Blood pressure

Blood pressure

It is lateral pressure exerted by the moving column of blood on the vessel wall per unit area by(sq. mm) by its contained blood while flowing through it.
Blood pressure=Cardiac output x peripheral resistance.

Importance of blood pressure :
1.It is essential for the flow of blood through the circulatory tree.
2.It provides motive force for filtration at the capillary bed which is essential for-
a.Tissue nutrition
b.Formation of urine
c.Formation of lymph
d.For venous return.

Lateral pressure

It is that pressure when forces is exerted at right angles to the direction of flow as any point within a tube filled with a circulation fluid.

Basal blood pressure : It is lowest pressure necessary in main-taining blood flow sufficient for needs of the body.

Causal blood pressure:Any pressure that is recorded under ordinary circumstance of life is known as the causal blood pressure.

Physiologial variation of blood pressure
   1year: 80/40  mm  of  Hg
 3year:100/60   mm  of  Hg
20year:120/80  mm  of  Hg
45year:145/90  mm  of  Hg
70year:170/95  mm  of  Hg

sex:In female,the blood pressure is slightly lower(5 mm of Hg),cause is unknown.After enopause,it reaches male lavel .

Exercise:In strenuous exercise, the systolic pressure rises,even up to 180 mm of Hg. In moderate exercise, it slightly rises.Posture:During  standing, diastolic pressure is slightly higher;systolic pressure low.In recumbent position,this condition is reversed.    
During sleep:During deep sleep, there is fall of blood pressure by  15-20 mm of Hg.
Emotion and excitement:Raises systolic pressure considerably.                

What is shock?

It is an abnormal physiological condition resulting from inadequate propultion of blood to the aorta thus causes inadequate blood flow perfusing the capillaries of tissues and organs.
Tissue necrosis in severe shock : Not all cells of the body are equally damaged by shock because some tissues have better blood supplies than others . For instance, the cells adjacent to the arterial ends of capillaries receive better nutrition than the cells adjacent to the venous ends of the same capillaries. Therefore, one would expect more nutritive deficiency around the venous ends
of capillaries than elsewhere. For instance necrosis in the center of a liver lobule, the portion of the lobule that is last to be bathed by  the blood as it passes through the liver sinusoids. Similar punctate lesions occur in heart muscle, although here definite repetitive pattern, such as occur in the liver, cannot be demonstrated. Neverthless, the cardiac lesions play an importent role in the leading to the final irreversible stage of shock. Deteriorative lesions also occur in the kidneys, especially in the epithelium of the kidney tubules, leading to kidney failure and occasionally uremic death several days later. Deterioration of the lungs also often leads to respiratory distress and death several days later - called the shock lung syndrome.     

Haemorrhage : It means abnormal internal or external discharge of blood. It may be arterial , venous or capillary.Arterial blood is bright red ; flows in spouts . Capillary blood is of a reddish colour ; exudes from tissue. Venous blood is dark red ; flow is continue.    

Hydrostatic pressure : Hydroststic pressure is the pressure which is caused by the effects of gravity ona a fluid filled system i.e it occurs as a result of the weight of the blood in the vessels.

Vascular endothelium : The walls of the blood vessels are made up of a single layer of endothelial cells. Endothlium occupies a stategic interface  between blood and body. The endothelial lining varies from organ to organ.

Regulation of blood pressure:Two major types of arterial pressure control system in the body-
1.Nervous mechanism.
2.Humoral mechanism.

1.Nervous mechanism :
Has two different types-
a.Short terms regulation: Occurs within seconds to minutes.

Mechanism occurs within seconds:

*Baroreceptor feed back mechanism.
*Chemoreceptor feed back mechanism.
*Central nervous system ischemic mechanism.

Mechanism occurs within minutes:

* Renin angiotensin vasoconstrictor mechanism.
*Capillary fluid shift mechanism.
*Stress relaxation changes in vasculature.

b.Longterm regulation:
1.Renal body fluid mechanism.
2.Renin angiotensin mechanism.

Humoral regulation:
a.Epinephrin-norepinephrin mechanism.
b.Vasopressin vasoconstrictor mechanism.
c.Renin angiotensin aldoterone mechanism.


Hypertension:
Definition: Hypertension is a clinical condition characterized by persistance rise of blood pressure  above
the normal range in respect of age and sex.Hypertension occurs when diastolic pressure is great than 90 mm of Hg and systolic pressure is above 150 mm of Hg. Hypertension is an increase in mean blood pressure that is usually chronic and is common in humans.Hypertension can result in serious health consequences if left untreated. The majority of hypertension is of unknown cause, but several gene mutations underlie rare forms of the disease and are informative about mechanisms that control the dynamics of the circulatory system and its integration with other organs.     

Type: Hypertension are two types-
1.Primary or essential hypertension.
2.Secondary hypertension.

Essential hypertension: When arterial blood pressure persistently exceeds 150/90 or 160/100 mm of Hg.Its causes is unknown.It is of two types-
a. Benign form: In the early stages the hypertension is moderate, e.g. 210/110 mm of Hg.
b.Malignant form: The condition is so named because death occurs within months to 2 years of its first ecognition.The BP is much higher than in the benign form e.g. 260/150 of Hg.

Secondary hypertension: It is due other diseases, as renal diseases,phaeochromo-cytoma, by excess secretion of  glucocorticoids or aldosterone, by coarctation of aorta.Volume loading hypertension:Hypertension occurs due to excess extracellular fluid volume .It is due to excess salt intake or salt retension from kideny.Vasoconstrictor hypertension: It is due to continuous infusion of vasoconstrictor agent into blood or by  excessive secretion of  vasoconstrictor from endocrine gland.The vasoconstrictors are-
1.Angiotension-II
2.Norepinephrine.
3.Epinephrine.