Study Guide: Respiratory, Digestive, Urinary, and Reproductive Systems

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Respiratory System

Chambers Shared by Respiratory and Digestive Systems

The respiratory and digestive systems share certain anatomical chambers, which play a role in both breathing and swallowing.

Pharynx: The pharynx is a muscular tube that serves as a common passageway for both air (respiratory system) and food/liquids (digestive system).
Oropharynx and Laryngopharynx: These regions of the pharynx are shared by both systems before the pathways diverge at the larynx (airway) and esophagus (food passage).
Clinical relevance: The shared pathway increases the risk of aspiration if swallowing and breathing are not properly coordinated.

General Structure and Function of Respiratory Organs/Structures

The respiratory system is responsible for gas exchange, supplying oxygen to the body and removing carbon dioxide.

Nasal Cavity: Warms, moistens, and filters incoming air.
Pharynx: Passageway for air and food.
Larynx: Contains vocal cords; routes air and food into proper channels.
Trachea: Windpipe; conducts air to bronchi.
Bronchi and Bronchioles: Branching airways leading to alveoli.
Alveoli: Tiny air sacs where gas exchange occurs.

Sympathetic and Parasympathetic Actions on the Respiratory System

The autonomic nervous system regulates airway diameter and respiratory rate.

Sympathetic Stimulation: Causes bronchodilation (widening of airways), increasing airflow.
Parasympathetic Stimulation: Causes bronchoconstriction (narrowing of airways), reducing airflow.
Clinical application: Sympathomimetic drugs (e.g., albuterol) are used to treat asthma by dilating bronchioles.

Definitions and Calculations of Respiratory Capacities and Volumes

Respiratory volumes and capacities measure the amount of air moved in and out of the lungs.

Tidal Volume (TV): Volume of air inhaled or exhaled in a normal breath (~500 mL in adults).
Inspiratory Reserve Volume (IRV): Additional air that can be inhaled after a normal inhalation.
Expiratory Reserve Volume (ERV): Additional air that can be exhaled after a normal exhalation.
Residual Volume (RV): Air remaining in lungs after maximal exhalation.
Vital Capacity (VC): Maximum amount of air exhaled after a maximal inhalation.

Formulas:

Vital Capacity:
Total Lung Capacity:

Percentages of Gases Carried by Each Type of Blood Vessel

Oxygen and carbon dioxide are transported in the blood in different forms and concentrations.

Oxygen: Most oxygen (about 98.5%) is carried bound to hemoglobin in red blood cells; the rest is dissolved in plasma.
Carbon Dioxide: Transported as bicarbonate ions (~70%), bound to hemoglobin (~23%), and dissolved in plasma (~7%).
Arterial Blood: High in oxygen, low in carbon dioxide.
Venous Blood: Low in oxygen, high in carbon dioxide.

Air Pressures and Their Components

Breathing depends on pressure differences between the atmosphere and the lungs.

Atmospheric Pressure (Patm): Pressure exerted by air outside the body.
Intrapulmonary (Alveolar) Pressure (Ppul): Pressure within the alveoli.
Intrapleural Pressure (Pip): Pressure within the pleural cavity; always slightly negative to keep lungs inflated.
Transpulmonary Pressure: Difference between alveolar and intrapleural pressures ().

Digestive System

Layers of the Digestive Tract

The wall of the digestive tract consists of four main layers, each with specific functions.

Mucosa: Innermost layer; secretes mucus, absorbs nutrients, and protects against pathogens.
Submucosa: Connective tissue containing blood vessels, nerves, and glands.
Muscularis Externa: Smooth muscle responsible for peristalsis and segmentation.
Serosa (or Adventitia): Outermost layer; reduces friction with surrounding organs.

Structure and Function of Digestive System Linings

The lining of the digestive tract varies by region to optimize function.

Esophagus: Lined with stratified squamous epithelium for protection against abrasion.
Stomach: Lined with simple columnar epithelium; contains gastric glands that secrete acid and enzymes.
Small Intestine: Lined with villi and microvilli to increase surface area for absorption.
Large Intestine: Lined with goblet cells for mucus secretion to ease passage of feces.

Specific pH of Digestive System Components

Different regions of the digestive tract have characteristic pH values to optimize enzyme activity.

Mouth: Slightly acidic to neutral (pH 6.5–7.5).
Stomach: Highly acidic (pH 1.5–3.5) due to hydrochloric acid.
Small Intestine: Slightly alkaline (pH 7.4–8.5) due to bicarbonate from pancreas.
Large Intestine: Slightly acidic to neutral (pH 5.5–7).

Structure and Function of Digestive System Cells

Specialized cells in the digestive tract perform various functions.

Parietal Cells (Stomach): Secrete hydrochloric acid and intrinsic factor.
Chief Cells (Stomach): Secrete pepsinogen, which is activated to pepsin for protein digestion.
Enterocytes (Small Intestine): Absorb nutrients.
Goblet Cells: Secrete mucus for protection and lubrication.
Enteroendocrine Cells: Secrete hormones that regulate digestion.

Function and Composition of Various Enzymes

Digestive enzymes break down food into absorbable molecules.

Amylase: Breaks down starches into sugars; found in saliva and pancreatic juice.
Pepsin: Breaks down proteins in the stomach.
Lipase: Breaks down fats; produced by pancreas and secreted into small intestine.
Trypsin and Chymotrypsin: Pancreatic enzymes that digest proteins in the small intestine.

Urinary System

Functions of Urinary Organs

The urinary system maintains homeostasis by filtering blood, removing wastes, and regulating fluid balance.

Kidneys: Filter blood, remove wastes, regulate electrolyte and fluid balance, and produce urine.
Ureters: Transport urine from kidneys to bladder.
Urinary Bladder: Stores urine until excretion.
Urethra: Conducts urine from bladder to outside the body.

Filtration

Filtration is the first step in urine formation, occurring in the renal corpuscle of the nephron.

Glomerular Filtration: Blood pressure forces water and solutes from glomerular capillaries into Bowman's capsule.
Filtrate: The resulting fluid, similar to plasma but lacking proteins and blood cells.

Water Reabsorption

Most water filtered by the kidneys is reabsorbed to maintain fluid balance.

Proximal Convoluted Tubule (PCT): Major site of water and solute reabsorption.
Loop of Henle: Descending limb reabsorbs water; ascending limb reabsorbs salts.
Distal Convoluted Tubule (DCT) and Collecting Duct: Regulated reabsorption under hormonal control (e.g., ADH).

Structures and Processes Involved in Glomerular Filtration

Glomerular filtration depends on specialized structures and pressure gradients.

Glomerulus: Network of capillaries with high hydrostatic pressure.
Bowman's Capsule: Surrounds the glomerulus and collects filtrate.
Filtration Membrane: Consists of capillary endothelium, basement membrane, and podocytes; selectively permeable.
Net Filtration Pressure (NFP): Determines the rate of filtration.

Equation:

Net Filtration Pressure: Where GHP = Glomerular Hydrostatic Pressure, CHP = Capsular Hydrostatic Pressure, GOP = Glomerular Oncotic Pressure

Flow of Urine

Urine flows through a series of structures from its formation to excretion.

Nephron (glomerulus → PCT → loop of Henle → DCT) → collecting duct → minor calyx → major calyx → renal pelvis → ureter → urinary bladder → urethra → outside the body.

Kidney Structures

The kidney is organized into distinct regions and microscopic units.

Cortex: Outer region containing renal corpuscles and convoluted tubules.
Medulla: Inner region with renal pyramids and loops of Henle.
Renal Pelvis: Central collecting region for urine.
Nephron: Functional unit of the kidney; each kidney contains about 1 million nephrons.

Reproductive System

Gonads – Function and Structure

Gonads are the primary sex organs responsible for producing gametes and hormones.

Testes (male): Produce sperm and testosterone; composed of seminiferous tubules.
Ovaries (female): Produce ova (eggs) and hormones (estrogen, progesterone); contain follicles at various stages of development.

Accessory Sex Organs – Function and Structure

Accessory sex organs support the transport and maturation of gametes.

Male: Epididymis (sperm maturation), vas deferens (sperm transport), seminal vesicles, prostate gland, bulbourethral glands (secrete fluids for semen).
Female: Uterine tubes (transport ova), uterus (site of implantation and fetal development), vagina (birth canal and copulatory organ).

Uterine Cycle Length

The uterine (menstrual) cycle prepares the endometrium for possible implantation of an embryo.

Average Length: 28 days (can range from 21 to 35 days in adults).
Phases: Menstrual phase, proliferative phase, secretory phase.