How it all fits together ... Cells and Energy

All animal cells are surrounded by tissue fluid.  This is the source of the water, oxygen and nutrients needed by the cells but it also removes any substances excreted from the cell.  As I explained in my blog about the Lymphatic System, the tissue fluid is where the exchange of substances happens between the cells and the blood vessels and lymph!

Cells need water because almost all processes that are essential to life take place in a solution! Oxygen and nutrients are necessary to produce energy.  All these elements are carried to the cells in the blood.  Water and nutrients enter the blood from the digestive system, oxygen enters through the respiratory system.

Horses (and all living things) need usable energy to move, grow, reproduce and repair.  Energy cannot be created (or destroyed) it is only changed from one form to another (the first law of thermodynamics).  Energy exists in many forms; including chemical, electrical, nuclear, heat, light, and mechanical.

For all living things,  energy is obtained from food, for a horse this is usually grass, hay or supplementary food.  How is the energy from food made available for the horse to use for these processes?  The process is called cellular respiration and it occurs in every living cell. 

In my blog about cells a couple of weeks ago I mentioned that mitochondria supply energy to the cell.

The form of energy used to fuel the biological processes mentioned above is ATP (adenosine triphosphate) but very little is stored in the body.  In fact, at any one moment the body only has enough ATP to keep it alive for 1 second!  So, ATP is continuously produced through cellular respiration, and there are 2 types: -

• Anaerobic respiration - is when energy is transferred from food to ATP without oxygen.  In this process food molecules are only partly broken down, not fully to result in carbon dioxide.  Glucose in the food molecules is broken down in to pyruvate (the process is called glycolysis) and then in animals the pyruvate is converted into lactate or lactic acid (lactate fermentation).  Lactic acid build up is what causes us to have stitch if we don't breathe properly when doing sitting trot!

•  Aerobic respiration - is when the glucose is broken down using oxygen,  this happens in a number of stages to limit the amount of heat produced.  As the food molecules are broken down the energy released is used to produce ATP .  Aerobic respiration can produce a much larger number of ATP molecules than anaerobic  respiration.

NB - a molecule is a small particle.

The stages of cellular respiration:-

1.       Glycolysis & Fermentation - occurs in both anaerobic and aerobic respiration, so can take place with or without oxygen. 

2.       The Krebs Cycle - takes place in the mitochondria of the cell and requires oxygen.

3.       The Electron Transport System - also takes place in the mitochondria and requires oxygen.

Once the energy from food has been converted to ATP it can be used to fuel other processes performed by the cells eg: muscle contraction or to move substances between cells such as glucose reabsorption in the kidneys.

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Until next time!

Jo