endocrine system chapter 50 table of contents section 1 hormones section 2 endocrine glands

Endocrine SystemChapter 50

Table of Contents

Section 1 Hormones

Section 2 Endocrine Glands

Section 1 HormonesChapter 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.


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.


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.

Chapter 50

The Endocrine System

Section 1 Hormones

Chapter 50

Click below to watch the Visual Concept.

Visual Concept

Comparing Endocrine and Exocrine Glands

Section 1 Hormones


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.


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.


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.

Chapter 50

How Amino Acid-Based Hormones Work

Section 1 Hormones

Chapter 50


Visual Concept

Action of Amino Acid-Based Hormones

Section 1 Hormones


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.

Chapter 50

How Steroid Hormones Work

Section 1 Hormones

Chapter 50


Visual Concept

Action of Steroid Hormones

Section 1 Hormones


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.

Chapter 50


Visual Concept

Comparing Hormones and Prostaglandins

Section 1 Hormones

Section 2 Endocrine GlandsChapter 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.


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.


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.


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.

Chapter 50

The Hypothalamus and the Pituitary Gland


Chapter 50

The Hormones Secreted by the Pituitary Gland


Chapter 50


Visual Concept

Anatomy of the Human Pituitary Gland



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.

Chapter 50


Visual Concept

Anatomy of the Human Thyroid Gland



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.

Chapter 50

Hyperthyroidism


Chapter 50

Hypothyroidism



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.


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.


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.

Chapter 50

The Adrenal Gland


Chapter 50

Adrenal Gland



Visual Concept


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.


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.

Chapter 50


Visual Concept

Gonads



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.

Chapter 50


Visual Concept

Pancreas



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.


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.


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.


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.

Chapter 50

Pineal Gland



Visual Concept



• 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.

Chapter 50


Visual Concept

Parathyroid Gland




• 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.


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.


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.

Chapter 50

Negative Feedback




• 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.

Chapter 50


Visual Concept

Comparing Positive and Negative Feedback




• Antagonistic Hormones

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

– Example: Both glucagon and insulin regulate blood sugar levels.

endocrine system chapter 50 table of contents section 1 hormones section 2 endocrine glands

Documents

secret hormones

lipid hormones

amino acidbased hormones

thyroid hormones act

structure of steroid

target cells

major functions of hormones

specific cells