Lecture 7 Flashcards Preview

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Flashcards in Lecture 7 Deck (32):

Overall function of cardiovascular
system and blood flow in
general is affected by

Blood Pressure
Venous Return
Velocity and Volume


definition blood pressure:

force exerted by circulating blood on the walls of blood vessels


Systolic pressure:

BP during ventricular systole


Diastolic pressure:

BP during ventricular diastole


Normal value:

young adult: 120/75 mm Hg


Pulse pressure:

systolic - diastolic
important measure of stress exerted on small arteries



Factors that determine systemic vascular resistance
Blood viscosity
Vessel length
Radius – subject to change = changes in flow
Laminar flow


Venous Return

Pressure gradient
7-13 mm Hg venous pressure towards heart
venules (12-18 mm Hg) to central venous pressure (~5 mm Hg)
Gravity drains blood from head and neck
Skeletal muscle pump in the limbs
Thoracic pump (respirator)
inhalation - thoracic cavity expands (pressure ) abdominal pressure , forcing blood upward
central venous pressure fluctuates
2mmHg- inhalation, 6mmHg-exhalation
blood flows faster with inhalation


Exercise increases venous return in many ways

heart beats faster, harder - increases cardiac output (CO) and BP
vessels of skeletal muscles, lungs and heart dilate increases flow
increases respiratory rate increases action of thoracic pump
increases skeletal muscle pump


Venous pooling occurs with inactivity

venous pressure not enough force blood upward
with prolonged standing, CO may be low enough to cause dizziness or syncope
prevented by tensing leg muscles, activate skeletal m. pump
Jet pilots wear pressure suits


It is important to adjust blood flow to organ needs

Flow of blood to
particular organ can be regulated by varying resistance to flow


Vasoconstriction of blood vessel smooth muscle is controlled

both by the
autonomic nervous system 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


Importance of BP:

is a key factor for providing blood (thus oxygen
and energy) to organs. Systolic pressure must be at least 70 to sustain kidney
filtration and adequate blood flow to the brain


Role of Cardiovascular center

Collection of nuclei that affect rate, force, vessel diameter
help regulate heart rate & stroke volume
specific neurons regulate blood
vessel diameter - sympathetic
vasomotor nerves
Signals sent out through vagus
(parasympathetic) –
lowers heart rate



carotid and aortic sinuses sense the blood pressure in the aortic arch and internal carotid then send signal to the vasomotor center in the medulla oblongata
Other information are sent from the hypothalamus, cortex


Chemoreceptor Reflexes

activated by hypoxia, hypocapnia, and acidosis are located in the aortic arch and carotid sinus.


chemoreceptor reflexes Stimulated during

asphyxia and severe hypotension.


chemoreceptor reflexes changes

breathing, and include sympathetic constriction of (mainly skeletal muscle) arterioles and tachycardia resulting indirectly from the increased lung inflation.


chemoreceptor reflexes effects help maintain

the blood flow to the brain at arterial pressure too low to activate the baroreceptors.


The Kidney

Monitor blood pressure and take corrective action if it should drop.
Leads to a cascade of events eventually producing angiotensin II


Angiotensin II

constricts the walls of arterioles closing down capillary beds;
stimulates the proximal tubules in the kidney to reabsorb sodium ions;
stimulates the adrenal cortex to release aldosterone. Aldosterone causes the kidneys to reclaim still more sodium and thus water
stimulates the pituitary to release the ADH


The Heart

A rise in blood pressure stretches the atria of the heart, triggers release of atrial natriuretic peptide (ANP).
ANP lowers blood pressure
The effects on the kidney reduce the reabsorption of water = increase flow of urine - the net effect = reduce blood pressure by reducing the volume of blood in the system.


The Adrenal Glands

Epinephrine & norepinephrine
increases heart rate & force of contraction
causes vasoconstriction in skin & abdominal organs
vasodilation in cardiac & skeletal muscle


Autoregulation of Blood Pressure

Physical changes and chemical mediators that induce responses through vascular smooth muscles in various tissues
Local factors cause changes in each capillary bed
autoregulation is ability to make these changes as needed by demand for O2 & waste removal
important for tissues that have major increases in activity (brain, cardiac & skeletal muscle)
Local changes in response to physical changes
warming & decrease in vascular stretching promotes vasodilation
Vasoactive substances released from cells alter vessel diameter
(K+, H+, lactic acid, NO)
systemic vessels dilate in response to low levels of O2
pulmonary vessels constrict in response to low levels of O2



Constriction of arterioles leading to resistance in blood flow and strain on the heart
chronic resting BP > 140/90
can weaken small arteries and cause aneurysms
Increased heart size, lower blood volume, chest pain



chronic low resting BP
caused by blood loss, dehydration, anemia


Shock and Homeostasis

Any state where cardiac output insufficient to meet metabolic needs (inadequate cardiac output = not enough O2 to meet metabolic needs)
cardiogenic shock - inadequate pumping of heart
low venous return (LVR) shock - 3 principle forms
1. hypovolemic shock - most common
loss of blood volume: trauma, burns, dehydration
2. obstructed venous return shock
tumor or aneurysm
3.venous pooling (vascular) shock


Venous pooling (vascular) shock

long periods of standing, sitting or widespread vasodilation
neurogenic shock - loss of vasomotor tone, vasodilation
causes from emotional shock to brainstem injury


Septic shock

bacterial toxins trigger vasodilation and increases capillary permeability


Anaphylactic shock

severe immune reaction to antigen, histamine release, generalized vasodilation, increases capillary permeability


Signs and Symptoms of Shock

An extremely low blood pressure
Fast but weak pulse
Dizziness, faintness or
Moist, clammy skin
Profuse sweating
Rapid, shallow breathing
Chest pain
Blue lips and fingernails