Endocrine System Overview Quiz

Endocrine System Overview

• The endocrine system works with the nervous system to coordinate and integrate body cell activity.
• It influences metabolic activities through hormones carried in the blood.
• Responses are slower but longer-lasting than nervous system responses.
• Endocrinology is the study of hormones and endocrine organs.
• The endocrine system controls and integrates reproduction, growth and development, electrolyte, water, and nutrient balance of the blood, cellular metabolism and energy balance, and mobilization of body defenses.

Cell Communication

• There are four basic mechanisms for cellular communication: direct contact, paracrine signaling, endocrine signaling, and synaptic signaling.
• Endocrine signaling involves hormones (ligands) released from a cell affecting other cells throughout the body.

Chemistry of Hormones

• Hormones are categorized into two main classes: amino acid-based hormones (amino acid derivatives, peptides, and proteins) and steroids (synthesized from cholesterol, including gonadal and adrenocortical hormones).

Mechanisms of Hormone Action

• Water-soluble hormones (most amino acid-based hormones except thyroid hormones) act on plasma membrane receptors, often activating G protein second messengers, but cannot enter the cell.
• Lipid-soluble hormones (steroid and thyroid hormones) act on intracellular receptors that directly activate genes and can enter the cell.

Chemical Messengers

• Hormones are long-distance chemical signals traveling in blood or lymph.
• Autocrines affect the same cells secreting them.
• Paracrines affect different cells locally.
• Autocrines and paracrines are local chemical messengers, and are not considered part of the endocrine system.

Target Cell Specificity

• Target cells must have specific receptors for a given hormone to bind.
• ACTH receptors are found only on certain adrenal cortex cells.
• Thyroid receptors are found on nearly all body cells.

Target Cell Activation

• Hormones influence receptor numbers.
• Up-regulation occurs when target cells increase receptor numbers in response to low hormone levels.
• Down-regulation occurs when target cells decrease receptor numbers in response to high hormone levels.

Hormonal Stimuli

• Hormones stimulate other endocrine organs.
• Hypothalamic hormones stimulate most anterior pituitary hormones.
• Anterior pituitary hormones stimulate target cells.
• Hypothalamic-pituitary-target endocrine organ feedback loops: hormones from final target organs inhibit anterior pituitary hormone release

Duration of Hormone Activity

• Hormone activity ranges from 10 seconds to several hours.
• Effects may disappear as blood levels decrease.
• Some hormones persist at low blood levels.

Interaction of Hormones at Target Cells

• Multiple hormones may act on a single target cell.
• Permissiveness: One hormone needs another hormone to exert its effects.
• Synergism: Multiple hormones produce the same effect on a target cell.
• Antagonism: One hormone opposes the effects of another hormone.

The Pituitary Gland and Hypothalamus

• The pituitary gland (hypophysis) has two lobes: posterior and anterior.
• Posterior pituitary is neural tissue.
• Anterior pituitary has glandular tissue.

Posterior Pituitary and Hypothalamic Hormones

• Oxytocin and ADH are composed of nine amino acids.
• They are almost identical, differing in two amino acids.

Anterior Pituitary Hormones

• Anterior pituitary hormones include growth hormone (GH), thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin (PRL).

Calcitonin

• Produced by parafollicular (C) cells.
• No known physiological role in humans at normal doses.
• An antagonist to parathyroid hormone (PTH), inhibiting osteoclast activity and stimulating Ca2+ uptake into bone matrix.

Parathyroid Glands

• Four to eight tiny glands embedded in the thyroid.
• Contain oxyphil and parathyroid cells.
• Parathyroid hormone (PTH) is crucial for calcium homeostasis.

Adrenal (Suprarenal) Glands

• Paired, pyramid-shaped glands atop kidneys.
• Structurally and functionally, a mix of adrenal medulla and adrenal cortex.
• Adrenal medulla—nervous tissue part of the sympathetic nervous system, produces catecholamines.
• Adrenal cortex—three layers of glandular tissue producing corticosteroids.

Homeostatic Imbalances of Aldosterone

• Aldosteronism (hypersecretion): leads to hypertension and edema due to Na+ retention and K+ excretion.

Glucocorticoids

• Keep blood glucose levels constant.
• Maintain blood pressure.
• Cortisol (hydrocortisone) is the primary glucocorticoid.

Homeostatic Imbalances of Glucocorticoids

• Hypersecretion (Cushing's syndrome/disease): depresses cartilage and bone formation, inhibits inflammation, depresses immune system, and disrupts cardiovascular and digestive functions.
• Hyposecretion (Addison's disease): decreases glucose and sodium levels. Results in weight loss, dehydration, and hypotension.

Gonadocorticoids (Sex Hormones)

• Weak androgens (male sex hormones), converted to testosterone and to some estrogens in tissue cells.
• Can contribute to puberty onset, secondary sex characteristics, and sex drive in women and estrogens in postmenopausal women .

Hypersecretion of Gonadocorticoids

• Adrenogenital syndrome (masculinization) is a result of this.
• Not noticeable in adult males
• In females and prepubertal males, boys –reproductive organs mature early, and females-beard-like hair as well as masculine body hair pattern; a clitoris that resembles a small penis

Adrenal Medulla

• Medullary chromaffin cells synthesize epinephrine (80%) and norepinephrine (20%).
• Effects include vasoconstriction, increased heart rate, increased blood glucose, and blood diversion to brain, heart and skeletal muscles.

Homeostatic Imbalances of Adrenal Medulla

• Hypersecretion: symptoms include hyperglycemia, increased metabolic rate, rapid heartbeat, palpitations, hypertension, intense nervousness, and sweating.
• Hyposecretion: Not problematic; adrenal catecholamines are not essential to life.

Pineal Gland

• Small gland hanging from roof of third ventricle.
• Pinealocytes secrete melatonin, derived from serotonin.
• Melatonin may affect timing of sexual maturation and puberty, day/night cycles, and other physiological processes such as body temperature, sleep, and appetite.
• It also produces antioxidant and detoxification molecules.

Pancreas

• Triangular gland partially behind stomach.
• Has both exocrine and endocrine cells.
• Acinar cells produce enzyme-rich digestive juices.
• Pancreatic islets (islets of Langerhans) contain endocrine cells, alpha cells (glucagon) and beta cells (insulin).

Glucagon

• Major target—liver.
• Causes increased blood glucose levels by glycogenolysis (breakdown of glycogen to glucose) and gluconeogenesis (synthesis of glucose from lactic acid and noncarbohydrates). It also releases glucose to the blood.

Insulin

• Lowers blood glucose level.
• Enhances glucose transport into fat and muscle cells.
• Inhibits glycogenolysis and gluconeogenesis.
• Participates in neuronal development and learning and memory..
• Not needed for glucose uptake in liver, kidney, or brain.

Factors That Influence Insulin Release

• Elevated blood glucose levels, amino acids, and fatty acids are primary stimuli.
• [Hormones like glucagon, epinephrine, growth hormone and thyroxine and glucocorticoids], and somatostatin, and the sympathetic nervous system also influence insulin release.