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Humans have a similar temperature regulation feedback system that works by promoting either heat loss or heat gain ( [link] b ). When the brain’s temperature regulation center receives data from the sensors indicating that the body’s temperature exceeds its normal range, it stimulates a cluster of brain cells referred to as the “heat-loss center.” This stimulation has three major effects:

  • Blood vessels in the skin begin to dilate allowing more blood from the body core to flow to the surface of the skin allowing the heat to radiate into the environment.
  • As blood flow to the skin increases, sweat glands are activated to increase their output. As the sweat evaporates from the skin surface into the surrounding air, it takes heat with it.
  • The depth of respiration increases, and a person may breathe through an open mouth instead of through the nasal passageways. This further increases heat loss from the lungs.

In contrast, activation of the brain’s heat-gain center by exposure to cold reduces blood flow to the skin, and blood returning from the limbs is diverted into a network of deep veins. This arrangement traps heat closer to the body core and restricts heat loss. If heat loss is severe, the brain triggers an increase in random signals to skeletal muscles, causing them to contract and producing shivering. The muscle contractions of shivering release heat while using up ATP. The brain triggers the thyroid gland in the endocrine system to release thyroid hormone, which increases metabolic activity and heat production in cells throughout the body. The brain also signals the adrenal glands to release epinephrine (adrenaline), a hormone that causes the breakdown of glycogen into glucose, which can be used as an energy source. The breakdown of glycogen into glucose also results in increased metabolism and heat production.

Water concentration in the body is critical for proper functioning. A person’s body retains very tight control on water levels without conscious control by the person. Watch this video to learn more about water concentration in the body. Which organ has primary control over the amount of water in the body?

Positive feedback

Positive feedback intensifies a change in the body’s physiological condition rather than reversing it. A deviation from the normal range results in more change, and the system moves farther away from the normal range. Positive feedback in the body is normal only when there is a definite end point. Childbirth and the body’s response to blood loss are two examples of positive feedback loops that are normal but are activated only when needed.

Childbirth at full term is an example of a situation in which the maintenance of the existing body state is not desired. Enormous changes in the mother’s body are required to expel the baby at the end of pregnancy. And the events of childbirth, once begun, must progress rapidly to a conclusion or the life of the mother and the baby are at risk. The extreme muscular work of labor and delivery are the result of a positive feedback system ( [link] ).

Positive feedback loop

This diagram shows the steps of a positive feedback loop as a series of stepwise arrows looping around a diagram of an infant within the uterus of a pregnant woman. Initially the head of the baby pushes against the cervix, transmitting nerve impulses from the cervix to the brain. Next the brain stimulates the pituitary gland to secrete oxytocin which is carried in the bloodstream to the uterus. Finally, the oxytocin simulates uterine contractions and pushes the baby harder into the cervix. As the head of the baby pushes against the cervix with greater and greater force, the uterine contractions grow stronger and more frequent. This mechanism is a positive feedback loop.
Normal childbirth is driven by a positive feedback loop. A positive feedback loop results in a change in the body’s status, rather than a return to homeostasis.

The first contractions of labor (the stimulus) push the baby toward the cervix (the lowest part of the uterus). The cervix contains stretch-sensitive nerve cells that monitor the degree of stretching (the sensors). These nerve cells send messages to the brain, which in turn causes the pituitary gland at the base of the brain to release the hormone oxytocin into the bloodstream. Oxytocin causes stronger contractions of the smooth muscles in of the uterus (the effectors), pushing the baby further down the birth canal. This causes even greater stretching of the cervix. The cycle of stretching, oxytocin release, and increasingly more forceful contractions stops only when the baby is born. At this point, the stretching of the cervix halts, stopping the release of oxytocin.

A second example of positive feedback centers on reversing extreme damage to the body. Following a penetrating wound, the most immediate threat is excessive blood loss. Less blood circulating means reduced blood pressure and reduced perfusion (penetration of blood) to the brain and other vital organs. If perfusion is severely reduced, vital organs will shut down and the person will die. The body responds to this potential catastrophe by releasing substances in the injured blood vessel wall that begin the process of blood clotting. As each step of clotting occurs, it stimulates the release of more clotting substances. This accelerates the processes of clotting and sealing off the damaged area. Clotting is contained in a local area based on the tightly controlled availability of clotting proteins. This is an adaptive, life-saving cascade of events.

Chapter review

Homeostasis is the activity of cells throughout the body to maintain the physiological state within a narrow range that is compatible with life. Homeostasis is regulated by negative feedback loops and, much less frequently, by positive feedback loops. Both have the same components of a stimulus, sensor, control center, and effector; however, negative feedback loops work to prevent an excessive response to the stimulus, whereas positive feedback loops intensify the response until an end point is reached.

Water concentration in the body is critical for proper functioning. A person’s body retains very tight control on water levels without conscious control by the person. Watch this video to learn more about water concentration in the body. Which organ has primary control over the amount of water in the body?

The kidneys.

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Questions & Answers

knuckle of the middle finger
James Reply
because of the gases (nitrogen, oxygen)
Nejat
why the heart is protected with that sac
Joshua Reply
To prevent collision with the lungs, lubricates the heart, protects the heart from infection in the event a peripheral organ is effected, and stabilizes the heart within the mediastinum.
Jeremiah
This app should be updated too much as there is very little information for some topics.I hope you will consider my information....
aman Reply
adenohypophysis is made up of what type of cells and what is the name of those cells?
Mannu Reply
whatpassesthroughmaleovale
armstrong Reply
motor root of the trigeminal nerve
Vandana
what is the nervous system about
Joshua
what passes through foramen ovale?
Farah Reply
what are the organelles of a cell
Amina Reply
muscular system
Vandana
nucleus ribosome Golgi body call membrane cytoplasm
Sabina
these are the cellular components that functions to provide energy,remove waste and cell division
Waziri
Organelles of the cell are: Mitochondria,Ribosome,golgi apparatus, nucleus, secretory granules, nuclear e t c
Khadijah
what are local hormones
Richard
Local hormones are hormones that effect the cell that released them or cells near the releasing cell and they do not circulate within the blood stream.
Jeremiah
the trachea bifurcated into how many branches on the right lung
barbie
three lobes
Richard
Explain the normal flow of blood.
Shikha
how can we maintain the internal living things
Choolwe Reply
how many seconds does a human will stop if you sneeze
Kharl Reply
idk
Erika
1 sec not specific
Jane
1_3seconds
Mannu
physiology of vision
Sudipta Reply
Can pure water become gel like?
ovie Reply
No
Abdulazeez
what is Homeostasis
Laura Reply
It is the ability of an organism to co ordinate it's internal environment so as to achieve balance in all areas
ovie
what is anatomy
Sandra Reply
what is physiology
Sandra
The study of how the body works
Joseph
the branch of biology dealing with the functions and activities of leaving organisms and their parts including all physical and chemical processes
Maria
the study of human body . phicically and chemically it's called anotomy physiology
Raj
the branch of biology dealing with the functions and activities of living organisms
Salman
which vein do we inject to give infusions
Belinda
it is the scientific study of the body structure
Choolwe
What Choolwe Muselitata said is the definition of anatomy
KWAKU
Physiology can also be described as the way in which a living organism or bodily part functions
KWAKU
Anotomy is the science which we humen body of structure and function know as the anotomy
Aman
study of the body funtion and structure
Kaoum
functional study of the body
Mosele
it is the study about the functions of body organs
Mannu
what are the vital sign procedure
jeniffer Reply
You start the TPR then BP after explaining the procedure to the patient and your requirements ready.
Dauda
which type of vein to you inject to give infusions?
Belinda
*do
Belinda
how long do u take radial pulse
Flavian Reply
1 minute
Mannu
You can take it for 15 seconds , the number you got you multiply wth 2
Likius
but in the aspect of the multiplying that isn't right
Sabina
radial pulse kya hai?
OM
?
OM
for more accurate values you must do the 1 minute
Jane
1 minute.
Andrew
60 seconds
Richard
1 minute
Kaoum
yes @sabina
Mannu

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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