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Homeostasis

Demonstrate understanding of how an animal maintains a stable

internal environment

Biology 3.4 AS91604

Achievement Criteria

• Explain the purpose of the homeostatic mechanism

• Be able to explain the basis of the homeostatic mechanism

• Describe one way in which internal or external environmental factors can disrupt the homeostatic mechanism

Excellence Criteria

• Be able to explain why it gives and adaptive advantage

• An explanation of the biochemical/biophysical pathways involved

• An analysis of how internal or external environmental factors can disrupt the homeostatic mechanism

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Objectives

To find out how homeostasis works: • To explore how and why the human animal maintains a stable

internal environment, • including how a specific disruption results in responses within a

control system to re-establish a stable internal environment And • the adaptive advantage for humans of their various homeostatic

control systems • the biochemical and biophysical processes underpinning each

mechanism (e.g. equilibrium reactions, changes in membrane permeability, metabolic pathways).

And

Explore the control systems regulating…

• body temperature

• blood pressure

• osmotic balance

• level of blood glucose

• levels and balance of respiratory gases in tissues.

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And the environmental factors that may disrupt them

• External influences such as: – exposure to extreme environmental

conditions ,

– disease or infection,

– drugs or toxins,

• Internal influences such as: – genetic conditions or metabolic disorders

The big questions

• What is the purpose of the system?

• What are the components of the system?

• What is the mechanism of the system (how it responds to being disrupted within a normal range of environmental fluctuations)?

• What can happen when extreme disruption to the system, by internal or external influences, results in its breakdown.

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Homeostasis

• homeo = same or unchanged Greek homoio-, combining form of hómoios similar, like

• stasis = to remain still or steady Greek, from sta- base of histanai 'to stand‘ - a period or state of inactivity or equilibrium

Involves control systems by which an animal maintains a stable internal environment, despite fluctuations in their environment.

Why bother?

• Normal metabolic reactions in animals produce metabolic wastes such as CO2 and urea. The build up of these wastes is toxic.

• Enzymes that control metabolic pathways operate within a narrow range Ph and Temperature range within the body.

Enzymes https://www.youtube.com/watch?v=myORDWVzNhc

Amoeba sisters https://www.youtube.com/watch?v=XUn64HY5bug • Homeostasis is maintained through a combination of hormonal

and nervous mechanisms.

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Make a statement

Animals maintain stable internal environments because…

Include:

• Ph

• Temperature

• Enzymes

Homeostasis Unit 1. Control Systems • Feedback loops • Endocrine system • Blood system

2. Osmoregulation • Purpose • Components • Mechanism 3. Blood Glucose • Purpose • Components • Mechanism • Diabetes

4. Body Temperature • Purpose • Components • Mechanism • Hypothermia • Hyperthermia 5. Blood Pressure • Purpose • Components • Mechanism • Hypotension and hypertension

6. Respiratory Gases • Purpose • Components • Mechanism • Asthma?

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Homeostatic Control Systems

Thing that needs to be controlled is to high

Thing that needs to be controlled is to low

Activate a

feedback

process to

increase the

thing

Activate a

feedback

process to

decrease the

thing

For example

What are the parts of this system? And what is the equilibrium set point it is maintaining?

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Homeostatic Control Systems

3 Key components Example

Receptor • Receives information • Sends information to the controller

Sensory nerves or organs

Controller • Registers information • Co-ordinates information if more

than one receptor is involved • Sends out instructions

Usually the brain (Especially the Hypothalamus)

Effector • Receives signals from the controller • Reacts accordingly

Glands, muscles or organs

Homeostatic Control Systems

Brain (control centre)

Muscle

cells

(effector) in

the hand

Rod or cone cells (receptor)

in the eye (sense organ)

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How does the controller know?

The controller has a set point that it is constantly measuring information from the receptors against.

• All systems fluctuate around the set point. As long as the fluctuation remains within range the system can restore itself to ‘normal’.

• Extreme conditions can cause the system to slow down or break down – resulting in damage or death.

Fluctuations

• Are totally fine, up to a point…

With the exception of some prokaryotes, life can only exist between -2°C and 50°C.

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Negative feedback control

Feedback mechanisms can be positive or negative.

Negative feedback control is most common. In this type of control, the output of the

system feeds information back to the controller which responds by reducing output so levels return to the set point.

The stimulus from one part of the body

produces a response that will stop or reduce the original stimulus.

Examples of negative feedback control

High body temperature

Stomach is full CO2 level high

Receptor Hypothalamus Stretch receptors in stomach wall

Respiratory centre in brain

Controller Hypothalamus/ nerves Submucosal plexus Respiratory centre/ nerves

Effector Sweat glands release sweat

Stomach muscles begin contractions

Diaphragm

Output Sweat evaporates Mixing and emptying of stomach content

Breathing rate increases

Result Body temperature is reduced

Stomach empties CO2 levels drop

Feed

bac

k

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Positive feedback control

Positive feedback systems are uncommon in the body.

They form a looped system that causes a large departure from the original condition.

The stimulus in one part of your body causes another part to enhance the effect of the stimulus.

These systems are unstable because they cause as escalation in the original condition.

An example of this childbirth.

Remember the big questions

• What is the purpose of the system?

• What are the components of the system?

• What is the mechanism of the system (how it responds to being disrupted within a normal range of environmental fluctuations)?

• What can happen when extreme disruption to the system, by internal or external influences, results in its breakdown.

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Systems involved in Homeostatic control

• Homeostasis is maintained through a combination of hormonal and nervous mechanisms.

• Nervous system • Endocrine system • Blood system • Liver and Kidneys

Nervous system

• Briefly define/describe the following • Central nervous system (CNS)

• Peripheral nervous system (PNS)

• Autonomic nervous system (ANS)

• Within the autonomic nervous system define the two systems: the parasympathetic and sympathetic.

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Central Nervous System (CNS)

• The brain and the spinal cord make up the central nervous system. The brain lies protected inside the skull and from there controls all the body functions by sending and receiving messages through nerves.

• The brain is the control centre for your body and it sits in your skull at the top of your spinal cord.

• The brain has three main parts.

• The cerebellum

• The cerebrum which has two parts, the left and right cerebral hemispheres

• The brain stem, that controls a lot of the 'automatic' actions of your body such as breathing and heart beat, and links the brain to the spinal cord and the rest of the body.

Peripheral Nervous System (PNS)

• The peripheral nervous system carries messages to and from the central nervous system. It sends information to the brain and carries out orders from the brain.

• Messages travel through the cranial nerves, those which branch out from the brain and go to many places in the head such as the ears, eyes and face. Messages can also travel through the spinal nerves which branch out from the spinal cord.

• There are two major parts to the peripheral nervous system. • The somatic system: • sends sensory information to the central nervous system through peripheral

nerve fibres. Sensory means that it sends the information coming from all your senses, touch, vision, hearing, taste, smell and position.

• sends messages to motor nerve fibres to get the muscles to move the body. • The autonomic system • is responsible for making sure that all the automatic things that your body

needs to do to keep you going, like breathing, digesting etc. continue working smoothly without your having to think about them. (How hard would it be to have to keep thinking, "Breathe in, breathe out," or "Start digesting the food stomach!")

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Autonomic Nervous System (ANS)

• The autonomic nervous system (ANS) regulates the functions of our internal organs (the viscera) such as the heart, stomach and intestines. The ANS is part of the peripheral nervous system and it also controls some of the muscles within the body. We are often unaware of the ANS because it functions involuntary and reflexively. For example, we do not notice when blood vessels change size or when our heart beats faster. However, some people can be trained to control some functions of the ANS such as heart rate or blood pressure. The ANS regulates:

• Muscles

• vis -- in the skin (around hair follicles; smooth muscle

• -- around blood vessels (smooth muscle)

• -- in the eye (the iris; smooth muscle)

• -- in the stomach, intestines and bladder (smooth muscle)

• -- of the heart (cardiac muscle)

• Glands

• The ANS is divided into three parts:

• The sympathetic nervous system

• The parasympathetic nervous system

• The enteric nervous system

Sympathetic Nervous System Parasympathetic Nervous System

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Endocrine System

• Describe the endocrine system • Give the essential function of the following

hormones • Insulin • ADH • Adrenalin (epinephrine) • Aldosterone • Thyroxine • Give reasons why the hypothalamus and

pituitary are important organs in homeostatic control.

Blood (circulatory) System

• Distinguish between vasoconstriction and vasodilation

• Name the homeostatic control mechanisms that vasoconstriction and vasodilation are essential components of

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Blood System Vasodilation means the smooth muscles in your blood vessel

walls relax causing them to widen. This widening results in less

vascular resistance, thus the blood flowing through the dilated

vessel increases. Vasodilation may occur locally or system wide.

Some basic health benefits resulting from vasodilation include:

•lowering blood pressure

•assists in eliminating excess metabolic produced heat

•enhances clotting factor & leukocyte entry into damage tissue

•increases delivery of oxygen & nutrients during energy consuming

activities

The natural signals for causing vessels to dilate are referred to

as vasodilators and the source varies,

including parasympathetic nerve impulses, hormones and

bradykinin release. The term vasodilator is also used in reference

to drugs that treat certain conditions that benefit from vasodilation,

such as hypertension, angina, congestive heart failure, pulmonary

hypertension and erectile dysfunction.

Vasoconstriction means the smooth muscles in your blood

vessel walls contract causing them to narrow. This action results in

blood flow through your vessels to be restricted. Some health

benefits of vasoconstriction are:

•retain heat in cold climates

•reduce excessive blood loss

•prevent orthostatic hypotension

Vasoconstriction can be caused by sympathetic nerve

impulses, prostaglandins, serotonin and epinephrine. Certain

drugs can also stimulate blood vessels to constrict, referred to as

vasoconstrictors or vasopressors, for instance:

•cocaine

•stimulants

•decongestants

•amphetamines

•antihistamines

Caffeine causes vasoconstriction as well.

Homeostatic Control Systems

Temperature (as vasoconstriction and vasodilation can control the heat loss from the body through the skin)

Blood vessels supplying blood to the skin can swell or dilate - called vasodilation. This causes more heat to be carried by the blood to the skin, where it can be lost to the air. Blood vessels can shrink down again - called vasoconstriction. This reduces heat loss through the skin once the body’s temperature has returned to normal.

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Liver and Kidneys

• Distinguish excretion and secretion

• Give a reason that the liver is important for maintaining homeostasis

• Give a reason that the kidneys are important for maintaining homeostasis

Difference between excretion and secretion

Secretion and excretion are the same in nature since both are involved in the passage or movement of materials. These words and body processes are needed in order to control and maintain homeostasis in the body. Both processes move and eliminate unwanted components in the body.

Excretion is the removal of material from a living thing while secretion is the movement of material from one point to another.

Example of excretion: Humans excrete such materials as tears, feces, urine, carbon dioxide, and sweat while

Example of secretion: secretion doesn’t leave the body some examples for secretion are enzymes, hormones, or saliva.

Excretion is mostly body wastes while secretion is important materials that can be metabolized and used by our bodies.

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Reason why the liver is important for maintaining homeostasis

The liver plays a big role in Glucose Homeostasis: Blood glucose homeostasis is an important biologic process that involves a variety of

mechanisms. The muscles, kidneys and liver all have important functions in glucose regulation. The liver is especially important for its ability to store glycogen and prevent low blood glucose.

Maintaining blood glucose within the normal range is referred to as glucose homeostasis.

Your liver plays a key role in blood glucose homeostasis. After a meal when blood glucose is high, the liver has the ability to remove glucose from the blood and store it as part of a molecule called glycogen. In between meals, as blood glucose begins to decline, the liver can make new glucose to release into the blood. Hormones, such as insulin and glucagon, regulate these homeostatic processes.

The liver: The liver filters and processes blood as it circulates through the body. It metabolizes

nutrients, detoxifies harmful substances.

The kidneys

The kidneys are two bean-shaped organs that extract waste from blood, balance body fluids, form urine, and aid in other important functions of the body.

The kidneys are very important to keep the body balanced. The kidneys control water levels.