Endo 3

• Thyroid Gland

  • Highly vascular
  • 15 to 20 grams in adults
  • Thyroids hormones profoundly increase the metabolic rate of the body
  • Complete lack of thyroid secretion usually causes the basal metabolic rate to fall 40 to 50 percent below normal, and extreme excesses of thyroid secretion can increase the basal metabolic rate to 60 to 100 percent above normal
• Thyroid Gland

  • Thyroid hormones – the body’s major metabolic hormone

  1. Thyroxine (T4)- 90%
  2. Triiodothyronine (T3)- 10%
  3. 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
• Most of the thyroid tissue consists of the follicular cells, which secrete the iodine-containing thyroid hormones
• The parafollicular cells (also called 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 1mg/week
• 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 through out body
• Parathyroid Glands

  • Small lumps of glandular epithelium
  • Usually four parathyroid glands, and they are found on the posterior surfaces of the thyroid gland
• Parathyroid hormone (PTH): Increases blood calcium concentration by increasing the breakdown of bone with the release of calcium into the blood
• Action of PTH on bone

  • PTH causes resorption of bone (osteoclastic activity)
  • Causes mobilization of Ca++ from the bone or demineralization
  • Hence it increases serum Ca++ levels
• Adrenal Glands: Located on the superior surface of each kidney
• Adrenal cortex (80%): Outer region is glandular
• Adrenal medulla (20%): Inner region and is secretory nervous tissues
• 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 (androgens) secreted by adrenal cortex of both sexes)
• Aldosterone is the most important mineralocorticoid hormone 
• Aldosterone secretion is stimulated by:

  • Decreasing blood volume or pressure (renin-angeotensin system) is the major stimulant
  • Rising blood levels of K+
  • Low blood Na+
  • ACTH
• Help the body resist stress by:

  • Glucocorticoids are essential for life, without them the person will die
  • Without Glucocorticoids, the body cannot cope with even mild stressors
• Cortisol promotes:

  • Gluconeogenesis (formation of glucose from noncarbohydrates)
  • Rises in blood glucose, fatty acids, and amino acids
  • Mobilization of amino acids from proteins
  • Lipolysis
• 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 (Circadian rhythm)
• Adrenal medulla

  • Catecholamines

  1. Produces epinephrine (80%)
  2. Produces norepinephrine (20%)

  • They are released from chromaffin cells
  • Secretion of these hormones causes:

  1. Blood to be diverted to the brain, heart, and skeletal muscle
• Effects of Catecholamines

  1. Glycogenolysis in liver and skeletal muscle (can lead to hyperglycemia) which increases blood glucose level
  2. Increase heart rate and blood pressure
  3. Cause vasoconstriction of blood vessels
  4. Mobilization of free fatty acids
  5. Increase metabolic rate
  6. Increase O2 consumption
• Adrenal Medulla

  • Secretes hormones

  1. Epinephrine (Epi), or adrenaline
  2. Norepinephrine (NR)
• Adrenal medulla

  • Functions of hormones

  1. Help the body resist stress by intensifying and prolonging the effects of sympathetic stimulation
  2. Increased epinephrine secretion is the first endocrine response to stress
• Pancreas

  • A triangular gland, which has both exocrine and endocrine cells, located behind the stomach
  • Strategic location
  • 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: 1-2million 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: Increases the blood glucose level by accelerating liver glycogenolysis (conversion of glycogen to glucose)
• Insulin: 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)

  • Cause: Inadequate insulin secretion (insulin-dependent diabetes mellitus)
  • Caused by an immune-mediated selective destruction of β cells
  • β cells are destroyed while α cells are preserved:

  1. No insulin >> high glucagon >>> high production of glucose and ketones by liver
  2. Glucose & ketones >>> osmotic diuresis
  3. Keto acids >>> diabetic ketoacidosis
• Type 2 diabetes (affects adults)

  • Cause: Defect in insulin action (insulin resistance)

  1. Non-insulin-dependent diabetes mellitus

  • Treatment: Diet and change life style

  1. Can develop into type 1 diabetes if uncontrolled
• Type 3 gestational diabetes

  1. Placenta produces hormones
  2. These hormones inhibit the functioning of insulin
  3. Blood glucose level is increased
• Type 3 gestational diabetes

  1. Mother's blood brings extra glucose to fetus
  2. Fetus makes more insulin to handle the extra gluscose
  3. Extra glucose gets stored as fat and fetus becomes larger than normal
• Type 3 gestational diabetes

  1. Occurs in 2-5% of pregnancies
  2. Associated with decreased insulin levels and/or insulin resistance
  3. Resembles type 2 diabetes
  4. Usually transient: Symptoms improve following delivery
  5. If untreated --> Macrosomia (high birth weight)
• Diabetes mellitus

  • Cause

  1. Inadequate secretion of insulin
  2. Defects in the action of insulin

  • Metabolic disturbance (hyperclycemia and glycosuria)
• The ovaries contain two structures that secrete hormones

  • Ovarian follicles
  • Corpus luteum
• Effects of estrogen (feminizing hormone)

  • Development and maturation of breasts and external genitals
  • Development of adult female body contours
  • Initiation of menstrual cycle
• A woman’s primary sex organs are her two ovaries
• Ovarian follicles are little pockets in which egg cells (ova) develop; they also secrete estrogen