I Putu Gede ADIATMIKADepartment of Physiology, Udayana University – School of Medicine

Blood pressure in various parts of the vascular system

Baroreceptor reflex helps to compensate for a fall in blood pressure

Correlation of dehydration and rapid pulse

Effect of epinephrine in blood pressure Hypovolemic shock have a fast pulse

and cold clammy skin

Def : the force exerted by the blood against any unit area of the vessel wall

Measure unit : millimeter of mercury (mmHg) 50 mmHg force to push the mercury

up to 50 mm 1 mmHg = 1,36 cm water

A constant flow of blood is necessary to transport oxygen to the cells of the body

The arteries maintain an average blood pressure of around 90 mmHg

This helps push the blood from the arteries into the capillaries

In the capillaries, oxygen transfers from the blood to the cells

The arteries fluctuate between a state of systole and diastole

In systole, the pressure in the arteries increases as the heart pumps blood into the arterial system

As the pressure increases, the elastic walls of the arteries stretch

This can be felt as a pulse in certain arteries

In diastole, the recoil of the elastic arteries forces blood out of the arterial system into the capillaries

The pressure in the arteries falls as blood leaves the system

Minimum diastolic pressure is typically 70-80 mmHg

Maximum systolic pressure is typically 110-120 mmHg

Blood pressure depends on cardiac output (CO) and systemic vascular

resistance (SVR)BP = CO x SVR*

Cardiac output depends on heart rate and stroke volume

CO = HR x SV**SVR = total resistance of arterioles to flow of blood*SV = the amount of blood pumped by the heart each cycle

Pulse pressure: PP = SP-DP

Mean arterial blood pressure : SBP + (2 x DBP) MABP = ------------------------

3 Cardiac output:

MABP CO = ----------- = SV x HR

TPR

Figure 14.8

Using stethoscope to hear the Korotkoff sound Put the head of stethoscope on the fossa

cubiti Hear the sound while pump the balloon

Sound that must be heard : 1st sound : systolic Last sound : diastolic

Several measurements should be done as the respiration and vasomotor waves modulate the blood pressure levels

ADVANTAGES

The blood pressure can be measured in noisy environment too

Technique does not require much equipment

DISADVANTAGES

Only the systolic pressure can be measured (not DP)

The technique does not give accurate results for infants and hypotensive patients

The body responds quickly to falls in arterial pressure

This immediate response is to increase cardiac output (CO) and systemic vascular resistance (SVR)

Sympathetic activity causes vasoconstriction. This increases SVR

The baroreceptor reflex and other reflex mechanisms are important for the short term control of blood pressure.

However control of heart rate, contractility and peripheral resistance can do little if blood volume is not regulated.

Long term control of blood pressure requires control of blood volume.

Blood volume is controlled by the kidney.

Changes in central arterial pressure are detected by baroreceptors (pressure receptors) in the carotid and aortic arteries. These receptors provide

information to the cardiovascular centres in the hind brain.

Aortic baroreceptors are less sensitive than carotid pressure receptors.

Increased baroreceptor activity increases parasympathetic activity to the heart.

Baroreceptor activation suppresses sympathetic tone to the heart and blood vessels

Increased parasympathetic tone to the heart.Decreased heart rateDecreased cardiac output and blood pressure.

Increased sympathetic tone to the heart. Increased heart rate and contractility increased stroke volume. Increased cardiac output and blood pressure.

Reduced arterial blood pressure decreased baroreceptor activity.

Increased sympathetic tone to blood vessels.Elevated venous tone. Increased circulating volume, increased

venous return. Increased stroke volume, cardiac output

and blood pressure.

At rest heart rate is under both sympathetic and parasympathetic tone.

Normally the parasympathetic inhibition of rate is larger than the sympathetic stimulation.

It regulates the action potential frequency of the SA node.

Regulates vasoconstriction.Regulates venomotor tone.Stimulate the secretion of

epinephrine and renin.

Through the release of Ach, it controls the action potential frequency of the SA node.

Blood volume Blood vessel radius

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

Aldosterone:- Secretion by the

adrenal cortex triggered by angiotensin II

- Promotes sodium reabsorption

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

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