Exam 4 Review:  Chapter 24:  Absorptive States

absorptive state - That period of time in the body during which cell metabolism is primarily fueled by nutrients derived by absorption from the most recent meal; this state is dominated by insulin release from the beta cells of the pancreatic islets in response to hyperglycemia; most cells in the body are responsive targets to insulin and, therefore, in response to insulin arrival, extract glucose from the plasma to use in oxidative pathways to generate ATP; the liver and skeletal muscle responds to insulin in an additional way, storing glucose as glycogen (glycogenosis); most other nutrients from the meal are routed to the liver via the hepatic portal system where they are processed and stored, however, fats are routed to the general circulation via the lacteals and lymphatic drainage, where they are processed and stored as neutral fats (lipogenesis); nervous tissue is not responsive to insulin, but does utilize glucose for fuel use in oxidative pathways to generate ATP; non-nervous tissue will also respond to insulin by taking up and using plasma amino acids for protein synthesis as needed; this time period usually lasts from approximately two hours after the meal was ingested to four hours after the meal was ingested; during this same period, digestive activities are being regulated by the hormones gastrin, secretin, and cholecystokinin, etc.
 

postabsorptive state - That period of time in the body during which cell metabolism is primarily fueled by nutrients stored from previous meals; this state is dominated by glucagon release from the alpha cells of the pancreatic islets in response to hypoglycemia; various "insulin antagonists," thyroid hormones (T3 and T4), glucocorticoids (cortisone, cortisol, hydrocortisone) from the adrenal cortex, epinephrine from the adrenal medulla, and human growth hormone from the anterior pituitary = adenohypophysis are also present in increased amounts and contribute to the physiological processes which occur in this state; primarily, hepatocytes are the responsive targets to glucagon and, in response to glucagon arrival, release glucose into the plasma to be used by nervous tissue in oxidative pathways to generate ATP; the liver obtains this glucose in two ways: (1) by releasing glucose which had been stored as glycogen (glycogenolysis) and (2) by synthesizing new glucose molecules from the breakdown products of lipid and protein catabolism (gluconeogenesis); if skeletal muscle tissue becomes active, it will also utilize glucose stored as glycogen (glycogenolysis); most other tissues shift to energy production from lipid and protein catabolism; adipocytes liberate fats into the bloodstream (lipolysis) to support the metabolsim of these other tissues, adipocytes may also use the glycerol from fat catabolism to synthesize glucose (gluconeogenesis); the liver will oxidize free fatty acids for fuel, producing ketone bodies (ketogenesis) as by-products; nervous tissue is not responsive to glucagon, but does continue to utilize the glucose, released by the liver and adipocytes, for fuel use in oxidative pathways to generate ATP; this time period usually lasts from approximately four hours after the meal was ingested to two hours after the next meal is ingested; during this same period, digestive system activities are minimal, other than for continued peristalsis of and water extraction from the feces.
 

An adequate supply of clean water is about thirteen gallons per person per day.  Ten percent of it is needed for drinking, the rest for sanitation and hygiene (40 percent), bathing (30 percent), and cooking (20 percent).  In 2006 the UN estimated that more than half a billion people -- one sixth of the world's population -- lack even the bare minimum gallon-plus per day of safe drinking water, and 2.6 billion people lack access to basic sanitation.  In contrast, those who live in the United States and Canada each consume, on average, more than 150 gallons a day for domestic and municipal purposes (not including agricultural and industrial usage).  In the United Kingdom people do fine with about a fifth as much.  [Source:  Natural History Magazine November 2007]

 

 

 

Describe:

5.  the regulation of nutrient usage for storage and/or energy production in the absorptive state.

 
Insulin dominates during the absorptive state.  All tissues (including nervous tissue) respond by absorbing glucose from the blood and using it to fuel oxidative metabolism to generate ATPs.  In addition, many tissues also absorb nutrients provided by the recent meal and store them as proteins and glycogen (liver, skeletal muscle, etc.,) or as neutral fats = triglycerides (liver, adipose tissue, etc.).  The liver will also deaminate excess amino acids and convert them to keto acids which may be used for oxidative metabolism or stored as neutral fats = triglycerides.


6.  the regulation of nutrient usage for storage and/or energy production in the postabsorptive state.
 

Glucagon, assisted by the group of insulin-antagonists (human growth hormone, thyroid hormones T3 & T4, glucocorticoids (cortisol, cortisone, hydrocortisone, etc.), and epinephrine = adrenalin, dominates during the post-absorptive state.  Nervous tissue, which is unresponsive to insulin, continues to absorb glucose from the blood and using it to fuel oxidative metabolism to generate ATPs.  To provide this glucose, the liver catabolizes proteins and lipids to synthesize new glucose molecules, the process of gluconeogenesis, as well as hydrolyzing glycogen, glycogenolysis, to liberate stored glucose.  The glucose molecules from these two sources are passed into the blood stream to support the requirements of nervous tissue.  All the other, insulin-responsive tissues of the body shift to the catabolism of neutral fats = triglycerides to fuel oxidative metabolism to generate ATPs.  Both fat and protein catabolism generate ketone bodies as by-products which may also serve as fuels for oxidative metabolism to generate ATPs.  The liver and adipose tissue provide the bulk of the fats used for oxidative metabolism in the post-absorptive state. 

7.  describe the time sequence between the absorptive and postabsorptive states during a typical 24 hour day.

          The time sequences for absorptive and postabsorptive states during a typical 24 hour day are quite variable and depend on the size, content, and number of meals and snacks ingested, as well as the times of ingestion.  As a general rule, the body enters the absorptive state approximately two hours after a normal full meal (as opposed to a snack), allowing time for initial digestion in the stomach, and remains in the postabsorptive state for approximately four hours while the nutrients from the meal are being absorbed from the chyme passed to the small intestine.  After absorption is nearly complete and after nutrients, especially glucose, from the meal have been transferred to the cells of the various body tissues, then the body enters the post-absorptive state and continues in the post-absorptive state until the next meal is digested by the stomach and passed to the small intestine.  thus, the body is typically in the post-absorptive state for the longest continuous period of time during a night's sleep.  Individuals who snack frequently may never make a complete shift to the post-absorptive state during waking hours.  This is not a problem for their physiology; in fact, it is simply appropriate to their digestive status.