Endocrinology Quiz: Hormones and Their Functions

Endocrine Glands

• Endocrine glands are ductless glands, secreting hormones directly into the bloodstream.
• Hormones act on target cells with specific receptors.
• Many organs secrete hormones besides those discussed in the endocrine system (e.g., heart, liver, kidneys, adipose tissue).
• Some glands secrete more than one hormone, and some hormones are produced by more than one gland.

Learning Objectives - Endocrine System

• Identify glands involved in endocrine function.
• Understand hormone types.
• Learn about hormone regulation and control mechanisms.
• Examine hormone structures and synthesis.
• Study permissiveness and synthesis mechanisms.
• Explore diseases from over or under hormone production.

Endocrine vs Exocrine Glands

• Endocrine glands secrete hormones directly into the blood.
• Exocrine glands secrete products into ducts, often to body surface or internal lumens.

Inputs That Act Directly on Endocrine Gland Cells

• Ions or nutrients
• Neurotransmitters
• Hormones

General Info on Endocrine Glands

• Endocrine glands are ductless and secrete hormones into the bloodstream.
• Hormones are transported to target cells with specific receptors.
• Hormones help regulate metabolism, growth, and reproduction.

Classification of Hormones by Action

• Polar Hormones (water-soluble): Cannot pass through plasma membranes; must be injected. Examples include polypeptides, glycoproteins, catecholamines (epinephrine, norepinephrine).
• Nonpolar Hormones (lipid-soluble): Can enter target cells directly; can be taken orally. Examples include steroids, thyroid hormone, and melatonin.

Chemical Classification of Hormones

• Amines: Derived from tyrosine and tryptophan. Examples include hormones from adrenal medulla, thyroid, and pineal glands (e.g., epinephrine, norepinephrine, dopamine, and thyroid hormones).
• Polypeptides and Proteins: Examples include antidiuretic hormone (ADH), insulin, growth hormone, and oxytocin.
• Glycoproteins: Long polypeptides bound to a carbohydrate. Examples include follicle-stimulating hormone (FSH), luteinizing hormone (LH), and erythropoietin (EPO).
• Steroids: Lipids derived from cholesterol. Examples include testosterone, estradiol, progesterone, cortisol, aldosterone, and vitamin D.

Polypeptide and Glycoprotein Hormones - Examples

Hormone Interactions

• Synergistic Effects: Two hormones working together to amplify the effect (1 + 1 > 2).
• Permissive Effects: One hormone enhancing the effect of another hormone.
• Antagonistic Effects: Two hormones having opposing effects.

Hormone Synthesis and Secretion

• Peptide hormones are synthesized in the rough endoplasmic reticulum and processed in the Golgi apparatus.
• Steroid hormones are derived from cholesterol.
• Hormones are often packaged into secretory vesicles.

Hormone Pathways

• Hypothalamus regulates the anterior pituitary via releasing and inhibiting hormones.
• A hypophysiotropic hormone is the first in a three-hormone sequence. It regulates the secretion of an anterior pituitary hormone, which in turn may regulate the secretion of another hormone from another gland.
• Hypothalamic hormones influence anterior pituitary function and may possess spontaneous or rhythmic activity.

Hypothalamus and Pituitary Gland

• The hypothalamus is essential for homeostasis and autonomic system regulation.
• Contains centers for hunger/satiety, thirst, body temperature regulation, sleep, arousal, emotions, and the control of the endocrine system.
• It controls pituitary gland hormone secretion via hypothalamic releasing and inhibiting hormones.

Posterior Pituitary Hormones (Note: Neurohormones)

• Stores and releases ADH (antidiuretic hormone).
• Stores and releases oxytocin (a posterior pituitary hormone, but produced in the hypothalamus).

Feedback Control of the Anterior Pituitary

• The final product (hormone) of the pathway negatively regulates secretion.
• The relationship between the hypothalamus, pituitary, and target tissue is called an "axis".
• Inhibition can occur at pituitary or hypothalamus level via negative feedback mechanisms.
• Short and long-loop feedback mechanisms exist to regulate hormone secretion.

Higher Brain Controls

• The hypothalamus receives input from the brain regions, influencing hormone secretion.
• Stressors increase CRH production.
• Circadian rhythms affect hormone secretion.

Thyroid Gland

• Located below the larynx, with two lobes connected by an isthmus.
• Consists of follicles filled with colloid, containing thyroglobulin. Follicular cells produce thyroxine (T4) and triiodothyronine (T3). Parafollicular cells secrete calcitonin.
• Iodine is crucial for thyroid hormone production.
• Thyroid hormone regulation is controlled by TRH and TSH.
• Thyroid hormone functions include metabolic rate, heat production, growth, and development.
• Iodine deficiency can lead to hypothyroidism and goiter.
• Grave's disease causes excessive thyroid hormone production.

Adrenal Gland

• Atop the kidneys, with cortex and medulla responsible for different hormones.
• Adrenal medulla (neural tissue): secretes epinephrine and norepinephrine (fight or flight).
• Adrenal Cortex (glandular epithelium): secretes corticosteroids (mineralocorticoids, glucocorticoids, adrenal androgens).
• The adrenal cortex is comprised of distinct layers (glomerulosa, fasciculata, reticularis) which secrete different steroid hormones.

Adrenal Cortex - Hormones

• Mineralocorticoids (aldosterone): regulate sodium (Na+) and potassium (K+) balance.
• Glucocorticoids (cortisol): regulate glucose metabolism.
• Adrenal androgens (weak sex hormones): supplement those produced by gonads (e.g., DHEA).

Cortisol Actions

• Stimulates protein degradation.
• Stimulates gluconeogenesis and inhibits glucose utilization.
• Stimulates lipolysis.

Adrenal Insufficiency

• The general term for any condition where cortisol levels are chronically below normal.
• Symptoms include weakness, fatigue, loss of appetite, and potentially low blood pressure and blood sugar.
• Causes include primary (adrenal gland destruction) and secondary (inadequate ACTH secretion) insufficiency.

Cushing's Syndrome

• Result of chronically high cortisol levels, even in non-stressed situations.
• Causes include primary adrenal defects or secondary pituitary defects (Cushing's Disease).
• Symptoms include osteoporosis, muscle weakness, thin easily-bruised skin, high blood sugar, immunosuppression, redistribution of fat (e.g. buffalo hump, moon face), and hypertension.

Actions of the Sympathetic Nervous System, Including Epinephrine from the Adrenal Medulla

• Increased hepatic and muscle glycogenolysis.
• Increased breakdown of adipose tissue.
• Increased cardiac function.
• Diversion of blood from viscera to skeletal muscle tissue.
• Increased lung ventilation.

Endocrine Control of Growth

• The endocrine system regulates growth through various hormones.
• Factors include multiple hormones (e.g., growth hormone, IGF-1 and IGF-2, thyroid hormone, insulin, sex hormones (testosterone/estradiol), and cortisol ).
• Growth occurs through cell division and protein synthesis, primarily in skeletal growth.
• Environmental factors (nutrition) and genetics are also influential.
• Hormonal regulation of growth occurs through various feedback loops (positive and negative).

Pancreas (Endocrine Function)

• The pancreas contains endocrine cells located in islets of Langerhans (alpha and beta).
• Alpha cells secrete glucagon (raises blood glucose).
• Beta cells secrete insulin (lowers blood glucose).

Diabetes Mellitus

• Characterized by fasting hyperglycemia (and glucose in urine).
• Type 1: Beta cell destruction = lack of insulin secretion.
• Type 2: Insulin resistance (decreased tissue sensitivity).
• Gestational: Insulin secretion inadequate during pregnancy.

Types of Endocrine Disorders

• Hyposecretion: Secretion of too little hormone.
• Hypersecretion: Secretion of too much hormone.
• Hyporesponsiveness: Decreased responsiveness of target cells.
• Hyperresponsiveness: Increased responsiveness of target cells.

Hormone Transport

• Most peptide and catecholamine hormones are water-soluble, and so transported dissolved in plasma.
• Steroid and thyroid hormones are poorly soluble and transported bound to plasma proteins; only the free, unbound hormone can interact with target cells.

Regulation of Responsiveness of Hormones

• Ability of a cell to respond is dependent on the presence of specific receptors (up-regulation/down-regulation).
• Permissiveness: One hormone must be present for another hormone to exert its full effect.

Effects of Hormone-Receptor Binding

• Peptide and Catecholamine (Amine) Hormones: Bind to receptors on cell membranes; mechanisms include enzyme activity or G protein activation which may affect secondary messengers (e.g., cAMP, Ca2+).
• Steroid and Thyroid Hormones: Bind to intracellular receptors (nuclear or cytoplasmic); resulting in activation or inhibition of gene transcription.

Pharmacological Effects of Hormones

• Very high concentrations of hormones administered for medical purposes might produce different effects than seen at physiological levels.
• These abnormal hormone levels can also occur in diseases involving excessive hormone secretion.

Hormones that Control Other Hormones

• Tropic hormones control hormone secretion from another endocrine gland.
• Trophic hormones also control hormone secretion, but with the added effect of stimulating the growth of the target gland.

Hormones of the Gonads

• Compared to adrenal cortex, gonads (testes, ovaries) use different enzyme pathways to produce different steroid hormones.
• Testes produce primarily testosterone, while the ovaries produce estradiol and progesterone.
• Release of sex hormones (testosterone, estradiol) is controlled by pituitary hormones FSH/LH.

Hypothalamo-Hypophyseal Portal System

• A specialized network of blood vessels that delivers hypothalamic hormones to the anterior pituitary gland.
• Allows for rapid and targeted delivery of regulatory hormones, preventing widespread effects in the body.

Other Hormones Released During Stress

• Other hormones (e.g., aldosterone, vasopressin, growth hormone, glucagon, beta-endorphin) are also released during times of stress. These hormones may also be released in response to non-stress factors.

Test your knowledge on key hormones, their regulation, and physiological roles in the human body. This quiz covers various aspects of the hypothalamic-pituitary axis, growth hormone functions, and the impact of stress on hormone levels. Perfect for students studying endocrinology or related fields.