Respiratory and Digestive System Study Notes

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.

O2 and CO2 Transport in the Blood

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

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

• Carbon Dioxide: Transported as dissolved CO2, carbaminohemoglobin, and 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 driver.

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

• O2: Low oxygen levels stimulate peripheral chemoreceptors, but less strongly than CO2.

• 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 dissolved in a liquid is proportional to its partial pressure and solubility.

Surfactant and Wall Cells

Surfactant is a substance produced by type II alveolar cells that reduces surface tension in the alveoli, preventing collapse.

• Type I Alveolar Cells: Form the structure of the alveolar wall.

• Type II Alveolar Cells: Secrete surfactant.

Anatomical Differences Between Left and Right Lungs

• 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

• Mucus and Cilia: Trap and move particles out of the airways.

• Epiglottis: Prevents food from entering the trachea.

Anatomy of the Trachea

• Structure: C-shaped cartilage rings, lined with pseudostratified ciliated epithelium.

• Function: Conducts air to the bronchi.

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.

Mechanisms for CO2 Transport

• Dissolved in Plasma

• Carbaminohemoglobin: CO2 bound to hemoglobin.

• Bicarbonate Ions: Main form; formed via carbonic anhydrase.

Internal and External Respiration

• External Respiration: Gas exchange between alveoli and blood.

• Internal Respiration: Gas exchange between blood and tissues.

Pulmonary Ventilation

Pulmonary ventilation is the process of moving air into and out of the lungs.

• Inspiration: Diaphragm contracts, thoracic volume increases, air flows in.

• Expiration: Diaphragm relaxes, thoracic volume decreases, air flows out.

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

• Type I Alveolar Cells: Structural cells for gas exchange.

• Type II Alveolar Cells: Secrete surfactant.

• Alveolar Macrophages: Remove debris and pathogens.

Anatomical Parts of the Respiratory Membrane

• 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 lacteals.

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

Peristalsis and Its Function

Peristalsis is the wave-like contraction of smooth muscle that moves food through the digestive tract.

Anatomical Features of the Stomach Mucosal Barrier

• Mucus Secretion: Protects stomach lining from acid.

• Tight Junctions: Prevent leakage of gastric juices.

• Rapid Cell Turnover: Replaces damaged cells.

Difference Between Long and Short Reflexes

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

• Long Reflexes: Involve CNS, coordinate digestive activity with other systems.

Events Triggering GI Tract Motility

• Stretching of the Wall

• Chemical Stimuli (e.g., food components)

• Nervous and Hormonal Signals

Submucosal Glands and Their Role

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

Functions of Gastrin, Secretin, and Cholecystokinin

• Gastrin: Stimulates gastric acid secretion.

• Secretin: Stimulates bicarbonate secretion from pancreas.

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

Bile Salts and Their Chemical Composition

• Bile Salts: Derived from cholesterol; emulsify fats for digestion.

• Chemical Composition: Bile acids conjugated with glycine or taurine.

Functions of Hepatocytes in Chemical Composition

• Detoxification

• Protein Synthesis

• Bile Production

Differences Between Bile and Blood

• Bile: Contains bile salts, bilirubin, cholesterol, and electrolytes.

• Blood: Contains plasma, cells, proteins, and nutrients.

Hepatic Portal Circulation

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

Functions of the Liver

• Metabolism of Carbohydrates, Proteins, and Fats

• Detoxification

• Storage of Vitamins and Minerals

• Bile Production

Enzymes Secreted by the GI Tract

• Amylase: Digests carbohydrates.

• Proteases: Digest proteins.

• Lipases: Digest fats.

Hormonal and Neural Control of GI Secretion

• Hormones: Gastrin, secretin, CCK regulate secretion and motility.

• Neural: Parasympathetic stimulation increases secretion; sympathetic decreases it.

Intrinsic Factor and Its Purpose

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

Regulation of HCl Secretion in the Stomach

• Stimulated by: Gastrin, acetylcholine, and histamine.

• Inhibited by: Low pH, somatostatin.

Cells and Chemicals Secreted in the Stomach

Cell Type	Secretion	Function
Parietal Cells	HCl, Intrinsic Factor	Acidifies stomach, B12 absorption
Chief Cells	Pepsinogen	Protein digestion
Mucous Cells	Mucus	Protects lining
G Cells	Gastrin	Stimulates acid secretion
Goblet Cells	Mucus	Lubrication and protection

Function of Goblet Cells

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

Additional info: Some details were inferred and expanded for completeness and clarity.