46/47 Anterior and Posterior Pituitary

Question 1

Classify hormones according to their chemical structure. Which types of hormone are water soluble? Lipid soluble? Which bind to surface receptors? Which bind to receptors in the cytosol or the nucleus?

Answer 1

• Polypeptides: 100 AA…ex] growth hormone…water soluble so easily enter circulatory system for transport to organs…preprohormones (ER)  prohormones (GA)  hormones (in vesicles), bind to receptors on surface
• Steroid hormones: derived from cholesterol…ex] Adrenal steroid hormones (aldosterone, cortisol, adrenal androgens), gonadal steroid hormones (testosterone, estrogen, progesterone), Vit D …lipid soluble so not stored in vesicles (diffuse as soon as created), cells that create can store cholesterol esters to more readily prepare for synthesis; circulate in blood bound to plasma proteins (slows clearance from blood)
• Amine hormones: amino acid derived…ex] norepinephrine, epinephrin…stored in vesicles and released bia exocytosis; water-soluble and can be transported by dissolving in blood or thru conjugation with other substance, bind to receptors on surface
• Thyroid hormones: derived from tyrosine, as well  so sometimes classified as amine hormones
• Intracellular receptors can be soluble receptor proteins found in the cytosol or in the nucleus. Once the hormone-receptor complex is in the nucleus it can bind to a hormone response element (HRE) and activate/repress transcription of a gene

Question 2

Describe feedback regulation in the endocrine system. What do we mean by short-loop feedback? Long-loop feedback?

Answer 2

short loop: anterior
pituitary feedback to hypothalamus

ultra-short loop: hypo to hypo feedback

long loop feedback: target to hypothalamus

Question 3

3. Describe the anatomical and physiological relationship between the hypothalamus and the pituitary gland. What hormones are made and released by the hypothalamus? What is the action of each hypothalamic hormone on the anterior pituitary? Which hormones are made by hypothalamic cells and released by the posterior pituitary? Where are posterior pituitary hormones made? (Know names of the two hypothalamic nuclei) 4. Explain the control of secretion and the functions of the pituitary gland. Be able to list the anterior and posterior pituitary hormones and give their functions. 7. Describe the actions of oxytocin and the stimulus for the milk let down reflex. What is the role of oxytocin in childbirth.

Answer 3

• Anterior Pituitary: Direct vascular link between the anterior pituitary and the hypothalamus. Portal circulation: primary plexus (arise in the median eminence)  hypophyseal vessels  capillaries of anterior pituitary (4 of the 6 are trophic hormones…which means they have effects on morphology/secretory activity of other endocrine glands)
• Hypothalmic corticotropin-releasing hormone (CRH) leads to release of Adrenocorticotrophin (ACTH)…POMC (proopiomelanocortin) is hydrolyzed to ACTH  ACTH released  stimulates synthesis/secretion of adrenocortical hormones (mainly cortisol). ACTH also binds to melanocytes and accelerates melanin synthesis. In primary adrenal insufficiency you would get hyperpigmentation because feedback inhibtion of cortisol does not occur.
• Hypothalmic thyrotropin-releasing hormone (TRH) leads to release of thyroid stimulating hormone (TSH) and stimulation of prolactin secretion…TSH stimulates the synthesis/secretion of thyroid hormones (T4 and T3). Prolactin promotes development of female breast/milk production
• Hypothalmic gonadotropin-releasing hormone controls release of FSH and LH…FSH causes grother of follicles in ovaries and sperm maturation. LH functions as a testosterone synthesis in testes and stimulates ovulation/formation of corpus luteum/estrogen and progesterone synthesis in ovaries
• Growth hormone-releasing hormone (GHRH)…Ghrelin (released from the stomach) also increases GH secretion. GH stimulates protein synthesis and overall growth of cells/tissues. Also produces insulin-like growth factor (IGF aka somatomedins). Has pulsatile secretory pattern (max @ deep sleep, high in adolesence)
• Growth hormone-inhibiting hormone (somatostatin)…inhibits action of GHRH
• Prolactin-inhibiting factor (dopamine)
• Posterior Pituitary: Supraoptic and paraventricular nuclei of hypothalamus send nerves that have axon endings located in the posterior pituitary. This tract is called the Hypothalamohypophysel tract.
  
  • Vasopressin (AVP aka ADH)
• Oxytocin: stimulated during breast feeding/childbirth. Infant sucks on booby  afferent signals  oxytocin release  milk let-down reflex (which can also be caused by emotional stimuli like hearing the baby’ cries)
  
  • Also have receptors on uterus during pregnancy that has a positive feedback. Distention of the cervix/cx of uterus  stimulate oxytocin release  stimulates contractility of uterus even more (Aids in childbirth)
• Milk let-down reflex = myoepithelial cells lining breast ducts contracts causing milk ejaculation

Question 4

5. Explain how hormones can be cleared form the blood. How does whether of not the hormone is free or bound to a protein carrier affect its half-life in the blood?

Answer 4

• Clearance of hormones:
  - Metabolic destruction by the tissues or by enzymes in the blood
  - Binding to the tissues
  - Excretion by the liver into bile
  - Excretion by the kidneys into urine
• Any small water soluble hormone will be filtered at the kidney glomerulus so hormones bound to plasma proteins tend to have much longer half lives in the blood.

Question 5

Describe the different types of diabetes insipidus.

Answer 5

• Neurogenic/Central Diabetes insipidus: problem is in the hypothalamus/posterior pituitary that results in an interefered production/release of AVP (ADH). Patients will produce a large amount of diluted urine.
• Nephrogenic Diabetes insipidus: caused by problem in kidneys themselves. Could be from mutationin receptor for ADH or issue with insertion of aquaporins. Patients once again have diluted urine.

Question 6

Describe the physiological functions of growth hormone including effect on bone growth.

Answer 6

• Typically promotes increased size of cells and increased number of cells through increased mitosis
• Increased rate of protein synthesis, increased release of FA from adipose tissue, decreased use of glucose  leads to an increase in glucose in blood  leads to increase in insulin secretion.
• Bone growth: long bones grow at epiphyseal cartilages until there is no more left and the growth plate closes. GH strongly stimulates osteoblasts so bones growth thicker throughout life.

Question 7

Describe the relationship between growth hormone and the insulin like growth factors. Where is each produced? What is the other name for the insulin-like growth factors?

Answer 7

GH exerts a lot of its effects through IGF aka somatomedins. Liver is main site of IGF synthesis but possibly also in local tissue affected by GH. Somatomedin C lives longer because it attaches to protein. The action on the liver by GH to create IGF is considered a tropic effect.

Question 8

Define term panhypopituitarism and describe its effect in general term

Answer 8

Condition in which the pituitary gland does not produce normal amounts of some or all of its hormones. Can be congenital or acquired.

Question 9

Describe the effect of too much or too little growth hormone. How do the effects differ if the problem is present from birth or occurs in adulthood.

Answer 9

• Giantism: too much growth hormone if happened during younger age (Acromegaly if older)
  
  • Dwarfism: too little growth hormone (could be due to just inability to create somatomedin C)

Question 10

Describe the symptoms seen in patients with acromegaly.

Answer 10

Abnormal growth of hands, feet, face.