Chapter 4,   Stress, Metabolism, and Liquidating Your Assets


I.     Putting energy in the      bank

A.    Digestion: “Breaking down chunks of animals and vegetables so that they can then be transformed into chunks of human.”  Done by enzymes in saliva and throughout the digestive tract, acid in stomach.

               1.    Amino acids: building blocks of proteins

2.    Simple sugars (glucose, sucrose, fructose…): building blocks of complex sugars and carbohydrates (starches, glycogen).

3.        Free fatty acids and glycerol: constituents of fat (triglycerides).

B.        Digestive tract:  (Tubular GI tract from mouth to anus.  In a sense, stuff inside GI tract is outside body and has to be absorbed or transported into the body.  Mucus is secreted along the whole length to both protect the lining of the tract and to help food slide along.)

1.        Mouth:  Chewing breaks down chunks of food and mixes it with saliva, which contains amylase to

digest carbohydrates and also makes food slippery.  (Pavlov discovered amylase in saliva.) 

2.        Stomach: Acid helps digest proteins; it also converts pepsinogen (inactive) to pepsin (active),

which digests proteins.  There are small amounts of other digestive enzymes.  Mechanical action

breaks up food. 

3.        Small intestine:  (duodenum: top 12 “finger widths”):  Site of most ulcers. 

a.       Receives bile from liver (1 qt/day, acts like detergent to emulsify fats: break into small globules). 

b.      Also receives pancreatic juice containing enzymes to digest all 3 types of food and lots of bicarbonate ion to neutralize the acid from the stomach. 

c.       Secretes cholecystokinin (CCK) to inhibit stomach emptying.  (contributes to satiety)

4.        Large intestine (colon):  reabsorbs water (pumps Na+ “into body,” similar to action in kidney; Cl- and H2O follow passively, due to electrostatic attraction and osmosis, respectively. 

       C.    Construction:  like converting cash into stocks, bonds, and Swiss bank accounts.

1.    Insulin from pancreas stimulates transport and storage of fatty acids into fat cells, and glucose and amino acids into other cells.

2.    Insulin is released by parasympathetic stimulation before, during, and after a meal.

II.    Energy mobilization during a stressor

       A.    Increase sympathetic and decrease parasympathetic activity.

B.    Glucocorticoids (from adrenal cortex), glucagon (from pancreas), epinephrine (from adrenal

medulla), norepinephrine (from sympathetic nerve endings and a bit from adrenal medulla):

1.    Block transport of nutrients into cells (counteracts insulin).

2.    Convert triglycerides à fatty acids and glycerol; glycogen à glucose; protein in

nonexercising muscle à amino acids.  (Exercising muscles have a local override to grab nutrients

from the circulation.  Mechanism probably includes increased vasodilation due to metabolic

breakdown products.)

               3.    Gluconeogenesis in liver: production of glucose from amino acids: chops off amino group (NH3)

from amino acids to make glucose (analogous to chopping up furniture to burn in fireplace to stay

warm). Also, glycerol (from triglycerides) can be converted into glucose.

III.   So why do we get sick?

       A.    Analogy: paying a penalty for withdrawing from a high-interest savings account.  If you do it

frequently, you lose a lot in penalties.  You tire more readily.

               1.    Not usually too much of a problem.

2.    If massive amounts of glucocorticoids are given to control a disease (leukemia, edema…), steroid

myopathy can occur. 

       B.    Increase in diabetes mellitus

               1.    Type 1 (juvenile) diabetes: autoimmune attack on cells in pancreas that secrete insulin.  Therefore,

amino acids and fatty acids can’t be transported into cells.  This results in starvation of cells and in gumming up of blood vessels.  That, in turn, results in kidney problems, atherosclerotic plaques, little strokes in the tissues where the plaques occur, and cataracts in the eyes. 

                      a.     Treated by insulin injections

                      b.    But too much insulin stores too many nutrients and deprives brain of needed glucose. 

               2.    Type 2 (adult onset) diabetes (non-insulin-dependent):  failure of cells to respond to insulin. 

a.     Due to inactivity and fat surplus.  Fat cells get full and no longer make insulin receptors

(receptor down-regulation”).

                      b.    Excess circulating fatty acids gum up blood vessels, kidneys, and eyes. 

               3.    Glucocorticoids, epinephrine, and norepinephrine make fat cells less sensitive to insulin.  After

stressor, tissues regain insulin sensitivity at different rates. 

               4.    There is genetic susceptibility to Type 2 diabetes.

               5.    15% of people over 65 have Type-2 diabetes.  It doubles mortality, triples heart disease in men,

and is a leading cause of blindness.