The Endocrine System Overview

The Endocrine System

• The endocrine system is a second messenger system in the body
• It uses chemical messages called hormones, released into the bloodstream
• Hormones control major bodily processes, including:
  • Reproduction
  • Growth and development
  • Body defense mechanisms
  • Homeostasis
  • Metabolism regulation

Hormone Overview

• Specialized cells produce hormones
• Cells release hormones into extracellular fluids
• Blood carries hormones to target cells
• Hormones regulate the activity of other cells

Chemistry of Hormones

• Amino acid-based hormones:
  • Proteins
  • Peptides
  • Amines
• Steroids: derived from cholesterol
• Prostaglandins: made from highly active lipids

Mechanisms of Hormone Action

• Hormones affect specific target tissues or organs
• Target cells must have specific protein receptors
• Hormone binding impacts the cell's function

Control of Hormone Release

• Blood hormone levels are regulated by negative feedback
• A stimulus or low hormone levels trigger hormone release
• Hormone release stops when the appropriate blood level is reached

Hormonal Stimuli of Endocrine Glands

• Endocrine glands are activated by other hormones
• Changing blood levels of certain ions can stimulate hormone release

Location of Major Endocrine Organs

• Pituitary gland: size of a grape, hangs from the hypothalamus, protected by the sphenoid bone, two functional lobes (anterior and posterior)

Hormones of the Anterior Pituitary

• Six anterior pituitary hormones
  • Two affect non-endocrine targets
  • Four stimulate other endocrine glands (tropic hormones)
• All anterior pituitary hormones are proteins or peptides
• Regulated by hormonal stimuli, mostly negative feedback

Growth Hormone (GH)

• General metabolic hormone, primarily affecting skeletal muscle and bone growth
• Influences protein synthesis, breakdown of fats, and amino acid absorption

Functions of Other Anterior Pituitary Hormones

• Prolactin (PRL): stimulates milk production after childbirth; function in males is unknown
• Adrenocorticotropic hormone (ACTH): regulates the adrenal cortex endocrine activity
• Thyroid-stimulating hormone (TSH): influences thyroid growth and activity
• Gonadotropic hormones: regulate the gonads (ovaries and testes)
  • Follicle-stimulating hormone (FSH): stimulates follicle development in ovaries and sperm development in testes
  • Luteinizing hormone (LH): triggers ovulation and stimulates testosterone production

Hormones of the Posterior Pituitary

• Oxytocin: stimulates uterine contractions during labor and milk ejection
• Antidiuretic hormone (ADH): inhibits urine production and increases blood pressure

Thyroid Gland

• Located in the throat
• Consists of two lobes connected by an isthmus
• Produces thyroid hormone and calcitonin

Thyroid Hormones

• Major metabolic hormone
• Composed of two active iodine-containing hormones (T4 and T3)
• T3 and T4 conversion at target tissues

Calcitonin

• Decreases blood calcium levels by promoting deposition on bones
• Antagonistic to parathyroid hormone

Parathyroid Glands

• Tiny masses on the posterior of the thyroid
• Secrete parathyroid hormone
• Stimulate removal of calcium from bone
• Stimulate absorption of calcium
• Raises blood calcium levels

Adrenal Glands

• Two glands (cortex and medulla), located atop the kidneys
• Cortex: outer region with three layers
• Medulla: inner neural tissue region

Hormones of the Adrenal Cortex

• Mineralocorticoids (mainly aldosterone): regulate mineral content, water, and electrolyte balance; stimulated by renin and aldosterone, inhibited by ANP
• Glucocorticoids (cortisone and cortisol): promote normal cell metabolism, help resist long-term stress; released in response to ACTH
• Sex hormones: produced in inner layer; androgens (male), estrogens (female)

Hormones of the Adrenal Medulla

• Produces epinephrine and norepinephrine (catecholamines) - prepares the body for short-term stress

Pancreatic Islets

• Pancreas is a mixed gland
• Islets produce insulin and glucagon
• Insulin: allows glucose to enter cells from the blood to lower blood sugar
• Glucagon: moves glucose from storage sites back into the blood to raise blood sugar
• Blood sugar homeostasis maintained by insulin and glucagon responses

Pineal Gland

• Located in the brain's third ventricle
• Secretes melatonin
• Influences wake/sleep cycles

Thymus

• Located posterior to the sternum
• Largest in infants and children
• Produces thymosin that matures some types of white blood cells
• Important in developing the immune system

Hormones of the Ovaries

• Estrogens: Produced by Graafian follicles or placenta, promoting female characteristics and reproductive organs, preparing the uterus for fertilization, maintaining pregnancy, and breast preparation
• Progesterone: Produced in the corpus luteum, working with estrogen to regulate the menstrual cycle, aiding in embryo implantation

Hormones of the Testes

• Interstitial cells produce androgens, mainly testosterone
• Important for secondary sex characteristics of males, maturation of the male reproductive system, and sperm production

Other Hormone-Producing Tissues/Organs

• Parts of the small intestine, stomach, kidneys, and heart also produce hormones.

Endocrine Function of the Placenta

• Produces hormones that maintain pregnancy, some helping in delivery.

Developmental Aspects of the Endocrine System

• Most endocrine organs function normally until old age.
• Menopause occurs due to ovarian function decrease.
• Hormone production generally decreases with age.

This quiz covers the fundamentals of the endocrine system, including the role hormones play in bodily processes such as reproduction, growth, and metabolism. Explore how hormones are produced, their chemical composition, and the mechanisms behind their action and regulation.