The Endocrine System.

The Endocrine System

The Endocrine System Second-messenger system of the body
Uses chemical messengers (hormones) that are released into the blood Hormones control several major processes Reproduction Growth and development Mobilization of body defenses Maintenance of much of homeostasis Regulation of metabolism

Hormone Overview Hormones are produced by specialized cells
Cells secrete hormones into extracellular fluids Blood transfers hormones to target sites These hormones regulate the activity of other cells

The Chemistry of Hormones
Hormones are classified chemically as Amino acid–based, which includes Proteins Peptides Amines Steroids—made from cholesterol Prostaglandins—made from highly active lipids

Mechanisms of Hormone Action
Hormones affect only certain tissues or organs (target cells or target organs) Target cells must have specific protein receptors Hormone-binding alters cellular activity

Effects Caused by Hormones
Changes in plasma membrane permeability or electrical state Synthesis of proteins, such as enzymes Activation or inactivation of enzymes Stimulation of mitosis Promotion of secretory activity

The Chemistry of Hormones
Two mechanisms in which hormones act Direct gene activation Second-messenger system

Direct Gene Activation (Steroid Hormone Action)
Diffuse through the plasma membrane of target cells Enter the nucleus Bind to a specific protein within the nucleus Bind to specific sites on the cell’s DNA Activate genes that result in synthesis of new proteins

Hormone-receptor complex
Cytoplasm Nucleus Steroid hormone Receptor protein Hormone-receptor complex DNA mRNA New protein Plasma membrane of target cell Figure 9.1a

Plasma membrane of target cell
Steroid hormone Cytoplasm Nucleus Plasma membrane of target cell Figure 9.1a, step 1

Plasma membrane of target cell
Steroid hormone Cytoplasm Nucleus Plasma membrane of target cell Figure 9.1a, step 2

Nucleus Steroid hormone Cytoplasm Receptor protein Hormone-receptor complex Plasma membrane of target cell Figure 9.1a, step 3

Nucleus Steroid hormone Cytoplasm Receptor protein Hormone-receptor complex DNA Plasma membrane of target cell Figure 9.1a, step 4

Cytoplasm Nucleus Steroid hormone Receptor protein Hormone-receptor complex DNA mRNA Plasma membrane of target cell Figure 9.1a, step 5

Cytoplasm Nucleus Steroid hormone Receptor protein Hormone-receptor complex DNA mRNA New protein Plasma membrane of target cell Figure 9.1a, step 6

Second-Messenger System (Nonsteroid Hormone Action)
Hormone binds to a membrane receptor Hormone does not enter the cell Sets off a series of reactions that activates an enzyme Catalyzes a reaction that produces a second-messenger molecule Oversees additional intracellular changes to promote a specific response

Nonsteroid hormone (first messenger) Cytoplasm
Enzyme ATP Second messenger cAMP Receptor protein Effect on cellular function, such as glycogen breakdown Plasma membrane of target cell Figure 9.1b

Receptor protein Plasma membrane of target cell Figure 9.1b, step 1

Enzyme Receptor protein Plasma membrane of target cell Figure 9.1b, step 2

Enzyme ATP Second messenger cAMP Receptor protein Plasma membrane of target cell Figure 9.1b, step 3

Enzyme ATP Second messenger cAMP Receptor protein Effect on cellular function, such as glycogen breakdown Plasma membrane of target cell Figure 9.1b, step 4

Major Endocrine Glands and Hormones
Table 9.1 (1 of 4)

Table 9.1 (2 of 4)

Table 9.1 (3 of 4)

Table 9.1 (4 of 4)

Control of Hormone Release
Hormone levels in the blood are mostly maintained by negative feedback A stimulus or low hormone levels in the blood triggers the release of more hormone Hormone release stops once an appropriate level in the blood is reached

3 Types of Endocrine Gland Stimuli
Hormonal Humoral Neural Slide 9.11 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Hormonal Stimuli of Endocrine Glands
Most common stimuli Endocrine glands are activated by other hormones Examples: Anterior pituitary hormones

Humoral Stimuli of Endocrine Glands
Changing blood levels of certain ions stimulate hormone release Humoral indicates various body fluids such as blood and bile Examples: Parathyroid hormone Calcitonin Insulin

Neural Stimuli of Endocrine Glands
Nerve impulses stimulate hormone release Most are under the control of the sympathetic nervous system Examples: norepinephrine and epinephrine by the adrenal medulla

Major Endocrine Organs
Pituitary gland Thyroid gland Parathyroid glands Adrenal glands Pineal gland Thymus gland Pancreas Gonads (Ovaries and Testes) Hypothalamus

Location of Major Endrocrine Organs
Figure 9.3

Pituitary Gland Size of a pea
Hangs by a stalk from the hypothalamus in the brain Protected by the sphenoid bone Has two functional lobes Anterior pituitary—glandular tissue Posterior pituitary—nervous tissue Often called the “master endocrine gland”

Hormones of the Anterior Pituitary
Six anterior pituitary hormones Two affect non-endocrine targets Growth hormone Prolactin Four stimulate other endocrine glands (tropic hormones) Thyroid-stimulating hormone (thyrotropic hormone) Adrenocorticotropic hormone Two gonadotropic hormones

Characteristics of all anterior pituitary hormones Proteins (or peptides) Act through second-messenger systems Regulated by hormonal stimuli, mostly negative feedback

Figure 9.4

Growth hormone General metabolic hormone Major effects are directed to growth of skeletal muscles and long bones Plays a role in determining final body size Causes amino acids to be built into proteins Causes fats to be broken down for a source of energy

Growth hormone (GH) disorders Pituitary dwarfism results from hyposecretion of GH during childhood Gigantism results from hypersecretion of GH during childhood Acromegaly results from hypersecretion of GH during adulthood

Gigantism Figure 9.5a

Dwarfism Figure 9.5b

Prolactin (PRL) Stimulates and maintains milk production following childbirth Function in males is unknown Adrenocorticotropic hormone (ACTH) Regulates endocrine activity of the adrenal cortex Thyroid-stimulating hormone (TSH) Influences growth and activity of the thyroid gland

Gonadotropic hormones Regulate hormonal activity of the gonads Follicle-stimulating hormone (FSH) Stimulates follicle development in ovaries Stimulates sperm development in testes Luteinizing hormone (LH) Triggers ovulation of an egg in females Stimulates testosterone production in males

Pituitary–Hypothalamus Relationship
Hormonal release is regulated by releasing and inhibiting hormones produced by the hypothalamus Hypothalamus produces two hormones These hormones are transported to neurosecretory cells of the posterior pituitary Oxytocin Antidiuretic hormone The posterior pituitary is not strictly an endocrine gland, but does release hormones

Hormones of the Posterior Pituitary
Oxytocin Stimulates contractions of the uterus during labor, sexual relations, and breastfeeding Causes milk ejection in a nursing woman

Antidiuretic hormone (ADH) Inhibits urine production by promoting water reabsorption by the kidneys In large amounts, causes vasoconstriction leading to increased blood pressure Also known as vasopressin

Figure 9.6

Thyroid Gland Found at the base of the throat
Consists of two lobes and a connecting isthmus Produces two hormones Thyroid hormone Calcitonin

Thyroid Gland Figure 9.7a

Thyroid Gland Thyroid hormone Major metabolic hormone
Composed of two active iodine-containing hormones Thyroxine (T4)—secreted by thyroid follicles Triiodothyronine (T3)—conversion of T4 at target tissues

Thyroid Gland Figure 9.7b

Thyroid Gland Thyroid hormone disorders Goiters
Thyroid gland enlarges due to lack of iodine Salt is iodized to prevent goiters Cretinism Caused by hyposecretion of thyroxine Results in dwarfism during childhood

Thyroid Gland Figure 9.8

Thyroid Gland Thyroid hormone disorders (continued) Myxedema
Caused by hypothyroidism in adults Results in physical and mental slugishness Graves’ disease Caused by hyperthyroidism Results in increased metabolism, heat intolerance, rapid heartbeat, weight loss, and exophthalmos

Thyroid Gland Figure 9.9

Thyroid Gland Calcitonin
Decreases blood calcium levels by causing its deposition on bone Antagonistic to parathyroid hormone Produced by parafollicular cells Parafollicular cells are found between the follicles

Thyroid Gland Figure 9.7b

Parathyroid Glands Tiny masses on the posterior of the thyroid
Secrete parathyroid hormone (PTH) Stimulate osteoclasts to remove calcium from bone Stimulate the kidneys and intestine to absorb more calcium Raise calcium levels in the blood

Hormonal Regulation of Calcium in Blood
Calcium homeostasis of blood 9–11 mg/100 ml Rising blood Ca2+ levels Thyroid gland releases calcitonin Osteoclasts degrade bone matrix and release Ca2+ into blood PTH Calcitonin Calcitonin stimulates calcium salt deposit in bone Parathyroid glands release parathyroid hormone (PTH) Thyroid gland Parathyroid glands Falling blood Ca2+ levels Imbalance Figure 9.10

Calcium homeostasis of blood 9–11 mg/100 ml Rising blood Ca2+ levels Imbalance Figure 9.10, step 1

Calcium homeostasis of blood 9–11 mg/100 ml Rising blood Ca2+ levels Thyroid gland Imbalance Figure 9.10, step 2

Calcium homeostasis of blood 9–11 mg/100 ml Rising blood Ca2+ levels Thyroid gland releases calcitonin Calcitonin Thyroid gland Imbalance Figure 9.10, step 3

Calcium homeostasis of blood 9–11 mg/100 ml Rising blood Ca2+ levels Thyroid gland releases calcitonin Calcitonin Calcitonin stimulates calcium salt deposit in bone Thyroid gland Imbalance Figure 9.10, step 4

Calcium homeostasis of blood 9–11 mg/100 ml Rising blood Ca2+ levels Thyroid gland releases calcitonin Calcitonin Calcitonin stimulates calcium salt deposit in bone Thyroid gland Figure 9.10, step 5

Calcium homeostasis of blood 9–11 mg/100 ml Falling blood Ca2+ levels Imbalance Figure 9.10, step 6

Calcium homeostasis of blood 9–11 mg/100 ml Thyroid gland Parathyroid glands Falling blood Ca2+ levels Imbalance Figure 9.10, step 7

Calcium homeostasis of blood 9–11 mg/100 ml PTH Parathyroid glands release parathyroid hormone (PTH) Thyroid gland Parathyroid glands Falling blood Ca2+ levels Imbalance Figure 9.10, step 8

Calcium homeostasis of blood 9–11 mg/100 ml Osteoclasts degrade bone matrix and release Ca2+ into blood PTH Parathyroid glands release parathyroid hormone (PTH) Thyroid gland Parathyroid glands Falling blood Ca2+ levels Imbalance Figure 9.10, step 9

Calcium homeostasis of blood 9–11 mg/100 ml Osteoclasts degrade bone matrix and release Ca2+ into blood PTH Parathyroid glands release parathyroid hormone (PTH) Thyroid gland Parathyroid glands Figure 9.10, step 10

Calcium homeostasis of blood 9–11 mg/100 ml Rising blood Ca2+ levels Thyroid gland releases calcitonin Osteoclasts degrade bone matrix and release Ca2+ into blood PTH Calcitonin Calcitonin stimulates calcium salt deposit in bone Parathyroid glands release parathyroid hormone (PTH) Thyroid gland Parathyroid glands Falling blood Ca2+ levels Imbalance Figure 9.10, step 11

Adrenal Glands Sit on top of the kidneys Two regions
Adrenal cortex—outer glandular region has three layers Mineralocorticoids secreting area Glucocorticoids secreting area Sex hormones secreting area Adrenal medulla—inner neural tissue region

Hormones of the Adrenal Cortex
Figure 9.11

Mineralocorticoids (mainly aldosterone) Produced in outer adrenal cortex Regulate mineral content in blood Regulate water and electrolyte balance Target organ is the kidney Production stimulated by renin and aldosterone Production inhibited by atrial natriuretic peptide (ANP)

Figure 9.12

Glucocorticoids (including cortisone and cortisol) Produced in the middle layer of the adrenal cortex Promote normal cell metabolism Help resist long-term stressors Released in response to increased blood levels of ACTH

Roles of the Hypothalamus and Adrenal Glands in the Stress Response
Short term More prolonged Stress Hypothalamus Nerve impulses Adrenal cortex Releasing hormone Corticotropic cells of anterior pituitary ACTH Mineralocorticoids Glucocorticoids Retention of sodium and water by kidneys Increased blood volume and blood pressure 1. Proteins and fats converted to glucose or broken down for energy 2. Increased blood sugar 3. Suppression of immune system Long-term stress response Short-term stress response Spinal cord Adrenal medulla Preganglionic sympathetic fibers Catecholamines (epinephrine and norepinephrine) 1. Increased heart rate 2. Increased blood pressure 3. Liver converts glycogen to glucose and releases glucose to blood 4. Dilation of bronchioles 5. Changes in blood flow patterns, leading to increased alertness and decreased digestive and kidney activity 6. Increased metabolic rate Figure 9.13

Short term Stress Hypothalamus Figure 9.13, step 1

Short term Stress Hypothalamus Nerve impulses Spinal cord Figure 9.13, step 2

Short term Stress Hypothalamus Nerve impulses Spinal cord Adrenal medulla Preganglionic sympathetic fibers Figure 9.13, step 3

Short term Stress Hypothalamus Nerve impulses Short-term stress response Spinal cord Adrenal medulla Preganglionic sympathetic fibers Catecholamines (epinephrine and norepinephrine) Figure 9.13, step 4

Short term Stress Hypothalamus Nerve impulses Short-term stress response Spinal cord Adrenal medulla Preganglionic sympathetic fibers Catecholamines (epinephrine and norepinephrine) 1. Increased heart rate 2. Increased blood pressure 3. Liver converts glycogen to glucose and releases glucose to blood 4. Dilation of bronchioles 5. Changes in blood flow patterns, leading to increased alertness and decreased digestive and kidney activity 6. Increased metabolic rate Figure 9.13, step 5

More prolonged Stress Hypothalamus Figure 9.13, step 6

More prolonged Stress Hypothalamus Releasing hormone Corticotropic cells of anterior pituitary Figure 9.13, step 7

More prolonged Stress Hypothalamus Adrenal cortex Releasing hormone Corticotropic cells of anterior pituitary ACTH Figure 9.13, step 8

More prolonged Stress Hypothalamus Adrenal cortex Releasing hormone Corticotropic cells of anterior pituitary ACTH Mineralocorticoids Long-term stress response Figure 9.13, step 9

More prolonged Stress Hypothalamus Adrenal cortex Releasing hormone Corticotropic cells of anterior pituitary ACTH Mineralocorticoids Glucocorticoids Long-term stress response Figure 9.13, step 10

More prolonged Stress Hypothalamus Adrenal cortex Releasing hormone Corticotropic cells of anterior pituitary ACTH Mineralocorticoids Glucocorticoids Retention of sodium and water by kidneys Increased blood volume and blood pressure Long-term stress response Figure 9.13, step 11

More prolonged Stress Hypothalamus Adrenal cortex Releasing hormone Corticotropic cells of anterior pituitary ACTH Mineralocorticoids Glucocorticoids Retention of sodium and water by kidneys Increased blood volume and blood pressure 1. Proteins and fats converted to glucose or broken down for energy 2. Increased blood sugar 3. Suppression of immune system Long-term stress response Figure 9.13, step 12

Short term More prolonged Stress Hypothalamus Nerve impulses Adrenal cortex Releasing hormone Corticotropic cells of anterior pituitary ACTH Mineralocorticoids Glucocorticoids Retention of sodium and water by kidneys Increased blood volume and blood pressure 1. Proteins and fats converted to glucose or broken down for energy 2. Increased blood sugar 3. Suppression of immune system Long-term stress response Short-term stress response Spinal cord Adrenal medulla Preganglionic sympathetic fibers Catecholamines (epinephrine and norepinephrine) 1. Increased heart rate 2. Increased blood pressure 3. Liver converts glycogen to glucose and releases glucose to blood 4. Dilation of bronchioles 5. Changes in blood flow patterns, leading to increased alertness and decreased digestive and kidney activity 6. Increased metabolic rate Figure 9.13, step 13

Sex hormones Produced in the inner layer of the adrenal cortex Small amounts are made throughout life Mostly androgens (male sex hormones) are made but some estrogens (female sex hormones) are also formed

Adrenal Glands Adrenal cortex disorders Addison’s disease
Results from hyposecretion of all adrenal cortex hormones Bronze skin tone, muscles are weak, burnout, susceptibility to infection Hyperaldosteronism May result from an ACTH-releasing tumor Excess water and sodium are retained leading to high blood pressure and edema

Adrenal Glands Adrenal cortex disorders Cushing’s syndrome
Results from a tumor in the middle cortical area of the adrenal cortex “Moon face,” “buffalo hump” on the upper back, high blood pressure, hyperglycemia, weakening of bones, depression Masculinization Results from hypersecretion of sex hormones Beard and male distribution of hair growth

Hormones of the Adrenal Medulla
Produces two similar hormones (catecholamines) Epinephrine (adrenaline) Norepinephrine (noradrenaline) These hormones prepare the body to deal with short-term stress (“fight or flight”) by Increasing heart rate, blood pressure, blood glucose levels Dilating small passageways of lungs

Figure 9.11

Pancreatic Islets The pancreas is a mixed gland and has both endocrine and exocrine functions The pancreatic islets produce hormones Insulin—allows glucose to cross plasma membranes into cells from beta cells Glucagon—allows glucose to enter the blood from alpha cells These hormones are antagonists that maintain blood sugar homeostasis

Pancreatic Islets Figure 9.14a–b

Pancreatic Islets Figure 9.14b–c

Homeostasis: Normal blood glucose levels (90 mg/100ml)
Insulin-secreting cells of the pancreas activated; release insulin into the blood Uptake of glucose from blood is en- hanced in most body cells Blood glucose levels decline to set point; stimulus for insulin release diminishes Elevated blood sugar levels Liver takes up glucose and stores it as glycogen Stimulus: rising blood glucose levels (e.g., after eating four jelly doughnuts) Imbalance Homeostasis: Normal blood glucose levels (90 mg/100ml) Stimulus: declining blood glucose levels (e.g., after skipping a meal) Imbalance Low blood sugar levels Rising blood glucose levels return blood sugar to homeostatic set point; stimulus for glucagon release diminishes Glucagon-releasing cells of pancreas activated; release glucagon into blood; target is the liver Liver breaks down glycogen stores and releases glucose to the blood Figure 9.15

Figure 9.15, step 1

Stimulus: rising blood glucose levels (e.g., after eating four jelly doughnuts) Imbalance Homeostasis: Normal blood glucose levels (90 mg/100ml) Imbalance Figure 9.15, step 2

Elevated blood sugar levels Stimulus: rising blood glucose levels (e.g., after eating four jelly doughnuts) Imbalance Homeostasis: Normal blood glucose levels (90 mg/100ml) Imbalance Figure 9.15, step 3

Insulin-secreting cells of the pancreas activated; release insulin into the blood Elevated blood sugar levels Stimulus: rising blood glucose levels (e.g., after eating four jelly doughnuts) Imbalance Homeostasis: Normal blood glucose levels (90 mg/100ml) Imbalance Figure 9.15, step 4

Insulin-secreting cells of the pancreas activated; release insulin into the blood Uptake of glucose from blood is en- hanced in most body cells Elevated blood sugar levels Stimulus: rising blood glucose levels (e.g., after eating four jelly doughnuts) Imbalance Homeostasis: Normal blood glucose levels (90 mg/100ml) Imbalance Figure 9.15, step 5

Insulin-secreting cells of the pancreas activated; release insulin into the blood Uptake of glucose from blood is en- hanced in most body cells Elevated blood sugar levels Liver takes up glucose and stores it as glycogen Stimulus: rising blood glucose levels (e.g., after eating four jelly doughnuts) Imbalance Homeostasis: Normal blood glucose levels (90 mg/100ml) Imbalance Figure 9.15, step 6

Insulin-secreting cells of the pancreas activated; release insulin into the blood Uptake of glucose from blood is en- hanced in most body cells Blood glucose levels decline to set point; stimulus for insulin release diminishes Elevated blood sugar levels Liver takes up glucose and stores it as glycogen Stimulus: rising blood glucose levels (e.g., after eating four jelly doughnuts) Homeostasis: Normal blood glucose levels (90 mg/100ml) Figure 9.15, step 7

Imbalance Stimulus: declining blood glucose levels (e.g., after skipping a meal) Homeostasis: Normal blood glucose levels (90 mg/100ml) Imbalance Figure 9.15, step 8

Imbalance Stimulus: declining blood glucose levels (e.g., after skipping a meal) Homeostasis: Normal blood glucose levels (90 mg/100ml) Imbalance Low blood sugar levels Figure 9.15, step 9

Imbalance Stimulus: declining blood glucose levels (e.g., after skipping a meal) Homeostasis: Normal blood glucose levels (90 mg/100ml) Imbalance Low blood sugar levels Glucagon-releasing cells of pancreas activated; release glucagon into blood; target is the liver Figure 9.15, step 10

Imbalance Stimulus: declining blood glucose levels (e.g., after skipping a meal) Homeostasis: Normal blood glucose levels (90 mg/100ml) Imbalance Low blood sugar levels Glucagon-releasing cells of pancreas activated; release glucagon into blood; target is the liver Liver breaks down glycogen stores and releases glucose to the blood Figure 9.15, step 11

Stimulus: declining blood glucose levels (e.g., after skipping a meal) Homeostasis: Normal blood glucose levels (90 mg/100ml) Low blood sugar levels Rising blood glucose levels return blood sugar to homeostatic set point; stimulus for glucagon release diminishes Glucagon-releasing cells of pancreas activated; release glucagon into blood; target is the liver Liver breaks down glycogen stores and releases glucose to the blood Figure 9.15, step 12

Insulin-secreting cells of the pancreas activated; release insulin into the blood Uptake of glucose from blood is en- hanced in most body cells Blood glucose levels decline to set point; stimulus for insulin release diminishes Elevated blood sugar levels Liver takes up glucose and stores it as glycogen Stimulus: rising blood glucose levels (e.g., after eating four jelly doughnuts) Imbalance Homeostasis: Normal blood glucose levels (90 mg/100ml) Stimulus: declining blood glucose levels (e.g., after skipping a meal) Imbalance Low blood sugar levels Rising blood glucose levels return blood sugar to homeostatic set point; stimulus for glucagon release diminishes Glucagon-releasing cells of pancreas activated; release glucagon into blood; target is the liver Liver breaks down glycogen stores and releases glucose to the blood Figure 9.15, step 13

Pineal Gland Found on the third ventricle of the brain
Secretes melatonin Helps establish the body’s wake and sleep cycles Believed to coordinate the hormones of fertility in humans

Figure 9.3

Thymus Gland Located posterior to the sternum
Largest in infants and children Produces thymosin Matures some types of white blood cells Important in developing the immune system

Gonads Ovaries Produce eggs Produce two groups of steroid hormone
Estrogens Progesterone Testes Produce sperm Produce androgens, such as testosterone

Figure 9.3

Hormones of the Ovaries
Estrogens Stimulate the development of secondary female characteristics Mature female reproductive organs With progesterone, estrogens also Promote breast development Regulate menstrual cycle

Hormones of the Ovaries
Progesterone Acts with estrogen to bring about the menstrual cycle Helps in the implantation of an embryo in the uterus Helps prepare breasts for lactation

Hormones of the Testes Produce several androgens
Testosterone is the most important androgen Responsible for adult male secondary sex characteristics Promotes growth and maturation of male reproductive system Required for sperm cell production

Other Hormone-Producing Tissues and Organs
Parts of the small intestine Parts of the stomach Kidneys Heart Many other areas have scattered endocrine cells

Table 9.2 (1 of 2)

Table 9.2 (2 of 2)

Endocrine Function of the Placenta
Produces hormones that maintain the pregnancy Some hormones play a part in the delivery of the baby Produces human chorionic gonadotropin (hCG) in addition to estrogen, progesterone, and other hormones

Developmental Aspects of the Endocrine System
Most endocrine organs operate smoothly until old age Menopause is brought about by lack of efficiency of the ovaries Problems associated with reduced estrogen are common Growth hormone production declines with age Many endocrine glands decrease output with age

The Endocrine System.

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