ANP 1115 - The Heart (Pt. 3) & Blood Vessels Flashcards
What is the Frank Starling Law?
Within defined limits, the heart will pump whatever volume of blood it receives
What is Preload?
The degree to which cardiac muscle cells are stretched just before they contract
- how much ventricles are being filled
What does the Frank Starling Mechanism ensure?
FS mechanism ensures that each ventricle pumps same volume over a period of time
What is Afterload?
Pressure that ventricles must overcome to force open valves & eject blood from heart
What are the effects of Hypertension?
Reduces the ability of ventricles to eject blood leading to increased ESV and decreased SV
- decreased blood being pumped
What are the Effects of Chronically elevated blood pressure on cardiac muscle cells themselves?
- Heart works harder all the time due to constant high pressure
- Continuous pumping
- Cardiac muscle get worn out and eventually lead to heart failure
What are the effects of physical training on Chronic Disease?
- increase pressure during extensive activities
- heart gets stronger because it has down time during rest
What are the effects of Pulmonary Stenosis?
- Valves don’t fully open
- Heart has to work harder to compensate for leaky valves
- heart becomes exhausted
What is the difference between Arteries and Veins?
- Arteries carry blood away from the heart
- Veins carry blood toward the heart
- Only capillaries directly serve cells
What are the Three types of Arterial Vessels?
- Elastic (Conducting) Arteries
- Muscular (Distributing) Arteries
- Arterioles
What are Elastic (Conducting) Arteries?
- thick-walled, large-diameter arteries near heart
- highest proportion of elastin
- smooth out pressure fluctuations (stretch & recoil)
- recoil helps maintain pressure & flow of blood
What are Muscular (Distributing) Arteries?
- deliver blood to specific organs
- more smooth muscle than elastin
- finite blood to send to where it’s most needed
What are Arterioles?
- 10 μm to 0.3 mm diameter
- tunica media primarily smooth muscle
- a single layer in smallest arterioles
- arterioles determine which capillary beds are flushed, minute-to-minute
What are the Three types of Capillaries?
- Continuous
- Fenestrated
- Sinusoidal
What are Continuous Capillaries?
- skin, muscle, brain
- endothelial cells linked by tight junctions providing an uninterrupted lining
- except for in CNS, there are intercellular clefts that allow
limited passage of fluids, small solutes
What are Fenestrated Capillaries?
endothelial cells riddled with pores (fenestrations)
- increased permeability to fluids/small solutes
- small intestine (absorption), endocrine organs (protein hormone), kidney (filter waste out + reabsorption)
What are Sinusoidal Capillaries?
highly modified, leaky capillaries
- liver, bone marrow, lymphoid tissues, endocrine organs
- large, irregular lumens & usually fenestrated
- fewer tight junctions & large intercellular clefts for passage of proteins, RBCs
What is Microcirculation?
flow of blood from an arteriole to a venule through a capillary bed
What is the Flow through Capillary Bed regulated by?
Flow through a capillary bed is regulated by the diameter of the terminal arteriole
What are Venules?
- 8-100 μm diameter
- post capillary venules = just endothelium + a few fibroblasts
- larger venules have a couple of layers of smooth muscle & thin tunica adventitia
What are Veins?
- 3 tunics but walls thinner & lumens larger
- less smooth muscle in tunica media than in corresponding artery and minimal elastin
- tunica adventitia is heaviest layer
- up to 65% of blood in veins at any one time = capacitance vessels or blood reservoirs
What is Blood Flow measured in?
Blood flow is measured in ml/min
- can be regulated independently for various tissues & organs
What is Blood Pressure?
force per unit area exerted on the wall of a blood vessel by its contained blood (mm Hg)
- usually refers to systemic arterial blood pressure in the largest arteries near the heart
How is Flow Calculated?
Blood Flow = (difference in blood pressure) / (peripheral resistance)
Flow = (P1 - P2) / R
What is the Major Determinant of Blood Flow?
Resistance is the major determinant of blood flow because a decrease in blood vessel radius increases resistance to the 4th power
What can the Regulation of Arteriole Diameter allow?
Arterioles can regulate their diameters allowing for very quick and effective changes in resistance to flow
What is Resistance?
- measures total of frictional forces that impede flow
- flow & resistance are inversely related
What is Resistance influenced by?
Blood Viscosity (ƞ): due to formed elements, plasma proteins
Bessel Length (L): more length = more resistance
Vessel Diameter (D): can be regulated; fluid not touching walls moves faster
What is Pulse Pressure?
systolic bp - diastolic bp
- indicates vigor of contraction of ventricle
- provides info on elasticity of aorta & major arteries
What is Mean Arterial Pressure (MAP)?
diastolic pressure + 1/3 pulse pressure
- MAP is the pressure that propels blood to tissues during the cardiac cycle
- MAP & pulse pressure decrease with distance from heart
- by end of arterial tree, blood flow is steady & pulse pressure has disappeared
What is Venous Blood Pressure?
steady, changes very little during cardiac cycle (gradient only ~15 mm Hg)
- there is a gradient and veins provide more open pathways so blood will keep moving forward
What are the three factors that Aid in Venous Return?
(i) Venous valves plus muscular pump: physical activity
(ii) Respiratory pump: inhalation
(iii) Sympathetic venoconstriction: squeeze blood by 60% to propel forward
- all three increase SV
What is a Pulse and why is it called pressure points?
pressure wave due to alternating expansion & recoil of elastic arteries
- called pressure point because compression can reduce blood flow
Where is Blood Pressure measured?
usually measured in the brachial artery
- 2 values that reflect stage of cardiac cycle
What is Blood Pressure influenced by?
Influenced by age, gender, weight, race, stress, nutrition, mood, posture, fitness
What is Short Term Regulation of Blood Pressure?
work with total peripheral resistance (blood vessel diameter) and cardiac output
What is Long Term Regulation of Blood Pressure?
work with blood volume
- adjustments made at level of kidneys
What are the two main goals of Short-Term Neural & Chemical Mechanisms?
(i) alter blood distribution to respond to specific demands
(ii) maintain adequate MAP by altering blood vessel diameter
What do Reflex Arcs involve?
usually reflex arcs involving baroreceptors, vasomotor centre of medulla, vascular smooth muscle
Where are the Clusters of Sympathetic Neurons found?
cluster of sympathetic neurons in medulla: part of cardiovascular centre
What is Vasomotor Tone?
constant output, especially to arterioles (NE)
What does the Cardiovascular Centre respond to?
cardiovascular centre (including the vasomotor centre) responds to input from:
(i) baroreceptors
(ii) chemoreceptors (CO2, O2, H+)
(iii) higher brain centres or hormones
Where are Baroreceptors located?
baroreceptors located in:
- carotid sinuses (blood flow to brain)
- aortic arch (blood flow to rest of systemic circulation)
- other large arteries of neck & thorax
What happens to Baroreceptors when MAP is increased?
increasing MAP stretches receptors; response (via vasomotor centre) is:
(i) dilation of arterioles
(ii) venodilation to shift blood to venous reservoirs
(iii) afferents also to cardiac centres to stimulate parasymp ns & inhibit symp ns, thereby decreasing heart rate & contractile force
decreasing MAP initiates the opposite responses
What is the Goal of Baroreceptor-Initiated Reflexes?
protect against short-term changes in bp (standing, bending); ineffective chronically (e.g. body adapts to hypertension)
What is Orthostatic Hypotension?
Lightheaded due to insufficient blood flow to brain
- getting up too quick
What are Chemoreceptor-Initiated Reflexes?
drop in O2, pH or rise in CO2: chemoreceptors in aortic arch & large arteries of neck to vasomotor centre »» reflex vasoconstriction
- results in rise in bp that speeds return of blood to heart & lungs
- more important in regulating respiration than blood pressure
What is the Influence of Higher Brain Centres?
“fight-or-flight”, stress, exercise
- cerebral cortex & hypothalamus get involved because you are aware
What is the Regulation of BP wrt Adrenal Medulla Hormones?
NE/E & fight-or-flight
(a) generalized vasoconstriction (except skeletal/cardiac muscle)
(b) increase CO
What is the Regulation of BP wrt Angiotensin II?
renin-angiotensin system; decreased renal perfusion
(a) intense generalized vasoconstriction to increase systemic bp
(b) release of aldosterone, ADH that will lead to long-term regulation
What is the Regulation of BP wrt Atrial Natriuretic Peptide (ANP)?
produced by atria of heart when bp elevated
(a) blood pressure to decrease via generalized vasodilation
What is the Regulation of BP wrt Antidiuretic Hormone (ADH)?
source = hypothalamus/posterior pituitary
(a) primarily long-term regulation
(b) not usually important in short term unless bp drops very low – then much more ADH is released, and high levels can cause vasoconstriction
What is the Role of the Kidneys in Long-Term Regulation?
kidneys adjust blood volume – a more complete response but it takes time
- anything that changes blood volume will change blood pressure
E.g., if blood volume increases, kidneys respond by unloading salt & water
What is the Direct Action of Kidneys on Long-Term Regulation?
increased blood volume/pressure causes increased rate of filtrate formation
- insufficient time to reclaim water leads to increased volume of urine
What is the Indirect Action of Kidneys on Long-Term Regulation?
renin-angiotensin system
- if MAP decreases, kidney cells release renin→ cascade of reactions to yield angiotensin II (potent vasoconstrictor)
What does Angiotensin II stimulate?
angiotensin II stimulates secretion of aldosterone (adrenal cortex)
- Aldosterone stimulates increased renal absorption of Na+ (& water if antidiuretic hormone [ADH] present)
Angiotensin II increases release of ADH → promotes water reabsorption
