endocrine system

Question 1

overview of endocrine system

Answer 1

as the second control system of the body, the endocrine system releases chemicals called hormones to regulate major processes in the body.”
“Hormones released by the endocrine system travel through the bloodstream to alter the activity of target cells.”
The endocrine system regulates complex processes such as growth, metabolism, reproduction, and development.

Question 2

more about the endocrine adventures

Answer 2

Our body is constantly undergoing dynamic adventures. For example, the endocrine system releases insulin, which enters the bloodstream and helps move glucose into cells. This is one of the remarkable functions of the endocrine system. It works alongside the nervous system to control and coordinate the body’s activities—but while the endocrine system acts more slowly, the nervous system responds much faster.The nervous system and endocrine system work at different speeds. The nervous system is designed to make rapid changes by sending electrical signals instantly through neurons. In contrast, the endocrine system works more slowly because it releases hormones into the bloodstream, which take longer to reach their target organs.

Question 3

more about what the endocrine system does

Answer 3

Hormones have widespread effects and control several major processes: reproduction; growth and development; mobilizing the body’s defenses against stressors; maintaining the balance of electrolytes, water, and nutrients in the blood; and regulating cellular metabolism and energy balance. As you can see, the endocrine system regulates processes that occur over long periods of time and, in some cases, continuously. The scientific study of hormones and endocrine organs is called endocrinology.

Question 4

endocine system are true gians

Question 5

hormones

Answer 5

Hormones are chemical messengers produced by endocrine cells.
They are released into the extracellular fluid (the fluid around cells), and then they enter the bloodstream.
From there, they travel throughout the body to reach target cells and control how those cells function, especially when it comes to metabolism (how cells use and manage energy).“All other hormones are nonsteroidal amino acid derivatives.” means:
Besides the steroid hormones (which are made from cholesterol),

All the other hormones are made from amino acids or parts of amino acids.

These hormones are called nonsteroidal because they are not steroids.

“Derivatives” means they are chemically related to or made from amino acids.

Question 6

target organs or cells

Answer 6

Although hormones circulate to all the organs of the body via blood, a given hormone affects only certain tissue cells or organs, referred to as its target cells or target organs.🔹 How do hormones “talk” to cells?
For a target cell to respond to a hormone:

The cell must have a specific protein receptor — kind of like a lock.

That receptor can be on the outside (plasma membrane) or inside the cell.

The hormone is like a key that fits only the right lock.

Only when the hormone binds to its matching receptor can it cause a change in the cell.

What does the word “hormone” mean?
It comes from a Greek word that means “to arouse” or “to stir up.”

🔹 What do hormones do in the body?
Hormones “arouse” or activate the cells they target.

They change how a cell works, but they don’t usually make the cell do something totally new.

Instead, they increase or decrease the rate of something the cell already does — like:

How fast it breaks down food

How much energy it uses

How fast it grows or divides

🔹 The exact effect depends on:
The type of hormone

The type of target cell

✅ Simple summary:
Hormones don’t create new jobs for cells — they adjust how fast or slow the cells do what they’re already built to do.

Question 7

what hormones could tell cells to do

Answer 7

What can hormones do in target cells?
Hormones can:

Change plasma membrane permeability

Open or close ion channels (affecting what can enter/exit the cell)

This also changes the cell’s electrical state (called membrane potential)

Activate or inactivate enzymes

Enzymes control chemical reactions inside the cell

Turning them on/off changes what the cell can do

Stimulate or inhibit cell division

Hormones can tell cells to grow or stop multiplying

Promote or inhibit secretion

Hormones can make a cell release or stop releasing certain substances (like insulin, sweat, or digestive juices)

Turn on or off gene expression

They can start or stop transcription (the process of making RNA from DNA)

This affects what proteins the cell produces — which can change its function

Question 8

direct gene activation

Answer 8

Despite the huge variety of hormones, there are really only two mechanisms by which hormones trigger changes in cells. Steroid hormones (and, strangely, thyroid hormone) can use the mechanism of direct gene activation (Figure 9.1a). Because they are lipid-soluble molecules, the steroid hormones can diffuse through the plasma membranes of their target cells . Once inside, the steroid hormone enters the nucleus and binds to a specific hormone receptor . In this specific example, the hormone-receptor complex then binds to specific sites on the cell’s DNA , activating certain genes to transcribe messenger RNA (mRNA) . The mRNA is translated in the cytoplasm , resulting in the synthesis of new proteins. Alternatively, the steroid hormone may bind to receptors in the cytoplasm, and then the complex moves into the nucleus to activate certain genes. Instead of turning genes on, some hormones turn genes off in step 4.

Question 9

seccond messenger system

Answer 9

Second-Messenger System (Used by Most Non-Steroid Hormones)
🧪 What hormones use this method?
Protein and peptide hormones

These hormones are water-soluble, so they can’t pass through the cell membrane

🔹 How it works (step-by-step):
The hormone (called the first messenger) binds to a receptor on the outside of the target cell’s plasma membrane.

This binding activates the receptor, which then starts a cascade of chemical reactions inside the cell.

These reactions activate an enzyme inside the cell.

The enzyme creates a second messenger (like cAMP).

The second messenger causes changes inside the cell — like turning on enzymes, changing ion channels, or activating certain genes.

📬 Easy analogy:
Think of the hormone (first messenger) as a postal worker delivering a message to the front desk of a building (the cell membrane).
The second messenger is like a mailroom employee who takes that message inside the building to the right room (inside the cell).

🔁 Extra info:
Common second messengers:

cAMP (cyclic AMP)

cGMP (cyclic GMP)

Calcium ions

The response depends on the type of cell — the same hormone can do different things in different tissues.

✅ Summary:
Water-soluble hormones (like proteins and peptides) can’t enter cells directly. Instead, they bind to a receptor on the cell surface and use a second-messenger system to send the signal inside the cell and trigger changes. As you might guess, the same hormone may have a variety of possible second messengers (including cyclic guanosine monophosphate, or cGMP, and calcium ions) and many possible target cell responses, depending on the tissue type stimulated.

Question 10

the endocrine system using negative feedback

Answer 10

Negative Feedback in Hormone Control
Most hormones are controlled by negative feedback — this is the body’s way of keeping hormone levels stable and balanced.

Here’s how it works:

🔹 Step-by-step:
Something inside or outside the body triggers hormone release
(like low blood sugar triggering insulin release).

The hormone causes a response in the target organ or cells.

As hormone levels in the blood rise, they signal the body to stop releasing more of that hormone.

This keeps hormone levels from getting too high — they stay in a narrow, healthy range.

💬 A good phrase to remember:
“A little goes a long way” — you don’t need a lot of hormone to cause a big effect.

✅ Example:
Blood sugar gets too high → triggers insulin release

Insulin helps lower the blood sugar

Once sugar is back to normal, insulin release slows down or stops

Question 11

the three types of stimuli

Answer 11

The stimuli that activate endocrine glands fall into three major categories—hormonal, humoral, and neural (Figure 9.2). These three mechanisms represent the most common systems that control hormone release, but they by no means explain all of them. Some endocrine organs respond to many different stimuli.

Question 12

humoral stimuli

Answer 12

The most common stimulus is a hormonal stimulus, in which endocrine organs are prodded into action by other hormones. For example, hormones of the hypothalamus stimulate the anterior pituitary gland to secrete its hormones, and many anterior pituitary hormones stimulate other endocrine organs to release their hormones into the blood (Figure 9.2a). As the hormones produced by the final target glands increase in the blood, they “feed back” to inhibit the release of anterior pituitary hormones and thus their own release. Hormone release promoted by this mechanism tends to be rhythmic, with hormone blood levels rising and falling again and again.