Human transport system
أحياء لغات - الباب الثانى| The Human Blood
أحياء لغات - الباب الثانى| The Structure Of The Heart
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Human transport system
The vascular circulatory system
Blood vascular system and lymphatic system are closely connected with each other.
Human circulatory system is a closed circulatory system because its blood vessels form a complete circuit.
The circulatory system in insects is said to be opened because the blood not moves inside close blood vessels but move in the body cavities
The Structure of the heart
It is a hollow muscular pear shaped organ,
It lies in the middle of the hest cavity bending slightly towards to the left.
The heart is surrounded by a double membrane Called pericardium to protect the heart against Shocks & also to facilitate the hearts Pumping action
Anatomically the heart is divided into 4 chambers.
a) Two atria (auricles) they have thin walls & receive the blood coming from the body through blood vessels called veins.
b) Two lower ventricles
• They have thicker walls than, the atria (the left ventricle has the thickest wall ).
• They send the blood to all parts of the body through blood vessels called arteries.
• The heart is divided longitudinally into two main haves, left & right.
• The left half occupies with oxygenated blood & the right half occupies with deoxygenated blood.
• Each atrium connected to a ventricle below it through an opening controlled by a special valve to allow the passage of blood in one direction.
The valves
• Tricuspid valve ( it has 3 flaps )
It allow the blood to pass from the right atrium to the right ventricle and prevent it to return back.
• Mitral valve Bicuspid valve ( it has 2 flaps )
It allows the blood to pass from the left atrium to the left ventricle and prevent it to return.
• Pulmonary Simi-lunar valve (It has 3 pockets)
It allows the blood to pass from the right ventricle to the lunges through the Pulmonary artery and prevent it to return to the heart.
• Aortic Simi-lunar valve (It has 3 pockets)
It allows the blood to pass from the left ventricle to the body organs through the aorta artery and prevent it to return to the heart.
• The internal valves of vein can be observed in the arm veins when the arm is tied tightly with a bandage (tourniquet) {discovered by William Harvey}
NB
1- Malpighi who discovered the blood capillaries.
2- Ebn El Nafeeth discovered the blood circulation in the 10 Century.
3- William Harvey discovered the system of internal valves in veins and the blood circulation in the 17 Century.
The Blood vessels
They are 1- Arteries 2- Veins 3- Blood capillaries
3- Blood capillaries
Malpighi was the first (who discovered that arterioles & venules are connected together by microscopic vessels called blood capillaries.
The wall of the capillary is formed of one raw of thin epithelial cells its diameter is
7 : 10 microns the thickness of the wall is about 0.1 micron The cells have tiny pores in-between each other to facilitate the exchange of materials between the blood & the body cells.
If all the blood capillaries are put end to end, they will cover a length of about 80.000 Km
3- The human blood
Properties of the blood
1- It is a liquid tissue consists of plasma & cells (RBCs, WBCs & blood platelets)
2- The plasma which is the matrix )
3- It is a red viscous liquid due to the presence of hemoglobin.
4- It is weakly alkaline (pH=7.4)
5- The human’s body contains about 5 : 6 liters blood
The functions of the blood:
1- It transports digested food,O2, CO2 ,Nitrogenous wastes, hormones &some enzymes
2- It regulates metabolic activities.
3- It regulates the body temperature.
4- It regulates the internal environment of the body, such as osmotic potential, quantity of water inside the tissues & the PH value of the tissue fluids.
5- It protects the body against microbes & pathogen by means of the lymphatic system.
6- It protects itself against bleeding by the formation of the blood clot.
The contents of the blood are
The blood of the superficial wounds is darker than that of the deep wounds.
Because
The RBCs contain Haemoglobin (made of protein and iron).
* When the Haemoglobin carry O2 & change into Oxyhaemoglobin (light red) then the blood said to be oxygenated blood that passes through the arteries
*The arteries imbedded between muscles which affected by the deep wounds.
When Haemoglobin carry CO2 & change into Carboxyhaemoglobin ( dark red ) then the blood said to be deoxygenated blood that passes through the veins.
* The superficial wounds damage the veins that located near the body surface
The white blood cells has an important role in the immunity system
1- WBCs surround the pathogen & engulf them.
2- WBCs remove died cells & the wastes from the blood.
3- WBCs discover the foreign materials (foreign antigen) and stop their action .
4- WBCs Produce antibodies.
Antibodies:
They are chemical substance discover the harmful
foreign materials and stop their action to be harmless.
The heart beating
The origin of the heartbeats is the cardiac tissue itself because the heart continues beating regularly even after it has been disconnected to the body & the cardiac nerves..
The heart beats regularly due to the following
1) The sino-atrial node (pace maker) (S-A node)
It is a specialized bundle of thin cardiac fibers buried between the right atrium & the two large veins.
The sino-atrial node sends impulses to the muscles of the 2 atria causing their contraction.
2) The atrio-ventricular node (A-V node)
It lies at the connection between the atria & the ventricles .
It receives electrical impulses from the sino-.atrjal node.
The impulses spread rapidly through special fibers (named Hess & Perkinjs apparatus) to the muscles in the ventricle walls causing their contraction.
The sino atrial node regulates the beating at a regular rate of about 70 beats /minute
Their are two nerves connected to the sino-atrial node.
a) The vagus nerve inhibits the rate of the heart beating.
b) The sympathetic nerve accelerates the rate of the heart beating.
The rate of the heart beating varies according to various factors for example:
During sleeping and sadness, the rate lowers but during exciting and physical activities, the rate rises.
The heart sounds
Lubb-Dubb ….. Lubb-Dubb….. Lubb-Dubb….. Lubb-Dubb
Two different sounds can heard by stethoscope during the heart beating as following:
1- Lubb sound It is long & low pitched.
It heard during the contraction of the ventricles due to the closure of the bicuspid & tricuspid valves.
2-Dubb sound It is short & high pitched.
It heard during the contraction of the atria & relaxation of the ventricles due to the closure of the pulmonary & aortic Simi-lunar valves
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