THE LYMPHATIC SYSTEM [CSEC HSB]

-

SYLLABUS REFERENCE 

[B3.13] describe the structure and function of the lymphatic system 

[B3.14] describe how tissue fluid and lymph are formed 


THE LYMPHATIC SYSTEM IS A
DRAINAGE SYSTEM

It takes the tissue fluid that is not reabsorbed by capillaries, and eventually empties it back into the circulatory system, via the right and left subclavian veins. 

KEY POINTS 

  • When tissue fluid enters the lymph capillaries it is then called 'lymph'. 
  • Lymph consists of plasma and white blood cells, but not red blood cells or large plasma proteins. 
  • The lymphatic system has a separate circulation, which returns lymph to blood. 
  • Lymphocytes in lymph nodes multiply during infection & produce antibodies. 

TISSUE FLUID 

This is a liquid that surrounds all of our cells. 

It is formed when the liquid part of the blood, coming from the blood plasma, leaks out of the capillaries into the spaces surrounding the cells. 


This leakage occurs as the blood pressure in the arterioles pushes the blood against its walls. It thus forces water & other small molecules through gaps in the capillary walls. 
Tissue fluid contains no blood cells. However, it does have some of the large protein molecules from the blood plasma. 

IMPORTANCE OF TISSUE FLUID 

  • It provides a constant physical & biochemical environment for the cells 
  • It facilitates the transfer of materials between the blood & the cells, via diffusion. Materials such as nutrients & carbon dioxide. 
  • It allows for the movement of white blood cells amongst the various tissues and cells, in pursuit of pathogens. 

90% of it is reabsorbed into the plasma, with the rest draining into the lymphatic system. 


FEATURES OF LYMPHATIC SYSTEM 

Functions

  • Returns excess tissue fluid to the blood 
  • Transports fats, particularly from villi in small intestine to blood 
  • Removes microbes to the lymph nodes, where they are destroyed by phagocytes & lymphocytes. 

Components 

  • Lymph capillaries. These are blind-ending, tiny vessels that absorb the excess fluid from around the cells. They have clefts that only allows tissue fluid to flow into the vessels. 
PNG version of the original
  • Lymph vessels. They form a network throughout the entire body, connecting lymph nodes, adenoids, tonsils and lacteals. They expand into the lymph capillaries at tissue level. 
    • They have semi-lunar valves, which only allows the tissue fluid to move in one direction. 
    • They are thin-walled. 
  • Ducts. These are two large lymph vessels into which the smaller lymph vessels merge. They then empty into left and right subclavian veins, located under the collar bone. 


The lymphatic system has no pump. As a result, the flow of lymph is much slower than in the cardiovascular system, Like veins though, they depend on the contraction of surrounding muscles to help with flow. 





Popular posts from this blog

HUMAN REPRODUCTION [CSEC HSB & BIOLOGY]

-
Image
SYLLABUS REFERENCE  CSEC BIOLOGY  [B9.2] describe the structure & function of the reproductive systems in humans;  [B9.3] describe the menstrual cycle;  [B9.4] outline the mechanism for bringing gametes together, their fusion, and the development of the embryo in humans;  CSEC HSB [B7.2] describe the structure and function of the reproductive systems in human beings;  [B7.3] describe the menstrual cycle;  [B7.4] explain ovulation, fertilisation, implantation, and development of the embryo;  [B7.5] describe the stages of the birth process; 
Read more

RESPIRATION, GASEOUS EXCHANGE, AND BREATHING [CSEC BIOLOGY & HSB]

-
Image
SYLLABUS REFERENCE  CSEC HSB  [B2.1] explain the importance of breathing in humans;  [B2.2] relate the structures of the respiratory tract to their functions;  [B2.3] describe the breathing mechanism;  [B2.6] distinguish between gaseous exchange and breathing;  [B2.7] identify characteristics common to gaseous exchange surfaces;  [B2.8] differentiate between aerobic and anaerobic respiration;  CSEC BIOLOGY  [B3.1] describe the process of aerobic respiration; [B3.2] distinguish between aerobic and anaerobic respiration;  [B3.3] describe the mechanism of breathing in humans and gaseous exchange in flowering plants;  [B3.4] identify characteristics common to gaseous exchange surfaces; 
Read more

NERVOUS vs ENDOCRINE SYSTEM [CSEC HSB & Biology]

-
Image
SYLLABUS REFERENCE  CSEC HSB [B6.1] describe the main divisions of the nervous system;  [B6.2] distinguish between a neuron and a nerve;  [B6.3] explain the functions of motor and sensory neurons and spinal synapses;  [B6.4] describe the functions of the parts of the brain;  [B6.5] describe the mechanisms of a reflex action;  [B6.6] explain the process by which voluntary actions occur;  [B6.7] distinguish between a voluntary and involuntary action;  [B6.8] explain the response of the sense organs to stimuli;  [B6.13] compare and contrast endocrine and nervous control systems;   [B6.14] identify the sites of hormone production;   [B6.15] explain the roles of selected hormones in the human body;  CSEC Biology  [B7.1] define 'stimulus' and 'response';  [B7.2] describe the response of: (a) green plants to stimuli; (b) invertebrates to variations in light intensity, temperature and moisture;  [B7.3] define r...
Read more