chapter 75: pituitary hormones and their control by the hypothalamus guyton and hall, textbook of...

Unit Fourteen: Endocrinology and

Reproduction

Chapter 75: Pituitary Hormones and Their

Control by the Hypothalamus

Guyton and Hall, Textbook of Medical Physiology, 12 edition

Pituitary Gland and Its Relation to the Hypothalamus

• Pituitary Gland Has Two Distinct Parts

a. Anterior pituitary (adenohypophysis)

b. Posterior pituitary (neurohypophysis)

c. Between the two is the pars intermedia


• Pituitary Gland Has Two Distinct Parts

Fig. 75.1 Pituitary gland


• Pituitary Gland

a. Anterior pituitary produces 6 important peptide hormones (and several of lesser importance)

b. Posterior pituitary secretes two important peptidehormones (produced in the hypothalamus)


Fig. 75.2 Metabolic functions of the anterior pituitary hormones. ACH, adrenal corticosteroid hormones


• Control of Metabolic Functions (Anterior Pituitary)

a. Growth hormone-promotes growth of the entire body affecting protein formation, cell growth, and celldifferentiation

b. Adrenocorticotropin-controls the secretion of some ofthe adrenocorticotropical hormones, which affect themetabolism of glucose, proteins, and fats

c. Prolactin-promotes mammary gland developmentand milk production


• Control of Metabolic Functions (Anterior Pituitary)

d. Thyroid stimulating hormone-controls the rate of secretion of thyroxine and T3 which controls the rates ofmost intracellular chemical reactions

e. Follicle stimulating hormone and leutinizing hormone-control the growth of the ovaries and testes, as well astheir hormonal and reproductive activities


• Control of Metabolic Functions (Posterior Pituitary)

a. Antidiuretic hormone (vasopressin)-controls the rateof water excretion in the urine

b. oxytocin-helps express milk from the mammary glandsduring suckling and helps in the delivery of the baby


• Anterior Pituitary Gland Contains Different CellTypes That Synthesize and Secrete Hormones

a. Somatotropes-human growth hormoneb. Corticotropes-ACTHc. Thyrotropes-TSHd. Gonadotropes-LH and FSHe. Lactotropes-PRL


• Hypothalamus Controls Pituitary Secretion

a. Posterior pituitary-controlled by nerve signals thatoriginate in the hypothalamus

b. Anterior pituitary-controlled by hormones calledhypothalamic releasing or hypothalamic inhibitinghormones

Hypothalamus Controls Pituitary Secretion

Fig. 75.4 Hypothalamic-hypophyseal portal system


• Hypothalamic-Hypophysial Portal Blood Vesselsof the Anterior Pituitary Gland

a. Small arteries penetrate the median eminence, andadditional vessels return to the surface coalescingto form the portal system

b. These vessels pass downward along the pituitary stalk to supply blood to the anterior pituitary sinuses


• Hypothalamic Releasing and Inhibitory Hormonesare Secreted into the Median Eminence

a. The endings of the neurons are special in that theirfunction is not to transmit signals from one neuronto another but rather to secrete the hormones

b. The hormones are absorbed into the portal systemand carried directly to the anterior pituitary


• Hypothalamic Releasing and Inhibitory HormonesControl Anterior Pituitary Secretion

a. Thyrotropin releasing hormone (TRH)b. Corticotropin releasing hormone (CRH)c. Growth hormone releasing hormone (GHRH)d. Gonadotropin releasing hormone (GnRH)e. Prolactin inhibitory hormone (PIH)

Physiological Functions of Growth Hormone

• Growth Hormone Promotes Growth of ManyBody Tissues

a. GH is also called somatotropin and is a single chainof 191 amino acids

b. Causes growth of almost all tissuesc. Promotes increased sizes of cells and increased

mitosisd. Promotes the greater development of cells and

specific differentiation


• Growth Hormone Promotes Growth of ManyBody Tissues

Fig. 75.5 Comparison of weight gain of a rat injected daily with GH with that of a normal littermate


• Growth Hormone Metabolic Effects

a. Promotes protein deposition in tissues

1) Enhancement of aa transport through the cellmembranes

2) Enhancement of RNA translation to cause protein synthesis by the ribosomes

3) Increased nuclear transcription of nuclear DNAto form RNA

4) Decreased catabolism of protein and amino acids



b. GH enhances fat utilization for energy

1) Causes the release of fatty acids from adipose2) Enhances the conversion of fatty acids to

acetyl coA3) If too great a release, then ketosis can occur



c. GH decreases carbohydrate utilization

1) Decreased glucose uptake in tissues such as skeletal muscle and fat

2) Increased glucose production by the liver3) Increased insulin secretion



d. GH stimulates cartilage and bone growth

1) Increased deposition of protein chondrocytes andosteoprogenitor cells

2) Increased rate of reproduction of these cells3) A specific effect of converting chondrocytes into

osteogenic cells4) Strongly stimulates osteoblasts in the periosteum

and cavities5) Effects bone bone growth in length and width



e. GH exerts much of its effects through intermediatescalled somatomedins or insulin-like growth factors


• Regulation of Growth Hormone Secretion

Stimulate GH Secretion Inhibit GH Secretion

Decreased blood glucose Increased blood glucose

Decreased blood free fatty acids

Increased blood free fatty acids

Increased blood amino acids (Arg)

Aging

Starvation, fasting, protein deficiency

Obesity

Trauma, stress, excitement GHIH (somatostatin)

Exercise Growth hormone (exogenous)

Testosterone, estrogen Somatomedins (insulin-like growth factors)

Deep sleep (stages II and IV)

GHRH

Ghrelin


• Abnormalities of GH Secretion

a. Dwarfismb. Giantismc. Acromegaly

Posterior Pituitary and Its Relation to the Hypothalamus

• Pituicytes- glial like cells that make up the posteriorpituitary

a. Pituicytes do not secrete hormones but act as supporting structures for terminal nerve fibers andnerve endings

b. Nerve fibers and endings contain bulbous knobsthat contain secretory granules which release twohormones—oxytocin and vasopressin (ADH)

c. The two hormones originate in two different nucleiof the hypothalamus


Fig. 75.9 Hypothalamic control of the posterior pituitary


• Physiological Functions of Antidiuretic Hormone

a. In the presence of ADH the permeability of the collecting ducts and tubules of the kidney to waterincreases greatly and allows water to be reabsorbed,conserving water in the body and producing veryconcentrated urine

b. Mechanism is probably by increased insertion ofaquaporins in the membranes (cAMP mediated)


• Regulation of ADH Production

a. Increased ECF osmolarity stimulates ADH secretion

b. Low blood volume and low blood pressurestimulate ADH secretion (called the vasoconstrictoreffects of ADH)


• Oxytocic Hormone

a. Causes contraction of the pregnant uterus

b. Aids in milk ejection by the breasts

chapter 75: pituitary hormones and their control by the hypothalamus guyton and hall, textbook of...

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