Study Guide: The Respiratory System, Urinary System, and Fluid, Electrolyte, and Acid-Base Balance

Chapter 23: The Respiratory System

Overview of the Respiratory System

The respiratory system is responsible for gas exchange, supplying oxygen to the body and removing carbon dioxide. It interacts closely with the digestive, circulatory, and urinary systems to maintain homeostasis and support cellular respiration.

• Main Functions: Provides oxygen, removes carbon dioxide, regulates blood pH, and enables vocalization.

• Relationship to Other Systems: Works with the circulatory system for gas transport, the digestive system for energy metabolism, and the urinary system for acid-base balance.

• Cellular Respiration: Oxygen is required for cellular respiration, which produces ATP; carbon dioxide is a waste product.

Anatomy of the Respiratory System

• Major Divisions: Upper respiratory system (nose, nasal cavity, pharynx) and lower respiratory system (larynx, trachea, bronchi, lungs).

• Conducting Portion: Includes all structures that transport air but do not participate in gas exchange (nose to terminal bronchioles).

• Respiratory Portion: Includes structures where gas exchange occurs (respiratory bronchioles, alveolar ducts, alveoli).

Structures and Functions

• Larynx: Contains vocal cords; involved in sound production and protecting the airway during swallowing.

• Trachea and Bronchi: Conduct air to the lungs; lined with cilia and mucus to trap particles.

• Lungs: Main organs of respiration; divided into lobes (right lung: 3 lobes, left lung: 2 lobes).

• Alveoli: Tiny air sacs where gas exchange occurs; surrounded by capillaries.

Mechanics of Breathing

• Inspiration: Diaphragm and external intercostal muscles contract, increasing thoracic volume and decreasing pressure, drawing air in.

• Expiration: Usually passive; diaphragm and intercostals relax, thoracic volume decreases, pressure increases, air is expelled.

• Forced Breathing: Involves additional muscles (e.g., internal intercostals, abdominal muscles).

Gas Exchange and Transport

• Dalton's Law: Each gas in a mixture exerts its own partial pressure; total pressure is the sum of partial pressures.

• Henry's Law: The amount of gas dissolved in a liquid is proportional to its partial pressure and solubility.

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

• Carbon Dioxide Transport: Transported as bicarbonate ions, bound to hemoglobin, or dissolved in plasma.

Hemoglobin and Gas Exchange

• Hemoglobin Structure: Protein with four subunits, each binding one oxygen molecule.

• Factors Affecting Oxygen Binding: pH, temperature, partial pressure of CO2, and 2,3-BPG.

• Oxygen-Hemoglobin Dissociation Curve: Shows the relationship between oxygen partial pressure and hemoglobin saturation.

Summary Table: Forms of CO2 Transport in Blood

Form	Description
Bicarbonate ion (HCO3-)	Formed in red blood cells, transported in plasma
Carbaminohemoglobin	CO2 bound to hemoglobin
Dissolved CO2	Small amount dissolved directly in plasma

Chapter 26: The Urinary System

Overview of the Urinary System

The urinary system maintains homeostasis by filtering blood, removing waste, regulating fluid and electrolyte balance, and controlling blood pressure.

• Main Organs: Kidneys, ureters, urinary bladder, urethra.

• Functions: Excretion of metabolic wastes, regulation of blood volume and pressure, regulation of electrolytes and pH.

Kidney Structure and Function

• Regions: Cortex (outer), medulla (inner), renal pelvis (collects urine).

• Nephron: Functional unit; consists of renal corpuscle (glomerulus + Bowman's capsule) and renal tubule (proximal tubule, loop of Henle, distal tubule, collecting duct).

• Blood Supply: Renal artery → segmental arteries → interlobar arteries → arcuate arteries → cortical radiate arteries → afferent arteriole → glomerulus → efferent arteriole → peritubular capillaries/vasa recta.

Urine Formation

• Filtration: Occurs in the glomerulus; blood pressure forces water and solutes into Bowman's capsule.

• Reabsorption: Movement of substances from filtrate back into blood (mainly in proximal tubule).

• Secretion: Additional wastes are secreted into the tubule from blood.

• Excretion: Final urine is excreted via collecting ducts, renal pelvis, ureter, bladder, and urethra.

Regulation of Kidney Function

• Hormonal Control: Antidiuretic hormone (ADH), aldosterone, and atrial natriuretic peptide (ANP) regulate water and sodium reabsorption.

• Autoregulation: Kidneys adjust their own blood flow and filtration rate.

Histology

• Bladder: Lined by transitional epithelium, allowing for expansion.

• Ureter and Urethra: Muscular tubes for urine transport.

Chapter 27: Fluid, Electrolyte, and Acid-Base Balance

Overview

Maintaining fluid, electrolyte, and acid-base balance is essential for normal cellular function and homeostasis. The body regulates the distribution and composition of body fluids, the concentration of electrolytes, and the pH of body fluids.

Fluid Compartments

• Intracellular Fluid (ICF): Fluid within cells (~2/3 of body water).

• Extracellular Fluid (ECF): Fluid outside cells (includes plasma, interstitial fluid).

Electrolytes

• Major Cations: Na+ (ECF), K+ (ICF), Ca2+, Mg2+

• Major Anions: Cl-, HCO3-, HPO42-

• Functions: Nerve impulse transmission, muscle contraction, fluid balance.

Acid-Base Balance

• Normal pH: 7.35–7.45 for arterial blood.

• Buffer Systems: Bicarbonate, phosphate, and protein buffers help maintain pH.

• Respiratory Regulation: Lungs remove CO2 (acidic), adjusting blood pH.

• Renal Regulation: Kidneys excrete H+ and reabsorb HCO3-.

Summary Table: Major Electrolytes in Body Fluids

Electrolyte	Major Location	Function
Na+	ECF	Osmotic balance, nerve function
K+	ICF	Resting membrane potential, muscle contraction
Ca2+	ECF	Muscle contraction, neurotransmitter release
Cl-	ECF	Osmotic balance, acid-base balance
HCO3-	ECF	Buffering of blood pH

Buffering and Compensation

• Buffer Systems: Minimize pH changes by binding or releasing H+.

• Respiratory Compensation: Adjusts CO2 exhalation to regulate pH.

• Renal Compensation: Adjusts H+ and HCO3- excretion/reabsorption.

Key Equations

• Bicarbonate Buffer System:

$\mathrm{CO}_2 + \mathrm{H}_2\mathrm{O} \leftrightarrow \mathrm{H}_2\mathrm{CO}_3 \leftrightarrow \mathrm{H}^+ + \mathrm{HCO}_3^-$

• pH Calculation (Henderson-Hasselbalch Equation):

$\mathrm{pH} = \mathrm{p}K_a + \log \left( \frac{[\mathrm{HCO}_3^-]}{0.03 \times \mathrm{P}_{\mathrm{CO}_2}} \right)$

Examples

• Dehydration: Loss of water increases ECF osmolarity, causing water to move out of cells.

• Acidosis: Blood pH < 7.35; can result from respiratory (CO2 retention) or metabolic causes (e.g., lactic acid buildup).

• Alkalosis: Blood pH > 7.45; can result from hyperventilation (respiratory) or excessive loss of acids (metabolic).