(20 points) An individual stands up rapidly from a lying position and becomes li
ID: 3523478 • Letter: #
Question
(20 points) An individual stands up rapidly from a lying position and becomes light-headed due to a drop in blood pressure in the brain. This is known as postural hypotension. The body responds by triggering the baroreceptor reflex that targets the heart and blood vessels. a. Explain how heart rate could be increased due to the baroreceptor reflex. Include which cells are involved and the electrical changes that occur in the cells to influence heart rate. Make sure to discuss what is happening at the cellular level and focus on specific ions/gated ion channels that affect membrane potential. b. Explain how blood vessels would be affected by the baroreceptor reflex and why this would help alter blood pressure. What cells are functioning as the effectors in this mechanism and what are they doing?
Explanation / Answer
Baroreceptor- These are the receptors present in the blood vessels of all vertibrate animals. Whenever these receptors sense blood pressure, they send the information to brain and maintain required blood pressure.
Baroreceptor Reflex- it is body's homeostatic mechanism and it helps in maintaining the blood pressure at nearly constant levels.
Cardiac cells that are involved in baroreceptor reflex are divided into two types on the basis of their working as follows:
A. Electrical cells: Electrical cells make the conduction system of the heart and they are distributed in an orderly fashion through the heart. Characteristics: 1. Automaticity – the ability to spontaneously generate and discharge an electrical impulse. 2. Excitability – the ability of the cell to respond to an electrical impulse. 3. Conductivity – the ability to transmit an electrical impulse from one cell to the next.
B. Myocardial cells: These are the cells which makes the muscular walls of the atrium and ventricles of the heart. Characteristics: 1. Contractility – the ability of the cell to shorten and lengthen its fibers. 2. Extensibility – the ability of the cell to stretch.
The following process happens at the cellular level:
1. Opening of an ion channel and the subsequent movement of ions through the channel necessarily changes the membrane potential. This, of course, is because the moving ions are moving charges. But in what direction does the membrane potential change? You are now equipped to answer this in every case.
2. Specific ion moving through an open ion channel causes the membrane potential to move towards the equilibrium potential for that specific ion. For reference, the typical equilibrium potentials we determined earlier are shown to the right.
3. The membrane potential moves towards the average of the equilibrium potentials for the specific ions that can cross the membrane. The average is not a true average, but an average weighted by the relative permeabilities for the different ions -- the more permeable the membrane is for an ion, the more the equilibrium potential of that ion will influence the membrane potential.
4. We have been using a resting membrane potential of -70 mV. Refer back to the table of equilibrium potentials. We know that the resting membrane is mainly permeable to K+, and thus the resting membrane potential should be close to the K+ equilibrium potential. However, the resting membrane potential is not exactly at the equilibrium potential for K+, but a bit higher at -70 mV. This is because the resting membrane is slightly permeable to Na+.
5. Cl- is not actively transported; its intracellular concentration typically must adjust to put the ion near equilibrium. For this reason, the equilibrium potential for Cl- is equal here to the resting membrane potential at -70 mV.
Blood vessels are affected by the baroreceptor reflex and this would help alter blood pressure as follows:
1. Blood pressure in the blood vessels is closely monitored by baroreceptors, they send messages to the cardio regulatory center of your medulla oblongata to regulate your blood pressure minute by minute. In this lesson, you will learn how baroreceptors regulate your short-term blood pressure.
2. Blood Pressure in your cardiovascular system must maintain an adequate blood pressure in order for blood to be delivered to all of your organs and tissues. If the pressure drops too low, the organs will not receive an adequate perfusion of nourishing blood. If the pressure rises too high, it could damage the delicate inner lining of your blood vessels and eventually lead to heart disease or a stroke.
3. Mean Arterial Pressure: Pressure fluctuates with each beat of your heart, what we call one cardiac cycle. We remember that a cardiac cycle has two phases: diastole, which is the phase where the heart is filling with blood but not pumping, and systole, which is the phase when the ventricles contract and pump blood.
4. Blood pressure is recorded in millimeters of mercury (mmHg) with systolic pressure written first, followed by diastolic pressure. Therefore, a normal blood pressure would be written like this: 120/80. Instead of trying to consider the constant fluctuations of blood pressure, we will look at blood pressure in terms of mean arterial pressure (MAP).
Following cells are functioning as the effectors in baroreceptor reflex:
The receptor receives the information that something in is changing. The control center receives and processes information from the receptor and at the end the effector responds to the commands of the control center by either opposing or enhancing the stimulus. This is an ongoing process that continually works to restore and maintain homeostasis. There are four effectors 1. Cardiac nodal cells. 2. Cardiac cells 3. VSM. 4. Adrenal medulla.
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