Circulation Study Notes
Circulation
Overview
The circulatory system is a critical biological system responsible for the transport of gases, nutrients, waste products, and hormones throughout the body while regulating body temperature, blood clotting, and maintaining homeostasis.
Functions of the Circulatory System
Transport of Gases
Moves oxygen and carbon dioxide between lungs and tissues.
Transport of Nutrients and Waste
Distributes nutrients absorbed from the digestive system and removes waste products.
Regulation of Body Temperature
Helps maintain thermal homeostasis through adjustments in blood flow.
Blood Clotting
Essential for preventing blood loss in case of injury.
Maintenance of Homeostasis
Regulates pH, electrolytes, and fluid balance.
Circulatory Systems Across Organisms
Organisms without a Circulatory System:
Flatworms and jellyfish utilize diffusion for transport.
Diffusion: A passive process effective for distances less than 1 mm and in organisms with small cell diameters (5-10 μm to 1 mm).
Diffusion Time is proportional to the square of the distance: time ∝ distance².
Organisms with a Circulatory System:
Larger organisms require bulk flow mechanisms to efficiently transport substances over longer distances.
Major Functions:
Bulk Flow: Involves the movement of fluids over long distances; involves transport costs.
Material Exchange: Diffusion at the destination where materials are exchanged.
Components and Structure of the Circulatory System
Human Circulatory System Components
Pumps: Heart
Comprising chambers (atria, ventricles) and valves that ensure unidirectional blood flow.
Pathway through the Heart:
Blood flow starts from Superior vena cava → Right atrium → Tricuspid valve → Right ventricle → Pulmonary artery → Lungs → Pulmonary veins → Left atrium → Bicuspid valve (mitral) → Left ventricle → Aorta.
Blood Vessels: Arteries, Veins, and Capillaries
Arteries: Carry oxygenated blood away from the heart (except pulmonary arteries).
Veins: Return deoxygenated blood to the heart (except pulmonary veins).
Capillaries: Site of exchange between blood and tissues; very thin walls (1 endothelial cell thick) facilitate diffusion.
Comparison of Arteries and Veins
Arteries:
Thick muscular walls; maintain shape due to higher pressure.
Carry blood away from the heart.
Veins:
Thinner walls that are more flexible and stretchable.
Contain valves to prevent backflow; carry low-pressure blood back to the heart.
Circulatory Systems Classification
Open Circulatory Systems:
Found in invertebrates (e.g., mollusks); hemolymph circulates in open sinuses surrounding organs.
Closed Circulatory Systems:
Found in vertebrates including humans; blood is contained within vessels.
Change in Blood Pressure and Flow
Fluid dynamics: Influences blood flow; velocity and pressure can be manipulated by altering vessel diameter through vasodilation and vasoconstriction.
Increased resistance decreases flow, while decreased resistance increases flow.
Cardiac output (Q) is defined as the volume of blood pumped by the heart per minute.
The relationship is described as
Q = ext{Heart Rate (HR)} imes ext{Stroke Volume (SV)}
Hemodynamics
Blood Pressure: Can be affected by hydrostatic pressure considerations; veins above the heart may collapse under certain conditions.
Vasodilation/Vasoconstriction: Increases or decreases blood flow to specific tissues as needed; controlled by autonomic nervous system.
Mechanisms of Gas Exchange in Capillaries
The primary exchange between blood and interstitial fluid occurs across the capillary walls, determining nutrient and gas exchange.
Osmotic Pressure vs Hydrostatic Pressure:
ext{Net Flow} = ext{Hydrostatic Pressure (HP)} - ext{Osmotic Pressure}
High blood pressure favors fluid outflow, whereas lower pressures allow for absorption.
Control of Circulatory Functions
Heart Rate Regulation: Influenced by the autonomic nervous system (parasympathetic and sympathetic responses regulate heart functions).
Blood Flow Regulation: Achieved through autonomic control, adjusting vessel diameter based on the metabolic needs of tissues.
Oxygen Transport and Carbon Dioxide Regulation
Oxygen in Blood: Transported physically dissolved in plasma (~1.5%) and bound to hemoglobin (~98.5%).
Carbon Dioxide Transport: Primarily through bicarbonate ions (60%), carbamino compounds (30%), and dissolved CO2 (10%).
Maintains pH balance in blood; can buffer changes in H+ concentration.
Conclusion
The circulatory and respiratory systems collaborate efficiently to maintain homeostasis, ensuring oxygen delivery and carbon dioxide removal from the body. Understanding their interdependence is vital in physiology and clinical practice
Circulation
Overview
The circulatory system is a critical biological system responsible for the transport of gases (like oxygen and carbon dioxide), nutrients (such as glucose, amino acids, and fatty acids), waste products (e.g., urea, lactic acid), and hormones throughout the body while regulating body temperature, blood clotting, and maintaining homeostasis.
Functions of the Circulatory System
Transport of Gases
Moves oxygen and carbon dioxide between lungs and tissues.
Transport of Nutrients and Waste
Distributes nutrients absorbed from the digestive system (e.g., glucose, amino acids) and removes metabolic waste products (e.g., urea from protein metabolism, lactic acid from muscle activity).
Regulation of Body Temperature
Helps maintain thermal homeostasis through adjustments in blood flow to the skin's surface for heat dissipation or retention.
Blood Clotting
Essential for preventing blood loss in case of injury, facilitated by platelets and clotting factors.
Maintenance of Homeostasis
Regulates pH, electrolytes (e.g., sodium, potassium, calcium ions), and fluid balance throughout the body.
Circulatory Systems Across Organisms
Organisms without a Circulatory System:
Simple organisms like flatworms and jellyfish utilize diffusion for transport over short distances.
Diffusion: A passive process effective for distances less than 1 mm and in organisms with small cell diameters (5-10 μμm to 1 mm).
Diffusion Time is proportional to the square of the distance: time∝distance2time∝distance2.
Organisms with a Circulatory System:
Larger and more complex organisms require bulk flow mechanisms to efficiently transport substances over longer distances.
Major Functions:
Bulk Flow: Involves the movement of fluids (blood or hemolymph) over long distances, requiring energy and transport costs.
Material Exchange: Diffusion occurs at the destination (e.g., capillaries) where materials are exchanged between the fluid and tissues.
Components and Structure of the Circulatory System
Human Circulatory System Components
Pumps: Heart
Structure: A muscular, four-chambered organ situated in the chest, responsible for pumping blood throughout the body. It acts as two separate pumps operating in parallel for pulmonary and systemic circulation.
Right Atrium (RA): Receives deoxygenated blood from the body via the superior and inferior vena cava.
Right Ventricle (RV): Pumps deoxygenated blood to the lungs via the pulmonary artery.
Left Atrium (LA): Receives oxygenated blood from the lungs via the pulmonary veins.
Left Ventricle (LV): Pumps oxygenated blood to the rest of the body via the aorta; it has the thickest muscular wall due to the high pressure required for systemic circulation.
Valves: Ensure unidirectional blood flow and prevent backflow between chambers and into vessels.
Atrioventricular (AV) Valves: Prevent backflow into the atria during ventricular contraction.
Tricuspid Valve: Located between the right atrium and right ventricle.
Bicuspid (Mitral) Valve: Located between the left atrium and left ventricle.
Semilunar (SL) Valves: Prevent backflow into the ventricles from the arteries.
Pulmonary Valve: Located between the right ventricle and pulmonary artery.
Aortic Valve: Located between the left ventricle and aorta.
Pathway through the Heart:
Deoxygenated blood enters the heart from the body (Superior/Inferior Vena Cava) →→ Right atrium →→ Tricuspid valve →→ Right ventricle →→ Pulmonary valve →→ Pulmonary artery →→ Lungs (for oxygenation).
Oxygenated blood returns from the lungs (Pulmonary veins) →→ Left atrium →→ Bicuspid (mitral) valve →→ Left ventricle →→ Aortic valve →→ Aorta →→ Rest of the body.
Cardiac Cycle: The rhythmic sequence of events that occurs with each heartbeat, involving relaxation (diastole) and contraction (systole) phases of the atria and ventricles.
Diastole: The heart chambers relax and fill with blood.
Systole: The heart chambers contract and pump blood out.
Cardiac Conduction System: An intrinsic electrical system that generates and transmits electrical impulses, coordinating heart contractions. The Sinoatrial (SA) node acts as the heart's natural pacemaker.
Blood Vessels: Arteries, Veins, and Capillaries
Arteries: Carry oxygenated blood away from the heart (except pulmonary arteries which carry deoxygenated blood to the lungs).
Veins: Return deoxygenated blood to the heart (except pulmonary veins which carry oxygenated blood from the lungs).
Capillaries: Microscopic blood vessels that form networks within tissues; they are the primary site of exchange between blood and tissue interstitial fluid, having very thin walls (1 endothelial cell thick) to facilitate diffusion of gases, nutrients, and waste products.
Comparison of Arteries and Veins
Arteries:
Possess thick, muscular, and elastic walls; maintain shape and withstand high pressure due to direct pumping action from the heart.
Carry blood away from the heart.
Veins:
Have thinner, less muscular, and more flexible walls that are more distensible.
Contain valves (especially in limbs) to prevent backflow of blood, as they carry low-pressure blood back to the heart.
Circulatory Systems Classification
Open Circulatory Systems:
Found in many invertebrates (e.g., mollusks like snails, arthropods like insects such as grasshoppers and spiders); hemolymph (a fluid similar to blood) circulates in open sinuses or hemocoel, bathing the organs directly.
Closed Circulatory Systems:
Found in vertebrates (e.g., fish, birds, mammals including humans) and some invertebrates (e.g., earthworms); blood is contained entirely within a continuous network of vessels (arteries, capillaries, veins), ensuring more efficient and controlled transport.
Change in Blood Pressure and Flow
Fluid dynamics: Influences blood flow; velocity and pressure can be manipulated efficiently by altering vessel diameter through processes like vasodilation (widening) and vasoconstriction (narrowing).
Increased resistance (e.g., vasoconstriction) decreases flow, while decreased resistance (e.g., vasodilation) increases flow.
Cardiac output (Q) is defined as the volume of blood pumped by the heart per minute.
The relationship is described as Q=Heart Rate (HR)×Stroke Volume (SV)Q=Heart Rate (HR)×Stroke Volume (SV).
Hemodynamics
Blood Pressure: Can be significantly affected by hydrostatic pressure considerations, especially in different body positions (e.g., veins above the heart may collapse under certain conditions due to low pressure).
Vasodilation/Vasoconstriction: These mechanisms, largely controlled by the autonomic nervous system, increase or decrease blood flow to specific tissues or organs as needed, optimizing nutrient and oxygen delivery and waste removal based on metabolic demands.
Mechanisms of Gas Exchange in Capillaries
The primary exchange of substances, including gases, nutrients, and waste, between blood and interstitial fluid occurs across the capillary walls, driven by pressure gradients.
Osmotic Pressure vs Hydrostatic Pressure (Starling Forces):
Net Flow=Hydrostatic Pressure (HP)−Osmotic PressureNet Flow=Hydrostatic Pressure (HP)−Osmotic Pressure .
High capillary hydrostatic pressure at the arterial end favors fluid outflow into the interstitial space, whereas lower hydrostatic pressures and relatively higher osmotic pressure at the venule end allow for fluid reabsorption.
Control of Circulatory Functions
Heart Rate Regulation: Primarily influenced by the autonomic nervous system: parasympathetic stimulation (via the vagus nerve) slows heart rate, while sympathetic stimulation increases it, adapting to the body's physiological demands.
Blood Flow Regulation: Achieved through complex autonomic control, often influenced by local metabolic needs (e.g., increased CO2 or decreased O2 in tissues causing vasodilation). This finely tunes vessel diameter, ensuring efficient distribution of blood to active tissues.
Oxygen Transport and Carbon Dioxide Regulation
Oxygen in Blood: Transported in two main forms:
Physically dissolved in plasma (approximately 1.5%).
Reversibly bound to hemoglobin within red blood cells (approximately 98.5%), forming oxyhemoglobin.
Carbon Dioxide Transport: Primarily transported in three ways:
As bicarbonate ions (approximately 60%) in plasma, formed from CO2 and water.
Bound to hemoglobin as carbamino compounds (approximately 30%).
Physically dissolved in plasma (approximately 10%).
The bicarbonate system is crucial for maintaining pH balance in blood, acting as a buffer against changes in H+ concentration.
Respiratory Systems Across Organisms (Gas Exchange Organs)
Gills: Specialized respiratory organs in aquatic animals (e.g., fish, sharks, crustaceans, amphibians in larval stages).
Mechanism: Extract dissolved oxygen from water and excrete carbon dioxide. Water flows over gill filaments, typically in a countercurrent exchange system, maximizing oxygen uptake. For example, fish maintain a continuous, unidirectional flow of water over their gills.
Examples: Bony fish use opercula to pump water, while sharks rely on ram ventilation (swimming continuously with mouth open) or buccal pumping.
Lungs: Internalized respiratory organs in terrestrial vertebrates (e.g., mammals, birds, reptiles, adult amphibians).
Mechanism: Facilitate gas exchange between air and blood. In mammals, lungs contain millions of alveoli, tiny air sacs that provide a vast surface area for diffusion. Breathing involves ventilation (inhalation and exhalation) to bring air in and out.
Examples: Mammals have tidal breathing, birds have a more efficient unidirectional airflow through parabronchi with air sacs, and reptiles generally have simpler sac-like lungs.
Tracheal Systems: Networks of air tubes found in insects and some other arthropods.
Mechanism: Deliver oxygen directly to individual cells and tissues without the need for a circulatory system to transport gases. Air enters through spiracles and travels through a branching system of tracheae and tracheoles.
Examples: Grasshoppers use muscle contractions to ventilate their tracheal system, while smaller insects rely solely on diffusion.
Cutaneous Respiration (Skin): Gas exchange across the moist surface of the skin.
Mechanism: Requires a thin, moist skin surface and a high surface area-to-volume ratio. Often supplemented by other respiratory organs.
Examples: Earthworms and most amphibians utilize cutaneous respiration; frogs can exchange significant amounts of gas through their skin.
Conclusion
The circulatory and respiratory systems collaborate efficiently to maintain homeostasis, ensuring optimal oxygen delivery to tissues and effective carbon dioxide removal from the body. Understanding their intricate interdependence is fundamental in physiology and clinical practice.