Download feedback loop

Chapter 25
Man versus Mountain
Jon Krakauer
• Read about his climb up Mount Everest
• He reached the highest and one of the coolest
places on Earth
• Wind chill temperatures average -53C.
• Some people survive the climb and some do
not. Why?
How is the human body organized?
• Like a car or a computer, the human body is
made up of many parts working together in a
coordinated fashion.
• The parts are organized hierarchically, so that
smaller components are organized into
increasingly larger units, which are themselves
organized into more complex systems.
How is the human body organized?
• Anatomy
– is the study of the physical structures that make up an
organism.
• Human bodies have an anatomical structure that
well adapted to living in certain environments
and performing certain functions
• We evolved in the hot, flat savannahs of Africa
– Environment favored big brains, bipedal posture, etc.
– We don’t do well swimming at bottom of ocean or
living on mountaintops.
How is the human body organized?
• For all living things, the
smallest anatomical unit is
the cell. Human bodies
are made up of trillions of
cells, each of which can be
classified as one of a few
hundred different types.
How is the human body organized?
• Cells are organized into
tissues – layers of
specialized cells working
together to execute a
particular function.
• Humans and other animals
have four different kinds of
specialized tissue –
epithelial, connective,
muscle, and nervous.
How is the human body organized?
• An organ is a structure
made up of different
tissue types working
together to carry out a
common function.
• Stomach is composed
of four different
tissues for digestion.
How is the human body organized?
• At the highest level of
organization, organs
interact chemically and
physically as part of organ
systems.
How is the human body organized?
• Physiology is the study of the way a living
organism’s physical parts function.
• Physiologists want to understand how organ
systems cooperate to accomplish basic tasks,
– such as obtaining energy from food
– taking in nutrients to build new molecules during
growth and repair
– and ridding the body of wastes.
Maintaining Homeostasis
• The body is an
integrated system for
processing inputs
and outputs and
maintaining
homeostasis – the
maintenance of a
relatively stable
internal
environment.
Maintaining Homeostasis:
Thermoregulation
• Like many animals, humans have an optimal
temperature and are sensitive to temperature changes.
– We can toleration external temperature changes over a
wide range.
– We are extremely sensitive to changes in our internal
temperature.
• Through thermoregulation – the maintenance of a
relatively stable internal body temperature – our body
temperature is kept at a consistent 37°C (98.6°F).
• This is just one example of how the body tries to
maintain homeostasis.
Maintaining Homeostasis:
Thermoregulation
• How do we respond to cold temperature???
– Conserving heat and generating more
• To conserve heat, the body performs peripheral
vasoconstriction – the reduction in diameter of
blood vessels just below the surface of the skin.
• This pushes blood from the skin to the body core,
where the internal organs are, decreasing the
amount of heat loss from your skin to the
environment.
Maintaining Homeostasis:
Thermoregulation
• To generate more
heat, the body
shivers.
• Shivering is the
involuntary
contraction of
normally voluntary
muscles.
• When muscles
contract through
shivering, they
create heat.
Maintaining Homeostasis:
Thermoregulation
• To help prevent overheating, peripheral
vasodilation, or the expansion in diameter of
blood vessels, increases blood flow to the
skin, and evaporative cooling (otherwise
known as sweating) cools the body by
releasing heat to the air.
• We are doing a lot of sweating this summer?
Balance
• If vasoconstriction goes on for too long
(helping to retain heat), frostbite may occur
– Death of tissues caused by lack of blood flow
• During the Everest climb, they had more than
the cold to deal with? What else?
Altitude
• At high altitudes, the percentage of oxygen
molecules in the air is the same as sea level
– 20% oxygen at sea level
• Problem is with barometric pressure of oxygen is
much lower, as it is with all molecules at high
altitudes.
– Number of oxygen molecules banging around in a given
volume of the atmosphere
– Lower pressure means few oxygen molecules bind to
hemoglobin in blood
• Low oxygen in blood is termed hypoxia
• Have serious effects on brain
How do you cope with low oxygen
• For condition of low oxygen, climbers train or
acclimate their bodies to the low oxygen
condition.
• Acclimatization
– The process of physiologically adjusting to an
environmental change over a period of time.
Generally reversible
• How long did they train? What did they have as a
backup for the climb?
• Body increases output of red blood cells
Maintaining Homeostasis:
Feedback Loops
• Thermoregulation does not require conscious
thought.
– Automated response (thermostat)
– The body’s thermostat is the hypothalamus
• The hypothalamus is a structure that sits at the
base of the brain, right above the brain stem.
– The hypothalamus is responsible for a variety of
physiological functions.
– It receives signals from many different sensors –
specialized cells that detect changes in the internal
and external environment.
• temperature, pressure, or solute concentration.
Maintaining Homeostasis:
Feedback Loops
• The hypothalamus acts as a thermostat. It has
a specific temperature set point below which
a warning message is triggered that body
temperature is dropping when cold outside.
– When that happens, the hypothalamus essentially
tells the body to take corrective action.- What
happens to blood vessels? What else happens?
– Signals are sent from the hypothalamus to their
target tissues along nerve fibers.
Maintaining Homeostasis:
Feedback Loops
• An effector is a cell or tissue that acts to exert
a response on the basis of information relayed
from a sensor.
• They act to cause a change in the internal
environment.
• Once effectors have raised the body
temperature, the sensors sense the changed
conditions and the signals are turned off.
Maintaining Homeostasis:
Feedback Loops
• A feedback
loop is a
pathway that
involves input
from a sensor, a
response via an
effector, and
detection of the
response by the
sensor.
Maintaining Homeostasis:
Feedback Loops
• In a negative feedback loop, the output of
the circuit inhibits the input of the circuit,
thereby helping to bring the system back to
its set point.
• Opposite effect
• Temperature goes up, bring temperature
back down to set point.
Maintaining Homeostasis:
Feedback Loops
• In a positive
feedback loop,
the output of
a system acts
to further
increase the
input of the
system.
• Delivery of
child, blood
clotting
Maintaining Homeostasis:
Feedback Loops
• Hypothalamus regulates many body functions:
hunger, thirst, and sleep.
– Body’s main homeostasis control center
– Key part of nervous system and endocrine system
– Right below the hypothalamus is the pituitary
gland that releases hormones for homeostasis.
What happened on the climb down
Everest?
• Hypothermia
– A drop of body temperature below 35C (95F)
which causes enzyme malfunction and eventually,
death
• Thermoregulation cannot do so indefinitely
– Work takes energy. Need food for fuel
• The body uses the sugar glucose, a breakdown
product of carbohydrate digestion, as fuel.
• When we eat carbohydrates, sugars are
released and absorbed into circulation, and
blood sugar increases.
Maintaining Homeostasis:
Feedback Loops
• Some of this sugar may be used immediately as
fuel for aerobic respiration in cells of the body.
• Whatever is not needed right away will be
converted into glycogen – an energy-storing
carbohydrate – which is stored in muscles and the
liver.
• By converting excess glucose to glycogen, the
body maintains a relatively stable blood-glucose
level.
Maintaining Homeostasis:
Feedback Loops
• Blood-glucose levels are controlled by
endocrine tissue in the pancreas, an organ
that functions in both the endocrine and
digestive systems.
Maintaining Homeostasis:
Feedback Loops
• In response to high blood sugar, the pancreas
produces the hormone insulin, which binds to
receptors on muscle and liver cells, signaling
them to remove sugar from the blood.
• Insulin also signals these cells to make
glycogen, using the sugars taken up from the
blood.
Maintaining Homeostasis:
Feedback Loops
• When blood-sugar levels are low, the body
first prompts us to eat by sending a signal to
the hypothalamus. If eating isn’t an option,
the body begins to break down its stored
glycogen.
• Glucagon, a hormone produced by the
pancreas in response to low blood sugar,
triggers muscle and liver cells to convert their
stored glycogen to glucose.
Organ Systems
• The integumentary system serves
to protect the body from damage.
It includes the skin, hair, fat, and
nails.
Organ Systems
• The muscular system is
responsible for the movement
of body parts. Skeletal limbs,
the heart, and other internal
organs all move with the aid of
this system.
Organ Systems
• The skeletal system provides
structural support for the
body and includes the bones,
cartilage, ligaments, and
tendons.
Organ Systems
• The circulatory system pumps
blood between the lungs and
the body cells using the heart,
blood, and blood vessels. These
organs transport molecules all
over the body.
Organ Systems
• The endocrine system provides
communication within the
body using hormones made by
tissues including the
hypothalamus, pituitary,
thyroid, and adrenal glands.
Organ Systems
• The nervous system includes
organs that sense and respond
to information from all over
the body. This system includes
the brain, spinal cord, and
peripheral nerves.
Organ Systems
• The lymphatic system transfers
lymph fluid from tissues into the
blood and includes the cells and
organs of the immune system,
such as the lymph nodes,
spleen, and bone marrow.
Organ Systems
• The respiratory system is
involved in the exchange of
oxygen and carbon dioxide
between the air and the blood.
Respiratory system organs
include the trachea, lungs, and
diaphragm.
Organ Systems
• The digestive system breaks
down and absorbs food
molecules using organs such as
salivary glands, stomach, small
intestine, liver, and large
intestine.
Organ Systems
• The urinary system is involved
in the regulation of fluid
balance in the body and the
elimination of waste in urine.
The kidneys and bladder are
key organs in this system.
Organ Systems
• The reproductive system is
involved in the
development of offspring.
Male organs include the
testes and penis. Female
organs include the ovaries
and uterus.
Maintaining Homeostasis:
Feedback Loops
• Osmolarity is the concentration of
dissolved solutes in the blood.
• Among the solutes dissolved in the blood
are electrolytes – ions such as sodium
and potassium that are critical for nerve
signaling and muscle contraction.
Maintaining Homeostasis:
Feedback Loops
• Osmolarity is monitored by the hypothalamus
as part of osmoregulation.
• When you are dehydrated – when you have
less fluid in your blood – the concentration of
dissolved solutes is higher.
Maintaining Homeostasis:
Feedback Loops
• If the hypothalamus registers that the
concentration of solutes in the blood is high, it
will trigger a sense of thirst, as well as triggering
the release of antidiuretic hormone (ADH) from
the pituitary, which travels through the
bloodstream and acts on the kidneys.
• The kidneys are the organ involved in
osmoregulation, filtration of blood to remove
wastes, and production of several important
hormones.
Maintaining Homeostasis:
Feedback Loops
• ADH signals the kidneys to excrete less water
in the urine.
• By reducing the amount of water lost in urine,
ADH causes more water to be reabsorbed by
the kidneys back into the bloodstream.
• Water in the bloodstream dilutes dissolved
solutes and lowers the osmolarity.
Maintaining Homeostasis:
Feedback Loops
• Osmoregulation also depends on sensors that
detect changes in blood volume and pressure,
both of which depend on the amount of water
in the blood.
How do other organisms
thermoregulate?
• Because humans
use internal
metabolic heat to
thermoregulate,
humans are
classified as
endotherms.
How do other organisms
thermoregulate?
• Animals that rely on environmental sources of
heat, such as sunlight, to maintain body
temperature are classified as ectotherms.
How do other
organisms
thermoregulate?
• Some organisms generate
heat from nonshivering
thermogenesis.