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Lesson 7 - The Circulatory System

Blood Vessels

Arteries - Have thick walls and a smaller internal diameter to withstand the pressure of the blood that has just been pumped from the heart - they carry blood away from the heart. They usually carry oxygen-rich blood away from the heart to the rest of the body, with the exception of the pulmonary artery which carries oxygen-poor blood to the lungs from the right ventricle of the heart.

Arterioles - Arteries divide into arterioles as they get further away from the heart.

Capillaries - Arterioles further divide into capillaries. Capillaries are microscopic blood vessels that enable the exchange of oxygen, carbon dioxide, nutrients and waste products to and from the tissues they are supplying, eg muscles.

Venuoles - The oxygen-poor blood returns to the heart from the capillaries via the venoules (sub divisions of the veins), to the veins, and ultimately the vena cava, before reaching the right atrium of the heart.

Veins - Carry oxygen-poor blood towards the heart. They have thinner walls than arteries but a wider internal diameter, and contain valves to ensure the blood flows in the correct direction.

Functions of the Blood

The functions of the blood include transport, protection, temperature regulation and clotting.

1. Transport

  • red blood cellsRed blood cells (erythrocytes) transport oxygen and carbon dioxide around the body through an iron protein molecule that it contains, called haemoglobin. When the blood is oxygen-rich, the haemoglobin has combined with oxygen to make oxyhaemoglobin). Red blood cells are made in the red bone marrow. The red blood cell does not contain a nucleus.
  • Plasma, a yellowish watery fluid carried in the blood, transports water, nutrients, waste products (eg urea), hormones (produced by the endocrine system), antibodies and enzymes.
  • Carbon dioxide dissolves in blood plasma so it can be transported to the lungs.

2. Protection

White blood cells fight disease in the body, both bacterial infections and viruses. Types of white blood cells include:

  • Granulocytes and Monocytes - which pass through small blood vessel walls to fight pathogens.
  • Lymphocytes - these cells form antibodies.
  • Basophils - less numerous, are thought to be concerned with allergic reactions.

Differences between red blood cells and white blood cells

  Red blood cells White blood cells
Ratio 600 1
Have nucleus No Yes
Function Transport oxygen Fight disease
Formed where? Red bone marrow Red bone marrow, lymph nodes and spleen

3. Temperature Regulation

Heat is transferred from the warmer areas of our body, such as muscles, and evenly distributed around the body. Temperature is controlled via vasodilation and vasoconstriction.

4. Clotting

A complicated mechanism involving blood platelets (thrombocytes - no nucleus, 2 week lifespan) that prevents the body from losing too much blood when injured. Blood clots are prevented from forming in undamaged blood vessels by enzymes, so avoiding a thrombosis.

Factors Affecting Heart Rate

  1. Chemicals eg adrenaline, caffeine, sodium, potassium, nicotine
  2. Temperature
  3. Emotions
  4. Gender
  5. Age

(The bigger the animal, the lower the heart rate, on average)

Blood Pressure

Hypertension - high blood pressure
Hypotension - low blood pressure

Blood pressure is the pressure on the wall ot the artery where the blood pressure is measured. The systolic pressure (or peak) is measured when the heart beats, the diastolic is measure inbetween beats. It is measured in mmHG (mm of mercury) and is given as systolic/diastolic. A typical reading would be 120/70. A raised blood pressure would be in the region of 145/90.

Factors Affecting Blood Pressure

1. Cardiac Output - The amount of blood pumped in one minute (volume/min)

Stroke Volume - The amount of blood pumped per heartbeat (volume/beat)

Heart Rate - (beat/min)

Cardiac Output = Stroke Volume x Heart Rate

(Look at the units - volume/min = volume/beat x beat/min).

An increased heart rate leads to an increase in blood pressure and vice versa.

2. Blood volume - approximately 5l. Increased or decreased blood volume will lead to increased / decreased blood pressure.

3. Peripheral Resistance - resistance to blood flow by friction between blood and blood vessel wall.

4. Postural Hypotension - caused by disorders that cause damage to the nerve supply to blood vessels, such as diabetic neuropathy.

The Effects of Exercise on the Cardio Respiratory System

Short Term

  • Increased heart rate
  • Increased blood pressure
  • Increased breathing rate
  • Increase in cardiac output
  • Build up of carbon dioxide in the blood stream

Long Term

  • Increase in resting stroke volume
  • Increase in maximum cardiac output
  • Lower resting heart rate
  • Reduced risk of heart disease.