2.8 TRANSPORT SYSTEM

Human Circulatory System

MAMMALIAN HEART

            (i) Initiation of heart beat and its control.          

The sinoatrial (SA) node act as a pacemaker. SA node generate electrical impulses. Impulses from the SA node spread rapidly through the wall of atria causes atrial systole. The impulses then passed to atrioventricular (AV) node which located in the wall between the left and right atria. Here, impulses are delayed 0.1 second before spreading to the heart apex. This delay ensure the atria to empty completely before the ventricles contract. Then the impulses from AV node are conducted to the heart apex and ventricular walls by bundle of His and Purkinje fibers which causes the ventricular systole.  Ventricular systole pumps blood into the pulmonary arteries and the aorta.  

(ii) Flow of oxygenated and deoxygenated blood (cardiac cycle)

 

Atrial systole and ventricular diastole. Atria contract. The pressure in atria increases higher than in the ventricles. The atrioventricular (AV) valves open. Then blood is pumped from the atria into the ventricles.

Ventricular systole and atrial diastole. The ventricles received impulse from the Purkinje fibers. Both ventricles contract. The pressure in the ventricles increases higher than in the atria. The atrioventricular (AV) valves close, ‘lub’ sound produced. The pressure in the ventricles increases higher than in the aorta and the pulmonary artery. The semilunar valves open. Then blood is pumped from the ventricles into the aorta and the pulmonary artery.

Atrial and ventricular diastole. Both ventricles and atria relax. The oxygenated blood from the pulmonary vein enters the left atrium and the deoxygenated blood from the vena cava enters the right atrium. The pressure in the ventricles decreases lower than in the aorta and the pulmonary artery. The semilunar valves close and ‘dub’ sound produced.

LYMPHATIC SYSTEM

Composed of:
(I)  Lymphatic vessels
(II) Lymphatic organs: thymus gland, spleen, tonsils, lymph nodes

Functions:

(I)   Helps to defend body the against infection.

(II) Transport fats from the digestive tract to the circulatory system.

Interstitial fluid enters lymph capillaries, then become lymph. Lymph is clear and watery fluid. Then lymph passes from lymph capillaries into lymphatics. When lymph moves through the lymph nodes, phagocytes filter out bacteria and other harmful materials. 

Function: 

Transportation of lipid which in the form of chylomicron (fatty acids and glycerol coated with protein) from the lacteal of villi to the blood circulatory system, through right and left subclavian veins.

TRANSPORT IN PLANTS: XYLEM

 
Transport of water and minerals from surrounding soil to the cortex or endodermis

Apoplastic route/pathway = water and minerals move along the cell walls and extracellular spaces.

Symplastic route/pathway = water and minerals move along the continuum of cytoplasm in a cell to the adjacent cells through plasmodesmata.

Vacuolar route/pathway =  water and minerals move from vacuole of a cell to the vacuole of adjacent cells through plasmodesmata.

TRANSPORT IN PLANTS: XYLEM

 Water moves from high water potential to low water potential. Water potential in the soil is higher than in the root. So, water diffuse from the soil to the root hair by osmosis.

Water and minerals from soil enter the plant through the epidermis of roots, then to the cortex before pass to the xylem of the vascular cylinder. 

Root pressure:

At night when there is almost no transpiration, the root cells actively pumping the mineral ions into the xylem of the vascular cylinder. The accumulation of the minerals lowers the water potential in the vascular cylinder. Thus, water molecules  flow in from the root cortex, generating the root pressure which is a push of the xylem sap.

TRANSPORT IN PLANTS: PHLOEM

(Translocation of sugar/sucrose)