chapter 45 hormones and the endocrine system. internal communication animals have 2 systems of...

Chapter 45Chapter 45

Hormones and the Endocrine System

Hormones and the Endocrine System

Internal CommunicationInternal Communication

Animals have 2 systems of internal communication and regulation:

1. The nervous system.2. The endocrine system.

Animals have 2 systems of internal communication and regulation:

1. The nervous system.2. The endocrine system.

1. The Nervous System1. The Nervous System

The nervous system is the pathway of communication involving high speed electrical signals.

The nervous system is the pathway of communication involving high speed electrical signals.

2. The Endocrine System

2. The Endocrine System

The endocrine system is all of the animal’s hormone secreting cells.

The endocrine system coordinates a slow, long-lasting response.

The endocrine system is all of the animal’s hormone secreting cells.

The endocrine system coordinates a slow, long-lasting response.

Endocrine GlandsEndocrine Glands

Endocrine glands are hormone secreting organs.

They are ductless glands.Their product is secreted into extracellular fluid and diffuses into circulation.

Endocrine glands are hormone secreting organs.

They are ductless glands.Their product is secreted into extracellular fluid and diffuses into circulation.

Endocrine and Nervous Systems

Endocrine and Nervous Systems

It is convenient to think of the nervous system and the endocrine as separate.

They are actually very closely linked.

Neurosecretory cells are specialized nerve cells that release hormones into the blood. They have characterisitics of both nerves and endocrine cells.

It is convenient to think of the nervous system and the endocrine as separate.

They are actually very closely linked.

Neurosecretory cells are specialized nerve cells that release hormones into the blood. They have characterisitics of both nerves and endocrine cells.

Neurosecretory CellsNeurosecretory Cells

The hypothalamus and the posterior pituitary gland contains neurosecretory cells.

These produce neurohormones which are distinguishable from endocrine hormones.

Some hormones serve as both endocrine hormones and neurotransmitters.

The hypothalamus and the posterior pituitary gland contains neurosecretory cells.

These produce neurohormones which are distinguishable from endocrine hormones.

Some hormones serve as both endocrine hormones and neurotransmitters.

Neurosecretory CellsNeurosecretory Cells

They can stimulate a response, or they can induce a target cell to elicit a response.For example, a suckling infant and oxytocin release is an example.

They can stimulate a response, or they can induce a target cell to elicit a response.For example, a suckling infant and oxytocin release is an example.

Biological Control Systems

Biological Control Systems

Recall, These are comprised of a receptor/sensor which detects a stimulus and sends information to a control center that controls an effector.

The control center processes the information and compares it to a set point.

The control center sends out processed information and directs the response of the effector.

Recall, These are comprised of a receptor/sensor which detects a stimulus and sends information to a control center that controls an effector.

The control center processes the information and compares it to a set point.

The control center sends out processed information and directs the response of the effector.

3 General Hormonal Pathways

3 General Hormonal Pathways

1. A simple endocrine pathway.

2. A simple neurohormone pathway.

3. A simple neuroendocrine pathway.

1. A simple endocrine pathway.

2. A simple neurohormone pathway.

3. A simple neuroendocrine pathway.

1. A Simple Endocrine Pathway


A stimulus elicits a response on an endocrine cell causing a hormone release.

The hormone diffuses into the blood where it reaches a target effector eliciting a response.

A stimulus elicits a response on an endocrine cell causing a hormone release.

The hormone diffuses into the blood where it reaches a target effector eliciting a response.

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For example: A low glucose level in the blood stimulates the pancreas to release glucagon.

Glucagon acts on liver cells to release glycogen.

Glycogen breaks down into glucose and gets into the blood.

For example: A low glucose level in the blood stimulates the pancreas to release glucagon.

Glucagon acts on liver cells to release glycogen.

Glycogen breaks down into glucose and gets into the blood.



2. Simple Neurohormone Pathway


In the simple neurohormone pathway, a stimulus travels via a sensory neuron to the hypothalamus/posterior pituitary gland.

Neurosecretory cells here release hormones into the blood.

These hormones travel to the target cells and elicit a response.

In the simple neurohormone pathway, a stimulus travels via a sensory neuron to the hypothalamus/posterior pituitary gland.

Neurosecretory cells here release hormones into the blood.

These hormones travel to the target cells and elicit a response.





For example: A suckling infant’s stimulation is sent via a sensory neuron to the hypothalamus/posterior pituitary where oxytocin is made and released into the blood.

The hormones travel to the smooth muscle in the breast which responds by contracting and releasing milk.

For example: A suckling infant’s stimulation is sent via a sensory neuron to the hypothalamus/posterior pituitary where oxytocin is made and released into the blood.

The hormones travel to the smooth muscle in the breast which responds by contracting and releasing milk.



3. A Simple Neuroendocrine Pathway


A stimulus sends the signal to the hypothalamus via a sensory neuron.

The neurosecretory cells of the hypothalamus release hormones into the blood.

These act on endocrine cells to release hormones into the blood.

These hormones have an effect on target cells and elicit a response.

A stimulus sends the signal to the hypothalamus via a sensory neuron.

The neurosecretory cells of the hypothalamus release hormones into the blood.

These act on endocrine cells to release hormones into the blood.

These hormones have an effect on target cells and elicit a response.





For example: Neural and hormonal signals tell the hypothalamus to secrete prolactin releasing hormone.

The hormone travels through the blood to the anterior pituitary which releases prolactin.

Prolactin travels through the blood to the mammary glands stimulating milk production.

For example: Neural and hormonal signals tell the hypothalamus to secrete prolactin releasing hormone.

The hormone travels through the blood to the anterior pituitary which releases prolactin.

Prolactin travels through the blood to the mammary glands stimulating milk production.



Positive and Negative Feedback

Positive and Negative Feedback

Recall,Positive feedback acts to reinforce the stimulus. It leads to a greater response.

Negative feedback acts to reduce the response of the stimulus.

Recall,Positive feedback acts to reinforce the stimulus. It leads to a greater response.

Negative feedback acts to reduce the response of the stimulus.

Molecules Functioning as Hormones

Molecules Functioning as Hormones

There are 3 major classes of molecules that function as hormones:

1. Proteins/peptides-water soluble.

2. Amines-water soluble.3. Steroids-not water soluble.

There are 3 major classes of molecules that function as hormones:

1. Proteins/peptides-water soluble.

2. Amines-water soluble.3. Steroids-not water soluble.

Key EventsKey Events

There are 3 key events involved in signaling:

1. Reception-is when the signal binds to the receptor protein in or on the target cell. Receptors can be inside or outside the cell.

2. Signal transduction-signal binds and triggers events within the cell (cascade events).

3. Response-changes a cell’s behavior.

There are 3 key events involved in signaling:

1. Reception-is when the signal binds to the receptor protein in or on the target cell. Receptors can be inside or outside the cell.

2. Signal transduction-signal binds and triggers events within the cell (cascade events).

3. Response-changes a cell’s behavior.

Signal TransductionSignal Transduction

Receptors for most water soluble proteins are embedded in the plasma membrane.

Binding of a hormone initiates a signal transduction pathway.

Receptors for most water soluble proteins are embedded in the plasma membrane.

Binding of a hormone initiates a signal transduction pathway.

Signal TransductionSignal Transduction

The pathway is a series of changes where cellular proteins convert an extracellular chemical signal into an intracellular response.

Examples: Activation of an enzyme Uptake or secretion of a specific molecule

Rearrangement of a cytoskeleton

The pathway is a series of changes where cellular proteins convert an extracellular chemical signal into an intracellular response.

Examples: Activation of an enzyme Uptake or secretion of a specific molecule

Rearrangement of a cytoskeleton

Signal TransductionSignal Transduction The signals can activate proteins that can act to directly or indirectly regulate transcription of certain genes.

Hormones can cause a variety of responses in target cells with different receptors.

These responses are types of signal transductions.

The signals can activate proteins that can act to directly or indirectly regulate transcription of certain genes.

Hormones can cause a variety of responses in target cells with different receptors.

These responses are types of signal transductions.

Water Soluble HormonesWater Soluble Hormones

Most water soluble hormones have receptors embedded in the membrane.

Surface receptor proteins activate proteins in the cytoplasm which then move into the nucleus and regulate transcription.

Most water soluble hormones have receptors embedded in the membrane.

Surface receptor proteins activate proteins in the cytoplasm which then move into the nucleus and regulate transcription.

Epinephrine Example-Water Soluble HormoneEpinephrine Example-Water Soluble Hormone

Liver cells and smooth muscle of blood vessels supplying skeletal muscle contain -type epinephrine receptors.

Liver cells and smooth muscle of blood vessels supplying skeletal muscle contain -type epinephrine receptors.

Epinephrine Example-Water Soluble HormoneEpinephrine Example-Water Soluble Hormone

Smooth muscle of intestinal blood vessels contain -type receptors.

The tissues respond differently to epinephrine. Increased blood flow and glucose to the skeletal muscles.

Decreased blood flow to the digestive tract.

Smooth muscle of intestinal blood vessels contain -type receptors.

The tissues respond differently to epinephrine. Increased blood flow and glucose to the skeletal muscles.

Decreased blood flow to the digestive tract.

Lipid Soluble HormoneLipid Soluble Hormone Lipid soluble hormones have their receptors located inside of the cell. Either in the cytoplasm or the nucleus.

Entrance of the signal and binding of the signal to the receptor initiates the signal transduction pathway. Binding to DNA stimulates transcription of genes.

mRNA produced is translated into protein within the cytoplasm.

Lipid soluble hormones have their receptors located inside of the cell. Either in the cytoplasm or the nucleus.

Entrance of the signal and binding of the signal to the receptor initiates the signal transduction pathway. Binding to DNA stimulates transcription of genes.

mRNA produced is translated into protein within the cytoplasm.

Estrogen Example-Lipid Soluble Hormone

Estrogen Example-Lipid Soluble Hormone

Estrogen induces cells within the female bird’s reproductive system to make large amounts of ovalbumin.

Estrogen induces cells within the female bird’s reproductive system to make large amounts of ovalbumin.

Paracrine SignalingParacrine Signaling Neighboring cells signal local regulators that convey signals between these neighboring cells.

Neurotransmitters, cytokines, and growth factors are all examples of local regulators.

Neighboring cells signal local regulators that convey signals between these neighboring cells.

Neurotransmitters, cytokines, and growth factors are all examples of local regulators.

Paracrine Signaling-Example

Paracrine Signaling-Example

Nitric oxide (NO). When blood O2 levels fall, endothelial cells in the blood vessel walls synthesize and release NO.

NO activates an enzyme that relaxes neighboring smooth muscle.

This results in the dilation of blood vessels and improves blood flow.

Nitric oxide (NO). When blood O2 levels fall, endothelial cells in the blood vessel walls synthesize and release NO.

NO activates an enzyme that relaxes neighboring smooth muscle.

This results in the dilation of blood vessels and improves blood flow.

Endocrine ControlEndocrine Control The hypothalamus integrates the vertebrates’ nervous and endocrine systems.

It is found on the underside of the brain.

It receives information from nerves throughout the body and brain.

It initiates the appropriate endocrine signals for varying conditions.

The hypothalamus integrates the vertebrates’ nervous and endocrine systems.

It is found on the underside of the brain.

It receives information from nerves throughout the body and brain.

It initiates the appropriate endocrine signals for varying conditions.

The HypothalamusThe Hypothalamus

Contains 2 sets of neurosecretory cells.

The secretions from these cells are stored in or regulate the activity of the pituitary gland.

Contains 2 sets of neurosecretory cells.

The secretions from these cells are stored in or regulate the activity of the pituitary gland.

The PituitaryThe Pituitary

The pituitary gland has 2 parts.

The anterior and the posterior.

The pituitary gland has 2 parts.

The anterior and the posterior.

The Anterior Pituitary Gland


It is regulated by hormones produced by neurosecretory cells in the hypothalamus.

Some inhibit hormone release, others stimulate it. The adenohypophysis consists of endocrince cells that make and secrete at least 6 different hormones.

Many of them target and stimulate endocrine glands.

It is regulated by hormones produced by neurosecretory cells in the hypothalamus.

Some inhibit hormone release, others stimulate it. The adenohypophysis consists of endocrince cells that make and secrete at least 6 different hormones.

Many of them target and stimulate endocrine glands.



FSH-stimulates production of ova and sperm.

LH-stimulates ovaries and testes. TSH-stimulates the thyroid gland. ACTH-stimulates production and secretion of the hormones of the adrenal cortex.

MSH-stimulates concentration of melanin in skin.

Prolactin-stimulates mammary gland growth and milk synthesis.

FSH-stimulates production of ova and sperm.

LH-stimulates ovaries and testes. TSH-stimulates the thyroid gland. ACTH-stimulates production and secretion of the hormones of the adrenal cortex.

MSH-stimulates concentration of melanin in skin.

Prolactin-stimulates mammary gland growth and milk synthesis.

The Posterior Pituitary GlandThe Posterior

Pituitary Gland The neurohypophysis is an extension of the hypothalamus.

It stores and secretes 2 hormones: ADH and oxytocin. ADH acts on the kidneys increasing H2O retention.

Oxytocin signals uterine muscle contraction and mammary gland excretion of milk.

The neurohypophysis is an extension of the hypothalamus.

It stores and secretes 2 hormones: ADH and oxytocin. ADH acts on the kidneys increasing H2O retention.

Oxytocin signals uterine muscle contraction and mammary gland excretion of milk.

The Thyroid GlandThe Thyroid Gland

The thyroid produces 2 hormones.Triiodothyroxine (T3)Thyroxin (T4)

In mammals, T4 is converted to T3 by target cells.

T3 is mostly responsible for the cellular response.

The thyroid produces 2 hormones.Triiodothyroxine (T3)Thyroxin (T4)

In mammals, T4 is converted to T3 by target cells.

T3 is mostly responsible for the cellular response.


The thyroid is crucial to development. It controls metamorphosis in frogs. It is required for normal functioning of bone-forming cells.

It promotes branching of nerves in utero. It helps skeletal growth and mental development.

It helps maintain muscle tone, digestion, reproductive functions, b.p., h.r.

The thyroid is crucial to development. It controls metamorphosis in frogs. It is required for normal functioning of bone-forming cells.

It promotes branching of nerves in utero. It helps skeletal growth and mental development.

It helps maintain muscle tone, digestion, reproductive functions, b.p., h.r.


The thyroid creates calcitonin.

It works in conjunction with the parathyroid to maintain calcium homeostasis.

The thyroid creates calcitonin.

It works in conjunction with the parathyroid to maintain calcium homeostasis.

Parathyroid HormoneParathyroid Hormone Released by the parathyroid gland in response to low blood calcium levels.

PTH induces the breakdown of osteoclasts.

Ca2+ is then released into the blood.

PTH stimulates Ca2+ uptake by the renal tubules.

Released by the parathyroid gland in response to low blood calcium levels.

PTH induces the breakdown of osteoclasts.

Ca2+ is then released into the blood.

PTH stimulates Ca2+ uptake by the renal tubules.

Parathyroid HormoneParathyroid Hormone

PTH also promotes the conversion of vitamin D into its active form.

The active form of vitamin D acts on the intestines stimulating the uptake of Ca2+ from food.

When Ca2+ gets above a certain setpoint, it promotes the release of calcitonin which opposes the effects of PTH lowering blood Ca2+ levels.

PTH also promotes the conversion of vitamin D into its active form.

The active form of vitamin D acts on the intestines stimulating the uptake of Ca2+ from food.

When Ca2+ gets above a certain setpoint, it promotes the release of calcitonin which opposes the effects of PTH lowering blood Ca2+ levels.

PancreasPancreas

The pancreas is both an endocrine and a exocrine gland.Exocrine-releases secretions into ducts.

Endocrine-secretions diffuse into bloodstream.

Islets of Langerhans are scattered throughout the exocrine portion of the pancreas.

The pancreas is both an endocrine and a exocrine gland.Exocrine-releases secretions into ducts.

Endocrine-secretions diffuse into bloodstream.

Islets of Langerhans are scattered throughout the exocrine portion of the pancreas.

PancreasPancreas

Each islet contains -cells and -cells.

-cells produce glucagon. -cells produce insulin.Insulin and glucagon oppose each other and regulate the concentration of glucose in the blood.

Each islet contains -cells and -cells.

-cells produce glucagon. -cells produce insulin.Insulin and glucagon oppose each other and regulate the concentration of glucose in the blood.

Blood GlucoseBlood Glucose Glucagon gets released when blood glucose falls below a setpoint.

Insulin gets released when blood glucose is elevated.

Insulin stimulates most cells to take up glucose from the blood.

It also acts to slow glycogen breakdown in the liver.

Glucagon gets released when blood glucose falls below a setpoint.

Insulin gets released when blood glucose is elevated.

Insulin stimulates most cells to take up glucose from the blood.

It also acts to slow glycogen breakdown in the liver.

Diabetes MellitusDiabetes Mellitus

Diabetes is an endocrine disorder caused by a deficiency in insulin or decreased response to insulin.

There are 2 types:Type I-insulin dependent.Type II-non-insulin dependent.

Diabetes is an endocrine disorder caused by a deficiency in insulin or decreased response to insulin.

There are 2 types:Type I-insulin dependent.Type II-non-insulin dependent.

Type I DiabetesType I Diabetes

Insulin dependent. It’s an autoimmune disease resulting in the destruction of the body’s -cells.

The pancreas can’t produce insulin and the person requires insulin injections.

Insulin dependent. It’s an autoimmune disease resulting in the destruction of the body’s -cells.

The pancreas can’t produce insulin and the person requires insulin injections.

Type II DiabetesType II Diabetes

Non-insulin dependent.It is caused either by a deficiency in insulin, or usually by a reduced responsiveness by the cells to insulin.

Non-insulin dependent.It is caused either by a deficiency in insulin, or usually by a reduced responsiveness by the cells to insulin.

Adrenal GlandsAdrenal Glands

They are adjacent to the kidneys.

They are made up of 2 different cell types.Adrenal cortex-the outer portion.

Adrenal medulla-the inner portion.

They are adjacent to the kidneys.

They are made up of 2 different cell types.Adrenal cortex-the outer portion.

Adrenal medulla-the inner portion.

Adrenal CortexAdrenal Cortex

Responds to endocrine signals. ACTH released from the anterior pituitary stimulates the release of corticosteriods. Glucocorticoids-cortisol involved in bioenergetics.

Mineralcorticoids-aldosterone acts on salt balance.

The cortex also releases sex hormones.

Responds to endocrine signals. ACTH released from the anterior pituitary stimulates the release of corticosteriods. Glucocorticoids-cortisol involved in bioenergetics.

Mineralcorticoids-aldosterone acts on salt balance.

The cortex also releases sex hormones.

Adrenal MedullaAdrenal MedullaThe medulla responds to endocrine signals.

Produces the catecholamines epinephrine and norepinephrine.

These are involved in the ‘fight-or-flight’ response.

The medulla responds to endocrine signals.

Produces the catecholamines epinephrine and norepinephrine.

These are involved in the ‘fight-or-flight’ response.