Physiology Lecture 22 PDF

Physiology Lecture 22 Hypothalamus and pituitary hormones, what causes what What stimulates the synthesis of growth hormone (GH)? The synthesis of growth hormone is stimulated by growth hormone-releasing hormone (GHRH) from the hy...

Physiology Lecture 22 Hypothalamus and pituitary hormones, what causes what What stimulates the synthesis of growth hormone (GH)? The synthesis of growth hormone is stimulated by growth hormone-releasing hormone (GHRH) from the hypothalamus. What is required for the formation of normal amounts of growth hormone? Thyroid hormone is required for the formation of normal amounts of growth hormone. What condition results from absent thyroid hormone, and how does it affect growth? The absence of thyroid hormone leads to Cretinism, which includes short stature as a characteristic. GH half life Physiology Lecture 22 1  short major inhibit and excite for GH IGF1 and Ghrelin What is the role of incretin (Ghrelin) in GH secretion? Incretin, specifically Ghrelin released from the gut, is a known stimulator of GH secretion, though its precise physiological function is not well understood. What role does IGF-1 play in the regulation of GH secretion? IGF-1 serves as the primary negative feedback regulator of GH secretion due to its longer half-life, aided by binding proteins. What are some stimulatory factors for GH secretion? Stimulatory factors for GH secretion include stress, hypoglycemia, amino acids (like arginine), and traumatic or psychogenic stress. picture Physiology Lecture 22 2  Multiple episodes of GH secretory activity Largest release is with early hours of sleep Diurnal rhythm Secretion persists throughout life, long after growth has stopped How do GH levels differ between children and adults? GH levels are higher in children than in adults, with a peak period during puberty. What happens to GH secretion with aging? Physiology Lecture 22 3  GH secretion declines with aging. Do adults continue to produce GH, and why? Yes, adults continue to produce GH because of its role in metabolism. What happens to GH levels during senescence? GH levels fall during senescence. Growth Hormone Actions Growth: Promotes growth of long bones. Aids in stature development. Metabolic: Stimulates production of Insulin-like Growth Factors (IGFs). Enhances lean body mass by promoting protein synthesis and fat utilization. Target Tissue Response to GH Bone Metabolism: Stimulates osteoblast activity, promoting bone formation and remodeling. Linear Growth: Encourages growth of long bones by stimulating chondrocyte proliferation at the epiphyseal plate. Adipose Tissue: Promotes lipolysis, reducing fat stores and increasing free fatty acid availability for energy. Muscle: Enhances protein synthesis, leading to increased muscle mass and strength. Physiology Lecture 22 4  to extend bone, you need both Growth Hormone (GH): Stimulates the production of insulin-like growth factors (IGFs) and promotes chondrocyte proliferation at the growth plate. Insulin-like Growth Factors (IGFs): Act directly on the growth plate to stimulate the differentiation and activity of chondrocytes, driving linear bone growth. Direct effects of GH Adipose tissue Lipolysis Release of fatty acids Most tissues Decreased glucose utilization Indirect effect of GH by IGF1 Cartilage and bone Growth Muscle and other organs Protein synthesis Growth Physiology Lecture 22 5  How are the effects of GH on stature primarily mediated? The effects of GH on stature are largely mediated by the release of somatomedin. What is the role of the liver in GH-mediated growth? The liver is a target organ for GH and releases somatomedin in response to GH. Physiology Lecture 22 6  Besides the liver, which other cell types release somatomedin in response to GH? Other cell types, such as those in bone, can also release somatomedin in response to GH. Physiology Lecture 22 7  Adult stature absolutely requires GH What causes pituitary dwarfism in childhood? lack of growth hormone (GH) during childhood. What causes Laron dwarfism, and how is it different from pituitary dwarfism? a lack of response to GH due to a GH receptor issue, unlike pituitary dwarfism, which involves GH deficiency. What characterizes gigantism? Gigantism is characterized by overproduction of GH during childhood, leading to a stature of approximately 8 feet. What is acromegaly, and how is it different from gigantism? Physiology Lecture 22 8  Acromegaly is caused by overproduction of GH in adulthood, unlike gigantism, which occurs in childhood. What role does GH play in genetic growth potential? GH acts as a facilitator of the genetic expression of growth. How much of genetic growth potential is influenced by GH? GH effects approximately ±30% of genetic growth potential. Metabolic Actions of GH Fed state (excess calories): GH is anabolic, promoting protein synthesis, cell growth, and tissue repair. Fasting state (caloric deficit): GH is catabolic, mobilizing energy by stimulating lipolysis and reducing glucose uptake to preserve blood glucose levels. What are the physiological actions of GH and IGF-1 in the fed state? In the fed state, GH and IGF-1 promote anabolic growth when nutritional status is favorable. This is represented by green arrowheads, with IGF-1 playing a major role. Physiology Lecture 22 9  What are the metabolic effects of GH during fasting? During fasting, GH mobilizes fat while sparing glucose and protein, as indicated by red arrowheads. Physiology Lecture 22 10  Prolactin Growth and Development of Mammary Gland Metabolic Plays a major role in pregnancy and post-partum lactation What hormone is secreted by lactotropes in the anterior pituitary? Lactotropes secrete prolactin (PRL). Are lactotropes part of an endocrine axis? No, lactotropes are not part of an endocrine axis. What is the normal influence of the hypothalamus on prolactin secretion? The hypothalamus normally exerts an inhibitory influence on prolactin secretion. What happens to prolactin secretion if the pituitary stalk is compromised? Physiology Lecture 22 11  If the pituitary stalk is compromised, prolactin secretion increases. What type of control mechanism regulates prolactin secretion? Prolactin secretion is regulated by a neuro-endocrine feedback loop. What is the role of oxytocin in lactation? Oxytocin is responsible for the ejection of milk from the mammary gland. What is the role of prolactin in lactation? Prolactin is responsible for the synthesis and secretion of milk. alveolus nipple When does the last stage of epithelial cell arrangement, involving the basement membrane and tight junctions, occur? after the loss of pregnancy hormones with the delivery of the placenta. When should nursing be initiated to establish lactation? Nursing must be initiated immediately to maintain exposure to high levels of prolactin (PRL) during baseline, which is necessary to establish lactation. What is required for the production of milk in the mature mammary gland? Physiology Lecture 22 12  The production of milk in the mature mammary gland depends on continued stimulation by prolactin (PRL). What is necessary for the maintenance of lactation? The maintenance of lactation requires continued secretion of prolactin (PRL) associated with suckling. suckling causes inihibition of dopamine estrogen effect prolactin increases Estrogen increases PRL, but Physiology Lecture 22 13  blocks the metabolic effects on mammary gland during pregnancy Prolactin Actions Trophic action on Breasts Milk Synthesis May act at level of hypothalamus to slow GnRH pulse generator. Decreased levels of LH, and loss of LH surge Because of its actions on breast tissues and GnRH, pathological levels of PRL (prolactinoma – most prevalent of pituitary adenomas) lead to reproductive problems Physiology Lecture 22 14