BLOOD PRESSURE AND ITS REGULATION

BLOOD PRESSURE

•Arterial blood pressure is defined as  the lateral pressure exerted by the contained column of blood on  the wall of arteries.

•Generally , the term blood pressure refers to  arterial blood pressure.

•Normal blood pressure  is 120 /80 mmHg

                  Systolic 120 mmHg

                  Diastolic 80 mmHg

 

•The arterial blood pressure is expressed mainly in four ways.

 

1.Systolic blood pressure

2.Diastolic blood pressure

3.Pulse pressure

4.Mean arterial pressure  

SYSTOLIC BLOOD PRESSURE 

•Systolic blood pressure is defined as the maximum pressure exerted in the arteries during  systole of the heart

      •Normal value     - 120 mm Hg

      • Normal range    - 110  to 140 mm Hg

DIASTOLIC BLOOD PRESSURE

•Diastolic blood pressure is the minimum pressure in the arteries during diastole of the heart

 

        •Normal value.    - 80 mmHg

        • Normal range   -  60 – 80 mmHg

 

PULSE  PRESSURE

•Pulse pressure is the difference between the Systolic  and   Diastolic pressure.

 

         •Normal value  – 40 mmHg

MEAN ARTERIAL PRESSURE

•It is the average pressure existing in the arteries .

•It is the diastolic pressure plus one - third of pulse pressure.

 

         •Normal value  - 93 mmHg

BLOOD PRESSURE – VARIATIONS

1. Age

2.Sex

3.Body built

4.Diurnal variation

5.After meals

6.During sleep

7.Emotional conditions

8.After exercise

 

 

AGE :

Arterial blood pressure increases as age advances

Systolic blood pressure at various ages 

In newborn baby  - 40 mmHg

After 15 days         - 70 mmHg

After one month      - 90 mmHg

At puberty                 - 120 mmHg

At 50 years                 - 140 mmHg

At 70 years                  -160mmHg

At 80 years                 -180 mmHg

 

•Diastolic blood pressure at various ages 

 

At puberty        - 80 mmHg

At 50 years       - 85 mmHg

At 70 years        -90 mmHg

At 80 years        - 95 mmHg

SEX 

•In females ,up to the period of menopause , the arterial pressure is low up to 5mmHg  as compared to the males  of same age.

 

•After menopause the blood pressure  in the females becomes equal to that in the  males of same age .

BODY BUILT

•The arterial blood pressure is more in the obese persons than lean persons  

DIURNAL VARIATION

•In the early morning blood pressure is low.

•IN the afternoon  it reaches maximum.

•In the evening  blood pressure becomes low again.

AFTER MEALS

•The blood pressure is increased for few hours after meals.

•This  is due to increase in cardiac out 

DURING  SLEEP

•The blood pressure is reduced up to 15 to 20 mmHg during deep sleep.

EMOTIONAL CONDITIONS

•The blood pressure increases during excitement or anxiety.

•This is due to release of ADRENALINE in the blood circulation

AFTER EXERCISE

•After moderate exercise systolic pressure increases by 20 -30 mmHg.

•This is due increase in force of contraction and stroke volume.

•Normally diastolic pressure is not effected by moderate exercise , Its  because  diastolic pressure depends upon the peripheral resistance.

•After sever exercise the systolic pressure rises by 40 – 50 mmHg above the basal level.

•But the diastolic pressure reduces because the peripheral resistance decreases in severe muscular exercise.

REGULATION BY BLOOD VESSELS

It occurs by following mechanisms :

• Alteration in the diameter of arterioles which changes peripheral resistance and blood pressure.

 

•Alteration in diameter  of  veins which changes venous return and cardiac output eventually blood pressure.

 

NEURAL  REGULATION

•It  is very important.

•It  responds with in seconds .

•Redistribution of blood flow  to the body.

•Increasing the heart rate .

•Rapid control of the blood pressure.

 

NEURAL  REGULATION COMPONENTS

 

•Medullary CVR control center.

•ANS  supplying the heart & blood vessels

•Afferent impulses to medulla

•Role of skeletal muscles

 

MEDULLARY CVR CONTROL CENTRE

•It is popularly known as VASOMOTOR center.

•It is medullary sympathetic center .

•Located in the M.O. of BRAIN STEM.

•It consists of groups  of neurons at the floor of Fourth ventricle

PRESSOR AREA

•Pressor area is located at  RVLM.

•It contains glutaminergic neurons .

•This has the excitatory effect on neurons.

Continuous sympathetic vasoconstrictor tone

•Shows continuous tonic activity in the  body

•The discharge rhythmically *1  impulse/ sec

MEDULLARY PARA SYMPATHETIC CENTER

•Cardiac vagus center.

•Earlier also called Cardiac inhibitory center.

•Now it is called as NUCLEUS AMBIGUOUS 

•N.A. receives  afferents via  NTS.

•To decrease heart  rate  F.C.

•It is a relay station  cardio respiratory afferents.

•It gets afferents from Baroreceptors &  Chemoreceptors.

VAGUS  EFFECT

PARA SYMPATHETIC CENTER

BARORECEPTOR MECHANISM

• High- pressure baroreceptors are present in following areas 

1.Carotid sinus 

2.Aortic arch

3.Walls of left ventricle

4.Root of left subclavian artery

5.Junction of thyroid artery

BARORECEPTOR MECHANISM

• Low- pressure baroreceptors are present in following areas 

 

1.Walls of right & left atrium

2.Entrance of S.V & I.V

3.Walls of pulmonary trunk

4.Right & left pulmonary artery

 AUTOREGULATION OF BLOOD PRESSURE

•In any tissue of the body, an acute increase in arterial pressure causes immediate rise of blood flow but with in no time the blood flow in most tissues returns normal.

HUMORAL  REGULATION

Humoral control means control by substances

secreted into the body fluids.

  Ex : Hormone & ions

        •Vasoconstrictor agents

        •Vasodilator agents

Vasoconstrictor agents include :

1.Vasopressin

2.Endothelin - A

3.Epinephrine

4.Norepinephrine

5.Angiotensin - II

 

Vasodilator agents include 

1.Bradykinin

2.Histamine

 

VASOCONSTRICTORS

•Epinephrine  & Nor-epinephrine are two important vasoconstrictors.

•During stress,fright they are released in ample amounts 

•They have same effect as sympathetic stimulation.

•They lead to contraction of veins & arterioles.

Adrenal medulla secretes  these hormones.

 

ANGIOTENSIN ǁ 

• As little as 1 millionth of a gram can increase

arterial pressure by 50mm of Hg.

•It constrict small arterioles powerfully.

•It increase total peripheral resistance , thus it plays important role in the regulation of arterial pressure.

VASOPRESSIN or ANTI DIURETIC HORMONE 

•It is also  called antidiuretic hormone (ADH)

•It is more powerful than angiotensin II.

•MOST POTENT vascular constrictor.

•It is formed in nerve cells, in hypothalamus.

and is transported downwards though nerve axons to get stored in posterior pituitary.

•It acts mainly by increasing water reabsorption from renal tubules.

ENDOTHELIN-A

•It is large 21 amino acids containing peptide .

•This substance is present in endothelial cells.

•Causes powerful vasoconstriction.

•After severe blood vessel damage , endothelin-a is released from endothelial cells.

•It prevent  bleeding of arteries by constricting them.

 

VASODILATORS

      •Bradykinin

      •Histamine 

BRADYKININ

•Several substances called KININ, causes powerful vasodilatation.

•Kinins are small peptides, Kallikrinin which is its inactivate form.

•When their is tissue inflammation it  becomes activated.

HISTAMINE

•In allergic reaction histamine is released.

•Histamine is derived from MAST cells and 

from the BASOPHILS in the blood.

•POWERFUL VASODILATOR in the tissue .

•Due to action of histamine fluid leaks out in the tissue and causes OEDEMA

VASCULAR CONTROL BY IONS AND   CHEMICALS

•Calcium ion con causes vasoconstriction.

 •Potassium ion causes vasodilatation .

•Magnesium ion is powerful vasodilator.

•Hydrogen  ion is powerful vasodilatatior.

HYPERTENSION

•DEFINITON :

•Hypertension is defined as sustained elevation of systemic arterial pressure .

 

Usually hypertension means rise in diastolic pressure .

When Systolic Pressure is elevated above  150 mmHg and  Diastolic Pressure is elevated  above  90mmHg

TYPES OF HYPERTENSION

 

1.Primary (or ) Essential Hypertension

2.Secondary Hypertension  

 

PRIMARY (OR ) ESSENTIAL HYPERTENSION

•The blood pressure is elevated in the absence of any underlying disease.

•It is also known as essential hypertension

•The arterial blood pressure increased because of increased peripheral resistance due to some unknown causes.

It is again of two types :

      1. Benign Hypertension

      2. Malignant Hypertension  

BENIGN HYPERTENSION

•In early stages of condition, 

There is moderate increase in blood pressure

systolic to 200mmHg and the diastolic pressure of about 100mmHg.

In resting conditions and sleep the BP returns to normal level.

Later there is further increase in blood pressure and it does not come back to normal  level.

 

MALIGNANT HYPERTENSION 

•It is also called accelerated hypertension.

•In this case the blood pressure is increased to 250 mmHg systolic pressure and 150 mmHg diastolic pressure

•It always develops due to the combined effect of primary and secondary hyper tension

•Malignant hypertension produces renal diseases ,retinal hemorrhage.

•It is fatal disease and causes death with in few years

SECONDERY  HYPERTENSION

•It is due to some underlying disease

•CVS DISORDERS 

             Atherosclerosis 

             coarctation of aorta

•Endocrine disorders like  – 

             Tumors in adrenal medulla 

             Hyper aldosteronism                                            

             Cuishings syndrome

•RENAL DISORDERS         

             Stenosis of renal artery

             Glomerulonephritis

•CNS DISEASES             

             increased intra cranial pressure

             lesion in tractus solitarius

HYPOTENSION

•DEFINITION :

•The low blood pressure is called hypotension.

When the systolic pressure is less than 90 mmHg then it is considered as hypotension .

Types :

1.Primary hypotension

2.Secondary hypotension