Unit Fourteen: Endocrinology and Reproduction

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Unit Fourteen Endocrinology and Reproduction

• Chapter 75 Pituitary Hormones and Their
• Control by the Hypothalamus

Guyton and Hall, Textbook of Medical Physiology,
12 edition
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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

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Pituitary Gland and Its Relation to the
Hypothalamus

• Pituitary Gland Has Two Distinct Parts

Fig. 75.1 Pituitary gland
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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)

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

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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

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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

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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

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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

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

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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

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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)

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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

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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
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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

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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

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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

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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

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Physiological Functions of Growth Hormone

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

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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
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Physiological Functions of Growth Hormone

• Abnormalities of GH Secretion
• Dwarfism
• Giantism
• Acromegaly

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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
• hormonesoxytocin and vasopressin (ADH)
• The two hormones originate in two different
  nuclei
• of the hypothalamus

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

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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)

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Posterior Pituitary and Its Relation to the
Hypothalamus

• Oxytocic Hormone
• Causes contraction of the pregnant uterus
• Aids in milk ejection by the breasts