Comprehensive Study Guide: Biology 20 Unit D3 - Respiration, Muscles, and Excretion

Overview of Biological Respiration, Muscles, and Excretion

Conceptual Definitions: * Breathing: The physical exchange of gases between the external environment and the body. * Respiration: The sum of all processes involved in the exchange of $\text{O}_2$ and $\text{CO}_2$ between cells and the environment. This includes the utilization of $\text{O}_2$ for the breakdown of glucose in cellular respiration. * Respiratory Membrane: The site of diffusion where $\text{O}_2$ enters and $\text{CO}_2$ is released.
Levels of Respiration: * Pulmonary Ventilation: Inspiration (inhaling) and expiration (exhaling); the exchange between the atmosphere and the lungs. * External Respiration: Exchange of gases between the lungs and the blood. * Internal Respiration: Exchange of gases between the blood and the individual cells.

Anatomy of the Human Respiratory System

1. Nasal Cavity: * Nostrils: Two openings lined with hair (cilia) that filter large dust particles. * Upper Nasal Cavity: Lined with mucous-secreting cells and olfactory receptors for smell. * Function: Moistens air via tear glands, warms the air, and moves trapped dust out using mucus.
2. Pharynx (Throat): * An air-filled channel starting at the nasal cavity and extending to the larynx. It is a shared passage for both the respiratory (trachea) and digestive (esophagus) tracts. * Cilia: Hair-like structures that sweep debris out of the respiratory tract. * Subdivisions of the Pharynx: * Nasopharynx: Exchanges air with ears to maintain steady pressure via the Eustachian tubes. * Oropharynx: Located behind the mouth; contains the palatine tonsils. * Laryngopharynx: Located above the larynx.
3. Larynx (Voice Box): * Made of cartilage, connecting pharynx to trachea. Known as the "Adam's Apple." * Vocal Cords: Two thin sheets of elastic ligaments. Sounds are produced by air pushing through and vibrating the cords; pitch is altered by changing cord tension. * Laryngitis: Inflammation and swelling of the vocal cords.
4. Trachea (Windpipe): * Lined with ciliated cells and mucus to capture and expel pollutants. * Layers: * Inner: Ciliated mucous membrane. * Middle: Strengthened with cartilage. * Outer: Composed of $10-20$ C-shaped rings for structural protection. * Epiglottis: An elastic flap at the top of the larynx covering the glottis (the trachea opening) to prevent food/fluid from entering via reflex action.
5. Bronchi and 6. Bronchioles: * The trachea divides into the right and left primary bronchi, which further divide into secondary bronchi and then into bronchioles. * Bronchi: Supported by bands of cartilage to prevent collapse. * Bronchioles: Thin as a hair, made of smooth muscle without cartilage; they slow down the rate of air movement.
7. Alveoli: * Cluster-like functional units of the lungs located at the end of bronchioles. * Surface Area: Increases lung surface area by $300 \times$ . Each lung contains approximately $150$ million alveoli, providing a total surface area equivalent to $40 \times$ the human body. * Membrane: Single layer of cells surrounded by capillary nets for gas/fluid exchange via concentration gradients (diffusion).
8. Blood Supply: * Pulmonary Artery: Carries oxygen-poor blood to alveoli for gas exchange. * Bronchial Arteries: Carry oxygen-rich blood to nourish lung tissue; joins the pulmonary vein before returning to the heart.
9. Lungs: * Visceral Pleura: Membrane attached directly to the lungs. * Parietal Pleura: Sac surrounding the visceral pleura, attached to the thoracic cavity. * Pleural Fluid: Lubricant between the sacs to reduce friction. * Lobes: The right lung has three lobes; the left lung has two. Includes macrophages for cleaning. Lungs lack muscle and cannot inflate themselves.

Gas Exchange and Transport Mechanics

Oxygen Transport: * Oxygen is carried by hemoglobin in red blood cells. * Binding: High partial pressure of oxygen in lungs favors binding. Low partial pressure in tissues favors release. * pH Influence: Normal blood pH is $7.35-7.45$ . Increased acidity (lower pH) causes hemoglobin to release oxygen more easily. * Kreb’s Cycle Connection: $CO_2$ released as a byproduct converts to carbonic acid, lowering pH and triggering oxygen release.
Carbon Dioxide Transport: * $7\%$ dissolved in plasma. * $23\%$ carried by hemoglobin. * $70\%$ transported as bicarbonate ions ( $HCO_3^-$ ) in plasma. * Chemical Reaction: $CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons H^+ + HCO_3^-$ . * $H^+$ ions are carried by hemoglobin while $HCO_3^-$ remains in the plasma. In the lungs, they rejoin to form gaseous $CO_2$ and water for expulsion.
Carbon Monoxide (CO): * Colorless, odorless, tasteless gas. It diffuses $200$ times faster than oxygen and binds much more strongly to hemoglobin, preventing oxygen transport.

Mechanics of Ventilation and Lung Volume

Inhalation (Inspiration): * Air moves from high to low pressure. Inside pressure must be lower than outside. * The diaphragm (muscle sheet separating chest and abdominal cavities) contracts and flattens, creating a vacuum. * External Intercostal Muscles contract to elevate ribs, increasing thoracic cavity volume and decreasing pressure.
Exhalation (Expiration): * Outside pressure is lower than inside. * The diaphragm relaxes into a dome shape. Lungs utilize elastic recoil. * Internal Intercostal Muscles pull the rib cage down. This is typically a passive process.
Lung Volumes (Measured via Spirometer): * Tidal Volume: Normal amount breathed in/out; approximately $500\,mL$ (only $350\,mL$ reaches lungs; the rest stays in airways). * Residual Volume: Air that cannot be breathed out (~ $1000\,mL$ ). * Inspiratory Reserve: Extra air that can be forced in (~ $3500\,mL$ ). * Expiratory Reserve: Extra air that can be forced out (~ $1200\,mL$ ). * Vital Capacity: Tidal volume + Inspiratory reserve + Expiratory reserve (~ $4000\,mL$ ). * Dead Space: Areas without gas exchange (approx. $1\,mL$ per pound of body weight). * Minute Respiratory Volume: $\text{Respiratory rate} \times \text{Volume of air breathed in}$ .

Regulation of Respiration

1. Brain Control: * Managed by the medulla oblongata and the pons. * Apneustic Area: Prolongs inspiration. * Pneumotaxic Area: Limits inspiration period. * Inflation Reflex: Prevents overfilling; Deflation Reflex: Stimulates inspiration upon lung collapse.
2. Chemoreceptors: * Specialized nerve receptors sensitive to chemicals (located in aorta and carotid arteries). * Aortic/Carotid Bodies: Detect low $O_2$ levels. * CO2 Receptors: Much more sensitive than $O_2$ receptors; detect acidity from increased $CO_2$ . * Hyperventilation: Increase in $CO_2$ triggers a higher respiration rate to remove excess gas. * Hypoventilation: Decrease in $CO_2$ signals a decrease in respiration rate.

Respiratory Disorders

Hypoxia: Inadequate oxygen.
Asphyxia: Oxygen starvation of tissues.
Respiratory Arrest: Permanent cessation of breathing.
Bronchial Asthma: Allergic response; narrowing of bronchi and muscle spasms.
Bronchitis: Inflammation of bronchioles; acute (infection) or chronic (irritant).
Tuberculosis: Bacterial infection causing fibrous walls to form.
Emphysema: Alveoli lose elasticity and burst, fusing into larger spaces; reduces surface area for gas exchange.
Pleurisy: Inflammation of the pleura; results in painful adhesions.
Cystic Fibrosis: Fatal hereditary disease causing thick mucus production.
Pneumonia: Infection/inflammation where alveoli fill with thick fluid.
Pulmonary/Lung Cancer: Uncontrolled cell growth starting in the epithelium; causes lung collapse.

Muscle Tissue and The Motor System

Types of Muscles (Human body has > 600 muscles): * Skeletal Muscle: Attached to bones via tendons (connective tissue). Striated, multiple nuclei, and under voluntary (conscious) control. * Cardiac Muscle: Found only in the heart. Striated and involuntary (automatic). Controlled by the autonomic nervous system. * Smooth Muscle: Found in organ linings (stomach, esophagus, uterus, blood vessels). Non-striated and involuntary.
Antagonistic Muscle Pairs: * Muscles work against each other; as one contracts (Flexor), the other relaxes (Extensor). * Example: Biceps (flexor) contract to bend the elbow while Triceps (extensor) relax via inhibitory impulses.

Skeletal Muscle Structure and The Sliding Filament Theory

Microscopic Anatomy: * Sarcolemma: The membrane enclosing muscle fibers. * Myofilaments: Protein threads within fibers. * Actin: Thin myofilaments. * Myosin: Thick myofilaments. * Sarcomere: The functional unit between two Z lines (which anchor actin).
The Sliding Filament Model: * Knoblike protrusions on myosin form cross-bridges with receptor sites on actin. * Actin filaments slide over myosin; the light bands shrink as Z lines move closer together. * Chemical Initiation: Neurotransmitter at the sarcoplasmic reticulum triggers $Ca^{2+}$ release. $Ca^{2+}$ binds to actin, facilitates cross-bridge formation, and starts $ATP$ breakdown for contraction. $Ca^{2+}$ is then recycled for relaxation.

Energy for Muscle Contraction

1. Creatine Phosphate Breakdown: High-energy molecule used when a muscle starts sliding; provides roughly $8$ seconds of energy.
2. Aerobic Cellular Respiration: Converts glucose (from glycogen) and fatty acids into energy ( $CO_2$ , $H_2O$ , and $ATP$ ). Myoglobin delivers oxygen to the cells.
3. Fermentation (Anaerobic): Occurs when oxygen is low. Without oxygen for >3 minutes, lack of $ATP$ prevents $Ca^{2+}$ from being pumped back to the sarcoplasmic reticulum, causing permanent cross-bridge binding. * Rigor Mortis: Post-mortem rigidity caused by the inability of cross-bridges to disconnect.

Muscle Conditions and Injuries

Hypertrophy: Increase in muscle mass (size of fibers, not number) from use; increases mitochondria and enzymes.
Atrophy: Reduction in muscle tissue from lack of use (surgery, casting, paralysis).
Summation and Tetanus: If stimuli are applied before relaxation, summation occurs; maximal contraction is called tetanus.
Muscle Fiber Types: * Fast Twitch: High glycogen, low myoglobin/mitochondria; uses anaerobic respiration; suited for sprinting/weightlifting; fatigues easily. * Slow Twitch: High myoglobin/mitochondria/fat; uses aerobic respiration; suited for swimming/marathons; slow to fatigue.
Selected Pathologies: * Muscular Dystrophy: Hereditary skeletal muscle degeneration replaced by fatty tissue. * Botulism: Toxin from Clostridium botulinum prevents acetylcholine release, causing paralysis. * Crush Syndrome: Massive muscle crushing causes heart irregularities (released $K^+$ ) and kidney failure (myoglobin blockage). * Fibromyalgia: Chronic pain, fatigue, and tenderness.

The Excretory System: Waste and Equilibrium

Purpose of Excretion: * Regulate blood volume/pressure and stabilize blood pH ( $H^+$ and $HCO_3^-$ ). * Eliminate nitrogenous wastes: Urea (formed from ammonia in the liver), Uric acid (from nucleic acids), and Creatinine. * Deamination: Liver process removing amino groups from proteins, producing toxic ammonia.
Anatomy of the Kidney: * Renal Capsule: Fibrous outer surface. * Cortex: Outer connective tissue containing filtering units (nephrons). * Medulla: Contains renal pyramids, the loop of Henle, and collecting ducts. * Renal Pelvis: Upper end of the ureter; connects the kidney to the drainage system.

The Nephron: Functional Unit of the Kidney

Glomerulus: High-pressure capillary bed for filtration. Afferent arterioles supply blood; Efferent arterioles carry blood to the peritubular capillary net.
Bowman’s Capsule: Surrounds the glomerulus; collects filtrate.
Renal Tubule Sections: * Proximal Convoluted Tubule: Active transport of $Na^+$ , glucose, and amino acids; passive transport of $Cl^-$ and water (osmosis). * Loop of Henle: Deep in the medulla. Descending limb is water-permeable; ascending limb actively transports $Na^+$ and $Cl^-$ and is water-impermeable. * Distal Convoluted Tubule: Impermeable to water; absorbs ions. * Collecting Duct: Final tube where urine is concentrated and sent to the renal pelvis.

Urine Formation and Regulation

1. Filtration: Movement of fluid from blood to Bowman’s capsule. Large proteins and blood cells stay in the blood. Regulated by myogenic mechanisms and sympathetic stimulation.
2. Reabsorption: Transfer of essential solutes/water back to blood. Stops at the threshold level (maximum transport capacity).
3. Secretion: Movement of materials (e.g., $K^+$ , $H^+$ , urea) from blood back into the tubule.
Hormonal Control: * Antidiuretic Hormone (ADH): Produced by the pituitary; increases water reabsorption by making collecting ducts more permeable. Alcohol suppresses ADH. * Aldosterone: Produced by adrenal glands; increases $Na^+$ reabsorption to control salt levels.

Excretory Disorders

Kidney Stones: Formed in pelvis/bladder from uric acid or calcium oxalate; causes urine retention.
Bright’s Disease (Nephritis): Inflammation of the nephron.
Cystitis: Bladder inflammation; frequent burning urination; common in women due to a short ( $4\,cm$ ) urethra.
Diabetes Mellitus: Elevated blood sugar; high sugar in nephron causes osmotic pressure to decrease, leading to large amounts of sweet, dilute urine.
Diabetes Insipidus: Destruction of ADH-producing cells; causes massive water loss.
Uremia: Accumulation of urea in the blood due to system malfunction.