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Homeostatis: Internal Environment


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"Staying the same." Refers to the observation that many feature that make up the environment of the cells in the human body are subject to negative feedback regulation and are, therefore, relatively constant,
Negative Feedback
In negative feedback SENSORS measure the state of the regulated variable and pass this information to the CONTROLLER that compares it with a predetermined SETPOINT. If the controller detects a difference between the setpoint and the actual value of the regulated variable, it issues a command to EFFECTORS to change the regulated variable in the direction of the setpoint.
What is the sensor?
Controlled variable
heat production/heat loss
core temp
Homeostatically regulated variables include the following:
Core body temp
Blood concentrations of Na+ K+ H+ and ca++
Blood sugar concentrations
Extracellular fluid volume
Arterial blood pressure
Thermoregulatory center
hypothalamus: part of the brain concerned exclusively with homeostatic control
Sensors for core body temperature are located where?
The brain itself, spinal cord, abd, possiblu other internal organs.
What do a second set of cutaneous thermosensors do?
Provide advanced notice of threats to the core body temp and also give subjective sensations of discomfort that can result in appropriate behavioral responses.
The Effectors for thermoregulation include the following:
Cutaneous blood vessels
Sweat glands
skeletal muscles
entire body energy metabolism
What is the temperature of the hypothalamus normally maintained at?
37.6 C
Heat releasing chemical reaction.
What is the most potent source of heat?
The breakdown of foodstuffs to release energy
What is the most immediate means of increasing metabolic heat production?
To increase the frequency of the steady outflow of nerve impuses to sketal muscles that maintain a constant low level of tension (muscle tone)
almost unnoticable nonshivering reaction when exposed to cold increases muscle tone, stimulating the energy metabolism of muscle and increasing its rate of breakdown of foodstuff for energy.
Thermogensis can increase total body heat production by how much?
If hypothalamic temp continues to fall what transition takes place?
Shivering thermogenesis: Large muscle groups contract spasmodically and uncontrollably.
Shivering can increase heat production by how much?
Five fold
What is the second means of heat production within the body?
release of norepinephrine and epinephrine within the sympathic branch of autonomic nervous system.
How does this chemical reaction increase heat production?
Epi and norepi are chemical messengers that increase the metabolic rate of many cells and tissues. The effect is heat production.
What is the difference in effect for adults and infants? Why?
Adults is small ( 10-15%)
Infants have a weak ability to shiver but have a specialized heat producing organ called brown fat around the neck and thorax and can double the heat production when stimulated by epi and norepi
fever inducers
Where do pyrogens originate?
Some released by damaged tissue or produced by the immune system.
From infectious agents
As little as a nanogram of pyrogen can cause the hypothalamic thermostat to reset itself to a value of...
as much as 2-3 degrees higher than normal
How do you know that the thermostat is really reset and not just broken?
the hypothalamus defends this new higher temp increasing shivering measures are taken to warm the pt if the temp falls below the new setpoint and sweating is initiated if the core temp rises above the new setpoint.
Why do studies show that recovery from infection is improved by high temps?
when recovery begins, chills and shivering mark the resetting of the thermostat back to the normal level: this is teh "crisis" phase of a febrile illness.
movement of a substance due to the random movement of it's individual particles.
Net movement by diffusion occurs form regions of HIGHER CONCENTRATION to regions of LOWER CONCENTRATION.
Tends to make the concentration of the diffusing substance the same throughout the system.
concentration gradient
a difference in the concentration of the diffusing substance within the space of the system in which diffusion is occurring.
Greater distances over which diffusion has what effect on net movement of particles?
REDUCES the rate of net movement
The greater the area available which diffusion occurs...
the GREATER the rate of diffusion
Diffusion coefficient
a property that depends on the particle size of the substance and the nature of the medium in which diffusion is occurring.
Generally, smaller particles have _________ coefficients which means they diffuse_____.
Diffusion in gaseous media is more ________ than diffusion in water solution
The higher the temp the more vigorous the movement of the individual particles and thus the ______ the rate of net movement by diffusion.
The magnitude of concentration gradient is said to be the driving force for the net movement by diffusion. The larger the gradient the ______ the rate of net movement.
passive transport
Does not require the input of extra energy from cellular metabolism.
Net movement of substances by diffusion is done by what type of transport?
passive transport
Because diffusion is based on movements that occur on the scale of individual molecules or atoms, it is an effective means of delivering over ______distances.
Within individual cells and in the fluid surrounding them, essentially all movement of dissolved substances including what is difussive?
carbon dioxide
waste products, etc.
In the case of diffusion of an uncharged substance, only one form of potiental energy is involved...
chemical energy
atoms or molecules that have an electrical charge
when the diffusing particles are ions, what type of energy is involved?
electrical potiential energy
Diffusion potiential
electrical voltage between two chambers (explain on p. 3.5)
A state of equilibrium will rapidly be established in which the "pull" of the left behind negative charges exactly balances the "push" of the chemical gradient, so that every K+ that starts off in the direction of the other chamber, a
This is the balancing of + and - charges. One must be in close proximity of the other.
The magnitude of the EQUILIBRIUM POTENTIAL is directly related to the magnitude of what?
Concentration gradient, since one must balance the other.
The mathematical relationship between the two forms of energy-electrical and chemical- is described by what?
Nernst equation
EK+ = 60 mV log (K+ left/K+ right)
simple says that for each tenfold difference in chemical concentration, 60 mV of electrical potential will be needed to establish electrochemical equilibrium.
For a hundredfold concentration difference of an ion with a valence of 1, the corresponding equilibrium potential would be _________ mV
120 mV
resting potential (all cells have this)
a differnce in electrical charge between the cytoplasmic and extracellular sides of the plasma membrance.
Explain how a cell can be thought of as a tiny battery.
the cell has a negative pole inside and a positive pole outside and a rated voltage that carries somewhat form one cell to another and between cell types, but roughly 70mV. When battery is charged, the membrance is POLARIZED with some number of positive charges associated with the outside of the membrance and an equal number of negative charges associated with the inside.
A decrease in the number of ion pairs associated with the membrane, make the membrance less inside negative
an increase in the number, making the cell more inside negative.

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