Transcript 9 - smw15.org

Chapter 9:
Internal Regulation
Homeostasis
 Refers to temperature regulation
and other biological processes
that keep certain body variables
within a fixed range
Set point
 Refers
to a single value that
the body works to maintain
• Examples: Levels of water,
oxygen, glucose, sodium
chloride, protein, fat and acidity
in the body
Negative Feedback
 Processes that reduce discrepancies
from the set point
Allostasis
 Refers to the adaptive way in which the
body changes its set point in response to
changes in life or the environment
Temperature regulation is one of the
body’s biological priorities
Basal Metabolism
 Is the energy used to maintain a constant
body temperature while at rest
Poikilothermic
 Refers to the idea that the body
temperature matches that of the
environment
• Amphibians, reptiles and most
fish
 The organism lacks the internal,
physiological mechanisms of
temperature regulation
 Temperature regulation is
accomplished via choosing
locations in the environment
Homeothermic
 Refers to the use of internal
physiological mechanisms to
maintain an almost constant body
temperature
• Characteristic of mammals and
birds
 Requires energy and fuel
 Sweating and panting decrease
temperature
 Increasing temperature is
accomplished via shivering,
increasing metabolic rate, decreasing
blood flow to the skin, etc.
Mammals evolved to have a constant
temperature of 37˚ C (98˚ F)
 Muscle activity benefits from being as warm
as possible and ready for vigorous activity
 Proteins in the body break their bonds and
lose their useful properties at higher
temperatures
 Reproductive cells require cooler
temperatures
Behavior regulation of body temperature 
Meerkats huddle together in a touching
scene as they scramble to keep the heat
Surviving in Extreme Cold
 Sometimes behavioral mechanisms are
needed for survival
Click on picture for video 
 Body
temperature regulation is
predominantly dependent upon areas in the
preoptic area/ anterior hypothalamus
(POA/AH)
 The POA/AH partially monitors the body’s
temperature by monitoring its own
temperature
• Heating the POA/AH leads to panting or sweating;
cooling leads to shivering
 Cells
of the POA/AH also receive input from
temperature sensitive receptors in the skin
 Bacterial
and viral infections can cause a fever,
part of the body’s defense against illness
 Bacteria and viruses trigger the release of
leukocytes which release small proteins called
cytokines
 Cytokines attack intruders but also stimulate the
vagus nerve
 The vagus nerve stimulates the hypothalamus to
initiate a fever
 Water
constitutes 70% of the mammalian
body
 Water in the body must be regulated
within narrow limits
 The concentrations of chemicals in water
determines the rate of all chemical
reactions in the body
 Water
can be conserved by:
• Excreting concentrated urine
• Decreasing sweat and other autonomic
responses
• Most often water regulation is accomplished
via drinking more water than we need and
excreting the rest
Vasopressin
 A hormone released by the posterior pituitary
which raises blood pressure by constricting
blood vessels
 It’s an antidiuretic hormone because it enables
the kidneys to reabsorb water and excrete
highly concentrated urine

Two different kinds of thirst include:
Osmotic thirst – a thirst resulting from eating
salty foods
Click on picture for video 
Hypovolemic thirst – a thirst resulting from
loss of fluids due to bleeding or sweating
Osmotic thirst occurs because the human
body maintains a combined concentration
of solutes at a fixed level of .15 M (molar).
 Solutes inside and outside a cell produce
osmotic pressure, the tendency of water
to flow across a semi-permeable
membrane from an area of low solute
concentration to an area of high solute
concentration
 Eating
salty food causes sodium ions to
spread through the blood and
extracellular fluid of the cell
 The higher concentration of solutes
outside the cell results in osmotic
pressure, drawing water from the cell to
the extracellular fluid
 The
brain detects osmotic pressure from:
• Receptors around the third ventricle
• The OVLT (organum vasculosum laminae
terminalis) and the subfornical organ (detect
osmotic pressure and salt content)
• Receptors in the periphery, including the
stomach, detect high levels of sodium
 Receptors
in the OVLT, subfornical organ,
stomach and elsewhere relay information to
areas of the hypothalamus including:
 Receptors also relay information to the
lateral preoptic area which controls drinking
 When osmotic thirst is triggered, water that
you drink has to be absorbed through the
digestive system
 To inhibit thirst, the body monitors
swallowing and detects the water contents of
the stomach and intestines
Thirst associated with low volume of body fluids
• Triggered by the release of the hormones
vasopressin and angiotensin II, which
constrict blood vessels to compensate for a
drop in blood pressure
 Angiotensin II stimulates neurons in areas
adjoining the third ventricle.
 Neurons in the third ventricle send axons to
the hypothalamus where angiotensin II is also
released as a neurotransmitter

Sports drinks vs. H2O
Click on picture for video 
Click on picture for video 
 Animals
with osmotic thirst have a
preference for pure water
 Animals with hypovolemic thirst have a
preference for slightly salty water as pure
water dilutes body fluids and changes
osmotic pressure
 Sodium-specific hunger, a strong craving
for salty foods
• Develops automatically to restore solute levels in
the blood
 Animals
vary in their strategies of eating,
but humans tend to eat more than they
need at the given moment
 A combination of learned and unlearned
factors contribute to hunger
 The
function of the digestive system is
to break down food into smaller
molecules that the cells can use
 Digestion begins in the mouth where
enzymes in the saliva break down
carbohydrates
 Hydrochloric acid and enzymes in the
stomach digest proteins
 The
small intestine has enzymes that digest
proteins, fats, and carbohydrates and
absorbs digested food into the bloodstream
 The large intestine absorbs water and
minerals and lubricates the remaining
materials to pass as feces
 At
the age of weaning, most mammals lose
the intestinal enzyme lactase, which is
necessary for metabolizing lactose
 Lactose is the sugar found in milk
 Milk consumption after weaning can cause
gas and stomach cramps
 Declining levels of lactase may be an
evolutionary mechanism to encourage
weaning
 Most
human adults
have enough lactase
to consume milk and
other dairy products
throughout the
lifetime
 Nearly all people in
China and
surrounding countries
lack the gene that
enables adults to
metabolize lactose
Lactose Intolerance Around The World
Ellis et al. (2008)
Procedure
 Children were given snacks with sugar on
some days and snacks that were
artificially sweetened on other days
Results
 No difference on children’s activity level,
play behaviors, or school performance
The brain regulates eating
through messages from the
mouth, stomach, intestines, fat
cells and elsewhere.
 The desire to taste and other
mouth sensations, such as
chewing, are also motivating
factors in hunger and satiety
 Sham feeding experiments, in
which everything an animals
eats leaks out of a tube
connected to the stomach or
esophagus, do not produce
satiety

 The
main signal to stop eating is the
distention of the stomach
 The vagus nerve conveys information about
the stretching of the stomach walls to the
brain
 The splanchnic nerves convey information
about the nutrient contents of the stomach
 The
duodenum is the part of the small
intestine where the initial absorption of
significant amounts of nutrients occurs
 Distention of the duodenum can also
produce feelings of satiety
 The duodenum also releases the
hormone cholecystokinin (CCK), which
helps to regulate hunger
Cholecystokinin (CCK)
 Released by the duodenum, this hormone
regulates hunger by:
• Closing the sphincter muscle between the
stomach and duodenum and causing the
stomach to hold its contents and fill faster
• Stimulating the vagus nerve to send a
message to the hypothalamus that releases a
chemical similar to CCK
 Glucose, insulin, and
glucagon levels also
influence feelings of hunger
 Most digested food enters the bloodstream
as glucose, an important source of energy
for the body and nearly the only fuel used
by the brain
 When glucose levels are high, liver cells
convert some of the excess into glycogen
and fat cells convert it into fat
 When low, liver converts glycogen back into
glucose
Insulin
 A pancreatic hormone that enables glucose
to enter the cell
 Insulin levels rise as someone is getting
ready for a meal and after a meal
 In preparation for the rush of additional
glucose about to enter the blood, high
insulin levels let some of the existing
glucose in the blood to enter the cells
 Consequently, high levels of insulin
generally decrease appetite
Glucagon
 Is also a hormone released by the pancreas
when glucose levels fall
 Glucagon stimulates the liver to convert
some of its stored glycogen to glucose to
replenish low supplies in the blood
 As insulin levels drop, glucose enters the
cell more slowly and hunger increases
If insulin levels constantly stay high, the body
continues rapidly moving blood glucose into
the cells long after a meal
 Blood glucose drops and hunger increases
in spite of the high insulin levels
 Food is rapidly deposited as fat and
glycogen
 The organism gains weight
 In
people with diabetes, insulin levels
remain constantly low, but blood glucose
levels are high
• People eat more food than normal, but excrete the
glucose unused and lose weight
 Long-term
hunger regulation is
accomplished via the monitoring of fat
supplies by the body
 The body’s fat cells produce the peptide
leptin, which signals the brain to increase or
decrease eating
 Low levels of leptin increase hunger
 High
levels of leptin do not necessarily
decrease hunger
• Most people are obese because they are less
sensitive to leptin
• Some people are obese because of a genetic
inability to produce leptin
Mouse with obesity gene is on right
 Information
from all parts of the body
regarding hunger impinge into two kinds of
cells in the arcuate nucleus.
 The arcuate nucleus is a part of the
hypothalamus containing two sets of
neurons:
1. neurons sensitive to hunger signals
2. neurons sensitive to satiety signals
 Neurons
of the arcuate nucleus
specifically sensitive to hunger signals
receive input from:
• The taste pathways
• Axons releasing the neurotransmitter ghrelin
 Ghrelin
is released as a neurotransmitter
in the brain and also in the stomach to
trigger stomach contractions
 Output
from the arcuate nucleus goes to the
paraventricular nucleus of the hypothalamus
 The paraventricular nucleus (PVN) is a part
of the hypothalamus that inhibits the lateral
hypothalamus (LH) which is important for
feelings of hunger
 Axons from the satiety-sensitive cells of the
arcuate nucleus deliver an excitatory
message to the paraventricular nucleus
which triggers satiety
 Input
from the hunger-sensitive neurons of the
arcuate nucleus is inhibitory to both the
paraventricular nucleus and the satiety-sensitive
cells of the arcuate nucleus itself
 Neuropeptide Y (NPY) and agouti-related
peptide (AgRP) are inhibitory transmitters that
block the satiety action of the paraventricular
nucleus and provoke overeating
 GABA also involved in this inhibitory process
 Output
from the paraventricular nucleus
acts on the lateral hypothalamus
 Animals with damage to the LH area
refuse food and water and may starve to
death unless force fed
The lateral hypothalamus contributes to
feeding by:
 Detecting hunger and sending messages to
make food taste better
 Arousing the cerebral cortex to facilitate
ingestion, swallowing, and to increase
responsiveness to taste, smell and sights of food
 Increasing the pituitary gland’s secretion of
hormones that increase insulin secretion
 Increasing digestive secretions
 Damage
to the ventromedial hypothalamus
that extends to areas outside can lead to
overeating and weight gain
 Those with damage to this area eat normal
sized but unusually frequent meals
VMH lesioned rat is on left 
 Although
a single gene can not be
identified, a genetic influence has been
established in many factors contributing
to obesity
 Monozygotic twins resemble each other
more the dizygotic twins in factors
contributing to obesity
Some slides prepared with the help of the following websites:

http://web.campbell.edu/faculty/asbury/ppt/chapter10.ppt