10.1 - Hormones: Chemical Regulators

What happens during puberty?

• Development of secondary sex characteristics

• Body undergoes physical and hormonal changes

• Marks transition to sexual maturity

What are male secondary sex characteristics?

• Growth of body and facial hair

• Deepening of voice

• Development of reproductive organs

What are female secondary sex characteristics?

• Growth of body hair

• Onset of menstrual cycle

• Development of breasts and wider hips

What causes the changes during puberty?

Hormones

What are hormones?

• Chemical messengers produced by cells in one part of the body

• Regulate processes in cells in other parts of the body

• Travel through the blood or extracellular fluid

What is the endocrine system?

• A system of glands that produces and secretes hormones

• Controls long-term body functions like growth, metabolism, and reproduction

What are endocrine glands?

• Glands that release hormones directly into the blood or extracellular fluid

• Do not use ducts

What are target cells?

• Cells that have specific receptors for a hormone

• Only these cells respond to that hormone

How are hormones removed from the body?

• Broken down by enzymes in target cells

• Cleared from the body at a steady rate

Why don’t all cells respond to all hormones?

Only target cells have the correct receptors for specific hormones

What are target hormones?

• Hormones that act on specific cells or organs

• Only affect cells with the correct receptors

• Produce precise, localized effects

What are non-target hormones?

• Hormones that have broader effects on the body

• Can affect multiple tissues or systems

• Less specific than target hormones

What do the nervous and endocrine systems both do?

• Provide integration and control of body functions

• Work together to maintain homeostasis

How do the nervous and endocrine systems differ?

• Nervous system: fast, short-term responses

• Endocrine system: slower, long-term regulation

What are some hormones we have already discussed?

• ADH (antidiuretic hormone)

• Insulin

• Glucagon

• Oxytocin

What is a prohormone?

• An inactive form of a hormone

• Must be activated before it can function

How are prohormones activated?

Converted into active hormones by target tissues

Why are hormones released in small amounts?

• Because they are very powerful chemical messengers

• Small amounts can produce large effects

What is hormone amplification?

• A small hormone signal triggers a large chain reaction

• The effect becomes much larger than the original signal

Why is amplification important in hormone control?

• Allows the body to respond efficiently with minimal hormone release

• Ensures strong and coordinated physiological responses

what are the two types of hormones?

1. protein hormones

2. steroid hormones

How many hormones are known in humans?

More than 60 hormones

What are the two main types of hormones?

• Protein hormones

• Steroid hormones

What are protein hormones made of?

• Chains of amino acids

• They are proteins

Are protein hormones water or fat soluble?

• Water soluble (hydrophilic, polar)

• Not fat soluble

How do protein hormones travel in the body?

• Dissolve easily in blood and extracellular fluids

• Move freely through watery environments

Where do protein hormones act on target cells?

• Bind to receptors on the cell membrane (cell surface)

• Do not enter the cell directly

How do protein hormones cause effects inside the cell?

• Trigger a cascade of reactions inside the cell

• Amplifies the original signal

What is an example of a protein hormone?

Insulin

What do growth factors do?

• Regulate cell division and differentiation

• Help control growth and development of tissues

What happens when a protein hormone binds to a receptor?

• The hormone binds to a receptor on the cell surface

• The receptor changes shape

• This activates a signal inside the cell

• A chain reaction (signal cascade) begins

What happens inside the cell after the receptor is activated?

• Enzymes are activated

• Phosphate groups are added to proteins (phosphorylation)

• This turns proteins on or off

• Leads to a specific cellular response

What is an example of a protein hormone mechanism?

Glucagon receptor pathway

What happens when we have extra glucose in the body?

It is stored in the liver as glycogen

What happens to glucagon when blood sugar levels rise?

• Glucagon secretion decreases from the pancreas

• Less glucagon is released into the bloodstream

• Glycogen breakdown in the liver slows down

• Blood sugar levels are no longer being raised

• This helps return blood glucose to normal (homeostasis)

What are steroid hormones made of?

Cholesterol

Are steroid hormones water soluble or fat soluble?

• Fat soluble (hydrophobic)

• Not soluble in blood

How do steroid hormones travel in the bloodstream?

• Bind to hydrophilic carrier proteins

• This forms water-soluble complexes so they can travel in blood

How do steroid hormones enter target cells?

• They pass directly through the cell membrane

• Because they are non-polar and lipid-soluble

Where do steroid hormones bind inside the cell?

Internal receptors in the cytosol or nucleus

What is the main difference between steroid and protein hormones?

• Steroid hormones enter the cell and bind internal receptors

• Protein hormones bind to receptors on the cell surface

What are examples of steroid hormones?

• Aldosterone

• Cortisol

• Sex hormones (estrogen, testosterone, progesterone)

How do steroid hormones work inside a cell?

• They are lipid-soluble and pass through the plasma membrane

• Bind to receptors inside the cytosol or nucleus

• Hormone–receptor complex forms

What happens after the hormone binds to an internal receptor?

• The complex attaches to specific DNA control sequences (genes)

• This turns gene expression on or off

What is the result of steroid hormone action?

• Changes in protein synthesis

• Alters cell activity and function

Why do steroid hormones have long-lasting effects?

• They directly affect gene expression

• This changes protein production over time

• Effects continue even after hormone levels drop

How does aldosterone regulate blood pressure?

• Released from the adrenal glands when blood pressure is low

• Acts as a steroid hormone

Where does aldosterone act in the body?

• Released from the adrenal glands when blood pressure is low

• Acts as a steroid hormone

Where does aldosterone act in the body?

• Kidney cells

• Sweat glands

• Colon

• Only target cells with specific receptors respond

What does aldosterone do inside cells?

• Binds to intracellular receptors

• Acts as a transcription factor

• Activates genes that produce proteins for sodium (Na⁺) reabsorption

How does sodium reabsorption increase blood pressure?

• More Na⁺ is reabsorbed into the blood

• Water follows sodium by osmosis

• Blood volume increases

• Blood pressure rises

Why is aldosterone important for homeostasis?

• Helps restore normal blood pressure when it drops

• Maintains fluid and electrolyte balance in the body

What happens to thyroid hormone levels when they increase?

• They trigger negative feedback inhibition

• The hypothalamus reduces TRH (thyroid-releasing hormone) secretion

• The pituitary gland reduces TSH (thyroid-stimulating hormone) release

• The thyroid gland slows down production of thyroid hormones

• This brings hormone levels back to normal (homeostasis)

Why does this happen?

• To prevent hormone levels from becoming too high

• To maintain a stable internal environment

• This is an example of a negative feedback system

Why do body processes involve more than one hormone?

• Most physiological processes are complex and require fine control

• Multiple hormones work together to produce balanced effects

• Some hormones have opposite (antagonistic) effects

What is an example of hormones working in opposition?

• Insulin lowers blood glucose

• Glucagon raises blood glucose

• Together they maintain stable blood sugar levels

What is the role of negative feedback in hormone systems?

• Detects when hormone levels are too high or too low

• Adjusts secretion to restore balance

• Prevents overcorrection in the body

Why do some hormones act in opposite ways?

• To allow precise control of body conditions

• Helps the body respond to changing needs (stress, growth, metabolism, etc.)

What is the overall purpose of multiple hormone systems working together?

• Maintain homeostasis

• Coordinate complex body functions like growth, digestion, and stress response

• Ensure stability despite internal and external changes