HUMAN BLOOD STRESS

BLOOD STRESS 



It is defined as the lateral pressure exerted by column of blood of the walls of blood  vessels. Venous pressure is less than arterial pressure. Contraction of the left ventricle during systole
pushes blood into the arterlal syatem. he pressture produced is called the systolic hl lood
pressure (SBP) and is about 120 mm Hg, During the diastole the pressure in the arteries is
called the diastolic blood pressure (DBP). It is about 80 mm Hg.

Factors affecting blood pressure are:

⚫Age                  
⚫Body built
⚫Posture
⚫Exercise
⚫Sleep
Blood pressure (BP) is measured by an instrument called sphygmomanometer.
There are two methods by which one can
record BP. 

1. Palpatory
2. Auscultatory.

🔘Palpatory Methods :

The subject is either seated comfortably
or is lying supine on the examination
couch for 5 minutes. The blood pressure
cuff is placed firmly around the bare arm
2.5-3 cm above the elbow joint. The instrument should be placed at the level of the heart
Feel the radial pulse. Inflate the cuff 20-30 mm Hg above the point when the radial pulse
disappears. Now slowly deflate the cuff (2 mm/sec) and note the reading when the radial
pulse becomes palpable. This is the systolic blood pressure (SBP). The diastolic blood
pressure (DBP) cannot be measured by this method.

🔘Auscultatory Method:

Now place the diaphragm of the stethoscope on the brachial artery at the elbow. Inlate tne
cuff till 180 mm Hg or SBP+ 10 whichever is higher. Then, gradually deflate the cult.
the reading when clear sharp tapping sounds (Korotkoff's sounds) are heard. This is SBP. These sound gradually become dull and muffled and then disappear. The cuff pressure at the muftling disappearance of the Korotkoff sound is recorded as the diastolic blood pressure.
The blood pressure is expressed as SBP/DBP mm Hg.
Normal BP in adult is 120/80 mm Hg.
Arterlal blood pressure maintains the essential flow of substances into and out of the organs of body. Control of blood pressure especially to the vital organs is essental to maintain homeostasis.


⬛Factors lnilunncing Blood Pressure:

Cardiac output :It depends upon volume of blood ejected (stroke volume) and heart rate.
Peripheral resistance: It depends on tone of arterioles. It is also affected by elasticity of
        arteriolar wall.
Regulation of Blood Pressure:
    Blood pressure is controlled in two ways:
     1. Short-term control, on a moment to         moment basis. It involves mainly baroreceptor reflex and also chemoreceptors, higher centres and circulating hormones.
     2.Long-term control, involves regulation of blood volume by kidneys and renin-angiotensin-
aldosterone system.
The cardiovascular centre (CVC) in pons and medulla sends sympathetic and para-
sympathetic nerves to heart and blood vessels. It regulates blood pressure by affecting heart
rate and by dilating or constricting blood vessels.

🔘Baroreceptors

These are nerve endings sensitive to pressure changes, present in arch of aorta and carotid
sinus. These are important for short term control of BP. High BP increases baroreceptor activity
which increases parasympathetic activity and decreases sympathetic activity which causes
dilatation of blood vessels leading to fall in BP. If pressure decreases in arch of aorta and carotid
sinus, sympathetic activity is increased. 1This leads to increase heart rate and vasoconstriction
of blood vessels, causing rise in BP

🔘Chemoreceptors

These are nerve endings situated in carotid and aortic bodies. These respond to changes in
levels of CO, 0, and pH of blood. Discharge from these affect the cardiovascular centre

🔘Higher Centres

Higher centres, eg. hypothalamus, cerebral cortex also help in regulating BP.

🔘Renin-Angiotensin-Aldosterone System

In response to decreased renal blood flow, enzyme renin is secreted by renal tubular cells. Renin
converts angiotensinogen (a plasma protein produced by liver) to angiotensin L. Angiotensin
converting enzyme (ACE) produced by lungs converts angiotensin I to angiotensin , which

stimulates secretion of aldosterone. It also causes vasoconstriction and increases BP. 

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