Summary BIOS 256 AP 4 Lecture Notes.

BIOS 256 AP 4 Lecture Notes.Chapter 24: The Digestive System part two Basic GI Functions  Primary function: movement of nutrient molecules from the external environment to the internal environment. (Absorption of nutrients) Food-Digestion-motility and absorption Pancreas  Gland in the retroperitoneal space behind the stomach  Produces enzymes that digest carbs, proteins, fats, and nucleic acids  Produces the sodium bicarbonate buffer  Empties the contents into duodenum Relationship of the Pancreas to the Liver, Gallbladder, and Duodenum Know: Hepatopancreatic ampulla (ampulla of vater) and Sphincter of Oddi  Sphincter of Oddi regulates the passage of bile and pancreatic juices through the ampulla of vater into the duodenum of the small intestines. Activation of Pancreatic Proteolytic Enzymes Pancreas  Exocrine portion secretes pancreatic juices. o Made up of acini (99% of pancreas) o Pancreatic juice is made up of  Amylase to digest starch  Trypsin, Chymotrypsin, carboxypeptidase, and elastase to digest protein.  Lipase digests triglyceride  Ribonuclease  Deoxyribose o Protein Digesting enzymes secreted in inactive form o NaCO3 buffers acidic gastric juice to allow digestion to begin in small intestines  Endocrine portion secretes hormones like insulin, glucagon o Made up of pancreatic islet cells Liver Split into right and left lobes, separated by the falciform ligament. Right lobe is larger than the left. Histology of the Liver  Hepatocytes o Functional cell of the liver o Produce and secrete bile  Bile canaliculi o Small ducts between hepatocytes that collect bile produced by hepatocytes o Bile canaliculi- bile ductules-bile ducts-right and left hepatic ducts-common hepatic duct-cystic duct=common bile duct  Hepatic sinusoids o Blood capillaries between hepatocytes Right and left hepatic ducts merge to form the common bile duct. Blood Supply of the Liver Oxygenated blood from hepatic artery and Nutrient rich deoxygenated blood from hepatic portal vein go to hepatic sinusoids. Then to central vein. Then hepatic vein. The inferior vena cava. And finally right atrium of the heart Functions of the Liver and Gallbladder  Carbohydrate, lipid, and protein metabolism  Processing of drugs and hormones (detoxifies)  Bilirubin excretion (derived from Heme and metabolized in small intestine by bacteria and eliminated feces. )  Bile salt synthesis  Storage of vitamins  Phagocytosis of aged RBCs and WBCs and some bacteria  Vitamin D activation Liver and Gallbladder  The liver makes bile o Both and excretory product and a digestive secretion o Bile= water, bile salts, bile pigments (bilirubin) o Bile salts play a role in emulsification  Break down of large lipid globules into a suspension of small lipid globules  Enhances role of pancreatic lipase  The gallbladder stores bile until it is needed Regulation of Bile Production and Secretion  CCK and secretin released into blood when acidic, fatty chime enters intestines  CCK causes o Gallbladder contraction o Pancreatic juice secretion o Relaxation of sphincter of Oddi  Secretin stimulates o Production of bicarbonate by pancreas and bile by liver Anatomy of the Small Intestine  90% of absorption occurs in the small intestine  3 parts o Duodenum o Jejunum o Ileum  Circular folds are permanent ridges of the mucosa and submucosa that enhance absorption because of the increased surface area and it causes chime to spiral as it moves through small intestine. Villi are fingerlike projections of the mucosa that aid in digestion and absorption. The mucosa contains absorptive cells, goblet cells, enteroendocrine cells (make hormones), and Paneth cells (help with phagocytosis)… and the villi have their own villi like microvilli. Mechanical Digestion in the SI Two types of movements:  Segmentation o Localized mixing contractions o Mix chime with digestive juices bringing food into contact with mucosa. o Do not push food along  Peristalsis o After most of meal has been absorbed, segmentation stops and peristalsis begins o Pushes chime down SI Intestinal Juice and Brush Border Enzymes  Intestinal juice provides a vehicle for absorption of substances from chime as they come in contact with the villi.  Brush border enzymes, found on the surface of the microvilli of absorptive cells, break down food products Chemical Digestion in the SI Digestion of:  Carbohydrates  Proteins  Lipids  Nucleic acids Carbohydrate Digestion  Ingested molecules of sucrose, lactose, and maltose are not acted upon until they reach SI (disaccharides)  Brush border enzymes digest the disaccharides into monosaccharides Protein Absorption  Begins in stomach (pepsin)  Enzymes in pancreatic juice continues digestion (trypsin)  Completed by 2 peptides in brush border Lipid Absorption  Most lipid digestion occurs in small intestine through actions of pancreatic lipase  TG broken down into fatty acids  Emulsification must first occur via action of bile salts. o Produces larger surface area for action of pancreatic lipase. Large Intestine  Cecum first part of the large intestine  Ileocecal sphincter controls what goes in.  Ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anus The Cecum  Is an expanded pouch  Receives material arriving from the ileum  Stores materials and begins compaction Appendix  Also called vermiform appendix  Slender hollow appendage  Dominated by lymphoid tissue Histology of Colon There is no villi on the mucosa only glands to absorb water.  Absorptive cell- absorbs water  Goblet cell- secretes mucus. Large intestine Functions  Reabsorb water  Compaction of contents into feces  Absorption of important vitamins produced by bacteria  Storage of fecal matter prior to defecation Defecation Reflex  Rectal wall distends  Stretch receptors send sensory nerve impulses to the sacral spinal cord  Motor impulses travel back to the descending colon, sigmoid colon, rectum, and anus  Longitudinal Rectal muscles contract and the internal anal sphincter opens o If the external anal sphincter is voluntarily relaxed, defecation occurs and the feces are expelled. Aging and the Digestive System Aging results in  Decreased secretory mechanisms and motility  Loss of strength and tone of digestive muscular tissue  Changes in neurosecretory feedback  Diminished response to pain and internal sensation. Week 3: Chapter 25: Metabolism and Nutrition Metabolic Reactions  Metabolism: refers to all of the chemical reactions taking place in the body  Two types o Catabolic- break down complex molecules into simpler ones. They are exergonic which means that they produce more energy than they consume. o Anabolic- combine simple molecules to make complex molecules. They are endergonic which means that they consume more energy than they produce.  ATP is the energy source that couples the two types of reactions.  The coupling of energy-releasing and energy-requiring reactions is achieved through ATP. o Catabolic reactions transfer energy from complex molecules to ATP, which releases heat. o Simple molecules such as glucose, amino acids, glycerol, and fatty acids are produced through catabolic reactions. o Anabolic reactions transfer energy from ATP to complex molecules, which releases heat. o Complex molecules such as glycogen, proteins, and triglycerides are produced through anabolic reactions. Metabolism Anabolism Catabolism Material synthesis Material Release energy breakdown Require energy Energy Transfer  Catabolic reactions transfer energy into the high-energy phosphate bond of ATP.  Two important aspects: o Redox reactions o Mechanisms of ATP generation  Redox- oxidation is the removal of electrons. Example: conversion of lactic acid to pyruvic acid. o This results in a decrease in the potential energy of the atom or molecule.  Redox- reduction involves the addition of electrons to a molecule. Example: Conversion of pyruvic acid to lactic acid. o This results in an increase in potential energy  When a substance is oxidized, the liberated hydrogen atoms do not remain free but are transferred to 2 of the following compounds: NAD and FAD.  Oxidation and reduction are always coupled. o Oxidation is an exergonic reaction which means it releases energy Mechanism of ATP Generation  Some of the energy released during oxidation reactions is captured when ATP is formed.  The high-energy phosphate bond that attaches the third phosphate group contains the energy stored in this reaction. Organisms Use 3 Mechanisms of Phosphorylation to Generate ATP  Substrate-level phosphorylation o Generates ATP by transferring high energy phosphate group from a substrate directly to ADP o Occurs in cytosol  Oxidative Phosphorylation o Removes electrons from organic molecules and passes them through a series of electron receptors to molecules of oxygen. o Occurs in the inner mitochondrion of cells  Photophosphorylation o Occurs only in chlorophyll-containing plant cells Carbohydrate Metabolism  Catabolism (cellular respiration) o Glycolysis- anaerobic or aerobic o Formation of acetyl coA o Krebs cycle o Electron transport train  Anabolism o Gluconeogenesis  Functions o Stored as glycogen o ATP synthesis o Synthesize other carbohydrates  Mostly glucose metabolism since it’s the body’s preferred source for ATP  Fate of glucose depends on the needs of the body cell o ATP production o Amino acid synthesis o Glycogen synthesis  Hepatocytes and muscle fibers o Triglyceride synthesis  Hepatocytes can transform glucose to glycerol and fatty acids  Glucose must pass through the plasma membrane into the cytosol before it can be used by the cell. o Facilitated diffusion o Insulin increases the rate of facilitated diffusion of glucose into cells  On entering the cell, glucose becomes phosphorylated o Reaction traps glucose within the cell Carbohydrate Metabolism (really glucose catabolism)  Oxidation of glucose to produce ATP is cellular respiration it involves: o Glycolysis o Formation of acetyl coA o Krebs cycle o Electron transport mmmmchain Glycolysis  Can occur with or without oxygen  Occurs in the cytoplasm  One glucose is oxidized, and 2 molecules of pyruvic acid are produced o 2 ATP and 2 NADH are also formed  When oxygen is present all occur (glycolysis, formation of acetyl coA, Krebs, and ETC)  Without oxygen- pyruvic acid is converted to lactic acid called anaerobic respiration or fermentation o RBC: glycolysis only (no mitochondria) o Skeletal muscle: Fermentation when no oxygen o Neurons and cardiac muscle: need oxygen cannot ferment.  Form 1 glucose to two pyruvate  Main catabolic pathway of cytoplasm  Does not require oxygen  Starts with phosphorylation of glucoses Fate of pyruvic Acid  Oxygen is present : pyruvic acid is converted to acetyl coA and enters krebs cycle o Links glycolysis (cytosol) with kerbs cycle (mitochondria)  No oxygen- most pyruvic acid is converted to lactic acid Krebs Cycle  Also known as the citric acid cycle. Occurs in the mitochondria matrix and consists of 8 reactions.  Acetyl coA is formed from pyruvic acid and enters krebs cycle  Completes a series of redox reactions  Energy is transferred in the form of nad and fad  Formation of nadh and fadh is most important because these reduced coenzymes contain energy originally stored in glucose  This will yield many atps via etc Electron Transport Chain  Electron transport chain is a series of electron carriers in the mitochondria  As electrons pass through the chain, a series of exergonic reactions release small amounts of energy which is used to form ATP  The mechanism of atp generation links chemical reactions with the pumping of hydrogen ions is called chemiosmosis Summary of Cellular Respiration  Cellular respiration will generate either 30 or 32 ATP molecules for each molecule of glucose catabolized.  Glycolysis yields 2 ATP molecules  Krebs cycle yields 2 ATP molecules  ETC generates 26 or 28 ATP molecules  To total 30 or 32  Glycolysis, Krebs, etc provide all of the ATP for cellular activities  Krebs and ETC are aerobic processes which means that they require oxygen. Glucose Anabolism  Glucose not needed immediately is stored as glycogen. The process that creates it is called glycogenesis.  When ATP is needed, stored glycogen is broken down by a process called glycogenolysis  Glucose may take part in or be formed via several anabolic reactions o Synthesis of glycogen o Synthesis of new glucose molecules form products of protein and lipid breakdown Glucose Storage and Release  If not needed it is stored as glycogen  If needed, the glycogen stored in hepatocytes is broken down into glucose and transported to cells.  Glycogenesis is stimulated by insulin  Glycogenolysis is simulated by glucagon and epinephrine Formation of Glucose From protein and fats (Gluconeogenesis)  When the liver runs low on glycogen, it means that it is time to eat.  If you do not, your body will start to catabolize triglycerides and proteins.  The glycerol portion of triglycerides, lactic acid and certain amino acids can be converted in the liver to glucose, this is known as gluconeogenesis.  Gluconeogenesis vs. glycogenesis vs. glycogenolysis o Gluconeogenesis makes newly formed glucose  Gluconeogenesis is stimulated by cortisol, glucagon and thyroid hormones.  Gluconeogenesis is the conversion of non-carb molecules into glucose Lipid Metabolism  Lipid catabolism o Triglycerides are most common o Lipolysis: triglycerides yields glycerol and a fatty acid  Glycerol yields pyruvic acid gets sent to krebs cycle  Fatty acids undergo beta oxidation yields acetyl then goes to krebs cycle  Lipid anabolism o Lipogenesis: Triglycerides formed from cellular respiration intermediates o Cholesterol: from saturated fats o Essential fatty acids that are ingested  Functions o ATP synthesis o Cell membranes o Myelin o Steroid hormones o Storage o Insulation  Transport o Free fatty acids bound to albumins in blood o Others bound to proteins to form lipoproteins include:  Chylomicrons  VLDL  LDL  HDL  To be transported in blood, lipids need to be more water soluble by combining with proteins  Lipoproteins are lipid and protein combinations  Spherical particles with an outer shell of proteins phospholipids, and cholesterol molecules surrounding an inner core of triglycerides and other lipids Lipoproteins  All lipoproteins are transport vehicles  Provide delivery and pickup services so that lipids can be available when cells need them or removed from circulation when not needed  Lipoproteins are characterized and named according to density which varies with the ratio of lipids to proteins. o High density lipoproteins (HDL) contain more protein than lipid. Classes of Lipoproteins  There are four classes of lipoproteins from largest and lightest to smallest and heaviest o Chylomicrons- transport dietary lipids to adipose tissue o Very low density lipoproteins (VLDL)- Transport triglycerides synthesized in hepatocytes to adipocytes o Low density lipoproteins (LDL)- carry about 75% of the total cholesterol in blood and deliver it to cells o High density lipoproteins (HDL)- Remove excess cholesterol from body cells and the blood and transport it to the liver for elimination Lipid Metabolism  Cholesterol comes from some foods but most is synthesized by hepatocytes  Fatty foods that don’t contain cholesterol can still increase blood cholesterol levels o When saturated fats are broken down in the body, hepatocytes use some of the breakdown products to make cholesterol  Increases in total cholesterol levels are associated with a greater risk of coronary artery disease  Exercise, diet and certain drugs are used to reduce high cholesterol levels The Fate of Lipids  Lipids may be oxidized to produce ATP  If the body does not need lipids at any given time, they get stored in adipose tissue  Some are used as structural molecules or to synthesize other essential substances o Phospholipids o Lipoproteins o Myelin Lipid Metabolism  Lipid Catabolism is the process of splitting triglycerides into fatty acids and glycerol o In order for muscle, liver, and adipose tissue to oxidize fatty acids from triglycerides to produce ATP triglycerides need to be split o Catalyzed by lipase o Stimulated by epi and norepi, inhibited by insulin  Lipid anabolism (lipogenesis) is the process of synthesizing lipids from glucose or amino acids. It occurs when individuals consume more calories than needed to satisfy ATP needs o Insulin stimulates lipogenesis o Excess dietary carbs, proteins, and fats all have the same fate- they are all converted into triglycerides.  If ATP supply in a cell is high, glycerol is converted into glucose  If ATP supply is low, glycerol enters the catabolic pathway to pyruvic acid  Fatty acids are catabolized differently than glycerol and yield more ATP  Large fatty acids can lead up to 129 ATPs following complete oxidation  As part of normal fatty acid catabolism, hepatocytes can form acetoacetic acid from acetyl coA  Formation of acetoacetic acid, beta-hydroxybutxric acid, and acetone in the liver is called ketogenesis Protein Metabolism  Protein catabolism  Deanimation- animo group is removed by liver before entering krebs cycle  Generates ammonia which is toxic, converted by liver to urea which is excreted in the urine.  Krebs cycle to produce ATP  Last resort for energy (protein starvation)  Anabolism o Essential amino acids: must be ingested o Synthesis  Functions o Structure o Enzymes o Hormones The Fate of Proteins  Protein catabolism yields amino acids which are converted to other amino acids, fatty acids, ketone bodies, or glucose  Cells oxidize amino acids to generate ATP via the krebs cycle o Before amino acids can enter kreb cycle they must first undergo deamination in the liver, the ammonia produced must be detoxified in the liver into urea  Protein anabolism creates new proteins by bonding together amino acids on ribosomes Metabolic Adaptations  Some aspects of metabolism depend on how much time has passed since the last meal o During absorptive state, ingested nutrients are entering the blood stream and glucose is readily available for ATP productin o Durign the post- absorptive state, absorption of nutrients from GI tract is complete, and energy needs must be met by fuels already in the body  Because the nervous system and RBCs continue to depend on glucose for ATP production during the post- absorptive state, maintaining a steady blood glucose level is critical during this period Principle Metabolic Pathways During the Absorptive State  Nutrients enter bloodstream mainly as glucose, amino acids, and triglycerides  Two main metabolic reactions dominate o Oxidation of glucose for ATP production o Storage of excess fuel for future between meal use Hormonal Regulation of Metabolism in the Absorptive State  The effects of insulin dominate in the absorptive state (anabolic hormone) Hormonal Regulation of Metabolism in the Post- Absorptive State  During the post absorptive state, energy needs are met by fuels already in the body  Homeostasis of blood glucose level is especially important for nervous system and RBCs Metabolism During Fasting and Starvation  During fasting and starvation, the body must make metabolic changes to survive  Fasting is going without food for several hours or a few days  fasting is going without food for several hours or a few days  starvation is going without for or inadequate food intake for weeks or months  catabolism of stored triglycerides and structural proteins can provide energy for several weeks  amount of adipose tissue the body contains determines the life span possible without food  The most dramatic metabolic change is an increase in production of ketone bodies by the liver as catabolism of fatty acids increases  Lipid soluble ketone bodies cab be used as alternative fuel for ATP production  Presence of ketone reduces the use of glucose for ATP production which in turn decreases the demand for gluconeogenesis and slows catabolism of muscle proteins later in starvation Heat and Energy Balance  The metabolic rate is the overall rate at which metabolic reactions use energy  The rates of metabolic reactions control the amount of heat produced by the body o The rate of heat loss must equal the rate of heat productionto maintain homeostasis of body temperature  Metabolic rate is measured with the body in a quiet, resting and fasting state. This is basal metabolic rate (BMR) Measurement of Heat  Heat is a form of energy that can be measured as temperature and expressed in units called calories  Because calorie is a relatively small unit, the kcal is often used to meause the body’s metabolic rate  1kcal= 1 Calorie= 1000 calories  BMR about Cal/day Heat and Energy Balance= heat production  The production of body heat is proportional to metabolic rate  Factors affecting metabolic rate include: o Exercise o Hormones o Nervous system o Body temp o Ingestion of food o Age o Gender, climate, sleeping, malnutrition Heat and energy balance: mechanisms of heat transfer  Maintaining normal body temp depends on the ability to lose heat to the environment at the same rate as it is produced by metabolic reactions  Heat is transferred from the body to the environment by: o Conduction o Convection o Radiation o Evaporation Energy Homeostasis and Regulation of food intake  Energy homeostasis= precise matching of energy intake to energy expenditure over time o When energy content of food balances the energy used by all cells of the body, body weight remains constant  Energy intake depends only on the amount of food consumed and absorbed  Three components contribute to total energy expenditure: o Basal metabolic rate 60% o Physical activity rate 30-35% Week 4: The Urinary System Urinary System Organs  Kidneys are major excretory organs- located in the retroperitoneal space  Urinary bladder is the temporary storage reservoir for urine  Ureters transport urine from the kidneys to the bladder  Urethra transports urine out of the body. External Layers of the Kidney Three layers of supportive tissue  Renal Fascia- the anchoring outer layer of dense fibrous connective tissue  Adipose capsule- a fatty middle layer, protects and anchors  Renal capsule- innermost layer, barrier to infection, continuous with outer layer of ureter. Kidney Functions  Removal of toxins, metabolic wastes, and excess ions from the blood  Regulation of blood volume, chemical composition, and pH  Gluconeogenesis during prolonged fasting  Endocrine functions (hormones) o Renin- regulation of blood pressure and kidney function o Erythropoietin- regulation of RBC production o Activation of vitamin D