Grade 11 Life Sciences - Blood Pressure

Blood Pressure in Physiology

  • Definition: Blood pressure is the force exerted by blood against the walls of blood vessels.

Factors Affecting Blood Pressure

  • Key Influences:
    • Pumping of the Heart: The heart's pumping action drives blood through the circulatory system.
    • Narrowness of Arterioles: The diameter of smaller arterioles creates peripheral resistance to blood flow, impacting blood pressure.

Main Factors That Help Maintain Blood Pressure

  • Blood pressure experiences fluctuations based on two main phases of the heart:
    • Systolic Pressure:
    • Occurs during ventricular contraction (systole), leading to an increase in blood pressure.
    • Average Healthy Value: 120 mm Hg.
    • Diastolic Pressure:
    • Occurs during the relaxation of heart muscles (diastole), resulting in a decrease in pressure.
    • Average Healthy Value: 80 mm Hg.

Understanding Blood Pressure Measurements

  • Measurement Method: Blood pressure is typically measured using a Baumanometer.
  • Readings:
    • First Reading (Systolic): The upper reading indicating the pressure during heart contraction.
    • Second Reading (Diastolic): The lower reading indicating the pressure when the heart is relaxed.
    • Typical Measurement Format: Expressed as mm Hg (e.g., 120/80 mm Hg).

Importance of Blood Pressure

  • Essential Role: Blood pressure ensures a continuous flow of blood through the capillaries, which is crucial for supplying body cells with nutrients, oxygen, and other vital requirements.

Blood Pressure Classification Chart

  • Classification of Blood Pressure Levels:
    • Low:
    • Systolic: <90
    • Diastolic: <60
    • Normal:
    • Systolic: <120
    • Diastolic: <80
    • Prehypertension:
    • Systolic: 120 - 139
    • Diastolic: 80-89
    • High: Stage 1 Hypertension:
    • Systolic: 140 - 159
    • Diastolic: 90-99
    • High: Stage 2 Hypertension:
    • Systolic: ≥160
    • Diastolic: ≥100
  • Note: Low blood pressure (<120/80) is generally considered a good thing unless accompanied by symptoms of hypotension, which should be discussed with a healthcare provider.
  • Source: Data from the Seventh report of the Joint National Committee on Hypertension.

Health Implications of High Blood Pressure (Hypertension)

  • Common Issues Caused by Hypertension:
    • Stroke: Damage to blood vessels can cause them to burst or become clogged.
    • Mood Disorders: Antihypertensive drugs may cause depression or anxiety.
    • Vision Loss: Conditions like retinopathy or glaucoma can develop due to high blood pressure.
    • Kidney Disease: High blood pressure can damage kidney filters, leading to clogging or damage.
    • Heart Disease: Increased stress on the heart can raise the risk of heart failure and angina (heart pain).
    • Bone Loss: Increased calcium loss due to high blood pressure may reduce bone density.
    • Sexual Problems: Conditions such as erectile dysfunction and decreased libido may arise.

Signs and Symptoms of Low Blood Pressure (Hypotension)

  • Common Symptoms:
    • Dizziness
    • Headaches
    • Fainting
    • Stiff neck
    • Shortness of breath
    • Seizures
    • Pale skin
    • Sweating and fever
    • Irregular heartbeat
    • Nausea, diarrhea, or vomiting
    • Thirst, fatigue, and depression.

Blood Pressure in Capillaries

  • Requirements for Capillary Pressure: Blood pressure must be lower in capillaries than in arterioles because:
    • Structural Integrity: Capillaries have thin walls that may rupture at high pressures.
    • Diffusion Efficiency: Lower pressure facilitates slower blood movement, allowing for more effective diffusion of substances between blood and body cells.

Daily Activity Reminder

  • Task: Complete learning activity 11 on page 95.