Lecture 7 Flashcards by Katie Hostetter

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

Blood Pressure
Resistance
Venous Return
Velocity and Volume

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definition blood pressure:

force exerted by circulating blood on the walls of blood vessels

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Systolic pressure:

BP during ventricular systole

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Diastolic pressure:

BP during ventricular diastole

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Normal value:

young adult: 120/75 mm Hg

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Pulse pressure:

systolic - diastolic

important measure of stress exerted on small arteries

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Resistance

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

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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

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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

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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

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It is important to adjust blood flow to organ needs

Flow of blood to

particular organ can be regulated by varying resistance to flow

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Vasoconstriction of blood vessel smooth muscle is controlled

both by the

autonomic nervous system and at the local level

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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

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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

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Role of Cardiovascular center

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

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Baroreceptors:

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 ```