Endocrine Physiology

Chapter 3 Endocrine Physiology

I. Hormones
A. Overview

3. Hormones maintain homeostasis by using various feedback mechanisms.

TABLE 3-1 Hormones

Hormones Physiologic Actions Pathophysiology
Hypothalamic Hormones
Corticotropin-releasing hormone (CRH) Stimulates adrenocorticotropic hormone (ACTH) secretion from anterior pituitary Increase in adrenal insufficiency due to loss of negative feedback
Gonadotropin-releasing hormone (GnRH) Stimulates gonadotropin secretion from anterior pituitary

Thyrotropin-releasing hormone (TRH) Stimulates thyroid-stimulating hormone (TSH) secretion from anterior pituitary Decrease in primary or secondary hyperthyroidism due to feedback inhibition
Growth hormone-releasing hormone (GHRH) Stimulates growth hormone secretion from anterior pituitary Decrease in growth hormone (GH)-secreting tumor of anterior pituitary
Somatostatin Inhibits GH secretion from anterior pituitary Synthetic version (octreotide) used in GH-secreting pituitary adenomas
Dopamine Inhibits prolactin secretion from anterior pituitary

Anterior Pituitary Hormones
Adrenocorticotropic harmone (ACTH) Stimulates glucocorticoid and androgen synthesis in adrenal medulla

Thyroid stimulating harmone (TSH) Stimulates thyroid hormone synthesis in the thyroid gland

Luteinizing hormone (LH)

Follicle-stimulating hormone (FSH)

Growth hormone (GH) Anabolic hormone with multiple anabolic and insulin-antagonizing metabolic effects

Prolactin Stimulates breast maturation and milk letdown Prolactinoma: hypersecreting prolactinoma resulting in galactorrhea and infertility in women
Posterior Pituitary Hormones
Antidiuretic hormone (ADH) Stimulates water absorption from the distal nephron

Oxytocin Stimulates uterine contraction during labor  
Thyroid Hormones
Thyroxine (T4) Prohormone that becomes bioactive on peripheral conversion to T3

Triiodothyronine (T3) Increases basal metabolic rate by up-regulating expression and insertion of Na+,K+-ATPase pump
Adrenal Cortex Hormones
Aldosterone Promotes renal Na retention and expands plasma volume Hypersecreted in primary aldosteronism → hypertension with hypokalemic metabolic alkalosis
Cortisol Helps maintain glucose for glucose-dependent tissues during fasting state by promoting hepatic gluconeogenesis, peripheral resistance to insulin, and lipolysis in adipose tissue

Dehydroepiandrosterone (DHEA) Converted to testosterone in peripheral tissues Congenital adrenal hyperplasia: oversecretion of androgens results in virilization, precocious puberty, ambiguous genitalia
Adrenal Medulla Hormones

Ovarian Hormones

Testicular Hormones

Dihydrotestosterone (DHT) Development of the male external genitalia (penis, scrotum) and prostate gland

Pancreatic Hormones
Insulin Promotes peripheral uptake of glucose in nonfasting (fed) state

Glucagon Promotes hyperglycemia and insulin resistance Glucagonoma

Used to treat GH-secreting pituitary adenomas
Vasoactive-intestinal peptide (VIP)

C. Types of hormones and their individual effector mechanisms
1. Steroid hormones

3. Proteoglycan, protein, peptide, and amino acid hormones

D. Hormone-binding proteins

E. Hierarchical control of hormone secretion

II. Hormonal Control Systems of the Anterior Pituitary
A. Hypothalamic-pituitary-adrenal axis
1. Overview

3. Biosynthetic pathway of adrenal corticosteroids

5. Physiologic actions of cortisol (Fig. 3-8)
Fuel metabolism

5. Pathophysiology of the CRH-ACTH-cortisol axis
Hypercortisolism (Cushing syndrome)

e. Other causes of Cushing syndrome (Fig. 3-10) include cortisol-hypersecreting adrenal tumors and ectopic (paraneoplastic) production of ACTH by tumors (e.g., small cell lung cancer).

Hypocortisolism (adrenal insufficiency)

c. In primary adrenal insufficiency, ACTH levels should be high, whereas in secondary causes or with chronic use of steroids, ACTH levels should be low.

Jul 4, 2016 | Posted by in PHYSIOLOGY | Comments Off on Endocrine Physiology
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