Lecture 7 Flashcards
Overall function of cardiovascular
system and blood flow in
general is affected by
Blood Pressure
Resistance
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
Resistance
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 rateBaroreceptors:
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
Hypertension
Constriction of arterioles leading to resistance in blood flow and strain on the heart
chronic resting BP > 140/90
consequences
can weaken small arteries and cause aneurysms
Increased heart size, lower blood volume, chest pain
Hypotension
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
light-headedness
Moist, clammy skin
Profuse sweating
Unconsciousness
Rapid, shallow breathing
Chest pain
Blue lips and fingernails
