form) carry harmful substances from the body (ex. excessive cholesterol, used hormones) (soluble form)
PART FOUR Assimilation of Absorbed Nutrients Nutrition s Effect on Body Systems
Circulatory System Water soluble nutrients are absorbed directly through the intestinal cells into the bloodstream and then carried to the liver before being dispersed via the bloodstream to cells throughout the body
Circulatory System Bloodstream picks up metabolic waste products and delivers them to the kidney and lungs for excretion.
Lymphatic System Part of the immune system Second line of defence from harmful substance that enter with food (mucosal lining is the first) Lymph vessels in the small intestine carry fat-soluble nutrients and then empty them into the bloodstream for dispersion to cells throughout the body
Immune System 70% of the immune system is located in and around the digestive tract GI is the largest area in the body where harmful substance can gain access A healthy GI tract is the first line of defence for a healthy immune system This is why keeping the digestive system in optimal health reduces occurrences of disease
Central Nervous System Carries signals or messages from the brain and other body tissues
Central Nervous System Enteric Nervous System: Part of the CNS nerves in the gut wall that are stimulated by the chemical composition of the chyme AND the stretching of the lumen resulting from food in the GI tract Signals secretions and muscle movement in the GI
Central Nervous System Autonomic Nervous System Part of the CNS that controls organ function Responds to sight, smell and thought of food Stimulates secretion of digestive juices and muscle movement in the GI Carries signals to and from the GI tract to the brain via the vagus nerve
Hormonal System Hormones are produced in one location and travel via blood to another location in the body where they cause an effect Gastrointestinal hormones signal increase or decreased GI movements and influence appetite
Metabolism PART FIVE
Metabolism The collective processes that occur in the body Biochemical reactions Include: Extraction of energy/nutrients from food Production of energy for cell/body use Building of new body tissues, organs and substances
Cell Structure
Production of Energy takes place in the cell
Chemical Reactions of Metabolism (Rely on vitamins and minerals to run)
References Insel, P. M., Ross, D., McMahon, K., & Bernstein, M. (2010). Discovering Nutrition.Third Edition. Burlington, MA: Jones & Bartlett Learning. Lipski, E. (2012). Digestive Wellness: Strengthen the Immune System and Prevent disease Through Healthy Digestion. New York, NY: McGraw-Hill.