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 and Its Relation to the Hypothalamus
• Pituitary Gland Has Two Distinct Parts
Fig. 75.1 Pituitary gland
Pituitary Gland and Its Relation to the Hypothalamus
• Pituitary Gland
a. Anterior pituitary produces 6 important peptide
hormones (and several of lesser importance)
b. Posterior pituitary secretes two important peptide
hormones (produced in the hypothalamus)
Pituitary Gland and Its Relation to the Hypothalamus
Fig. 75.2 Metabolic functions of the anterior pituitary hormones.
ACH, adrenal corticosteroid hormones
Pituitary Gland and Its Relation to the Hypothalamus
• Control of Metabolic Functions (Anterior Pituitary)
a. Growth hormone-promotes growth of the entire body
affecting protein formation, cell growth, and cell
differentiation
b. Adrenocorticotropin-controls the secretion of some of
the adrenocorticotropical hormones, which affect the
metabolism of glucose, proteins, and fats
c. Prolactin-promotes mammary gland development
and milk production
Pituitary Gland and Its Relation to the Hypothalamus
• Control of Metabolic Functions (Anterior Pituitary)
d. Thyroid stimulating hormone-controls the rate of
secretion of thyroxine and T3 which controls the rates of
most intracellular chemical reactions
e. Follicle stimulating hormone and leutinizing hormonecontrol the growth of the ovaries and testes, as well as
their hormonal and reproductive activities
Pituitary Gland and Its Relation to the Hypothalamus
• Control of Metabolic Functions (Posterior Pituitary)
a. Antidiuretic hormone (vasopressin)-controls the rate
of water excretion in the urine
b. oxytocin-helps express milk from the mammary glands
during suckling and helps in the delivery of the baby
Pituitary Gland and Its Relation to the Hypothalamus
• Anterior Pituitary Gland Contains Different Cell
Types That Synthesize and Secrete Hormones
a.
b.
c.
d.
e.
Somatotropes-human growth hormone
Corticotropes-ACTH
Thyrotropes-TSH
Gonadotropes-LH and FSH
Lactotropes-PRL
Pituitary Gland and Its Relation to the Hypothalamus
• Hypothalamus Controls Pituitary Secretion
a. Posterior pituitary-controlled by nerve signals that
originate in the hypothalamus
b. Anterior pituitary-controlled by hormones called
hypothalamic releasing or hypothalamic inhibiting
hormones
Hypothalamus Controls Pituitary Secretion
Fig. 75.4 Hypothalamic-hypophyseal portal system
Hypothalamus Controls Pituitary Secretion
• Hypothalamic-Hypophysial Portal Blood Vessels
of the Anterior Pituitary Gland
a. Small arteries penetrate the median eminence, and
additional vessels return to the surface coalescing
to form the portal system
b. These vessels pass downward along the pituitary
stalk to supply blood to the anterior pituitary
sinuses
Hypothalamus Controls Pituitary Secretion
• Hypothalamic Releasing and Inhibitory Hormones
are Secreted into the Median Eminence
a. 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
b. The hormones are absorbed into the portal system
and carried directly to the anterior pituitary
Hypothalamus Controls Pituitary Secretion
• Hypothalamic Releasing and Inhibitory Hormones
Control Anterior Pituitary Secretion
a.
b.
c.
d.
e.
Thyrotropin releasing hormone (TRH)
Corticotropin releasing hormone (CRH)
Growth hormone releasing hormone (GHRH)
Gonadotropin releasing hormone (GnRH)
Prolactin inhibitory hormone (PIH)
Physiological Functions of Growth Hormone
• Growth Hormone Promotes Growth of Many
Body Tissues
a. GH is also called somatotropin and is a single chain
of 191 amino acids
b. Causes growth of almost all tissues
c. Promotes increased sizes of cells and increased
mitosis
d. Promotes the greater development of cells and
specific differentiation
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
Physiological Functions of Growth Hormone
• Growth Hormone Metabolic Effects
a. Promotes protein deposition in tissues
1) Enhancement of aa transport through the cell
membranes
2) Enhancement of RNA translation to cause
protein synthesis by the ribosomes
3) Increased nuclear transcription of nuclear DNA
to form RNA
4) Decreased catabolism of protein and amino acids
Physiological Functions of Growth Hormone
• Growth Hormone Metabolic Effects
b. GH enhances fat utilization for energy
1) Causes the release of fatty acids from adipose
2) Enhances the conversion of fatty acids to
acetyl coA
3) If too great a release, then ketosis can occur
Physiological Functions of Growth Hormone
• Growth Hormone Metabolic Effects
c. GH decreases carbohydrate utilization
1) Decreased glucose uptake in tissues such as
skeletal muscle and fat
2) Increased glucose production by the liver
3) Increased insulin secretion
Physiological Functions of Growth Hormone
• Growth Hormone Metabolic Effects
d. GH stimulates cartilage and bone growth
1) Increased deposition of protein chondrocytes and
osteoprogenitor cells
2) Increased rate of reproduction of these cells
3) A specific effect of converting chondrocytes into
osteogenic cells
4) Strongly stimulates osteoblasts in the periosteum
and cavities
5) Effects bone bone growth in length and width
Physiological Functions of Growth Hormone
• Growth Hormone Metabolic Effects
e. GH exerts much of its effects through intermediates
called somatomedins or insulin-like growth factors
Physiological Functions of Growth Hormone
• 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
Physiological Functions of Growth Hormone
• Abnormalities of GH Secretion
a. Dwarfism
b. Giantism
c. Acromegaly
Posterior Pituitary and Its Relation to the Hypothalamus
• Pituicytes- glial like cells that make up the posterior
pituitary
a. Pituicytes do not secrete hormones but act as
supporting structures for terminal nerve fibers and
nerve endings
b. Nerve fibers and endings contain bulbous knobs
that contain secretory granules which release two
hormones—oxytocin and vasopressin (ADH)
c. The two hormones originate in two different nuclei
of the hypothalamus
Posterior Pituitary and Its Relation to the Hypothalamus
Fig. 75.9 Hypothalamic control of the posterior pituitary
Posterior Pituitary and Its Relation to the Hypothalamus
• Physiological Functions of Antidiuretic Hormone
a. 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
b. Mechanism is probably by increased insertion of
aquaporins in the membranes (cAMP mediated)
Posterior Pituitary and Its Relation to the Hypothalamus
• Regulation of ADH Production
a. Increased ECF osmolarity stimulates ADH secretion
b. Low blood volume and low blood pressure
stimulate ADH secretion (called the vasoconstrictor
effects of ADH)
Posterior Pituitary and Its Relation to the Hypothalamus
• Oxytocic Hormone
a. Causes contraction of the pregnant uterus
b. Aids in milk ejection by the breasts