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Endocrinology:. Chapter 11. Endocrine System Function. Major control and communication system Controls… body fluid composition and volume nutrient levels growth and development reproduction physiological cycles (“biological clocks”). Nervous vs. Endocrine Control.

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endocrinology

Endocrinology:

Chapter 11

endocrine system function
Endocrine System Function
  • Major control and communication system
  • Controls…
    • body fluid composition and volume
    • nutrient levels
    • growth and development
    • reproduction
    • physiological cycles (“biological clocks”)
nervous vs endocrine control
Nervous vs. Endocrine Control
  • The nervous system controls rapid, precise responses (ex. reflex)
  • The endocrine system controls activities that require long duration (ex. body growth)
    • energetically more efficient
  • Specific actions of chemical messengers are at the level of the target cell
  • These two systems interact and regulate each other
the endocrine system
The Endocrine System
  • Endocrine glands
    • Lack ducts
    • Secrete products into the interstitial fluid
  • Endocrine organs may be solely endocrine or multifunctional
major endocrine organs
Major Endocrine Organs
  • Pituitary and Hypothalamus
  • Adrenal glands (2)
  • Thyroid
  • Parathyroid glands (4)
  • Pancreas
  • Ovaries, Testes

Fig 11.1

hormones

Hormones

Chemicals that are broadcast throughout the body which induce physiological changes in specific target cells.

hormone classes
Hormone Classes
  • Amines
    • hormones derived from tyrosine and tryptophan
    • adrenal medulla hormones, thyroid hormones, pineal gland hormones
  • Peptide Hormones
    • made from polypeptide chains
    • most hormones (insulin, FSH)
  • Steroids
    • derivatives of cholesterol
    • adrenal cortex hormones, gonadal hormones

Figs 11.2,

3.25, 11.3

mechanism of action steroids thyroid hormones
Mechanism of Action:Steroids & Thyroid Hormones
  • nonpolar
    • pass directly through the cell membrane
  • bind to protein receptor in cytoplasm or in nucleus
  • protein binds to gene on DNA in the nucleus
  • stimulates expression of that gene (protein production)

Figs 11.4

and 11.6

mechanism of action peptides and most amines
Mechanism of Action: Peptides and Most Amines
  • Polar
    • cannot pass through hydrophobic lipid bilayer
  • bind to receptor proteins on cell surface
    • activation of membrane-bound enzymes
  • production of a second messenger inside the cell
    • e.g. cAMP
  • 2nd messenger activates or deactivates various enzymes

Figs. 11.8, 11.9

and 11.11

hormonal regulatory mechanisms
Hormonal Regulatory Mechanisms
  • Regulating hormone levels
    • e.g. Negative feedback
      • Change causes change in opposite direction
      • e.g. thyroxine/TSH
  • Regulating tissue response
    • e.g. down regulation
      • Decrease # of receptors on target cell with chronically elevated hormone levels

Fig 11.16

hypothalamus pituitary axis
Hypothalamus-Pituitary Axis
  • Hypothalamus
    • part of the diencephalon
    • controls release of pituitary hormones
      • Neural control of endocrine function
  • Pituitary gland
    • extends from the inferior surface of the hypothalamus
    • Two distinctive lobes (posterior and anterior)
    • Linked to hypothalamus by infidiubulum

Fig 11.12

posterior pituitary
Posterior Pituitary
  • Composed of nervous tissue
  • Neurosecretory cells produce two peptide hormones
  • Released when neurons undergo an AP

Fig 11.13

posterior pituitary hormones
Posterior Pituitary Hormones
  • ADH (Anti-Diuretic Hormone)
    • increases reabsorption of H2O by kidneys
    • induces vasoconstriction in arterioles -  BP
    • stim. by H2O deficit,  BP
  • Oxytocin
    • Uterine contraction during childbirth
    • milk letdown during breast feeding
    • male function unclear ( occurs during ejaculation)

Fig 11.13

anterior pituitary
Anterior Pituitary
  • Composed of epithelial cells
  • Different cell types secrete one of six peptide hormones

Fig 11.12

anterior pituitary hormones
Anterior Pituitary Hormones
  • TSH (Thyroid Stimulating Hormone)
    • Synthesis/ release of thyroid hormones
    • Thyroid growth
  • ACTH (Adrenocorticotrophin)
    • Activates adrenal cortex to release glucocorticoids

Fig 11.14

anterior pituitary hormones1
Anterior Pituitary Hormones
  • GH (Growth Hormone, or Somatotropin)
    • Stimulates secretion of growth factors from various tissues
    • GF’s timulate growth, protein synthesis, fat breakdown and  blood glucose levels
  • PRL (Prolactin)
    • breast development and milk production during pregnancy
    • Modulatory roles in male reproduction and ion balance

Figs 11.14,

19.18

anterior pituitary hormones2
Anterior Pituitary Hormones
  • LH (Luteinizing Hormone)
    • Females
      • ovulation, regulation of female sex hormones
      • induces corpus luteum formation after ovulation
    • Males
      • regulation of male sex hormones (androgens)

Fig 11.14

anterior pituitary hormones3
Anterior Pituitary Hormones
  • FSH (Follicle Stimulating Hormone)
    • Females
      • regulates female sex hormones, egg development
    • Males
      • Induces local mediator secretion from Sertoli cells that trigger sperm development

Fig 11.14

hypothalamal control of the anterior pituitary
Hypothalamal Control of the Anterior Pituitary
  • Hypothalamal neurons produce releasing/inhibiting hormones
    • Stimulate or inhibit secretion of hormones from the anterior pituitary
  • Released into Hypothalamo-hypophyseal portal blood vessels

Fig 11.15

hypothalamal regulatory hormones
Hypothalamal Regulatory Hormones
  • TRH (thyrotrophin-releasing hormone)
    • stimulates TSH release
  • CRH (corticotrophin-releasing hormone)
    • stimulates ACTH release
  • GHRH (growth hormone releasing hormone)
    • stimulates GH release
  • Somatostasin
    • inhibits GH release
  • PIH (prolactin inhibiting hormone)
    • inhibits prolactin release
  • GnRH (gonadotrophin-releasing hormone)
    • simulates FSH and LH release
adrenal gland
Adrenal Gland
  • Located above each kidney
  • Releases hormones in response to stress
  • Medulla hormones (amines)
    • Epinephrine & Norepinephrine- similar to effects of sympathetic NS (“flight or fight”)

Fig 11.18

adrenal gland1
Adrenal Gland
  • Cortex hormones (steroids)
    • glucocorticoids (blood glucose)
      • Cortisol – elevates blood glucose and fatty acid levels, inflammation suppression
    • mineralocorticoids (salt)
      • Aldosterone – increases K+ secretion and Na+ uptake by kidneys
    • androgens
      • (DHEA) – secondary sex character development, sexual behavior

Fig 11.18

glucocorticoid regulation
Glucocorticoid Regulation
  • Cortisol - helps body cope with stress
    • Hypothalamus releases CRH
    • Stimulates ACTH from anterior pituitary
    • Stimulates cortisol release from adrenal gland
    • Cortisol inhibits CRH release and desensitizes ant. pit. to its effects

Fig 11.20

thyroid gland
Thyroid Gland
  • Produces two groups of hormones
    • Thyroid hormones (amines)
      • Thyroxine (T4) and triiodothyronine (T3) - Increase metabolic rate and body heat production
    • Calcitonin (peptide)
      • increases bone matrix formation and Ca2+ secretion from kidneys
      • reduces blood Ca2+ levels

Fig 11.21

thyroxine regulation
Thyroxine Regulation
  • Secretion regulated by the hypothalamus-pituitary axis
    • Hypothalamus releases TRH
    • TRH stimulates ant. pituitary to release TSH
    • TSH stimulates thyroid to secrete T4
  • negative feedback of T4 onto ant. pituitary
    •  T4,  TSH release

Fig 11.16

thyroid abnormalities hyperthyroidism
Thyroid Abnormalities:Hyperthyroidism
  • Grave’s Disease
    • production of thyroid stimulating immunoglobin
      • Mimics TSH function, not subject to negative feedback regulation
      • Overproduction of thyroid hormones
    • Symptoms
      •  BMR =  body weight,  body temp
      • Hyperexcitability of nervous system
        • Restless behavior,  HR, etc.
      • Exopthalmos - bulging eyes

Fig 11.26

thyroid abnormalities hypothyroidism
Thyroid Abnormalities:Hypothyroidism
  • General symptoms
    • Decreased BMR
    •  Body temperature
    •  Weight gain
    •  Alterness (impaired CNS function)
    • Easily fatigued
thyroid abnormalities hypothyroidism1
Thyroid Abnormalities:Hypothyroidism
  • Cretinism
    • low TH production during infancy
    • Reduced growth rate (dwarfism)
    • Severe mental retardation

Fig 11.27

thyroid abnormalities hypothyroidism2
Thyroid Abnormalities:Hypothyroidism
  • Goiter Formation
    • Reduced thyroid hormone production due to iodine deficiency
    •  TSH production
    • Abnormal thyroid growth

Figs 11.24,

11.25

parathyroid glands
Parathyroid Glands
  • Four small organs located on posterior surface of the thyroid
  • Secrete parathyroid hormone (PTH)
    • promotes bone matrix breakdown
    • Reduces Ca2+ secretion in the kidneys
    • Elevates Ca2+ in blood

Figs 11.28,

11.29

pancreas
Pancreas
  • Both an endocrine organ and digestive organ
  • Endocrine cells located in Islets of Langerhans
  • Contain 2 cell types
    •  cells - secrete glucagon
    •  cells - secrete insulin
  • Important in regulating glucose levels of the blood

Fig 11.30

insulin
Insulin
  • Induces glucose uptake and utilization by cells (esp. muscle and liver)
  • Lowers blood glucose levels
    • promotes removal of glucose from blood
  • Promotes formation of glycogen
    • polymer of glucose for storage
  • Promotes conversion of glucose into fat in adipose tissue
  • Stimulates amino acid uptake by cells and protein formation
insulin regulation
Insulin Regulation
  • Blood glucose level is the major factor controlling insulin and glucagon secretion
    •  glucose → insulin → glucose
    •  glucose → insulin → glucose
  • Maintenance of blood glucose at homeostatic levels via negative feedback

Fig 11.31

glucagon
Glucagon
  • Secreted when blood glucose levels are VERY LOW
  • Increase in blood glucose:
    • Activates liver enzymes to convert glycogen into glucose
  • Stimulates breakdown of stored fat and release of fatty acids into blood
    • used as secondary energy source
  • Opposes the actions of insulin
diabetes mellitus
Diabetes Mellitus
  • Insulin deficiency or excessive tolerance
    • cells do not take up glucose
    • results in excess glucose in blood (hyperglycemia)
  • Problems
    • dehydration
      • lose excessive water from urination
      • blood volume/pressure problems
    • starvation - body cannot use glucose
      • break down of fats, formation of ketone bodies
      • metabolic acidosis
diabetes mellitus1
Diabetes Mellitus

Two types:

  • Type-I (Insulin-dependent, juvenile-onset)
    • Degeneration of b-cells
    • no endogenous insulin
    • Must give exogenous insulin
  • Type-II (non-insulin dependent, adult-onset)
    • Cells desensitized (tolerant) of diabetes
    • Often due to obesity
    • controlled by regulating dietary glucose
hypoglycemia
Hypoglycemia
  • Overproduction of insulin or hypersensitivity
  • Reactive hypoglycemia
    • -cells overproduce insulin in response to increased glucose levels
    • too much glucose driven into cells from blood
      • depressed brain function