Bloodflow & Pressure

Blood pressure

The pressure exerted by the blood on the inner wall of blood vessels.

Hypotension risks

bloodflow to organs is too low, causing problems in organs.

• brain damage begins after only 4 minutes without oxygen, and death can occur after 4 to 6 minutes

Hypertension risks

Damage can occur to the walls of blood vessels from the excess pressure

• organs like the brain and kidneys can become damaged

Vasculature

The vessel systems of the body.

• A pressure gradient must be maintained across the body’s blood vessels to enable passive transportation of blood

Venous system

Low pressure system

There is less pressure in the veins than the arteries

Mean arterial pressure

the average arterial pressure throughout one cardiac cycle (systole and diastole)

Most people need at least 60 mmHg

Systolic blood pressure

The pressure exerted against the arterial wall when the ventricles are contracting

• Top line of the arterial pressure

• Normal 120 mmHg

Diastolic Blood pressure

the pressure exerted against the arterial wall when the ventricles are relaxing

• Bottom line of the arterial pressure

• Normal 80 mmHg

2 Factors effecting blood pressure

• Cardiac Output

• Peripheral Resistance

Peripheral resistance

Resistance present within arteries towards bloodflow.

• Effected by blood vessel diameter

• Arterioles have the greatest impact on peripheral resistance (constrict and dilate the most)

Blood Pressure & Peripheral resistance:

Vasoconstriction

When arterioles constrict, resistance increase, so blood pressure increases.

Blood Pressure & Peripheral resistance:

Vasodilation

When arterioles dilate, resistance decreases, so blood pressure decreases.

Blood Pressure & cardiac output/stroke volume/heart rate

Increasing cardiac output/stroke volume/heart rate increases blood pressure, as there is more blood being pumped out of the heart and pushing against the arterial walls

Blood flow & Vasodilation/vasoconstriction

organs receive either less or more blood depending on how constricted or dilated the arteries are.

Venous return

The volume of heart flowing back to the heart in the systemic veins.

• Veins are a low pressure system. Thus, additional mechanisms must be used to increase pressure and thus, bloodflow

• avg pressure of around 2 mmHg

Increasing Venous return:

Skeletal muscle pump

when skeletal muscles contract, they squeeze surrounding veins, increasing pressure and venous return.

Increasing Venous return:

Abdominal pump from breathing

When breathing, there is a stage where the abdominal pressure is higher than the thoracic pressure (due to the diaphragm), causing an increased bloodflow and venous return towards the thorax, where the heart is located.

Increasing Venous return:

Nerve system stimulation

Nervous system causes contraction of veins, stimulating the smooth muscle layer in veins, causing them to contract, forcing blood through them.

Blood volume & venous return

increased blood volume causes increased venous return

Effects of increased venous return

• increases blood entering ventricles, which

• increases stroke volume, which

• increases cardiac output