1QQ # 2
Name on top edge, back side of paper
Answer on blank side of paper.
1. For the negative feedback loop for thermoregulation
a) The hypothalmus is an afferent pathway
b) Somatic nerves are the efferent pathway to sweat
glands
c) Skeletal muscle tone would be increased as a
response to a drop in core body temperature
d) Peripheral nerves are the afferent pathway that
convey skin temperature information
e) Cutaneous arterioles would dilate in response to a
drop in core body temperature.
Add covers
Conductive heat loss
Skin temp And Core body temp
or clothing
Radiative heat loss
or enter
Convective heat loss
Central
sleeping
thermoreceptors
bag
Detected by thermoreceptors in skin
Cerebral cortex
Activity in sensory nerves
Somatic nerves
Hypothalamus
Sympathetic nerves
Relax smooth muscle in
cutaneous arterioles
Blood flow to skin
Somatic nerves
Sweat Glands
Voluntary behaviors
Muscle tone
Heat production
Sweat production
Skeletal
Muscles
Heat loss
Evaporative heat loss
Heat loss by conduction & radiation
Remove covers
Turn on fan, etc via
Core temp.
Acclimatization & Feedforward
• Deviations from set point are minimized
• Learned (by experience)
• Anticipates changes of a physiological
parameter
• Response begins before there is a change
in the physiological variable
• Minimizes fluctuations
If setpoint is suddenly reset
to a higher temperature,
then actual temperature is
LESS THAN the new set
•point,
Explain
“chills”
at
so one
feels “cold”
onset
a fevercurls up,
and
addsof
clothing,
shivers.“sweat”
These are
•and
Explain
“Chills.”
a isfever
If when
setpoint
reset to a
“breaks”
lower
temperature or back
normal,
then actual
•toHow
does
temperature is GREATER
Tylenol reduce a
THAN the new lower set
fever?
point,
so one feels “hot” and
removes clothing, fans, and
sweats. These are “the
sweats” when a fever
breaks.
p. 579 Fig 16-18
Central &
Peripheral
Thermoreceptors
Tylenol and other nonsteroidal antiinflammatory drugs
(NSAIDS) suppress the
production of
eicosanoids (IL-1, IL-6,
etc) so effect of these
on the set point in
hypothalamus
is new,
To reach
minimized. Higher set point
Heat Stroke
Massive Cutaneous Vasodilation
Increase
cell
Excessive Sweating
metabolism
Failure of
1. Brain function &
2. Heat loss mechanisms
Blood volume
Blood Pressure
Increase
Body Temp.
Blood Flow to brain
Cutaneous vasodilation
Disrupted function
of neurons
Sympathetic outflow
Treating Heat Stroke
Sweating
Positive feedback
• Inherently unstable
• Examples of Positive Feedback in Physiology
– Heat stroke
– formation of blood clot
– menstrual cycling of female sex hormone
concentrations at ovulation
– generation of action potentials in nerve fibers
– uterine contractions during childbirth
• Each of these examples terminate naturally (self
limiting)
Homeostasis is achieved by negative feedback loops: the integrator
detects deviations from set point and orchestrates responses produced
by effectors that return the parameter toward the set point.
Plasma Glucose Homeostasis
•
•
•
•
Glucose metabolism
Hormonal Control
Disruptions of glucose homeostasis
A Case Study
Homeostasis of Plasma
Glucose Concentration
•
•
•
•
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:
–
–
–
–
–
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
?
?
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
Typical vasculature: Artery-Arteriole-Capillary-Venule-Vein-Heart
Islets of Langerhans
Alpha cells secrete glucagon
Beta cells secrete insulin
Delta cells secrete somatostatin
Route of blood
Hepatic portal system
Artery-Arteriole-Capillary-Portal Vessel- Capillary-Venule-Vein-Heart
Fig. 16.02
Special case:
Muscle
wasting of
starvation
Glucose
Sparing
Special term:
Glycogenolysis &
Gluconeogenesis
Post-absorptive
phase
Note: Nervous tissue
can use glucose and
ketones
Major Points
• Absorptive phase lasts ~ 4 hours, cells “burn” glucose.
• 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, most cells “burn” fatty acids,
nervous tissue uses glucose and ketones.
• 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?
Identify sensors,
afferent pathway,
integrator,
efferent pathway,
effectors
Fig. 16.07
How is insulin secretion
affected if plasma
glucose is lower than
set point?
Which cell types have
insulin receptors?
Exercise (via an undescribed mechanism)
increases the number of glucose
transporters in muscle cell membrane
Peptide hormone
GLUT-4
Activates some enzymes, inactivates others:
see next slide!
↑ 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
Stimulatory
actions of
insulin in
green
Inhibitory
actions of
insulin in
dashed red
Absorptive Phase
Post-Absorptive Phase
Thinking
about food
Factors that influence Insulin Secretion
?
FF
WHY?
The Integrator
integrates multiple
inputs
FF
Glucose
uptake,
Storage,
Lipogenesis
Another
hormone that
regulates
plasma glucose
concentration
Glucagon prevails
during postabsorptive phase
Transition from
absorptive to postabsorptive phase?
Graph your daily caloric intake
over a 48 hour period
Plasma
Glucose
Calories
consumed
100
65
6am
Noon
6pm
MN
6am
Noon
6pm
MN
6am
Overlay INSULIN SECRETION on the graph
Overlay GLUCAGON SECRETION on the graph
Noon
Glucose-counterregulatory
controls
(oppose effects of insulin)
Glucagon
Epinephrine
Cortisol (permissive effect)
Growth hormone (permissive effect)
Fig. 16.10
EPI, yet another horomone in
glucose homeostasis, effects
opposite of Insulin
Don’t fret about
receptors, afferent
pathway, and
integrator for this
feedback loop.
Who
Cares?
A Case Study
• On our website at
• http://webs.wofford.edu/davisgr/bio342/oggt.htm
A Case Study of Glucose Homeostasis
A 35 year old male presented with the following complaints: frequent severe
headaches upon awakening at 4:30 am, blurred vision, and fatigue due to excessive
stress at work. The patient complained of routine 16 hr workdays followed by a
midnight snack of breakfast cereal.
An OGTT was ordered and provided the following results:
During the second hour of the OGTT, the patient exhibited anxiety, paleness, hunger,
tremulousness, and cold sweat. No additional tests were ordered. The patient was
instructed to replace the midnight snack of cereal with a protein-rich snack.
Oral Glucose Tolerance Test
• Overnight fast, no
beverages other than water
• Fasting blood sample
• Ingest 75 grams glucose
• Blood samples every 0.5
hours for 3-5 hours
• Plot plasma glucose
concentration over time
• Compare curves
Sugar content
of Red Bull?
60
Stress,
Emergency
(fight or flight)
Effect on
Alpha Cells
Effect on
Beta cells
The Answer to the Problem?
• Rationale for substituting protein
for carbohydrate midnight snack?