Ch. 22: The Respiratory System

Pressures Associated with the Lungs

The lungs are subject to several pressures that influence breathing and gas exchange.

• Atmospheric Pressure: The pressure exerted by air outside the body.

• Intrapulmonary Pressure: The pressure within the alveoli.

• Intrapleural Pressure: The pressure within the pleural cavity, usually lower than atmospheric pressure.

• Transpulmonary Pressure: The difference between intrapulmonary and intrapleural pressures; keeps lungs inflated.

Oxygen and Carbon Dioxide Transport in Blood

O2 and CO2 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 gas, bound to hemoglobin, and as bicarbonate ions.

• Equation for CO2 conversion:

Stimuli for Breathing

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

• CO2 concentration: The primary driver for breathing rate and depth.

• O2 levels: Become significant in cases of hypoxia.

• pH: Changes in blood pH also influence respiratory 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: 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 dissolved in a liquid is proportional to its partial pressure and solubility.

Surfactant and Wet Cell Surface

Surfactant is a substance produced by alveolar cells that reduces surface tension, preventing alveolar collapse.

• Wet cell surface: Refers to the moist lining of the alveoli, essential for gas exchange.

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 Dust and Debris Entry

The respiratory system has several defenses against inhaled particles.

• Mucus: Traps dust and microbes.

• Cilia: Move trapped 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: Prevents collapse during breathing.

• Lining: Contains ciliated epithelium and mucus-producing cells.

Bohr Effect and Oxygen Loading/Unloading

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

• Oxygen loading: Occurs in the lungs where pH is higher and CO2 is lower.

• Oxygen unloading: Occurs in tissues where pH is lower and CO2 is higher.

Mechanisms for CO2 Transport

CO2 is transported in three main forms:

• Dissolved in plasma

• Bound to hemoglobin

• As bicarbonate ions (see equation above)

Internal and External Respiration; Pulmonary Ventilation

Respiration involves gas exchange at two levels:

• External respiration: Exchange of gases between alveoli and blood.

• Internal respiration: Exchange of gases 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.

• Areas with high oxygen receive more blood flow.

• Areas with low oxygen receive less blood flow.

Types of Cells in the Alveoli

The alveoli contain two main types of cells:

• Type I alveolar cells: Form the structure of the alveolar wall; involved in gas exchange.

• Type II alveolar cells: Secrete surfactant to reduce surface tension.

Anatomical Parts of the Respiratory Membrane

The respiratory membrane is the site of gas exchange and 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 wave-like contraction of smooth muscle that propels food through the digestive tract.

• Ensures movement of food from esophagus to anus.

Anatomical Features of the Stomach Mucosal Barrier

The stomach mucosal barrier protects the stomach lining from acidic gastric juice.

• Mucus: Coats the stomach lining.

• Tight junctions: Prevent leakage of gastric juice.

• Rapid cell turnover: Replaces damaged cells quickly.

Difference Between Long and Short Reflexes

Digestive reflexes coordinate GI tract activity.

• Short reflexes: Local, mediated by the enteric nervous system.

• Long reflexes: Involve the central nervous system and extrinsic nerves.

Events Triggering GI Tract Activity

Food in the stomach or smell of food can initiate digestive processes.

• Stretching of the stomach wall

• Chemical signals from food

• Nervous system activation

Submucosal Glands and Their Role

Submucosal glands secrete mucus and enzymes to protect and lubricate the GI tract.

Functions of Gastrin, Secretin, and Cholecystokinin

These hormones regulate digestive processes.

• Gastrin: Stimulates gastric acid secretion.

• Secretin: Stimulates bicarbonate secretion from pancreas.

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

Bile Salts: Function and Chemical Composition

Bile salts emulsify fats for 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.

Hepatic Portal Circulation

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

Difference Between Bowman's Capsule and Glomerulus

Bowman's capsule and glomerulus are part of the nephron in the kidney.

• Bowman's capsule: Surrounds the glomerulus; collects filtrate.

• Glomerulus: Network of capillaries where filtration occurs.

Additional info: This topic is more related to the urinary system, but is included here as per the notes.

Function of the Hepatic Portal Circulation

Transports blood from the digestive organs to the liver for detoxification and nutrient processing.

Phases of Gastric Secretion

Gastric secretion occurs in three phases:

• 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.

Enzymes Secreted by the GI Tract

The GI tract secretes various enzymes for digestion.

• Amylase: Digests carbohydrates.

• Proteases: Digest proteins.

• Lipases: Digest fats.

Hormonal and Neural Control of GI Secretion

GI secretion is regulated by hormones (e.g., gastrin, secretin, CCK) and neural signals (vagus nerve, enteric nervous system).

Intrinsic Factor and Its Purpose

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

Regulation of HCl Secretion in the Stomach

HCl secretion is controlled by neural, hormonal, and paracrine mechanisms.

• Gastrin: Stimulates HCl secretion.

• Histamine: Enhances HCl production.

• Acetylcholine: Released by vagus nerve, stimulates parietal cells.

Cells in the Stomach and Their Secretions

Function of Goblet Cells

Goblet cells secrete mucus to protect and lubricate the lining of the digestive tract.