Endocrine System Types of hormones and homeostasis Negative

Endocrine System Types of hormones and homeostasis Negative feedback Endocrine glands overview The pituitary Posterior pituitary Anterior pituitary Thyroxin - metabolism PTH and Calcitonin - blood calcium Insulin / glucagon – blood sugar Adrenal Glands Other glands

Homeostasis • Homeostasis – is a state of equilibrium where an organism’s internal environment remains relatively constant, despite ongoing environmental changes. • Most of the body’s systems are designed and adapted to work together to maintain homeostasis. The nervous system is the ultimate “collector of information” about the body’s internal and external environments. As a result, the nervous system is a key element in initiating responses from other body systems.

Chemical Messengers • – substances such as neurotransmitters, hormones and pheromones that send information to various tissues • Hormones – are chemical messengers that are sent through the bloodstream and act on target tissues and cells separate from their origin. Hormones are produced and secreted by the endocrine glands, and usually have longer term affects on the organism. • Neurotransmitters – are chemical messengers that travel across the synaptic cleft from one neuron to the next, to either continue or inhibit the action potential. • Pheromones – are chemical messengers that travel between individuals

Glands can be classified into two general categories: • • Exocrine Glands – are glands whose products do not enter the bloodstream, but are released by ducts or tubes into a body cavity, or out of the body. Examples include sweat glands, pancreatic glands, and salivary glands. Endocrine Glands – are glands whose products are carried through the bloodstream where they are transported to target tissues. The hormones are broken down once their task is completed.

Types of Hormones • Protein Hormones – are composed of chains of amino acids and are not fat soluble, so they do not pass through the cell membrane. Protein hormones combine with a second messenger (c. AMP), which activates enzymes within the cell to complete protein synthesis. • Examples: ADH, oxytocin, glucagon, FSH, LH, ACTH, thyroxin, adrenaline, somatotropin, calcitonin, PTH. Zoo 202: Endocrine System • Steroid Hormones – are made form cholesterols, and are fat soluble, so they pass into the cell and bind to receptors inside the cell. Protein hormones directly initiate protein synthesis. • Examples: estrogen, progesterone, testosterone, cortisol, aldosterone.

Negative Feedback • is a control mechanism designed to prevent chemical imbalances in the body. Once the body has responded to a change in the environment, the effect is detected, receptors are activated, and further response is inhibited.

Pituitary Hormones • Pituitary Gland – is often called the master gland, because it influences the activity of many other glands. The pituitary receives information from specialized nerves from the hypothalamus, which secretes releasing factors that control the release of hormones from the pituitary.

Posterior Pituitary – hormones of the posterior pituitary are produced in the hypothalamus, and stored and released by the posterior pituitary. These hormones include: • Anti-Diuretic Hormone / Vasopressin (ADH) – increases water re-absorption by the kidneys when the blood becomes too concentrated with solutes – Diabetes insipidus – excessive urination, dehydration and thirst resulting from a lack of ADH, usually caused by a tumour • Oxytocin – stimulates uterine contractions during childbirth, and triggers initial milk production – Pitocin – is a synthetic form of oxytocin that is often given to induce labour.

Anterior Pituitary – produces hormones which are controlled by releasing factor secreted by the hypothalamus. • Thyroid Stimulating Hormone (TSH) – stimulates the thyroid gland to release thyroxin (controls metabolism) and calcitonin (controls blood calcium) • Adrenocorticotropic Hormone (ACTH) – stimulates the adrenal cortex to release aldosterone and cortisol which regulate the release of fatty acids in the blood and regulate fat metabolism • Prolactin / Lactogenic Hormone (PRL) – stimulates milk production in the mammary glands after birth, suckling or other stimulation may result in the “let down” reflex

• Follicle Stimulating Hormone (FSH) – stimulates the production o gametes (sperm and egg) in the male and female reproductive systems • Luteinizing Hormone (LH) – stimulates the production of hormones (estrogen, progesterone and testosterone) in the male and female reproductive systems • Melanocyte Stimulating Hormone (MSH) – affects skin pigmentation in lower vertebrates (function unknown in humans) • Somatotropin / human Growth Hormone (STH / h. GH) – regulates the growth of bones and tissues during childhood by assisting amino acids across cell membranes for protein synthesis.

• Gigantism – overproduction of growth hormone during the growth years, results in very large individuals (7 -9 ft), who also have diabetes and other medical issues.

• Acromegaly – overproduction of growth hormone during the adult years, results in excessive growth of the cartilage of he nose, hands, feet, jaw, tongue and internal organs.

• Dwarfism – underproduction of growth hormone during the growth years and adolescence, results in individuals of short stature with proportionate or disproportionate size.

Thyroid Gland The thyroid gland is responsible for the secretion of two hormones: 1. Thyroxin – increases the rate of cellular respiration by increasing oxygen uptake in cells 2. Calcitonin – decreases the concentration of blood calcium by decreasing the rate that calcium leaves the bones, reducing intestinal uptake of calcium, and increasing secretion of calcium by the kidneys. (Works in opposition to parathyroid hormone)

• Hyperthyroidism – excessive production of thyroxin results in Thyroid nervousness, weight loss, Disorders sweating, tachycardia, hyperactivity • Hypothyroidism – underproduction of thyroxin results in sluggishness, depression, weight gain, tiredness, goiter • Cretinism – hypothyroidism in a developing infant results in permanent and severe retardation and stunted growth Thyroid Surgery

Parathyroid Gland • The parathyroid glands are a set of four pea-sized glands embedded in the posterior portion of the thyroid. The parathyroid produces the hormone: • Parathyroid Hormone (PTH) – increases blood calcium by increasing calcium absorption by the intestine, increasing removal of calcium ions from bones and increasing re-absorption of calcium ions from the kidneys. • Tetany – underproduction of the parathyroid (low blood calcium) resulting in muscle spasms, convusions and nervous twitches • Osteoporesis – demineralization of the bones due to overproduction of the parathyroid, or lack of calcium • very common after menopause due to lowered estrogen levels (estrogen counters the effect of PTH)

The Pancreas • Islets of Langerhans – are glandular clusters of cells in the pancreas that produce insulin and glucagons – Alpha cells – produce glucagon, which stimulates the conversion of glycogen to glucose by the liver raising blood glucose – Beta cells – produce insulin, which stimulates the uptake of glucose by the body’s cells, lowering blood glucose

Regulation of Blood Sugar

Blood Sugar Disorders • Diabetes Mellitis – also known as sugar diabetes or hyperglycemia, blood sugar is very high (while cellular glucose is too low) resulting in increased urination, fruity odour on the breath, weight loss, fatigue, blindness – Type I /Juvenille Onset – the inability to produce insulin, often due to a defect in the pancreas – Type II / Adult Onset – the failure of cells to produce insulin, often due to an excessive amount of insulinase (common in obese individuals) • Diabetic Coma – slow onset, lack of insulin that result in the brain being deprived of glucose, and eventually shutting down (insulin is required) • Insulin Shock – sudden excess amount of insulin causing dizziness, sweating, hunger, confusion, normal urine output (sugar is required) • main

Adrenal Glands • The adrenal glands are located just above the kidneys, and are composed of two parts, an outer cortex and an inner medulla. The adrenal cortex and adrenal medulla each produce different hormones.

Adrenal Medulla • Adrenaline – released to elicit the fight of flight response during stress, causes: • increased blood glucose • increased metabolism • increased blood flow to the skeletal muscles • decreased rate of digestion • relaxes smooth muscles in the walls of the bronchioles • increases coagulability of the blood

Adrenal Cortex • The adrenal cortex is responsible for the production and release of three classes of hormones: • Sex hormones – small amounts of both male and female sex hormones are released by the adrenal cortex. Over-activity causes masculinization of females and feminization of males. • Cortisol – is a glucocorticoid that breaks down muscle proteins to produce amino acids, and stimulates the metabolism of fatty acids raising the blood glucose. Glucocorticoids also counter the inflammatory response. • Aldosterone – is a mineralocorticoid that regulates Na+/K+ levels and maintains blood pressure. Aldosterone promotes absorption of Na+ ions by the kidney, drawing in water and thus increasing blood pressure.

Adrenal Disorders • Cushing’s Syndrome – overactivity of the adrenal cortex resulting in edema, moonlike face, masculinization of females, and high blood sugar. • Addison’s Disease – underactivity of the adrenal cortex resulting in low blood pressure, acidosis, fainting, increased risk of infection and bronzing of the skin.

Other Hormones, etc. • Thymus – secrete thymosin that stimulates maturation and differentiation of the T-cells in the immune system (most active in children with developing immune systems) • Melatonin – secreted by the pineal gland, regulates circadian rhythms such as sleep/wake cycles, migration, mating and sexual development. • Pheromones – are messengers that act between individuals of a species, secreted to attract a mate, mark territory, provide warning of danger. • Prostoglandins – local messengers made from phospholipids that act on the cells they touch.