Blood Pressure

Required to move blood and all its constituents throughout the body

What is blood pressure?

• The pressure of blood against the walls of the arteries

• Blood pressure is caused by two forces:– The heart pumping blood into the arteries– The opposite force of the arteries resisting blood

flow

Animated cardiac cycle

• First, the physiology...• Then, how it can create a graph...• http://library.med.utah.edu/kw/pharm/hyper

_heart1.html

Heart Rate

• Each heart beat spreads out from one point on the heart – the sino-atrial node, or SA Node.

• http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter22/animation__conducting_system_of_the_heart.html

Heart Rate

• What’s your current heart rate?• The cardiac cycle is what takes place over one

heart beat. If the heart rate of an individual is 60 beats per minute, what is the length of the cardiac cycle for that individual?

How is blood pressure measured?

• The higher number is known as the SYSTOLIC pressure– while the heart contracts to pump blood to the

body. • The lower number is known as the DIASTOLIC

pressure – when the heart relaxes between beats.

All these numbers...• The systolic pressure is always first. – For example: 118/76 (118 over 76); – systolic = 118, diastolic = 76.

• Blood pressure of 120 /80 mmHg (millimeters of mercury) is NORMAL for adults -

• Systolic blood pressure ranges between 90 and 120mmHg; diastolic pressure between 60 and 80mmHg

All these numbers...

• A blood pressure reading of 140 /90 is HIGH• A systolic pressure of 120 to 139 mmHg or a

diastolic pressure of 80 to 89 mmHg is considered "prehypertension" and needs to be watched carefully.

Mean Arterial Pressure (MAP)

• Averages! Hurray!• A little more complicated...

• DP = diastolic pressure• SP = Systolic pressure

Simply – the average pressure over all of the cardiac cycle

Why is it important?• Low blood pressure will mean that there is a low

perfusion of blood through the end organs – they will not be able to respire enough to function properly and so eventually tissue damage will occur.

• Most often, low blood pressure results in feeling faint or dizzy.

• High blood pressure puts stress on the walls of the blood vessels and may lead to tissue growth. It is also a risk factor for strokes, heart attacks and renal failure

TASKS

• Worksheet – answer questions 1 – 10

Quick Recap on the Nervous System

• Control of all biological mechanisms• Split into the SYMPATHETIC and

PARASYMPATHETIC systems• Sympathetic – Stimulates (e.g. Increases heart

rate)• Parasympathetic – Inhibits (e.g. Decreases

heart rate)

Physiological Control

• Baroreceptors in the carotid sinus and aortic arch

• Information to VMC – vasomotor centre

• Negative feedback loops attempt to restore the blood pressure back to normal

Baroreceptors

• Low BP = low rate of activity

• Decreased activity (lowering the BP) stimulates the sympathetic nervous system

Lowered blood pressure - hypotension

• Activates sympathetic nervous system– Vasoconstriction– Increased contraction within the heart

• Fluid shifts from interstitial spaces (between cells) into the blood – increased blood volume

Lowered blood pressure - hypotension

• Hormonal mechanisms– Adrenaline and noradrenaline increase

vasoconstriction and cardiac output– Renin and angiotensin production is increased in

the kidney – potent vasoconstriction– ADH can be released by the hypothalamus as a

response to excessive blood loss

– The kidney is the most important organ for long term blood pressure control

http://www.nda.ox.ac.uk/wfsa/html/u01/u01c_p02.htm

Baroreceptors

• High BP = high rate of activity

• Increased activity (raising the BP) stimulates the parasympathetic nervous system

Raised blood pressure - hypertension

• Activates parasympathetic nervous system– Vasodilation– Reduced contraction within the heart

• Fluid shifts from blood into interstitial spaces (between cells)– decreased blood volume

• Vasodilator hormones are released