PHYSIO- blood pressure and blood vessels

What are the three main components of the circulatory system?

Heart, blood vessels, and blood

What is the function of the heart in the circulatory system?

Serves as a pump that establishes the pressure gradient needed for blood to flow to tissues

What is the function of blood vessels in the circulatory system?

passageways through which blood is distributed from heart to all parts of body and back to heart

What is the function of blood in the circulatory system?

transport medium within which materials being transported are dissolved or suspended

What are the two main circulatory circuits in the body?

Pulmonary circulation and systemic circulation

what is pulmonary circulation?

closed loop of vessels carrying blood between heart and lungs

what is systemic circulation?

circuit of vessels carrying blood between heart and other body systems

Describe the circuit of blood flow

1. deoxygenated blood from the body

2. vena cava

3. right atrium

4. right ventricle

5. pumped blood from the right ventricle goes through the pulmonary artery to the lungs

6. in the lungs oxygen diffuses down concentration gradient to blood received from the right side of the heart

7. CO2 diffuses down concentration gradient into alveoli

8. lungs

9. pulmonary veins

10. left atrium

11. left ventricle

12. aorta

13. to the body

What direction does blood flow in relation to pressure?

From areas of high pressure to low pressure

What is the function of vessel radius?

major determinant of resistance to flow

What are the three main determinants of vascular resistance?

Blood viscosity, vessel length, and vessel radius

What is the difference between laminar and turbulent blood flow?

laminar is smooth and quiet, blood in the middle flows the fastest, slowest is near the walls. turbulent blood flow is chaotic and noisy, higher resistance

How does doubling the radius of a vessel affect blood flow?

Increases flow by 16 times and decreases resistance to 1/16th its previous value

What are the five types of blood vessels in the vascular tree?

Arteries, arterioles, capillaries, venules, and veins

What is the primary function of arteries?

carry blood away from heart to tissues

what are arterioles?

smaller branches of arteries

describe capillaries

smaller branches of arterioles, smallest of vessels across which all exchanges are made with surrounding cells

Arterial connective tissue contains what?

collagen fibers which provide tensile strength and elastin fibers which provide elasticity to arterial walls

What acts as a pressure reservoir to provide driving force for blood when the heart is relaxing?

arteries

Arteries are specialized to

serve as rapid transit passageways for blood from heart to organs, due to large radius they offer little resistance to flow

describe venules

formed when capillaries rejoin, return blood to heart

describe veins

formed when venules merge, return blood to heart

What does structure determines function mean in regards to arteries, veins, and capillaries?

arteries withstand pressure, veins store volume, and capillaries optimize exchange

What is blood pressure?

The force exerted by blood against vessel walls

What two factors determine blood pressure?

1. volume of blood contained within vessel

2. compliance (flexibility or distensibility) of vessel walls

what is systolic pressure?

peak pressure exerted by ejected blood (ventricular contraction) against vessel walls during cardiac systole

What is diastolic pressure?

minimum pressure in arteries (ventricular relaxation) when blood is draining off into vessels downstream

What are Korotkoff sounds?

Sounds produced by turbulent blood flow during BP measurement. sounds are distinct from heart sounds associated with valve closure

What is pulse pressure?

The pressure difference between systolic and diastolic pressure

How is pulse pressure calculated?

Systolic pressure - Diastolic pressure

What is mean arterial pressure (MAP)?

Average pressure driving blood forward into tissues throughout cardiac cycle

How is MAP estimated?

MAP = Diastolic + ⅓ (Pulse Pressure)

What vessels are called "resistance vessels"?

Arterioles, due to their small radius

Radius supplying individual organs can be adjusted independently to

1. distribute cardiac output among systemic organs, depending on body momentary needs

2. help regulate arterial blood pressure

what mechanisms are involved in adjusting arteriolar resistance?

vasoconstriction and vasodilation

What is vasoconstriction?

Narrowing of blood vessels due to contraction of smooth muscle layer

What is vasodilation?

Enlargement in circumference and radius of vessel that results from relaxation of smooth muscle layer. leads to decreased resistance and increased flow through that vessel

What is active hyperemia?

Increased blood flow due to enhanced organ activity

What is reactive hyperemia?

When blood flow is occluded, chemical changes in tissues dilates arterioles. When flow is returned, blood flow is much higher than normal.

What are some examples of specific local chemical factors that cause vessel dilation?

decreased O2, increased CO2, increased H+, increased K+, increased osmolarity, adenosine release

What cells release chemical mediators that play a key role in locally regulating arteriolar caliber?

endothelial cells

What endothelial-derived chemical causes vasoconstriction?

Endothelin

What does nitric oxide do?

1. vasodilator that increases concentration of cyclic GMP

2. activates enzyme that reduces phosphorylation of myosin

What does vascular endothelial growth factor (VEGF) do?

Stimulates new vessel growth (angiogenesis)

Explain the relationship between histamine release and myogenic response

local histamine release dilates arterioles, the myogenic response of arterioles to stretch helps tissues auto regulate their blood flow

What is autoregulation of blood flow?

Local mechanisms maintaining constant flow despite pressure changes

What nervous system extrinsically controls arterioles?

Primarily Sympathetic nerve influence

Sympathetic nerve fibers supply arteriolar smooth muscle everywhere in systemic circulation except for where?

the brain

Describe norepinephrine in regards to arterioles

Norepinephrine released from sympathetic nerve endings & binds to α₁-adrenergic receptors, leading to vasoconstriction

A decrease in sympathetic nerve fibers leads to what?

generalized vasodilation

What hormones influence arteriolar radius?

adrenal medullary hormones; epinephrine and norepinephrine

Which hormone causes vasodilation in skeletal muscle and heart?

Epinephrine via β₂ receptors

β₂ receptors are found most abundantly in what tissues?

skeletal muscles and heart tissue

Arterioles in digestive organs and kidneys only have what receptors?

α₁ receptors, causing vasoconstriction

Which hormones help regulate fluid balance by way of salt retention?

Vasopressin and angiotensin II (via RAAS)

Where is the cardiovascular control center located?

In the medulla of the brainstem

What role does the hypothalamus play in circulation?

Controls blood flow to skin to adjust heat loss to environment

What factors enhance diffusion across capillaries?

1. minimized diffusion distance

2. surface area

3. velocity of blood flow through capillaries is relatively slow

In the kidneys and intestines what allows rapid movement of fluid during urine formation and food absorption?

fenestrations

What structures control blood flow into capillary beds?

Precapillary sphincters

What is a metarteriole?

A vessel that runs between an arteriole and a venule

What is bulk flow?

large scale fluid exchange where protein free plasma filters out of the capillaries, mixes with interstitial fluid, and is reabsorbed

what is the role of bulk flow?

to regulate the distribution of ECF between plasma and interstitial fluid

What are the forces that influence bulk flow?

1. Capillary hydrostatic pressure (forces fluid OUT OF capillaries)

2. plasma colloid oncotic pressure (proteins primarily albumin, that encourages movement into capillaries)

3. interstitial fluid hydrostatic pressure (forces fluid into capillaries

4. interstitial fluid colloid oncotic pressure (rarely contributes much to bulk flow, but when it does it encourages fluid out of the capillaries)

What blood protein is highly effective as osmoles?

albumin

There is very little protein in the interstitial fluid which forms

a strong osmotic force to draw fluid into the capillaries

What is lymph?

interstitial fluid that enters a lymphatic vessel

Where does lymph ultimately drain?

Into the right lymphatic and and left lymphatic duct (aka thoracic duct) → these ducts connect to subclavian vein

What directs the flow of lymph towards venous outlet in the chest?

smooth muscle, skeletal muscle, and one way valves spaced at intervals

What are the functions of the lymphatic system?

Return of excess filtered fluid, defend against disease (lymph nodes have phagocytes which destroy bacteria filtered from interstitial fluid), transport of absorbed fat, and return of filtered protein

What is edema?

Swelling of tissues due to excessive interstitial fluid accumulation

List the causes of edema

1. reduced concentration of plasma proteins (protein loss in kidney disease, reduced protein synthesis from liver disease, etc)

2.increased permeability of capillary wall (histamine induced widening of capillary pores)

3. increased venous pressure (lack of skeletal muscle use)

4. blockage of lymph vessels (filariasis is a mosquito borne parasite that blocks lymph vessels and causes elephantiasis)

Why are veins called "capacitance vessels"?

they have large radius that offers little resistance to blood flow and serve as a blood reservoir

What enhances venous return?

sympathetic activity on venous return (causes vasoconstriction), skeletal muscle activity on venous return (venous valves are one way), countering effects on gravity on the venous system (respiratory activity pulls venous blood to heart, cardiac suction on venous return (creates negative pressure drawing blood into heart from venous system)

What does the respiratory pump counteract?

counteracts gravity effect on venous return

What are the two primary determinants of mean arterial blood pressure?

Cardiac output (CO) and total peripheral resistance (TPR)

What is the formula for MAP?

MAP = CO × TPR

What receptors detect changes in MAP?

Baroreceptors within circulatory system

What are the short term control adjustments of MAP?

adjustments made by alterations in CO and TPR, mediated by means of ANS influences on heart, veins, and arterioles

What are the long term control adjustments of MAP?

involves adjusting total blood volume by restoring normal salt and water balance through mechanisms that regulate urine output and thirst

What helps regulate the long-term control adjustments of MAP?

hypothalamus, Vasopressin and angiotensin II, renin-angiotensin-aldosterone system (RAAS)

What are the most important baroreceptors involved in the baroreceptor reflex?

carotid sinus and aortic arch baroreceptors

What are the additional reflexes and responses that influence blood pressure?

1. left arterial receptors and hypothalamic osmoreceptors- control plasma volume

2.chemoreceptors in carotid and aortic arteries are sensitive to low O2 or high acid levels in blood-reflexively increase respiratory activity

3. cardiovascular responses associated with certain behaviors and emotions mediated through cerebral cortex-hypothalamic pathway

4. hypothalamus controls skin arterioles for temperature regulation

5. exercise modifies cardiac responses

What are two types of hypertension?

Primary (essential) and secondary

What complications can result from chronic hypertension?

congestive heart failure, stroke, heart attack, spontaneous hemorrhage, renal failure, retinal damage

What is orthostatic hypotension?

Transient hypotensive condition resulting from insufficient compensatory responses to gravitational shifts in blood when person moves from horizontal to vertical position

What is circulatory shock?

occurs when blood pressure falls so low that adequate blood flow to the tissues can no longer be maintained.

What are the four main types of shock?

Hypovolemic, cardiogenic, vasogenic, and neurogenic