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Unit 5: the Endocrine System

Book Chapter(s): 16 (pgs. 591-630)

Unit Objectives:

Describe the control of hormone release

Describe half-life, onset, and duration of hormone activity

Describe the interaction of hormones at target cells

Describe the pituitary-hypothalamic relationships

Describe the posterior-pituitary and hypothalamic hormones

Describe the anterior pituitary hormones

Describe the thyroid, parathyroid, adrenal, and pineal glands

Describe other endocrine glands and tissues

Describe developmental aspects of the endocrine system

Unit 7: Endocrine System

Table of Contents

The Endocrine System: Overview

Hormones

The Pituitary Gland and Hypothalamus

The Thyroid Gland

The Parathyroid Glands

The Adrenal (Suprarenal) Glands

The Pineal Gland

Other Endocrine Glands and Tissues

Developmental Aspects of the Endocrine System

Endocrine System

• Second controlling system of the body
• Nervous system is the fast-control system
• 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

The Endocrine System: Overview

How do glands secrete hormones? Remember this…? :)

(slides 25-32)

The Endocrine System: Overview

Endocrine System

• Endocrine glands - release hormones into the surrounding tissue fluid
• Pituitary gland
• Thyroid
• Parathyroid
• Adrenal
• Pineal

The Endocrine System: Overview

Endocrine System

• Neuroendocrine organ - along with neural functions, secretes and release hormones
• Hypothalamus
• Pancreas
• Gonads / Testes
• Placenta

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The Endocrine System: Overview

Endocrine System

• Other organs contain scattered/clustered endocrine cells
• Adipose cells - Leptin
• Thymus - thymic hormones
• Small intestines, stomach, kidneys, heart

The Endocrine System: Overview

The Chemistry of Hormones

Hormones are classified chemically as:

1. Amino acid–based (most abundant), which includes:
1. Proteins
2. Peptides
3. Amines (thyroxine)
2. Steroids—made from cholesterol
3. Prostaglandins and Leukotrienes (Eicosanoids) —made from highly active lipids that act as local hormones
• Not considered “hormones” in your book

Hormones

Hormones

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

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Hormones

Mechanisms of Hormone Action

Hormones arouse cells, or alter cellular activity. Typically, one or more of the following occurs:

• 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

Hormones

Mechanisms of Hormone Action

Hormones act on receptors one of two ways:

1. Water-soluble hormones (all amino acid based hormones except thyroid hormone) act on receptors in the plasma membrane
2. Lipid-soluble hormones (steroids and thyroid hormones) act on receptors inside the cell

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Hormones

Mechanisms of Hormone Action

Plasma Membrane Receptors and Second-Messenger Systems

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Second Messenger: stimulated when a hormone binds to a receptor on the plasma membrane; main methods:

1. The Cyclic AMP Signaling Mechanism
2. The PIP2-Calcium Signaling Mechanism
3. Other Signaling Mechanisms

Hormones

Mechanisms of Hormone Action

Plasma Membrane Receptors and Second-Messenger Systems

1. The Cyclic AMP Signaling Mechanism

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Referred to as a enzymatic cascade

Hormones

Mechanisms of Hormone Action

Plasma Membrane Receptors and Second-Messenger Systems

1. The Cyclic AMP Signaling Mechanism

Hormones

Mechanisms of Hormone Action

Plasma Membrane Receptors and Second-Messenger Systems

1. The Cyclic AMP Signaling Mechanism

Hormones

Mechanisms of Hormone Action

Plasma Membrane Receptors and Second-Messenger Systems

1. The Cyclic AMP Signaling Mechanism

Hormones

Mechanisms of Hormone Action

Plasma Membrane Receptors and Second-Messenger Systems

1. The Cyclic AMP Signaling Mechanism

Hormones

Mechanisms of Hormone Action

Plasma Membrane Receptors and Second-Messenger Systems

1. The Cyclic AMP Signaling Mechanism

Action of cAMP stops when it is degraded by phosphodiesterase

Hormones

Mechanisms of Hormone Action

Plasma Membrane Receptors and Second-Messenger Systems

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2. The PIP2-Calcium Signaling Mechanism

Hormones

Mechanisms of Hormone Action

Plasma Membrane Receptors and Second-Messenger Systems

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3. Other Signaling Mechanisms - Insulin and other growth factors appear to work without second messengers

• Insulin receptor is a tyrosine kinase enzyme that is activated by phosphorylation when insulin binds.
• The activated insulin receptor provides docking sites for relay proteins that initiate a series of protein phosphorylations

Hormones

Mechanisms of Hormone Action

Intracellular Receptors and Direct Gene Activation

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Can diffuse directly into target cells because they are lipid soluble

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Makes its way to chromatin and binds to specific regions of DNA

Hormones

Target Cell Specificity

Target cell activation depends equally on three factors:

1. Blood levels of the hormone
2. Relative numbers of receptors for that hormone on or in the target cells
3. Affinity of the binding between the hormone and the receptor

Hormones

Target Cell Specificity

Receptors are dynamic structures:

1. Up-regulation: target cells form additional receptors for that hormone is response to a low level of hormone
2. Down-regulation: target cells decrease number of receptors in response to persistent high levels of hormone
3. Receptors can be uncoupled from their signaling mechanism

Hormones

Control of Hormone Release

• Hormone levels in the blood are maintained mostly 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

Hormones

Control of Hormone Release - Endocrine Gland Stimuli

Three types of stimuli trigger endocrine glands to manufacture and release their hormones:

1. Humoral: release caused by altered levels of certain critical ions or nutrients
2. Neural: release caused by neural input
3. Hormonal: release caused by another hormone (a tropic hormone)

Hormones

Control of Hormone Release - Nervous System Modulation

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The nervous system can modify both “turn-on” factors and “turn off” factors.

Hormones

Half-Life, Onset, and Duration of Hormone Activity

The concentration of a circulating hormone in blood at any time reflects:

1. Its rate of release
2. The speed at which it is inactivated and removed from the body

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The length of time for a hormone’s blood level to decrease by half is its half life (water-soluble hormones have the shortest half life)

Hormones

Interaction of Hormones in Target Cells

1. Permissiveness: one hormone cannot exert its full effects without another hormone being present (ex: reproductive hormones and thyroid hormone)
2. Synergism: one hormone produces the same effects at the target cell and their combined effects are amplified (ex: glucagon and epinephrine)
3. Antagonism: one hormone opposes the action of another hormone (insulin and glucagon)

Hormones

Please get this out

PITUITARY

THYROID

HEART

KIDNEY

ADRENAL

TESTE

HYPOTHALAMUS

PINEAL BODY

PARATHYROID

THYMUS

PANCREAS

OVARY

STOMACH

The Pituitary Gland and the Hypothalamus

Pituitary Gland (or hypophysis):

• Pituitary gland is the size of a pea
• Hangs by a stalk from the hypothalamus in the brain (infundibulum)
• Protected by the sphenoid bone
• Has two functional lobes
• Anterior pituitary (adenohypophysis)—glandular tissue
• Posterior pituitary (neurohypophysis)—nervous tissue

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Often called the “master endocrine gland

The Pituitary Gland and Hypothalamus

The Pituitary Gland and Hypothalamus

The Hypophyseal Portal System and the Blood Supply to the Pituitary Gland

The Pituitary Gland and Hypothalamus

The Posterior Pituitary and Hypothalamic Hormones

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1. Antidiuretic Hormone (ADH): reduces water loss in the urine; increases thirst
1. Targets kidney tubules via cAMP; respond by reabsorption more water from the forming urine and returning it to the bloodstream
2. Also triggered by pain, low blood pressure, and drugs
2. Oxytocin: stimulates uterine contraction, milk delivery; stimulates prostate gland smooth muscle
• Acts on receptors in the uterus via PIP₂-Ca²⁺; reflex-initiated in breasts

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The Pituitary Gland and Hypothalamus

The Anterior Pituitary Hormones

6 hormones; all affect their target cells via a cyclic cAMP

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Four of the six are classified as tropic hormones, or tropins:

1. TSH
2. ACTH
3. FSH
4. LH

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Gonadotropins are FSH and LH

The Pituitary Gland and Hypothalamus

The Anterior Pituitary Hormones

1. Growth hormone (GH): stimulates cell growth;
1. Targets somatotropic cells
2. Directly impacts metabolism; indirectly impact growth vis IGFs (insulin-like growth factors)
3. Regulated by GHRH (growth hormone-releasing hormone) and GHIH (growth hormone-inhibiting hormone--somatostatin)
1. Thyroid-Stimulating Hormone (TSH) (thyrotropin): triggers thyroid hormone release
1. Thyrotropin-releasing hormone (TRH) by the hypothalamus → release of TSH from thyrotropic cells
2. Adrenocorticotropic Hormone (ACTH): Stimulates glucocorticoid release from adrenal gland
• Secreted by corticotropic cells
• Release is triggered by corticotropin-releasing hormone (CRH) from the hypothalamus

The Pituitary Gland and Hypothalamus

The Anterior Pituitary Hormones

4. Follicle-Stimulating Hormone (FSH): stimulates estrogen secretion, egg production (females), sperm production (males)
5. Luteinizing Hormone (LH): triggers ovulation, progestin production (females), androgen production (males)
1. Gonadotropin-releasing hormone (GnRH) produced by hypothalamus prompts gonadotropin release
6. Prolactin (PRL): Stimulates mammary gland development and milk secretion
• Produced by prolactin cells
• Controlled by an inhibitory hormone (PIH), now known as dopamine

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The Pituitary Gland and Hypothalamus

Negative Feedback Control of Endocrine Secretion

The Pituitary Gland and Hypothalamus

Negative Feedback Control of Endocrine Secretion

The Pituitary Gland and Hypothalamus

Pituitary Hormones and Their Targets

The Pituitary Gland and Hypothalamus

Pituitary Hormones and Their Targets

The Pituitary Gland and Hypothalamus

Pituitary Hormones and Their Targets

The Pituitary Gland and Hypothalamus

Pituitary Hormones and Their Targets

The Pituitary Gland and Hypothalamus

The Thyroid Gland

• Lies near thyroid cartilage of larynx
• Has a rich blood supply
• Contains numerous thyroid follicles
• Produce, store, release thyroid hormones

The Thyroid Gland

The Thyroid Gland- Hormones

Two hormones - Thyroid hormone and Calcitonin

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Thyroid Hormone:

• Increases basal metabolic rate and body heat production (calorigenic effect)
• Controls rate of oxidation of glucose to supply body heat and chemical energy
• Needed for tissue growth and development
• Composed of two active iodine-containing hormones
• Thyroxine (thi-rok’sin)(T4)—secreted by thyroid follicles
• Triiodothyronine (tri”i-odo-thi’ron-nēn) (T3)—conversion of T4 at target tissues

The Thyroid Gland

The Thyroid Gland- Hormones

Two hormones - Calcitonin

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Calcitonin

• Released by parafollicular or C cells
• Decreases blood calcium levels by causing calcium deposition on bone
• Antagonistic to parathyroid hormone

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The Thyroid Gland

The Parathyroid Glands

• Tiny masses on the posterior of the thyroid
• Secrete parathyroid hormone (PTH)
• Stimulates osteoclasts to remove calcium from bone
• Hypercalcemic hormone (increases blood calcium levels)
• Stimulates the kidneys and intestine to absorb more calcium

The Parathyroid Glands

The Parathyroid Glands

Negative Feedback Regulation of Blood Calcium Levels

The Parathyroid Glands

Negative Feedback Regulation of Blood Calcium Levels

The Parathyroid Glands

Negative Feedback Regulation of Blood Calcium Levels

The Adrenal Gland

• Lie along superior border of each kidney
• Made of two parts
• Adrenal cortex (outer)
• Adrenal medulla (inner)

The Adrenal (Suprarenal) Glands

The Adrenal (Suprarenal) Glands

The Adrenal Gland - Adrenal Cortex

Makes steroid hormones (corticosteroids)

1. Glucocorticoids (e.g., cortisol)
1. Promote normal cell metabolism
2. Help resist long-term stressors by increasing blood glucose levels (hyperglycemic hormone)
3. Anti-inflammatory properties
4. Released in response to increased blood levels of ACTH

The Adrenal (Suprarenal) Glands

The Adrenal Gland - Adrenal Cortex

Makes steroid hormones (corticosteroids)

2. Mineralocorticoids (e.g.,aldosterone);

• Produced in outer adrenal cortex
• Regulate mineral content in blood, particularly sodium and potassium ions
• Regulate water and electrolyte balance
• Target organ is the kidney

The Adrenal (Suprarenal) Glands

The Adrenal Gland - Adrenal Cortex

Makes steroid hormones (corticosteroids)

3. Androgens (male hormone)

• Small amounts are made throughout life
• Mostly androgens (male sex hormones) are made, but some estrogens (female sex hormones) are also formed

The Adrenal (Suprarenal) Glands

The Adrenal Gland - Adrenal Medulla

• Produces two related hormones (catecholamines)
• Epinephrine (adrenaline)
• Norepinephrine (noradrenaline)
• Increases heart rate and force, releases glucose, fatty acids into blood, opens airways

The Adrenal (Suprarenal) Glands

The Adrenal (Suprarenal) Glands

The Pineal Gland

• Located posterior to the third ventricle of the brain
• Secretes melatonin
• Helps establish the body’s sleep/wake cycles as well as biological rhythms
• Believed to coordinate the hormones of fertility in humans

The Pineal Gland

Other Endocrine Glands and Tissues - the Pancreas

• Located in the abdomen, close to stomach
• Mixed gland, with both endocrine and exocrine functions

The pancreatic islets produce hormones

• Insulin—produced by beta cells
• Glucagon—produced by alpha cells
• These hormones are antagonists that maintain blood sugar homeostasis

Other Endocrine Glands and Tissues

Other Endocrine Glands and Tissues

Pancreas - Pancreatic Islets

• Insulin
• Released when blood glucose levels are high
• Increases the rate of glucose uptake and metabolism by body cells
• Glucagon
• Released when blood glucose levels are low
• Stimulates the liver to release glucose to blood, thus increasing blood glucose levels

Other Endocrine Glands and Tissues

Other Endocrine Glands and Tissues

Other Endocrine Glands and Tissues

Other Endocrine Glands and Tissues

Other Endocrine Glands and Tissues - the Thymus

• 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

Other Endocrine Glands and Tissues

Other Endocrine Glands and Tissues

Other Endocrine Glands and Tissues - the Gonads

• Ovaries
• Produce eggs
• Produce two groups of steroid hormones:
• Estrogens
• Progesterone
• Testes
• Produce sperm
• Produce androgens, such as testosterone

Other Endocrine Glands and Tissues

The Gonads - Ovaries

• Estrogens
• Stimulate the development of secondary female characteristics
• Mature female reproductive organs

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With progesterone, estrogens also

1. Promote breast development
2. Regulate menstrual cycle

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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

Other Endocrine Glands and Tissues

The Gonads - Testes

• 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

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Other Endocrine Glands and Tissues

Other Endocrine Glands and Tissues - the Placenta

• Produces hormones that maintain 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

Other Endocrine Glands and Tissues

Other Endocrine Glands and Tissues

• Parts of the small intestine
• Parts of the stomach
• Kidneys
• Heart
• Many other areas have scattered endocrine cells

Other Endocrine Glands and Tissues

Developmental Aspects of the Endocrine System

• In the absence of disease, efficiency of the endocrine system remains high until old age
• Decreasing function of female ovaries at menopause leads to such symptoms as osteoporosis, increased chance of heart disease, and possible mood changes

Developmental Aspects of the Endocrine System

• Efficiency of all endocrine glands gradually decreases with aging, which leads to a generalized increase in incidence of:
• Diabetes mellitus
• Immune system depression
• Lower metabolic rate
• Cancer rates in some areas