Chapter 45 Hormones and the Endocrine System

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

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 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  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 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 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  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  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.

1. A Simple Endocrine Pathway  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.

2. Simple Neurohormone Pathway  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.

3. A Simple Neuroendocrine Pathway  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  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  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 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 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 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 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 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 Hormone  Liver cells and smooth muscle of blood vessels supplying skeletal muscle contain -type epinephrine receptors.

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

Paracrine 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  Nitric oxide (NO).  When blood O 2 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 O 2 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 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 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 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.

The Anterior Pituitary Gland  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 Gland  The neurohypophysis is an extension of the hypothalamus.  It stores and secretes 2 hormones: ADH and oxytocin.  ADH acts on the kidneys increasing H 2 O 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 H 2 O retention.  Oxytocin signals uterine muscle contraction and mammary gland excretion of milk.

The 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 Gland  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 Gland  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 Hormone  Released by the parathyroid gland in response to low blood calcium levels.  PTH induces the breakdown of osteoclasts.  Ca 2+ is then released into the blood.  PTH stimulates Ca 2+ uptake by the renal tubules.  Released by the parathyroid gland in response to low blood calcium levels.  PTH induces the breakdown of osteoclasts.  Ca 2+ is then released into the blood.  PTH stimulates Ca 2+ uptake by the renal tubules.

Parathyroid 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 Ca 2+ from food.  When Ca 2+ gets above a certain setpoint, it promotes the release of calcitonin which opposes the effects of PTH lowering blood Ca 2+ 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 Ca 2+ from food.  When Ca 2+ gets above a certain setpoint, it promotes the release of calcitonin which opposes the effects of PTH lowering blood Ca 2+ levels.

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.  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.

Pancreas  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 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 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 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 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 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 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 Medulla  The 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.