This document discusses how different organs regulate metabolism to maintain energy balance. The liver regulates sugar and fat storage and breakdown. The kidneys help produce glucose during starvation. Hormones like epinephrine, insulin, and glucagon signal the liver and muscles to store or release sugars and fats. Prolonged starvation causes the body to use ketone bodies instead of glucose for fuel. Uncontrolled diabetes occurs when cells cannot respond to insulin signals, leading to high blood sugar and dangerous ketone production. Dieting aims to mimic controlled starvation for weight loss but requires supervision.
2. At this point, we’ll
consider how
organisms
arrange/organize the
metabolic symphony
to meet their energy
needs.
Discussion will
include how:
Body maintains
energy balance
(homeostasis)
It deals with
starvation
It responds to the
loss of control from
diabetes mellitus
12. The liver can synthesize or degrade TAGs
When metabolic fuel is needed, f.acids are degraded
to acetyl-CoA and then to ketone bodies (export via
bloodstream to the peripheral tissues)
When the demand is low, f.acids are used to
synthesize TAGs (secreted into the bloodstream as
VLDL for uptake by adipose tissue)
Amino acids are important metabolic fuel
The liver degrades amino acids to a variety of
intermediates (begin with a.acid transamination to
yield α-keto acid, via urea cycle excreted urea)
Glucogenic a.acid – converted to pyruvate / OAA
(TCA cycle intermediates)
Ketogenic a.acid – converted to ketone bodies
13. Kidney Overall reaction in
kidney: Glutamine →
α-ketoglutarate +
Functions NH4+
: to filter out the waste During starvation, the
product urea from the α-ketoglutarate enters
bloodstream gluconeogenesis
: to concentrate it for (kidneys generate as
excretion much as 50% of the
body’s glucose supply)
: to recover important
metabolites (glucose)
α-ketoglutarate :
converted to malate
: to maintain the blood (TCA cycle)
pH
: pyruvate (oxidized to
CO2) or via OAA to PEP
: converted to glucose
via gluconeogenesis
14.
15.
16.
17. Hormones reacts as the intercellular messengers
Hormones transported from the sites of their synthesis to
the sites of action by the bloodstream
Fig. 24-5, p.671
18. Some typical
hormones:
- steroids
(estrogens,
androgens)
- polypeptides
(insulin and
endorphins)
- a.acid derivatives
(epinephrine and
norepinephrine)
Hormones help
maintaining
homeostasis (the
balance of biological
activities
20. The effects of hormones triggered
the responses within the cell
There are three hormones play a
part in the regulation of CHO
metabolism
Epinephrine, insulin and glucagon
Epinephrine: acts on muscle tissue,
to raise level of glucose on
demand, when it binds to specific
receptors, it leads to increased
level of glucose in blood, increased
glycolysis in muscle cells and
increased breakdown of f.acid for
energy
p.681
22. Glucagon: acts on
liver, to increase
the availability of
glucose, when it
binds to specific
receptors, it leads
to increased level
of glucose in
blood.
32. During prolonged starvation or fasting, the brain slowly
adapts from the use of glucose as its soul fuel source to the
use of ketone bodies, shift the metabolic burden form
protein breakdown to fat breakdown
Diabetes mellitus is a disease in which insulin either not
secreted or doesn’t stimulate its target tissues → high
[glucose] in the blood and urine. Abnormally high
production of ketone bodies is one of the most dangerous
effects of uncontrolled diabetes
Dieting – to lose excess weight. Diet forced the body to
follow the same adjustment like starvation or fasting but a
more moderate or controllable pace. Dieting is not free of
problems, therefore it is advisable to undergo diet under
supervision of physician or nutritionist.
Notas del editor
FIGURE 24.2 The Food Guide Pyramid (USDA). The recommended choices reflect a diet based primarily on carbohydrates. Smaller amounts of proteins and lipids are sufficient to meet the body’s needs.
FIGURE 24.5 Endocrine cells secrete hormones into the bloodstream, which transports them to target cells.
FIGURE 24.6 A simple feedback control system involving an endocrine gland and a target organ.
Tyrosine and epinephrine. The hormone epinephrine is metabolically derived from the amino acid tyrosine.
FIGURE 24.14 When epinephrine binds to its receptor, the binding activates a stimulatory G protein, which in turn activates adenylate cyclase. The cAMP thus produced activates a cAMPdependent protein kinase. The phosphorylation reactions catalyzed by the cAMP-dependent kinase suppress the activity of glycogen synthase and enhance that of phosphorylase kinase. Glycogen phosphorylase is activated by phosphorylase kinase, leading to glycogen breakdown.
FIGURE 24.15 Binding of glucagon to its receptor sets off the chain of events that leads to the activation of a cAMP-dependent protein kinase. The enzymes phosphorylated in this case are phosphofructokinase-2, which is inactivated, and fructose- bis phosphatase-2, which is activated. The combined result of phosphorylating these two enzymes is to lower the concentration of fructose-2,6- bis phosphate (F2,6P). A lower concentration of F2,6P leads to allosteric activation of the enzyme fructose- bis phosphatase, thus enhancing gluconeogenesis. At the same time, the lower concentration of F2,6P implies that phosphofructokinase is lacking a potent allosteric activator, with the result that glycolysis is suppressed.
FIGURE 24.16 Proinsulin is an 86-residue precursor to insulin (the sequence shown here is human proinsulin). Proteolytic removal of residues 31 through 65 yields insulin. Residues 1 through 30 (the B chain) remain linked to residues 66 through 86 by a pair of interchain disulfide bridges.