pt 3 3ndo

• Thyroid gland


  • Immediately caudal to the larynx and encircles the anterolateral portion of the trachea
  • Highly vascular, normally weighing 15 to 20 grams in adults
• Thyroid hormones


  • The body's major metabolic hormone
  • Thyroxine (T4) - 90%
  • Triiodothyronine (T3) - 10%
  • Accelerate catabolism (increase the body's metabolic rate)
• Calcitonin (CT)


  Decreases the blood calcium concentration by inhibiting breakdown of bone, which would release calcium into the blood
• Thyroid tissue


  • Consists of follicular cells and parafollicular cells
  • Follicular cells secrete the iodine-containing thyroid hormones
  • Parafollicular cells (C cells) secrete the hormone calcitonin
• To form normal quantities of thyroxine, about 50 milligrams of ingested iodine in the form of iodides are required each year, or about 1 mg/week
• To prevent iodine deficiency, common table salt is iodized with about 1 part sodium iodide to every 100,000 parts sodium chloride
• Hyperthyroidism


  • Overactive thyroid
  • Increased metabolic rate
  • Enlargement of thyroid gland
  • Weight loss, nervousness, irritability
  • Intolerance to heat
  • Increased cardiac output
  • Bulging eyeballs (Exophthalmos)
• Hypothyroidism


  • Underactive thyroid
  • 2-3 times increase in size (Goiter)
  • Slowed metabolic rate, fatigue, weight gain
  • Cretinism (physical and mental growth)
  • Myxoedema: edematous appearance throughout body
• Parathyroid hormone (PTH)


  Increases blood calcium concentration by increasing the breakdown of bone with the release of calcium into the blood
• Calcitonin and parathyroid hormones


  Have antagonistic (opposite) effects on calcium concentration in the blood
• Adrenal gland


  • Adrenal cortex (outer region) is glandular
  • Adrenal medulla (inner region) is secretory nervous tissues
  • Adrenal medulla (20%)
  • Adrenal cortex (80%)
• Adrenal cortex


  • Synthesizes and secretes steroid hormones called corticosteroids (Adrenocorticoids)
  • Different Corticosteroids are produced in each of the three layers:
  • Zona glomerulosa - Mineralocorticoids (Aldosterone)
  • Zona fasciculata - Glucocorticoids (hydroCortisol)
  • Zona reticularis - Androgens (Small amounts of male hormones secreted by adrenal cortex of both sexes)
• Mineralocorticoids (MCs)


  • Aldosterone is the most important mineralocorticoid hormone
  • Maintains Na+ balance by reducing excretion of Na+ from the body
  • Stimulates reabsorption of Na+ by the distal tubule and collecting duct in kidneys
  • Stimulates the active secretion of potassium from the tubular cell into the urine
  • Also stimulates sodium & potassium transport in sweat glands, salivary glands, & intestinal epithelial cells
• Regulation of Aldosterone secretion

  1. Aldosterone secretion is stimulated by:

  2. Decreasing blood volume or pressure (renin-angeotensin system)

  3. Rising blood levels of K+

  4. Low blood Na+

  5. ACTH
• Glucocorticoids (Cortisol)


  • Help the body resist stress by:
  • Promoting gluconeogenesis (formation of glucose from noncarbohydrates)
  • Rises in blood glucose, fatty acids, and amino acids
  • Mobilization of amino acids from proteins
  • Lipolysis
  • Maintaining normal renal function
  • Sensitizing arterioles to catecholamines (Permissive effect)
  • Suppression of immune response and anti-inflammatory effects
  • Inhibiting bone formation
  • Decreasing REM sleep
  • Negative feedback control on release of ACTH and modulating perception & emotion
• Regulation of Cortisol secretion


  The secretion of cortisol by zona fasciculata is regulated exclusively by the hypothalamic-pituitary axis
• The greatest cortisol secretory activity occurs in the early morning hours and diminish late in the afternoon
• Adrenal medulla


  • Produces epinephrine (80%)
  • Produces norepinephrine (20%)
  • Secretion of these hormones causes:
  • Blood to be diverted to the brain, heart, and skeletal muscle
  • Glycogenolysis in liver and skeletal muscle (can lead to hyperglycemia) which increases blood glucose level
  • Increase heart rate and blood pressure
  • Cause vasoconstriction of blood vessels
  • Mobilization of free fatty acids
  • Increase metabolic rate
  • Increase O2 consumption
• Pancreas


  • A triangular gland, which has both exocrine and endocrine cells, located behind the stomach
  • Acinar cells produce an enzyme-rich juice used for digestion (exocrine product)
  • Pancreatic islets (islets of Langerhans) produce hormones involved in regulating glucose, lipids, and protein metabolism
• Islets of Langerhans


  • 1-2 million islets
  • Beta (β) cells produce insulin (60%)
  • Alpha (α) cells produce glucagon (25%)
  • Delta (δ) cells produce somatostatin (10%)
  • PP cells produce pancreatic polypeptide (5%)
• Glucagon


  • Secreted by alpha cells
  • Increases the blood glucose level by accelerating liver glycogenolysis (conversion of glycogen to glucose)
• Insulin


  • Secreted by beta cells
  • Decreases the blood glucose by accelerating the movement of glucose out of the blood into cells, which increases glucose metabolism by cells
• Type 1 Diabetes


  • Affects children
  • Caused by an immune-mediated selective destruction of β cells
  • No insulin >> high glucagon>>> high production of glucose and ketones by liver
  • Glucose & ketones >>> osmotic diuresis
  • Keto acids >>> diabetic ketoacidosis
• Type 2 Diabetes


  • Affects adults
  • Caused by a defect in insulin action (insulin resistance)
  • Treatment: diet and change lifestyle
  • Can develop into Type 1 diabetes if uncontrolled
• Type 3 gestational diabetes

  • Occurs in 2-5% of pregnancies
  • Associated with decreased insulin levels and/or insulin resistance
  • Resembles Type 2 Diabetes
  • Usually transient: symptoms improve following delivery
  • If untreated >> macrosomia (high birth weight)
• Ovarian follicles


  • Little pockets in which egg cells (ova) develop
  • Also secrete estrogen
• Corpus luteum


  Secretes progesterone and also some estrogen
• Interstitial cells of testes


  Secrete the male hormone testosterone
• Effects of testosterone (masculinizing hormone)

  • Maturation of external genitals
  • Beard growth
  • Voice changes at puberty
  • Development of musculature and body contours typical of the male
• Thymosin


  Plays an important role in the development and function of the body's immune system
• Chorionic gonadotropins, Estrogen, Progesterone

  • Hormones produced by the placenta
  • Maintain the corpus luteum during pregnancy
• Pineal gland


  • A small gland near the roof of the third ventricle of the brain
  • Glandular tissue predominates in children and young adults
  • Becomes fibrous and calcified with age
  • Called the third eye because its influence on secretory activity is related to the amount of light entering the eyes
  • Secretes melatonin, which:
  • Inhibits ovarian activity
  • Regulates the body's internal clock
• Many organs (e.g., the stomach, intestines, and kidney) produce endocrine hormones
• Ghrelin


  Produced by the stomach lining, affects appetite and metabolism
• Atrial natriuretic hormone (ANH)

  Secreted by the atrial wall of the heart, stimulates sodium loss from the kidneys
• Leptin


  Secreted by fat-storing cells, controls how full or hungry one feels (Leptin decreases your appetite, while ghrelin increases it)
• Gigantism


  Hypersecretion of growth hormone during the early years of life
• Diabetes insipidus


  Hyposecretion of ADH
• Goiter


  Low dietary take of iodine
• Cretinism


  Hyposecretion of thyroid hormones during the formative years