Neural, endocrine, and autoregulatory mechanisms affect blood flow, blood pressure, and eventually perfusion of blood to body tissues. Neural mechanisms include the cardiovascular centers in the medulla oblongata, baroreceptors in the aorta and carotid arteries and right atrium, and associated chemoreceptors that monitor blood levels of oxygen, carbon dioxide, and hydrogen ions. Endocrine controls include epinephrine and norepinephrine, as well as ADH, the renin-angiotensin-aldosterone mechanism, ANH, and EPO. Autoregulation is the local control of vasodilation and constriction by chemical signals and the myogenic response. Exercise greatly improves cardiovascular function and reduces the risk of cardiovascular diseases, including hypertension, a leading cause of heart attacks and strokes. Significant hemorrhage can lead to a form of circulatory shock known as hypovolemic shock. Sepsis, obstruction, and widespread inflammation can also cause circulatory shock.
anaphylactic shock
type of shock that follows a severe allergic reaction and results from massive vasodilation
aortic sinuses
small pockets in the ascending aorta near the aortic valve that are the locations of the baroreceptors (stretch receptors) and chemoreceptors that trigger a reflex that aids in the regulation of vascular homeostasis
atrial reflex
mechanism for maintaining vascular homeostasis involving atrial baroreceptors: if blood is returning to the right atrium more rapidly than it is being ejected from the left ventricle, the atrial receptors will stimulate the cardiovascular centers to increase sympathetic firing and increase cardiac output until the situation is reversed; the opposite is also true
cardiogenic shock
type of shock that results from the inability of the heart to maintain cardiac output
carotid sinuses
small pockets near the base of the internal carotid arteries that are the locations of the baroreceptors and chemoreceptors that trigger a reflex that aids in the regulation of vascular homeostasis
circulatory shock
also simply called shock; a life-threatening medical condition in which the circulatory system is unable to supply enough blood flow to provide adequate oxygen and other nutrients to the tissues to maintain cellular metabolism
hypertension
chronic and persistent blood pressure measurements of 140/90 mm Hg or above
hypovolemic shock
type of circulatory shock caused by excessive loss of blood volume due to hemorrhage or possibly dehydration
myogenic response
constriction or dilation in the walls of arterioles in response to pressures related to blood flow; reduces high blood flow or increases low blood flow to help maintain consistent flow to the capillary network
neurogenic shock
type of shock that occurs with cranial or high spinal injuries that damage the cardiovascular centers in the medulla oblongata or the nervous fibers originating from this region
obstructive shock
type of shock that occurs when a significant portion of the vascular system is blocked
sepsis
(also, septicemia) organismal-level inflammatory response to a massive infection
septic shock
(also, blood poisoning) type of shock that follows a massive infection resulting in organism-wide inflammation
vascular shock
type of shock that occurs when arterioles lose their normal muscular tone and dilate dramatically
Listen to this CDC podcast to learn about hypertension, often described as a “silent killer.” What steps can you take to reduce your risk of a heart attack or stroke?
Take medications as prescribed, eat a healthy diet, exercise, and don’t smoke.
1. Clusters of neurons in the medulla oblongata that regulate blood pressure are known collectively as ________.
A) baroreceptors
B) angioreceptors
C) the cardiomotor mechanism
D) the cardiovascular center
D
2. In the renin-angiotensin-aldosterone mechanism, ________.
A) decreased blood pressure prompts the release of renin from the liver
B) aldosterone prompts increased urine output
C) aldosterone prompts the kidneys to reabsorb sodium
D) all of the above
C
3. In the myogenic response, ________.
A) muscle contraction promotes venous return to the heart
B) ventricular contraction strength is decreased
C) vascular smooth muscle responds to stretch
D) endothelins dilate muscular arteries
C
4. A form of circulatory shock common in young children with severe diarrhea or vomiting is ________.
A) hypovolemic shock
B) anaphylactic shock
C) obstructive shock
D) hemorrhagic shock
A
1. A patient arrives in the emergency department with a blood pressure of 70/45 confused and complaining of thirst. Why?
This blood pressure is insufficient to circulate blood throughout the patient’s body and maintain adequate perfusion of the patient’s tissues. Ischemia would prompt hypoxia, including to the brain, prompting confusion. The low blood pressure would also trigger the renin-angiotensin-aldosterone mechanism, and release of aldosterone would stimulate the thirst mechanism in the hypothalamus.
2. Nitric oxide is broken down very quickly after its release. Why?
Nitric oxide is a very powerful local vasodilator that is important in the autoregulation of tissue perfusion. If it were not broken down very quickly after its release, blood flow to the region could exceed metabolic needs.