Hormones and Their Functions

Endocrine System

• The endocrine system plays a critical role in integrating essential life functions, including growth, sex differentiation, metabolism, and adaptation to changing environmental conditions
• This system uses hormones to regulate and coordinate body functions
• It is closely associated with the nervous and immune systems
• The endocrine system utilizes chemical messengers called hormones to regulate and integrate various bodily processes
• Hormones are chemical messengers transported through body fluids
• Specialized organic molecules produced by endocrine organs to act on specific target cells
• Hormones do not start reactions but modulate cellular and systemic responses
• Hormones are released from several sites, including the endocrine glands, the brain, and other organs such as the heart, liver, and adipose tissue.

Hormones

• Definition: Chemical messengers transported through body fluids
• Specialized organic molecules: Produced by endocrine organs to act on specific target cells
• Do not start reactions: Modulate cellular and systemic responses

Hormone Effects and Actions

• Endocrine Effect: Hormones are released into the bloodstream and act on distant target cells
• Paracrine Effect: Hormones act locally on nearby cells without entering the bloodstream
• Autocrine Effect: Hormones act on the same cell that produced them
• Intracrine Effect: Hormones are synthesized and act within the same cell

Structural Classification of Hormones

• Amines and Amino Acids: Derived from single amino acids (e.g., norepinephrine, epinephrine, thyroid hormones)
• Peptides and Proteins: Range from small molecules to large proteins (e.g., thyrotropin-releasing hormone, growth hormone)
• Steroids: Derived from cholesterol (e.g., cortisol, estrogen, testosterone)

Synthesis, Release, Transport, and Elimination of Hormones

• Synthesis and Release: Varies based on hormone structure, with protein hormones synthesized and stored in vesicles and steroid hormones synthesized and secreted immediately.
• Mechanism: Protein hormones utilize vesicle-mediated release pathways. Precursor hormones are often modified, and if extra amino acids exist, they are considered a prohormone.
• Release Mechanism: Hormone cell stimulation triggers vesicle movement to the cell membrane, releasing hormones.
• Non-Vesicle-Mediated Hormones: Include some nonpolypeptide hormones and neurotransmitters, such as catecholamines.
• Transport: Hormones circulate as free or unbound molecules or bound to transport carriers.
• Half-life Examples: Thyroxine and Aldosterone have varying half-lives.
• Drugs: Certain drugs compete with hormones for binding to transport carriers.

Metabolism and Elimination of Hormones

• Hormones must be continuously inactivated to prevent accumulation.
• Mechanisms include intracellular and extracellular processes.
• Peptide hormones and catecholamines are degraded by enzymes in the blood or tissues.
• Steroid hormones are transported bound to protein carriers and remain inactive in the bound state.

Mechanisms of Hormone Action

• Hormones interact with high-affinity receptors linked to effector systems within the cell.
• These mechanisms influence metabolic activities such as ion transport at the cell surface and stimulation of nuclear transcription.
• Reaction time varies depending on the mechanism (e.g., milliseconds for neurotransmitters, days for thyroid hormones).

Hormone Receptors

• Cell-Surface Receptors: Used by peptide hormones and catecholamines; hormones bind to surface receptors
• Intracellular Receptors: Used by steroid and thyroid hormones, which cross the cell membrane and bind to intracellular receptors

Control of Hormone Levels

• Hormone secretion varies over a 24-hour period with diurnal fluctuations, cyclic secretion, and feedback regulation.
• Hypothalamic-Pituitary Regulation: The hypothalamus and pituitary form a control unit for various endocrine and physiological functions, connected by the hypophysial portal system.

Diagnostic Tests in Endocrinology

• Direct Measurement of Hormones: Measures hormone levels in blood or other samples
• Indirect Methods: Assess the physiological effects of hormones (e.g., blood glucose as a marker for insulin availability)
• Radioimmunoassay (RIA): Measures plasma hormone levels through competitive binding
• Immunoradiometric Assay (IRMA): A more specific version of RIA that uses two antibodies for better specificity.
• Autoantibody Testing: Detects autoimmune endocrine disorders

Stimulation and Suppression Tests

• Used to evaluate suspected hypofunction or hyperfunction of an endocrine organ
• Hormonal testing and imaging are important aspects of diagnosis and management in endocrinology.

Hypofunction and Hyperfunction of the Endocrine System

• Hypofunction: Decreased activity resulting in reduced hormone production (e.g., developmental issues, enzyme deficiencies, gland destruction, aging/atrophy, or receptor defects)
• Hyperfunction: Excessive hormone production due to overstimulation or abnormal gland activity (e.g., hyperplasia, hormone-producing tumors).

Hormone Secretion Patterns

• Hormone secretion varies over a 24-hour period (diurnal fluctuations).
• Cyclic secretion, such as in female sex hormones.
• Feedback regulation, such as insulin (glucose levels) and antidiuretic hormone (water levels)

Growth Hormones

• Growth hormone (GH) has several metabolic effects, including stimulating protein synthesis, mobilizing fatty acids, and antagonizing insulin actions.
• It plays a crucial role in growth, particularly during childhood, by promoting bone and cartilage formation.

Hormones Essential for Growth and Maturation

• Growth hormone (GH): Promotes bone and cartilage growth and regulates metabolic processes.
• Insulin: Supports growth by its role in carbohydrate and fat metabolism; deficiency can impair growth in children.
• Thyroid hormones: Essential for bone growth and epiphyseal closure; low levels delay growth processes.
• Androgens: Stimulate protein synthesis, contributing to growth.
• Glucocorticoids: Excessive levels inhibit growth.

Hypothalamic-Pituitary-Target Cell Feedback

• Complex hormone regulation within the thyroid, adrenal cortex, and gonads
• The hypothalamus secretes a releasing hormone, stimulating the anterior pituitary to secrete a tropic hormone.
• The tropic hormone then stimulates a peripheral target gland to produce its hormone

Positive and Negative Feedback

• Negative Feedback: Most common; hormone or its effect inhibits further secretion to maintain balance
• Positive Feedback: Less common; hormone stimulates continued secretion until a specific event occurs

Diabetes Mellitus

• Metabolic disorder characterized by hyperglycemia
• Imbalance between insulin availability, glucose utilization, and glucose production
• Type 1 Diabetes: Beta cell destruction, absolute insulin deficiency
• Type 2 Diabetes: Insulin resistance, relative insulin deficiency
• Other Types: Genetic defects, endocrinopathies, diseases of the pancreas, drug or chemical induction, or infections

Diagnostic Tests for Diabetes

• Fasting Blood Glucose Test (FPG): measures glucose levels after an 8-hour fast
• Casual Blood Glucose Test: measures blood glucose without regard for the time of the last meal
• Oral Glucose Tolerance Test (OGTT): measures the body's ability to store glucose after ingesting a glucose solution
• Capillary Blood Glucose Monitoring: Measures blood glucose from a finger-stick or forearm sample
• Continuous Glucose Monitoring (CGM): Provides frequent glucose readings using subcutaneous catheters
• Glycated Hemoglobin (A1C) test: Measures average blood glucose over the past 6-12 weeks.

Diabetes Treatment

• Goals: Normalize blood glucose to prevent short- and long-term complications
• Components: Medical Nutrition Therapy (MNT) tailored for individual needs, exercise, and pharmacological treatment

Acute and Chronic Complications of Diabetes

• Acute Complications: Diabetic ketoacidosis (DKA), hyperosmolar hyperglycemic state (HHS), and hypoglycemia
• Chronic Complications: Microvascular complications (neuropathies, nephropathies, retinopathies), macrovascular complications (coronary artery disease, cerebrovascular disease, and peripheral vascular disease), foot ulcers, and gastrointestinal motility disorders

Sex-Hormone Therapy

• Estrogen therapy for girls or testosterone therapy for boys can accelerate epiphyseal plate closure in precocious puberty

Other Pancreatic Disease and Endocrine Disorders

• Various diseases can cause diabetes by affecting pancreas function or increasing hepatic glucose production, or decreasing glucose utilization
• Diabetes is possible as a result of, or in combination with, other disorders

Adrenal Function

• The adrenal glands are involved in multiple metabolic functions, including response to stress and regulating electrolyte balance
• Cortisol: crucial for maintaining blood glucose levels, immune response and metabolic processes
• Aldosterone: regulates sodium and potassium balance, vital for blood pressure control

Adrenal Disorders

• Adrenal cortical insufficiency (Addison's disease): deficiency in adrenal cortical hormones and elevated ACTH levels, triggered primarily by autoimmune destruction of adrenocortical tissue.
• Congenital adrenal hyperplasia (CAH): Genetic disorder, resulting from abnormalities in adrenal steroid synthesis or excretion

Test your knowledge on hormones and their mechanisms in this quiz. Explore questions related to hormonal effects, synthesis, and classification of different types of hormones. Perfect for students studying biology or medicine.