Pituitary Gland Hormones

• The pituitary gland, also called the hypophysis, is a small gland - about 1 centimeter in diameter and 0.5 to 1 gram in weight.

• It is located in the sella turcica, which is a bony cavity, at the base of the brain.

• It connects to the hypothalamus via the pituitary (or hypophysial) stalk.

• The pituitary gland is divisible into two distinct portions: the anterior pituitary, also known as the adenohypophysis, and the posterior pituitary, also known as the neurohypophysis.

• Six important peptide hormones plus several less important ones are secreted by the anterior pituitary.

• Two important peptide hormones are secreted by the posterior pituitary.

• The hormones of the anterior pituitary play major roles in the control of metabolic functions throughout the body

• The anterior pituitary gland contains several different cell types that synthesize and secrete hormones.

• Usually, there is one cell type for each major hormone formed in the anterior pituitary gland.

• With special stains attached to high-affinity antibodies that bind with the distinctive hormones, at least five cell types can be differentiated

• The different cell types dound in the the anterior pituitary gland are:

  • Somatotropes - human growth hormone (hGH)
  • Corticotropes - adrenocorticotropin (ACTH)
  • Thyrotropes - thyroid-stimulating hormone (TSH)
  • Gonadotropes - gonadotropic hormones, which include both luteinizing hormone (LH) and follicle stimulating hormone (FSH)
  • Lactotropes — prolactin (PRL)

• About 30 to 40 percent of the anterior pituitary cells are somatotropes that secrete growth hormone.

• About 20 percent are corticotropes that secrete ACTH.

• Each of the other cell types accounts for only 3 to 5 per cent of the total; nevertheless, they secrete powerful hormones.

• These hormones play a major roles in controlling thyroid function, sexual functions, and milk secretion by the breasts.

• The cell bodies that secrete the posterior pituitary hormones are not in the pituitary gland itself.

• They are large neurons, called magnocellular neurons, located in the supraoptic and paraventricular nuclei of the hypothalamus.

• The hormones are transported in the axoplasm of the neurons' nerve fibers passing from the hypothalamus to the posterior pituitary gland

• Almost all secretion by the pituitary is controlled by either hormonal or nervous signals from the hypothalamus

• Secretion by the anterior pituitary is controlled by hormones called hypothalamic releasing and hypothalamic inhibitory hormones (or factors) secreted within the hypothalamus

• These hormones are then conducted to the anterior pituitary through minute blood vessels called hypothalamic-hypophysial portal vessels.

• Secretion from the posterior pituitary is controlled by nerve signals that originate in the hypothalamus and terminate there.

• In the anterior pituitary, releasing and inhibitory hormones act on the glandular cells to control secretion.

• The hypothalamus receives signals from many sources in the nervous system.

• When a person is exposed to pain, a portion of the pain signal is transmitted into the hypothalamus.

• When a person experiences some powerful depressing or exciting thought, a portion of the signal is transmitted into the hypothalamus.

• Hypothalamic releasing and inhibitory hormones control anterior pituitary secretion

• Thyrotropin-releasing hormone (TRH) causes release of thyroid-stimulating hormone

• Corticotropin-releasing hormone (CRH) causes release of adrenocorticotropin

• Growth hormone-releasing hormone (GHRH) causes release of growth hormone, and growth hormone inhibitory hormone (GHIH) inhibits release of growth hormone

• Gonadotropin-releasing hormone (GnRH) causes release of the two gonadotropic hormones, luteinizing hormone and follicle-stimulating hormone

• Prolactin inhibitory hormone (PIH) causes inhibition of prolactin secretion

• Hormones not under control of hypothalamus and pituitary gland are:

  • Parathyroid hormone
  • Calcitonin hormone (thyroid)
  • Aldosterone H (adrenal cortex)
  • Insulin and glucagon H(pancreas)

Growth Hormone

• It promotes growth of the entire body by affecting protein formation, cell multiplication, and cell differentiation
  • Growth hormone is protein in nature and similar to prolactin.
  • It is rapidly metabolized in the liver

Effect On Growth

• Bone and cartilage growth are types of skeletal growth
• Growth hormone is mediated by somatomedin; polypeptide is secreted from the liver under effect of GH
• It mediates the action of GH on the bone, and is called sulphation factor because it incorporate sulphate into the bone
  • Somatomedin C is the most common, and is called insulin like growth factor, because it has insulin like effect in contrast to GH itself.
  • GH stimulates growth of bone in length and thickness by stimulating the widening of the epiphysial cartilage, mineralization of the bone, and deposition of calcium and sulphate in bone.
  • It stimulates soft tissue growth due to it's anabolic effect which increases bulk.
  • GH increases deposition of proteins by chondrocytes and osteogenic cells
  • GH helps increase the reproduction of bone forming cells
  • GH helps with the conversion of chondrocytic cells into osteogenic cell
• GH helps increase deposition of cartilage and then calcification at the epiphyseal cartilage which causes the bone to elongate.

Metabolic Effect of Growth Hormone

• Growth hormone is responsible for protein synthesis.

• It helps increase the transport of amino acid across the cell membrane.

  • Growth hormone helps with a positive nitrogen as well as phosphorus balance, and stimulates erythropoiesis.

• Regarding Carbohydrates:

  • Growth hormone is diabetogenic and hyperglycemic.
  • It helps stimulate gluconeogenesis, inhibit glucose uptake by the tissue through anti-insulin effects, and stimulate glucogenolysis by stimulation the alpha cells of pancreatic cell to release the glucagon.

• Regarding Fat:

  • Growth hormone is Ketogenic as well as lipolytic
  • It mobilizes fatty acids, which causes lipaemia
  • It stimulates ketone body formation by the liver and is preferentially metabolized

• Regarding electrolytes:

• Growth hormone helps increase the GIT absorption of calcium, while decreasing the excretion of sodium and potassium.

Lactogenic Effect

• Growth hormone is similar in the structure and function to prolactin.
• It increases milk production through its stimulation of the mammary glands.

Control of Growth Hormone Secretion

• It is regulated by two factors:

  • Hypothalamic control using GHRH, and GHIH and feed back control.
  • GHRH is stimulated by sleep, stress, exercise, hypoglycemia, as well as sex hormones.

• GHIH is stimulated by hyperglycemia, cortisone, and FFA

• GH is inhibited by a high blood level of GH and somatomedin

• Stimuli that increase secretion are:

  • Hypoglycemia, 2-Deoxyglucose, Exercise, Fasting, Increase in circulating levels of certain amino acids, Protein meal, Infusion of arginine and some other amino acids, Glucagon, Lysine vasopressin, Going to sleep, L-dopa and a-adrenergic agonists that penetrate the brain, Apomorphine and other dopamine receptor agonists, Estrogens and androgens, Stressful stimuli (including various psychological stresses), and Pyrogen

• Stimuli that decrease secretion are:

  • REM sleep, Glucose, Cortisol, FFA, Medroxyprogesterone, Growth hormone and IGF-I

Disorders of Growth Hormone

• Excessive GH
  • Gigantism
  • Growth of soft tissue
  • Hypogonadism
  • Hyperglycemia
• Acromegaly
• Decreased GH
  • Dwarfism
  • Loss of some Body Proteins

Gigantism

• Over production of all bones (2 meter long) before fusion of epiphyseal growth plate.

• Bones grow disproportionate with increased effect on long bones.

• Arm span is greater than height.

• Feet to pubis distance is greater than height

• soft tissue growth:

  • Viscero-megaly :spleen- cardiac.
  • muscles are strong in early stage, later on, the muscle become weak(because muscle growth doesn't go parallel to skeletal growth, which Results to muscle weakness.

• Some other features include:

  • hypogonadism
  • hyperglycemia,

• 4%of female develop lactation in absence of pregnancy.

Acromegaly

• Over production of terminal portion of the skeleton
• Disproportional growth of thickness of long bones especially small bones of hands and feet result in thick and broad hand(spade like hand) and feet.
• Continued growth of membranous bones( that have no epiphysis to unite) as skull. Jaws. And vertebrae
• This may result in ape-like face and enlarged nose
• This may cause enlarged mandibule causing broad teeth separation and thick forward protrusion.
• Enlargement of the vertebrae may result in kyphosis

Pituitary Dwarfism

• Can be causes by an organic lesion or surgical removal of the pituitary, inheritied growth hormone deficiency (autosomal recessive gene), secretion of inactive growth hormone, or due to the lack of GH (Laron Dwarfism)
• The four characters are:
• Symmetrical retardation of growth-Height doesn't exceed 120cm., rapid union of epiphysis, but ossification centers appears normal, and dentition is not delayed
• symmetrical retardation of growth of soft tissue, birth weight is normal
• mentally normal- but dwarf is emotional unstable
• sexual activity is normal

Pituitary Infantilism

• Dwarfism accompanied by hypogonadism.
• Due deficiency of both GH and gonadotropins the secondary sexual organ remain infantile, and the secondary sexual characters does not appear.

Explore the intricate connections and functions of the pituitary gland. Questions cover the relationships between the hypothalamus and pituitary, ADH deficiency, and the roles of anterior pituitary hormones like ACTH and hGH. Also covers hyperthyroidism and mammary gland development.