Endocrine System Quiz

Hormone Inhibition by Steroids

• Steroids can inhibit the production of natural hormones.

Endocrine System

• The nervous and endocrine systems work together to control bodily functions.
• Endocrine glands release hormones into the bloodstream.
• The glands in the endocrine system are small but important.
• Endocrine glands are scattered throughout the body.

Learning Outcomes

• Students should be able to compare the nervous and endocrine systems.
• Students should be able to describe the function of hormones.
• Students should be able to outline the organization of endocrine glands and their component glands.
• Students should be able to describe general hormone characteristics and the three mechanisms that regulate hormone secretion.
• Students should understand the location and relationship of the hypothalamus and pituitary gland.
• Students should be able to describe the function of hormones secreted by the pituitary gland.

Introduction

• Nervous and endocrine systems work together to coordinate body functions.
• Endocrine glands secrete hormones into the bloodstream.
• Endocrine glands are small but important.

Comparison Between Nervous & Endocrine Systems

• Nervous system:
  • Controls bodily activities through nerve impulses and neurotransmitters.
  • Effects are short-lived (seconds) and localized.
  • Controls muscle contractions or glandular secretions.
  • Nervous system parts stimulate or inhibit hormone release.
• Endocrine system:
  • Controls bodily activities by releasing hormones.
  • Effects are longer-lasting and more generalized.
  • Influences growth, development, and metabolic activities.
  • Can promote or inhibit nerve impulses.

Summary of Nervous & Endocrine System Comparison

• Signals: the nervous system uses electrical impulses (action potentials); the endocrine system uses chemical impulses (hormones).
• Pathways: nervous system uses neurotransmitters; endocrine system uses blood transport.
• Speed of Information: nervous system is fast; endocrine system is slow.
• Duration of Effect: nervous system is short-lived; endocrine system can be short or long-lived.
• Type of Action/Response: nervous system can be voluntary or involuntary; endocrine system is usually involuntary.
• Target: nervous system targets localized cells connected to neurons; endocrine system often targets distant cells.

Functions of Hormones

• Regulate chemical composition and volume of internal environment (interstitial fluid)
• Regulate metabolism and energy balance
• Regulate smooth and cardiac muscle fiber contractions
• Control secretions by other glands
• Regulate immune system activities
• Regulate growth and development
• Regulate reproductive system function
• Regulate circadian rhythm

Types of Glands

• Exocrine glands: secrete their products into ducts that carry secretions to a target site (e.g., sweat glands, sebaceous glands, mammary glands, digestive glands).
• Endocrine glands (ductless glands): secrete hormones directly into blood capillaries or lymph, circulating them throughout the body.

Endocrine Glands

• Lists the major and minor endocrine glands (e.g., pituitary, thyroid, parathyroid, adrenal, pancreas, ovaries, testes, thymus, pineal).

Other Hormone-Producing Structures

• Structures outside the official endocrine system but producing hormones: Kidneys, gastrointestinal mucosa, skin, liver, small intestine, placenta, and atrial muscle cells (ANP).

Recap - Organ Producing Hormones

• Lists the hormones produced by different organs.

Chemical Nature of Hormones

• Hormones are proteins or steroids.
• Most hormones are proteins or protein derivatives and have receptors on the cell membrane.
• Difficult to administer orally because they are inactivated by stomach acid and pepsin, thus must be injected (e.g., insulin, glucagon, adrenaline, noradrenaline).
• Steroid hormones (e.g., glucocorticoids, mineralocorticoids, thyroid hormones) are derived from lipids and have receptors inside the cell.
• Lipid-soluble steroid hormones can be taken orally.

Mechanisms of Hormone Action

• Hormones circulate throughout the body in the blood.
• Hormones affect only specific cells with receptor sites that match.
• A hormone binding to its receptor can activate an enzyme, leading to a second messenger (e.g., cyclic AMP), affecting cellular functions or causing protein production.
• Steroid hormones bind within the cell to activate receptors, alter gene expression, and create new proteins.

Summary of Hormone Action

• Describes the two main mechanisms of hormone receptor interactions—protein hormones binding on the cell membrane, and steroid hormones binding inside the cell.

Control of Hormone Secretion

• Most hormones are released in short bursts with little or no release between bursts to control blood concentration.
• The regulation of hormone secretion maintains homeostasis.
• Disorders can occur if regulatory mechanisms do not function properly.

Control of Hormone Secretion (continued)

• Hormone secretion is regulated by neural stimulus, humoral stimulus, or hormonal stimulus.

Neural Stimulus

• Nerve fibers stimulate the release of hormones (e.g., norepinephrine, epinephrine during stress).

Humoral Stimulus

• Changes in blood ions or nutrient levels stimulate hormone release (e.g., parathyroid hormone and ADH).

Hormonal Stimulus

• Some hormones released stimulate the release of other hormones (e.g., hypothalamus triggering anterior pituitary).

Control of Hormone Secretion (continued)

• Most hormonal systems operate via negative feedback; some use positive feedback.
• Negative feedback mechanisms respond to hormone levels to regulate the output and maintain homeostasis when hormone levels are high or low.

Negative Feedback Example

• Parathyroid hormone (PTH), regulated by blood calcium levels (negative feedback).

Negative Feedback Example (continued)

• Calcitonin acts inversely with PTH, lowering blood calcium levels when high.

Positive Feedback Example

• Oxytocin release during childbirth, where uterine contractions stimulate further oxytocin release.

The Hypothalamus and Pituitary Gland

• The hypothalamus is the major link between the nervous and endocrine systems.
• The hypothalamus regulates virtually all aspects of growth, development, metabolism, and homeostasis.
• The hypothalamus receives input from many brain areas, like the thalamus and limbic system.

The Hypothalamus and Pituitary Gland (continued)

• The pituitary gland is attached to the hypothalamus and has anterior and posterior lobes.
• Release and inhibiting hormones of the hypothalamus control pituitary hormones.

Hypothalamus and Pituitary Gland (continued)

• Anterior pituitary: adenohypophysis; about 75% of the pituitary's weight; a distinct gland.
• Posterior pituitary: neurohypophysis; extension of the brain; consists of neurons and neuroglia.

Hypothalamus and Anterior Pituitary Lobe

• Neurosecretory cells in the hypothalamus secrete hormones into capillaries, and they travel via veins to the anterior pituitary, affecting glandular epithelium.
• Releasing and inhibitory hormones affect anterior pituitary function.

Anterior Pituitary Hormones

• Human Growth Hormone (hGH): stimulates bone, muscle, and organ growth by promoting protein synthesis.
• Thyroid Stimulating Hormone (TSH): stimulates thyroid hormones secretion.
• Prolactin (PRL): stimulates breast development and milk production.

Anterior Pituitary Hormones (continued)

• Follicle-Stimulating Hormone (FSH): stimulates egg and sperm development.
• Luteinizing Hormone (LH): stimulates ovulation and the production of estrogen and progesterone (female) and testosterone (male).

Anterior Pituitary Hormones (continued)

• Adrenocorticotropic Hormone (ACTH): controls glucocorticoid secretion by the adrenal cortex.
• Melanocyte-Stimulating Hormone (MSH): stimulates melanin production in skin and hair; may affect appetite and sexual arousal.

Anterior Pituitary Hormones (Clinical Applications)

• Dwarfism: lack of hGH in childhood.
• Giantism: excessive hGH in childhood.
• Acromegaly: excessive hGH in adulthood.

Hypothalamus and Posterior Pituitary Gland:

• Posterior pituitary (neurohypophysis) is an extension of the hypothalamus.
• Neurosecretory cells in the hypothalamus synthesize oxytocin and antidiuretic hormone (ADH).
• These hormones are stored in axon terminals in the posterior pituitary and released into the bloodstream.

Hypothalamus and Posterior Pituitary Gland (continued)

• Oxytocin: targets smooth muscle in the uterus and breasts, stimulating uterine contractions, milk ejection, and other bodily processes.
• Antidiuretic Hormone (ADH): promotes water reabsorption in kidney tubules and reduces water loss through sweat glands.

Hypothalamus and Posterior Pituitary Gland (Regulation of ADH Secretion):

• Blood osmotic pressure regulation of ADH release (negative feedback).
• High blood osmotic pressure triggers ADH release.
• Low blood osmotic pressure inhibits ADH release.

Regulation of Oxytocin Secretion (Positive Feedback):

• Stretch receptors in the cervix stimulate oxytocin, initiating contractions during childbirth.
• Contractions further stimulate more oxytocin release.

Posterior Pituitary Hormones (Clinical Applications)

• Insufficient ADH (Diabetes Insipidus): excessive water loss in urine leading to dehydration and thirst.
• Excessive ADH: constricted blood vessels and elevated blood pressure.

Recap/Quiz

• Summarizes the key concepts of nervous and endocrine functions, including their coordinated actions, types of glands, hormonal regulation, and examples of specific hormones' actions and effects.