What is the diastole cycle in the heart?

Correct Answer: A

Rationale: The diastole cycle in the heart refers to the relaxation phase, where the heart chambers relax and fill with blood. This phase is crucial for the heart to refill and prepare for the next contraction (systole), which pumps blood out of the heart. Therefore, the correct answer is choice A, 'Relaxation of the heart.' Choices B, C, and D are incorrect in the context of cardiac physiology. Choice B, 'Contraction of the heart,' refers to systole, the phase of heart contraction. Choice C, 'Pulse rate of the heart,' is related to the number of heartbeats per minute, not the diastole cycle specifically. Choice D, 'Blood circulation,' is a broader term that encompasses the entire circulatory system rather than focusing on the heart's specific relaxation phase.

Correct Answer: C

Rationale: The correct answer is C, continuous capillaries. Continuous capillaries are the most common and least permeable type of capillary. They are found in most tissues, including muscle and the nervous system. Continuous capillaries have a continuous endothelium without fenestrations or large gaps, which limits the movement of substances across their walls. Choice A, fenestrated capillaries, have pores (fenestrations) in their endothelial cells, making them more permeable than continuous capillaries. Choice B, sinusoidal capillaries, have a discontinuous endothelium with large gaps between cells, making them more permeable and allowing larger molecules and cells to pass through compared to continuous capillaries. Choice D, discontinuous capillaries, are similar to sinusoidal capillaries with a discontinuous endothelium, allowing for enhanced permeability compared to continuous capillaries.

Correct Answer: B

Rationale: The correct answer is B: Capillaries. Capillaries are the smallest blood vessels that connect arterioles (small arteries) with venules (small veins). They enable the exchange of oxygen, nutrients, and waste products between the blood and tissues. Arterioles are small arteries that carry blood away from the heart, while venules are small veins that carry blood towards the heart. Veins are larger blood vessels that transport blood back to the heart. Therefore, capillaries specifically serve as the vessels responsible for the exchange of substances between the blood and body tissues.

Correct Answer: C

Rationale: The corrected answer is C. Elastic arteries, like the aorta, are the largest arteries in the body. They possess elastic fibers in their walls, allowing them to stretch and recoil in response to the pulsatile nature of blood flow from the heart. This elasticity helps to maintain blood pressure by absorbing the pressure waves generated by the heart's contractions and ensuring continuous blood flow to the organs. Choices A, B, and D are incorrect because elastic arteries are not the smallest arteries, do not constrict and dilate frequently, are not medium-sized arteries for distributing blood to various organs, and are not thin-walled arteries supplying blood to capillaries. Elastic arteries have a specific structure and function related to their ability to accommodate blood pressure changes due to their elastic properties, which is essential for the cardiovascular system's proper functioning.

Correct Answer: C

Rationale: Blood pressure is controlled by baroreceptors located in the aortic arch and carotid arteries that detect changes in blood pressure levels. When blood pressure is high, these receptors signal for adjustments to lower it. Additionally, hormones such as renin from the kidneys are released when blood pressure drops, further aiding in blood pressure regulation. Choice A is incorrect because blood pressure regulation involves more than just adjusting heart rate; it also includes vasodilation and vasoconstriction. Choice B is incorrect as while blood volume can impact blood pressure, it is not the primary mechanism of blood pressure control. Choice D is incorrect as body temperature regulation is a separate physiological process and not directly related to blood pressure control.