bio 2
Distinguish between pressure and blood reservoirs, and where these terms are applicable when discussing the cardiovascular system. Why are each important?
Arteries are often described as pressure reservoirs due to their role in maintaining and regulating blood pressure within the cardiovascular system.
Elasticity: Arteries have muscular and elastic walls that allow them to expand and contract in response to the force of blood ejected from the heart. When the ventricles contract, they force blood into the arteries, causing them to stretch. The elastic nature of the arterial walls stores this energy.
Maintaining Pressure During Diastole: When the heart is in diastole (relaxation phase), the ventricles are not pumping blood, so the pressure within the system could drop significantly. However, the energy stored in the stretched arterial walls is released, allowing the arteries to contract and continue to push blood through the system. This helps maintain a relatively constant blood pressure even when the heart is not actively pumping.
Smooth Blood Flow: The elasticity of the arteries ensures that blood flow is more continuous and smoother, rather than a series of pulses corresponding to each heartbeat. This is important for delivering a constant supply of oxygen and nutrients to various tissues in the body.
Controlling Blood Distribution: The muscular walls of the arteries also help control blood flow to different parts of the body. By constricting or dilating, arteries can regulate the pressure and volume of blood delivered to specific organs or tissues, aligning with the body's needs at any given moment.
Veins are often described as a "blood or volume reservoir" due to their ability to hold a large portion of the body's blood supply at any given time. This plays a crucial role in the overall regulation of blood volume and pressure. Here's why veins function as a blood reservoir:
Greater Volume, Lower Pressure: Veins contain about 60-70% of the total blood volume in the body. They are designed to hold more blood at a lower pressure compared to arteries. The walls of the veins are thinner and less elastic, which allows them to expand easily and accommodate a larger volume of blood.
Reserve Supply: Because veins hold such a large volume of blood, they can act as a reserve supply. In times of need, such as during vigorous exercise or when experiencing blood loss, the nervous system can signal the veins to contract. This pushes more blood into the heart and arteries, increasing the blood supply to the tissues that need it most.
Valves and Muscular Assistance: Veins contain one-way valves that prevent blood from flowing backward, and they are often surrounded by muscles. As these muscles contract and relax (such as during movement), they help push blood back toward the heart. This design enables the veins to manage the large volume of blood efficiently.
Adaptation to Changing Needs: The body can alter the volume of blood in the veins through mechanisms like vasoconstriction and vasodilation, adapting to the physiological needs of the body. For example, standing up quickly can cause blood to pool in the legs, and the body responds by constricting veins to push blood back to the heart and brain.
Temperature Regulation: By controlling the amount of blood in the veins near the skin's surface, the body can regulate heat loss. Constricting these veins keeps warm blood deeper in the body, conserving heat, while dilating them allows more blood near the skin's surface, promoting heat loss.
Describe Poiseuille’s Law and how it relates to flow, pressure and resistance in the cardiovascular system.
Poiseuille’s Law is a fundamental principle in fluid mechanics that describes how fluid flows through a cylindrical tube. It is particularly relevant in physiology for understanding the flow of blood through vessels.
According to Poiseuille's Law, the flow of an incompressible fluid through a long cylindrical tube is directly proportional to the pressure difference (∆P) between the ends of the tube and the fourth power of the radius (r) of the tube. It is inversely proportional to the length (L) of the tube and the viscosity (η) of the fluid. Mathematically, it can be expressed as:
Here's how it relates to flow, pressure, and resistance:
Flow (Q): The flow rate of fluid through the tube is determined by the tube's dimensions and the properties of the fluid. A larger radius and greater pressure difference increase the flow, while greater viscosity and tube length decrease it.
Pressure (∆P): The pressure difference between the ends of the tube is the driving force for the fluid flow. A greater pressure difference leads to a higher flow rate.
Resistance: Resistance to flow in a tube arises from factors like viscosity, tube length, and tube radius. Longer tubes and more viscous fluids increase resistance, while a wider radius decreases it. The resistance can be expressed as the ratio of pressure difference to flow rate:
In the human circulatory system, Poiseuille’s Law helps explain how blood flows through blood vessels. Small changes in vessel diameter can lead to significant changes in blood flow due to the fourth power relationship with the radius. This principle is important for understanding phenomena such as the control of blood flow to various tissues and the impact of diseases like atherosclerosis, which narrows blood vessels and increases resistance.
Name and Describe the three factors affecting systemic vascular resistance (SVR).
Blood viscosity: directly proportional to resistance. The thicker blood is the more resistant it is to moving.
Vessel length: directly proportional to resistance. Length in the cardiovascular system does not necessarily change.
Vessel diameter: inversely proportional to resistance. The bigger the radius, the larger volume of blood that can go through at one time, decreasing the resistance
How and why does blood pressure decrease from arteries to veins? Include all 5 blood vessels in your description.
Blood pressure decreases from arteries to veins due to the progressive increase in resistance as blood moves through smaller vessels. Arteries maintain the highest pressure, as they experience the most pressure from the heart and have the ability to recoil. As blood flows into arterioles, pressure drops significantly due to their smaller diameter and increased resistance. In capillaries, the smallest vessels, pressure continues to decline as blood is distributed across a vast network, facilitating exchange of nutrients and waste. In veins and venules, pressure is lowest, as blood returns to the heart against less resistance, aided by valves and muscle contractions.
Describe what Korotkov sounds are and what they are associated with.
The first sound is the systolic pressure and the second sound is the diastolic pressure, these are the korotkov sounds. They are different to the heart sounds. The korotkov sounds are useful in determining blood pressure manually. The systolic pressure can be determined due to the turbulent flow of blood as it passes through a partially compressed artery. The last sound is heard at minimum diastolic pressure and no sound is heard thereafter due to lamina flow.
Christina is sitting watching her BIOM1071 lecture and eating salty chips when a bird flies into her window, giving her a fright and temporarily raising her mean arterial pressure.
a) Describe the short-term response that occurs to reduce Christina’s blood pressure back to homeostatic levels.
Baroreceptors are mecahnoreceptors that can respond to stretch. They are located in the coratid sinus and aortic arch. If there is an increase in pressure, the baroreceptor firing will increase. If pressure decrease, the baroreceptor firing will decrease. This information is then sent to the cardiovascular center in the medulla oblongata, which then adjusts sympathetic and parasympathetic output to the heart and blood vessels.
b) After 30 years, Christina’s love for salty food has caused her to develop hypertension. Describe the ‘vicious cycle’ that makes hypertension such a difficult disease to manage.
High blood pressure damages vessel walls à atherosclerosis à increase TRP à further increase in blood pressure
Consider a patient with decreased venous return due to severe dehydration. How might the Frank-Starling mechanism affect the heart's stroke volume in this scenario, and what compensatory mechanisms might you expect the body to activate to help maintain cardiac output?
In a patient with severe dehydration, decreased venous return results in lower end-diastolic volume (EDV), thereby reducing preload. According to the Frank-Starling mechanism, this reduced preload decreases the stroke volume because the heart's ventricles are less stretched and thus contract with less force. To compensate and maintain cardiac output, the body activates sympathetic nervous system responses, increasing heart rate and causing peripheral vasoconstriction to elevate blood pressure and improve venous return. Additionally, hormonal responses like the release of renin and antidiuretic hormone (ADH) help to conserve fluid and increase blood volume, indirectly supporting cardiac function.