1. Please compare the following aspects of skeletal and smooth muscle contraction:
(a) signal for crossbridge activation
(b) source(s) of calcium used during the contractile process
(c) signal that releases calcium from the sarcoplasmic reticulum
2. Please compare and contrast the structure and location of arteries, arterioles, capillaries, and veins.
How do these differences contribute to the differences in function of each?
3. Calcium channel blockers prevent Ca2+ movement through Ca2+ channels located in the cell
membrane and are often prescribed to help treat hypertension (high blood pressure.)
(a) Please explain two distinct ways this action lowers blood pressure. Your answer should include:
the specific cell types affected, how the cellular mechanisms change in the presence of the drugs,
and how these cellular changes affect our Guiding Light cardiovascular system equation to
ultimately change blood pressure.
(b) Why are neurons and other cells unaffected by these drugs?
4. You are treating a patient for severe allergies. Unfortunately, the medication you’ve prescribed for
your patient caused a nasty side effect, hypertension. How would your patient’s body initially
attempt to compensate for hypertension? Please explain the body’s response to this situation, from
initial stimulus all the way through the final response(s).
How to solve
Skeletal Muscle Questions
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Introduction:
In this written response, we will address four questions pertaining to various aspects of medical knowledge. The topics covered in these questions include skeletal and smooth muscle contraction, the structure and function of arteries, arterioles, capillaries, and veins, the action of calcium channel blockers in treating hypertension, and the body’s response to hypertension caused by medication. Each question will be answered separately, providing a comprehensive understanding of the topics at hand.
Answer to Question 1:
(a) Signal for crossbridge activation:
In skeletal muscle contraction, the signal for crossbridge activation is the release of acetylcholine from motor neurons at the neuromuscular junction. This neurotransmitter binds to receptors on the muscle cell membrane, which triggers an action potential and subsequent release of calcium ions from the sarcoplasmic reticulum.
In smooth muscle contraction, the signal for crossbridge activation differs. It can be initiated by various factors such as neurotransmitters, hormones, or changes in membrane potential. The exact signaling pathway depends on the specific type of smooth muscle.
(b) Source(s) of calcium used during the contractile process:
Skeletal muscle obtains its calcium from two sources. The majority of calcium ions required for contraction are released from the sarcoplasmic reticulum following the action potential. Additionally, a smaller amount of calcium enters the muscle cell from extracellular fluid through specialized channels.
Smooth muscle receives its calcium from both extracellular fluid and intracellular stores. The influx of extracellular calcium through membrane channels and the release of calcium from the sarcoplasmic reticulum are both involved in initiating the contractile process.
(c) Signal that releases calcium from the sarcoplasmic reticulum:
In skeletal muscle, the signal that releases calcium from the sarcoplasmic reticulum is the depolarization of the T-tubules. This depolarization causes the voltage-sensitive receptors in the sarcoplasmic reticulum to open, allowing calcium to be released into the cytoplasm.
In smooth muscle, calcium release from the sarcoplasmic reticulum is primarily triggered by intracellular signaling molecules, such as inositol triphosphate (IP3) or diacylglycerol (DAG). These molecules are generated in response to various extracellular signals and help mobilize calcium for contraction.
Answer to Question 2:
Arteries, arterioles, capillaries, and veins are all part of the circulatory system, but they differ in structure and function.
Arteries: Arteries have thick, elastic walls with smooth muscle and connective tissue. They carry oxygenated blood away from the heart to various body tissues. Arteries can withstand high pressure due to the elasticity of their walls.
Arterioles: Arterioles are smaller branches of arteries. They have muscular walls regulating blood flow to capillaries and other tissues. The contraction and relaxation of arterioles maintain blood pressure and distribution to different organs.
Capillaries: Capillaries are the smallest blood vessels and have thin walls composed of a single layer of endothelial cells. They facilitate the exchange of oxygen, nutrients, and waste between blood and tissues. The slow flow in capillaries allows efficient nutrient and gas exchange.
Veins: Veins have thinner walls and contain valves to prevent backflow of blood. They transport deoxygenated blood back to the heart from tissues. Veins have a larger diameter and lower pressure compared to arteries.
These differences in structure contribute to the different functions of each vessel. Arteries’ elastic walls maintain blood pressure and allow rapid blood flow. Arterioles regulate blood flow and distribution to specific tissues. Capillaries enable efficient exchange of substances between blood and tissues due to their thin walls. Veins help return blood to the heart with the assistance of valves and low-pressure flow.
Answer to Question 3:
(a) Calcium channel blockers prevent Ca2+ movement through Ca2+ channels located in the cell membrane, leading to several ways these drugs lower blood pressure. Specifically, these drugs primarily affect smooth muscle cells in the cardiovascular system, such as those found in arteries and arterioles. By blocking calcium channels, the entry of calcium ions into these smooth muscle cells is hindered, resulting in relaxation or vasodilation of the smooth muscle. This reduction in calcium availability reduces smooth muscle contraction and leads to peripheral vasodilation, reducing resistance to blood flow. Consequently, this lowers blood pressure.
(b) Neurons and other cells are unaffected by calcium channel blockers because their calcium channels differ from those found in smooth muscle cells. Calcium channel blockers have a higher specificity for the subtypes of calcium channels predominantly found in specific smooth muscle cells. These drugs have a minimal effect on other cell types, including neurons, due to the differences in their calcium channel composition and regulation.
Answer to Question 4:
When a patient experiences drug-induced hypertension, their body initiates compensatory mechanisms to counteract the increased blood pressure.
Initially, the baroreceptors in the walls of blood vessels detect the elevated pressure and stimulate sensory neurons. These sensory neurons send signals to the cardiovascular center in the brain to initiate a response. The brain then increases parasympathetic (vagal) activity and reduces sympathetic activity, leading to decreased heart rate and vasodilation of arterioles. This response aims to decrease cardiac output and peripheral resistance.
Moreover, the kidneys play a crucial role in long-term compensation. They retain less water and sodium, promoting diuresis and decreasing blood volume. This reduction in blood volume further lowers blood pressure. The kidneys also release renin, an enzyme that initiates a cascade leading to increased levels of angiotensin II, a powerful vasoconstrictor. However, this response may take more time to manifest and is typically not the initial compensatory mechanism.
Overall, the body’s response to hypertension caused by medication involves immediate adjustments in heart rate, vasodilation, and long-term modulation of blood volume and vasoconstrictor pathways. These compensatory mechanisms aim to restore the balance of blood pressure.
