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Comprehensive Study Notes: The Respiratory, Digestive, Metabolic, and Urinary Systems

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Chapter 22 – The Respiratory System

Overview and Functions

The respiratory system is responsible for gas exchange, supplying oxygen (O2) to cells and removing carbon dioxide (CO2). It works closely with the circulatory system and also plays roles in olfaction and speech.

  • Four processes of respiration:

    1. Pulmonary ventilation (breathing): movement of air in and out of lungs.

    2. Pulmonary gas exchange: exchange of O2 and CO2 between lungs and blood.

    3. Transport of respiratory gases: movement of O2 and CO2 in blood (cardiovascular system).

    4. Tissue gas exchange: exchange of O2 and CO2 between blood and tissues.

Major Organs of the Respiratory System

  • Upper respiratory system: Nose, paranasal sinuses, pharynx

  • Lower respiratory system: Larynx, trachea, bronchi (and branches), lungs, alveoli

  • Respiratory muscles: (e.g., diaphragm, intercostals) are part of the muscular system

Organs and Their Functions

Structure

Description

Function

Nose

External part supported by bone/cartilage; internal nasal septum; lined with mucosa

Filters, warms, moistens air; resonance for speech; olfaction

Paranasal sinuses

Air-filled cavities in cranial bones

Lighten skull; warm/moisten/filter air

Pharynx

Connects nasal cavity to larynx; three regions

Passage for air/food; immune exposure

Larynx

Cartilaginous structure; houses vocal folds

Air passage; prevents food entry; voice

Trachea

Flexible tube with C-shaped cartilage

Air passage; cleans, warms, moistens air

Bronchial tree

Branching bronchi/bronchioles

Air passage; cleans, warms, moistens air

Alveoli

Microscopic air sacs

Gas exchange; surfactant reduces surface tension

Lungs

Paired organs of alveoli and passageways

House respiratory passages; elastic recoil

Pleurae

Serous membranes

Lubricate and compartmentalize lungs

Functional Divisions

  • Respiratory zone: Sites of gas exchange (respiratory bronchioles, alveolar ducts, alveoli)

  • Conducting zone: All other airways; transport, cleanse, warm, humidify air

Mechanics of Breathing

  • Inspiration: Air flows into lungs

  • Expiration: Air flows out of lungs

  • Pressure relationships:

    • Atmospheric pressure (Patm): Pressure of air outside body

    • Intrapulmonary pressure (Ppul): Pressure in alveoli; equalizes with Patm

    • Intrapleural pressure (Pip): Pressure in pleural cavity; always negative relative to Ppul

    • Transpulmonary pressure: ; keeps lungs inflated

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

Physical Factors Influencing Ventilation

  • Airway resistance: Greatest in medium-sized bronchi; increases with constriction (e.g., asthma)

  • Alveolar surface tension: Surfactant reduces tension, preventing collapse

  • Lung compliance: Ease of lung expansion; decreased by fibrosis, low surfactant, thoracic deformities

Pulmonary Volumes and Capacities

Volume

Description

Typical Value

Tidal Volume (TV)

Air moved per breath

~500 mL

Inspiratory Reserve Volume (IRV)

Extra air inhaled after normal inspiration

2100–3200 mL

Expiratory Reserve Volume (ERV)

Extra air exhaled after normal expiration

1000–1200 mL

Residual Volume (RV)

Air remaining after forced expiration

~1200 mL

Gas Exchange

  • Pulmonary gas exchange: O2 and CO2 diffuse across respiratory membrane

  • Tissue gas exchange: O2 and CO2 exchange between blood and tissues

  • Factors affecting exchange: Partial pressure gradients, membrane thickness/surface area, ventilation-perfusion coupling

Oxygen Transport

  • 1.5% dissolved in plasma; 98.5% bound to hemoglobin (Hb)

  • Oxyhemoglobin: Hb + O2; Deoxyhemoglobin: Hb without O2

  • Loading/unloading influenced by PO2, temperature, pH, PCO2

Control of Respiration

  • Medullary respiratory centers: Ventral (VRG) and dorsal groups set rhythm

  • Factors affecting rate/depth: Chemical (CO2, O2, pH), higher brain centers, reflexes

Chapter 23 – The Digestive System

Functions and Processes

The digestive system ingests food, breaks it down into nutrients, absorbs them, and eliminates waste.

  • Six essential activities:

    1. Ingestion

    2. Propulsion (swallowing, peristalsis)

    3. Mechanical breakdown (chewing, churning, segmentation)

    4. Digestion (enzymatic breakdown)

    5. Absorption (nutrients into blood/lymph)

    6. Defecation (elimination of indigestible substances)

Organization

  • Alimentary canal: Mouth, pharynx, esophagus, stomach, small and large intestines, anus

  • Accessory organs: Teeth, tongue, salivary glands, liver, gallbladder, pancreas

Histology of the GI Tract

  • Mucosa: Secretes mucus, enzymes, hormones; absorbs nutrients; protects

  • Submucosa: Blood/lymph vessels, nerves, elastic tissue

  • Muscularis externa: Segmentation and peristalsis; circular and longitudinal muscle layers

  • Serosa: Protective outer layer

Regulation

  • Enteric nervous system: Intrinsic nerve plexuses (submucosal, myenteric)

  • Short reflexes: Local GI stimuli

  • Long reflexes: Involve CNS and autonomic input

  • Hormonal control: GI hormones regulate secretion and motility

Digestive Processes by Region

  • Mouth: Chewing, saliva (amylase), swallowing

  • Pharynx/Esophagus: Propulsion (swallowing)

  • Stomach: Churning, protein digestion (pepsin), acid secretion, intrinsic factor for B12

  • Small intestine: Main site for digestion and absorption; receives bile and pancreatic juice

  • Large intestine: Absorbs water/electrolytes, forms feces, houses bacteria

Accessory Organs

  • Liver: Produces bile (fat emulsification), processes nutrients, detoxifies

  • Gallbladder: Stores and concentrates bile

  • Pancreas: Produces digestive enzymes and bicarbonate; endocrine (insulin, glucagon)

Absorption

  • Most nutrients absorbed in small intestine

  • Water, vitamins, electrolytes absorbed in large intestine

  • Fat-soluble vitamins (A, D, E, K) absorbed with fats; water-soluble vitamins by diffusion/transporters

  • Vitamin B12 requires intrinsic factor

Chapter 24 – Nutrition, Metabolism, and Energy Balance

Definitions and Nutrients

  • Metabolism: All chemical reactions in the body

  • Macronutrients: Carbohydrates, lipids, proteins

  • Micronutrients: Vitamins, minerals

  • Essential nutrients: Must be obtained from diet

Digestion End Products

  • Proteins → amino acids

  • Carbohydrates → glucose, other sugars

  • Fats → glycerol, fatty acids

Metabolic Pathways

  • Carbohydrate metabolism: Glucose is main fuel for ATP production

  • Lipid metabolism: Triglycerides oxidized for energy; fatty acids undergo beta-oxidation

  • Protein metabolism: Amino acids recycled or used for energy if excess

Energy Balance

  • Energy intake: Energy from food oxidation

  • Energy output: Heat, work, storage

  • Basal metabolic rate (BMR): Energy needed for essential body functions

  • Factors affecting BMR: Age, gender, temperature, stress, thyroxine

Chapter 25 – The Urinary System

Functions

  • Regulate water volume and solute concentration

  • Regulate ion concentrations in extracellular fluid

  • Maintain acid-base balance

  • Excrete metabolic wastes, toxins, drugs

  • Produce erythropoietin and renin

  • Activate vitamin D

  • Carry out gluconeogenesis during fasting

Gross Anatomy

  • Kidneys: retroperitoneal, bean-shaped, protected by ribs and fat

  • Ureters: transport urine to bladder

  • Urinary bladder: stores urine

  • Urethra: expels urine

Internal Structure of Kidney

  • Renal cortex: Outer region

  • Renal medulla: Inner region with pyramids

  • Renal pelvis: Funnel for urine to ureter

  • Calyces: Collect urine from pyramids

Nephrons

  • Structural/functional units; ~1 million per kidney

  • Consist of renal corpuscle (glomerulus + Bowman's capsule) and renal tubule (PCT, loop of Henle, DCT)

  • Types: cortical (85%), juxtamedullary (long loops, concentrate urine)

Blood Supply

  • Renal arteries deliver ~25% of cardiac output to kidneys

  • Glomerulus fed/drained by arterioles; high pressure for filtration

  • Peritubular capillaries and vasa recta reabsorb water/solutes

Urine Formation

  • Glomerular filtration: Passive, driven by hydrostatic pressure; filters plasma minus proteins/cells

  • Tubular reabsorption: Returns useful substances to blood (Na+, glucose, amino acids, water)

  • Tubular secretion: Moves substances from blood to filtrate (e.g., drugs, H+, K+)

Regulation of Filtration

Intrinsic Control

Extrinsic Control

Maintains GFR despite BP changes (myogenic, tubuloglomerular feedback)

Maintains systemic BP (neural, hormonal: renin-angiotensin-aldosterone)

Hormonal Regulation

  • ADH: Increases water reabsorption in collecting ducts

  • Aldosterone: Increases Na+ (and water) reabsorption; reduces K+

  • Parathyroid hormone: Increases Ca2+ reabsorption

Urine Composition and Characteristics

  • 95% water, 5% solutes (urea, uric acid, creatinine, ions)

  • Color: pale yellow to deep amber (urochrome)

  • pH: ~6 (range 4.5–8)

  • Odor: slightly aromatic; may change with diet/disease

Urinary Tract Structures and Micturition

  • Ureters: Transport urine by peristalsis

  • Bladder: Stores urine; trigone region prone to infection

  • Micturition (urination): Requires contraction of detrusor, opening of internal and external sphincters

Clinical Implications (Selected)

  • Rhinitis, sinusitis, laryngitis, pleurisy, atelectasis, asthma, IRDS, emphysema, pneumonia (respiratory)

  • Peritonitis, ankyloglossia, gallstones, appendicitis (digestive)

  • Nephrotic syndrome, pyelonephritis, renal calculi, chronic renal disease, renal failure (urinary)

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