Taste, Smell, Pain, Heat and Cold

Taste, Smell, Pain, Heat and Cold
Taste is mainly smell. Hold
your nose, close your eyes,
and try to tell the difference
between coffee or tea.
Smell has a significant impact
on our perception of taste.
Figure 10-15a
Basic Taste Senses
There is sensed as a combination of
five different basic tastes:
Sweet (Nutritional molecules such as sugars)
Sour (Acid)
Salty (Na)
Bitter (Different toxic compounds)
Umami (Amino acid glutamate)
Figure 10-15a
Taste Bud
About 10,000 taste buds are
on the tongue.
The detection range is of
the order of 10 mM for
sugars and salt but 8 uM
for bitter compounds
such as Quinine.
Figure 10-15b
Figure 10-15c
Artificial Sweeteners in the US
All of these were discovered by accident:
1. Saccharin – 300 to 500 time sweeter than sucrose, discovered 1879
Sweet'N Low
2. Aspartame – 200 times sweeter, discovered in 1965
Equal, NutraSweet
3. Sucralose – chlorinated sugar, 600 times sweeter.
Splenda, Altern
4. Lead Acetate – used by the Romans, not any more!
Smell is a much more sophisticated sense than taste
and in many animals is highly developed.
Each sensory neurons detects one particular smell molecule.
There are about 300 or so genes (roughly 3% of the human genome)
that code for proteins that detect specific molecules or more
precisely specific parts of a molecule. Often a particular molecule
may activate multiple receptors according to the different parts
of the molecule resulting is a blended smell.
For example, one receptor may respond to a specific length of a
side chain while another receptor may respond to whether the same
molecule has an aldehyde group or not.
Other mammals have many more receptor
coding genes, 1000 or more different smell
receptors. Humans probably have all 1000
possible receptors but most are inactive.
Bettina Malnic, Junzo Hirono, Takaaki Sato and Linda B. Buck Cell, Vol. 96, 713–
723, March 5, 1999, Copyright ã1999 by Cell Press Combinatorial Receptor Codes
for Odors. Linda Buck won the 2004 Nobel prize for this work.
See: http://www.washington.edu/alumni/uwnewslinks/200410/article_nobel.html
Pain sensors are formed from bare nerve fibers.
Two types:
A-delta fibers – thinly myelinated (insulated), used to detect
acute pain
C fibers – unmyelinated (no insulation) use to detect diffuse,
dull pain.
A-beta - painless stimuli such as a light touch are transmitted by a
third class of thickly myelinated nerves.
Nerves can also be physically damaged resulting in Neuropathic pain.
Pain Killers
Two types of pain killers:
1. Non-steriodal anti-inflammatory drugs
2. Opioids (or opiates
Pain Killers: anti-inflammatory drugs
Non-steriodal anti-inflammatory drugs (NSAID) work by reducing the
inflammation caused by tissue damage which might be causing
the pain through the release of prostoglandins.
Prostoglandins are synthesized by a family of Cyclooxygenases –
COX-1, COX-2, COX-3. Sometimes
Examples include:
Acetaminophen (Called Paracetamol in the UK) - Tylenol
Pain Killers:Opioides
Opioids are extremely effective pain killers but are also additive
resulting in their regulation to prevent misuse.
Opioids bind to receptors on the neuron-neuron connections
(synapses). The brain has natural pain reducers called enkephalines.
The opioides act on the same receptors as the enkephalines.
Unfortunately the brain will adapt to continual use of opioides
resulting in patients requiring higher doses to achieve the same effect.
At this point if the drug use is remove the now relatively insensitive
synapses respond less well to the soothing effects of the natural
enkephalines resulting in withdrawal symptoms.
Pain Killers:Opioides
Examples include:
Morphine (Poppy)
Diacetylmorphine (Heroin, derived from morphine)
Codeine (Poppy)
Oxycodone (Tradename: OxyContin)
Hydrocodone (Tradename: Vicodin)
Heat and Cold
There are several types of heat receptors in the skin.
Together they cover a range of temperatures:
TRPV4 – Warm (27 – 34 C)
TRPV4 – Warmer (33 – 39 C)
TRVP 1 – Hot (> 42 C)
Also activated by Capsaicin (except birds),
Camphor and Acids
TRVP2 – Painfully Hot (> 52 C)
Heat and Cold
There are several types of heat receptors in the skin.
Together they cover a range of temperatures:
TRPV4 – Warm (27 – 34 C)
TRPV4 – Warmer (33 – 39 C)
TRVP 1 – Hot (> 42 C)
Also activated by Capsaicin (except birds),
Camphor and Acids
TRVP2 – Painfully Hot (> 52 C)
Capsaicin – chili peppers
What does the kidney do?
Ion balance
Removal of waste (eg Urea)
Control of pH together with Lungs
Control of Osmolarity of blood
Help control blood pressure and volume
Make Glucose
Blood System
Kidney: Cross Section
Kidney: Internal
Blood Supply
Bowman’s Capsule
There are about 1,000,000
nephrons in each kidney.
20% of the plasma is
emptied into the Bowman’s
capsule, this amounts to
about 150 Liters a day.
However, 148.5 Liters
is reabsorbed.
Four main sections:
1. Proximal
2. Descending
3. Ascending
4. Distal
Proximal Tubule:
100% of glucose and
amino acids are reabsorbed
90% of bicarbonate and phosphate
are reabsorbed.
Plasma proteins are reabsorbed by endocytosis.
The descending limb is
impermeable to ions but
permeable to water.
The ascending limb is
permeable to ions but
impermeable to water.
Ascending Limb:
In the ascending limb, Na,K,Cl
are pumped out into
the surrounding tissue.
Vasa recta:
Ions also move from the surrounding
tissues into the vasa recta.
High concentrations of
ions means that water will
move as well by osmosis.
In particular, water will
move from the descending
limb to the surrounding tissue
where the ion concentration is high.
Water will move from the surrounding
tissue into the vasa recta.
Counter Current
When fluids flow in opposite
directions in parallel and
adjacent tubes.
Sometimes used in birds
to transfer heat from
descending blood in the legs
to the ascending blood
especially in cold climates.
Counter Current
Parallel Tubes
Anti-parallel Tubes
Distal Tubule:
The distal tubule is where, under
hormonal control (parathyroid
hormone, calcitonin and
aldesterone) the body is able
to control the absorption of
calcium, phosphate,
sodium and potassium.
Hormonal Control of Water Balance
Water reabsorption can be controlled in the collecting
duct by the hormone
Vasopressin (also called Antidiuretic Hormone - ADH)
Vasopressin can change the number of aquaporins in the
membranes thus allowing more water to move from the
collecting duct into the surrounding tissue by
Vasopressin is therefore released when the
body feels dehydrated. Vasopressin is secreted by
the pituitary gland at the base of the brain.
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