Lymph: formation and functions Body Fluids | people | biology (2023)

In this article we will discuss: 1. Introduction to Lymph 2. Properties of Lymph 3. Composition 4. Functions 5. Flow Rate 6. Formation 7. Circulation.

Contents:

1. Introduction to the Lymph
2. Properties of the Lymph
3. composition of the lymph
4. functions of the lymph
5. flow rate in the lymph
6. formation of lymph
7. circulation of the lymph

1. Introduction to Lymph:

The peripheral lymphatics are microscopic blind (closed) terminal vessels known as lymphatic capillaries. These tiny vessels are located in the intercellular spaces and their walls are formed by endothelial cells supported by fibrous connective tissue (Fig. 5.3).

These capillaries repeatedly join together to form larger lymphatic vessels, which pass through the lymph nodes, receive further inflows and gradually become larger. All lymph from the body is eventually collected in two major ducts — the right lymph duct and the thoracic duct (or left lymph duct), which open at the right and left subclavian veins, respectively.

The right lymphatic duct, about 1.25 cm long, drains from the right forelimb and the right side of the neck and chest (Fig. 5.4). The thoracic duct, about 38-45 cm long and about 4-6 mm in diameter, exits the cisterna (receptaculum) chyli and also receives the left cervical duct, lymph from the left front leg, the left side of the neck and collects breast. The cisterna chyli, located at the front of the body of the second lumbar vertebra, receives all the lymph coming from two hind legs and the alimentary canal (Fig. 5.4A).

The lymph vessels have valves that allow the lymph to flow towards the chest. The primary lymphatic vessels that remain in the middle of the villi of the small intestine are called the mammary glands, and during digestion, the mammary glands become filled with milk-white fluid called the chyle. The chemical composition of the chyle is similar to that of the lymph in other parts of the body, apart from its high fat content. There are no lymphatic vessels in the central nervous system.

Liquor cerebrospinalis takes the place of lymph. Lymphatic capillaries are not also found in cartilage, spleen, epidermis, inner ear and eyeball. The function of the lymphatic vessels is to transport tissue fluid from the tissues to the veins and to return water and protein from the interstitial fluid to the blood from which it originates. And the function of lactic acids is to aid in the absorption of digested food materials, generally fats, from the gut.

2. Properties of the Lymph:

The lymph is to be regarded as a modified tissue fluid. Lymph is the clear, watery-looking fluid found in lymphatic vessels and formed by the passage of substances from blood capillaries into tissue spaces. This process is known as transudation, which includes the processes of diffusion and filtration. A pure lymph sample can be obtained by cannulating the thoracic duct of an animal.

Lymph collected from the thoracic duct during fasting is transparent, yellowish in color, has a weak alkaline reaction and slowly coagulates. Its colloidal osmotic pressure is lower than that of plasma but probably higher than that of tissue fluid. Its hydrostatic pressure is very low. After a fatty meal, the thoracic duct lymph appears milky due to the presence of tiny droplets of emulsified fat absorbed from the alimentary canal.

3. Composition of the lymph:

Microscopic examination of the lymph shows that it contains large numbers of leukocytes (mainly lymphocytes) ranging from 500 to 75,000 per cubic meter. mm. No platelets present.

The composition of the non-cellular part of the lymph (fasting) is as follows:

I. water-94%.

ii. Solids - 6%.

solids:

I. Protein:

The total protein content is about half of the plasma and varies between 2.0 and 4.5%. It varies according to the body part from which it is obtained and also according to the activity level of the region. Lymph from the liver contains three times (6%) as much protein as lymph from the limbs (2%).

Lymph from the gut contains protein that falls between these two (4%). Three types of proteins are found - albumin, globulin and fibrinogen. Traces of prothrombin are also found. The fibrinogen content is very low. It is probably because the lymph coagulates very slowly. Albumin is proportionally much more than globulin compared to plasma.

The albumin/globulin ratio, which is about 1.5:1.0 in plasma, is much higher in the lymph. The protein content of the lymph is higher than that of the tissue fluid. However, since lymph originates from tissue fluid, this difference is not easy to understand. It has been suggested that water may be removed from the lymph as it flows along the lymphatic vessels; In this way, the proteins are concentrated. The higher amount of albumin is said to be due to its lower molecular weight and size and consequently higher rate of diffusion.

ii. Slices:

The fat content is low when fasting, but after a high-fat diet it can be 5.0-15%.

iii. Carbohydrates:

Sugar, 132.2 mg per 100 ml (canine plasma contains an average of 123.0 mg per 100 ml).

IV. Other ingredients:

(Expressed in mg per 100 ml) urea, 23.5 mg (plasma, 21.7 mg); non-proteinaceous nitrogenous substance, 34.8 mg (plasma 32.6 mg); creatinine, 1.4 mg (plasma 1.37 mg); chlorides, 711 mg (plasma 678 mg); total phosphorus, 11.8 mgm (plasma 22 mgm); inorganic phosphorus 5.9 mg (plasma 5.6 mg); Calcium 9.84 mg (plasma 11.7 mg). Enzymes and antibodies are also present.

From the above, the difference between plasma and lymph can be established. Protein, calcium and total phosphorus are lower than in plasma. Chlorides and glucose are significantly higher. Other components are also sometimes higher than in the plasma.

4. Functions of the Lymph:

I. Nutritional value:

It provides nutrients and oxygen to the parts that the blood cannot reach.

ii. Drainage:

It drains excess tissue fluid and the metabolic products and tries to keep the volume and composition of the tissue fluid constant.

iii. Transfer of proteins:

The lymph returns proteins from the tissue spaces to the blood.

IV. Fat intake:

Fats from the intestine are also absorbed via the lymph vessels.

v. Defense:

The lymphocytes and monocytes of the lymph act as the body's defense cells. The lymph vessels also remove bacteria from tissues.

5. Velocity of flow in the lymph:

The rate of lymph flow along the human thoracic duct is 1.0-1.5 ml per minute. In dogs it is much higher. Lymphatogogue is the substance that increases the speed of lymph flow.

Lymph flow rate regulation depends on:

(a) interstitial pressure,

(b) arterial pulsation,

(c) intrathoracic pressure and

(d) Muscle massage.

6. Lymph formation:

Since lymph is formed from tissue fluid, anything that increases the amount of tissue fluid increases the rate of lymph formation. The formation of lymph depends on physical factors. No vital secretory process is involved in this.

The following factors are responsible for the formation of lymph:

1. Capillary pressure:

If the capillary pressure increases, the speed of lymph formation increases. This is evident in venous obstruction. [But over time, the rate slows down due to increased fluid accumulation in the tissue spaces and the consequent increase in tissue fluid hydrostatic pressure.]

2. Capillary Wall Permeability:

Under all conditions in which the permeability of the capillary wall is increased, more tissue fluid and consequently more lymph is formed.

The following factors increase capillary permeability:

I. temperature rise:

Elevated temperature at a specific location increases capillary permeability.

ii. Substances acting directly on the capillary wall:

Peptone, foreign proteins, histamine and extracts from strawberries, crayfish, mussels, leeches etc. have a damaging effect on the capillaries and thereby increase their permeability.

iii. Reduced oxygen supply:

When there is a lack of oxygen, the lymph flow increases due to the higher permeability of the vessels. It probably acts by damaging the capillary endothelium. Anoxia, anemia, congestion of blood due to vascular congestion leads to such results.

3. Substances that change osmotic pressure:

Everything that lowers the colloidal osmotic pressure of the blood promotes the formation of tissue fluid and lymph. Normal or hypotonic saline when given intravenously dilutes plasma colloids and lowers osmotic pressure. In addition, blood pressure increases. These two factors favor the formation of tissue fluid and lymph. Hypertonic solutions will exert the same effect in a better way.

Hypertonic solutions introduced into the blood initially draw more fluid from the tissue spaces and further increase the blood volume. The blood pressure is greatly increased and plasma colloids are further diluted. In this way, hypertonic solutions increase lymph formation much more than the normal or hypotonic solutions. Solutions of NaCl, glucose, Na₂SO₄etc. can be used for this purpose.

4. Increased metabolic activity of an organ:

Increased activity of a specific area increases lymph flow in the locality.

It is due to:

I. Formation of other metabolic products that increase the osmotic pressure of the tissue fluid.

ii. Local vasodilation and increased capillary pressure and permeability.

iii. Relative Anoxie.

IV. Increased temperature of the place.

The last two also work by increasing capillary permeability.

5. Massage and passive movements:

These increase lymph flow to a certain extent, just like active muscle contraction.

7. Circulation of the Lymph:

In frogs, the circulatory system is maintained by rhythmically contracting lymphatic hearts. But no such pump exists in higher animals, and the flow is maintained only by a number of physical factors.

They are as follows:

I. pressure drop:

In the tissues, the pressure of the lymph (8 to 10 mm Hg) is higher than in the thoracic duct (0 to 4 mm Hg).

ii. Presence of valves:

The presence of valves in the lymphatic channels helps maintain flow in one direction.

iii. muscle action:

Muscular (skeletal) contraction, active or passive, compresses the lymphatics and carries the lymph along because the valves within the lymphatics prevent backflow. Contraction of the villi helps pump chyle from the central mammary glands into the basal lymphatics. This lymph is transported to the cisterna chyli with the help of the intestinal movements.

IV. breathing movements:

When you breathe in, the intrathoracic pressure drops due to the lowering of the diaphragm, which in turn sucks lymph into the chest? In addition, the intra-abdominal pressure increases. This compresses the cisterna chyli, increasing lymph flow through the thoracic duct. These pressure changes during inspiration are very important factors in maintaining lymphatic circulation.