Cardiovascular system: Blood vessels, blood flow, blood ...libvolume6.xyz/.../physicsofcardiovascularsystempresentation1.pdfOutline • 1-Physical laws governing blood flow and blood

Cardiovascular system: Blood

vessels, blood flow, blood pressure

Outline

• 1- Physical laws governing blood flow and blood pressure

• 2- Overview of vasculature

• 3- Arteries

• 4. Capillaries and venules

• 5. Veins

• 6. Lymphatic circulation

• 7. Mean arterial pressure and its regulation

• 8. Other cardiovascular regulatory processes

Outline



• 3- Arteries


• 5. Veins




Physical laws governing blood flow and blood

pressure

• Flow of blood through out body = pressure gradientwithin vessels X resistance to flow

- Pressure gradient: aortic pressure – central venous pressure

- Resistance:

-- vessel radius

-- vessel length-- blood viscosity

Factors promoting total peripheral resistance

(TPR)

• Total peripheral

resistance = TPR

-- combined resistance of

all vessels

-- vasodilation �

resistance decreases

-- vasoconstriction �

resistance increases

Outline



• 3- Arteries


• 5. Veins




Vasculature

Arteries and blood pressure

• Pressure reservoir

• Arterial walls are able to

expand and recoil

because of the pressure of elastic fibers in the

arterial wall

• Systolic pressure: maximum pressure

occurring during systole

• Diastolic pressure:

pressure during diastole

Figure 14.8

Arterial blood pressure

Blood pressure values: what do they mean?

• Pulse pressure:

PP = SP-DP

• Mean arterial blood pressure = MABP

• MABP = SBP + (2XDBP)

3

CO = MABP = SV x HR

TPR

Figure 14.15

• Blood flow within each organ changes with body activities

• Reminder: The ANS controls blood flow to the various organs

Outline



• 3- Arteries


• 5. Veins




Capillaries

• Allow exchange of gases, nutrients and wastes between blood and tissues

• Overall large surface area and low blood flow

• Two main types:

- continuous capillaries: narrow space between cells �permeable to small or lipid soluble molecules

- fenestrated capillaries: large pores between cells�large molecules can pass

Local control of blood flow in capillaries

• Presence of precapillary

sphincters on the arteriole

and beginning of

capillaries

• Metarteriole: no sphincter

� continuous blood flow � controls the amount of

blood going to

neighboring vessels

Movement of materials across capillary walls

• Small molecules and lipid soluble molecules move by diffusion through the cell membrane

• Larger molecules, charged molecules must pass through membrane channels, exocytosis or in between 2 cells

• Water movement is controlled by the capillary hydrostatic and osmotic pressures

Forces controlling water movement• Arterial side of the capillary:

– High capillary hydrostatic pressure (BHP), lower capillary osmotic pressure (BOP, due to proteins and other molecules in the blood) � Net filtration pressure pushes fluid from the blood toward the tissue (but the proteins remain in the capillary

• Venous side of the capillary:

- Lower hydrostatic pressure (due to resistance) and higher capillary osmotic pressure � Net filtration pressure moves fluid back toward the capillary

• Interstitial fluid hydrostatic (IFHP) and osmotic pressures (IFOP) remain overall identical

Fluid movement in the capillary

• Arteriole side: fluid moves toward the tissues

• Venous side: fluid reenters the capillary

• Overall: for every 1 liter of fluid entering the tissues, only 0.85 l reenter the capillary

• The remaining 0.15 l is reabsorbed as lymph by lymphatic capillaries and eventually returned back to blood circulation

• When this system fails: Edema

Causes of edema

• Increased hydrostatic

blood pressure

- heart failure (left or right),

- excess fluid in the blood

• Decreased blood osmotic

pressure

– Liver, kidney diseases,

malnutrition (kwashiorkor),

burn injuries

• Increased interstitial

hydrostatic pressure

(lymphatic capillary

blockage)

- breast cancer surgery,

elephantiasis

• Leaking capillary wall

- histamine release during

allergic reaction

Outline



• 3- Arteries


• 5. Veins




Veins• Veins are blood volume reservoir

• Due to thinness of vessel wall � less resistance to stretch = more compliance

Factors influencing venous return

• 1- Skeletal muscle pump

and valves �

• 2- Respiratory pump

• 3- Blood volume

• 4- Venomotor tone

Outline



• 3- Arteries


• 5. Veins




Lymphatic circulation

• Driven by factors similar to venous circulation:

- muscle activity

- valves

- respiration

• Lymph = plasma-proteins

• Lymphatic circulation collects fluid not reabsorbed by the capillaries

• Lymph is filtered in nodes before return to blood circulation

Outline



• 3- Arteries


• 5. Veins




Mean arterial pressure and its

regulation

• Regulation of blood flow in arteries

- Intrinsic control

- Extrinsic control

-- Neural control

-- Hormonal control

* Control of blood vessel radius

* Control of blood volume


regulation


- Intrinsic control

- Extrinsic control

-- Neural control

-- Hormonal control



Regulation of blood flow in arteries

• It is important to adjust blood flow to organ needs � Flow of blood to particular organ can be regulated by varying resistance to flow (or blood vessel diameter)

• Vasoconstriction of blood vessel smooth muscle is controlled both by the ANS and at the local level.

• Four factors control arterial flow at the organ level:

- change in metabolic activity

- changes in blood flow

- stretch of arterial smooth muscle

- local chemical messengers

Intrinsic control of local arterial blood flow

• Change in metabolic

activity

– Usually linked to CO2 and

O2 levels (↑ CO2 �

vasodilation �↑ blood flow)

intrinsic control

• Changes in blood flow

- decreased blood flow �

increased metabolic wastes �

vasodilation

• Stretch of arterial wall =

myogenic response

- Stretch of arterial wall due to

increased pressure � reflex

constriction

• Locally secreted

chemicals can promote vasoconstriction or most

commonly vasodilation

- inflammatory chemicals,

(nitric oxide, CO2)


regulation


- Intrinsic control

- Extrinsic control

-- Neural control

-- Hormonal control



Extrinsic control of blood pressure

• Two ways to control BP:

- Neural control

- Hormonal control

** Use negative feedback

Control of blood pressure

• Importance: Blood pressure is a key factor for providing blood (thus oxygen and energy) to organs. SBP must be a minimum of 70 to sustain kidney filtration and adequate blood flow to the brain

• CO= HR X SV = MABP/TPR �

MABP= HRxSVxTPR � heart rate, stroke volume

and peripheral resistance affect MABP

• Main factors controlling BP: - Blood volume

- Blood vessel radius

Neural control of BP - 1

• Baroreceptors: carotid and aortic sinuses sense the blood pressure in the aortic arch and internal carotid � send signal to the vasomotor center in the medulla oblongata

• Other information are sent from the hypothalamus, cortex

• �

Neural control of BP - 2

• The vasomotor center integrates all these information

• The vasomotor sends decision to the ANS center:

- Both parasympathetic and sympathetic innervate the S/A node � can accelerate or slow down the heart rate

- The sympathetic NS innervates the myocardium and the smooth muscle of the arteries and veins � promotes vasoconstriction

Hormonal control of BP

• Hormones can control blood vessel radius and blood volume, stroke volume and heart rate

• On a normal basis, blood vessel radius and blood volume are the main factors

• If there is a critical loss of pressure, then the effects on HR and SV will be noticeable (due to epinephrine kicking in)

• Control of blood vessel radius

- Epinephrine

- Angiotensin II

- Vasopressin (?)

• Control of blood volume

- Anti-diuretic hormone (vasopressin)

- Aldosterone

• Control of heart rate and stroke volume

- Epinephrine

Control of blood vessel radius

• Epinephrine: secreted by the adrenal medulla and ANS reflex � increase HR, stroke volume and promotes vasoconstriction of most blood vessel smooth muscles.

• Angiotensin II � promotes vasoconstriction

• Angiotensin II secretion:

- Decreased flow of filtrate in kidney tubule is sensed by the Juxtaglomerular apparatus (a small organ located in the tubule) � secretion of renin

- Renin activates angiotensinogen, a protein synthesized by the liver and circulating in the blood �angiotensin I

- Angiotensin I is activated by a lung enzyme, Angiotensin-Activating Enzyme (ACE), �angiotensin II

- Angiotensin II is a powerful vasoconstricted of blood vessel smooth muscles

Control of blood volume

• Anti-diuretic hormone = ADH

- Secreted by the posterior pituitary in response to ↑blood osmolarity (often due to dehydration)

- Promote water reabsorption by the kidney tubules � H2O moves back into the blood �less urine formed

Control of blood volume

• Aldosterone:- Secretion by the adrenal cortex

triggered by angiotensin II

- Promotes sodium reabsorption by the kidney tubules (Na+

moves back into the blood)

- H2O follows by osmosis

- Whereas ADH promotes H2O reabsorption only (in response to dehydration), aldosterone promotes reabsorption of both H2O and salt (in response to ↓ BP)

Clinical application: Shock

• Stage I: reversible, compensated shock

• Stage II: reversible, noncompensated shock

• Stage III: irreversible shock

• Death

• Stage I: Body reacts to maintain BP � ↑HR, vasoconstriction..� BP remains within normal range

• Stage II: Body reacts to maintain BP � ↑HR, vasoconstriction..� BP drops below adequate range (SBP 70). Can be reversed by medical treatment

• Stage III: Body is fighting to maintain adequate BP without success � HR is very high � not enough O2 for cardiac, brain cells to survive � damages. Cannot be reversed by medical treatment

Cardiovascular system: Blood vessels, blood flow, blood ...libvolume6.xyz/.../physicsofcardiovascularsystempresentation1.pdfOutline • 1-Physical laws governing blood flow and blood

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