Blood Vessels: Main Blood Vessels and their Branches-1

Difference Between Vein and Artery:

Blood pressure and Pulse

The force that blood applies to blood vessel walls is known as blood pressure (BP). Blood moves from high-pressure areas to low-pressure areas. Millimeters of mercury are used to measure and express blood pressure (mmHg). For instance, a mercury column with a pressure of 110 mmHg would impose the same pressure on the body. As the ventricles contract, blood pressure rises. The aorta and large systemic arteries have the highest levels. The highest arterial pressure, or systolic blood pressure, occurs during systole.

Measurements of blood pressure are often done of arterial pressure alone because blood pressure lowers as it passes from arteries into capillaries and then into veins. A sphygmomanometer is the device used to monitor blood pressure, and it measures two things:

• Systolic pressure:
  • Achieved during ventricular systole (ventricular contraction), which typically averages 120 mm Hg, it is the highest pressure in arteries.
• Diastolic pressure:
  • This pressure, which typically hovers around 80 mm Hg during ventricular diastole (ventricular relaxation), is the lowest pressure that may be found in arteries.

Other types of blood pressure

• Pulse pressure:
  • It is the difference between systolic and diastolic pressure. It is about 30-40 mmHg.
  • Pulse pressure= SBP - DBP
• Mean pressure:
  • It is the diastolic pressure plus one third of pulse pressure. It is about 96 mmHg.
  • Mean pressure= DBP - pulse pressure

Measurement of Blood Pressure

BP is measured by:

• Direct method:
  • The artery is exposed, and an arterial cannula with one end directly inserted into the lumen of exposed vessels and the other end connected to a mercury manometer in the shape of a "U" that displays the actual blood pressure in millimeters of mercury (mmHg) is used.
• Indirect method:
  • Only the systolic pressure may be determined using palpatory methods.
  • Measures both systolic and diastolic pressure using auscultatory technique. Sphygmomanometer and stethoscope are used to measure it. The Korot-koff sound refers to the noises made during the auscultatory measurement of blood pressure. The left ventricle's stroke output reaches its highest or systolic pressure at the end, and its minimum or diastolic pressure reaches its peak late in the ventricular diastole. Normal BP monitoring occurs in the brachial artery. It can also be gauged in the leg's femoral artery.

Factors Affecting Blood Pressure

Blood volume, peripheral resistance, and cardiac output are the key determinants of blood pressure.

• Cardiac Output
  • As previously stated, cardiac output (ml/min) is determined by multiplying the stroke volume (ml/beat) by the heart rate (beats/min). The cardiac output is directly correlated with blood pressure. Therefore, as already stated, changes in stroke volume or heart rate or both will alter blood pressure. Cardiac output (ml/min) equals stroke volume (ml/beat).
• Blood volume:
  • The total volume of blood in the body controls blood pressure. The amount of circulating blood changes (as in a bleed), which causes a reduction in venous return and a corresponding drop in blood pressure. Contrarily, anything that raises blood volume, such as consuming too much salt, makes it easier to retain fluid, which raises fluid volume and raises blood pressure.
• Peripheral Resistance
  • The resistance to blood flow in tiny veins located far from the heart is known as peripheral resistance. The blood pressure will rise as the peripheral resistance increases. Vascular diameter decreases as blood arteries, particularly arterioles, contract, increasing peripheral resistance and blood pressure in the process. On the other hand, peripheral resistance and blood pressure originate from a dilated vessel lumen. increases the diameter of the vessel lumen, allowing blood to flow more freely and lowering blood pressure and peripheral resistance in the process.

Factors Controlling Blood Pressure

Under the close control of the brain, several systems regulate the blood pressure by controlling vascular resistance, heart rate, stroke volume, and blood volume. Neural, chemical, and renal mechanisms that alter peripheral resistance, blood volume, or cardiac output affect blood pressure.

Nervous Control of Blood Pressure:

Neural controls over blood vessels are mainly focused on I changing blood flow to accomplish a particular function and (ii) keeping a healthy level of systemic blood pressure. For instance, blood momentarily switches from the epidermis and digestive system to the skeletal muscles during exercise. Reflex arcs, which primarily involve baroreceptors, chemoreceptors, and the vasomotor region of the medulla, are how most neurological controls work.

• Baroreceptors:
  • Can recognize changes in artery pressure; also known as pressure sensitive sensory reception. They are mostly found in the aortic and carotid sinuses. Stretched by a rise in blood pressure, the baroreceptors fire quicker nerve impulses in response to a fall in sympathetic stimulation. Vasodilatation and a reduction in the systemic vascular cardiovascular (CV) center are the outcomes. The parasympathetic stimulation and resistance are increased by the CV center in response. Along with a reduction in cardiac output, decreased sympathetic stimulation also causes a decrease in heart rate and contraction force. Both a drop in cardiac output and a reduction in systemic vascular resistance lower blood pressure.
• Vasomotor center: 
  • The medulla oblongata sends impulses down the vasomotor fibers to arterioles all over the body, but particularly to those in the skin and abdominal viscera, to control blood pressure and blood flow to specific tissue. Generalized vasoconstriction and an increase in systemic blood pressure result from any increase in sympathetic activity and the pace of vasomotor impulse delivery. Reduced sympathetic activity enables the vascular muscle to relax, which lowers blood pressure and causes generalized vasodilatation.
• Chemoreceptors: 
  • Are the sensory receptors that keep track of the blood's chemical composition. The aortic arch and the neck's major arteries house these receptors. In reaction to the lower levels of oxygen, higher levels of CO2, and increased levels of H+ concentration in the blood, they send impulses to the CV center. Vasoconstriction and an increase in blood pressure are the results of the CV center's response, which involves increased sympathetic stimulation of arterioles and veins. As a result of their greater significance in controlling respiratory rate and depth than blood pressure, these chemoreceptors are fully discussed in the respiratory system.

Chemical Control of Blood Pressure

As the chemoreceptors' reflexes help control blood pressure through the changing levels of oxygen and carbon dioxide, other chemicals can also have an impact on blood pressure.

• Adrenal medulla hormone:
  • When under stress, the adrenal medulla hormone releases both epinephrine and nor epinephrine. These hormones raise the heart's pace and contractility, which raises cardiac output. Additionally, they have a vasoconstrictive effect, notably in the skin's and abdominal organs' arterioles and veins, which raises blood pressure.
• Antidiuretic hormone (ADH):
  • The posterior pituitary releases antidiuretic hormone (ADH), which encourages the kidney to retain water in response to a drop in blood volume. ADH causes severe vasoconstriction, which aids in restoring blood pressure.

Renal Control of Blood Pressure

The kidneys control blood pressure by regulating arterial pressure. The kidneys' unique cells release the enzyme renin into the blood when blood flow to the kidneys is reduced or the amount of circulating blood decreases. Angiotensin II is a powerful vasoconstrictor that elevates blood pressure by increasing vascular resistance. It is produced when renin and angiotensin converting enzyme interact. Additionally, angiotension II causes the adrenal cortex to release aldosterone, a hormone that boosts salt and water absorption from the kidneys. The water reabsorption raises the volume of all the blood, which raises blood pressure.

Pulse

Blood is routinely pumped from the ventricles into the arteries. A wave of elevated pressure that originates at the heart and moves along the arteries is caused by the force of the ventricular contraction. The pulse is the name of this wave. A healthy adult's pulse typically beats between 70 and 80 times per minute.

The wrist, where the radial artery crosses the bone on the thumb side of the forearm, is where the pulse is most frequently felt. The carotid artery in the neck and the dorsalis pedis on the top of the foot are two other vessels that are occasionally utilized to take the pulse.

When taking pulse, assess:

• Rate
• Character
• Condition of wall of artery
• Radio-radial delay
• Rhythm
• Volume
• Peripheral pulse
• Radio-femoral delay

Special points:

• Radial artery is most common site.
• For rate and rhythm - radial artery.
• For volume and character - carotid and brachial artery.

Factors Affecting the Pulse:

• Age:
  • Children have a higher heart rate than adults do.
• Gender:
  • Compared to men, women often have a faster heart rate.
• Emotion:
  • Different emotional states, like rage, enthusiasm, stress, and fear, lead to elevated heart rate.
• Position:
  • Shifting positions often causes the pulse rate to change. For instance, a person's heart rate is often higher when they are standing than when they are lying down.
• Activity:
  • Various forms of exercise, such as running, jumping, and walking, increase heart rate.