Endocrine System

• Endocrine system


  • Controls and monitors bodily functions using hormones
  • Works in tandem with the nervous system; slower but longer-lasting effects
• Anatomy of the endocrine system

  • Collection of organs and glands affecting all body functions
  • Overlap with the nervous system for integrated responses (e.g., hypothalamus)
• Types of glands

  • Endocrine glands: Ductless, secrete hormones directly into bloodstream
  • Exocrine glands: Have ducts, secrete externally
• Endocrine glands


  • hypothalamus
  • pancreas
  • pituitary
  • adrenal
  • thyroid
• Exocrine glands


  • sweat
  • salivary
  • mammary
  • lacrimal
• Hormones

  • Secreted by endocrine glands into bloodstream
  • Regulate metabolism, water balance, growth, stress response, etc.
• Classification of hormones

  • Steroid hormones: Lipid-based, from adrenal cortex and reproductive glands
  • Amino acid hormones: Protein-based, more common
• Hormone receptors


  • Affect only tissues/organs with specific receptors
  • Change cell permeability
  • Alter enzyme activity
  • Stimulate protein synthesis
  • Influence secretory activity
• Types of hormone receptors

  • Steroid hormones: Inside cell nucleus; affects DNA and messenger RNA
  • Amino acid hormones: On cell surface; triggers second messengers
• Receptor distribution

  • Wide distribution for hormones like adrenaline
  • Limited distribution for others
• Receptor sensitivity

  • Upregulation: Increases sensitivity (e.g., exercise for insulin receptors)
  • Downregulation: Decreases sensitivity (e.g., obesity for insulin receptors)
• Hormone secretion control

  • Neural control
  • Hormonal control
  • Humoral control
• Neural control


  • Nerve fibres stimulate hormone release (e.g., adrenaline during fight or flight)
  • Affects heart rate, blood pressure, and other functions
  • Hypothalamus can also be influenced by the nervous system
• Hormonal control


  • Hierarchical chain of command within endocrine system
  • Hypothalamus directs pituitary gland, which guides other endocrine glands
  • Negative feedback loops terminate hormone secretion (e.g., in homeostasis)
• Humoral control


  • Monitors substances in body fluids for regulation
  • Corrective actions taken when imbalances detected
• Hypothalamus


  • Located deep in the brain below the thalamus
  • Integrates nervous and endocrine system responses
  • Regulates metabolism, heart rate, body temperature, and more
  • Produces hypothalamic releasing and inhibiting hormones
• Pituitary Gland


  • Pea-sized gland with anterior and posterior lobes
  • Located in sphenoid bone, connected to hypothalamus by infundibulum
  • Functions: Direct action on tissue or stimulating other endocrine glands
  • Tropic hormones: adrenocorticotropin hormone (ACTH), thyroid stimulating hormone (TSH), follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
• Hormones of anterior pituitary

  • Growth hormone: Acts on muscles, cartilage, and bones
  • Prolactin: Stimulates mammary glands and milk production
  • ACTH: Stimulates adrenal cortex for steroid hormone release
  • TSH: Stimulates thyroid for thyroxine and triiodothyronine release
  • FSH: Stimulates oestrogen, eggs in women; sperm production in men
  • LH: Influences ovaries and testes; triggers egg release and testosterone production
• Hormones of the posterior pituitary


  • Extension of the hypothalamus, not a true endocrine gland
  • Stores, but doesn't produce, antidiuretic hormone and oxytocin
  • Hormone release triggered by hypothalamic neuroendocrine input
• Antidiuretic Hormone (ADH)


  • Decreases urine output, increasing body fluid volume
  • Targets kidneys for increased water reabsorption
  • Triggered by dehydration or high concentration of blood particles
  • Role in blood pressure regulation
  • Narrows arteries, increases blood volume, raises blood pressure
  • Inhibited by alcohol, caffeine, and some foods (e.g., asparagus)
• Oxytocin


  • Produced during labour and stays until nursing is complete
  • Stimulates uterine muscle contraction for childbirth
  • Released by suckling, stimulating milk secretion from mammary glands
• Thyroid gland


  • Located inferior to the larynx, at base of throat
  • Butterfly-shaped with two lobes divided by isthmus
  • Secretes thyroid hormone and calcitonin
  • Thyroid hormone consists of thyroxine and triiodothyronine
  • Controls energy metabolism and heat production
  • Requires dietary iodine for production
  • Regulated by hypothalamus and anterior pituitary
• Calcitonin


  • Maintains calcium homeostasis
  • Released when blood calcium levels rise
  • Reduces calcium absorption by intestines and kidneys
• Parathyroid glands


  • Located on the posterior of the thyroid gland
  • Secrete parathyroid hormone
  • Increases blood calcium levels
  • Acts on bone tissue, intestines, and kidneys
• Thymus gland


  • Located under the sternum, shrinks with age
  • Secretes thymosin
  • Essential for T lymphocyte development and immunity
• Pineal gland


  • Pine cone-shaped gland in the brain
  • Releases melatonin
  • Induces sleepiness, highest levels at night
• Adrenal glands


  • Located on top of the kidneys
  • Comprise adrenal cortex (glandular) and adrenal medulla (nervous system)
• Adrenal medulla hormones


  • Secretes adrenaline and noradrenaline (catecholamines)
  • Triggered by sympathetic nervous system
  • Induces 'fight or flight' response
  • Effects include increased heart rate, blood pressure, and breathing
• Adrenal cortex hormones


  • Mineralocorticoids: Main hormone is aldosterone, stimulates sodium and water reabsorption in kidneys, regulates blood pressure and plasma levels
  • Glucocorticoids: Main hormones are cortisone and cortisol, maintain blood glucose levels, convert fats and amino acids into glucose
  • Sex hormones: Produces estrogens and androgens, majority are androgens, primarily testosterone
• Pancreas


  • Located behind the stomach, upper abdominal cavity
  • Functions as both endocrine (hormones) and exocrine gland (digestive enzymes)
  • Islets of Langerhans: Composed of alpha cells (secrete glucagon) and beta cells (secrete insulin), maintain blood glucose levels
• Insulin


  • Secreted when blood glucose is high
  • Promotes glucose uptake in cells
  • Converts excess glucose into glycogen or fat in liver
• Glucagon


  • Secreted when blood glucose is low
  • Stimulates liver to convert glycogen into glucose
  • Most effective at raising blood glucose levels
• Testes (Men)


  • Located in the scrotum
  • Produce sperm and testosterone
  • Regulated by luteinizing hormone from anterior pituitary
• Ovaries (Women)


  • Located in the pelvic cavity
  • Produce eggs, oestrogen and progesterone
  • Regulate menstrual cycle and promote breast development
• Other Hormones


  • Kidneys produce erythropoietin (stimulates red blood cell production)
  • Adipose tissue produces leptin (suppresses appetite, increases energy)
  • Heart produces atrial natriuretic peptide (stimulates sodium excretion)
  • Stomach and intestines produce digestive hormones