Cardiovascular system: Blood vessels, blood flow, blood...
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Transcript of Cardiovascular system: Blood vessels, blood flow, 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
• 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
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
• 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
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
• 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
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
• 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
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
• 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
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
• 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
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
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 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)
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
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