Anatomy & Physiology Study Guide: The Respiratory and Digestive Systems

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The Respiratory System

Overview and Anatomy

The respiratory system is responsible for gas exchange, supplying oxygen to the body and removing carbon dioxide. It consists of organs located in the head, neck, and thoracic cavity, including the lungs, respiratory tract, blood vessels of the pulmonary circuit, rib cage, and respiratory muscles.

Respiratory Tract: A system of hollow tubes where gas exchange occurs in the alveoli.
Upper Respiratory Passages: From the nose and nasal cavity to the pharynx.
Lower Respiratory Passages: From the larynx to the alveoli.
Alveoli: Tiny air sacs where gas exchange occurs.
Lungs: Main organs of respiration, divided into lobes and situated in pleural cavities.

Conducting vs. Respiratory Zones

Conducting Zone: Passages that carry air but do not participate in gas exchange (nose to terminal bronchioles).
Respiratory Zone: Passages where gas exchange occurs (respiratory bronchioles, alveolar ducts, alveoli).

Functions of the Respiratory System

Primary Function: Respiration (oxygen intake, carbon dioxide removal).
Other Functions: Speech, olfaction, acid-base balance, blood pressure regulation, defense against pathogens, and blood flow regulation.

Anatomy of the Nose and Nasal Cavity

Functions: Warm, humidify, and filter inhaled air; house olfactory receptors; enhance voice resonance.
Olfactory Mucosa: Contains bipolar neurons for smell (Cranial Nerve I).
Respiratory Mucosa: Pseudostratified columnar epithelium with goblet cells; traps debris and moves it via cilia.

The Pharynx

Divisions: Nasopharynx, Oropharynx, Laryngopharynx.
Functions: Passageway for air and food; contains MALT (mucosa-associated lymphoid tissue) for immune defense.

The Larynx

Epiglottis: Elastic cartilage structure that covers the glottis during swallowing to prevent aspiration.
Thyroid Cartilage: Known as the Adam's apple; surrounds vocal cords.
Cricoid Cartilage: Forms the inferior border; associated with the cricothyroid membrane.
Vestibular Folds: False vocal cords; protect the true vocal cords.
Vocal Ligaments: Covered by true vocal cords; responsible for sound production.
Loudness: Related to force of air.
Pitch: Related to tension in vocal cords.

The Trachea and Bronchial Tree

Trachea: Windpipe; extends from cricoid cartilage into mediastinum; contains C-shaped hyaline cartilage rings.
Carina: Last tracheal ring; contains nerves for cough reflex.
Bronchi: Right bronchus is wider, shorter, and more vertical than the left; right has 3 secondary bronchi, left has 2.
Bronchioles: Smallest airways; conducting zone ends at terminal bronchioles, respiratory zone begins at respiratory bronchioles.

Alveoli and Respiratory Membrane

Type I Alveolar Cells: Simple squamous cells for gas exchange.
Type II Alveolar Cells: Secrete surfactant to reduce surface tension.
Alveolar Macrophages: Immune cells that remove debris.
Respiratory Membrane: Thin barrier for efficient gas exchange.

Lung Anatomy

Base: Sits on diaphragm.
Apex: Under clavicle.
Hilum: Entry/exit point for vessels and bronchi.
Cardiac Notch: Indentation in left lung for heart.
Lobes: Right lung has 3 (superior, middle, inferior); left lung has 2 (superior, inferior).
Pleura: Parietal (lines cavity), visceral (covers lung), pleural fluid (reduces friction).

Breathing Mechanics: Pressure and Volume

Inspiration: Diaphragm contracts, rib cage expands, lung volume increases, pressure decreases.
Expiration: Diaphragm relaxes, rib cage contracts, lung volume decreases, pressure increases.
Air Movement: From high to low pressure (diffusion).
Intrapulmonary Pressure: Pressure within alveoli.
Intrapleural Pressure: Pressure within pleural cavity; prevents lung collapse.
Muscles: Diaphragm and external intercostals for inspiration.

Physical Factors Affecting Ventilation

Airway Resistance: Resistance to airflow; increased in asthma.
Pulmonary Compliance: Ability of lungs to stretch.
Alveolar Surface Tension: Surfactant reduces tension, prevents collapse.

Pulmonary Volumes and Capacities

Spirometer: Device to measure lung volumes.
Tidal Volume: Air moved in/out per breath.
Inspiratory Reserve Volume: Extra air inhaled after normal inspiration.
Expiratory Reserve Volume: Extra air exhaled after normal expiration.
Capacities: Sums of volumes.
Alveolar Ventilation Rate: Volume of air reaching alveoli per minute.

Gas Exchange

Pulmonary Gas Exchange: Oxygen from alveoli to blood; carbon dioxide from blood to alveoli.
Tissue Gas Exchange: Oxygen from blood to tissues; carbon dioxide from tissues to blood.
Diffusion: Driven by partial pressure gradients.
Hypoxemia: Low blood oxygen.
Hypercapnia: High blood carbon dioxide.
Membrane Thickness: Thin membranes facilitate diffusion.
Surface Area: More alveoli/capillaries = more efficient gas exchange.

Transport of Gases

Oxygen: 1.5% dissolved in plasma, 98% bound to hemoglobin.
Carbon Dioxide: 7-10% dissolved in plasma, 20% bound to hemoglobin (carbaminohemoglobin), 70% as bicarbonate (HCO3-).
Carbonic Anhydrase: Enzyme converting CO2 to HCO3- and vice versa.
Buffer System: Carbonic acid-bicarbonate buffer maintains blood pH (7.35-7.45).

Key Equation: Carbonic Acid-Bicarbonate Buffer

Hyperventilation: Decreases CO2, increases pH (respiratory alkalosis).
Hypoventilation: Increases CO2, decreases pH (respiratory acidosis).

Control of Breathing

Dyspnea: Difficulty breathing.
Eupnea: Normal breathing.
Central Chemoreceptors: Monitor CO2 and H+ in CSF; main driver for breathing.
Medulla Oblongata: Controls breathing rate and depth.
Increased CO2/H+: Increases respiration.
Decreased CO2/H+: Decreases respiration.

Respiratory Diseases

Restrictive Lung Disease: Reduced lung expansion.
Obstructive Lung Disease: Increased airway resistance (e.g., asthma, COPD).

The Digestive System

Overview and Anatomy

The digestive system breaks down food for nutrient absorption, regulates fluid and electrolyte balance, and excretes waste. It consists of the alimentary canal (digestive tract) and accessory organs.

Alimentary Canal: Oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, anus.
Accessory Organs: Teeth, tongue, salivary glands, liver, gallbladder, pancreas.

Functions of the Digestive System

Ingestion
Secretion
Propulsion
Digestion (mechanical and chemical)
Absorption
Defecation
Hormone production

Serous Membranes and Mesenteries

Peritoneal Membrane: Largest serous membrane; two layers:
- Parietal Peritoneum: Lines abdominal wall.
- Visceral Peritoneum: Covers organs.
Peritoneal Cavity: Space between layers, contains fluid.
Mesenteries: Folds of peritoneum anchoring organs.
Intraperitoneal: Organs within peritoneal cavity.
Retroperitoneal: Organs behind peritoneal cavity.
Greater/Lesser Omentum: Fatty folds covering intestines.
Peritonitis: Inflammation of peritoneum.

Blood Supply

Splanchnic Circulation: Blood supply to abdominal organs.
Hepatic Portal Vein: Drains digestive organs to liver for processing.

Histology of the Alimentary Canal

Four Layers: Mucosa, submucosa, muscularis externa, serosa.
Mucosa: Simple columnar epithelium with goblet cells, lamina propria with MALT, muscularis mucosae.
Submucosal Plexus: Controls secretion and blood flow.
Myenteric Plexus: Controls peristalsis.

Oral Cavity and Accessory Organs

Accessory Organs: Teeth, tongue, salivary glands.
Digestive Processes: Ingestion, mechanical digestion, chemical digestion, propulsion.
Bolus: Chewed food ready for swallowing.
Structures: Soft palate, hard palate, uvula.

Teeth

Primary (Deciduous) Teeth: 20, erupt at 6-24 months, fall out by age 12.
Permanent Teeth: 32, complete by age 21.
Components: Crown (outer enamel, hardest substance), dentin (next layer), pulp (innermost).

Tongue and Papillae

Tongue: Skeletal muscle, innervated by hypoglossal nerve, attached via lingual frenulum.
Papillae: Four types; some lack taste buds.

Salivary Glands and Saliva

Three Glands: Parotid, submandibular, sublingual.
Cell Types: Mucous and serous cells.
Saliva Components: Water, enzymes, mucus, ions.
Functions: Salivary amylase (digests carbs), lysozyme (antibacterial), secretory IgA (immune), bicarbonate ions (buffer).

Pharynx and Swallowing

Divisions: Nasopharynx, oropharynx, laryngopharynx.
Deglutition: Swallowing process; bolus moves from oral cavity to esophagus.
Tonsils: Immune defense.

Esophagus

Muscular Tube: 10 inches long; connects pharynx to stomach.
Sphincters: Upper esophageal sphincter (pharynx-esophagus), gastroesophageal sphincter (esophagus-stomach).
Musculature: Unique mix of skeletal and smooth muscle.
Esophageal Hiatus: Passage through diaphragm.

Stomach

Shape: J-shaped; greater and lesser curvatures.
Regions: Cardia, fundus, body, pyloric antrum, pylorus.
Pyloric Sphincter: Controls passage to duodenum.
Layers: Four basic layers plus an extra oblique muscle layer.
Chyme: Partially digested food mixed with gastric juice.

Stomach Histology

Mucosa: Heavily indented with gastric pits.
Gastric Glands: Exocrine and endocrine cells.
Mucous Neck Cells: Produce mucus.
Parietal Cells: Produce HCl and intrinsic factor (for B12 absorption).
Chief Cells: Produce pepsinogen (converted to pepsin).
G Cells: Produce gastrin (stimulates HCl release and motility).

Stomach Functions

Secretion: Three phases: cephalic, gastric, intestinal.
Motility: Mixing, propulsion, emptying.
Neutralization: Chyme is neutralized by bicarbonate from pancreas.

Small Intestine

Sections: Duodenum, jejunum, ileum.
Processes: Digestion, absorption, secretion, propulsion.
Major Duodenal Papilla: Entry point for bile and pancreatic juice.
Duodenal Glands: Secrete mucus.
Cecum: First part of large intestine.
Ileocecal Valve: Controls passage from ileum to cecum.
Surface Area: Circular folds, villi, microvilli (brush border).
Lacteals: Carry absorbed lipids.
Motility: Segmentation (churning), peristalsis (propulsion).

Large Intestine

Segments: Cecum, ascending colon, transverse colon, descending colon, sigmoid colon.
Flexures: Hepatic and splenic.
Rectum: Last portion; contains important sphincters.
Functions: Absorbs water/electrolytes, secretes mucus, propulsion, defecation.
Gut Flora: Symbiotic bacteria; produce vitamin K, stimulate immunity.
Appendix: Contains MALT.
Taeniae Coli: Longitudinal muscle bands.
Haustra: Pouches formed by taeniae coli.
Diarrhea vs. Constipation: Differences in water absorption.

Pancreas

Exocrine Function: Acinar cells secrete digestive enzymes for all nutrient classes.
Secretion: Enzymes, water, bicarbonate ions (neutralize chyme).

Liver and Gallbladder

Liver: Produces bile, metabolizes nutrients, detoxifies, immune defense (Kupfer cells).
Liver Lobule: Functional unit; hepatocytes.
Bile Salts: Amphiphilic, emulsify lipids.
Portal System: Blood from digestive organs to liver.
Gallbladder: Stores and concentrates bile; releases via cystic duct.
Common Bile Duct: Formed by cystic and common hepatic ducts.

Absorption and Digestion

Monomers: Smallest units absorbed (amino acids, monosaccharides, fatty acids).
Carbohydrate Digestion: Salivary amylase (oral cavity), pancreatic amylase (small intestine), brush border enzymes (disaccharides).
Protein Digestion: Pepsin (stomach), proteolytic enzymes (small intestine).
Fat Digestion: Mechanical digestion, emulsification (bile salts), pancreatic lipase, micelles, chylomicrons (transport via lacteals).
Nucleotide Digestion: Similar to proteins.
B12 Absorption: Requires intrinsic factor from parietal cells.

Fluid and Electrolyte Balance

Alimentary Canal: Reclaims 8 liters of fluid/day.
Large Intestine: Excretes only 0.1 L/day; absorbs most water/electrolytes.

Table: Comparison of Respiratory and Digestive System Functions

System	Main Function	Key Organs	Major Processes
Respiratory	Gas exchange (O2 in, CO2 out)	Nose, pharynx, larynx, trachea, bronchi, lungs, alveoli	Pulmonary ventilation, gas exchange, transport, regulation
Digestive	Breakdown and absorption of nutrients	Oral cavity, pharynx, esophagus, stomach, intestines, liver, pancreas, gallbladder	Ingestion, digestion, absorption, propulsion, secretion, defecation

Example: The respiratory system's alveoli and the digestive system's villi both increase surface area for efficient exchange—of gases and nutrients, respectively.

Additional info: Academic context was added to clarify anatomical divisions, histological features, and physiological processes, as well as to fill in missing details from the original notes.