Page 40 - 86 human physiology part-2

Nutrition

Metabolism

Absorptive and post absorptive stage of metabolism

The body has two phases to it metabolic cycle. The first is known as the absorptive stage. This
stage happens 3-4 hours after a typical meal. during this phase nutrients are absorbed by the body. In
other words this is the stage where energy is stored into macromolecules. During the post-absorptive
stage the nutrients are not being absorbed instead this is the stage where it is being mobilized.

Insulin

The changes in the body that occur between the absorptive an post-absorptive state are triggered by
the changes in the plasma concentration of insulin. Insulin encourages the synthesis of energy storage
molecules. When plasma glucose levels in the bloodstream increase during the absorptive stage insulin
is secreted from the pancreas. When the plasma glucose levels decrease that begins the post-absorptive
phase. Insulin acts on several different tissues in the body and influences almost every major aspect of
energy metabolism. Insulin supports and promotes all aspects of the absorptive phase by helping store
energy in all tissues. It also inhibits the reactions of the post-absorptive phase. Insulin also affects the
transport of nutrients across the membrane of ALL body cells except for those located in the liver and
CNS. Insulin also has a part in growth where it needs to be present in the blood stream in order for the
hormones to effect normally.

Epinephrine and sympathetic nervous activity on metabolism

The sympathetic system and epinephrine suppress insulin and stimulate glycogen secretion. This
effects the post absorptive phase by making metabolic adjustments. During the post absorptive phase
plasma glucose levels decrease and cause an increase of glycogen secretion. It also acts directly on
glucose receptors in the CNS. This causes a rise in epinephrine secretion by the adrenal medulla. The
rise in epinephrine creates a cascade event where the body sends signals to all the tissues (except
skeletal muscles)to switch to the post absorptive phase.

Case Study

Diabetes

With insulin having such an effect throughout the body you can understand why a lack of proper
insulin control can effect the body. With insulin deficient people they have a uptake of glucose into
muscle and fat tissues and an increase of releasing glucose into the bloodstream. With the uptake of
glucose in the muscles it causes them to use their alternate energy. This will produce muscle wasting,
weakness and weight loss. The can be tested as hyperglycemia in the blood. These effects are caused
by abnormally high plasma glucose levels and although hyperglycemia has a suppressive effect on
glucagon secretion, glucagon secretion is often elevated in people with diabetes because the glucose
permeability of alpha cells in the pancreas is insulin dependent. Diabetes is the seventh leading cause
of death in the United States. Their are two different types of diabetes, Type I and Type II. Type I also
known as insulin dependent diabetes Mellitus (IDDM) occurs mostly in children as it is a result of of
the destruction of B cells within the body. Treatment for this type of diabetes is insulin injection

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