1. The Central Endocrine Glands
Chapter 18
The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

2. Endocrine System
Consists of ductless endocrine glands scattered throughout body
Glands secrete hormones which travel through blood to target cells
Target cells have receptors for binding with specific hormone
Regulates or directs particular function
Two hormone categories based on solubility
Hydrophilic
Peptide hormones
Catecholamines
Lipophilic
Steroid hormones
Thyroid hormone
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

3. Endocrine System
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

4. Endocrine System Overall functions
Regulate organic metabolism and H2O and electrolyte balance
Induce adaptive changes to help body cope with stressful situations
Promote smooth, sequential growth and development
Control reproduction
Regulate red blood cell production
Along with autonomic nervous system, control and integrate both circulation and the digestion and absorption of food
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

5. Tropic Hormones Regulates hormone secretion by another endocrine gland
Stimulates and maintains their endocrine target tissues
Example
Thyroid-stimulating hormone (TSH) secreted from anterior pituitary stimulates thyroid hormone secretion by thyroid gland
Also maintains structural integrity of thyroid gland
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

6. Hormones
Plasma concentration of each hormone is normally controlled by regulated changes in rate of hormone secretion
Direct regulatory inputs that influence secretory output of endocrine cells
Neural input
Input from another hormone
Effective plasma concentration also influenced by
Rate of removal from blood by metabolic inactivation and excretion
Rate of activation or its extent of binding to plasma proteins
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

7. Endocrine Dysfunction
Can arise from a variety of factors
Most commonly result from abnormal plasma concentrations of a hormone caused by inappropriate rates of secretion
Hyposecretion
Too little hormone is secreted
Hypersecretion
Too much hormone is secreted
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

8. Hyposecretion Primary hyposecretion
Too little hormone is secreted due to abnormality within gland
Causes
Genetic
Dietary
Chemical or toxic
Immunologic
Other disease processes such as cancer
Iatrogenic
Idiopathic
Secondary hyposecretion
Gland is normal but too little hormone is secreted due to deficiency of its tropic hormone
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

9. Hypersecretion Causes
Tumors that ignore normal regulatory input and continuously secrete excess hormone
Immunologic factors
Primary hypersecretion
Too much hormone is secreted due to abnormality within gland
Secondary hypersecretion
Excessive stimulation from outside the gland causes oversecretion
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

10. Hormone Influence at Target Cell
Hormone can influence activity of another hormone at given target cell in one of three ways
Permissiveness
One hormone must be present in adequate amounts for full exertion of another hormone’s effect
Synergism
Occurs when actions of several hormones are complimentary
Combined effect is greater than the sum of their separate effects
Antagonism
Occurs when one hormone causes loss of another hormone’s receptors
Reduces effectiveness of second hormone
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

11. Pituitary Gland Hypophysis
Small gland located in bony cavity just below hypothalamus
Thin stalk connects pituitary gland to hypothalamus
Consists of two anatomically and functionally distinct lobes
Posterior pituitary (neurohypophysis)
Composed of nervous tissue
Anterior pituitary (adenohypophysis)
Consists of glandular epithelial tissue
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

12. Anatomy of the Pituitary Gland
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

13. Pituitary Gland
Release of hormones from both anterior and posterior pituitary is controlled by hypothalamus
Posterior pituitary
Along with hypothalamus forms neuroendocrine system
Does not actually produce any hormones
Stores and releases two small peptide hormones
Vasopressin
Conserves water during urine formation
Oxytocin
Stimulates uterine contraction during childbirth and milk ejection during breast-feeding
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

14. Relationship of the Hypothalamus and Posterior Pituitary
The paraventricular and supraoptic nuclei both contain neurons that produce vasopressin and oxytocin. The hormone, either vasopressin or oxytocin depending on the neuron, is synthesized in the neuronal cell body in the hypothalamus.
The hormone travels down the axon to be stored in the neuronal terminals within the posterior pituitary.
On excitation of the neuron, the stored hormone is released from these terminals into the systemic blood for distribution throughout the body.
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

15. Pituitary Gland Anterior pituitary
Secretes six different peptide hormones that it produces itself
Tropic hormones
Thyroid-stimulating hormone (TSH)
Stimulates secretion of thyroid hormone
Adrenocorticotropic hormone (ACTH)
Stimulates secretion of cortisol by adrenal cortex
Follicle-stimulating hormone (FSH)
In females, stimulates growth and development of ovarian follicles; promotes secretion of estrogen by ovaries
In males, required for sperm production
Luteinizing hormone (LH)
In females, responsible for ovulation and luteinization; regulates ovarian secretion of female sex hormones
In males, stimulates testosterone secretion
Growth hormone (GH)
Primary hormone responsible for regulating overall body growth; important in intermediary metabolism
Not a tropic hormone
Prolactin (PRL)
Enhances breast development and milk production in females
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

16. Pituitary Gland
Hypothalamic releasing and inhibiting hormones help regulate anterior pituitary hormone secretion
Two most important factors that regulate anterior pituitary hormone secretion
Hypothalamic hormones
Feedback by target-gland hormones
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

17. Hypothalamic Releasing and Inhibiting Hormones
Secretion of each anterior pituitary hormone is stimulated or inhibited by one or more hypothalamic hypophysiotropic hormones
Hormone
Effect on Anterior Pituitary
Thyrotropin-Releasing hormone (TRH)
Stimulates release of TSH
Corticotropin-Releasing hormone (CRH)
Stimulates release of ACTH
Gonadotropin-releasing hormone (GnRH)
Stimulates release of FSH and LH
Growth-hormone releasing hormone (GHRH)
Stimulates release of growth hormone
Growth-hormone inhibiting hormone (GHIH)
Inhibits release of growth hormone and TSH
Prolactin-releasing hormone (PRH)
Stimulates release of prolactin
Prolactin-inhibiting hormone (PIH)
Inhibits release of prolactin
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

18. Vascular Link Between the Hypothalamus and Anterior Pituitary
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

19. Endocrine Control of Growth
Growth depends on growth hormone but is influenced by other factors as well
Genetic determination of an individual’s maximum growth capacity
An adequate diet
Freedom from chronic disease and stressful environmental conditions
Normal levels of growth-influencing hormones
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

20. Growth Rate Not continuous
Factors responsible for promoting growth are not the same throughout growth period
Fetal growth
Promoted largely by hormones from placenta
GH plays no role in fetal development
Postnatal growth spurt
Displayed during first two years of life
Pubertal growth spurt
Occurs during adolescence
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

21. Normal Growth Curve
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

22. Growth Hormone
Primarily promotes growth indirectly by stimulating liver’s production of somatomedins
Primary somatomedin is insulin-like growth factor (IGF-1)
Acts directly on bone and soft tissues to bring about most growth-promoting actions
Stimulates protein synthesis, cell division, and lengthening and thickening of bones
Exerts metabolic effects not related to growth
Increases fatty acid levels in blood by enhancing breakdown of triglyceride fat stored in adipose tissue
Increases blood glucose levels by decreasing glucose uptake by muscles
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

23. Growth Hormone Abnormalities
Growth hormone deficiency
Due to pituitary defect or hypothalamic dysfunction
Hyposecretion of GH in child is one cause of dwarfism
Deficiency in adults produces relatively few symptoms
Growth hormone excess
Most often caused by tumor of GH-producing cells of anterior pituitary
Symptoms depend on age of individual when abnormal secretion begins
Gigantism
Caused by overproduction of GH in childhood before epiphyseal plates close
Acromegaly
Occurs when GH hypersecretion occurs after adolescence
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

24. Growth
Other hormones besides growth hormone are essential for normal growth
Thyroid hormone
Growth severely stunted in hypothyroid children
Hypersecretion does not cause excessive growth
Insulin
Deficiency often blocks growth
Hyperinsulinism often spurs excessive growth
Androgens
Play role in pubertal growth spurt, stimulate protein synthesis in many organs
Effects depend on presence of GH
Estrogens
Effects of estrogen on growth prior to bone maturation are not well understood poorly
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

25. Pineal Gland Tiny, pinecone-shaped structure
Located in center of brain
Secretes melatonin
Hormone of darkness
Secretion falls to low levels during light of day
Functions
Helps keep body’s circadian rhythms in synchrony with light-dark cycle
Promotes sleep
Influences reproductive activity, including onset of puberty
Acts as antioxidant to remove free radicals
Enhances immunity
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

26. Circadian Rhythms Suprachiasmatic nucleus (SCN)
Body’s master biological clock
Self-induced cyclic variations in clock protein concentrations within SCN bring about cyclic changes in neural discharge from SCN
Cycle takes about a day
Drives body’s circadian (daily) rhythms
SCN must be set daily by external cues so body’s biological rhythms are synchronized with activity levels driven by surrounding environment
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning

27. Circadian Rhythms Daily changes in light intensity
Major environmental cue used to adjust SCN master clock
Photoreceptors in retina pick up light signals and transmit them directly to SCN
SCN relays message regarding light status to pineal gland
Chapter 18 The Central Endocrine Glands Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning