Lymph hearts
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While discussing types of muscles we considered the cardiac muscle, which is a very special type of muscle. It is peculiar in having some features of skeletal and some features of smooth muscles. Then we discussed the hearts of some vertebrates like human and some invertebrate animals like the octopus and apple snail.
By and large when we talk of heart/s we talk about the hearts which pump blood. But do you know that there are special types of hearts in some animals that pump lymph?
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[edit] Lymphatic system of frog
Lymphatic system of frog consists of lymph, lymph vessels, lymph heart, lymph spaces and spleen. Some mast cells can also be found in the lymphatics of the tongue of some of the frog species.
[edit] The lymphatics and the lymph
As it is a filtrate of blood it closely resembles the plasma in its composition that is it has water, small composition of matabolic waste materials but little amount of proteins. Lymphatics or lymph vessels carry the lymph and in frog open into the four lymph hearts. These lymph hearts are located on the dorsal side of frog's body. The anterior that is the front pair is situated below the shoulder blades that is the scapulae. The posterior that is the hind pair is on either side of a long, rod like bone called urostyle, formed by the fusion of last few vertebrae. The anterior pair opens into the subclavian vein and the posterior pair into femoral vein. Summerize it as: One pair by the 3rd vertebra-pumps lymph into jugular vein. Second pair at the end of vertebral column-pumps lymph into iliac vein in the legs.
[edit] Mast cells in the lymphatics of the tongue
Rana catesbiana and Rana nigromaculata have mast cells found in the lymphatics of the tongue these are round and in the monocellular layer of the lymphatic walls either as close adhesion or in contact with cytoplasmic process.
[edit] Mechanism of the lymph heart
The lymph hearts rhythmically and slowly contract to drive the lymph into the veins. It is possible to see the lymph hearts beat by looking on the dorsal surface on either side of the urostyle. In the toad normal lymph heart rate is about 50 beats per minute. Thus the lymph emerging out of blood ultimately merges into the blood. It returns the proteins back to blood.
[edit] In the human body
In our body there are no lymph hearts and the return of lymph depends to a great extent on squeezing action of skeletal muscles like the ones in calves. Any one who has to stand continuously for long hours on his feet benefits by shuffling the feet and wiggling the toes. Swelling of feet that is edema is common in people who as a professional hazard have to keep standing for a long time. By stretching limbs we feel better. By placing a couple of pillows beneath feet while lying down for rest helps lymphatic return to heart in people who find their feet and legs swollen due to inadequate lymphatic return.
Lymph hearts are organs found in lungfishes, all amphibians, reptiles and flightless birds. They function as small pumps that pump lymph (fluid, proteins and ions) that has leaked out of the circulatory system, back into the circulatory system.
[edit] Sizes of the lymph heart and the rate at which they pump
These hearts vary in size from microscopic in lungfish to an estimated 20-liter capacity in some of the largest dinosaurs. In frogs and turtles they pump at rates higher than the blood heart and the volumes pumped are quite remarkable.[says who?] In toads and frogs, this volume can amount to about 1/50 the output of the blood heart. In amphibians, lymph hearts lie at vein junctions. Frogs and salamanders have 10 to 20 lymph hearts, while caecilians have more than 100. Conversely, reptiles have single pair of lymph hearts in the pelvic area. In flightless (ratite) birds, the lymph heart function is less clear and the two almond-sized hearts located near the spinal column close to the hip joint are thought[by whom?] to be involved in inflating and deflating the phallus with lymph, which is of a significant size in both sexes of emus and ostriches.
