Transcript glucosehomeostatis2

1QQ # 4
Name on top edge, back side of paper
Answer on blank side of paper.
Answer one of the following:
1. Why is light colored, loose fitting
clothing that covers the entire body
except face and hands optimal for
desert dwellers?
2. Explain how it is possible to kill a
comatose person by covering them
with excessive blankets.
Plasma Glucose Homeostasis
Widmaier et al., p. 567-580
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Glucose metabolism
Hormonal Control
Disruptions of glucose homeostasis
A Case Study
Homeostasis of Plasma
Glucose Concentration
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Normal physiological range: 65-100 mg/dl
What is the set point?
Why is too much plasma glucose harmful?
Plasma glucose concentration = glucose entering the
plasma – glucose leaving the plasma
• What are the mechanisms that regulate plasma
glucose concentration?
• What are the components of the negative feedback
loop:
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Glucose receptors?
Afferent pathway?
Integrator?
Efferent pathway(s)?
Effector organ(s)?
Phases:
*absorptive,
*post-absorptive, and
fasting
Graph your daily caloric intake
over a 48 hour period
Plasma
Glucose
Calories
consumed
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6am
Noon
6pm
MN
6am
Noon
6pm
MN
6am
Noon
Overlay absorptive and post-absorptive phases on the graph
Absorptive
Phase
Fig. 16.01
Lipoprotein Lipase
=sink
Hepatic Portal System
Once inside, glucose is
converted to something else,
thereby maintaining a
concentration gradient
for facilitated diffusion of
glucose into cells.
Liver
Hepatic portal system
Islets of Langerhans
Alpha cells secrete glucagon
Beta cells secrete insulin
Delta cells secrete somatostatin
Route of blood
Fig. 16.02
Special case:
Muscle
wasting of
starvation
Glucose
Sparing
Note: Nervous tissue
can use glucose and
ketones
Post-absorptive
phase
Major Points
• Absorptive phase lasts ~ 4 hours
• During absorptive phase, energy needs
provided by recently digested food
• During absorptive phase, excess is converted
to stored fuel
• During post-absorptive phase, energy need
met by release of stored fuels
• Fasting defined as greater than 12 hours after
previous meal (some say 24 hrs)
• Fasting for several days has little effect on
plasma glucose levels
The Issues
• How do cells “know” which fuel to “burn?”
• How do cells “know” when to synthesize
glycogen or lipids and when to break down
glycogen or lipid?
• What is responsible for the transitions from
the absorptive and post-absorptive states?
• How does glucose get into “sink” cells?
Exercise (via an undescribed mechanism)
increases the number of glucose
transporters in muscle cell membrane
Peptide hormone
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GLUT-4
Activates some enzymes, inactivates others
↑ plasma glucose →↑insulin secretion→↑glucose uptake into cells →↓ plasma glucose
Diabetes mellitus:
T1DM =beta cells fail to produce adequate insulin (5%)
T2DM = target cells “resistant” (less responsive) to insulin
Questions based on this lecture
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What is the difference between
the post-absorptive phase and
fasting?
What is the normal range for
plasma glucose concentration?
(include the units.)
During the absorptive phase, what
is the fate of
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Excess amino acids
Glucose that enters the liver
Glucose that enters adipose tissue
Glucose that enters muscle tissue
What is the role, source, and
destination of VLDLs during the
absorptive phase?
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What is the location and role of
lipoprotein lipase?
What is the main cellular fuel used
by most cells during the
absorptive phase?
What marks the end of the
absorptive phase?
What tissues are the sinks of
glucose during the absorptive
phase?
Which of these constitutes the
largest “sink?”
How long does the absorptive
phase typically last?
During the absorptive phase, is
there net anabolism or net
catabolism of triglycerides?
Questions based on this lecture
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How is the gradient maintained
that favors the entry of glucose
into cells?
What is the name of the molecule
that is polymer of glucose and
which cell types can have this
polymer?
What is a portal system?
What is the function of the hepatic
portal system?
How do cells of the liver alter the
blood that arrives there from the
digestive tract?
The pancreas is actually two
glands in one. What are the two
glands and what is the function of
each?
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What are the names and
secretions of the two most
important cell types of the Islets of
Langerhans?
Speculate as to why pancreatic
cancer has a very high mortality
rate?
During the post absorptive phase,
what is the fate of amino acids
released from muscle tissue?
During the post absorptive phase,
what other molecules are release
from muscle cells and what is the
fate of these molecules?
During the post absorptive phase,
what is the source of glycerol
entering the plasma? Where does
that glycerol go and what is its
fate?
Questions based on this lecture
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What is the first source of glucose
during the early portion of the post
absorptive phase?
What is gluconeogenesis?
What is glycogenolysis?
What is/are the predominate fuel
molecules used by most cells
during the post absorptive phase
and during fasting?
What are the only two molecules
that can be used as fuel by the
nervous system?
What is meant by the term
“glucose sparing?”
By what means is plasma glucose
maintained in or near the normal
range even with prolonged fasting
of 1-2 weeks?
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Which two hormones would be
expected in large amounts in the
blood of a fasting person? (Didn’t
cover this yet, but figure it out.)
How might the composition of a
meal (protein, carbohydrate, fats)
be related to the duration of the
absorptive phase?
Since insulin is a peptide hormone,
where must the receptors for insulin
be situated on “sink” cells?
Do neurons have insulin receptors?
If not, how do neurons take up
glucose?
What is sequence of cellular events
that is initiated by the binding of
insulin to insulin receptors?
Questions based on this lecture
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By what means can the uptake of
glucose from the plasma be finely
adjusted in proportion to the
amount of glucose in the meal?
Are the levels of insulin high or
low during a fast?
During prolonged exercise during
a fast, insulin levels would be very
low, yet muscle cells can still take
up glucose. How can they do so?
Why is exercise recommended for
persons who tend to have
elevated plasma glucose?
Explain how an overdose of
insulin could result in loss of
consciousness and even death?
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On the graph that shows the 48
hour intake of food and the
fluctuations of plasma glucose,
add a plot that shows the
expected levels of insulin in the
plasma.