The Endocrine System: Glands and Hormones

The Endocrine System

• It is a collection of ductless glands that produce hormones.

Endocrine vs Exocrine Glands

• Exocrine glands include sweat (sudoriferous) glands.
• Other exocrine glands are mammary, salivary, lacrimal, sebaceous, mucous, and ceruminous glands.
• The pancreas and liver are also exocrine glands.

Functions of the Endocrine System

• Growth, metabolism, reproduction, and excretion are influenced by it.
• It also affects stress management, sleep cycles, and mood.
• Virtually every system and function in the body is impacted by it.
• The body uses this system to maintain homeostasis.

Definition of Hormones

• Chemical messengers are called hormones.
• Hormones are carried from the endocrine gland to target the body.

Types of Hormones

• Lipid hormones are derived from cholesterol, like estrogen and testosterone.
• Amino-acid derived hormones include epinephrine, norepinephrine, thyroxine, and melatonin.
• Peptide hormones are made of polypeptide chains, such as insulin, oxytocin, and antidiuretic hormone.

How Hormones Work

• Trigger changes in target cells.
• Hormones bind to hormone receptors.
• They only affect cells with the receptors inside or on the surface.
• The number of receptors changes over time.
  • Up-regulation can occur, such as oxytocin on the uterus during pregnancy.
  • Down-regulation can occur, such as cell sensitivity to insulin.

Major Endocrine Glands

• Pineal gland, hypothalamus, pituitary gland, parathyroid gland, and thyroid gland.
• Thymus, adrenal gland, pancreas, kidney, testis (in males), and ovary (in females) are also endocrine glands.

Hypothalamus

• Coordinates the autonomic nervous system and pituitary gland.
• Influences body temperature, blood pressure, heart rate, and thirst.
• Affects appetite, weight control, production of digestive juices, sleep patterns, and emotional activity.

Pituitary Gland

• Is considered the “master gland”.
• It is composed of the anterior and posterior pituitary.

Hormones of the Pituitary Gland

Posterior Pituitary

• Antidiuretic hormone (ADH) targets the kidneys, reducing water lost in urine.
• Oxytocin targets the uterus, inducing contractions, and mammary glands, inducing milk ejection.

Anterior Pituitary

• Adrenocorticotropic hormone (ACTH) targets the adrenal cortex, stimulating the release of glucocorticoids.
• Thyroid-stimulating hormone (TSH) targets the thyroid gland, stimulating the synthesis and secretion of thyroid hormones.
• Follicle-stimulating hormone (FSH) targets the ovaries in females, stimulating egg maturation and estrogen secretion, as well testes in males, stimulating the formation of sperm.
• Luteinizing hormone (LH) targets ovaries for ovulation (egg release) and progesterone secretion in females.
• Luteinizing hormone targets testes for testosterone secretion in males.
• Prolactin (PRL) targets mammary glands, stimulating mammary gland development and milk production.
• Growth hormone (GH) targets most cells: stimulating growth in youth and playing multiple roles in cell division, protein synthesis, and metabolism in adults.

Pituitary Gland Malfunctions

• Leads to conditions such as giantism versus dwarfism.
• Acromegaly can also be caused by a malfunctioning pituitary gland.

Pineal Gland

• This serves as a third eye; it produces melatonin, which regulates sleep.
• In other animals, it modulates photoperiodic functions in seasonal cycles.

Thyroid Gland Production

• Thyroxine (T4), triiodothyronine (T3), and calcitonin are produced.
• Calcitonin reduces calcium concentration in body fluids.
• Increases metabolic activity, Basal Metabolic Rate (BMR), and rate of food utilization
• Accelerates growth rate in youth

Thyroid Gland Conditions

• Hyperthyroidism? - Weight loss and rapid/irregular heart beat may occur. - Grave’s disease.
• Hypothyroidism? - Weight gain and fatigue/lethargy may occur. - Cretinism can occur.
• Goiter may also occur from thyroid malfunction.

Parathyroid Gland

• This area produces parathyroid hormone (PTH) to raise blood calcium levels.
• It acts in opposition to calcitonin, produced by C-cells of the thyroid.
• If the parathyroid malfunctions, this leads to brittle bones or kidney stones.

Pancreas

• Exocrine: Digestive enzymes are produced here.
• Endocrine (islets of Langerhans): alpha cells produce glucagon.
• Beta cells produce the hormone insulin.
• Together, glucagon and insulin regulate blood-glucose levels.

Blood Glucose Levels

• Hyperglycemia refers to high blood glucose levels.
• Hypoglycemia refers to low blood glucose levels.

Diabetes Mellitus

 - Type 1 diabetes is an autoimmune disease. It causes insulin deficiency
 - Type 2 diabetes is insulin resistance, the tissues do not respond to insulin
 - Gestational diabetes occurs during pregnancy.

Long-Term Effects of Hyperglycemia

• Long-term effects include cardiovascular disease and nerve damage (neuropathy).
• Kidney damage (diabetic nephropathy) and kidney failure.
• Damage to blood vessels of the retina (diabetic retinopathy), leading to potential blindness.
• Clouding of the lens of the eye (cataract) and feet problems from damaged nerves or blood flow.
• Bone, joint problems, skin problems, fungal/bacterial infections, and teeth/gum infections may occur.

Adrenal Glands

• Adrenal cortex produces aldosterone and glucocorticoids.
• Aldosterone maintains electrolyte balance in extracellular fluids.
• Electrolytes include ions of sodium, potassium, calcium, and bicarbonate.
• Aldosterone enhances sodium ion reabsorption and potassium ion secretion.
• Glucocorticoids stimulate glucose synthesis from amino acids and triglycerides.
• They also stimulate gluconeogenesis in the liver.
• Glucocorticoids promote release of fatty acids from adipose tissue.
• They inhibit glucose uptake in muscle and adipose tissue.
• Adrenal medulla produces epinephrine (adrenaline) and norepinephrine

Gonads (Ovaries and Testes)

• Testes produce testosterone.
• Ovaries produce estrogen and progesterone.

Synthetic Hormones

• Includes anabolic steroids, which build muscle mass (remember anabolism).
• Performance-enhancing drugs include growth hormone and erythropoietin.
• 'Roid rage may occur, exhibiting aggressive behavior.
• Long-term overuse often causes drastic side effects.

Risk Factors and Abuse

• Andreas Munzer was 32 yeasr old when he died and had an enlarged heart.
• He had tumors on his liver and he died of organ failure.

Non-Endocrine Gland: Kidneys

• (1) Renin (enzyme not a hormone): -Secreted in response to decreased blood pressure. -It is a part of the renin-angiotensin I and II system that causes: -(1) Vasoconstriction of all blood vessels. -(2) Release of aldosterone from adrenal cortex. -(stimulates reabsorption of sodium ions in distal tubule).
• (2) Erythropoietin (hormone) to increase red blood cell production

Explore the endocrine system, a network of ductless glands producing hormones. Learn the differences between endocrine and exocrine glands, hormone types and how the endocrine system influences growth, metabolism, reproduction, and overall homeostasis.