Endocrine

• Neuroendocrine system


  The two communication systems in the body that transmit messages, allowing coordination of function
• Communication systems


  • Nervous system
  • Endocrine system
• Nervous system


  Messenger: Electrochemical signals (APs and neurotransmitters), Goes to: Specific set of cells, Result: Muscle contract/relax, glands secrete/don't, Timing: Quick, within seconds and brief effects
• Endocrine system


  Messenger: Hormones, Goes to: All body cells, Result: Changes in the metabolic activities of tissues, Timing: Slower, requiring minutes to hours, but longer lasting effects
• Types of glands


  • Exocrine glands
  • Endocrine glands
• Exocrine glands


  Secrete their products into ducts that carry them to where they will be used. Examples are sebaceous and sudoriferous glands.
• Endocrine glands


  Secrete their products (hormones) into the interstitial fluid. True hormones then move into the blood. Hormones regulate the activity of smooth, cardiac muscle and glands, help the body respond to extreme environmental changes (stress), play a major role in growth, development and reproduction and regulate metabolism and energy balance.
• Target cells


  Cells with receptors for a hormone, allowing them to respond to that hormone. All cells are target cells for one or more hormones.
• Effects of hormones


  • Changing membrane permeability or potential by opening/closing ion channels
  • Stimulating protein synthesis (including enzymes)
  • Turn enzymes on or off
  • Cause secretion
  • Stimulate mitosis
• Hormone structure and methods of action

  • Lipid soluble hormones (steroids, thyroid hormone)
  • Water soluble hormones (peptides and proteins)
• Lipid soluble hormones


  Travel in blood attached to transport proteins, can travel through the cell membrane, their receptor proteins are located inside the target cell
• Water soluble hormones


  Travel in blood alone, no transport protein, cannot move through the cell's membrane, their receptors are located on the outer surface of the membrane and they rely on a 2nd messenger to carry their message inside the cell
• Response of a cell to a water soluble hormone

  1. Hormone binds to receptor on surface of cell

  2. Activated G protein activates adenyl cyclase which causes ATP to form cyclic AMP (cAMP)

  3. cAMP activates protein kinases

  4. Protein kinases then produce effects that generate the cell's response to the hormone
• Second messenger system


  Very effective due to amplification of the response at each step. One hormone molecule can activate 100 G proteins. For example if each activated adenyl cyclase produces 1000 cAMPs, there will be 100,000 cAMP present to activate protein kinases. Each protein kinase can act on hundreds or thousands of substrate molecules. Kept under control by phosphodiesterase quickly inactivating each cAMP.
• PIP-Calcium signal mechanism


  1. Hormone binds to G protein, activating it

  2. Active G protein binds to and activates phospholipase

  3. Active phospholipase splits PIP2 into DAG and IP3, both acting as second messengers

  - DAG activates protein kinasesIP3 releases stored Ca++ ions which act as 3rd messengers
• Receptor regulation


  Receptors are constantly being created and destroyed, varying in number within a cell over time. Hormone action may be to increase the number of receptors to a different hormone. An excess of a hormone causes a decrease in the number of receptors (down-regulation), a scarcity causes an increase (up-regulation).
• Hormone degradation and effects


  Hormones are degraded by target cells or removed by the kidneys or liver. The time a hormone spends in the bloodstream is limited, from seconds up to 30 minutes. The time frame for the effects of a hormone may be different from the time it is present in the blood.
• Hormone interactions

  • Permissiveness: effect of A requires the previous or simultaneous effect of B
  • Synergism: responses complement, so total effect is much greater than the response to each individual hormone
  • Antagonism: opposite effects
• Hormone secretion control

  • Chemical changes in the blood (humoral stimuli)
  • In response to signals from the nervous system (neural stimuli)
  • In response to other hormones (hormonal stimuli)
• Hypothalamus and pituitary

  The pituitary regulates many body activities and used to be called the "Master Gland". The hypothalamus regulates the pituitary. The pituitary is divided into the anterior pituitary (adenohypophysis) and posterior pituitary (neurohypophysis).
• Adenohypophysis


  Secretion of hormones is regulated by hormones produced by the hypothalamus that travel to the adenohypophysis through the hypophyseal portal system.
• Hypothalamus


  Regulates the pituitary gland
• Pituitary gland


  • Fits into the sella turcica of the sphenoid
  • Attached to the hypothalamus by a stalk called the infundibulum
• Divisions of the pituitary gland

  • Anterior pituitary (adenohypophysis)
  • Posterior pituitary (neurohypophysis)
• Anterior Pituitary - Adenohypophysis


  • Glandular section, comprises about 3/4 of the total pituitary
  • Connected to the hypothalamus by the hypophyseal portal circulation
• Posterior Pituitary - Neurohypophysis


  Contains the axon terminals of neurons located in the supraoptic and paraventricular (PVN) regions of the hypothalamus
• Regulation of adenohypophysis secretion

  1. Hypothalamus senses blood levels of hormones and other chemicals

  2. Releases releasing or inhibiting hormones

  3. Hypothalamic hormones travel through hypophyseal portal vein to anterior pituitary

  4. Anterior pituitary secretes (or stops secreting) hormones

  5. Pituitary hormones enter anterior hypophyseal vein and are delivered to the rest of the body
• Hypophyseal portal system


  Short, direct portal system that allows rapid communication between the hypothalamus and the anterior pituitary
• Hormones produced by the anterior pituitary

  • Growth hormone (GH)
  • Thyroid stimulating hormone (TSH)
  • Adrenocorticotropic hormone (ACTH)
  • Follicle stimulating hormone (FSH)
  • Luteinizing hormone (LH)
  • Prolactin (PRL)
• Growth hormone (GH)


  • Stimulates cell hypertrophy and mitosis (esp. bone and skeletal muscles)
  • Increases the use of fat for fuel
  • Increases glycogen breakdown in liver (increases blood glucose levels)
  • Stimulates the secretion of insulin like growth factors (IGFs) by liver, skeletal muscle, bone and other tissues
• Control of GH secretion

  1. Growth hormone releasing hormone (GHRH) is secreted in response to low GH levels

  2. Anterior pituitary responds to GHRH by secreting GH

  3. GHRH release is turned off by negative feedback in response to high GH or IGF levels

  4. Hypothalamus releases growth hormone inhibiting hormone (GHIH) which suppresses anterior pituitary release of GH

  5. There is a daily rhythm in GH release with the peak occurring during sleep
• Disorders of hGH in a child

  • Under secretion will slow growth, resulting in pituitary dwarfism
  • Oversecretion will cause very rapid growth, individual will be very large but have normal body proportions
• Disorders of hGH in an adult

  • Over secretion can't affect long bones because the epiphyseal plates have sealed
  • Increases growth of the bones of the hands, feet and face, increases size of facial tissues, condition is known as acromegaly
• Thyroid stimulating hormone (TSH)


  Increases the synthesis and secretion of thyroid hormone (TH)
• Control of TSH secretion

  Thyroid releasing hormone (TRH) is released in response to low blood sugar, low metabolic rate or low TSH levels
• Adrenocorticotropic hormone (ACTH)


  Controls the production and secretion of glucocorticoids from the adrenal cortex
• Control of ACTH secretion

  Corticotropic releasing hormone (CRH) is released in response to the presence of stress-related stimuli (low blood glucose, trauma, immune function)
• Follicle stimulating hormone (FSH) and Luteinizing hormone (LH)


  Together act on the gonads and are referred to as gonadotropins
• Thyroid


  Located just below the larynx, consists of left and right lateral lobes connected by an isthmus, has a rich supply of blood, can store hormones for steady long-term release or high levels in short time
• FSH in females


  Initiates development of the egg and stimulates the ovaries to produce estrogen