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By the end of this section, you will be able to:
  • Explain the concept of homeostasis
  • Describe the general process of thermoregulation in humans

Before moving on to discussing organ systems, it is important to review the concept of internal balance. Homeostasis refers to the relatively stable state inside the body. Human organs and organ systems constantly adjust to internal and external changes in order to maintain this steady state. Examples of internal conditions maintained homeostatically are the level of blood glucose, body temperature, and blood calcium level. These conditions remain stable because of physiologic processes that result in negative feedback relationships. If the blood glucose or calcium rises, this sends a signal to organs responsible for lowering blood glucose or calcium. The signals that restore the normal levels are examples of negative feedback. When homeostatic mechanisms fail, the results can be unfavorable. Homeostatic mechanisms keep the body in dynamic equilibrium by constantly adjusting to the changes that the body’s systems encounter. Even when a person is inactive, he/she is maintaining this homeostatic equilibrium. An examples of a factor that is regulated homeostatically is body temperature in a process called thermoregulation.

Homeostasis

The goal of homeostasis is the maintenance of equilibrium around a specific value of some aspect of the body or its cells called a set point    . While there are normal fluctuations from the set point, the body’s systems will usually attempt to go back to this point. A change in the internal or external environment is called a stimulus and is detected by a receptor; the response of the system is to adjust the activities of the system so the value moves back toward the set point. For instance, if the body becomes too warm, adjustments are made to cool it. If glucose levels in the blood rise after a meal, adjustments are made to lower them and to get the nutrient into tissues that need it or to store it for later use.

When a change occurs in an animal’s environment, an adjustment must be made so that the internal environment of the body and cells remains stable. The receptor that senses the change in the environment is part of a feedback mechanism. The stimulus—temperature, glucose, or calcium levels—is detected by the receptor. The receptor sends information to a control center, often the brain, which relays appropriate signals to an effector organ that is able to cause an appropriate change, either up or down, depending on the information the sensor was sending.

Thermoregulation

Animals, such as humans, that maintain a constant body temperature in the face of differing environmental temperatures, are called endotherms . We are able to maintain this temperature by generating internal heat (a waste product of the cellular chemical reactions of metabolism) that keeps the cellular processes operating optimally even when the environment is cold.

Endotherms use their circulatory systems to help maintain body temperature. Vasodilation, the opening up of arteries to the skin by relaxation of their smooth muscles, brings more blood and heat to the body surface, facilitating radiation and evaporative heat loss, cooling the body. Vasoconstriction, the narrowing of blood vessels to the skin by contraction of their smooth muscles, reduces blood flow in peripheral blood vessels, forcing blood toward the core and vital organs, conserving heat.

Thermoregulation is coordinated by the nervous system ( [link] ). The processes of temperature control are centered in a region of the brain called the hypothalamus. The hypothalamus maintains the set point for body temperature through reflexes that cause vasodilation or vasoconstriction and shivering or sweating. The hypothalamus directs the responses that effect the changes in temperature loss or gain that return the body to the set point. The set point may be adjusted in some instances. During an infection, compounds called pyrogens are produced and circulate to the hypothalamus resetting the thermostat to a higher value. This allows the body’s temperature to increase to a new homeostatic equilibrium point in what is commonly called a fever. The increase in body heat makes the body less optimal for bacterial growth and increases the activities of cells so they are better able to fight the infection.

Art connection

Flow chart shows how normal body temperature is maintained. If the body temperature rises, blood vessels dilate, resulting in loss of heat to the environment. Sweat glands secrete fluid. As this fluid evaporates, heat is lost from the body. As a result, the body temperature falls to normal body temperature. If body temperature falls, blood vessels constrict so that heat is conserved. Sweat glands do not secrete fluid. Shivering (involuntary contraction of muscles) releases heat which warms the body. Heat is retained, and body temperature increases to normal.
The body is able to regulate temperature in response to signals from the nervous system.

Section summary

Homeostasis is a dynamic equilibrium that is maintained in body tissues and organs. It is dynamic because it is constantly adjusting to the changes that the systems encounter. It is an equilibrium because body functions are kept within a normal range, with some fluctuations around a set point.

Art connections

[link] When bacteria are destroyed by leukocytes, pyrogens are released into the blood. Pyrogens reset the body’s thermostat to a higher temperature, resulting in fever. How might pyrogens cause the body temperature to rise?

[link] Pyrogens increase body temperature by causing the blood vessels to constrict, inducing shivering, and stopping sweat glands from secreting fluid.

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Questions & Answers

In the digestive system,what are nucleotides and what is their use
Leo Reply
what is the difference between kidney and liver
Raphael
what's an isomer
marybertiny Reply
is a chemical species with the same number and types of atoms as another chemical species but with distinct properties because rhe atoms are arranged into different chemical structures.
yaad
How are they important to anmals
Leo
immune system protect body from harmful foreign cells
Hira Reply
that's right some time when bacteria attached the body the immune system product
abdala
what is function of the body
Sarat Reply
Body funtion. Our bodies consist of a number of biological systems that carry out specific functions necessary for everyday living. The job of the circulatory system is to move blood, nutrients, oxygen, carbon dioxide, and hormones, around the body. It consists of the heart, blood, blood vessels,art
Sayed
what's the function of the lymphatic system
Samuel
how long does it take for food process to reach the deudenum
Braveson
how does it takes for food to digested
Kelliann
how long does it takes for food to digested
Kelliann
what are tissue
Nkeng Reply
what are the difference type of connective tissue
Nkeng
Types of connective tissue 1. Loose connective tissue: a.Areolar connective tissue b.Adipose connective tissue 2. Dense (fibrous) connective tissue: I. Compact tissue a.White fibrous tissue ( tendon and sheath) b.Yellow elastic tissue (Ligament) II. Supporting connective tissue: types- 1. Cartilag
iti
2. Bone III. Fluid or liquid connective tissue: Blood lymph
iti
What is cytoplasm
Uyi Reply
what is cytoplasm
Morgan
a cytoplasm is a fluid found inside the cell membrane which contains dissolved minerals e.t.c.
Fortune
ok
Morgan
why is the the mitochondria known as the power house?
Fortune
The mitochondria is involved in releasing energy from food..this process is known as cellular respiration.
Sherice
ok
Fortune
what is Deoxyribonucleic Acid (DNA)?
Jackson
is a molecule composed of two chains.
Fortune
is a molecule composed of two chains that coil around each other to form a double helix carrying the genetics instructions used in growth,development e.t.c.
Fortune
Thanks
Jackson
structur of the heart
Munyah Reply
hi
Unimke
Hello
Mariam
miss Mariam u are welcome
Emmanuel
hello
wana
hii
Dein-aboh
hi
Wani
how
Renzo
hello every one
BOBO
hello
iti
hello
Hilmi
hello
Eshiemoghie
hi
Vaishnavi
what is mutation?
Oliver
Hi to everybody
Hussein
essay for photosynthesis
NiCho Reply
essay of the human body
NiCho
how do female menstrual uterus prepare for fertilisation?
Jackson
what is blood pressure
Sid Reply
to my understanding blood pressure is where u are shock with something emergency I think that can also course blood pressure
Badu
what is the meaning of extended family
Shellyann Reply
extended family is two are more nuclear family living together under one roof
Nordalee
what is genetic engineering
Ebot Reply
good day please what is a cell?
Colota Reply
cell is the basic unit of all living things/organism
Hassan
differenciate b/w cilia and flagellum
Abshira
Cilia: 1. They are smaller in number. 2. Cilia usually occur throughout or major part of the surface of a cell. 3. They beat oar like and in a co-ordinated rhythm 4. Cilia help in locomotion, feeding, circulation, etc.. 5. Example: Paramecium
iti
Flagella: 1. They are larger in size. ADVERTISEMENTS: 2. Flagella are commonly found at one end of the cell. 3. The flagella beat whip-like and independently. 4. Flagella help in locomotion. 5. Example: Euglena
iti
smallest structural and functional unit of an organism!
zidane
cell is the basic unit of all living things
Lukman
A cell is a basic unit of life
Badu
please I want to know the meaning of Tissues
Badu
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Ebot
h2
Oliver
meaning of dispesing
Oliver
thnk u iti
Abshira
tissue is a group of identical cells having common origin
iti
what is the word? dispensing or dispersing...check the spelling of the word.
iti
dispersing
Oliver
Smaller in size not in number
Md
They are small in size and more in number
Md
Not identical but similar
Md
 cell is the smallest unit of life. Cellsare often called the "building blocks of life". The study of cells is called cellbiology. Cells consist of cytoplasm enclosed within a membrane, which contains many biomolecules such as proteins and nucleic acids.
Harun
hi
Vaishnavi
how are u doing
Emmanuel
this thing I don't know whether is an instruments use to measure pressure Sphygmomanometer is it true or not because in my formal school that's my master told me
Badu
dispersing means distribution or spreading
iti
sphygmomanometer is used for measuring blood pressure
iti
thanks
Oliver
mention the functions of mitochondria?
Oliver
mitochondria is the powerhouse of cell. it generates and stores energy in the form of ATP molecules in its oxysomes. it has its own DNA so its capable of self replicating and hence also called as semi autonomous organelle
iti
welcome
iti
explain briefly anatomy
Oliver
anatomy is thr study of internal structures and their organization as well as functions of living organisms
iti
OK thanky
Oliver
Yes
Hilmi
Good
Moses
welcome
iti
differenciate b/w red blood cell and whight blood cell
BOBO
d
Wani
what is homeostasis
alex Reply
the ability of an organism to maintain stable internal environment, even when the external environment changes
Bee
what's the function of the hypothalamus
Agyekum
The hypothalamus is apart of the lower middle brain that tells the pituitary glands when to release hormones
taehyunggg
what is homeostasis
Edward Reply
constant maintenance of internal body temperature
Agyekum
What is the function of the Pituitary Gland?
WeNdlovu
how can homeostasis be maintained?
alex
pituitary gland also known as the master gland secretes hormones which triggers other gland to secretes their hormones
Agyekum
what's the full meaning of DNA and RNA
Deborah Reply
DNA is Deoxyribonucleic acid and RNA means Ribonucleic acid
Christian

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Source:  OpenStax, Human biology. OpenStax CNX. Dec 01, 2015 Download for free at http://legacy.cnx.org/content/col11903/1.3
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