Block 3 - Bsf: Special Circulations

Front 1

T/F

Skin is a large organ with a high metabolic rate.

Back 1

False!

Skin is a large organ (~10-15% of total body mass) with very low metabolic rate hence low O2 requirements.

Front 2

Skin blood flow is dominated by (sympathetic/parasympathetic) nervous system.

Are these cholinergic or adrenergic nerves?

Back 2

Sympathetic (cholinergic nerves)

Front 3

Parasympathetic vasodilator nerve fibers (do/don't) innervate the cutaneous blood vessels.

Back 3

Don't

Front 4

What are the 2 types of resistance vessels in cutaneous circulation?

Back 4

Arterioles and arteriovenous anastomosis

Front 5

What controls the arterioles in cutaneous circulation?

Back 5

Under dual control of sympathetics and local control.

Front 6

What controls the arteriovenous anastomosis in cutaneous circulation?

Back 6

Exclusively under sympathetic control.

Front 7

What does sympathetic input in the arteriovenous anastomosis of cutaneous circulation cause?

Back 7

Vasoconstriction

Front 8

T/F

Ambient and body temperature play an important role in the regulation of skin blood flow.

Back 8

True!

Front 9

An increase in body core temperature increases skin circulation primarily by what two mechanisms?

Back 9

1) ↑T increases activity of sympathetic cholinergic nerves to sweat glands. Ach leads to the breaking down of a plasma protein (kininogen) to form bradykinin. Bradykinin, formed in tissue, acts in a paracrine manner as a potent vasodilator of skin blood vessels. Bradykinin also increases release of NO.

2) Amount of flow through anastomosis is a reflex that can be activated by tmeperature receptors or higher brain center of the CNS so that an ↑T causes vasodilation of skin vessels via reflexes.

Front 10

Counter-current exchange in skin helps maintain what?

Back 10

Temperature

Front 11

Blood flow in skeletal muscle varies directly with what 2 properties?

Back 11

Contractile activity of tissue and skeletal muscle type.

Front 12

Which type of skeletal muscles ("red" slow or "white" fast) have greater capillary density and flow?

Back 12

"Red" slow

Front 13

Why is total flow through resting skeletal muscle very low (1.4 – 4.5 mL/min/100g)?

Back 13

Because pre-capillary arterioles exhibit asynchronous, intermittent contraction and relaxation so that at any given time, only a small fraction of the muscle is perfused.

Front 14

During extreme physical exertion, more than 80% of cardiac output can be directed towards what?

Back 14

Contracting skeletal muscles.

Front 15

During exercise, what becomes the primary determinant of systemic vascular resistance?

Back 15

Skeletal muscle resistance.

Front 16

T/F

Blood flow in skeletal muscle increases only slightly with maximal vasodilation or active hyperemia.

Back 16

False!

Blood flow can increase 20x with maximal vasodilation or active hyperemia.

Front 17

Sympathetic innervation to vessels in skeletal muscle causes what?

Back 17

Vasoconstriction through alpha1 and alpha2 receptors located on the vascular smooth muscle (norepi)

Vasodilation via activation of vascular beta2 receptors (epi)

Front 18

T/F

There is evidence for vasodilation in skeletal muscle through the release of acetylcholine binding to muscarinic receptors.

Back 18

True!

(M receptors; endothelium dependent mechanism)

Front 19

At rest, what type of factors dominate skeletal muscle blood flow?

Back 19

Neural factors

Front 20

During activity, what factors dominate skeletal muscle blood flow?
Why?

Back 20

Local factors over-ride the neural vasoconstrictive response of sympathetics, due to the close coupling between oxygen consumption and blood flow.

Front 21

What local factors affect skeletal muscle blood flow?

Back 21

Tissue hypoxia, adenosine, K+, CO2, H+, and nitric oxide.

Front 22

What is the term for when local regulatory mechanisms override the sympathetic vasoconstrictor influences in skeletal muscle?

Back 22

Functional sympatholysis

Front 23

When can skeletal muscle blood flow be significantly decreased?

Back 23

By extravascular compression that occurs during strong muscular contractions, especially during sustained tetanic contractions.

Front 24

Coordinated, rhythmical contractions (e.g., running) enhance blood flow to skeletal muscle by what mechanism?

Back 24

Skeletal muscle pump mechanism

Front 25

During intermittent contraction, arterial inflow is (restricted/enhanced), and venous outflow is (restricted/enhanced).

Back 25

Restricted, enhanced

Front 26

During intermittent (phasic) skeletal muscle contraction, skeletal muscle arterial inflow is (decreased/increased) during contraction and (decreased/increased) during relaxation.

Back 26

Decreased, increased

Front 27

Why is the volume of blood and extravascular fluid in the brain fairly constant?

Back 27

Because of the confinement of the cranium.

Front 28

Rate of cerebral flow is (constant/fluctuating).

Back 28

Relatively constant. ~55mL.min/100g.

Front 29

Which organ is the least tolerant of ischemia?

Back 29

The brain. Interruption of flow for as little as 5 sec leads to unconsciousness.

Front 30

T/F

Cerebral vessels are innervated strongly by cranial sympathetics.

Back 30

False!

Cerebral vessels are innervated by cranial sympathetics, however neural regulation is very weak.

Front 31

Cerebral vessels are VERY sensitive to CO2 tension. What happens with changes in CO2?

Back 31

Increases in PaCO2 elicit vasodilation.
CO2 evokes changes by altering perivascular pH:
CO2 + H2O ↔H2CO3↔ HCO3- + H+
(in brain = high CO2 concentration)

Front 32

Distribution of cerebral flow is predominately regulated by what type of factors?

Back 32

Local metabolic factors

Front 33

What are examples of stimuli that affect cerebral flow?

Back 33

Touch, pain, hand motion, talking, reading, reasoning, and problem solving.

Front 34

T/F

Kidneys have high metabolic demand and use most of the O2 that is delivered.

Back 34

False!

Kidneys have high metabolic demand but use only about 10% of the O2 that is delivered.

Front 35

Due to high hydrostatic pressure in renal capillaries, about what percent of plasma that enters the capillaries is filtered?

Back 35

About 20%

Front 36

In renal flow, which type of regulation dominates?

Back 36

Autoregulation

Front 37

The myogenic mechanism in renal circulation (intrinsic property of vascular smooth muscle), responds to alterations in what?

Back 37

Stretch

Front 38

Tubuloglomerular feedback in renal circulation:
Flow of renal fluid is detected by a)__________ of b)_______________ and sends a signal to the afferent arterioles to restore normal renal blood flow and c)_____________.

Back 38

a) Macula densa
b) juxtraglomerular apparatus (JGA)
c) glomerular filtration rate

Front 39

In renal circulation, if blood flow (and hence GFR) is reduced, what does the JGA release?

Back 39

Renin

Front 40

Why does stimulation by sympathetics decrease renal blood flow substantially but reduces GFR only slightly?

Back 40

Because post-glomerular restriction is greater than pre-glomerular restriction.

Front 41

a) Activation of (atrial/arterial) baroreceptors increases renal vascular resistance.
b) Activation of (atrial/arterial) baroreceptor leads to only small changes.

Back 41

a) Atrial (low pressure)
b) Arterial

Front 42

Neural control of mesentaries is almost exclusively (sympathetic/parasympathetic).

Back 42

Sympathetic

Front 43

Increased sympathetic tone in splanchnic circulation causes vasoconstrion via what receptors?

Back 43

alpha-adrenergic receptors

Front 44

What is functional hyperemia in splanchnic circulation?

Back 44

Food ingestion increases blood flow. Secretion of GI hormones such as gastin and cholecystokinin (CCK) augment this response.

Front 45

T/F

Undigested food has little effect on intestinal blood flow but glucose and fatty acids enhance mesenteric hyperemia.

Back 45

True!

Level of digestion influences flow.

Front 46

Sympathetic vasoconstriction in the coronaries (overrides/is overridden by) metabolic vasodilation during sympathetic activation of the heart.

Back 46

Is overridden by

Front 47

What does hypoxia cause in pulmonary circulation?

Back 47

Vasoconstriction