CHP207 Human Physiology.docx

Compliance

Compliance

The ability of the lungs to stretch and expand in response to pressure changes during breathing.

Transpulmonary pressure

The pressure difference between the alveoli and the pleural cavity that keeps the lungs inflated.

Surface tension

The force that tends to collapse alveoli due to the attraction of water molecules in the alveolar fluid.

Surfactant

A substance that reduces surface tension in the alveoli, preventing their collapse and increasing lung compliance.

Airway resistance

The hindrance to airflow in the respiratory passageways, influenced mainly by the radius of the airways.

Poiseuille’s law

A formula describing the relationship between airway resistance, length, gas viscosity, and radius of the tube.

Dynamic Airway Compression

The phenomenon where airway resistance increases during expiration due to the recoil of the lung and chest wall.

Bernoulli principle

States that as airflow enters a constriction, linear velocity increases, causing pressure to decrease.

Ventilation-Perfusion (VA/Q) ratio

The matching of ventilation and perfusion in the lungs, crucial for efficient gas exchange.

Dead space

The portion of air that does not participate in gas exchange, leading to inefficient oxygenation of blood.

Venous Admixture

Units with no ventilation but normal perfusion, contributing to venous admixture.

Respiratory Dead Space

Units with normal ventilation but no perfusion, becoming part of the respiratory dead space.

Diffusion Factors

Anatomical features like high surface area to volume ratio and high vascularity facilitate effective gas diffusion.

Partial Pressure Gradient

Normal values for PO2 and PCO2 across the respiratory membrane are 40 mm Hg and 45 mm Hg, respectively.

Oxygen Transport

Only 3% of oxygen travels dissolved in the blood, while 97% is transported in chemical combination with hemoglobin.

Hemoglobin

Protein with four polypeptide chains, each capable of binding with up to four oxygen molecules.

Oxygen-Hb Dissociation Curve

Shows the relationship between PO2 and hemoglobin saturation, influencing oxygen loading and unloading.

Bohr Effect

Describes how CO2 and H+ affect hemoglobin's affinity for oxygen, influencing oxygen release at tissues and lungs.

Carbon Dioxide Transport

CO2 is carried in three forms:dissolved in plasma, bound to hemoglobin, and as bicarbonate ions.

Hypercapnia

Elevated PaCO2, which can result from reduced alveolar ventilation or increased CO2 production without compensatory changes in ventilation.

Ventilation-Perfusion Mismatch

Discrepancy in airflow and blood flow distribution in the lungs due to gravity, leading to varying V/Q ratios across lung regions.

V/Q Ratio

Ratio of ventilation (V) to perfusion (Q) in the lungs, influencing gas exchange efficiency.

Apex vs

Variances in intrapleural pressure, alveolar size, compliance, and ventilation between the top (apex) and bottom (base) of the lungs.

Central Chemoreceptors

Neurons in the medulla sensitive to changes in CO2 and H+ levels, regulating breathing based on chemical stimuli.

Peripheral Chemoreceptors

Receptors in carotid and aortic bodies responding to changes in PO2, PCO2, and H+ levels to modulate ventilation.

Resting Membrane Potential

Voltage difference across a cell membrane due to ion movement, crucial for cell function and signaling.

Voltage and Potential Difference

Energy per charged particle and voltage measurement between two points, akin to mass in a gravitational field.

Ohm's Law

Relationship between voltage (V), current (I), and resistance (R) in an electrical circuit, crucial for understanding electrical properties.

Equilibrium Potential

The voltage at which the flow of an ion into and out of a cell is equal, determined by the ion concentration inside and outside the cell, ion charge, and temperature.

Nernst Equation

An equation used to calculate the equilibrium potential of an ion based on factors like ion valence, temperature, and concentration gradients.

Resting Membrane Potential

The average of equilibrium potentials for all ions in a cell, weighted by ion channel conductance, determining the cell's voltage at rest.

Action Potential

The rapid change in membrane potential of a cell, involving depolarization by Na+ influx and repolarization by K+ efflux, essential for neuron signaling and muscle contraction synchronization.

Voltage-Gated Ion Channels

Channels that open in response to changes in membrane potential, such as sodium channels during depolarization and potassium channels during repolarization in an action potential.

Relative Refractory Period

A period after an action potential where the cell is hyperpolarized and less excitable, requiring stronger stimuli to reach threshold, before returning to resting potential.

Synaptic Cleft

The small gap (20nm wide) between the presynaptic terminal and the postsynaptic cell where neurotransmitter release occurs.

Ca2+ Influx

The entry of calcium ions into the cell, triggering synaptic release, with a time delay as brief as 100μs.

Synaptotagmin

The calcium sensor of the vesicle that initiates exocytosis upon activation by calcium.

SNARE Complex

A group of proteins that tether the vesicle to the membrane and facilitate release upon synaptotagmin activation.

Glutamate

The primary excitatory neurotransmitter in the brain, derived from glutamine and chemically similar to MSG.

Glutamate Receptors

Proteins that respond to glutamate, including AMPA/KA receptors, NMDA receptors, and metabotropic glutamate receptors.

GABA

Gamma-aminobutyric acid, an inhibitory neurotransmitter derived from glutamine, acting on GABAA and GABAB receptors.

GABAA Receptors

Ligand-gated Cl- channels found on postsynaptic terminals, hyperpolarizing the cell upon activation by GABA.

GABAB Receptors

Metabotropic receptors found pre- and postsynaptically, inhibiting neurotransmitter release and hyperpolarizing the cell.

Neurotransmitter Clearance

The removal of neurotransmitters from the synapse through enzymatic degradation or transporters to maintain low extracellular concentrations.

Parasympathetic Nervous System (PSNS)

Division of the autonomic nervous system responsible for periods of maintenance, conservation, and rebuilding in the body.

Dual control

Mechanism optimizing the body's performance to suit its needs by activating either the Sympathetic Nervous System (SNS) or the PSNS based on circumstances.

Autonomic reflexes

Quick corrective responses enabled by sensory inputs feeding into the autonomic nervous system (ANS).

Ganglion

Site where two neurons synapse in the ANS, located outside the central nervous system (CNS).

Smooth Muscle

Effector cells in the body that produce slow, prolonged contractions ideal for maintaining key bodily functions.

Neurotransmitters

Chemical messengers like acetylcholine and adrenaline/noradrenaline used in the ANS to transmit signals between neurons and target tissues.

Nicotinic receptors

Ionotropic receptors activated by acetylcholine in the ANS, playing a role in both the SNS and PSNS at the first synapse.

Muscarinic receptors

Metabotropic receptors activated by acetylcholine in the ANS, mediating many parasympathetic functions.

Autonomic reflexes

Rapid corrective responses to sensory events in the ANS, classified into short and long reflexes.

Cardiomyocyte

Excitable heart muscle cell responsible for coordinated contraction and relaxation in the heart.

Cardiomyocytes

Cells responsible for the contraction of the heart chambers, joined end-to-end at intercalated disks.

Gap junctions

Pores located at intercalated disks allowing the propagation of action potentials from cell to cell.

Functional syncytium

The ability of action potentials to spread like a wave throughout the heart chamber, depolarizing all cells.

Nernst Equation

Mathematical formula to calculate the equilibrium potential of ions based on their concentrations inside and outside the cell.

Pacemaker cells

Specialized cardiac cells that generate action potentials automatically at regular intervals.

Excitation-contraction coupling

Process where calcium influx leads to muscle contraction in cardiomyocytes.

Refractory period

Period during which a cardiomyocyte cannot be stimulated to generate another action potential.

Tetanic Contractions

Continuous contractions due to repeated stimulation, not desirable in the heart to allow relaxation and filling.

Autonomic Nervous System

Modulates heart rate and force of contraction through parasympathetic (PNS) and sympathetic (SNS) inputs.

Cardiac Output

Volume of blood ejected by the heart per minute, matching the venous return to maintain a closed circulatory system.

Cardiac Output (CO)

The volume of blood pumped by the heart in a minute, calculated as the product of stroke volume (SV) and heart rate (HR), typically measured in mL/min or L/min.

Venous Return

The flow of blood back to the heart, influenced by factors like venous constriction, blood volume, gravity, and muscle contraction.

Stroke Volume (SV)

The amount of blood ejected into the pulmonary artery or aorta per heartbeat, usually measured in mL/beat.

Heart Rate (HR)

The number of times the heart beats per minute, measured in beats/min.

Frank-Starling Mechanism

The intrinsic property of the heart muscle where the degree of stretch (preload) influences the force of contraction, ensuring that venous return matches stroke volume and cardiac output.

Afterload

The force against which the heart works during ejection, related to aortic pressure and ventricular wall stress.

Contractility

The performance of the heart muscle in generating force during contraction, independent of preload and afterload, also known as inotropy.

Mean Arterial Blood Pressure (MAP)

The average pressure in the arteries during a cardiac cycle, determined by cardiac output and total peripheral resistance, crucial for organ perfusion assessment.

Mean Arterial Pressure (MAP)

The average blood pressure in a person's blood vessels during a single cardiac cycle, crucial for organ perfusion.

Baroreceptors

Sensors that detect changes in blood pressure, located in the aorta and carotid arteries, regulating vasoconstriction and vasodilation.

Chemoreceptors

Sensors that monitor blood O2, CO2, and pH levels, located in the aortic and carotid bodies, influencing heart rate and blood vessel constriction.

Ohm's Law

Describes blood flow from high to low pressure during ventricular systole, a fundamental principle in hemodynamics.

Poiseuille's Law

States that resistance to blood flow is inversely proportional to the 4th power of vessel radius, directly proportional to vessel length and blood viscosity.

Resistance Vessels

Arterioles within tissues/organs that control blood flow by altering their radius, impacting resistance to flow.

Autoregulation

Mechanisms like myogenic and metabolic responses that maintain stable blood flow in organs despite changes in systemic blood pressure.

Cardiac Output

The total systemic blood flow, summing blood flow to all organs, regulated by parallel organ circulations and tissue demands for blood/nutrients.

Local flow regulation

In critical organs like the brain and heart, local flow regulation maintains perfusion, while in other organs like the skin and gut, SNS regulation leads to vasoconstriction and reduced perfusion.

Arterial system

Major distributing arteries branch into smaller vessels until they become capillaries, which then join to form veins returning blood to the heart.

Aortic function

The aorta dampens pulsatile pressure, with its compliance allowing it to stretch during systole and recoil during diastole, controlled by stretch receptors activating local reflexes.

Arterioles and small arteries

Arterioles regulate arterial blood pressure and blood flow within organs, responding to autonomic nerves and hormones by constricting or dilating.

Capillary functions

Capillaries facilitate nutrient exchange between blood and tissues, with pericytes regulating blood flow in individual capillaries.

Starling's forces

Movement of solutes across capillaries depends on the balance of hydrostatic and osmotic pressure, determining the net filtration pressure and capillary permeability.

Venous system

Veins contain valves for unidirectional blood flow, serving as capacitance vessels regulating blood volume and pressure, with the skeletal muscle venous pump aiding venous return.

Lymphatic system

Lymph vessels parallel systemic circulation, collecting excess interstitial fluid and returning it to the systemic circulation, preventing oedema and maintaining blood volume.

Regulation of lymphatic flow

Lymph flow rate is controlled by the balance between fluid delivery at capillaries and removal by lymphatics, with factors like capillary permeability and hydrostatic pressure affecting oedema formation.

Urinary System

Includes organs involved in the formation, storage, and release of urine, such as kidneys, ureters, bladder, and urethra.

Excretory Functions

Involves the elimination of metabolic waste, body water balance, electrolyte balance, blood pressure regulation, and acid-base balance.

Filtration

Process where blood is filtered from glomerular capillaries into Bowman’s capsule through a filtration barrier.

Reabsorption

Movement of fluid/solute from nephron tubules back into the body.

Secretion

Movement of fluid/solute from peritubular capillaries into the tubular network.

Glomerular Filtration Rate (GFR)

Rate at which filtrate is formed by nephrons, typically around 125ml/min in a healthy adult.

Renal Autoregulation

Intrinsic mechanism to maintain constant blood flow and GFR despite changes in systemic blood pressure.

Myogenic Mechanism

Fast-acting mechanism accounting for about 50% of renal autoregulation.

Tubulo-glomerular Feedback Mechanism

Slower mechanism accounting for about 35-40% of renal autoregulation.

Principles of Tubular Handling

Processes of reabsorption and secretion for movement of substances within the nephron.

K+ Excretion

Kidney can reduce reabsorption of K+ from filtrate and activate tubular secretion for further K+ excretion.