Endocrinology Quiz on Hormones

Introduction to Endocrine Physiology

• Hormones are transported in the blood. Some are bound to proteins, which affects their action.
• Hormone receptors have different types, each binding to specific hormones.
• The hypothalamic-pituitary axis (HPA) is made up of the hypothalamus, anterior pituitary, and posterior pituitary.
• The anterior pituitary releases hormones that regulate other endocrine glands.
• Negative feedback regulation controls the release of these anterior pituitary hormones.

Overview of Endocrinology

• The endocrine system is a major communication system in the body.
• Endocrine glands are not anatomically connected.
• Hormone action is specific due to receptors on the target tissues.
• Hormone responses vary in speed, from seconds to days.
• Hormone concentrations are very low in plasma (10⁻⁹ M to 10⁻¹² M).

Hormones from Previous Lectures

• Epinephrine and norepinephrine are related to the autonomic nervous system.
• Atrial natriuretic peptide (ANP) is related to the cardiovascular system.
• The gastrointestinal system includes hormones like gastrin, secretin, cholecystokinin, and motilin.
• Renin-angiotensin, aldosterone, parathyroid hormone, vitamin D, and antidiuretic hormone (ADH) are all components of the renal system.

Chemical Classification of Hormones

• Amines—derived from the amino acid tyrosine, including catecholamines (dopamine, norepinephrine, epinephrine, from adrenal medulla).
• Steroids—derived from cholesterol, including mineralocorticoids (aldosterone), glucocorticoids (cortisol), and sex steroids.
• Peptides—polypeptide chains, such as proopiomelanocortin (POMC) and insulin.

Thyroid Hormone

• 3,5,3',5'-Tetraiodothyronine (thyroxine, T4) and 3,5,3'-Triiodothyronine (T3) are thyroid hormones.
• Cholesterol is the precursor to all steroid hormones.

Steroid Secreting Glands

• The adrenal gland (above the kidneys) is divided into cortex and medulla.
• Cortex produces mineralocorticoids (aldosterone), glucocorticoids (cortisol), and androgens (DHEA).
• Gonads (testes and ovaries) produce sex steroids.
• Testes produce testosterone.
• Ovaries produce estrogen, progesterone.
• Placenta produces estrogen and progesterone.

Peptide Hormones

• Proopiomelanocortin (POMC) and insulin are examples.
• POMC processes into other hormones (ACTH, endorphins).
• Insulin synthesis involves preproinsulin, proinsulin, and insulin.

Hormonal Transport in Blood

• Water-soluble hormones (e.g., catecholamines, peptides) travel freely in blood.
• Protein-bound hormones (e.g., steroids, thyroid hormone) are bound to transport proteins.

Biotransformation

• Hormones are metabolized or deactivated in the liver or kidneys.
• Some metabolites are biologically active, while others are inactive.
• The transformation of hormones can be activation or inactivation.

Membrane Bound Receptors

• Hormone binding to receptors on the plasma membrane activates intracellular signaling pathways.
• These pathways can produce rapid effects or alter gene expression.

Intracellular Receptors

• Steroid hormones, thyroid hormones, and vitamin D use intracellular receptors.
• Hormone binding to receptor activates the receptor as a transcriptional factor.

Integration of Hormone Action

• Hormone actions can be complementary (similar effects), antagonistic (opposite effects), or permissive (one hormone needing another).

Control of Hormone Secretion

• Hormones can be secreted in pulses or cyclical patterns (e.g., circadian).
• Some hormonal releases are regulated by nutrient levels, physical stimuli, or neural control (e.g., autonomic and hypothalamic-pituitary axis).

Anatomy of Hypothalamus and Pituitary

• The hypothalamus regulates the release of hormones from the pituitary gland.
• The anterior pituitary is connected to the hypothalamus by portal vessels.
• The pituitary gland is divided into the anterior and posterior lobes.

Posterior Pituitary

• The posterior pituitary consists of axons and nerve endings from hypothalamic neurons.
• The posterior pituitary releases antidiuretic hormone (ADH) and oxytocin.

Hypothalamic-Pituitary Axis

• Hypophysiotropic hormones from the hypothalamus control the release of anterior pituitary hormones.
• Anterior pituitary hormones regulate other endocrine glands (tropic hormones).
• Several hypothalamic hormones (CRH, GHRH, TRH, GnRH, DA) control the release of other hormones.

Anterior Pituitary Hormones

• Anterior pituitary hormones are secreted from different cell types (e.g., lactotrophs, corticotrophs, thyrotrophs, gonadotrophs, somatotrophs).

Hormonal Feedback Control Systems

• Negative feedback loops regulate hormone levels.
• Downregulation occurs with excessive stimulation.
• Upregulation occurs with insufficient stimulation.

Endocrine Disorders

• Primary endocrine disorders affect the gland directly.
• Secondary endocrine disorders result from problems regulating the gland.
• Hypo-secretion results in decreased hormone levels.
• Hyper-secretion results in increased hormone levels.

Introduction to Metabolism

• Metabolism studies anabolic and catabolic processes.
• Anabolism builds new molecules, while catabolism breaks them down for energy.
• Key metabolic organs are liver, skeletal muscle, adipose tissue, and brain.

Carbohydrates, Lipids, and Protein Metabolism

• Post-prandial state is after eating and involves glucose, triglyceride, and amino acid usage.
• Fasting state involves glycogenolysis and gluconeogenesis.
• Proteins are metabolized for fuel and some energy creation pathways (e.g., glycolysis, Krebs cycle)
• Lipids, especially fatty acids are metabolized through beta-oxidation.

Absorptive State (Postprandial)

• Briefly described as post-meal and involves the metabolic processing of carbohydrates (glucose), protein, and fats to provide energy or store the excess as fat, glycogen, and protein, including some hormone regulation.

Fasting State (Post-absorptive)

• Briefly described as the period between meals and involves the use of stored energy (glycogen, fat, and protein) to maintain glucose levels and provide energy, including some hormone regulation.

Glucose-Counterregulatory Systems

• Describes the systems acting in opposition to insulin, maintaining blood glucose levels.
• Key hormones include glucagon (by liver), epinephrine (by adrenal medulla, effect on liver and muscles), cortisol (by adrenal cortex, effect on lipid, protein, and carbohydrate metabolism), and thyroid hormone.

Sympathetic Control of Plasma Glucose

• Sympathetic nervous system directs the body to increase carbohydrate and fat metabolism to provide glucose.
• Sympathetic activation increases gluconeogenesis, glycogenolysis, and lipolysis, leading to increased plasma glucose and other metabolic substrates (e.g., fatty acids, glycerol).

Cortisol and Growth Hormone

• Cortisol plays a permissive role in gluconeogenesis and lipolysis in the post-absorptive period.
• Growth hormone is responsible for stimulating protein synthesis and bone growth.
• Their effects can be permissive or active depending on blood levels.

Hypoglycemia and Symptoms

• Describes the symptoms and mechanisms associated with low blood glucose (e.g., headache, confusion, dizziness).
• Describes the cause of these symptoms, and possible triggers including insulin overdose or drugs.

Thyroid Diseases

• Goiter is an enlargement of the thyroid gland, possibly resulting from either hypothyroidism or hyperthyroidism.
• Hyperthyroidism causes increased metabolic rate, weight loss despite increased appetite, intolerance to heat, emotional instability and other symptoms.
• Hypothyroidism causes decreased metabolic rate, weight gain, intolerance to cold, and other symptoms.

Hypothalamic-Pituitary-Adrenal (HPA) Axis

• The HPA axis is responsible for the body's response to stress.
• Corticotropin-releasing hormone (CRH from hypothalamus) stimulates the anterior pituitary to release adrenocorticotropic hormone (ACTH).
• ACTH stimulates the release of cortisol from the adrenal cortex.
• Cortisol's release is regulated by negative feedback (cortisol inhibits the release of CRH and ACTH).

Calcium Homeostasis

• Involved mainly in the process of regulating calcium uptake, excretion (with hormone, Vitamin D) and bone health/regrowth, including the major factors regulating blood calcium homeostasis.
• The major regulators include parathyroid hormone (PTH), vitamin D, and calcitonin.

Bone Remodeling

• Explains the continuous process of bone breakdown and formation.
• Osteoclasts break down bone, releasing calcium.
• Osteoblasts create new bone, incorporating calcium.

Vitamin D Synthesis and Effects

• Vitamin D3 (cholecalciferol) is produced in the skin through UV light and obtained from foods, and is converted to 1,25 dihydroxyvitamin D3.
• This active form regulates calcium absorption from the intestines.

Parathyroid Hormone (PTH)

• PTH increases blood calcium by acting on the bone, kidneys, and intestines.
• PTH stimulates the release of calcium from the bone and the conservation of calcium by the kidneys.
• PTH encourages the production of vitamin D to stimulate calcium absorption by the intestines.

Calcitonin

• Calcitonin decreases blood calcium by inhibiting bone resorption by osteoclasts.

Growth

• Growth hormone (GH) is a key regulator of growth, affecting bones, muscle, and other tissues.
• Insulin plays an important role in growth—especially important during the periods of bone and cell growth, especially in adolescents.
• Thyroid hormone is necessary for growth and brain development.
• Sex hormones (androgens and estrogens) play a crucial role in growth spurts and bone maturation.