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HOW CIRCULATION IN INSECTS

This unit shows how circulation occurs in Insects
  • Systole (contraction). During systole, waves of contraction take place in the heart beginning at the posterior end and proceed to the anterior (Aortic) end.
  • This propels blood forward in the heart and when it reaches he anterior end, the blood leaves the heart and enter the haemocod (previsceral) cavity-where it flows.

 

  • Diastole (Relaxation of heart).
  • Blood re-enters the heart during diastole through the astia whose values allow it to enter but not leave. During this process;
  1. Stretching of heart ligaments.
  2. Contraction of alary muscles; which also serves to increase the tension on the heart ligament occurs.

 

  • These two adjustments, result in the pulling of the pericardial membrane downloads, thereby raising the blood pressure in the previseral cavity and lowering that in the pericardial cavity.
  • The resulting pressure difference causes blood to move from the previsceral cavity to the pericardial cavity and finally to the heart via the ostio.

INEFFICIENCY OF OPEN CIRCULATORY SYSTEM

– The low speed of circulation in the insect is due to:-

  1. The low pumping pressure
  2. The resistance offered to the fluid in the haemocoel.
  • This means that open circulatory systems are inefficient and are only suitable for small organisms.
  • It is on the above note that insect’s blood does not carry gases but exchange of gases is direct with the tissues via the tracheal system.

 

FUNCTIONS OF THE CIRCULATORY SYSTEM OF INSECTS

  1. Transports nutrients
  2. Transports nitrogenous wastes to points of elimination i.e. the malpigian tubules.
  • Defends the body against disease causing organisms using the phagocytes they contain.

ADVANTAGES OF A (DOUBLE) CLOSED CIRCULATORY SYSTEM OVER AN OPEN ONE.

  1. High blood pressure required for fast flow of blood is easily reached than in open circulation.
  2. Rapid circulation can be attained since the blood is rapidly returned to the heart for pumping.
  • There is complete separation of oxygenated and deoxygenated blood which improves efficiency of 02 distributions to cope with the high metabolic rates of the animal.
  1. Blood is pumped directly to where it is needed.

The amount flowing to a certain organ can be regulated by changing diameter of the blood vessels.

mamm

Similarities

  1. Both have muscular heat.
  2. Flow is unidirectional
  3. Both hearts have values
  4. Contraction of heart moves blood.
  5. Decrease in pressure around heart helps blood to flow towards it.
  6. Blood moves in pulses and waves.
  7. In both there is transport of food, harmones and wastes.
  8. In both blood is mainly sucked into heart.
  9. Both have supplementary systems i.e. lymph for mammalian circulation and contractive vessels in insect’s circulation.

manz

RELATIONSHIP BETWEEN CAPILLARIES, MELIS ………….AND LYMPHATIC

FORMATION OF TISSUE (INTERCELLULAR) FLIUD.

A high pressure at the arteride end of the capillary bed develops due to;-

  1. i) The narrow capillaries.
  2. ii) Pumping action of the heart.
  • This hydrostatic pressure forces blood plasma out through the capillary walls. The fluid bathes all cells of the body and hence called tissue fluid. It is similar to plasma, containing glucose, fatty acids, amino acids and salts but has a much lower concentration of proteins because the large proteins cannot pass through the thin pores of the capillary.

From it cells extract useful materials (glucose, amino acids, fatty acids and into it they secrete their CO2 and nitrogenous waste, hence acting as a means by which materials are exchanged between the blood and the body cells.

  • The narrow capillaries offer much, resistance to flow of blood which slows down its movement and thus facilitates exchange of the subsistence by diffusion.
  • The capillary resistance also results in a drop of pressure so tat the venous ends of the capillary bed, the blood pressure is less than that of the tissue fluid and the latter passes back into the capillaries.
  • Because plasma contains more proteins than the tissue fluid, it raises the concentration of solutes in the blood (low osmotic potential) which tends to draw H20 from the tissue from the tissue fluid into the capillary and at the venous erudit enters by osmosis.
  • The excess tissue fluid that does not go back through the veins is collected by the lymphatic vessels and taken back to the circulatory system.

THE LYMPHATIC SYSTEM

  • It is a system of “circulation” that collects excess tissue fluid and consists of vein like vessels, capillaries, ducts and glands.
  • When tissue fluid is inside the lymphatic vessel. It called LYMPH. They have very similar composition.
  • They lymphatic system is a one way system; with lymph flowing from tissues to the heart only. It also lacks a pump.
  • The movement of lymphatic is achieved in 3 ways.

. Hydrostatic pressure

The pressure of the tissue fluid leaving the arteroles helps push lymph along the lymph system.

Skeletal muscle contraction.

Which compresses vessels, exerting pressure on the lymph within them.

The vessels in the lymph (system) vessels ensure that this pressure pushes the lymph in one direction, i.e. towards the heart.

. Inspiratory movements

  • On breathing in pressure in the thorax is decreased. This helps to draw lymph towards the vessels in the thorax.
  • Lymph capillaries are similar to blood capillaries foe they are both one cell thick but lymph capillaries have blind or closed endings.
  • The lymphatic vessels carry lymph from all parts of the body towards the upper chest region.
  • The lymph vessels from the right side of the head and thorax and right arm combine to form the right lymphatic duct which drains into the right subclavion vein.

THE LYMPH NODES AND THEIR FUNCTIONS

The lymph nodes

Along the lymph vessels are a series of lymph glands or nodes. Most lymph nodes are found in the neck, the arm pits, the groin and around the intestines and ‘lungs’.

Functions

  1. Produces lymphocytes (type of White Blood Cells) which moves freely between the blood circulation and lymphatic system and these produce antibodies to kill any foreign matter they come across, hence they are an important part of the body’s immune system.
  2. The nodes also filter out bacteria and foreign particles from the lymph which are ultimately ingested by phagocytes.

During some infections, lymph nodes in the neck or art pits may swell due to accumulation of lymph and cells in them. That is why during physical examination a doctor sometimes presses the lymph nodes in the neck.

NB

Lymph is a milky liquid rich in lymphocytes and fats obtained from lacteals of the ileum.

 

 

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