Unit Fourteen: Endocrinology and Reproduction

1. Unit Fourteen: Endocrinology and Reproduction Chapter 75: Pituitary Hormones and Their Control by the Hypothalamus Guyton and Hall, Textbook of Medical Physiology, 12 edition

2. Pituitary Gland and Its Relation to the Hypothalamus • Pituitary Gland Has Two Distinct Parts • Anterior pituitary (adenohypophysis) • Posterior pituitary (neurohypophysis) • Between the two is the pars intermedia

3. Pituitary Gland and Its Relation to the Hypothalamus • Pituitary Gland Has Two Distinct Parts Fig. 75.1 Pituitary gland

4. Pituitary Gland and Its Relation to the Hypothalamus • Pituitary Gland • Anterior pituitary produces 6 important peptide • hormones (and several of lesser importance) • Posterior pituitary secretes two important peptide • hormones (produced in the hypothalamus)

5. Pituitary Gland and Its Relation to the Hypothalamus Fig. 75.2 Metabolic functions of the anterior pituitary hormones. ACH, adrenal corticosteroid hormones

6. Pituitary Gland and Its Relation to the Hypothalamus • Control of Metabolic Functions (Anterior Pituitary) • Growth hormone-promotes growth of the entire body • affecting protein formation, cell growth, and cell • differentiation • Adrenocorticotropin-controls the secretion of some of • the adrenocorticotropical hormones, which affect the • metabolism of glucose, proteins, and fats • Prolactin-promotes mammary gland development • and milk production

7. Pituitary Gland and Its Relation to the Hypothalamus • Control of Metabolic Functions (Anterior Pituitary) • Thyroid stimulating hormone-controls the rate of • secretion of thyroxine and T3 which controls the rates of • most intracellular chemical reactions • Follicle stimulating hormone and leutinizing hormone- • control the growth of the ovaries and testes, as well as • their hormonal and reproductive activities

8. Pituitary Gland and Its Relation to the Hypothalamus • Control of Metabolic Functions (Posterior Pituitary) • Antidiuretic hormone (vasopressin)-controls the rate • of water excretion in the urine • oxytocin-helps express milk from the mammary glands • during suckling and helps in the delivery of the baby

9. Pituitary Gland and Its Relation to the Hypothalamus • Anterior Pituitary Gland Contains Different Cell • Types That Synthesize and Secrete Hormones • Somatotropes-human growth hormone • Corticotropes-ACTH • Thyrotropes-TSH • Gonadotropes-LH and FSH • Lactotropes-PRL

10. Pituitary Gland and Its Relation to the Hypothalamus • Hypothalamus Controls Pituitary Secretion • Posterior pituitary-controlled by nerve signals that • originate in the hypothalamus • Anterior pituitary-controlled by hormones called • hypothalamic releasing or hypothalamic inhibiting • hormones

11. Hypothalamus Controls Pituitary Secretion Fig. 75.4 Hypothalamic-hypophyseal portal system

12. Hypothalamus Controls Pituitary Secretion • Hypothalamic-Hypophysial Portal Blood Vessels • of the Anterior Pituitary Gland • Small arteries penetrate the median eminence, and • additional vessels return to the surface coalescing • to form the portal system • These vessels pass downward along the pituitary • stalk to supply blood to the anterior pituitary • sinuses

13. Hypothalamus Controls Pituitary Secretion • Hypothalamic Releasing and Inhibitory Hormones • are Secreted into the Median Eminence • The endings of the neurons are special in that their • function is not to transmit signals from one neuron • to another but rather to secrete the hormones • The hormones are absorbed into the portal system • and carried directly to the anterior pituitary

14. Hypothalamus Controls Pituitary Secretion • Hypothalamic Releasing and Inhibitory Hormones • Control Anterior Pituitary Secretion • Thyrotropin releasing hormone (TRH) • Corticotropin releasing hormone (CRH) • Growth hormone releasing hormone (GHRH) • Gonadotropin releasing hormone (GnRH) • Prolactin inhibitory hormone (PIH)

15. Physiological Functions of Growth Hormone • Growth Hormone Promotes Growth of Many • Body Tissues • GH is also called somatotropin and is a single chain • of 191 amino acids • Causes growth of almost all tissues • Promotes increased sizes of cells and increased • mitosis • Promotes the greater development of cells and • specific differentiation

16. Physiological Functions of Growth Hormone • Growth Hormone Promotes Growth of Many • Body Tissues Fig. 75.5 Comparison of weight gain of a rat injected daily with GH with that of a normal littermate

17. Physiological Functions of Growth Hormone • Growth Hormone Metabolic Effects • Promotes protein deposition in tissues • Enhancement of aa transport through the cell • membranes • Enhancement of RNA translation to cause • protein synthesis by the ribosomes • Increased nuclear transcription of nuclear DNA • to form RNA • 4) Decreased catabolism of protein and amino acids

18. Physiological Functions of Growth Hormone • Growth Hormone Metabolic Effects • b. GH enhances fat utilization for energy • Causes the release of fatty acids from adipose • Enhances the conversion of fatty acids to • acetyl coA • 3) If too great a release, then ketosis can occur

19. Physiological Functions of Growth Hormone • Growth Hormone Metabolic Effects • c. GH decreases carbohydrate utilization • Decreased glucose uptake in tissues such as • skeletal muscle and fat • Increased glucose production by the liver • Increased insulin secretion

20. Physiological Functions of Growth Hormone • Growth Hormone Metabolic Effects • d. GH stimulates cartilage and bone growth • Increased deposition of protein chondrocytes and • osteoprogenitor cells • Increased rate of reproduction of these cells • A specific effect of converting chondrocytes into • osteogenic cells • Strongly stimulates osteoblasts in the periosteum • and cavities • 5) Effects bone bone growth in length and width

21. Physiological Functions of Growth Hormone • Growth Hormone Metabolic Effects • GH exerts much of its effects through intermediates • called somatomedins or insulin-like growth factors

22. Physiological Functions of Growth Hormone • Regulation of Growth Hormone Secretion

23. Physiological Functions of Growth Hormone • Abnormalities of GH Secretion • Dwarfism • Giantism • Acromegaly

24. Posterior Pituitary and Its Relation to the Hypothalamus • Pituicytes- glial like cells that make up the posterior • pituitary • Pituicytes do not secrete hormones but act as • supporting structures for terminal nerve fibers and • nerve endings • Nerve fibers and endings contain bulbous knobs • that contain secretory granules which release two • hormones—oxytocin and vasopressin (ADH) • The two hormones originate in two different nuclei • of the hypothalamus

25. Posterior Pituitary and Its Relation to the Hypothalamus Fig. 75.9 Hypothalamic control of the posterior pituitary

26. Posterior Pituitary and Its Relation to the Hypothalamus • Physiological Functions of Antidiuretic Hormone • In the presence of ADH the permeability of the • collecting ducts and tubules of the kidney to water • increases greatly and allows water to be reabsorbed, • conserving water in the body and producing very • concentrated urine • Mechanism is probably by increased insertion of • aquaporins in the membranes (cAMP mediated)

27. Posterior Pituitary and Its Relation to the Hypothalamus • Regulation of ADH Production • Increased ECF osmolarity stimulates ADH secretion • Low blood volume and low blood pressure • stimulate ADH secretion (called the vasoconstrictor • effects of ADH)

28. Posterior Pituitary and Its Relation to the Hypothalamus • Oxytocic Hormone • Causes contraction of the pregnant uterus • Aids in milk ejection by the breasts