Chapter 17
Table of Contents
Chapter Overview
Authors and Copyright
Authors: Michael P. McKinley, Valerie Dean O’Loughlin, Theresa Stouter Bidle
Copyright: 2022 © McGraw Hill LLC. All rights reserved.
17.1 Overview of the Endocrine System
17.1a Endocrine System
Definition: The endocrine system is composed of ductless glands that synthesize and secrete hormones.
Modes of Hormone Release:
Hormones are released into the blood.
Transported throughout the body to target cells, which have specific receptors for those hormones.
Hormones bind to these receptors and induce a response.
Transport of Hormones:
Released into interstitial fluid → enter the blood supply → leave blood randomly to bind target cells' receptors.
17.1b Comparison of the Two Control Systems: Endocrine vs Nervous
Commonalities:
Both systems release ligands (chemical messengers).
Ligands bind to receptors on target cells.
Endocrine System Differences:
Transmits hormones via blood to any correct receptors.
Widespread effects possible.
Longer reaction times than the nervous system.
Prolonged effects can last from minutes to weeks.
17.1c General Functions of the Endocrine System
Functions Include:
Regulating Development, Growth, and Metabolism:
Hormones regulate embryonic cell division and differentiation.
Influence metabolism (both anabolism and catabolism).
Maintaining Homeostasis of Blood Composition and Volume:
Regulate blood solute concentrations (e.g., glucose, ions).
Manage blood volume and cellular concentrations, including platelet numbers.
Controlling Digestive Processes:
Hormones affect secretory processes and material movement in the digestive tract.
Controlling Reproductive Activities:
Influence reproductive system development, function, and sexual behavior expression.
Section 17.1: Review Questions
How are hormones moved from an endocrine gland to target cells?
Compare how the endocrine and nervous systems target cells.
How does diabetes mellitus affect one of the endocrine system's functions?
17.2 Endocrine Glands
17.2a Location of Major Endocrine Glands
Structures Include:
Purely endocrine organs: pituitary, pineal, thyroid, parathyroid, adrenal glands.
Mixed glands: hypothalamus, skin, thymus, heart, liver, stomach, pancreas, small intestine, adipose connective tissue, kidneys, gonads.
17.2b Stimulation of Hormone Synthesis and Release
Hormonal Reflexes:
Hormonal stimulation (e.g., hormone triggering another hormone's release).
Humoral stimulation (certain changes in blood nutrient or ion levels stimulate release).
Nervous system stimulation (neuron stimulation of gland cells).
Section 17.2: Review Questions
What are the major endocrine organs within the human body?
Classify ACTH's stimulation type: hormonal, humoral, or nervous system?
17.3 Types of Hormones
17.3a Circulating Hormones
Steroids:
Lipid-soluble molecules derived from cholesterol (e.g., estrogen from ovaries, cortisol from adrenal cortex).
Biogenic Amines (Monoamines):
Modified amino acids (e.g., catecholamines, thyroid hormone, melatonin).
Water-soluble except for thyroid hormone, which is lipid-soluble.
Proteins:
Water-soluble chains of amino acids; most hormones belong here.
17.3b Local Hormones
Local hormones do not circulate in blood; they function via autocrine (act on the secreting cell) and paracrine (act on neighboring cells) mechanisms.
Eicosanoids:
Derived from fatty acids within cell membranes. Examples include prostaglandins, which stimulate pain and inflammatory responses.
Nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin block prostaglandin formation.
Section 17.3: Review Questions
Identify categories of lipid-soluble hormones.
Discuss how solubility impacts hormone action.
Is prostaglandin-induced blood vessel dilation an autocrine or paracrine action?
17.4 Hormones in the Blood
17.4a Transport in the Blood
Lipid-soluble hormones require carrier proteins for transport, as they do not dissolve well in blood. Ensure protection from rapid breakdown.
Water-soluble hormones generally travel freely through the blood, with a few exceptions using carrier proteins.
17.4b Levels of Circulating Hormone
Blood concentration correlations:
Hormone levels depend on synthesis and elimination rates: Increased synthesis → higher blood concentrations, with similar inverse effects for elimination.
Elimination mechanisms:
Enzymatic degradation in the liver.
Excretion by kidneys or uptake by target cells.
Half-Life:
Time needed to reduce a hormone's concentration to half its initial level, impacting secretion frequency.
Water-soluble hormones generally have short half-lives, e.g., short peptides.
Lipid-soluble hormones often have long half-lives due to binding with carriers, e.g., testosterone (12 days).
Section 17.4: Review Questions
Why are carrier proteins important for lipid-soluble hormones?
Explain the benefits of carrier proteins.
Discuss the relationship between hormone synthesis and blood concentration.
17.5 Mechanisms of Hormone Action
17.5a Lipid-Soluble Hormones
Lipid-soluble hormones can diffuse across target cell membranes. Their receptors are situated in the cytosol or nucleus.
Mechanism Overview:
Hormone binds to the receptor, forming a hormone-receptor complex.
Complex binds to hormone-response elements (HRE) in DNA, influencing transcription and protein synthesis, affecting cellular functions.
17.5b Water-Soluble Hormones
Water-soluble hormones require membrane-bound receptors since they cannot diffuse through cell membranes.
Signal Transduction Pathway:
Binding of the hormone activates a G-protein (an internal membrane protein).
Activation of the G-protein enables enzyme actions, such as adenylate cyclase or phospholipase C.
Resulting second messengers (like cAMP or IP3) modify cellular activity.
Specific Pathways:
Adenylate Cyclase Pathway:
Hormone activation → G-protein activation → adenylate cyclase catalyzes cAMP formation → activation of protein kinases.
Phospholipase C Pathway:
Activation leads to the splitting of PIP2 yielding DAG (which activates protein kinase C (PKC)) and IP3 (which influences calcium levels).
Section 17.5: Review Questions
Where are lipid-soluble hormone receptors located?
What is the role of protein kinase enzymes in water-soluble hormone pathways?
17.6 Target Cells' Responses to Hormones
17.6a Number of Receptors
A target cell’s hormone response varies with the number of receptors:
Up-regulation: Increases receptor numbers → greater sensitivity to hormones.
Down-regulation: Decreases receptor numbers → reduced sensitivity.
17.6b Hormonal Interactions
Types of Interactions:
Synergistic: One hormone enhances another's effects (e.g., estrogen and progesterone).
Permissive: One hormone's actions depend on another’s presence (e.g., oxytocin requires prolactin).
Antagonistic: One hormone opposes another (e.g., glucagon increases glucose; insulin decreases it).
Section 17.6: Review Questions
What is the impact of down-regulation on cell sensitivity?
Describe effects of hormones acting synergistically.
17.7 Hypothalamus and Pituitary Gland Interaction
17.7a Anatomy of Hypothalamus and Pituitary Gland
Pituitary Gland:
Lies below the hypothalamus; connected by the infundibulum.
Composed of anterior and posterior lobes.
17.7b Posterior Pituitary Functions
Stores/releases ADH (vasopressin) and oxytocin.
Hormones synthesized in the hypothalamus then transported to the posterior pituitary via axons.
ADH Functions:
Reduces urine production, stimulates thirst, constricts blood vessels.
Oxytocin Functions:
Induces uterine contractions, milk ejection, and emotional bonding.
17.7c Anterior Pituitary Functions
Hormonal Stimulation: Hypothalamus secretes releasing/inhibiting hormones to control anterior pituitary hormone release.
Regulatory Hormones Include:
Releasing: TRH, PRH, GnRH, CRH, GHRH.
Inhibiting: PIH, GIH.
Anterior Pituitary Hormones Include:
TSH (thyroid-stimulating hormone), Prolactin (PRL), ACTH (adrenocorticotropic hormone), FSH (follicle-stimulating hormone), LH (luteinizing hormone), GH (growth hormone).
Section 17.7: Review Questions
What anatomical connections exist between the hypothalamus and posterior pituitary?
Explain how the hypothalamus regulates ADH release from the posterior pituitary.
List the primary hormones from the anterior pituitary and the hypothalamic regulators for each.
Describe the interrelated functions of GHRH, GH, and IGFs in growth regulation.
Identify primary target organs/areas of GH and IGFs and their effects.
17.8 Thyroid Gland Anatomy and Functions
17.8a Anatomy
The thyroid gland is located below the thyroid cartilage and anterior to the trachea.
Composed of follicles (cuboidal epithelial cells) that synthesize thyroglobulin and release thyroid hormones T3 and T4. Also contains parafollicular cells that produce calcitonin.
17.8b Regulation and Effects of Thyroid Hormone
Regulation:
TRH from hypothalamus → TSH from anterior pituitary → release of T3 and T4 from thyroid.
Functions of T3/T4:
Increase metabolism, protein synthesis, and thermogenesis.
Influence glucose and lipid levels in the body, enhancing energy production.
Section 17.8: Review Questions
Describe the anatomical relationship and specific hormones released by follicular and parafollicular cells of the thyroid gland.
Define TRH, TSH, and their role in metabolism regulation.
Identify primary target organs/tissues of thyroid hormone and describe their effects.
Does calcitonin increase or decrease blood calcium levels?
17.9 Adrenal Gland Anatomy and Functions
17.9a Anatomy
Located on kidneys' superior surface, divided into the adrenal cortex and adrenal medulla.
Cortex Regions:
Zona glomerulosa: produces mineralocorticoids (e.g., aldosterone).
Zona fasciculata: produces glucocorticoids (e.g., cortisol).
Zona reticularis: produces gonadocorticoids (sex hormones).
17.9b Regulation and Effects of Cortisol
Regulation: Cortisol release is regulated through HPA axis. Stressors raise CRH → ACTH release → cortisol from near cortex.
Cortisol Effects:
Raises blood nutrient levels by stimulating gluconeogenesis and inhibiting glycogenesis, influencing protein and fat metabolism to provide energy resources.
Section 17.9: Review Questions
Identify the hormone produced in the zona fasciculata of the adrenal cortex.
Describe the interplay between CRH, ACTH, and cortisol secretion.
List primary target organs of cortisol and describe their responses.
17.10 Pancreas Anatomy and Hormones
17.10a Anatomy
The pancreas is located posterior to the stomach with both endocrine (islets of Langerhans) and exocrine (acinar cells) functionalities.
Islets:
Alpha cells → glucagon; Beta cells → insulin; Delta cells → somatostatin.
17.10b Regulation of Blood Glucose
Normal blood glucose: 70 to 110 mg/dL.
Insulin Function:
Lowers high glucose levels post-meal by binding to its receptor to promote glucose uptake, glycogenesis, and fat storage while inhibiting gluconeogenesis.
Glucagon Action:
Raises blood sugar levels by promoting glycogenolysis and gluconeogenesis when blood sugar levels drop.
Section 17.10: Review Questions
Explain dual functions of the pancreas as an endocrine and exocrine gland.
Classify stimuli for insulin/glucagon release.
Outline the control feedback loop for insulin release and resultant effects on nutrient levels.
Which hormone is responsible for increasing blood glucose: GH, TH, cortisol, insulin, or glucagon?
17.11 Other Endocrine Structures
Additional Structures with Endocrine Functions:
Pineal Gland:
Secretes melatonin, which affects sleep and mood.
Parathyroid Glands:
Located on thyroid's posterior surface; release PTH to regulate calcium levels in blood.
Thymus:
Releases hormones for T-lymphocyte maturation; shrinks with age.
Heart:
Secretes ANP to lower blood pressure.
Kidney:
Releases erythropoietin (EPO) in response to low oxygen levels.
Liver:
Releases IGFs and angiotensinogen (precursor to a blood pressure-regulating substance).
Stomach and Small intestine:
Produce hormones to manage digestive activities (e.g., gastrin, secretin).
Skin:
Produces vitamin D precursors.
Adipose Tissue:
Produces leptin, which regulates appetite.
Section 17.11: Review Questions
How does melatonin vary throughout the day?
State the primary hormone from the parathyroid and its function.
What role does the kidney play in the regulation of red blood cell count?
Which organ produces angiotensinogen, and what is its role?
17.12 Aging Effects on the Endocrine System
Changes in Endocrine Function with Aging:
Secretory activity decreases with age, leading to various hormonal deficiencies, affecting body metabolism, growth, and development processes.
Consequences:
Decreased GH and sex hormones can lead to loss of muscle mass and weight in elderly individuals.
Section 17.12: Review Questions
What general changes occur in hormone production as one ages?