Medical Physiology Block 3 Week 3

Question 1

Which of the four mechanisms of controlling regional blood flow is responsible for auto-regulation?

Answer 1

myogenic response: increased pressure and the accompanying stretch of VSMCs elicit vasoconstriction

Question 2

Describe the vascular anatomy of the cerebrum. What are characteristics specific to the brain circulation?

Answer 2

the common carotid artery bifurcates into the internal and external carotid arteries; the internal carotid artery anastomoses into the anterior cerebral artery and middle cerebral artery (the collateral artery in the anterior circulation is the anterior communicating artery; the posterior circulation arises from the two vertebral arteries that join together to become the basilar artery. The basilar artery then anastomoses into the posterior cerebral artery and posterior communicating artery; together the anterior and posterior circulation form the “Circle of Willis”; does not tolerate ischemia; limited total vascular volume due to being encased in the boney cranium

Question 3

T/F Veins in the brain are devoid of smooth muscle and valves?

Answer 3

True

Question 4

Describe how the major cerebral arteries (middle cerebral artery) branch into arterioles and capillary beds

Answer 4

the middle cerebral artery courses the lateral surface of the brain giving rise to pial arteries; pial arteries anasastomose into arterioles which enter at right angles to the parenchyma (branch centripetally to give rise to capillaries

Question 5

Does the brain have lymphatics?

Answer 5

No

Question 6

What is unique about the blood brain barrier? Is flux different in this circulation?

Answer 6

continuous endothelial cells (lots of mitochondria); no solute is excluded from the brain, but its flow is significantly attenuated by the BBB

Question 7

How is cerebral blood flow controlled?

Answer 7

Neurovascular coupling: neural activity stimulates vasodilation by release of neurotransmitters that increase calcium in neurons leading to upregulation of NO and other vasodilators (signal upstream to arterioles ); Neural activity leads to release of adenosine into BECF, lowers arterial oxygen, increases arterial carbon dioxide, and lowers BECF pH → vasodilation (also signal to pial arteries); increased transmural pressure leads to vasoconstriction (myogenic); ANS stimulation is weak in the cerebrum

Question 8

What is the reflex that occurs when intracranial pressure rises due to a mass or obstruction?

Answer 8

Cushing reflex: increased arterial pressure, decreased heart rate, and shallow breathing

Question 9

What is normal cerebral perfusion pressure (definition and value)?

Answer 9

Cerebral perfusion pressure is the difference between the systemic arterial pressure and intracranial venous pressure, which is nearly equal to intracranial pressure (about 10 mm Hg); normally 70 mm Hg;

Question 10

What happens to the cerebral circulation when MAP falls to 60 with normal intracranial pressures? What happens when intracranial pressue increases to over 25 mm Hg for patients with a normal MAP?

Answer 10

In both situations, the brain will become ischemic because the cerebral perfusion pressure has dropped below the levels for which the brain’s circulation can auto-regulate flow

Question 11

Describe the vascular anatomy supplying the left ventricle.

Answer 11

the left coronary artery (supplying both the LA & LV) divides into two branches: left circumflex artery and left anterior descending artery (“widowmaker” supplies apex and interventricular septum); Very high capillary density (ability to recruit more capillaries during exercise); drain into epicardial veins

Question 12

Describe blood flow to the left ventricle. Is flow increased in diastole?

Answer 12

Myocardial contraction effectively compresses its own vascular supply (lower wall tension in right ventricle thus most flow occurs during systole; LV: diastole); Tachycardia (decrease in diastole reduces time for left ventricle perfusion; More blood flow to the epicardium compared to endocardium; Increase in myocardial blood flow during exercise

Question 13

What is a mechanism to increase blood flow corresponding to increased oxygen demand?

Answer 13

The heart can meet large increases in oxygen demand only by increasing coronary blood flow (vasodilation; adenosine = effector by lower intracellular calcium);

Question 14

What are the two myocardial energy sources? Which are more prominent?

Answer 14

Glucose and fatty acids (ketones, lactate, and pyruvate); fatty acids are more prominent

Question 15

What metabolite is most important for regulating coronary blood flow?

Answer 15

adenosine (breakdown product of ATP) causes vasodilation

Question 16

What is coronary steal?

Answer 16

administration of a vasodilator to counteract ischemia may backfire as downstream vasculature may already maximally dilated (the drug only dilates other vessels and lowers the CBF to the ischemic region)

Question 17

Which blood vessels are directly attached to skeletal muscle? What is a microvascular unit?

Answer 17

Transverse arterioles and terminal arterioles (last vessel with VSMCs) are attached to skeletal muscle (1st and 2nd order arterioles are in the periphery); The group of capillaries supplied by a terminal arteriole represents one microvascular unit

Question 18

What is the mechanism for rapid vasodilation of skeletal muscle?

Answer 18

The rapid vasodilation that occurs with skeletal muscle activation is initiation by K-mediated hyperpolarization of VSMCs

Question 19

Since most skeletal muscles are controlled by sympathetic tone, what counteracts vasoconstriction during exercise?

Answer 19

1. redistribution of blood supply 2. metabolic demand counteracts sympathetic tone 3. flow to splanchnic system is reduced 4. venous return increases due to the muscle pump in the lower extremities and abdomen

Question 20

Is the muscle pump activated during isometric contraction?

Answer 20

No

Question 21

Describe the vascular anatomy of the splanchnic circulation.

Answer 21

most of the system is supplied by the celiac artery (superior mesenteric artery supplies intestines; the distal 2/3 of the colon are supplied by the inferior mesenteric artery); the liver receives blood from the portal vein and hepatic artery and drains into hepatic vein; Arterioles run along the muscularis layer (branch into arterioles at submucosal layer and branch into capillaries at the villus)

Question 22

An increase in portal venous pressure results in what?

Answer 22

ascites (edema); remember that blood flows from high to low pressure

Question 23

Describe counter-current exchange.

Answer 23

movement of oxygen from the arterioles to the venules before the arteriovenous villi tip (predisposition from ischemia)

Question 24

What are causes for increased splanchnic blood flow?

Answer 24

Active transport of nutrients across epithelium increases metabolic activity(decrease oxygen, increase CO2 and adenosine), causing vasodilation; the uptake of nutrients in the villus vessels results in hyperosmolality and increases blood flow; During digestion, locally produced hormones and kinins cause vasodiliation (cholecystokinin and neurotensin) (increase sequentially during a meal and blood flow is sustained for a few hours)

Question 25

How does the splanchnic system remain viable with decreased blood flow during exercise?

Answer 25

Preservation of intestinal viability in response to decreased blood flow requires increased oxygen extraction. If this is insufficient, necrosis & sloughing of tips of villi occurs (sepsis)

Question 26

What uptakes lipophilic molecules in the splanchnic circulation?

Answer 26

lacteals

Question 27

What is apical skin?

Answer 27

glomus bodies (arteriovenous anastomoses) in the nose, lips, ears, hands, and feet

Question 28

does the epidermis have a direct blood supply?

Answer 28

no

Question 29

What happens to cutaneous blood vessels when the skin is directly heated? when body temperature rises?

Answer 29

dilate; also dilate

Question 30

what is the mechanism of sympathetic tone in response to a decrease in core body temperature?

Answer 30

vasoconstriction of the glomus bodies (noepinephrine; no active vasodilation in glomus bodies)

Question 31

What is the proposed mechanism of vasodilation of nonapical tissue?

Answer 31

sympathetic acetylcholine stimulates sweat glands, causing secretion of sweat and release of kinins (bradykinin) which cause vasodilation; alternate method: sympathetic acetlycholine stimulates vasoactive intestinal peptide and calcitonin gene-related peptide

Question 32

What happens to the cutaneous vasculature following scratching of skin?

Answer 32

1. activation of histamine 2. reinforced by neural parasympathetic vasodilation (wheal: local edema from increased capillary permeability)

Question 33

Of the endocrine factors, which drives a decrease in blood pressure when released? increase in blood pressure?

Answer 33

atrial natriuretic peptide & NO; endothelin, angiotensin, NE, E, and antidiuretic hormone

Question 34

An elderly patient of generally good health has complained of feeling faint upon getting out of bed in the morning. Which would not be on your list of things to try at home?

Answer 34

sleep with head below the legs (sleeping with head raised above legs can induce a compensatory response)

Question 35

The fight-or-flight response and vasovagal syncope vary in their physiological outcomes, but share what?

Answer 35

vasopressin release and cortical stimulation

Question 36

A healthy patient undergoes a non-cardiac procedure, but has sedentary for several weeks. The patient’s rehabilitation includes an exercise regimen. Upon exercising, cardiac output will increase rapidly. Why?

Answer 36

increase in heart rate (and contractility)

Question 37

During irreversible hemorrhage, the failure of the capillary refill directly results in what?

Answer 37

hemoconcentration

Question 38

What is orthostasis?

Answer 38

response to a rapid change in blood pressure as a result of getting up from a recumbent position

Question 39

What is orthostasis? Describe it. What does an individual not faint or what might induced fainting?

Answer 39

response to a rapid change in blood pressure as a result of getting up from a recumbent position; Move to upright position → fluid shift from thorax to legs → decreased venous return → decreased right atrial pressure → decrease in stroke volume → decrease in cardiac output; LE vessels are stiffer (also non-uniform distribution of blood); increased body temperature results in vasodilation to extremities and thus a greater effect associated with orthostasis

Question 40

What is the body’s response to orthostasis?

Answer 40

high pressure baroreceptor reflex → increase in sympathetic output → increase in vascular tone, heart rate, and contractility → MAP returns to normal; plus skeletal muscle pump

Question 41

What happens during the fight-or-flight response?

Answer 41

skeltal: activation of sympathetic cholinergic neurons → increase blood flow; release of epinephrine → beta2 receptor → vasodilation → increase in blood flow; muscle metabolites → vasodilation → increase in blood flow; reduced splanchnic blood flow; venous constriction (increase MAP and cardiac output);

Question 42

What is vasovagal syncope? Describe the Bezold-Jarisch reflex.

Answer 42

neurally-mediated response to psychological (or pharmacological) stimulus to cause transient drop in cerebral perfusion; Vagal afferents carry signals to higher CNS centers, which act through autonomic nuclei in the medulla to massively stimulate parasympathetic system & abolition of sympathetic tone. (bradycardia, hypotension or decrease MAP, and hypoventilation; also inefficient high pressure baroreceptor response)

Question 43

Describe the early response to exercise.

Answer 43

(mediated by CNS) Increase in heart rate and contractility; decreased blood flow to inactive muscle splanchnic regions; transient decrease in blood flow to skin; ­cholinergic sympathetic vasodilator fibers innervate vascular smooth muscle cells & skeletal muscle & peripheral vasodilation (TPR) in active skeletal muscle

Question 44

Describe the late response to exercise.

Answer 44

exercise pressor reflex: In peripheral skeletal muscles, chemically- and mechanically sensitive receptors monitor the concentration of waste products and the amount of tension within muscle tissue. Thus, the receptors detect the intensity of exercise in a working muscle. Type III and IV afferent fibres carry this message from the muscles to the dorsal horn of the spinal cord, where ascending neurons relay the message to autonomic control centres in the medulla. Subsequently, autonomic nerves travel down from the brainstem and elicit coordinated changes that increase the oxygen supply to working muscles; arterial baroreflexes: resetting of high pressure baroreceptors; increaesed venous return; histamine increases capillary filtration; increase in sweat production and blood flow to cutaneous circulation; epinephrine increases cardiac output

Question 45

What reflexes are active to increase MAP during hemorrhage?

Answer 45

high pressure baroreceptor; low pressure baroreceptors (decreased blood flow to kidney); peripheral chemoreceptors; Central chemoreceptors (in the brain sense low pH): brain ischemia (from hypovolemic shock) lowers pH increasing sympathetic output; capillary refill

Question 46

What are signs of irreversible blood loss? Why does this happen?

Answer 46

MAP below 70; Faintness, weak pulse, cold & moist skin, oliguria; failure of vasoconstrictor response, failure of capillary refill response, and failure of either or both the cardiac response and sympathetic tone (CNS)

Question 47

What other organs function to stabilize blood flow during hemorrhage?

Answer 47

brain (thirst); liver (albumin production); kidney (salt and water conservation)

Question 48

What is the result of myocardial acidosis?

Answer 48

reduces calcium and contractility

Question 49

Which three organs’ actions can reduce blood volume?

Answer 49

breathing (expiration); skin (sweat); kidney (urine)

Question 50

What hormone is released in the low pressure baroreceptor reflex?

Answer 50

atrial natrieretic peptide