UNIT 6: Systems involved in nutritionII: Circulatory and excretory systems

1- Circulatory system

There two types of circulatory systems:

A-Blood circulatory system

B-Linfatic circultory system

A -Blood circulatory system:

It consists of:

-Blood:is a liquid tissue made up of:

-Red cells orerythrocytes: contains hemoglobin (a protein with iron that causes its reddish color). They carry oxygen to the body. They are biconcave in shape.

- Leukocytes or white blood cells:are involved in protecting the body against both infectious disease and foreign invaders.

-Platelets: Are fragments of cells involved in blood clotting (coagulation) during bleeding when a blood vessel breaks.

-Plasma:is a yellowish mixture of water, nutrients and waste products produced by cell metabolism, CO2, proteins (like antibodies), and hormones.

-Blood vessels: pipes that transport blood throughout the human body.There are three types:

- Arteries: are vessels that carry blood away from the heart to the organs. Their walls are thick and elastic to bear the high blood pressure when the heart pumps.

-Veins: are vessels that return the blood to the heart from the organs. They have valves to prevent blood from flowing in the wrong direction.

-Capillaries: are tiny vessels that connect the arteries and veins; it is through the capillaries that nutrients and wastes are exchanged between the blood and tissues. Nutrients and oxygen flow from capillaries to the interstitial fluid (liquid that bathes and surrounds the tissue cells) then from the interstitial fluid to inside the cells. Wastes and carbon dioxide flow from the cells to the interstitial fluid and finally enter the capillaries.

-Heart: Is the pump that moves the blood through the body. It is formed by heart muscle cells. The heart is surrounded by a layer called pericardium.

Heart structure:



Blood flow through the circulatory system is double (blood goes through the heat twice following two different circuits) and complete(there is no mixture between oxygenated blood and non oxygenated one).

The heart has three movements to pump blood:


Cardiovascular disorders:

-Atherosclerosis: when a substance called plaque builds up in the walls of the arteries. The plaque narrows the arteries, making it harder for blood to flow through.

-A heart attack occurs when the blood flow to a part of the heart is blocked by a blood clot. If this clot cuts off the blood flow completely, the part of the heart muscle supplied by that artery begins to die. When the clot partially cuts off the flow, the heat attack is known as angina pectoris.

B -Lymphatic circulatory system:

It consists of:

-Lymphatic vessels: Transport lymph throuhg the body. They comunicate with blood vessels

-Lymph: Liquid similar to blood but without red cells, and with more proteins.

-Lymph nodes: Where a type of leukocytes known as lymphocytes fight against infections by producing antibodies that destroy them. We have lymph nodes distributed all along the body (armpits, chest, kneck, inguinal area,...)

2- Excretory system

The function of excretion is thedischarging of wastes produced by cell metabolism. These wastes products would be very poisonous if they acumulate in the body. The process of excretion is carried out by the excretory system.

There are different excretory organs involved in this function:

  • Lungs: Eliminate carbon dioxide produced by cell breathing.
  • Liver: Release bile acids into the intestine. Bile acids are produced when hemoglobin from red cells is digested in the liver.
  • Sweat glands (in the skin): Release urea as sweat.
  • Kidneys: Produce urine with urea (nitrogen produced from protein metabolism).


Urinary system:



Nephron structure:

Steps of urine production in nephrons:


1-Filtration: small substances (water, mineral salts, protein, gluscose,...) are filtrated from the blood (Malpighio’s glomerulus) into the Bowman’s capsule.

2-Reabsorption: Useful materials (such as glucose, proteins and part of water and mineral salts) go back into the blood capillaries that surround the proximal convoluted tubule.

3-Secretion: Ions are released from the blood capillaries that surround the distal convoluted tubules into the nephron in order to become a part of urine.