Module 8- GI- PN-Anatomy - student version-1(1) PDF

PN STRUCTURE AND FUNCTION Chapter 23 THE DIGESTIVE SYSTEM Week 5 Module Topics: The location of selected organs of the GI system Physiological structure of the GI tract Metabolism of nutrients by the GI system Physiological structure of the GI system and how it facilitat...

PN STRUCTURE AND FUNCTION Chapter 23 THE DIGESTIVE SYSTEM Week 5 Module Topics: The location of selected organs of the GI system Physiological structure of the GI tract Metabolism of nutrients by the GI system Physiological structure of the GI system and how it facilitates the activities of ingestion, physical and chemical digestion, propulsion, absorption and defecation Pathway of mechanical and chemical digestion of carbohydrates, fats and proteins through the GI tract and where and how the process are accomplished. Functions of the liver Functions of the pancreas Understanding the Gastrointestinal (GI) System Overview: Understanding the structure and functions of the gastrointestinal (GI) system is vital for nursing assessments and managing GI disorders. It enables nurses to assess patients' nutritional status, monitor waste elimination, and comprehend the pathophysiology of GI conditions. Recognizing the GI system's interaction with the nervous and endocrine systems is crucial for holistic patient care. Five Stages of Digestion System 1. Ingestion 2. Digestion 3. Absorption 4. Compaction 5. Defecation The digestive system processes food, extracts nutrients from it, and eliminates the residue. Digestion 1. Ingestion: the taking of food, medication, liquids, or other substances in the body by mouth 2. Mechanical Digestion: Physical breakdown of large pieces of food into smaller pieces. 3. Propulsion: Mechanical digestion in the stomach occurs via peristaltic contractions of the smooth muscle from the fundus towards the contracted pylorus, termed propulsion. 4. Chemical Digestion: Hydrolysis reactions carried out by digestive enzymes produced by the salivary glands, stomach, pancreas and small intestine. 5. Absorption: The process by which the products of digestion are absorbed by the blood to be supplied to the rest of the body. 6. Elimination: The removal of indigestible wates through the anus, in the form of feces. Argosy Publishing, Inc. (2019). Small Intestine. Visiblebody.com. https://www.visiblebody.com/learn/digestive/digestive-10-facts Digestive Processes The digestive processes are ingestion, propulsion, mechanical digestion, chemical digestion, absorption, and defecation. The video https://www.khanacademy.or g/science/health-and-medici ne/gastro-intestinal-system/ gastrointestinal-intro/v/meet -the-gastrointestinal-tract  Digestive System Components Alimentary Canal (GI tract) includes: 1. Mouth 2. Pharynx 3. Esophagus 4. Stomach 5. Small intestine 6. Large intestine Accessory Digestive Structures: 7. Teeth 8. Tongue 9. Salivary Glands 10. Liver 11. Pancreas 12. Gallbladder The human digestive system ( optional video 3:52 minutes) https://www.youtube.com/watch?v=URrXh0LJ6JE Digestive System Contribution of Other Body Systems to Digestive System Digestive System: Two Main Groups 1. Alimentary Canal Organs Comprise the gastrointestinal (GI) tract. Includes mouth, pharynx, esophagus, stomach, small intestine, and large intestine. Main function is to digest food and absorb nutrients 2. Accessory Digestive Organs Support the breakdown of food and absorption of nutrients. Consist of teeth, tongue, salivary glands, liver, pancreas, and gallbladder. Despite the term "accessory," they play crucial roles in digestion. Digestive System -Alimentary Canal Organs Aliment= “to nourish” Is a one-way tube. Measures approximately 7.62 meters (25 feet) in length during life. Can reach around 10.67 meters (35 feet) in length when measured post-mortem due to loss of smooth muscle tone. Main function is to nourish the body by digesting food and absorbing nutrients. Begins at the mouth and ends at the anus. Is modified along its length to suit specific functional requirements. Both the mouth and anus are open to the external environment, making the contents of the canal technically outside the body. Nutrients from food are absorbed into the body's "inner space" through the process of absorption. Digestive System -Accessory Digestive Organs Accessory digestive organs support food breakdown: In the mouth, teeth and tongue perform mechanical digestion, while salivary glands initiate chemical digestion with saliva. In the small intestine, the gallbladder, liver, and pancreas release bile and enzymes crucial for digestion. Termed "accessory" because they originate from gut's mucosal lining during development. Malfunction of these organs can lead to serious diseases. They maintain connections to the gut via ducts. Alimentary Canal Wall Alimentary Canal has 4 layers: 1. Mucosa 2. Submucosa 3. Muscularis 4. Serosa Layer of alimentary canal( optional video 1 minutes) https:// www.youtube.com/ watch?v=a6fTNDKHMTg  Histology of the Alimentary Canal: Mucosa Four Tissue Layers: Mucosa: Functions as a mucous membrane and produces mucus. Contains epithelium in direct contact with ingested food. Epithelium varies: non-keratinized stratified squamous in the mouth, pharynx, esophagus, and anal canal; simple columnar in the stomach and intestines. Goblet cells secrete mucus, and enteroendocrine cells secrete hormones. Epithelial cells have a short lifespan to maintain canal health despite contact with food. Lamina propria: Contains blood and lymphatic vessels for nutrient transport. Houses mucosa-associated lymphoid tissue (MALT) for immune function. Prominent in the distal ileum as Peyer's patches to defend against pathogens. Muscularis mucosa: A thin layer of smooth muscle under tension, creating folds to increase surface area for digestion and absorption Histology of the Alimentary Canal: Submucosa Submucosa: Lies beneath the mucosa and connects it to the muscularis. Contains blood vessels, lymphatics for nutrient transport, and submucosal glands releasing digestive secretions. Houses the submucosal plexus, a dense nerve network. Histology of the Alimentary Canal: Muscularis Muscularis (muscularis externa): In the small intestine, it consists of an inner circular and outer longitudinal layer of smooth muscle. Promotes mechanical digestion, exposes food to digestive chemicals, and propels it along the canal. In certain regions (mouth, pharynx, esophagus, anal sphincter), it's composed of skeletal muscle, allowing voluntary control. The stomach adds a third layer, the oblique muscle, for churning. The colon has two layers with the longitudinal layer divided into three bands, giving it a pouch-like appearance. Histology of the Alimentary Canal: Serosa Serosa: Found in the abdominal cavity region of the alimentary canal. Comprises visceral peritoneum over loose connective tissue. In the mouth, pharynx, and esophagus, it's replaced by a dense sheath called the adventitia. These tissues secure the alimentary canal near the ventral surface of the vertebral column.  Nerve Supply and Blood Supply Nerve Supply: Cranial nerves detect and enable taste and sensation, while motor branches control actions like chewing. Intrinsic innervation via the enteric nervous system spans the alimentary canal, regulating functions and secretions. Extrinsic innervation by the autonomic nervous system includes sympathetic (restricting) and parasympathetic (stimulating) nerves. Blood Supply: Arteries from aortic arch, thoracic aorta (anterior parts) and abdominal aorta (remaining parts) serve the digestive system. Veins from the small intestine connect to the hepatic portal system for nutrient processing in the liver. Blood circulates back to the heart after liver processing. Figure 23.4 The Peritoneum A cross-section of the abdomen shows the relationship between abdominal organs and the peritoneum (darker lines).  The Peritoneum Peritoneum Broad serous membrane in the abdominal cavity Two Regions: 1. Parietal peritoneum (lines abdominal wall) 2. Visceral peritoneum (covers abdominal organs) – contains large folds that envelop abd. organs and secure them to the dorsal body wall. Peritoneal cavity: space enclosed by these surfaces Watery Fluid: Acts as a lubricant to reduce friction between the serosal surfaces.  Peritonitis Inflammation of the peritoneum Various causes: Chemical breaches of the alimentary canal wall, such as stomach ulcer perforation, leading to gastric juice spilling into the peritoneal cavity. Hemorrhagic peritonitis can occur due to ruptured tubal pregnancy or traumatic injuries causing blood to accumulate in the peritoneal cavity. Severe peritonitis is associated with bacterial infections seen in conditions like appendicitis, colonic diverticulitis, and pelvic inflammatory disease (often caused by sexually transmitted bacteria). Peritonitis is a life-threatening condition and typically requires emergency surgery to address the underlying issue, along with intensive antibiotic therapy. Advances in surgery, anesthesia safety, critical care, and antibiotics have significantly reduced mortality rates for peritonitis. However, it still carries a mortality rate ranging from 30 to 40 percent. The stomach In the stomach, cells lining the gastric pits secrete enzymes that break down food proteins The acidic environment of the stomach favours the neutralisation of most ingested pathogens The muscles in the stomach wall perform vigorous churning that supports mechanical digestion Ghrelin, a hormone produced in the stomach, helps to regulate hunger and satiety Pathologies of the stomach include hiatus hernia, gastric ulcer, pernicious anaemia and stomach cancer Function of the Stomach The Function of the Stomach in the Digestive System The Stomach, a muscular sac located in the upper left part of your abdomen, plays a crucial role in the digestive system by helping to break down food for absorption by the body. T Structure of the Stomach The Stomach is a muscular sac located in the upper left area of the abdomen. Its structure allows it to hold up to 1.5 litres of food. When you eat a meal, the Stomach muscles relax to allow the food to enter. In the Stomach, the food mixes with the gastric juices, which contain acids and enzymes, making the digestion process easier. Function of Stomach in Digestive System The Stomach performs three main functions in the digestive system – Food Storage Breaking down food: Passage of the food into the Small Intestine KNOWLEDGE CHECK Which of these processes occurs in the mouth? 1. Ingestion 2. mechanical digestion 3. chemical digestion 4. all of the above What is the role of the mucus glands in the stomach? A. protects the stomach lining from digestion. B. contains antibodies to kill bacteria in food. C. prevents hydrochloric acid from sticking to the food. D. helps the cardiac and pyloric sphincters to remain closed. Accessory Organs in Digestion Liver, Pancreas and Gallbladder  Accessory Organs in Digestion: The Liver, Pancreas, and Gallbladder Chemical Digestion Chemical Digestion: Chemical digestion in the small intestine relies on the activities of three accessory digestive organs 1. Liver 2. Pancreas 3. Gallbladder. Liver: produces bile and exports to duodenum Gallbladder: stores, concentrates and releases bile Pancreas: produces pancreatic juice (contains digestive enzymes, and bicarbonate ions, and delivers to duodenum. Accessory Organs in Digestion: Liver Overview Body’s largest gland Weighs 3 pounds in adults Function: Metabolism and regulation and digestion Location: below diaphragm in right upper quadrant of abdominal cavity; Protected by the ribs Structure: Two primary lobes: large right lobe, and smaller left lobe Histology: Three main components Hepatocytes: Make up 80% of the liver volume and perform various functions, including secretion, metabolism, and endocrine activity. Bile Canaliculi: Collect bile produced by hepatocytes. Hepatic Sinusoids: Open blood spaces that receive nutrient-rich blood from hepatic portal veins and oxygen-rich blood from hepatic arteries. Hepatic Triads: These structures consist of a: bile duct, hepatic artery branch, and hepatic portal vein branch, collectively important for liver function. Figure 23.5.2 – Microscopic Anatomy of the Liver The liver is lobules made up of hepatocytes (A hepatocyte is the liver’s main cell type). receives oxygenated blood from the hepatic artery and nutrient drains the bile formed by the hepatocytes into the bile duct.  Accessory Organs in Digestion: Bile Bile and Its Functions: Bile is produced by the liver and aids in the digestion of lipids in the small intestine. Bile is composed of: Water Bile salts Bile pigments Phospholipids (e.g., lecithin) Electrolytes Cholesterol Triglycerides Key components for emulsification of lipids: Bile Salts: Have hydrophobic and hydrophilic regions, which interact with large lipid molecules and watery chyme, breaking large lipid globules into tiny fragments for better digestion. Phospholipids: Contribute to emulsification. Bile salts also play a crucial role in the absorption of digested lipids. Accessory Organs in Digestion: Bile Bilirubin: A waste product produced when old or damaged red blood cells are removed by the spleen. It gives bile its green color. Bilirubin is eventually transformed into stercobilin by intestinal bacteria, giving stool its brown color. The video: https://youtu.be/FHqrQDIy_5w?si=zvMuUiWQjN-7GF7y The Pancreas - Figure 23.26 Exocrine and Endocrine Pancreas The pancreas has a head, a body, and a tail. It delivers pancreatic juice to the duodenum through the pancreatic duct. The Role and Anatomy of the Pancreas The role and Anatomy of the pancreas (Optional video 3.16 minutes) https://www.youtube.com/watch? v=NZ4zcrTzUjA  Pancreas Anatomy of the Pancreas: The pancreas is an oblong, glandular organ located transversely in the retroperitoneum. It consists of a head, body, and tail. The head is nestled into the "c-shaped" curvature of the duodenum, while the tail tapers and extends to the hilum of the spleen. The pancreas has both exocrine (digestive enzymes) and endocrine (hormones) functions. Exocrine Pancreas: Exocrine pancreas consists of acinar cells that secrete enzyme-rich pancreatic juice. These cells are clustered at the terminal ends of pancreatic ducts. Pancreatic juice is delivered into two dominant ducts. The larger duct joins the common bile duct before entering the duodenum via the hepatopancreatic ampulla. The accessory duct (duct of Santorini) is a smaller duct that enters the duodenum directly. Endocrine Pancreas (Islets of Langerhans): Scattered within the exocrine acini are islets of Langerhans, clusters of endocrine cells. These cells produce hormones, including pancreatic polypeptide, insulin, glucagon, and somatostatin. The Gallbladder - Figure 23.27 Gallbladder The gallbladder stores and concentrates bile, and releases it into the two-way cystic duct when it is needed by the small intestine. The Gallbladder Anatomy of the Gallbladder: About 8–10 cm long. Located on the posterior aspect of the liver's right lobe. Divided into fundus, body, and neck. Cystic duct connects neck to hepatic duct Functions: Stores, concentrates, and propels bile into the duodenum via the common bile duct. Fatty chyme in the duodenum triggers release of cholecystokinin (CCK), causing gallbladder contraction. Vagal nerve stimulation can also induce gallbladder contraction. Both CCK and vagal stimulation release stored bile for lipid emulsification in chyme. Hepatic Bile versus Gallbladder Bile Knowledge check Which duct collects bile from the right or left lobe of the liver? A. portal duct. B. hepatic duct. C. cystic duct. D. pancreatic duct. What is the function of bile? A. synthesizes fat soluble vitamins. B. breaks down starches into monosaccharides. C. releases energy stored in fats to produce glucose. D. assists in the digestion of fats. Small intestine and Large Intestine Small Intestine: Divided into duodenum, jejunum, and ileum. Site for digestion completion and absorption. Mucosal surface area increased by circular folds, villi, and microvilli. About 200 million microvilli per square millimeter. Microvilli contain brush border enzymes for carb and protein digestion. Intestinal juice, along with pancreatic juice, aids digestion. Mechanical movements: segmentation for mixing and migrating motility complexes for propulsion. Small Intestine The three regions of the small intestine are the duodenum, jejunum, and ileum. The small intestine ( optional video 1:54 minutes) https://www.youtube.com/watch?v=P3om5aofVuc Mechanical and Chemical Digestion in Small Intestine Mechanical Digestion in the Small Intestine: Segmentation and migrating motility complexes facilitate mechanical digestion. Segmentation mixes chyme with digestive juices and aids absorption. Migrating motility complexes propel chyme through the small intestine. The ileocecal valve controls food passage from the small to the large intestine. Chemical Digestion in the Small Intestine: Small intestine completes protein and carbohydrate digestion. Lipid digestion occurs with bile and pancreatic lipase. Intestinal and pancreatic juices provide a digestion medium. Water absorption primarily occurs in the small intestine. Figure 23.6.2 – Histology of the Small Intestine The wall of the small intestine consists of the same four layers that are generally found in the digestive system. However, the mucosa and submucosa have three unique features that significantly increase the absorptive surface area of the small intestine by over 600 times. Large Intestine: Consists of the cecum, colon, and rectum. Absorbs water, forms feces, and handles defecation. Bacterial flora break down carbs and synthesize vitamins. Abundant goblet cells secrete mucus to ease feces passage. Entry of feces into the rectum triggers the defecation reflex Large Intestine – Absorption and Elimination The Large Intestine: Responsible for nutrient absorption completion, vitamin synthesis, and feces formation. Components include the cecum, colon, rectum, and anus. Mechanical digestion in the large intestine involves contractions. Chemical digestion is carried out by bacteria. Absorption occurs primarily for water and certain vitamins. Feces Formation and Elimination: Feces consist of undigested food, bacteria, and waste. Rectal muscles facilitate feces elimination. External anal sphincter allows voluntary control. Delayed or rapid passage can lead to constipation or diarrhea. Bowel movement frequency varies among individuals. The Small and Large Intestines Figure 23.21 Large Intestine The large intestine includes the cecum, colon, and rectum. Knowledge check What structural feature in the small intestine helps the process of absorption? A. mucous coat arranged in projections called villi. B. cilia readily absorb nutrients. C. mucous coat arranged in longitudinal folds. D. muscle coat arranged in various layers. Four Quadrants of the Abdomen Colon cancer: https://www.canada.ca/en/public-health/services/publications/diseases-conditions/colorectal-cancer.h tml  Colorectal Cancer https://www.canada.ca/en/pu blic-health/services/publicati ons/diseases-conditions/color ectal-cancer.html Chemical Digestion Chemical digestion breaks down large food molecules into chemical building blocks for absorption Enzymes facilitate chemical digestion through hydrolysis, altering the chemical makeup of food Carbohydrate Digestion Carbohydrates in the diet include: monosaccharides (glucose, galactose & fructose)- readily absorbed disaccharides (sucrose, lactose, maltose) –occurs in small intestine Polysaccharides - Fibrous polysaccharides like cellulose are indigestible but provide dietary fiber. Starch Digestion: Begins in the mouth with salivary amylase. Continues in the small intestine with pancreatic amylase. Brush border enzyme α-dextrinase breaks down α-dextrin into glucose units. Lactose Intolerance: Insufficient lactase enzyme leads to lactose intolerance. Lactase deficiency results in digestive issues with lactose- containing foods. Knowledge check Saliva initiates the chemical digestion of which substance? A. fats. B. sugars. C. proteins. D. complex carbohydrates Protein Digestion Proteins are large polymers composed of amino acids linked by peptide bonds. Digestion reduces proteins into their constituent amino acids. Approximately 15 to 20 percent of calorie intake comes from protein. Stomach Digestion: Protein digestion starts in the stomach. HCl denatures proteins, making them more accessible for digestion. Pepsin begins breaking proteins into smaller polypeptides. Small Intestine Digestion: Small intestine continues chemical digestion of proteins. Pancreatic enzymes (e.g., trypsin, chymotrypsin, carboxypeptidase) act on specific peptide bonds. Brush border enzymes (e.g., aminopeptidase, dipeptidase) further break down peptide chains. Result: Small molecules (amino acids) ready for absorption into the bloodstream. Lipid Digestion Lipid Digestion: Lipid intake in a healthy diet is limited to 35 percent of total calorie intake. Most dietary lipids are triglycerides, consisting of glycerol and three fatty acid chains. Small amounts of dietary cholesterol and phospholipids are also consumed. Lipase Enzymes: Three lipases involved in lipid digestion: Lingual lipase Gastric lipase Pancreatic lipase Digestion Location: The majority of lipid digestion occurs in the small intestine. Pancreatic lipase plays a crucial role in this process. Lipid Breakdown: Pancreatic lipase breaks down each triglyceride into: Two free fatty acids One monoglyceride Fatty acids include short-chain (less than 10-12 carbons) and long-chain fatty acids Dietary Lipid Overload and Metabolic Diseases Metabolism Introduction to Metabolism Metabolism Metabolism Overview: Metabolism encompasses the chemical reactions essential to life. It includes anabolic (building up) and catabolic (breaking down) reactions. Metabolic processes provide energy for cellular functions, protein synthesis, and recycling materials within cells. Nutrient Absorption: The body requires a range of nutrients obtained through diet. These nutrients serve as building blocks for metabolic processes. Importance of Oxygen: Oxygen is vital for cellular respiration, where cells produce energy (ATP) from glucose. Mitochondria play a key role in transferring energy during cellular respiration. Metabolic Variations: Metabolism varies based on factors such as age, gender, activity level, diet, and lean body mass. Modifying diet and exercise can increase lean body mass and metabolic rate. Aging and Metabolism: Aging can lead to a gradual decrease in metabolic rate (up to 5 percent per year). Men generally have a higher basal metabolic rate due to greater lean muscle mass. Genetic factors also contribute to an individual's inherent metabolic rate. Metabolic Reactions Metabolism Overview: Metabolism encompasses catabolic (breakdown) and anabolic (synthesis) reactions in the body. It measures the energy used to sustain life, known as metabolic rate. Adequate food intake is essential to maintain metabolic rate and ensure survival. Catabolic Reactions: Catabolic reactions break down larger molecules from ingested food and ATP into smaller components. These reactions release energy required for cellular processes. Anabolic Reactions: Anabolic reactions, or biosynthetic reactions, build larger molecules from smaller constituents. ATP serves as the energy source for anabolic reactions, contributing to the formation of bone, muscle, proteins, fats, and nucleic acids. Metabolic Errors and Diseases: Errors in metabolism can disrupt the processing of carbohydrates, lipids, proteins, and nucleic acids. Such errors can lead to various disease states, emphasizing the importance of proper metabolic functioning. Metabolic Disorders Aging and Digestion Aging impacts the digestive system from the mouth onwards. Reduced sensitivity of taste buds leads to decreased appetite. Dental issues, gum disease, and decreased saliva production affect eating. Swallowing becomes challenging, and food moves slowly due to muscle weakness. Neurosensory feedback is reduced, slowing enzyme and hormone release. Age-related pathologies include hiatal hernia, gastritis, and peptic ulcers. Small intestine issues: duodenal ulcers, maldigestion, and malabsorption. Large intestine problems: hemorrhoids, diverticular disease, and constipation. Accessory organs affected: jaundice, acute pancreatitis, cirrhosis, and gallstones. Carbohydrate Metabolism Carbohydrates are Energy Blocks: Carbohydrates are like tiny energy blocks made of carbon, hydrogen, and oxygen. Some are simple, like one piece (glucose), and some are complex, like many pieces stacked together (starch). Breaking Down Carbohydrates: When you eat carbs, your body breaks them down into tiny pieces called glucose. This happens in your mouth, stomach, and small intestine. Glycolysis - Making Energy: Inside your cells, glucose goes through something called glycolysis. It's like a factory turning glucose into energy packets called ATP (like batteries for your cells). Glycolysis also makes helpers called NADH. Video: https://app.nearpod.com/presentation?pin=IXURP Glycolysis = “Sugar Splitting” Glycolysis is a central process in cellular respiration that takes place in the cytoplasm of cells. It is the first step in the breakdown of glucose to produce energy in the form of ATP Glucose as Energy Source: Glucose is a type of sugar and a primary source of energy for the body. Digestion and Absorption: Polysaccharides from our food are broken down into simple sugars, including glucose, during digestion. These simple sugars are absorbed through the small intestine into the bloodstream. Transport to the Liver: Glucose enters the bloodstream and is transported to the liver. Liver Functions: In the liver, glucose can be used in two ways: Released into the bloodstream for immediate use by body cells. Stored as glycogen for later use. Cellular Energy Production: Body cells, such as muscles and brain cells, require glucose for energy. During glycolysis, cells convert glucose into ATP, a molecule that stores energy. Glycolysis Process: Glycolysis is a series of reactions where glucose is transformed into ATP. Pyruvate is the end product of glycolysis and can be used for further energy production. Overall Function: Glucose from our diet fuels our cells through glycolysis, with pyruvate as a key outcome, ensuring our bodies have the energy needed to function. Carbohydrate Metabolism Exercise and Lactic Acid: When you exercise and use lots of energy, your muscles need ATP. If you need more energy than glycolysis can make, your muscles make lactic acid as a backup. Lactic acid helps you keep moving but can make your muscles tired. More Energy in Mitochondria: When you're not running super fast and have enough oxygen, glucose pieces (pyruvate) go into the mitochondria (power plants of your cells). Inside the mitochondria, pyruvate turns into more ATP, lots of NADH, and FADH2 (super batteries). Electron Transport Chain (ETC): NADH and FADH2 go through the ETC, which is like a conveyor belt for energy. They help create a lot of ATP Total ATP - Lots of Energy: Your body gets plenty of ATP from glycolysis, mitochondria, and the ETC. It gives you the energy to run, exercise and do your day to day activities Just like building awesome things with LEGO blocks, your body takes small pieces and turns them into something fantastic - ENERGY! Lipid Metabolism Sources of Lipids: Dietary Intake: We get lipids (fats) from the food we eat, like butter, oils, and meat. Storage in Adipose Tissue: Some fats are stored in a special place called adipose tissue. It's like a fat bank in our bodies. Liver Production: Our liver can also make its own lipids. Digesting Dietary Fats: In our small intestine, fats are broken down into smaller pieces called monoglycerides and free fatty acids. These pieces are then absorbed into our body. Transport to Liver and Fat Tissues: Once absorbed, these pieces are put back together into triglycerides. These triglycerides can travel to the liver or be stored in adipose tissue for later use. Turning Fats into Energy: Fatty acids can be turned into energy in a process called "fatty acid oxidation" or "β-oxidation." They are transformed into two-carbon units called acetyl CoA, which enter a cycle (Krebs cycle) to make ATP (our energy currency). Protein Metabolism Protein Functions: Proteins serve various essential roles in the body: Cell signaling receptors Signaling molecules Structural components Enzymes Transporters (e.g., hemoglobin) Storage (e.g., collagen in bones) Growth, repair, and more Protein Metabolism Proteins as Metabolic Fuel: Excess proteins not stored; they can be used for energy or reserves. Amino acids from food supply necessary building blocks. Humans can't produce all 20 amino acids required for protein synthesis. Protein Digestion: Starts in the stomach with pepsin and HCl denaturing and breaking proteins. In the small intestine, enzymes and hormones further digest proteins. Amino acids transported across intestinal mucosa into the bloodstream. Metabolic States of the Body Absorptive State: Occurs after eating. Nutrient digestion and storage. Insulin promotes glucose use and storage. Postabsorptive State: Occurs between meals or during fasting. Relies on stored glycogen. Glucagon promotes glycogenolysis and gluconeogenesis. Starvation: Prolonged nutrient deprivation. Prioritizes brain glucose. Muscle uses fatty acids. Ketones become primary fuel. Protein sparing. Last resort: muscle protein breakdown Absorptive vs Postabsorptiv e State Nutrition Introduction to Nutrition Nutrition and Diet Energy Storage and Diet: Carbohydrates, lipids, and proteins from food are used for energy. Excess energy is stored as fats. Diet quality and quantity impact health. Calories and Daily Needs: Calories measure energy. An average person needs 1500 to 2000 calories daily. Individual needs depend on factors like age, activity level, and gender. A 3500-calorie excess adds one pound of weight. 200 extra daily calories lead to one pound gained in 18 days. Food Type and Metabolic Rate: Carbohydrate processing requires the least energy. Protein processing demands the most energy. Caloric intake vs. expenditure determines weight. Canada's Food Guide: Offers dietary guidelines. Emphasizes fruits, vegetables, whole grains, and protein foods. Encourages water consumption. Provides clear visual recommendations for balanced meals. Vitamins Importance of Vitamins: Vitamins are organic compounds in food. Essential for various biochemical reactions in the body. Play roles in mineral metabolism, bone health, cell growth, and energy metabolism. Act as cofactors for enzymes. Role of B Vitamins in Metabolism: B vitamins have significant roles in metabolism. Refer to Table 24.3 and Table 24.4 for details. Vitamin Sources: Obtained primarily from the diet. Some vitamins can be synthesized from precursors absorbed during digestion. Example: Vitamin A from β-carotene in orange vegetables. Fat-Soluble vs. Water-Soluble Vitamins: Fat-soluble vitamins: A, D, E, and K. Absorbed with lipids in the intestinal tract. Can accumulate in lipid stores in the body, leading to hypervitaminosis. Vitamin D can be synthesized in the skin through sunlight exposure. Water-soluble vitamins: B vitamins (eight types) and vitamin C. Absorbed with water in the gastrointestinal tract. Not stored in the body and are excreted in urine. Hypervitaminosis of water-soluble vitamins is rare, mainly due to excess vitamin supplements. Obesity Epidemic Obesity Epidemic: Obesity rates have been increasing since the 1980s. Approximately 1 in 4 adult Canadians are obese. Childhood obesity rates in Canada have nearly tripled over 30 years. Childhood Obesity Risks: Obese children are at a higher risk of health issues. Weight problems in childhood often persist into adulthood. BMI Definition: Obesity is defined by Body Mass Index (BMI). Normal BMI range: 18.5 to 24.9 kg/m². Overweight: BMI 25 to 29.9 kg/m². Obesity: BMI greater than 30 kg/m². Obesity Epidemic Causes of Obesity: Multiple factors contribute to obesity. Causes include overeating, poor diet, sedentary lifestyle, limited sleep, genetics, diseases, and medications. Health Risks of Severe Obesity: Severe obesity (morbid obesity) leads to serious medical conditions. These include heart disease, type 2 diabetes, cancer, hypertension, high cholesterol, stroke, liver disease, and more. Weight loss can help reduce or reverse these complications. Water Water is the most important nutrient necessary for life as it serves many purposes in the body. It acts as a solvent within which all the chemical reactions of metabolism occur and helps the body regulate its temperature. Water also forms part of several important chemical reactions, such as digestion, and acts as a cushion to absorb shocks in the central nervous system and musculoskeletal system. Additionally, it acts as a lubricant, allowing body organs to move smoothly against each other and sustaining cellular life. Fat Soluble vs Water Soluble Vitamins