Chapter 50 Table of Contents

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Endocrine System

Chapter 50 Section 1 Hormones

Section 2 Endocrine Glands

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Section 1 Hormones

Chapter 50 Objectives

• State the major functions of hormones.

• Differentiate between endocrine and exocrine glands.

• Compare the structure of amino acid-based hormones with the structure of steroid hormones.

• Compare how amino acid-based hormones act on their target cells with how steroid or thyroid hormones act on their target cells.

• Relate how neuropeptides and prostaglandins act like

hormones.

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Section 1 Hormones

Chapter 50 Function and Secretion

• Hormones are substances secreted by cells that act to regulate the

activity of other cells in the body.

– Hormones affect all cells in the body and are made and secreted by endocrine glands.

• Endocrine glands are ductless

organs that secret hormones either

into the bloodstream or the fluid

around cells.

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Section 1 Hormones

Chapter 50 Function and Secretion, continued

• The endocrine glands can be found through out the body and are collectively known as the endocrine system.

• Endocrine glands, such as the pancreas, can also be exocrine glands.

– Exocrine glands secrete substances through

ducts to specific locations inside and outside the

body.

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Chapter 50 The Endocrine System

Section 1 Hormones

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Chapter 50 Click below to watch the Visual Concept.

Visual Concept

Comparing Endocrine and Exocrine Glands

Section 1 Hormones

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Section 1 Hormones

Chapter 50 Types of Hormones

• Hormones can be grouped into two types based on their

structure. Hormones can either be amino acid-based hormones or steroid hormones.

– Amino acid based-hormones are made of amino acids, either a single modified amino acid or a protein made of 3-200 amino acids, and are water soluble.

– Steroid hormones are lipid hormones that the body makes from cholesterol and are fat soluble.

• Similar to steroid hormones are thyroid hormones.

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Section 1 Hormones

Chapter 50 Hormone Action

• Regardless of which type of hormone is being

activated, all hormones affect only their target cells.

– Target cells are specific cells to which a hormone travels to produce a specific effect.

– On the target cells are receptors. Receptors are

proteins that bind to specific signal molecules,

such as hormones, that cause a cell to respond.

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Section 1 Hormones

Chapter 50 Hormone Action, continued

• Amino acid-based hormones

– Amino acid-based hormones bind to receptor proteins on the cell membrane and are called first messengers.

– Second messengers are then activated. A second

messenger is a molecule that initiates changes inside a cell in response to the binding of a specific substance to a

receptor on the outside of a cell.

• Changes to the cell through enzyme action then occur in

a cascade fashion.

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Chapter 50 How Amino Acid-Based Hormones Work

Section 1 Hormones

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Chapter 50 Click below to watch the Visual Concept.

Visual Concept

Action of Amino Acid-Based Hormones

Section 1 Hormones

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Section 1 Hormones

Chapter 50 Hormone Action, continued

• Steroid and Thyroid Hormones

– Steroid and thyroid hormones are similar because they are both fat soluble.

– Because these hormones are fat soluble they can pass through the cell membrane.

– Thus, these hormones can enter their target cells

and bind directly to receptor sites in the cytoplasm

or nucleus and directly activate enzymes.

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Chapter 50 How Steroid Hormones Work

Section 1 Hormones

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Chapter 50 Click below to watch the Visual Concept.

Visual Concept

Action of Steroid Hormones

Section 1 Hormones

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Section 1 Hormones

Chapter 50 Other Types of Hormones

• Two other types of chemical messengers that are classified as hormones are neuropeptides and prostaglandins.

– Neuropeptides are hormones secreted by the

nervous system and tend to affect many cells near the nerve cells that release them.

– Prostaglandins are modified fatty acids that are

secreted by most cells and tend to accumulate in

areas where tissues are disturbed or injured.

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Chapter 50 Click below to watch the Visual Concept.

Visual Concept

Comparing Hormones and Prostaglandins

Section 1 Hormones

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Section 2 Endocrine Glands

Chapter 50 Objectives

• Identify the relationship between the hypothalamus and the pituitary gland in the release of hormones.

• List the functions of the major endocrine glands and hormones.

• Explain the role of feedback mechanisms in maintaining homeostasis.

• Compare how negative feedback and positive feedback mechanisms are used to regulate hormone.

• Summarize how antagonistic hormones work as pairs to

maintain homeostasis.

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Section 2 Endocrine Glands

Chapter 50 Hypothalamus and Pituitary Gland

• Two organs, the hypothalamus and the pituitary

gland, control the initial release of many hormones for the endocrine system.

– The hypothalamus is the area of the brain that

coordinates many activities of the nervous and

endocrine systems.

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Section 2 Endocrine Glands

Chapter 50 Hypothalamus and Pituitary Gland, continued

• The hypothalamus responds to information it receives from the body by issuing instructions, as hormones, to the pituitary gland.

• The pituitary gland has two parts, anterior and posterior, and

stores and releases hormones produced by the hypothalamus.

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Section 2 Endocrine Glands

Chapter 50 Hypothalamus and Pituitary Gland, continued

• The nerve cells in the hypothalamus that secrete hormones are called neurosecretory cells.

– These cells secrete two types of hormones to the pituitary gland.

• Releasing hormones stimulate the anterior pituitary to make and secrete hormones.

• Release-inhibiting hormones inhibit production

and secretion of anterior-pituitary hormones.

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Chapter 50 The Hypothalamus and the Pituitary Gland

Section 2 Endocrine Glands

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Chapter 50 The Hormones Secreted by the Pituitary Gland

Section 2 Endocrine Glands

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Chapter 50 Click below to watch the Visual Concept.

Visual Concept

Anatomy of the Human Pituitary Gland

Section 2 Endocrine Glands

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Section 2 Endocrine Glands

Chapter 50 Thyroid Gland

• The thyroid gland is

located near the larynx and helps maintain a normal

heart rate, blood pressure, and body temperature by increasing or decreasing cellular metabolic rates.

• The thyroid gland is also

important for development.

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Chapter 50 Click below to watch the Visual Concept.

Visual Concept

Anatomy of the Human Thyroid Gland

Section 2 Endocrine Glands

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Section 2 Endocrine Glands

Chapter 50 Thyroid Gland, continued

• Abnormal thyroid activity can result in hypothyroidism or hyperthyroidism.

• Overproduction of thyroid hormones is called

hyperthyroidism and can have symptoms that vary from overactivity to high body temperature.

• A deficiency in a thyroid hormone is known as

hypothyroidism and can have symptoms that vary

from weight gain to retardation.

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Chapter 50 Hyperthyroidism

Section 2 Endocrine Glands

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Chapter 50 Hypothyroidism

Section 2 Endocrine Glands

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Section 2 Endocrine Glands

Chapter 50 Adrenal Glands

• Humans have an adrenal gland located above each kidney. Each adrenal gland has an inner core, the medulla, and an outer core, also

called the cortex.

• The medulla and the cortex function as separate endocrine glands.

– The medulla is controlled by the nervous system, and the cortex is controlled by the anterior

pituitary.

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Section 2 Endocrine Glands

Chapter 50 Adrenal Glands, continued

• Adrenal Medulla

– The adrenal medulla secretes the hormones that stimulate a

“flight-or-fight” response to a stress.

– In this response, the hormones epinephrine, also called adrenaline, and norepinephrine are released.

• These hormones increases heart rate, blood pressure,

blood glucose levels, and blood flow into the heart and

lungs so the body can respond to the initial stress.

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Section 2 Endocrine Glands

Chapter 50 Adrenal Glands, continued

• Adrenal Cortex

– In the presence of some stresses the pituitary

gland will secrete the adrenocorticotropic hormone (ACTH).

– This hormone stimulates the adrenal cortex to produce the hormone cortisol.

• Cortisol promotes the production of glucose

from proteins to help cells make usable energy.

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Chapter 50 The Adrenal Gland

Section 2 Endocrine Glands

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Chapter 50 Adrenal Gland

Section 2 Endocrine Glands

Click below to watch the Visual Concept.

Visual Concept

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Section 2 Endocrine Glands

Chapter 50 Gonads

• Gonads are the gamete-producing organs that also produce a group of steroid sex hormones.

– Gonads, ovaries in females and the testes in males, are regulated by sex hormones, which begin production at puberty.

• Puberty is the adolescent stage during which the sex organs mature and secondary sex characteristics

appear.

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Section 2 Endocrine Glands

Chapter 50 Gonads, continued

• The production of sex hormones is stimulated by the release of two hormones by the pituitary.

– The first hormone is luteinizing hormone (LH). This hormone stimulates ovulation and the release of

progesterone in females and the release of androgens, such as testosterone, in males.

– The second hormone is follicle-stimulating hormone

(FSH). This hormone stimulates the growth and maturation

of the ovarian follicles in females and sperm production in

males.

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Chapter 50 Click below to watch the Visual Concept.

Visual Concept

Gonads

Section 2 Endocrine Glands

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Section 2 Endocrine Glands

Chapter 50 Pancreas

• The pancreas contains both exocrine and endocrine cells. The endocrine cells are called islets of

Langerhans.

• These cells secrete hormones that regulate the level of sugar in the blood. The hormone insulin is one of the hormones produced.

– Insulin lowers the blood sugar level by stimulating body cells to store glucose or use it

for energy.

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Chapter 50 Click below to watch the Visual Concept.

Visual Concept

Pancreas

Section 2 Endocrine Glands

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Section 2 Endocrine Glands

Chapter 50 Pancreas, continued

• A condition called diabetes mellitus occurs when cells are unable to obtain glucose from the blood.

This results in a high glucose level in the blood

• There are two types of diabetes: Type I and Type II.

– Type I occurs when immune cells attack and destroy the islet of Langerhans cells.

– Type II occurs when cells don’t have sufficient

insulin levels or when the organism’s cells have

become less responsive.

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Section 2 Endocrine Glands

Chapter 50 Pancreas, continued

• A condition called hypoglycemia occurs when

excessive insulin is stored and not properly delivered to body cells.

• This leads to a lowered blood glucose concentration,

which can cause such symptoms as overactivity and

dizziness.

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Section 2 Endocrine Glands

Chapter 50 Other Endocrine Glands

• There are several other glands in the endocrine

system, including thymus gland, the pineal gland and the parathyroid glands.

• Thymus Gland

– The thymus gland is located beneath the sternum and plays a role in the development of the immune system by secreting thymosin.

• This amino acid-based hormone stimulates

formation of T cells.

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Section 2 Endocrine Glands

Chapter 50 Other Endocrine Glands, continued

• Pineal Gland

– The pineal gland is located near the base of the brain and helps regulate sleep

patterns by secreting

melatonin.

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Chapter 50 Pineal Gland

Section 2 Endocrine Glands

Click below to watch the Visual Concept.

Visual Concept

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Section 2 Endocrine Glands

Chapter 50 Other Endocrine Glands, continued

• Parathyroid Gland

– The parathyroid glands is made up of four glands embedded in the two thyroid glands.

• These glands secrete the parathyroid

hormone, which

stimulates the transfer

of calcium ions from

the bones to the blood.

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Chapter 50 Click below to watch the Visual Concept.

Visual Concept

Parathyroid Gland

Section 2 Endocrine Glands

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Section 2 Endocrine Glands

Chapter 50 Other Endocrine Glands, continued

• Digestive Cells

– Some of the digestive organs also act as endocrine cells by secreting a variety of hormones that control digestive

processes. Two hormones that are secreted are gastrin and secretin.

• Gastrin is released by the stomach when food is eaten.

• Secretin is released by the small intestine and helps

stimulates the release of various digestive fluids from the

pancreas.

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Section 2 Endocrine Glands

Chapter 50 Feedback Mechanisms

• The endocrine system plays an important role in the maintenance of a stable internal environment, or

homeostasis.

• Maintenance of homeostasis is controlled by

feedback mechanisms. A feedback mechanism is one in which the last step in a series of events

controls the first.

• Feedback mechanisms can be either negative or

positive.

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Section 2 Endocrine Glands

Chapter 50 Feedback Mechanisms, continued

• Negative Feedback

– When the final step in a series of events inhibits the initial signal in the series it is called

negative feedback.

– An example of negative

feedback is the regulation

of thyroid hormones.

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Chapter 50 Negative Feedback

Section 2 Endocrine Glands

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Section 2 Endocrine Glands

Chapter 50 Feedback Mechanisms, continued

• Positive Feedback

– Positive feedback occurs when the release of an initial hormone stimulates release or production of other hormones or substances.

– An example of positive

feedback is the stimulation and

increase in luteinizing hormone

by estrogen.

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Chapter 50 Click below to watch the Visual Concept.

Visual Concept

Comparing Positive and Negative Feedback

Section 2 Endocrine Glands

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Section 2 Endocrine Glands

Chapter 50 Feedback Mechanisms, continued

• Antagonistic Hormones

– Antagonistic hormones work together in pairs to regulate the levels of critical substances.

– Example: Both glucagon and insulin regulate

blood sugar levels.