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Exam 3 Study Guide Notes

Ions in Action Potential Production:
Cardiac pacemaker cells utilize sodium (Na+), calcium (Ca2+), and potassium (K+) in generating action potentials.

  • Sodium ions (Na+) rapidly enter the pacemaker cells during depolarization, leading to the initial phase of the action potential.

  • Calcium ions (Ca2+) then enter the cells, sustaining depolarization and contributing to the plateau phase.

  • Finally, potassium ions (K+) exit the cells during repolarization, returning the cell to its resting state.

ECG Components:

  • P wave: Represents atrial depolarization; electrical impulses cause the atria to contract and push blood into the ventricles.

  • QRS complex: Reflects ventricular depolarization and atrial repolarization simultaneously; indicates that the ventricles are contracting to pump blood out of the heart.

  • T wave: Shows ventricular repolarization; the ventricles are resetting their electrical state to prepare for the next contraction.

  • Identify segments (e.g., PR interval, ST segment) and their clinical significance:

    • PR interval: The time taken for electrical impulses to travel from the atria to the ventricles; prolonged intervals may suggest an AV block.

    • ST segment: Represents the time between ventricular depolarization and repolarization; elevation or depression can indicate ischemia or myocardial infarction.

Systemic vs. Pulmonary Circulation:

  • Systemic circulation: Delivers oxygenated blood to the body, providing necessary nutrients and oxygen to tissues while collecting carbon dioxide and other metabolic waste.

  • Pulmonary circulation: Transports deoxygenated blood to the lungs; in the lungs, blood releases carbon dioxide and picks up oxygen, returning oxygenated blood to the heart to start the systemic circulation.

Systole and Diastole:

  • Systole: The contraction phase of the heart; during this phase, the ventricles contract and pump blood into the aorta and pulmonary artery.

  • Diastole: The relaxation phase; the heart fills with blood as atria contract and open to allow blood flow into the ventricles.

  • Sounds during auscultation include Lub (closure of AV valves) and Dub (closure of semilunar valves); these sounds are indicative of the cardiac cycle phases.

Pathway of the Cardiac Pacemaker:

  • Sinoatrial (SA) node: Located in the right atrium, the primary pacemaker of the heart that initiates the electrical impulse.

  • Atrioventricular (AV) node: Receives the impulse from the SA node and delays it slightly to allow the ventricles to fill.

  • Bundle of His: This pathway conducts impulses to the ventricles; travels through the interventricular septum.

  • Purkinje fibers: Spread throughout the ventricles; they signal the ventricles to contract.

Valve Functionality:

  • Heart valves open when pressure in the atria or ventricles increases, allowing blood to flow forward.

  • Valves close when the pressure decreases to prevent backflow, maintaining unidirectional blood flow throughout the heart.

Cardiac Muscle Contraction:

  • Involves a calcium-induced calcium release mechanism; this differs from skeletal muscle contraction, which relies directly on action potentials on the muscle fibers.

  • The release of Ca2+ from the sarcoplasmic reticulum is triggered by the influx of Ca2+ from the extracellular fluid during action potential, causing muscle fibers to contract effectively.

Cardiac Output

Calculation:
ext{Cardiac Output (CO)} = ext{Heart Rate (HR)} \ times ext{Stroke Volume (SV)}

  • Heart Rate (HR): The number of heartbeats per minute, typically 60 to 100 beats for a resting adult.

  • Stroke Volume (SV): The amount of blood pumped by the heart per beat; depends on factors like preload, afterload, and myocardial contractility.

Factors affecting CO:

  • End-Diastolic Volume (EDV): The volume of blood in the ventricles just before contraction; higher EDV increases stroke volume due to the Frank-Starling principle.

  • End-Systolic Volume (ESV): The volume of blood remaining in the ventricles after contraction; higher ESV reduces stroke volume.

  • Preload: The stretching of cardiac muscle fibers before contraction; increased preload enhances the force of contraction.

  • Afterload: The resistance the heart must work against to eject blood; higher afterload reduces stroke volume.

  • Contractility: The inherent strength and vigor of the heart's contraction; influenced by the availability of calcium ions and neural input.

  • Autonomic Nervous System (ANS):

    • Sympathetic stimulation increases heart rate and force of contraction, enhancing cardiac output.

    • Parasympathetic stimulation decreases heart rate, reducing cardiac output.

  • Venous Return: The flow of blood back to the heart; higher venous return increases EDV, which in turn increases cardiac output.

Blood & Lymph

Blood Types:

  • Established by antigens on red blood cells; the presence or absence of specific antigens determines a person’s blood type.

  • Compatible types:

    • Type A can donate to A and AB blood types, as it has A antigens.

    • Type B can donate to B and AB blood types, as it has B antigens.

    • Type AB can donate to AB blood type only, as it has both A and B antigens, but is a universal recipient.

    • Type O can donate universally to all blood types, as it lacks A and B antigens—this makes Type O individuals valuable as blood donors.

Hydrostatic vs. Osmotic Pressure:

  • Hydrostatic Pressure: The force exerted by fluid against vessel walls; it pushes fluid out of capillaries into tissues.

  • Osmotic Pressure: Influenced by plasma proteins, helps retain fluid within the blood vessels by pulling water back into the bloodstream, essential for maintaining fluid balance.

Plasma Components:

  • Blood plasma consists of:

    • Water: Approx. 90% of plasma volume, serves as a solvent for carrying various substances.

    • Electrolytes: Essential for maintaining osmotic pressure and pH balance.

    • Proteins: Include albumin (regulates osmotic pressure), globulins (immune function), and fibrinogen (clotting).

    • Nutrients: Such as glucose and amino acids used by cells for energy production and growth.

    • Hormones: Chemical messengers that regulate bodily functions.

    • Waste products: Metabolic byproducts like urea and creatinine that need to be excreted.

Hemoglobin Function:

  • Hemoglobin in red blood cells carries oxygen from the lungs to body tissues and facilitates the return transport of carbon dioxide from the tissues back to the lungs.

  • High affinity for oxygen under certain conditions, such as low pH (Bohr effect), where increased CO2 leads to the release of oxygen to tissues more effectively.

White Blood Cells (WBCs):

  • Include lymphocytes (adaptive immunity), neutrophils (first responders to infection), monocytes (transform into macrophages), eosinophils (defense against parasites), basophils (allergic responses).

  • Normal WBC distribution: Neutrophils (50-70%), Lymphocytes (20-45%); monitoring WBC levels can help assess health and diagnose infections or disorders.

Formed Elements in Blood:

  • Erythrocytes: Primary function is to carry oxygen; their biconcave shape increases surface area for gas exchange.

  • Leukocytes: Participate in immune defense against pathogens.

  • Thrombocytes: Platelets involved in hemostasis, the process of blood clotting.

Blood Pressure

Vascular Tree Function:

  • Arteries and arterioles play a critical role in redirecting blood flow; they adjust diameter to regulate blood pressure and distribution to different organs based on need.

Active vs. Reactive Hyperemia:

  • Active Hyperemia: Increased blood flow in response to heightened metabolic demands; for example, during exercise, tissues like muscles receive increased blood supply.

  • Reactive Hyperemia: Increased blood flow following a period of decreased blood flow; for instance, after a blood vessel has been temporarily occluded.

Factors Affecting Blood Pressure:

  • Cardiac output: Greater output increases blood pressure.

  • Vascular resistance: Higher resistance (due to constricted vessels) raises blood pressure.

  • Blood volume: More volume increases pressure in the circulatory system.

  • Elasticity of blood vessels: Stiffer vessels lead to higher blood pressure due to reduced ability to expand.

Vasodilators & Vasoconstrictors:

  • Common vasodilators include nitric oxide (widely released during activation of endothelial cells) and prostaglandins that widen blood vessels.

  • Common vasoconstrictors include angiotensin II and norepinephrine, which narrow blood vessels and increase blood pressure.

Myogenic Control:

  • The reaction of vascular smooth muscle to changes in blood pressure; as pressure increases, smooth muscle contracts to reduce vessel diameter, thereby regulating blood flow and pressure autonomously.

Respiratory Physiology I

Inspiration and Expiration Processes:

  • Inhalation occurs when the diaphragm contracts, reducing pressure in the thoracic cavity, causing air to flow into the lungs.

  • Exhalation is typically a passive process, aided by the relaxation of the diaphragm; forced exhalation involves additional muscles, such as the abdominal muscles.

Pressure-Volume Relationship in Ventilation:

  • Boyles's law: P \ times V = \text{Constant} ; as volume increases, pressure decreases, facilitating airflow in and out of the lungs.

Compliance, Surface Tension, and Elasticity:

  • Compliance: The ability of the lungs to stretch; decreased compliance indicates lung disease such as fibrosis which impairs breathing.

  • Surface tension within alveoli, tend to collapse them; surfactant is a substance produced by Type II alveolar cells that reduces surface tension, preventing alveolar collapse.

  • Elasticity: The lungs’ tendency to return to their original shape after expansion; essential for enabling efficient exhalation.

Surfactant:

  • Produced by Type II alveolar cells, surfactant reduces surface tension within the alveoli, thus preventing alveolar collapse at low lung volumes and improving lung compliance.

Muscles Involved in Ventilation:

  • Diaphragm: The primary muscle of respiration during normal breathing.

  • Intercostal muscles: Assist in expanding and contracting the thoracic cavity.

  • Accessory muscles: Used during exertion or respiratory distress (e.g., thoracic and neck muscles).

CNS Control of Heart and Respiratory Rate:

  • The medulla oblongata regulates autonomic functions, including heart rate and respiratory patterns; it integrates input from chemoreceptors and baroreceptors to maintain homeostasis.

Partial Pressures and Gas Exchange:

  • Gas exchange depends on the different partial pressures of gases; gases diffuse from areas of high to low partial pressures, enabling oxygen uptake and carbon dioxide elimination.

Factors Affecting Hemoglobin’s Affinity for Oxygen:

  • pH levels: Lower pH decreases affinity (Bohr effect).

  • Temperature: Higher temperatures decrease oxygen affinity; this occurs during active tissue metabolism.

  • 2,3-DPG levels: At higher concentrations, it decreases hemoglobin's oxygen affinity, facilitating better oxygen unloading in tissues.

Respiratory Physiology II

Hyperventilation and Hypoventilation Effects:

  • Hyperventilation: Leads to decreased blood PCO2, causing respiratory alkalosis; this occurs when breathing is too rapid or deep.

  • Hypoventilation: Causes increased blood PCO2 leading to respiratory acidosis; this occurs when breathing is too shallow or slow.

Automatic vs. Conscious Breathing:

  • Automatic: Driven by the brainstem's respiratory centers; adjusts respiration rates based on CO2 and O2 levels without conscious thought.

  • Conscious: Breathing under voluntary control; examples include speaking, singing, or voluntary hyperventilation.

Chemoreceptors:

  • Central chemoreceptors: Located in the brainstem; primarily respond to changes in CO2 levels, affecting breathing rate similarly.

  • Peripheral chemoreceptors: Located in carotid and aortic bodies; they monitor oxygen levels and respond to significant decreases in O2.

Blood Oxygen Content Calculation:

  • Primarily determined by hemoglobin concentration and saturation levels; it reflects the blood's capacity to carry oxygen to tissues.

Oxyhemoglobin and Its Concentration:

  • Oxyhemoglobin forms when oxygen binds to hemoglobin; its concentration varies and is crucial for evaluating oxygenation in arterial and venous blood.

Oxygen Loading/Unloading:

  • Oxygen loading occurs in the lungs where there is high oxygen concentration; unloading happens at the tissues where the oxygen concentration is lower, facilitated by the Bohr effect, where increased CO2 leads to hemoglobin releasing oxygen more readily.

2,3-DPG Effect:

  • 2,3-DPG binds to hemoglobin; at higher concentrations, it decreases hemoglobin's affinity for oxygen, facilitating the unloading of oxygen in metabolically active tissues.

CO2 Transport in Blood:

  • Carbon dioxide is mainly transported as bicarbonate ions (HCO3-), dissolved in plasma, and also in a bound form to hemoglobin.

Bicarbonate-Carbonic Acid Buffer System:

  • The system helps maintain blood pH by compensating for changes in carbon dioxide levels; carbonic acid dissociates into bicarbonate and protons, buffering blood pH changes.

Chloride Shift:

  • Movement of Cl- ions into red blood cells as HCO3- ions exit during CO2 transport; this helps maintain ionic balance and facilitates gas exchange.

Reverse Chloride Shift:

  • Cl- ions exit red blood cells as HCO3- enters, promoting the bicarbonate buffer response; essential for homeostasis in blood pH regulation.