Anatomy and Physiology: Circulatory system

Trunk

A term indicating that the vessel gives rise to several smaller arteries. For example, the celiac trunk gives rise to the left gastric, common hepatic, and splenic arteries.

Digestive

Absorbs nutrients and water, delivers nutrients (except most lipids) to live for processing by hepatic portal vein; provides nutrients essential for hematopoiesis and building hemoglobin.

Reproductive

Aids in erection of genitalia in both sexes during sexual arousal; transports gonadotropic hormones that regulate reproductive functions.

Internal thoracic artery

Also called the mammary artery; arises from the subclavian artery; supplies blood to the thymus, pericardium of the heart, and anterior chest wall.

Arterial circle or circle of Willis

An anastomosis located at the base of the brain that ensures continual blood supply; formed from the branches of the internal carotid and vertebral arteries; supplies blood to the brain.

Anterior communicating artery description

An anastomosis of the right and left internal carotid arteries; supplies blood to the brain.

Middle Cerebral artery

Another branch of the internal carotid artery; supplies blood to the temporal and parietal lobes of the cerebrum.

Internal carotid artery

Arises from the common carotid artery and begins with the carotid sinus; goes through the carotid canal of the temporal bone to the base of the brain; combines with the branches of the vertebral artery, forming the arterial circle; supplies blood to the brain.

External carotid artery

Arises from the common carotid artery; supplies blood to numerous structures within the face, lower jaw, neck, esophagus, and larynx.

Anterior cerebral artery description

Arises from the internal carotid artery; supplies blood to the frontal lobe of the cerebrum.

Vertebral artery

Arises from the subclavian artery and passes through the vertebral foramen through the foramen magnum to the brain; joins with the internal carotid artery to form the arterial circle; supplies blood to the brain and spinal cord.

Thyrocervical artery

Arises from the subclavian artery; supplies blood to the thyroid, the cervical region, the upper back, and shoulder.

Secreted by cells in the atria of the heart,

Atrial natriuretic hormone (ANH), also know as atrial natriuretic peptide, is secreted when blood volume is high enough to cause extreme stretching of the cardiac cells. Cells in the ventricle produce a hormone with similar effects, call B-type natriuretic hormone. Natriuretic hormones are antagonists to angiotensin II. They promote loss of sodium and water from the kidneys, and suppress renin, aldosterone, and ADH production and release. All of these actions promote loss of fluid from the body, so blood volume and blood pressure drop.

The pressure created by the concentration of colloidal proteins in the blood is called the

BLOOD COLLOIDAL OSMOTIC PRESSURE (BCOP). Its effect on capillary exchange accounts for the reabsorption of water.

Baroreceptor reflexes:

Baroreceptors are specialized stretch receptors located within thin areas of blood vessels and heart chambers that respond to the degree of stretch caused by the presence of blood. They send impulses to the cardiovascular system to regulate blood pressure.

Posterior cerebral artery

Branch of the basilar artery that forms a portion of the posterior segment of the arterial circle of Willis; supplies blood to the posterior portion of the cerebrum and brain stem.

Ophthalmic artery

Branches of the internal carotid artery; supplies blood to the eyes.

Posterior communicating artery description

Branches of the posterior cerebral artery that form part of the posterior portion of the arterial circle; supplies blood to the brain.

Integumentary

Carries clotting factors, platelets, and white blood cells for hemostasis, fighting infection, and repairing damage; regulates temperature by controlling blood flow to the surface, where heat can be dissipated; provides some coloration of integument; acts as a blood reservoir.

Anterior communicating artery

Connects right and left anterior cerebral arteries (anastomosis).

Urinary

Delivers 20% of resting circulation to kidneys for filtering, reabsorption of useful products, and secretion of excesses; regulates blood volume and pressure by regulating fluid loss in the form of urine and by releasing the enzyme renin that is essential in the renin-angiotensin-aldosterone mechanism.

Endocrine

Delivers hormones: atrial natriuretic hormone (peptide) secreted by the heart atrial cells to help regulate blood volume and pressures; epinephrine, ANH, angiotensin II, ADH, and thyroxine to help regulate blood pressure; estrogen to promote vascular health in women and men.

Vessel:

Description:

Basilar artery description:

Formed from the fusion of the 2 vertebral arteries; sends branches to the cerebellum, brain stem, and the posterior cerebral arteries, the main blood supply to the brain stem.

Unfortunately shock is an example of a POSITIVE-FEEDBACK LOOP that, if uncorrected, may lead to the death of a patient. There are several recognized forms of shock:

HYPOVOLEMIC SHOCK: in adults is typically caused by hemorrhage, although in children it may be caused by fluid losses related to severe vomiting or diarrhea. Other causes include, extensive burns, exposure to some toxins, and excessive urine loss related to diabetes insipidus (ketoacidosis). Patients present with tachycardic heart rate (rapid), weak pulse (thready), cool clammy skin (extremities, due to restricted peripheral blood flow), rapid shallow breathing, hypothermia, thirst, and dry mouth. Treatment is intravenous fluids, and drugs like dopamine, epinephrine, and norepinephrine to raise blood pressure. CARDIOGENIC SHOCK: results from the inability of the heart to maintain cardiac output. Often, it results from a myocardial infarction (heart attack), may also lead to arrhythmias, valve disorders, cardiomyopathies, cardiac failure, or simply insufficient flow of blood through the cardiac vessels. Treatment is repairing damage to the heart/vessels to restore the underlying cause, rather than treating cardiogenic shock directly. (CONTINUED ON SLIDE 53)

We can also say that the BCOP is higher than the

INTERSTITIAL FLUID COLLOIDAL OSMOTIC PRESSURE (IFCOP), which is always very low because interstitial fluid contains few proteins. Thus, water is drawn from the tissue fluid back into the capillary, carrying dissolved molecules with it. This difference in colloidal osmotic pressure accounts for REABSORPTION.

atrial reflex (bainbridge reflex)

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 homeostasis is achieved. The opposite is also true.

The cardiovascular centers in the brain

Neurological regulation of blood pressure and flow depends on the cardiovascular centers located in the MEDULLA OBLONGATA. This cluster of neurons responds to changes in blood pressure as well as blood concentration of oxygen, carbon dioxide, and hydrogen ions.

VASCULAR SHOCK: occurs when arterioles lose their normal muscular tone and dilate dramatically. It could arise from a variety of causes, and treatments almost always involve fluid replacement and medications, called INOTROPIC OR PRESSURE AGENTS, which restore tone to the muscles of the vessels. In addition, eliminating or at least alleviating the underlying cause of the condition is required. This might include antibiotics and antihistamines, or select steroids, which may aid in the repairs of nerve damage. A common cause is SEPSIS (SEPTICEMIA), also called "blood poisoning," which is a widespread bacterial infection that results in an organism-level inflammatory response known as septic shock. NEUROGENIC SHOCK is a form of vascular shock that occurs with cranial or spinal injuries that damage the cardiovascular centers in the medulla oblongata or the nervous fibers originating from this region. ANAPHYLACTIC SHOCK is a severe allergic response that causes the widespread release of histamines, triggering vasodilation throughout the body.

OBSTRUCTIVE SHOCK: as the name would suggest, occurs when a significant portion of the vascular system is blocked. It is not always recognized as a distinct condition and may be grouped with cardiogenic shock, including pulmonary embolism and cardiac tamponade. Treatments depend upon the underlying cause and, in addition to administering fluids intravenously, often include the administration of anticoagulants, removal of fluid from the pericardial cavity, or air from the thoracic cavity, and surgery is required. The most common cause is a pulmonary embolism, a clot that lodges in the pulmonary vessels and interrupts blood flow. Other causes include stenosis (stiffness) of the aortic valve; cardiac tamponade, in which excess fluid in the pericardial cavity interferes with the ability of the heart to fully relax and fill with blood (resulting in decreased preload); and a pneumothorax, in which an excessive amount of air is present in the thoracic cavity, outside of the lungs, which interferes with venous return, pulmonary function, and delivery of oxygen to the tissues.

Nervous

Produce cerebrospinal fluid (CSF) within choroid plexuses; contributes to blood-brain barrier; cardiac and vasomotor centers regulate cardiac output and blood flow through vessels via autonomic system.

Respiratory

Provides blood for critical exchange of gases to carry oxygen needed for metabolic reactions and carbon dioxide generated as byproducts of these processes.

Skeletal

Provides calcium, phosphate, and other minerals critical for bone matrix, transport hormones regulating buildup and absorption of matrix including growth hormone (somatotropin), thyroid hormone, calcitonins, and parathyroid hormone; erythropoietin stimulates myeloid cells hematopoiesis; some level of protection for select vessels by bony structures.

Muscular

Provides nutrients and oxygen for contraction; removes lactic acid and distributes heat generated by contraction; muscular pumps aid in venous return; exercise contributes to cardiovascular health and helps to prevent atherosclerosis.

What steps can you take to reduce your risk of a heart attack or stroke?

Quit smoking, keep your blood pressure in the normal range, keep your blood glucose in the normal range, keep your cholesterol levels in the normal range, stay at a healthy weight, be active, and eat healthy.

As we discuss osmotic pressure in blood and tissue fluid, it is important to recognize that the formed elements of blood do not contribute to osmotic concentration gradients.

Rather, it is the plasma proteins that play the key role. Solutes also move across the capillary wall according to their concentration gradient, but overall, the concentrations should be similar and not have a significant impact on osmosis.

Brachiocephalic artery

Single vessel located on the right side of the body; the first vessel branching from the aortic arch; gives rise to the right subclavian artery and the right common carotid artery; supplies blood to the head, neck, upper limb, and wall of thoracic region.

The cardiovascular center contains 3 distinct paired components:

The CARDIOACCELERATOR CENTERS stimulate cardiac function by regulation heart rate and stroke volume via sympathetic stimulation from the CARDIAC ACCELERATOR NERVE. The CARDIOINHIBITOR CENTERS slow cardiac function by decreasing heart rate and stroke volume via parasympathetic stimulation from the VAGUS NERVE. The VASOMOTOR CENTERS control vessel tone or contraction of the smooth muscle in the tunica media. Changes in diameter affect peripheral resistance, pressure, and flow, which affect cardiac output. The majority of these neurons act via the release of the neurotransmitter NOREPINEPHRINE from sympathetic neurons.

Posterior communicating artery

The artery of the Circle of Willis that transports blood from the internal carotid artery to the (branches from the) posterior cerebral artery is the? Provides blood to the posterior portion of the cerebrum and brain stem.

Since tissues consume oxygen and produce carbon dioxide and acids as waste products, when the body is more active, oxygen levels fall and carbon dioxide levels rise as cells undergo cellular respiration to meet the energy needs of activities. This causes more hydrogen ions to be produced, causing the blood pH to drop. When the body is resting, oxygen levels are higher, carbon dioxide levels are lower, more hydrogen is bound, and pH rises.

The chemoreceptors respond to increasing carbon dioxide and hydrogen ion levels (falling pH) by stimulating the cardioaccelerator and vasomotor centers, increasing cardiac output and constricting peripheral vessels. The cardioinhibitor centers are suppressed. With falling carbon dioxide and hydrogen ion levels (increasing pH), the cardioinhibitor centers are stimulated, and the cardioaccelerator and vasomotor centers are suppressed, decreasing cardiac output and causing peripheral vasodilation.

Arteries suppling the head and neck

The common carotid artery gives rise to the external and internal carotid arteries. The external carotid artery remains superficial and gives rise to many arteries of the head.The internal carotid artery first forms the carotid sinus and then reaches the brain via the carotid canal and carotid foramen, emerging into the cranium via the foramen lacerum. The vertebral artery branches from the subclavian artery and passes through the transverse foramen in the cervical vertebrae, entering the base of the skull at the vertebral foramen. The subclavian artery continues toward the arm as the axillary artery.

Circulatory SHOCK

The loss of too much blood, a life-threatening condition in which the circulatory system is unable to maintain blood flow to adequately supply sufficient oxygen and other nutrients to the tissues to maintain cellular metabolism. Typically, the PATIENT in circulatory shock will demonstrate an INCREASED HEART RATE bu DECREASED BLOOD PRESSURE. Urine output will fall dramatically, and the patient may appear confused or lose consciousness. Urine output less than 1 mL/kg body weight/hour is cause for concern.

The nervous system plays a critical role in the regulation of vascular homeostasis.

The primary regulatory sites include the cardiovascular centers in the brain that control both cardiac and vascular functions. In addition, more generalized neural responses from the limbic system and autonomic nervous system are factors.

Common carotid artery

The right common carotid artery arises from the brachiocephalic artery and the left common carotid artery arises from the aortic arch; each give rise to the external and internal carotid arteries; supplies the respective sides of the head and neck.

Subclavian artery

The right subclavian artery arises from the brachiocephalic artery while the left subclavian artery arises from the aortic arch; gives rise to the internal thoracic, vertebral, and thyrocervical arteries; supplies blood to the arms, chest, shoulders, back, and central nervous system.

Lymphatic

Transports various white blood cells, including those produced by lymphatic tissue, and immunoglobulins (antibodies) throughout the body to maintain health; carries excess tissue fluid not able to be reabsorbed by the vascular capillaries back to the lymphatic system for processing.

20.5 CIRCULATORY PATHWAYS

Virtually every cell, tissue, organ, and system in the body is impacted by the circulatory system. This includes the generalized and more specialized functions of transport of materials, capillary exchange, maintaining health by transporting white blood cells and various immunoglobulins (antibodies), hemostasis, regulation of body temperature, and helping to maintain acid-base balance. In addition to these shared functions, many systems enjoy a unique relationship with the circulatory system.

When the cardiovascular center in the medulla oblongata receives this input, it triggers a reflex that maintains HOMEOSTASIS:

When blood pressure rises too high, the baroreceptors fire at a higher rate and trigger parasympathetic stimulation of the heart. As a result the cardiac output falls. Sympathetic stimulation of the peripheral arterioles will also decrease, resulting in vasodilation. Combined, these activities cause blood pressure to fall. When blood pressure drops too low, the rate of baroreceptor firing decreases. This will trigger an increase in sympathetic stimulation of the heart, causing cardiac output to increase. It will also trigger sympathetic stimulation of the peripheral vessels, resulting in vasoconstriction. Combined, these activities cause blood pressure to rise.

End artery

a single artery that is the only source of blood for an organ, one that undergoes progressive branching without development of channels connecting with other arteries.

The catecholamines epinephrine and norepinephrine are released by the

adrenal medulla, and enhance and extend the body's sympathetic or "fight-or-flight" response. They increase heart rate and force of contraction, while temporarily constricting blood vessels to organs not essential for flight-or-flight responses and redirecting blood flow to the liver, muscles, and heart.

Arterial circle (or circle of Willis)

an anastomosis that is remarkably like a traffic circle that sends off branches (in this case, arterial branches to the brain).

AORTIC SINUSES

are found in the wells of the ascending aorta just superior to the aortic valve.

CAROTID SINUSES

are in the base of the internal carotid arteries.

Because of their large size and chemical structure, plasma proteins

are not truly solutes, that is, they do not dissolve but are dispersed or suspended in their fluid medium, forming a colloid rather than a solution.

In response to blood loss, stimuli from the

baroreceptors trigger the cardiovascular centers to stimulate sympathetic responses to increase cardiac output and vasoconstriction. This typically prompts the heart rate to increase to about 180-200 contractions per minute, restoring cardiac output to normal levels.

In order to maintain homeostasis in the cardiovascular system and provide adequate blood to tissues,

blood flow must be redirected continually to the tissues as they become more active. In a very real sense, the cardiovascular system engages in resource allocation, because there is not enough blood flow to distribute blood equally to all tissues simultaneously. For example, when an individual is exercising, more blood will be directed to skeletal muscles, the heart, and the lungs. Following a meal, more blood is directed to the digestive system. Only the brain receives a more or less constant supply of blood whether you are active, resting, thinking, or engaged in any other activity.

3 HOMEOSTATIC MECHANISMS ensure adequate blood flow

blood pressure, distribution, and ultimately perfusion: neural, endocrine, and autoregulatory mechanisms.

The plasma proteins suspended in blood

cannot move across the semipermeable capillary cell membrane, and so they remain in the plasma. As a result, blood has a higher colloidal concentration and lower water concentration than tissue fluid. It therefore attracts water.

The renin-angiotensin-aldosterone mechanism has a major effect upon the

cardiovascular system. Renin is an enzyme, although because of its importance in the renin-angiotensin-aldosterone pathway, some sources identify is as a hormone. Specialized cells in the kidney are found in the JUXTAGLOMERULAR APPARATUS respond to decreased blood flow by secreting renin into the blood. Renin converts the plasma protein angiotensinogen, which is produced by the liver, into its active form - angiotensin I. Angiotensin I circulates in the blood and is then converted into angiotensin II in the lungs. This reaction is catalyzed by the enzyme angiotensin-converting enzyme (ACE).

Endocrine control of the cardiovascular system involves the

catecholamines, epinephrine and norepinephrine, as well as several hormones that interact with the kidneys in the regulation of blood volume.

elastic artery

closest to the heart experience the greatest blood pressure greatest amount of elastin expand and recoil to propel blood

Vasodilators (Relax precapillary sphincters, increasing blood flow)

decreases oxygen, increased carbon dioxide, increased metabolic acids such as lactate, increased NO, increased potassium, increased H+, inflammation, and increased body temperature.

Cardiac output =

heart rate X stroke volume

Minor blood loss is managed by

hemostasis and repair. Hemorrhage is a loss of blood that cannot be controlled by hemostatic mechanisms. Initially, the body responds to hemorrhage by initiating mechanisms aimed at increasing blood pressure and maintaining blood flow. Ultimately, however, blood volume will need to be restored, either through physiological processes or through medical intervention.

The internal carotid arteries along with the vertebral arteries are the 2 primary suppliers of blood to the

human brain.

Chronically elevated blood pressure is known clinically as

hypertension. It is defined as chronic and persistent blood pressure measurements of 140/90 mm Hg or above. Pressures between 120/80 and 140/90 mm Hg are defined as prehypertension. About 68 million Americans currently suffer from hypertension. Unfortunately, hypertension is typically a silent disorder, therefore, hypertensive patients may fail to recognize the seriousness of their condition and fail to follow their treatment plan. The result is often a heart attack or stroke. Hypertension may also lead to an aneurism (ballooning of a blood vessel caused by a weakening of the wall), peripheral arterial disease (obstruction of vessels in peripheral regions of the body), chronic kidney disease, or heart failure.

Antidiuretic hormone (ADH), also known as vasopressin, is secreted by the cells in the

hypothalamus and transported via the hypothalamic-hypophyseal tracts to the posterior pituitary where it is stored until released upon nervous stimulation. The primary trigger prompting the hypothalamus to release ADH is increasing osmolarity of tissue fluid, usually in response to significant loss of blood volume. ADH signals its target cells in the kidneys to reabsorb more water, thus preventing the loss of additional fluid in the urine. This will increase overall fluid levels and help restore blood volume and pressure. In addition, ADH constricts peripheral vessels.

The thoracic aorta begins at the level of vertebra T5 and continues through to the diaphragm at the level of T12,

initially traveling within the mediastinum to the left of the vertebral column. As it passes through the thoracic region, the thoracic aorta gives rise to several branches, which are collectively referred to as visceral branches and parietal branches.

The MYOGENIC RESPONSE

is a reaction to the stretching of the smooth muscle in the walls of arterioles as changes in blood flow occur through the vessel. This may be viewed as a largely productive function against dramatic fluctuations in blood pressure and blood flow to maintain HOMEOSTASIS. If perfusion of an organ is too low (ischemia), the tissue will experience low levels of oxygen (hypoxia). In contrast, excessive perfusion could damage the organ's smaller and more fragile vessels. The myogenic response is a localized process that serves to stabilize blood flow in the capillary network that follows that arteriole.

Basilar artery

is an anastomosis that begins at the junctions of the 2 vertebral arteries and sends branches to the cerebellum and brain stem. It flows into the posterior cerebral arteries.

In order to maintain adequate supplies of oxygen to the cells and remove waste products such as carbon dioxide,

it is essential that the respiratory system respond to changing metabolic demands. In turn, the cardiovascular system will transport these gases to the lungs for exchange, again in accordance with metabolic demands. This interrelationship of cardiovascular and respiratory control cannot be overemphasized.

Erythropoietin (EPO) is released by the

kidneys when blood flow and/or oxygen levels decrease. EPO stimulates the production of erythrocytes within the bone marrow. Erythrocytes are the major formed element of the blood and may contribute to 40% or more to blood volume, a significant factor of viscosity, resistance, pressure, and flow. In addition, EPO is a vasoconstrictor. Overproduction of EPO or excessive intake of synthetic EPO, often enhances athletic performance, will increase viscosity, resistance, and pressure, and decrease flow in addition to its contribution as a vasoconstrictor.

Nutrient artery

large artery that enters compact bone near the middle of the diaphysis. Any artery that supplies the marrow, or medulla, of a long bone.

Autoregulation of Perfusion:

local mechanisms include chemical signals and myogenic controls.

The normal unit used to express pressures within the cardiovascular system is

millimeters of mercury (mm Hg). When blood leaving an arteriole first enters a capillary bed, the CHP is quite high - about 35 mm Hg. Gradually, this initial CHP declines as the blood move through the capillary so that by the time the blood has reached the venous end, the CHP has dropped to approximately 18 mm Hg. In comparison, the plasma proteins remain suspended in the blood, so the BCOP remains fairly constant at about 25 mm Hg throughout the length of the capillary and considerably below the osmotic pressure in the interstitial fluid.

Chemoreceptor reflexes: Chemoreceptors

monitor levels of oxygen, carbon dioxide, and hydrogen ions, and thereby contribute to vascular homeostasis. Chemoreceptors monitoring the blood are located in close proximity to the baroreceptors in the aortic and carotid sinuses. They signal the cardiovascular centers as well as the respiratory centers in the medulla oblongata.

During exercise, the body distributes

more blood to the body surface where it can dissipate the excess heat generated by increased activity into the environment.

Osmotic pressure is determined by

osmotic concentration gradients, that is, the difference in the solute-to-water concentrations in the blood and tissue fluid. A region higher in solute concentration (and lower in water concentration) draws water across a semipermeable membrane from a region higher in water concentration (and lower in solute concentration).

Whereas hydrostatic pressure forces fluid out of the capillary,

osmotic pressure draws fluid back in.

Chemical signals work at the level of the

precapillary sphincters to trigger either constriction or relaxation.

What is the main component of interstitial fluid?

primarily WATER, containing dissolved nutrients, hormones, gases, wastes and small proteins.

Vasoconstrictors (Constrict precapillary sphincters, decreasing blood flow)

prostaglandins, products released by activated platelets, leukocytes, and endothelins.

The ophthalmic artery, the 3rd major branch,

provides blood to the eyes.

Aldosterone increases the

reabsorption of sodium into the blood by the kidneys. Since water follows sodium, this increases the reabsorption of water. This in turn increases blood volume, raising blood pressure.

The NET FILTRATION PRESSURE (NFP)

represents the interaction of the hydrostatic and osmotic pressures, driving fluid out of the capillary. It is equal to the difference between the CHP and the BCOP. since filtration is, by definition, the movement of fluid out of the capillary, when reabsorption is occurring, the NFP is a negative number. NFP changes at different points in a capillary bed. Close to the arterial end of the capillary, it is approximately 10 mm Hg, because the CHP of 35 mm Hg minus the BCOP of 25 mm Hg equals 10 mm Hg. Thus, the NFP of 10 mm Hg drives a net movement of fluid out of the capillary at the arterial end. At approximately the middle of the capillary, the CHP is about the same as the BCOP of 25 mm Hg, so the NFP drops to zero. At this point, there is no net change of volume: Fluid moves out of the capillary at the same rate as it moves into the capillary. Near the venous end of the capillary, the CHP has dwindled to about 18 mm Hg due to loss of fluid. Because the BCOP remains steady at 25 mm Hg, water is drawn into the capillary, that is, reabsorption occurs. Another way of expressing this is to say that at the venous end of the capillary, there is an NFP of -7 mm Hg.

Transient ischemic attack (TIA), or mini stroke,

resulting in the loss of consciousness of temporary loss of neurological function. In some cases, the damage may be permanent. Loss of blood flow for longer periods, typically between 3-4 minutes, will likely produce irreversible brain damage or a stroke, also called a cerebrovascular accident (CVA).

Systems:

role of circulatory system:

Vascular baroreceptors are found primarily in

sinuses (small cavities) within the AORTA and CAROTID ARTERIES. There are also low-pressure baroreceptors located in the walls of the venae cavae and right atrium.

Exercise increases the

size and mass of the heart.

When blood pressure increases, the baroreceptors are

stretched more tightly and initiate action potentials at a higher rate. At lower blood pressures, the degree of stretch is lower and the rate of firing is slower.

The middle cerebral artery

supplies blood to the temporal and parietal lobes, which are the most common sits of CVAs.

Anastomosis

surgical joining of two ducts, vessels, or bowel segments to allow flow from one to another.

Each bronchial artery (typically 2 on the left and one on the right) supplies

systemic blood to the lungs and visceral pleura, in addition to the blood pumped to the lungs for oxygenation via the pulmonary circuit. The bronchial arteries follow the same path as the respiratory branches, beginning with the bronchi and ending with the bronchioles.

Anterior cerebral artery

that supplies blood to the frontal lobe of the cerebrum.

The net pressure that drives reabsorption -

the movement of fluid from the interstitial fluid back into the capillaries - is called osmotic pressure (oncotic pressure).

CHOLINERGIC neurons

they release ACETYLCHOLINE, which in turn stimulates the vessels' endothelial cells to release NITRIC OXIDE (NO), which causes vasodilation. Others release norepinephrine that binds to beta receptors. A few neurons release NO directly as a neurotransmitter.

The angiotensin-renin-aldosterone mechanism stimulates the

thirst center in the hypothalamus, which increases fluid consumption to help restore the lost blood. More importantly, it increases renal reabsorption of sodium and water, reducing water loss in urine output. The kidneys also increase the production of EPO, stimulating the formation of erythrocytes that not only deliver oxygen to the tissues but also increase overall blood volume. (Homeostatic responses to loss of blood volume)

Any disorder that affects blood volume, vascular tone, or any other aspect of vascular functioning is likely to affect

vascular homeostasis as well. This include hypertension, hemorrhage, and shock.

Angiotensin II is a powerful

vasoconstrictor, greatly increasing blood pressure. It also stimulates the release of ADH and aldosterone, a hormone produced by the adrenal cortex. Angiotensin II also stimulates the thirst center in the hypothalamus, so an individual will likely consume more fluids, again increasing blood volume and pressure.

Those branches that supply blood primarily to visceral organs are known as the

visceral branches and include the bronchial arteries, pericardial arteries, esophageal arteries, and the mediastinal arteries, each named after the tissues it supplies.

Vasoconstriction of the arterioles increase vascular resistance,

whereas constriction of the veins increases venous return to the heart. Both of these steps will help increase blood pressure. Sympathetic stimulation also triggers the release of epinephrine and norepinephrine, which enhance both cardiac output and vasoconstriction. If blood loss were less than 20% of total blood volume, these responses together would usually return blood pressure to normal and redirect the remaining blood to the tissues.