Anatomy & Physiology Study Notes: Respiratory and Digestive Systems

Ch. 22: The Respiratory System

Pressures Associated with the Lungs

The respiratory system relies on various pressures to facilitate the movement of air in and out of the lungs.

• Atmospheric Pressure: The pressure exerted by air outside the body; typically 760 mmHg at sea level.

• Intrapulmonary Pressure: The pressure within the alveoli; fluctuates during breathing.

• Intrapleural Pressure: The pressure within the pleural cavity; always slightly less than intrapulmonary pressure to keep lungs inflated.

• Transpulmonary Pressure: The difference between intrapulmonary and intrapleural pressures; maintains lung expansion.

Transport of O2 and CO2 in the Blood

Oxygen and carbon dioxide are transported in the blood via different mechanisms.

• Oxygen: Mostly bound to hemoglobin in red blood cells; a small amount is dissolved in plasma.

• Carbon Dioxide: Transported as dissolved CO2, bound to hemoglobin, and primarily as bicarbonate ions ($CO_2 + H_2O \rightarrow H_2CO_3 \rightarrow HCO_3^- + H^+$).

Stimuli for Breathing

Breathing is regulated by several stimuli, with CO2 levels being the most powerful.

• CO2 Concentration: Increased CO2 stimulates central chemoreceptors, increasing respiratory rate.

• O2 Concentration: Peripheral chemoreceptors respond to low O2 levels.

• pH: Changes in blood pH also affect breathing rate.

Boyle's, Dalton's, and Henry's Laws

These gas laws explain the movement and exchange of gases in the respiratory system.

• Boyle's Law: $P_1V_1 = P_2V_2$; pressure and volume are inversely related.

• Dalton's Law: Total pressure of a mixture of gases equals the sum of the partial pressures of each gas.

• Henry's Law: The amount of gas that dissolves in a liquid is proportional to its partial pressure and solubility.

Surfactant and Vital Capacity

Surfactant reduces surface tension in the alveoli, preventing collapse and aiding lung expansion.

• Surfactant: A lipoprotein produced by type II alveolar cells.

• Vital Capacity: The maximum amount of air a person can expel from the lungs after maximum inhalation.

Anatomical Differences Between Left and Right Lungs

The left and right lungs differ in size, shape, and number of lobes.

• Right Lung: Three lobes (superior, middle, inferior).

• Left Lung: Two lobes (superior, inferior) and a cardiac notch for the heart.

Mechanisms Preventing Debris Entry into Alveoli

Several anatomical features protect the alveoli from inhaled debris.

• Mucociliary Escalator: Cilia and mucus trap and move particles out of the airways.

• Epiglottis: Prevents food from entering the trachea.

Anatomy of the Trachea

The trachea is a tube supported by cartilaginous rings, conducting air to the lungs.

• Cartilage Rings: Prevent collapse during breathing.

• Lined with Ciliated Epithelium: Helps remove debris.

Bohr Effect and Hemoglobin

The Bohr effect describes how increased CO2 and decreased pH reduce hemoglobin's affinity for oxygen, facilitating oxygen release in tissues.

• Bohr Effect: $HbO_2 + H^+ \rightarrow HbH + O_2$

Mechanisms for CO2 Transport

CO2 is transported in three main forms.

• Dissolved in Plasma

• Bound to Hemoglobin

• As Bicarbonate Ions

Internal and External Respiration; Pulmonary Ventilation

Respiration involves gas exchange at the lungs and tissues.

• External Respiration: Gas exchange between alveoli and blood.

• Internal Respiration: Gas exchange between blood and tissues.

• Pulmonary Ventilation: Movement of air into and out of the lungs.

Ventilation-Perfusion Coupling

This mechanism matches air flow (ventilation) to blood flow (perfusion) in the lungs for efficient gas exchange.

Types of Cells in the Alveoli

The alveoli contain two main cell types.

• Type I Alveolar Cells: Form the structure of the alveolar wall; site of gas exchange.

• Type II Alveolar Cells: Secrete surfactant.

Anatomical Parts of the Respiratory Membrane

The respiratory membrane consists of:

• Alveolar epithelium

• Capillary endothelium

• Fused basement membranes

Ch. 23: The Digestive System

Function of Villi and Microvilli in the Small Intestine

Villi and microvilli increase the surface area for absorption in the small intestine.

• Villi: Finger-like projections containing blood vessels and lymphatics.

• Microvilli: Tiny extensions of epithelial cells forming the brush border.

Peristalsis and Its Function

Peristalsis is the coordinated contraction of smooth muscle that propels food through the digestive tract.

Anatomical Features Protecting the Stomach Mucosal Barrier

The stomach is protected from self-digestion by several features.

• Mucus Secretion: Forms a protective layer.

• Tight Junctions: Prevent leakage of gastric juices.

• Rapid Cell Turnover: Damaged cells are quickly replaced.

Swallowing and Stomach Reflexes

Swallowing involves voluntary and involuntary muscle actions, while stomach reflexes regulate digestion.

• Swallowing Reflex: Coordinated by the medulla oblongata.

• Gastric Reflexes: Include the enterogastric and gastroileal reflexes.

GI Tract Events Triggered by Sight or Smell of Food

The cephalic phase of digestion is initiated by sensory stimuli, increasing gastric secretions.

Submucosal and Myenteric Plexuses

These neural networks regulate digestive tract motility and secretion.

• Submucosal Plexus: Controls secretions.

• Myenteric Plexus: Controls muscle contractions.

Main Digestive Hormones

Key hormones include gastrin, secretin, and cholecystokinin (CCK).

• Gastrin: Stimulates gastric acid secretion.

• Secretin: Stimulates bicarbonate secretion from pancreas.

• Cholecystokinin (CCK): Stimulates bile and pancreatic enzyme release.

Bile Salts: Function and Chemical Composition

Bile salts emulsify fats, aiding digestion and absorption.

• Chemical Composition: Derived from cholesterol; contain both hydrophobic and hydrophilic regions.

Hepatocytes and Liver Function

Hepatocytes are liver cells responsible for metabolism, detoxification, and bile production.

Differences Between Bile and Hormones

Bile is a digestive fluid, while hormones are chemical messengers.

• Bile: Produced by the liver, stored in the gallbladder, aids fat digestion.

• Hormones: Regulate physiological processes throughout the body.

Hepatic Portal Circulation

The hepatic portal system transports nutrient-rich blood from the digestive tract to the liver for processing.

Phases of Gastric Secretion

Gastric secretion occurs in three phases:

• Cephalic Phase: Triggered by sight, smell, or thought of food.

• Gastric Phase: Initiated by food entering the stomach.

• Intestinal Phase: Begins when chyme enters the small intestine.

Enzymes Secreted by the GI Tract

Digestive enzymes break down macromolecules:

• Amylase: Digests carbohydrates.

• Proteases: Digest proteins.

• Lipases: Digest fats.

Intrinsic Factor and Vitamin B12 Absorption

Intrinsic factor, secreted by the stomach, is essential for vitamin B12 absorption in the small intestine.

Hormonal Control of HCl Secretion

Gastrin stimulates parietal cells to secrete hydrochloric acid (HCl).

Goblet Cells: Function

Goblet cells secrete mucus, protecting and lubricating the lining of the digestive tract.

Summary Table: Digestive Hormones and Their Functions

Hormone	Source	Function
Gastrin	Stomach (G cells)	Stimulates gastric acid secretion
Secretin	Duodenum	Stimulates bicarbonate secretion from pancreas
Cholecystokinin (CCK)	Duodenum	Stimulates bile and pancreatic enzyme release

Additional info: Academic context and expanded explanations have been added to ensure completeness and clarity for exam preparation.