Endocrine System Overview

Endocrine System Glands

• There are 4 types of cell secretions: autocrine, paracrine, neurotransmitter, and hormones.
• Autocrine secretions have a local effect on the same cell type.
• Paracrine secretions affect other cell types in close proximity.
• Neurotransmitters are secreted by nerve cells.
• Hormones are secreted into the blood and bind to receptor sites.

Endocrine System Functions

• The endocrine system's functions include:
  • metabolism
  • control of food intake and digestion
  • tissue development
  • ion regulation
  • water balance
  • heart rate and blood pressure regulation
  • control of blood glucose and other nutrients
  • control of reproductive functions
  • uterine contraction and milk release
  • immune system regulation

Characteristics

• The endocrine system is composed of endocrine glands and specialized endocrine cells located throughout the body.
• Endocrine glands secrete minute amounts of chemical messengers called hormones into the bloodstream.
• Hormones travel through the general blood circulation to target tissues.
• Target tissues have receptors for a specific hormone.
• Hormones produce a particular response in target tissues.

Types of Hormones

• Water-soluble Hormones:
  • include proteins, peptides, amino acids
  • most common
  • Examples include: growth hormone, antidiuretic, prolactin.
• Lipid-soluble Hormones:
  • include steroids and eicosanoids
  • Examples include: LH, FSH, androgens

Control of Hormone Release

• Hormone release can be controlled by blood-borne chemicals, neural control, and other hormones.
• Humoral stimuli, circulating in the blood, can stimulate hormone release.
• Neural control involves the release of a neurotransmitter into the synapse with cells that produce the hormone.
• Hormonal control involves one hormone stimulating the secretion of another hormone.
• The three types of stimuli can stimulate or inhibit hormone release.

Target Tissue Specificity and Response

• Hormones bind to specific receptors on target tissues.
• The response in target tissues depends on the receptor and the hormone.
• Hormones can have different effects in different tissues.

Nuclear and Membrane-Bound Receptors

• Nuclear Receptors:
  • Found inside the cell.
  • Bind to lipid-soluble hormones.
  • Regulate gene expression by binding to hormone response elements on DNA.
• Membrane-Bound Receptors:
  • Found on the cell membrane.
  • Bind to water-soluble hormones.
  • Initiate a signal transduction cascade through various pathways, such as G proteins or directly altering intracellular enzymes, leading to specific cell responses.

Action of Nuclear Receptors

• Lipid-soluble hormones stimulate protein synthesis.
• Lipid-soluble hormones diffuse across the cell membrane and bind to their receptors.
• The hormone-receptor complex binds to hormone response elements on DNA.
• This action regulates transcription of specific mRNA molecules, leading to protein synthesis.

Membrane Receptor Actions

• Membrane receptors act by:
  • altering the activity of G proteins on the inner surface of the cell membrane
  • directly altering intracellular enzymes
• Activation of G proteins or intracellular enzymes elicits specific responses in cells, including the production of second messengers.

Posterior Pituitary Hormones

• Antidiuretic Hormone (ADH)
  • Target tissues: kidneys
  • Functions: conserve water
  • Abnormalities: Diabetes insipidus (low ADH), which causes kidneys to produce large amounts of dilute urine, leading to dehydration and thirst.
• Oxytocin
  • Target tissues: uterus
  • Functions: increases uterine contractions during labor.

Hypothalamus and Posterior Pituitary

• The hypothalamus regulates the posterior pituitary gland.
• The posterior pituitary gland stores and releases hormones produced in the hypothalamus.

Thyroid Gland

• One of the largest glands in the body.
• Requires iodine to function.
• Secretes thyroid hormone and calcitonin.
• Thyroid Hormones (secreted by follicular cells):
  • Target tissues: most
  • Functions: regulate metabolic rates and are needed for growth.
• Calcitonin (secreted by parafollicular cells):
  • Target tissues: bone and some other tissues
  • Function: reduces blood calcium level when high.

Thyroid Hormone Disorders

• Hypothyroidism:
  • Decreased metabolism
  • Weight gain, reduced appetite, fatigue
  • Low temperature and pulse
• Hyperthyroidism:
  • Increased metabolism
  • Weight loss, increased appetite, nervousness
  • Higher temperature

Adrenal Glands

• Located above the kidneys.
• Composed of the adrenal medulla and adrenal cortex.

Adrenal Gland Hormones

• Adrenal medulla hormones:
  • Epinephrine/Norepinephrine:
    • Target tissues: heart, blood vessels, liver, fat cells
    • Functions: released as part of the fight or flight response.
• Adrenal cortex hormones:
  • Aldosterone:
    • Type of mineralocorticoid
    • Target tissues: kidneys
    • Functions: causes Na+ and H2O to be retained and K+ to be secreted, indirectly involved in blood pressure and blood volume regulation.
  • Cortisol:
    • Type of glucocorticoid
    • Target tissues: most
    • Functions: increases breakdown of fat and protein for energy uses and reduces inflammatory and immune responses.
  • Androgens:
    • Target tissues: most
    • Functions:
      • Males: secondary sexual characteristics
      • Females: sex drive

Pancreas Actions

• The pancreas is a mixed gland, with an exocrine portion and an endocrine portion.
• The endocrine portion (islets of Langerhans) secretes insulin and glucagon.
• Insulin, secreted by beta cells, lowers blood glucose levels.
• Glucagon, secreted by alpha cells, increases blood glucose levels.

Explore the fascinating world of the endocrine system, focusing on its glands, cell secretions, and vital functions. This quiz delves into how hormones, neurotransmitters, and other secretions play a crucial role in regulating various bodily processes. Test your knowledge on metabolism, reproductive functions, and more!