Endocrine Glands Physiology Quiz

Endocrine Glands Physiology

• Endocrine hormones are released by specialized glands or cells into the bloodstream.
• These hormones affect target cells in other locations within the body.
• The circulatory system transports hormones to target cells.
• Hormones bind to receptors and trigger cellular reactions.

Human Endocrine System

• The human endocrine system includes numerous glands and organs.
• These organs and glands are located throughout the body in various parts.
• Major organs and glands include the hypothalamus, pituitary gland (divided into anterior and posterior lobes), pineal gland, thyroid gland, thymus gland, adrenal glands, pancreas, and reproductive system (male/female).

Pituitary Gland

• Located on the inferior surface of the brain.
• Structurally and functionally divided into two parts.
• Anterior lobe (adenohypophysis) and posterior lobe (neurohypophysis).

Hypothalamus

• Secretes releasing and inhibiting hormones.
• These hormones control the pituitary.
• The hypothalamus secretes hormones that are directed to the anterior pituitary.
• Anterior pituitary hormones are released into the blood stream.

Anterior Pituitary Hormones

• Six important peptide hormones are secreted by the anterior pituitary.
• These hormones control various functions in the body.
• Growth hormone (GH).
• Prolactin (PRL).
• Thyroid-stimulating hormone (TSH).
• Adrenocorticotropic hormone (ACTH).
• Gonadotropic hormones (FSH and LH).

Growth Hormone (GH)

• Also known as somatotropin.
• Promotes growth of tissues.
• Stimulates liver to produce somatomedins that enhance bone and cartilage growth.
• Has metabolic effects including increased protein synthesis, mobilization of fatty acids, and decreased glucose utilization.
• Secretion patterns include pulsatile pattern and increases during deep sleep.

Metabolic Functions (Growth Hormone)

• Increases protein synthesis in most cells.
• Mobilizes fatty acids from adipose tissue leading to increased free fatty acids in the blood.
• Enhances body protein use, uses fat stores and conserves carbohydrates.

Posterior Pituitary Hormones

• These hormones, ADH and Oxytocin, are formed in the hypothalamus and stored in the posterior pituitary.
• Antidiuretic hormone (ADH) regulates water balance by affecting the kidneys.

Actions of ADH

• Acts on the kidneys, causing water reabsorption in the collecting ducts.
• Acts on blood vessels, it is the most potent vasoconstrictor, raising blood pressure.

ADH Regulation

• Blood osmotic pressure increases stimulate the release of ADH.
• Drinking reduces blood osmotic pressure which inhibits the release of ADH.

Effects of ADH Deficiency

• Diabetes insipidus: manifests with polyuria (excessive urine volume) and polydipsia (excessive water intake).

Oxytocin

• Stimulates uterine contractions during childbirth.
• Stimulates milk ejection in lactating mothers.

Thyroid Gland

• Located in the neck, below the larynx.
• One of the largest endocrine glands.
• Secretes two major hormones: thyroxine (T4) and triiodothyronine (T3).
• Also secretes calcitonin.

Thyroid Hormones

• Triiodothyronine (T3) and tetraiodothyronine (T4).
• Calcitonin Hormone.

Functions of T3 and T4

• Calorigenic effect: increases oxygen consumption and metabolism in body tissues.
• Metabolic effects (Protein Metabolism, Fat Metabolism, Carbohydrate Metabolism, Cardiovascular system, Gastrointestinal tract, Central nervous system.

Parathyroid Gland

• Four small glands located on the posterior surface of the thyroid.
• Secretes parathyroid hormone (PTH).

Functions of Parathyroid Hormone (PTH)

• Increases blood calcium levels.
• Decreases excretion of calcium in kidneys.
• Increases calcium absorption from small intestine.

Adrenal Gland

• Located on top of each kidney.
• Composed of two parts: cortex and medulla.
• Cortex secretes corticosteroids (mineralocorticoids, glucocorticoids, androgens).
• Medulla secretes catecholamines (epinephrine and norepinephrine).

Adrenal Medulla

• Modified sympathetic ganglion.
• Postganglionic sympathetic neurons lose axons and become secretory cells releasing catecholamines.
• Primarily epinephrine.
• Small percentage of norepinephrine.

Pheochromocytoma

• Tumor of adrenal medulla resulting in increased catecholamines.
• Manifestations include sustained hypertension, tachycardia, palpitation, hyperglycemia, and increased basal metabolic rate.

Adrenal Cortex

• Aldosterone: Principal mineralocorticoid.
• Cortisol: Principal glucocorticoid.
• Androgens: Small amounts of sex hormones.

Aldosterone

• Exclusively synthesized in the Zona glomerulosa.
• Essential for life, it promotes sodium retention and potassium and hydrogen elimination by the kidney.
• Expands ECF volume.

Hyperaldosteronism

• Primary hyperaldosteronism includes idiopathic hyperaldosteronism, adenomas, and glucocorticoid-suppressible aldosterone excess.
• Results in increased aldosterone resulting in hypertension.

Effects of Mineralocorticoid Deficiency

• Reduced sodium reabsorption.
• Reduced extracellular fluid volume.
• Reduced plasma volume.
• Decreased cardiac output and circulatory shock.
• Increased potassium and hydrogen ions.
• Possible cardiac and other toxicity.

Cortisol (Glucocorticoids)

• Affects many tissues, including immune systems, bones, liver, skeletal muscle, and more.
• Provides catabolic, lipolytic, hyperglycemic, anti-allergic, anti-inflammatory, and anti-stress actions.

Pancreas

• Contains endocrine and exocrine tissues.
• Includes pancreatic islets (islets of Langerhans containing alpha, beta, and delta cells).
• Alpha cells produce glucagon.
• Beta cells produce insulin and amylin.
• Delta cells produce somatostatin.

Insulin

• Lowers blood glucose levels (hypoglycemic effect) by increasing glucose uptake by tissues and increasing glycogenesis in the liver.
• Decreasing glycogenolysis and gluconeogenesis.
• Increasing lipogenesis. (lipogenic).
• Increasing protein synthesis (anabolic).

Glucagon

• Elevates blood glucose levels by activating glycogenolysis enzymes, inhibiting glycogenesis enzymes, and activating enzyme gluconeogenesis enzymes:
• Increases lipolysis and releases fatty acids into the blood, contributing to ketone body formation.

Diabetes Mellitus

• Characterized by chronic hyperglycemia and disturbances in carbohydrate, fat, and protein metabolism.
• Resulting from defects in insulin secretion, insulin action, or both.

Type 1 Diabetes

• Insulin-dependent diabetes mellitus (IDDM) or juvenile-onset diabetes.
• Develops when the body's immune system destroys pancreatic beta cells.
• Usually occurs in children and young adults.

Type 2 Diabetes

• Non-insulin-dependent diabetes mellitus (NIDDM) or adult-onset diabetes.
• Characterized by insulin resistance; cells do not use insulin properly.
• Pancreas gradually loses its ability to produce insulin.
• Associated with older age, obesity, family history of diabetes, history of gestational diabetes, and impaired glucose metabolism.

Polyphagia, Polydipsia, Polyuria

• Polyphagia: excessive hunger.
• Polydipsia: excessive thirst.
• Polyuria: excessive urine production.
• Symptoms common to diabetes.