BackHigh-Yield Study Notes: The Respiratory and Digestive Systems
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Chapter 22: The Respiratory System
Pleura
The pleura are double-layered serous membranes surrounding each lung and lining the thoracic cavity.
Visceral pleura: Covers the lungs themselves.
Parietal pleura: Lines the thoracic wall and diaphragm.
Pleural cavity: The space between the two layers, filled with pleural fluid to reduce friction during breathing.
Control of Respiration
Respiratory rhythm and rate are controlled by centers in the brainstem.
Medulla oblongata: Contains the ventral respiratory group (VRG) (main rhythm generator) and dorsal respiratory group (DRG) (integrates sensory input).
Pons: Modifies and fine-tunes breathing rhythms (pneumotaxic and apneustic centers).
Gas Laws Relevant to Respiration
Boyle's Law: The pressure of a gas is inversely proportional to its volume at constant temperature. Equation:
Henry's Law: The amount of gas dissolved in a liquid is proportional to its partial pressure and solubility.
Dalton's Law: The total pressure of a mixture of gases equals the sum of the partial pressures of each gas.
Surfactant
Surfactant is a lipoprotein complex produced by type II alveolar cells.
Reduces surface tension in alveoli, preventing collapse during exhalation.
Essential for normal lung function, especially in newborns.
Pressures in the Lungs
Intrapulmonary pressure (Ppul): Pressure within the alveoli.
Intrapleural pressure (Pip): Pressure within the pleural cavity; always negative relative to Ppul.
Transpulmonary pressure: Difference between Ppul and Pip; keeps lungs inflated. Equation:
Lung Volumes and Capacities
Tidal Volume (TV): Air moved in or out during normal breathing (~500 mL).
Inspiratory Reserve Volume (IRV): Extra air inhaled after normal inspiration.
Expiratory Reserve Volume (ERV): Extra air exhaled after normal expiration.
Vital Capacity (VC): Total amount of exchangeable air. Equation:
Bronchial vs Pulmonary Circulation
Pulmonary circulation: Carries deoxygenated blood from the right ventricle to the lungs and returns oxygenated blood to the left atrium.
Bronchial circulation: Supplies oxygenated blood to lung tissue (except alveoli).
Bohr Effect
The Bohr effect describes how decreased pH (acidosis) reduces hemoglobin's affinity for O2, promoting oxygen release to tissues.
Ciliated Epithelium in the Trachea
Ciliated cells and mucus trap and move dust and pathogens out of the airway (mucociliary escalator).
Carbon Monoxide (CO) Poisoning
CO binds to hemoglobin with higher affinity than O2, reducing oxygen transport and causing hypoxia.
Causes of Hypoxia
Hypoxemic hypoxia: Low arterial PO2 (e.g., high altitude, lung disease).
Anemic hypoxia: Decreased hemoglobin or abnormal hemoglobin.
Ischemic hypoxia: Impaired blood circulation.
Histotoxic hypoxia: Cells unable to use O2 (e.g., cyanide poisoning).
Respiratory Stimulus
The most powerful stimulus for breathing in healthy individuals is increased CO2 (hypercapnia).
Hering-Breuer Reflex
Prevents over-inflation of the lungs by inhibiting inspiration when stretch receptors are activated.
Chapter 23: The Digestive System
Small Intestine: Villi and Circular Folds
Villi: Fingerlike projections that increase surface area for absorption.
Circular folds (plicae circulares): Deep folds of mucosa and submucosa that slow chyme movement and increase absorption.
Anal Sphincter Innervation
Internal anal sphincter: Involuntary, smooth muscle, autonomic control.
External anal sphincter: Voluntary, skeletal muscle, somatic control.
Food Pyramid
Represents recommended proportions of different food groups for a balanced diet.
Anabolism vs Catabolism
Anabolism: Building complex molecules from simpler ones (requires energy).
Catabolism: Breaking down complex molecules into simpler ones (releases energy).
Oxidative Phosphorylation
Main process for ATP production during cellular respiration.
Occurs in mitochondria; uses electron transport chain and chemiosmosis.
Hormones of the (Post)-Absorptive State
Absorptive state: Insulin is the main hormone (not post-absorptive).
Post-absorptive state: Glucagon, epinephrine, cortisol, and growth hormone promote energy release.
Heat Loss Mechanisms
Radiation: Loss of heat as infrared rays.
Conduction: Direct transfer of heat to another object.
Convection: Transfer of heat by movement of air or liquid.
Evaporation: Heat loss as water vaporizes from skin or respiratory tract.
Large Intestine: Peristalsis
Peristalsis in the large intestine is controlled by stretch receptors in the haustra (pouches).
Smooth Muscle Layers of the Intestine
Two main layers: inner circular and outer longitudinal.
Responsible for peristalsis and segmentation.
Bile
Produced by the liver, stored in the gallbladder, secreted into the small intestine.
Emulsifies fats to aid digestion.
Secretin
Hormone released by the small intestine in response to acidic chyme.
Stimulates secretion of bicarbonate-rich pancreatic juice.
Chyme
Semi-fluid mass of partially digested food first found in the stomach.
Chief and Parietal Cells
Chief cells: Secrete pepsinogen (inactive form of pepsin).
Parietal cells: Secrete hydrochloric acid (HCl) and intrinsic factor.
Amylase
Enzyme that breaks down starch into sugars.
Found in saliva and pancreatic juice.
Intrinsic Factor
Glycoprotein required for vitamin B12 absorption in the small intestine.
Gastrin
Hormone released by G cells in the stomach in response to protein and peptide fragments.
Stimulates gastric acid secretion.
Carboxypeptidase
Pancreatic enzyme that removes amino acids from the carboxyl end of proteins during digestion.
Cholecystokinin (CCK)
Hormone released in response to lipids in the small intestine.
Stimulates secretion of enzyme-rich pancreatic juice and contraction of the gallbladder.
Hepatocytes
Liver cells that process nutrients, detoxify substances, and store fat-soluble vitamins.
Do not produce digestive enzymes.
Parts of the Small Intestine
Duodenum
Jejunum
Ileum
Trypsinogen Activation
Trypsinogen (from pancreas) is activated to trypsin by enterokinase (from small intestine).
Acinar Cells
Pancreatic cells that produce digestive enzymes (pancreatic juice).
Phases of Gastric Secretion
Cephalic phase: Triggered by sight, smell, or thought of food.
Gastric phase: Triggered by food in the stomach.
Intestinal phase: Triggered by chyme entering the small intestine.
Gall Stones
Solid deposits (mainly cholesterol) that form in the gallbladder and can block bile ducts.
Saliva
Moistens food, begins starch digestion (amylase), contains lysozyme and antibodies.
Gastrointestinal Tract (GIT) Function and Physiology
Ingestion, propulsion, mechanical digestion, chemical digestion, absorption, and defecation.
Hepatic Portal Circulation
Transports nutrient-rich blood from the digestive tract to the liver for processing.
Uvula and Epiglottis
Uvula: Prevents food from entering the nasopharynx during swallowing.
Epiglottis: Prevents food from entering the trachea.
Chemical vs Mechanical Digestion
Mechanical digestion: Physical breakdown of food (chewing, churning).
Chemical digestion: Enzymatic breakdown of macromolecules.
Stages of Swallowing (Deglutition)
Buccal phase: Voluntary, tongue pushes food into oropharynx.
Pharyngeal phase: Involuntary, food passes through pharynx.
Esophageal phase: Involuntary, peristalsis moves food to stomach.
Cellular Respiration: Mitochondrial Processes
Glycolysis: Occurs in cytoplasm, not mitochondria.
Krebs cycle and oxidative phosphorylation: Occur in mitochondria.
Hepatopancreatic Ampulla
Formed by the union of the bile duct and pancreatic duct; delivers bile and pancreatic juice to the duodenum.
Glycogen Formation
Occurs in the liver during the absorptive state (after eating) to store excess glucose.
Absorptive vs Post-Absorptive State
Absorptive state: Nutrients are being absorbed; glycogen is synthesized in the liver.
Post-absorptive state: Body relies on stored nutrients; glycogen is broken down.
