The circulatory and cardiovascular system:

The circulatory system includes:

  • Heart
  • Blood vessels
  • Blood 

The transport medium is blood which is a thick viscous fluid, heavier than water and it takes up 7 – 8%% of the body weight.


Functions of the blood constituents:

Liquid components: 

1. Plasma – straw coloured fluid in which the different cells are suspended.
Liquid transport medium for the cells and materials. Around 55% of the blood is made up of plasma

2. Plasma proteins - protein bodies that act as substrates for different nutrients (to help binding).
Plasma proteins are the bigger proteins, the albumin and globulins which are formed in the liver. Plasma proteins are very important in the immune response.

Globulins: They bind to, neutralise and destroy foreign materials
               Help with transportation of some hormones eg thyroglobulin
               Help to transport mineral salts eg transferrin carries mineral iron

Albumin: Maintain osmotic pressure
              Act as carriers for lipids and steroid hormones

Cellular / formed components: 

1. Red blood cells - called erythrocytes 

Formation of Red blood cells: Called hemopoiesis. Before birth: this is done in the embryionic sac, liver, spleen, thymus gland, lymph nodes, and red bone marrow. After birth RBC are made in the red bone marrow of flat bones

Function: carry haemoglobin which attahces to oxygen and transports oxygen to the cells and carbon dioxide away from the cells.

2.  White blood cells – or leukocytes which are responsible for the immune response of the body, and there are many different types of leukocytes 

3. Inorganics salts - used  in various processes in the body eg Calcium is essential for the heart to beat 

4. Waste products - breakdown products after metabolism, unused products and by-products where only part of a substance was used. 

5. Gases - carbon dioxide is carried to the lungs for excretion oxygen for uptake.

6. Hormones - carried to the various target organs from the endoa dn exocrine glands. 

7. Nutrients - taken from the stomach and intestines and transported to the body




The circulatory system is a connective system which connects the parts of the body together, help with transports of blood and all its compounds. The heart and circulatory system is also known as the cardiovascular system as it is responsible for circulating the blood to the body. The circulatory system is divided into systemic circulation and pulmonary circulation.

Oxygenated blood from the left ventricle travels through the aorta, which branches off into the descending and ascending aorta, and also to itself via the coroanry circulation to replenish the oxygen in the organs. 

The coronary circulation: 

Right and left coronary arteries branch off just above the semi lunar valve (which stop the blood flowing back). 

Deoxygenated blood from the heart is transported through the coronary veins through the coronary sinus which empty into the left atrium. 

Portal circulation

The portal circulation is the system of veins and its tributaries which supply the intestines and the liver. It is also called the portal venous system. 

The portal vein system is responsible for transporting hte blood from the intestines, to the liver with all the nutrients which can then be metabolised and processed before continuing to the heart. It also includes drainage from the spleen and pancreas. this metabolism before moving to the rest of the body is called the first pass effect. 

The portal system has the following branches: 

  • Superior mesenteris vein - from the small intestine and beginning of the large intestine. 
  • Gastric vein from the stomach
  • Splenic vein form the spleen and pancreas
  • Inferior mesenteric vein from the large intestine
  • Cystic vein from the gall bladder

The heart is essential to survival, and thus called a vital organ. It is a unique muscular pump that forces the blood to the body parts. 

The circulatory system is a transport system, taking oxygen and nutrients to cells in the body, while removing the toxins, byproducts out of the system and transporting deoxygenated blood back to the  lungs. 

The cardiovascular system includes the heart, veins, arteries, capillaries and is divided into central and peripheral areas.

  • Central areas of the body means the heart itself with the immediate vessels, and the vital organs
  • Peripheral means the areas moving away from the heart to the limbs.

Another name for the heart is cardiac muscle or myocardium and the system is known as the cardiac system. In summary, the hearts function is to feed the central organs, peripheral organs and itself with essential nutrients, gases and remove toxins from those areas so that the body can function optimally. 


The vessels are:

Cardiac veins : carrying deoxygenated blood to the heart muscle

Cardiac arteries: feeding oxygenated blood to the heart muscle

An enlarged heart means that the heart over  works over a long period of time, due to over exercising, obesity, congenital problems.

When the heart is not able to pump enough oxygen to the body, it is known as cardiac INSUFFICIENCY.As the oxygen grows less, the area of the heart muscle dies and this is called infarction. A myocardial infarction is commonly known as a “heart attack”. Myocardial infarctions/ heart attacks can be caused by a clot of blood preventing the blood taking oxygen to the area, or a fat embolism () or an enlarged heart is too overworked to get the blood to the correct areas.

An enlarged heart occurs when the heart has been overworked over a long period of time due to 

  • exercise
  • illness (rheumatic fever)
  • obesity
  • congenital abnormalities.

The symtoms include: 

  • Swelling in the legs
  • Increased weight due to water retention
  • Shortness of breath
  • increase size around the abdomen
  • Fatigue
  • Palpitations / feels like skipped beats in the heart when lying flat)

Blood is divided into “formed”/cellular parts and plasma/liquid

55 % Liquid


Liquid transport medium for the cells and materials. Around 55% of the blood is made up of plasma

Plasma Proteins:

– these are the bigger proteins, the albumin and globulins which are formed in the liver.

Plasma proteins are very important in the immune response. Globulins and Albumin are 2 examples. 

Globulins: They bind to, neutralise and destroy foreign materials. Functions of globulins: 1) they help with transportation of some hormones eg thyroglobulin. 2) Help to transport mineral salts eg transferrin carries mineral iron

Albumin: Functions of albumin 1)Maintain osmotic pressure 2) Act as carriers for lipids and steroid hormones

45 % Cellular/ formed parts

Red blood cells:

Red blood cells are called Erythrocytes.

Formation of RBC is called hemopoiesis. Before and after birth hemopoeisis works differently.Before birth formation of RBC is done in the embryionic sac, liver, spleen, thymus gland, lymph nodes, and red bone marrow. After birth RBC are made in the red bone marrow of flat bones

Function: carries oxygen to the cells and carbon dioxide away from the cells.


  • Selectively permeable membrane
  • Erythrocytes are biconcave discs
  • no nucleus
  • contain haemoglobin which combines with oxygen and carries it to the body

Interesting facts:

  • RBC do not use any of the Oxygen that it transports because there is no metabolism inside the cell.
  • RBC Cannot divide or metabolise

White blood cells:

Also known as Leukocytes. There are different types of leukocytes, whcih will be discussed in a later slide

The Heart

The heart is a muscular pump situated in the centre of the thorax, between the lungs, behind the sternum. The apex (tip of the heart) points slightly to the left. A normal heart size is about the size of the persons fist. 

The heart is made up of 4 compartments, the right and left sides are divided by a septum (wall of muscle), while the top and bottom compartments on the left and right side are dividies by valves , allowing the blood to pass through. it serves to pump blood to the lungs to be oxygenated, then to pump the blood to the rest of the body with teh oxydenated blood. 

The heart receives the blood from the body through the superior (body above the level of the heart) and inferior (below the level of the heart) vena cava (big veins transporting deoxygenated blood). THe blood comes into the first compartment canlled the right atrium.

From the right atrium is goes down through the tricsupid valve to the right ventricle. From here the blood follows the Pulmonary artery to the lungs to fetch the oxygen from the alveoli.

Once the blood is oxygenated, the capillaries form veins and these all come together to form teh pulmonary vein which goes back to the heart. the oxygenated blood returns to the heart through the left arium, passes though the mitral valve into the largest and strongest part of the heart, the left ventricle.

The left ventricle pumps the blood throught the aorta to the body.

Structure of the heart:

The heart has 4 chambers, 2 atria (one top, one bottom) and 2 ventricles (one top one bottom).

The main artery leaving the heart is the aorta

The main veins are the inferior vena cava and the superior vena cava

The top atrium have thinner muscular walls as the blood does not get pumped very far.

The bottom ventricles have much thicker walls because there is more pressure needed and the thickest/strongest muscular wall is the left verntricle.

The aorta is the biggest artery in the body, almost as wide as 2 fingers together. While the vena cavas are the biggest of the veins. 

Structure of the muscle:

The heart wall is made up of 3 layers:

Epicardium: thin outermost layer which protects the heart and helps to lubricate

Myocardium: the thick middle layer responsible for pumping the blood. 

Endocardium: inner lining of the heart, made up of simple squamous epithelium. The endothelium 's main function is to prevent the blood sticking to the wall of the heart. 

Summary of the valves of the cardiac system: 

the tricuspid vavle is found between teh right atrium and the right ventricle. 

The mitral valve (also know as biscuspid valve)is found between the left atrium and left ventricle. 

The semilunar valves are at the base of the pulmonary areter and arota, and prevent blood from slipping back into the heart 

The Atria

  • The atria is made up of cardiac muscle
  • There is a left and right atrium
  • The inferior vena cava (from the lower body) and superior vena cava (chest and upper body) pour deoxygenated blood into the right atrium.
  • The right atrium also received deoxygenated blood from the cardiac circulation (feeding the heart)
  • The oxygenated blood from the pulmonary vein fills the left atrium
  • There is a thin septum wall between the atria, compared to the thick ventricular wall
  • From here it moves to through the tricuspid valve to the right ventricle

The Ventricles

  • The ventricles receive blood from the atria; from the tricuspid valve on the right, and through the mitral valve on the left.
  • There is a left and right ventricle, the left side is the thickest part of the cardiac muscle
  • The right receives deoxygenated blood which it pumps through the pulmonary artery to the lungs
  • The left pumps oxygenated blood to the aorta, and feeds the rest of the body
  • The other name for the mitral valve is the bicuspid valve

The Cardiac Electrical Conduction System Nerovus supply to the heart

There is a group of specialised cells in the wall of the heart which send electrical impulses to the heart muscle to allow it to contract. The contraction causes a pumping motion which pumps the blood to the next phase.

The 5 important parts of the elctrical conduction system are:

  1. SA (sinartial) node

  2. AV (atrio-ventricular) node

  3. Bundle of His

  4. Bundle fibres

  5. Purkinje fibres

The SA node is located in the right atrium, starts with an electrical impulse. 

the atria contract pushing blood through the valves to the ventricles. 

The impulse travels to the AV node which is located in the atria. 

The impulse follows to the bindle of His and then divides left and right to the Purkinje fibres causing the ventricles to contract. 

The left ventricle contracts slightly before the right.

The heart now relaxes.

This is called the CARDIAC CYCLE

Electrical activity is mesured using an ECG - electrocaridogram. This is one of the best ways to view the function of the heart. 








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