HOMEOSTASIS

I. THE ENDOCRINE SYSTEM

What is the endocrine system?

The endocrine system is composed of glands that secrete hormones directly into the bloodstream.

Its functions include:

  • Regulating the body’s daily activities

  • Controlling several development processes

  • Coordinating various functions of the body

Hormones

Hormones are chemical messengers that are carried through the blood to organs such as the skin, muscles, and other organs.

The endocrine system helps keep the body’s internal conditions balanced.

Endocrine system as a control system

The endocrine system works like a thermostat because it can turn on when the body needs a response and turn off when the desired condition is reached.

If the endocrine system does not work properly, the body may experience abnormal conditions such as:

  • Energy levels

  • Weight

  • Physical appearance

  • Ability to produce offspring


II. THERMOREGULATION

What is thermoregulation?

Thermoregulation is the process of maintaining and regulating the body’s internal temperature.

Humans are warm-blooded organisms because they can generate internal heat.

Normal body temperature

The hypothalamus maintains body temperature at approximately:

37°C


HYPOTHALAMUS

The hypothalamus checks the body’s temperature and helps maintain it at a normal level.

When body temperature becomes TOO LOW:

Low body temperature
↓
Hypothalamus detects the change
↓
Body generates and maintains heat

One mechanism involves goosebumps.

Goosebumps

Goosebumps happen when:

  • The hypothalamus triggers a response.

  • Small muscles attached to hair follicles contract.

  • The hairs rise.

  • Goosebumps appear.

Another mechanism is shivering.

Shivering

Shivering happens when muscles tighten and relax rapidly.

This produces heat and helps warm the body.

The book describes shivering as a natural response to cold temperatures.


When body temperature becomes TOO HIGH:

The body tries to release heat.

One mechanism is perspiration/sweating.

Perspiration

Perspiration helps cool the body because:

  • Sweat is released onto the skin.

  • Sweat evaporates.

  • Evaporation cools the body.


HYPOTHERMIA

Hypothermia occurs when the body has an abnormally low body temperature.

It can happen when a person is exposed to extremely cold conditions for a prolonged period.

Possible effects mentioned in the book include:

  • Prolonged shivering

  • Loss of consciousness

  • Abnormal nervous-system function

  • Organ failure

  • Possible death in severe cases

First aid for hypothermia

The book says to:

  • Move the person away from the source of cold.

  • Keep the person warm.

  • Use protective clothing such as jackets and gloves.

  • Avoid further exposure to extremely low temperatures.


HYPERTHERMIA

Hyperthermia occurs when the body has an abnormally high body temperature or overheats.

It can happen when the body cannot release enough heat.

Possible symptoms mentioned include:

  • Rapid heartbeat

  • Confusion

  • Fainting

  • Loss of consciousness

  • Even coma in severe cases

First aid for hyperthermia

The book recommends:

  • Remove excess clothing.

  • Place the person in a well-ventilated location.

  • Use cooling methods such as a cool shower or immersion in cold water.


III. BLOOD GLUCOSE REGULATION

What is glucose?

Glucose is the primary/main sugar found in the blood.

It is important because it:

  • Serves as a source of energy

  • Provides nourishment to the organs and body

The body gets glucose from carbohydrates in the food we eat.


PANCREAS

The pancreas helps regulate blood sugar levels.

It is located behind the stomach in the upper abdominal cavity.

The pancreas is both:

  • An endocrine gland

  • An exocrine gland

Endocrine gland

Releases hormones directly into the bloodstream.

Exocrine gland

Releases substances through ducts.


INSULIN

Insulin is a hormone that decreases blood glucose levels.

When blood glucose becomes high:

High blood glucose
↓
Pancreas detects the increase
↓
Pancreatic β-cells release insulin
↓
Body cells take up glucose
↓
Liver takes up glucose and stores it as glycogen
↓
Blood glucose decreases
↓
Normal level is restored

Important:

Insulin = decreases blood glucose


GLUCAGON

Glucagon is a hormone that increases blood glucose levels.

When blood glucose becomes low:

Low blood glucose
↓
Pancreas detects the decrease
↓
Pancreatic α-cells release glucagon
↓
Liver breaks down stored glycogen and releases glucose
↓
Blood glucose increases
↓
Normal level is restored

Important:

Glucagon = increases blood glucose

Easy memory trick:

INSULIN → IN = glucose goes IN to cells → blood sugar decreases

GLUCAGON → glucose goes UP → blood sugar increases


NORMAL BLOOD GLUCOSE

The book states that the normal blood sugar level is around:

70 mg/dL to 100 mg/dL

Blood glucose can be tested using a glucometer.

The book recommends testing it in the morning after fasting for around 8 hours.


HYPOGLYCEMIA

Hypoglycemia occurs when blood glucose levels are below healthy levels.

It can happen because of:

  • Extreme hunger

  • Not eating enough

  • Certain metabolic conditions

Possible symptoms include:

  • Extreme hunger

  • Shaking

  • Sweating

  • Confusion

  • Loss of consciousness

The book emphasizes eating a balanced diet at the right time to help prevent this.


HYPERGLYCEMIA

Hyperglycemia occurs when blood glucose levels are high.

The book explains that having too little insulin or the body’s inability to properly use insulin can cause high blood glucose.

If blood glucose remains elevated, it can lead to diabetes mellitus.

Type 1 diabetes

The pancreas is unable to make insulin because the body’s immune system attacks the cells in the pancreas that produce insulin.

Type 2 diabetes

The pancreas can still make insulin, but the body becomes resistant to insulin.


IV. BLOOD PRESSURE REGULATION

What is blood pressure?

Blood pressure is the pressure within the arteries in the systemic circulation.

Blood pressure is measured using a device called a sphygmomanometer.

It is measured in:

millimeters of mercury (mmHg)


SYSTOLIC AND DIASTOLIC PRESSURE

Systolic pressure

The highest pressure exerted within the large arteries when the heart muscle contracts to pump blood.

Diastolic pressure

The lowest pressure exerted within the large arteries when the heart muscle relaxes between beats.

So remember:

Systolic = heart contracts

Diastolic = heart relaxes


BARORECEPTOR REFLEX

The body regulates blood pressure through several mechanisms, including:

  • Baroreceptor reflex

  • Antidiuretic hormone

  • Renin-angiotensin-aldosterone system (RAAS)

Baroreceptors

Baroreceptors are sensors found within blood vessels.

They detect changes in blood pressure through vessel stretching.

There are two types:

  • High-pressure baroreceptors

  • Low-pressure baroreceptors

High-pressure baroreceptors include:

  • Carotid baroreceptors

  • Aortic arch baroreceptors

Carotid baroreceptor

Detects changes in pressure in the carotid artery.

Aortic arch baroreceptor

Detects changes in pressure in the aortic arch.


ANTIDIURETIC HORMONE (ADH)

Antidiuretic hormone, also called vasopressin, is synthesized by the hypothalamus.

It helps:

  • Increase water reabsorption in the kidneys

  • Increase plasma volume

  • Increase arterial blood pressure

When the concentration of ADH is high, it can cause vasoconstriction, which increases blood pressure.


RAAS

RAAS stands for:

Renin-Angiotensin-Aldosterone System

It is another mechanism for regulating blood pressure.

Basic sequence:

Low blood pressure
↓
Kidney releases renin
↓
Renin acts on angiotensinogen
↓
Forms angiotensin I
↓
Converted into angiotensin II
↓
Angiotensin II causes vasoconstriction
↓
Blood pressure increases

Angiotensin II also stimulates the release of aldosterone.

Aldosterone

Aldosterone helps the kidneys retain sodium, which contributes to an increase in blood volume and blood pressure.


HIGH BLOOD PRESSURE

Hypertension = abnormally high blood pressure.

The book explains that high blood pressure can cause damage because the blood is being pumped with excessive pressure.

LOW BLOOD PRESSURE

Hypotension = abnormally low blood pressure.

It may cause:

  • Dizziness

  • Weakness

  • Other problems when blood pressure becomes too low


V. FEEDBACK MECHANISMS

Many functions of the body operate using feedback systems.

These help the body maintain a state of balance called homeostasis.

The book explains that the:

  • Nervous system

  • Endocrine system

play important roles in feedback mechanisms.

Nervous system

The neurons can detect changes once hormones are released into the bloodstream and respond quickly.

Endocrine system

Hormones regulate body processes, but the system generally responds more slowly.


VI. NEGATIVE FEEDBACK MECHANISM

Definition

Negative feedback is a control system that reduces or minimizes changes or conditions of the body.

It helps the body remain stable.

Set point

The set point is the normal value or ideal requirement of the body for a particular condition.

Example:

Normal body temperature → approximately 37°C

If body temperature changes from the set point, the body responds to bring it back toward the normal level.


COMPONENTS OF NEGATIVE FEEDBACK

According to your textbook:

1. Control center

The brain, which establishes a set point.

2. Receptor

Detects changes within the body.

3. Effector

Responsible for the response to the change.

4. Stimulus

Produces a change to a variable.

Basic pattern:

Stimulus
↓
Receptor detects change
↓
Control center processes information
↓
Effector responds
↓
Condition moves back toward normal


EXAMPLES OF NEGATIVE FEEDBACK

Example 1: Body temperature

Body temperature increases
↓
Hypothalamus detects it
↓
Sweating increases
↓
Heat is released
↓
Body temperature decreases
↓
Homeostasis


Example 2: Breathing / Carbon dioxide

When carbon dioxide levels increase:

High CO₂
↓
Breathing increases
↓
More CO₂ is removed
↓
CO₂ level decreases
↓
Balance is restored

The book explains that this is a good example of a negative feedback loop because the response reverses the change.


Example 3: Blood glucose

Blood glucose increases
↓
Pancreas releases insulin
↓
Glucose enters cells / is stored
↓
Blood glucose decreases
↓
Normal blood glucose is restored


VII. POSITIVE FEEDBACK MECHANISM

Definition

Positive feedback is a control system that uses information from sensors to increase the rate of a process.

It is essentially the opposite of negative feedback.

Main idea:

Negative feedback → reduces change

Positive feedback → increases change

Positive feedback is important when a rapid change is necessary.


EXAMPLES OF POSITIVE FEEDBACK

Example 1: Blood clotting

When a blood vessel is injured:

Injury
↓
Blood clotting begins
↓
More clotting occurs
↓
Clot continues to grow
↓
Wound becomes sealed

The response increases the process of clotting until the wound is sealed.


Example 2: Childbirth

During childbirth:

Contractions begin
↓
Oxytocin is released
↓
Contractions become stronger
↓
More oxytocin is released
↓
Contractions become stronger
↓
Birth occurs

Once the baby is born, the release of oxytocin stops and the positive feedback mechanism ends.

Remember:

Oxytocin → stronger contractions


Example 3: Calcium regulation

Your book also gives an example involving blood calcium.

When blood calcium falls below a certain threshold:

Low blood calcium
↓
Parathyroid glands release PTH
↓
PTH stimulates cells in bones and kidneys
↓
Calcium enters the bloodstream
↓
Blood calcium level increases

The textbook describes this as a positive feedback mechanism for calcium-level regulation.


⭐ SUPER IMPORTANT COMPARISON