Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Depth and Rate of Breathing: PCO2 Changing PCO2 levels are monitored by chemoreceptors of the brain stem Carbon dioxide in the blood diffuses into the cerebrospinal fluid where it is hydrated Resulting carbonic acid dissociates, releasing hydrogen ions PCO2 levels rise (hypercapnia) resulting in increased depth and rate of breathing •Hyperventilation – increased depth and rate of breathing that: Quickly flushes carbon dioxide from the blood Though a rise CO2 acts as the original stimulus, control of breathing at rest is regulated by the hydrogen ion concentration in the brain •Hypoventilation – slow and shallow breathing due to abnormally low PCO2 levels Apnea (breathing cessation) may occur until PCO2 levels rise Arterial oxygen levels are monitored by the aortic and carotid bodies Substantial drops in arterial PO2 (to 60 mm Hg) are needed before oxygen levels become a major stimulus for increased ventilation If carbon dioxide is not removed (e.g., as in emphysema and chronic bronchitis), chemoreceptors become unresponsive to PCO2 chemical stimuli In such cases, PO2 levels become the principal respiratory stimulus (hypoxic drive) Depth and Rate of Breathing: Arterial pH Changes in arterial pH can modify respiratory rate even if CO2 and O2 levels are normal Increased ventilation in response to falling pH is mediated by peripheral chemoreceptors Respiratory Adjustments: Exercise Respiratory adjustments are geared to both the intensity and duration of exercise During vigorous exercise: Ventilation can increase 20 fold Breathing becomes deeper and more vigorous, but respiratory rate may not be significantly changed (hyperpnea) Exercise-enhanced breathing is not prompted by an increase in PCO2 or a decrease in PO2 or pH. These levels remain surprisingly constant during exercise As exercise begins: Ventilation increases abruptly, rises slowly, and reaches a steady state When exercise stops: Ventilation declines suddenly, then gradually decreases to normal Neural factors bring about the above changes, including: Psychic stimuli Cortical motor activation Excitatory impulses from proprioceptors (relationship receptors) in muscles Respiratory Adjustments: High Altitude The body responds to quick movement to high altitude (above 8000 ft) with symptoms of acute mountain sickness – headache, shortness of breath, nausea, and dizziness Acclimatization – respiratory and hematopoietic adjustments to altitude include: Increased ventilation – 2-3 L/min higher than at sea level Chemoreceptors become more responsive to PCO2 Substantial decline in PO2 stimulates peripheral chemoreceptors Digestive System Where enzymes are used to break down: – Protein – Carbohydrates – Triglycerides – Nucleic Acids Stages of Food Processing Digestive systems of vertebrates are variations on a common plan 1. Ingestion / Propulsion: eating 2. Digestion: breaking down food to smaller molecules {so they can get into the cell} • Mechanical digestion= chewing • Chemical digestion= digestive enzymes 3. Absorption: uptake of small nutrient molecules by the cells lining digestive tract 4. Egestion / Defecation: elimination of undigested material we eat Types of Digestive Systems / Digestive compartments Animals must have a digestive compartment to avoid digesting themselves! 1. Intracellular / Food Vacuole: simplest • Intracellular • Organelle filled with digestive enzymes • Once food is broken down it passes through the membrane to nourish the cell • Unicellular organisms 2. Gastrovascular Cavity: • Single opening that functions both as an entrance for food & an exit for undigested wastes • Enzymes are secreted into cavity • All Cells are in proximity to absorb nutrients • Ex: sponges, hydras, jellies 3. Complete Digestive Systems: complete alimentary canal aka “Alimentary Canal” or “gut” oral opening passes through a tube anal opening • Food enters through a mouth • Moves through special regions that digest & absorb nutrients - Has several accessory organs • Undigested wastes are eliminated from tube as feces via the anus Examples: • Vertebrates: such as humans, birds • Invertebrates: earthworms, grasshoppers EXTRACELLULAR! But INTERNAL 4. External Digestion Assassin Bug for example: • Inject powerful digestive enzymes into their pray • This liquefies the insides of the pray • The insides are sucked out by the assassin bug! Human Digestive System “complete digestive system” Has several accessory organs: – Salivary gland: secretes digestive enzymes via ducts into mouth – Stomach: enzymes & HCl – Pancreas: digestive enzymes for all 3 types of foods- into small intestines – Liver: secretes bile to breakdown fats- into small intestines Digestive System: Overview Alimentary canal / gastrointestinal (GI) tract • digests and absorbs food Alimentary canal mouth pharynx esophagus stomach small intestine large intestine Accessory digestive organs Teeth Tongue Gallbladder salivary glands Liver pancreas Segmentation Digestive Processes in the Mouth Food is ingested Mastication - Mechanical digestion (chewing) Propulsion is initiated by swallowing Salivary amylase -chemical breakdown of starch Saliva: Source and Composition Three pairs of extrinsic glands – Sublingual parotid (cheeks) gland submandibular (under jaw) sublingual (under tongue) Intrinsic salivary glands (buccal glands) scattered throughout the oral mucosa (epithelium) 97-99.5% water, hypo-osmotic, slightly acidic solution containing Electrolytes – Na+, K+, Cl–, PO42–, HCO3– Digestive enzyme – salivary amylase & lingual lipase Proteins – Lubrication –mucin, anti-microbial - lysozyme, defensins, and IgA Metabolic wastes – urea and uric acid Deglutition (Swallowing) Peristalsis moves food through the pharynx esophagus stomach Peristalisis: sequential contraction of smooth muscle to propel substances Stomach Esophageal Sphincter to Pyloric Sphincter • Holds ingested food • Degrades this food both physically and chemically - food is converted to chyme Pepsin Enzymatically digests proteins • Secretes intrinsic factor required for absorption of vitamin B12 • Delivers chyme to the small intestine Parotid gland Submandibular gland Gastric Contractile Activity • Most vigorous near the pylorus • Chyme is either: - Delivered in ~ 3 ml spurts to the duodenum, or - Forced backward into the stomach Pyloric valve closed Pyloric valve closed Pyloric valve slightly opened Musculature –additional oblique (outside) layer Allows the stomach to churn, mix, and pummel food physically Breaks down food into smaller fragments Chemical digestion in the stomach Epithelial lining is composed of: 1. Goblet cells that produce a coat of alkaline (basic) mucus - The mucous surface layer traps a bicarbonate-rich fluid beneath it 2. Gastric glands • Parietal cells secrete HCl and intrinsic factor • Chief cells – produce pepsinogen Pepsinogen is activated to pepsin (digesting enzyme) by: - HCl in the stomach - Pepsin itself via a positive feedback mechanism 3. Enteroendocrine cells – secrete gastrin, histamine, endorphins, serotonin, cholecystokinin (CCK), and somatostatin into the lamina propria Stomach Lining The stomach is exposed to the harshest conditions in the digestive tract To keep from digesting itself, the stomach has a mucosal barrier with: A thick coat of bicarbonate-rich mucus on the stomach wall Epithelial cells that are joined by tight junctions Gastric glands that have cells impermeable to HCl Damaged epithelial cells are quickly replaced Small Intestine: Gross Anatomy Runs from pyloric sphincter (stomach to intestine) to the ileocecal valve Has three subdivisions: Duodenum, Jejunum, Ileum The bile duct and main pancreatic duct: Join the duodenum at the hepatopancreatic ampulla Are controlled by the sphincter of Oddi The jejunum extends from the duodenum to the ileum The ileum joins the large intestine at the ileocecal valve Structural modifications of the small intestine wall increase surface area Plicae circulares: deep circular folds of the mucosa and submucosa Villi – fingerlike extensions of the mucosa Microvilli – tiny projections of absorptive mucosal cells’ plasma membranes Contain Brush boarder enzymes – enzymes attached to membrane Pancreas Exocrine (secretes into ducts) function • Secretes pancreatic enzymes as zymogens (inactive precusor) Endocrine function – release of insulin and glucagon • Islets of Langerhans – area containing hormone secreting cells • Alpha cells – secrete glucagon in response to low levels of blood glucose • Beta cells – secrete insulin in response to high levels of blood glucose Liver The largest gland in the body Hepatocytes’ functions include: • Production of bile • Processing bloodborne nutrients • Storage of fat-soluble vitamins • Detoxification Secreted bile flows between hepatocytes toward the bile ducts in the portal triads Central vein hepatocytes Bile Canaliculi (small passageway) Portal vein macrophages in sinusoid walls The Gallbladder • Thin-walled, green muscular sac on the ventral surface of the liver • Stores and concentrates bile by absorbing its water and ions Digestion Flowchart Enzymes are written over the chemical reaction they control All enzymes active at pH 7 except pepsin active at pH 2 Carbohydrates Amylase Starch Oligosaccharrides salivary or pancreatic ie – smaller fragments Dextrinase Glucoamylase Maltose Brush border Enzymes Sucrose Lactose sucrase Maltase Brush border Enzymes Glucose Glucose & Fructose Brush border Enzymes lactase Glucose & Galactose Brush border Enzymes Proteins Pepsin * only @ pH 2 stomach Protein Trypsin * Chymotrypsin * Protein fragments only @ pH 7 pancreatice dipeptidase aminopeptidase carboxypetidase* Individual amino acids Brush border enzymes Carboxypeptidase also pancreatic * - Activation of proteases Zymogen Active Enzyme HCl pepsinogen trypsinogen Brush border Enzymes & Trypsin chymotrypsinogen procarboxypeptidase Lipids pepsin Trypsin Trypsin trypsin chymotrypsin carboxpeptidase Triglycerides only, other lipids don’t require digestion Bile needed to separate triglycerides into smaller globs – no chemical digestion Tryiglycerides Lipase = 1 glycerol & 3 fatty acids pancreatic Monoglyceride & 2 fatty acids Nucleic Acids DNA Brush border enzymes deoxyribonuclease Deoxynucleotides pancreatic RNA deoxyribonuclease pancreatic nucleosidases phosphatases riobonucleotides nucleosidases phosphatases Phosphate Bases Pentose sugars Chemical Digestion: Carbohydrates Enzymes used: salivary amylase, pancreatic amylase, and brush border enzymes Absorption • Secondary active transport (cotransport) with Na+ • Facilitated diffusion of some monosaccharides Enter the capillary beds in the villi Transported to the liver via the hepatic portal vein Chemical Digestion: Proteins Enzymes used: pepsin in the stomach Enzymes acting in the small intestine 1. Pancreatic enzymes – trypsin, chymotrypsin, and carboxypeptidase 2. Brush border enzymes – aminopeptidases, carboxypeptidases, and dipeptidases Absorption: similar to carbohydrates Chemical Digestion: Fats Chemicals used: bile salts – emulsify fats Enzymes used: pancreatic lipase Absorption: • Form micelles with bile that fuse to intestinal cells • Inside, combine with proteins and extrude (exocytosis) chylomicrons (lipid-protein complex) • Enter lacteals (lymph structure) and are transported to systemic circulation via lymph Glycerol and short chain fatty acids are: •Absorbed into the capillary blood in villi •Transported via the hepatic portal vein Includes fat-soluble vitamins (A, D, E, and K) Chemical Digestion: Nucleic Acids Enzymes used: pancreatic ribonucleases and deoxyribonuclease in the small intestines Absorption: active transport via membrane carriers Absorbed in villi and transported to liver via hepatic portal vein Electrolyte Absorption Most ions are actively absorbed along the length of small intestine Na+ is coupled with absorption of glucose and amino acids Ionic iron is actively transported into mucosal cells where it binds to ferritin Anions passively follow the electrical potential established by Na+ K+ diffuses across the intestinal mucosa in response to osmotic gradients Ca2+ absorption: Is related to blood levels of ionic calcium Is regulated by vitamin D and parathyroid hormone (PTH) low calcium prompt PTH release which stimulates kidneys to activate vitamin D. Active Vitamin D accelerates calcium absorption in intestine Vitamins • • • • Only vitamins D, K, and B are synthesized in the body; all others must be ingested Water-soluble vitamins (B-complex and C) are absorbed in the gastrointestinal tract B12 additionally requires gastric intrinsic factor to be absorbed through endocytosis Fat-soluble vitamins (A, D, E, and K) bind to ingested lipids and are absorbed along with fatty acids Water Absorption 95% of water is absorbed in the small intestines by osmosis Water moves in both directions across intestinal mucosa Net osmosis occurs whenever a concentration gradient is established by active transport of solutes into the mucosal cells Water uptake is coupled with solute uptake, and as water moves into mucosal cells, substances follow along their concentration gradients Large Intestine Has three unique features: • Teniae coli – three bands of longitudinal smooth muscle • Haustra – pocketlike sacs caused by the tone of the teniae coli • Epiploic appendages – fat-filled pouches of visceral peritoneum Is subdivided into the cecum, appendix, colon, rectum, and anal canal Regulation of Gastric Secretion Neural and hormonal mechanisms regulate the release of gastric juice Stimulatory and inhibitory events occur in three phases 1. Cephalic (reflex) phase: prior to food entry Excitatory events include: Sight or thought of food Stimulation of taste or smell receptors Inhibitory events include: Loss of appetite or depression Decrease in stimulation of the parasympathetic division 2. Gastric phase: once food enters the stomach Excitatory events include: Stomach distension - Activation of stretch receptors (neural) Activation of chemoreceptors by peptides, caffeine, and rising pH Release of gastrin to the blood Inhibitory events include: A pH lower than 2 Emotional upset that overrides the parasympathetic division 3. Intestinal phase: as partially digested food enters the duodenum Excitatory phase low pH; partially digested food enters the duodenum and encourages gastric gland activity Inhibitory phase distension of duodenum, presence of fatty, acidic, or hypertonic chyme, and/or irritants in the duodenum Initiates inhibition of local reflexes (stomach action to push chyme into intestine) and parasympathetic branch Closes the pyloric sphincter (sympathetic branch) Releases enterogastrones that inhibit gastric secretion Regulation and Mechanism of HCl Secretion HCl secretion is stimulated by ACh (parasympathetic), histamine (enteroendocrine cells), and gastrin through second-messenger systems ( ie –cAMP therefore slow) Release of hydrochloric acid: Is low if only one ligand binds to parietal cells Is high if all three ligands bind to parietal cells Antihistamines block H2 receptors and decrease HCl release