Respiratory System

Conducting Zone: Functions and Structures

The conducting zone of the respiratory system consists of all the respiratory passageways that provide a pathway for air to reach the sites of gas exchange. Its primary functions are to filter, warm, and moisten incoming air.

• Structures: Nose, nasal cavity, pharynx, larynx, trachea, bronchi, and terminal bronchioles.

• Function: Conducts air to the respiratory zone; no gas exchange occurs here.

Nose: Structure and Epithelial Coverings

• External Nose: Formed by bone and cartilage; nostrils (external nares) allow air entry.

• Nasal Cavity: Lined with pseudostratified ciliated columnar epithelium containing goblet cells that secrete mucus.

• Borders: Divided by the nasal septum; bounded by the palate (floor) and ethmoid bone (roof).

Paranasal Sinuses: Location, Structure, and Function

• Location: Frontal, maxillary, ethmoid, and sphenoid bones.

• Structure: Air-filled spaces lined with mucous membrane.

• Function: Lighten skull, warm and moisten air, enhance voice resonance.

Pharynx: Structure and Functions

• Nasopharynx: Posterior to nasal cavity; air passage only.

• Oropharynx: Posterior to oral cavity; passage for food and air.

• Laryngopharynx: Posterior to larynx; leads to esophagus and larynx.

Larynx: Structure and Functions

• Structure: Cartilaginous structure (thyroid, cricoid, epiglottis, etc.).

• Functions: Maintains open airway, routes food and air, houses vocal cords for sound production.

Trachea and Mucociliary Escalator

• Structure: Tube with C-shaped cartilage rings; lined with ciliated epithelium.

• Mucociliary Escalator: Cilia move mucus and trapped particles upward toward the pharynx for removal.

Bronchial Tree: Structure and Function

• Structure: Primary bronchi → secondary bronchi → tertiary bronchi → bronchioles → terminal bronchioles.

• Function: Distributes air to lungs; smooth muscle controls airway diameter.

Respiratory Zone: Structure and Function

• Structures: Respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli.

• Function: Site of gas exchange between air and blood.

Route of Airflow

• External nares → nasal cavity → pharynx → larynx → trachea → bronchi → bronchioles → terminal bronchioles → respiratory bronchioles → alveolar ducts → alveolar sacs → alveoli.

Lung Organization

• Right Lung: 3 lobes (superior, middle, inferior).

• Left Lung: 2 lobes (superior, inferior); cardiac notch for heart.

Pleurae: Structure and Function

• Visceral Pleura: Covers lungs.

• Parietal Pleura: Lines thoracic cavity.

• Pleural Cavity: Contains lubricating fluid, reduces friction, assists lung expansion.

Muscles of Breathing

• Primary: Diaphragm, external intercostals.

• Accessory (forced breathing): Sternocleidomastoid, scalenes, internal intercostals, abdominal muscles.

Pulmonary Ventilation: Pressures and Boyle's Law

• Three Pressures: Atmospheric (Patm), Intrapulmonary (Ppul), Intrapleural (Pip).

• Boyle's Law: Pressure and volume are inversely related:

Respiratory Cycle and Types of Breathing

• One Cycle: Inspiration (inhalation) + expiration (exhalation).

• Types: Quiet (eupnea), forced (hyperpnea), shallow, deep.

Inspiration and Expiration: Volume and Pressure Changes

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

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

Lung Compliance and Recoil

• Compliance: Ease with which lungs expand; affected by elasticity and surfactant.

• Recoil: Tendency to return to original shape; necessary for expiration.

Respiratory Volumes and Capacities

• Tidal Volume (TV): Normal breath (~500 mL).

• Inspiratory Reserve Volume (IRV): Extra air inhaled after normal inspiration.

• Expiratory Reserve Volume (ERV): Extra air exhaled after normal expiration.

• Residual Volume (RV): Air remaining after maximal exhalation.

• Capacities: Combinations of volumes (e.g., Vital Capacity = TV + IRV + ERV).

Dead Space

• Anatomical Dead Space: Air in conducting zone not involved in gas exchange.

• Alveolar Dead Space: Non-functional alveoli.

Respiratory Minute Volume (RMV) and Alveolar Ventilation Rate (AVR)

• RMV: Total air moved per minute: (f = breaths/min).

• AVR: Air reaching alveoli per minute:

Restrictive vs. Obstructive Disorders

• Restrictive: Reduced lung expansion (e.g., fibrosis).

• Obstructive: Increased airway resistance (e.g., asthma, COPD).

Dalton’s Law of Partial Pressures

• Total pressure of a gas mixture equals the sum of partial pressures of each component:

Ventilation and Perfusion Regulation

• Ventilation: Airflow to alveoli.

• Perfusion: Blood flow to alveoli.

• Regulated to optimize gas exchange (V/Q matching).

External vs. Internal Respiration

• External: Gas exchange between alveoli and blood.

• Internal: Gas exchange between blood and tissues.

Oxygen and Carbon Dioxide Transport

• Oxygen: Mostly bound to hemoglobin; some dissolved in plasma.

• Carbon Dioxide: Dissolved in plasma, bound to hemoglobin, or as bicarbonate ion ().

Oxygen Dissociation from Hemoglobin

• Affected by pH, temperature, CO2 levels, and 2,3-BPG.

Respiratory Centers and CO2 Effects

• Medulla Oblongata: Contains dorsal and ventral respiratory groups; regulate rhythm and depth.

• Increased CO2 increases rate and depth of breathing (hypercapnia); decreased CO2 decreases rate (hypocapnia).

Urinary System

Kidney Location and Gross Anatomy

• Location: Retroperitoneal, on either side of vertebral column.

• Gross Anatomy: Renal cortex, medulla, pyramids, pelvis, calyces.

Connective Tissue Layers of the Kidney

• Renal Fascia: Anchors kidney.

• Perirenal Fat Capsule: Cushions kidney.

• Fibrous Capsule: Protects from infection and trauma.

Blood Flow Through Kidney Vasculature

• Renal artery → segmental arteries → interlobar arteries → arcuate arteries → cortical radiate arteries → afferent arterioles → glomerulus → efferent arterioles → peritubular capillaries/vasa recta → cortical radiate veins → arcuate veins → interlobar veins → renal vein.

Nephron Microanatomy

• Components: Renal corpuscle (glomerulus + Bowman's capsule), proximal convoluted tubule, nephron loop (loop of Henle), distal convoluted tubule, collecting duct.

Ureters, Urinary Bladder, and Urethra

• Ureters: Muscular tubes transporting urine from kidneys to bladder.

• Urinary Bladder: Muscular sac for urine storage.

• Urethra: Tube for urine excretion; longer in males, shorter in females.

Urine Formation: Route and Processes

• Glomerulus → Bowman's capsule → proximal tubule → nephron loop → distal tubule → collecting duct → minor calyx → major calyx → renal pelvis → ureter → bladder → urethra.

• Processes: Filtration, reabsorption, secretion.

Male vs. Female Urethra

• Male: Longer, passes through prostate and penis; also carries semen.

• Female: Shorter, opens anterior to vaginal opening; only urine passage.

Glomerular Filtration Rate (GFR) and Influencing Pressures

• GFR: Volume of filtrate formed per minute by both kidneys.

• Influencing Pressures: Glomerular hydrostatic pressure, blood colloid osmotic pressure, capsular hydrostatic pressure.

Tubular Reabsorption and Secretion

• Reabsorption: Movement of substances from filtrate back to blood (e.g., water, glucose, ions).

• Secretion: Movement of substances from blood into filtrate (e.g., H+, K+, drugs).

Medullary Osmotic Gradient and Countercurrent Multiplier

• Nephron Loop and Vasa Recta: Create and maintain osmotic gradient for water reabsorption.

• Countercurrent Multiplier: Mechanism in nephron loop that concentrates urine by increasing medullary osmolarity.

Intrinsic and Extrinsic Regulation of GFR

• Intrinsic: Renal autoregulation (myogenic mechanism, tubuloglomerular feedback).

• Extrinsic: Neural (sympathetic) and hormonal (renin-angiotensin-aldosterone system) controls.

Hormonal Regulation: ADH and Aldosterone

• ADH: Increases water reabsorption in collecting ducts.

• Aldosterone: Increases sodium (and water) reabsorption in distal tubule and collecting duct.

Fluid, Electrolyte, & Acid-Base Balance

Body Fluid Compartments and Solute Concentrations

• Compartments: Intracellular fluid (ICF), extracellular fluid (ECF: plasma, interstitial fluid).

• Solute Concentrations: ICF high in K+, ECF high in Na+ and Cl-.

Fluid Shifts and Water Balance

• Driven by osmotic and hydrostatic pressures between compartments.

Routes of Water Gain and Loss

• Gain: Ingestion (food, drink), metabolic water.

• Loss: Urine, feces, sweat, evaporation, respiration.

Thirst Mechanism and Hormonal Regulation

• Thirst: Stimulated by osmoreceptors in hypothalamus detecting increased plasma osmolarity.

• Hormones: ADH, aldosterone, and atrial natriuretic peptide (ANP) regulate water loss.

Disorders of Water Balance

• Dehydration: Water loss exceeds intake; cells shrink.

• Hypotonic Hydration: Excess water intake; cells swell (water intoxication).

• Edema: Accumulation of fluid in interstitial space.

Electrolytes: Definition and Major Types

• Electrolyte: Substance that dissociates into ions in solution, conducting electricity.

• Major Electrolytes: Sodium (Na+), potassium (K+), calcium (Ca2+), magnesium (Mg2+), chloride (Cl-), phosphate (PO43-).

Electrolyte Balance: Entry, Loss, and Hormonal Control

• Entry: Diet.

• Loss: Urine, sweat, feces.

• Hormonal Control: Aldosterone (Na+, K+), ANP, ADH.

Electrolyte Imbalances

pH, Acids, Bases, and Buffers

• pH: Measure of hydrogen ion concentration:

• Acid: Donates H+ (e.g., HCl).

• Base: Accepts H+ (e.g., HCO3-).

• Buffer: Resists changes in pH (e.g., bicarbonate, phosphate, protein buffers).

Effects of H+ and CO2 on pH

• Increased H+ or CO2 lowers pH (acidosis).

• Decreased H+ or CO2 raises pH (alkalosis).

Chemical Buffering Systems

• Bicarbonate Buffer:

• Phosphate Buffer:

• Protein Buffer: Amino acids accept or donate H+.

Respiratory and Renal Regulation of pH

• Respiratory: Adjusts CO2 exhalation to regulate pH.

• Renal: Adjusts H+ secretion and HCO3- reabsorption.

Hypercapnia and Hypocapnia

• Hypercapnia: Excess CO2 in blood; causes respiratory acidosis.

• Hypocapnia: Low CO2 in blood; causes respiratory alkalosis.

Acid-Base Disorders and Compensation

• Disorders: Acidosis (pH < 7.35), alkalosis (pH > 7.45); can be respiratory or metabolic.

• Compensation: Respiratory system compensates for metabolic disorders and vice versa.

Normal Parameters

Mechanisms of Compensation

• Respiratory Compensation: Alters ventilation to change CO2 levels.

• Renal Compensation: Alters H+ secretion and HCO3- reabsorption.

Additional info: Where details were not specified, standard textbook explanations were provided for completeness.