🩸 11.3 – BLOOD PRESSURE

🧠 What is Blood Pressure?

Let’s begin with a simple definition:

Blood pressure is the force or pressure that your blood exerts (pushes) against the walls of your blood vessels as it moves through your body.

📦 Imagine this:

Think of blood vessels like rubber water pipes and your heart like a water pump. The pump pushes water through the pipes — just like your heart pushes blood through arteries and veins.

The pressure of that flow is what we call blood pressure.

This pressure helps the blood reach every part of your body — from the top of your head to the tips of your toes.

🔄 Where is Blood Pressure Found?

Although blood pressure exists in all blood vessels, when we usually say “blood pressure”, we mean the pressure in the arteries — especially systemic arteries (the ones that take blood from the heart to the body).

🔝 Highest in Aorta, Lowest in Veins

Blood pressure is not the same in every part of the circulatory system.

• It is highest in the aorta, the largest artery.
• As blood travels farther from the heart through arteries → arterioles → capillaries, the pressure gradually decreases.
• By the time blood reaches veins, pressure is very low.

💓 Pulse: The Throbbing of Arteries

As blood flows through arteries, it causes a rhythmic expansion and contraction of the artery walls. This is what you feel when you check your pulse — for example, on your wrist or neck.

So, pulse is basically the feel of the pressure wave as blood is pushed through the arteries with each heartbeat.

🔁 Changes in Blood Pressure During a Heartbeat (Cardiac Cycle)

Your heart does not beat continuously — it contracts and relaxes in a cycle. This is called the cardiac cycle.

There are two key phases of this cycle:

1. Systolic Pressure (Highest Pressure)

• When the heart contracts (especially the ventricles), it pushes blood into the arteries with force.
• This increases pressure in the arteries.
• This highest pressure is called systolic pressure.
• In a healthy young adult, this is about 120 mm Hg.

💡 Real-life Example: Think of pressing a water pump handle. When you press hard, water shoots out quickly. That moment is like systole.

2. Diastolic Pressure (Lowest Pressure)

• When the heart relaxes between beats, the pressure in arteries drops.
• This lowest pressure is called diastolic pressure.
• Normal diastolic pressure is around 75–85 mm Hg.

💡 So when you see a blood pressure reading like 120/80, it means:

• 120 mm Hg = systolic pressure
• 80 mm Hg = diastolic pressure

🩻 How is Blood Pressure Measured?

The instrument used is called a sphygmomanometer (sfig-mo-ma-NOM-e-ter). It usually includes:

• A cuff that wraps around your upper arm
• A pump to inflate the cuff
• A dial or a mercury column to show pressure

How it works:

• The cuff is inflated to stop blood flow temporarily.
• Then it’s slowly released while listening to the pulse.
• When blood just starts to flow again, systolic pressure is recorded.
• When flow becomes smooth and pulse is no longer heard, diastolic pressure is recorded.