• or biosynthesis, is the process by which living organisms synthesize complex molecules of life from simpler ones
• together with catabolism, are the two series of chemical processes in cells that are, together, called metabolism
• requires input of energy "uphill process"

• produce smaller molecules used by the cell to synthesize larger molecules
• "downhill" process during which energy is released

1. Inside cells, glucose can be oxidized for energy
2. which generates carbon dioxide as a waste product; provides substrates for other metabolic reactions
3. or be converted to glycogen for storage
4. if glucose levels in the cell decrease, glycogen can be broken down to glucose by glycogenolysis

1. amino acids are used for the synthesis of proteins
2. or catabolized for energy by proteolysis
3. the proteins function as amino acid stores that can subsequently be broken down to amino acids
4. which can then be catabolized for energy or released into the bloodstream for use by other cells

• Glycolysis
• Krebs cycle
• Electron transport chain

• lipoprotein lipase
  • which is located on the inside surface of capillaries throughout the body and is particularly dense in capillaries running through adipose tissue (body fat)

• fatty acids and monoglycerides
  • fatty acids are then taken up by nearby cells
  • monoglycerides remain in the bloodstream and are eventually metabolized in the liver

• with glycerol to form new triglycerides
  • which are stored in fat droplets in the cytosol
  • storage occurs mainly in adipocytes

• catabolized for energy or released into the bloodstream for use by other cells

When a person takes in energy at a rate greater than that at which it is expended as heat and work.

Increase body weight

when the rate of energy intake is less than the rate at which energy is expended as heat or work, the quantity of stored energy decreases

decreases in body weight

• 3-4 hours after a typical meal, nutrients are absorbed
• rate of energy input generally exceeds energy input
• body is in postive energy balance
• glucose serves as the primary energy source for cells, while fats amino acids, and excess glucose are takin up by the liver, muscle, and fat cells and converted to energy storage molecules

• between meals, when nutrients are not being absorbed
• glucose serves as the energy source for cells in the central nervous sytem
• other cells in the body utilized other energy sources sparing glucose for the central nervous sytem

• glucose to glycogen (fatty acids)
• fattyacids to triglycerides

very low density lipoproteins

transport triglycerides to the cells of the body

Ketones

The production of ketones is important because during prolonged fasting, the central nervouls system acquires the ability to use ketones for energy, thereby freeing it from some of its dependence on glucose

• increase, as glucose is transported into the bloodstream from the GI tract
• this stimulates insulin secretion by a direct effect of  glucose on beta cells

• decrease, causing insulin secretion to fall

• hormones
• input from the autonomic nervous system
  • parasympatheitic
• glucose-dependent insulinotropic peptide (GIP)
  • a hormone secreted by cells in the wall of the gastrointestinal tract

• fatty acids and triglycerides in the liver and adipose tissues
• glycogen in the liver and skeletal muscle
• proteins in most tissues

• inhibiting the breakdown of proteins, triglycerides, and glycogen
• suppressing gluconeogenesis by the liver

• those of the liver and central nervous system

Glucose transport proteins in cell plasma membranes

found in

• skeletal muscle
• adipose tissue

• amino acids - which facilitates the hormone's stimulatory effect on protein synthesis
• glucose - increases the number of glucose transport proteins in cell membranes (GLUT 4)

• transport of glucose in the central nervous system and liver
• glucose permeability of cells in exercising muscle

a peptide hormone secreted by alpha cells of pancreatec islets of Langerhans

promotes processes of the postabsorptive state

• insulin promotes processes of the absorptive state
• glucagon promotes processes of the postabsorptive state

• stimulate glucaton secretion
• inhibit insulin secretion

• sympathetic nervous activity and epinephrine
  • which have a suppressive effect on insulin secretion

• glycogenolysis and gluconeogenesis (which increase blood glucose levels)
• ketone synthesis
• breakdown of proteins

while inhibiting the opposing processes of glycogen and protein synthesis.

Fasting blood levels greater than 140 mg/dL

indicative of diabetes mellitus

Fasting blood levels below 60 mg/dL

has widespread deleterious effects on nervous system function because the nervous system uses glucose almost exclusively as its source of energy

plasma glucose concentration through negative feedback

• increase in plasma glucose concentration increases insulin secretion and decreases glucagon secretion from the pancreas, both of which cause a decrease in plasma glucose

decreases insulin secretion

increases glucagon secretion

both of which cause an increase in plasma glucose

1. by promoting the uptake of glucose into cells by in creasing the number of glucose transporters in the plasma membrane
2. by reducing the concentration of free glucose within cells by converting it to glycogen, which promotes glucose uptake by increasing the size of the glucose concentration gradient
3. by suppressing gluconeogenesis, thereby reducing the rate at which new glucose is released into the bloodstream

• decease in plasma glucose stimulates glucagon secretion from alpha cells of the pancreas
• and the actions of glucagon increase plasma glucose

• increases plasma glucose concentration by promoting gluconeogenesis and glycogenolysis in the liver
  • which directly increases plasma glucose concentration
• by stimulating lipolysis in adipose tissue
  • which provides fatty acids as an alternate energy source to glucose

During glucagon's negative feedback, glucagon

       increases

• plasma glucose concentration by promoting gluconeogenesis and glycogenolysis in the liver
  • which directly increases plasma glucose concentration

the release of both insulin and glucagon

• nutrients are absorbed, plasma amino acid levels rise
• glucose levels do not change
• stimulation of insulin
  • promotes amino acid uptake by cells
  • promotes decease in plasma glucose
• rise in plasma amino acids stimulates secretion of glucagon
  • increase inplasma glucose