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BIOL 2304
The Endocrine System
Endocrine System
Includes all cells and endocrine tissues that produce hormones or paracrine factors
Endocrine vs Nervous System
Nervous system performs short term crisis management
Endocrine system regulates long term ongoing metabolic
Endocrine communication is carried out by endocrine cells releasing hormones
Alter metabolic activities of tissues and organs
Target cells
Paracrine communication involves chemical messengers between cells within one tissue
Control of Endocrine Activity
Endocrine reflexes are the counterparts of
neural reflexes
Hypothalamus regulates the activity of the
nervous and endocrine systems
Secreting regulatory hormones that
control the anterior pituitary gland
Releasing hormones at the posterior
pituitary gland
Exerts direct neural control over the
endocrine cells of the adrenal
medullae
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Hypothalamic Control of Adenohypophysis
Hypothalamus regulates secretion of hormones
Secretes releasing factors to release hormones
Secretes inhibiting hormones to turn off secretion of hormones
The Hypothalamus
The hypothalamus sends a chemical stimulus to the anterior pituitary to releasing hormones stimulate the
synthesis and release of hormones
TRH - Thyrotropin releasing hormone (TRH) >> release of TSH
CRH - Corticotropin releasing hormone (CRH) >> release of ACTH
GnRH - Gonadotropin releasing hormone (GNRH) >> release of FSH and LH
GHRH - Growth hormone releasing hormone >> release of GH
PRH - Prolactin releasing hormone >> release of PH
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Hypothalamic Stimulation–from CNS
The Pituitary Gland – Hypophysis
Attached to the hypothalamus by the infundibulum
Two basic divisions of the pituitary gland
Anterior pituitary or Adenohypophysis
Posterior pituitary or Neurohypophysis
The Pituitary Gland – Hypophysis
Releases nine important peptide hormones
All nine bind to membrane receptors and use cyclic
AMP as a second messenger
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Anterior Pituitary
Pars distalis - largest division of the adenohypophysis
Contains five different types of endocrine cells
Somatotropic cells -secrete growth hormone (GH)
Mammotropic cells - secrete prolactin (PRL)
Thyrotropic cells - secrete thyroid-stimulating hormone (TSH)
Corticotropic cells - secrete adrenocorticotropic hormone (ACTH) and melanocyte-stimulating
hormone (MSH)
Gonadotropic cells - secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH)
Tropic hormones
TSH, ACTH, FSH, and LH
Regulate the secretion of hormones by other endocrine glands
Hormones of the Adenohypophysis
Thyroid stimulating hormone (TSH) triggers the release of thyroid hormones (T3 & T4) from thyroid gland
Thyrotropin releasing hormone from Hypothalamus promotes the release of TSH
Adrenocorticotropic hormone (ACTH) stimulates the release of glucocorticoids by the adrenal gland
Corticotropin releasing hormone from Hypothalamus causes the secretion of ACTH
Follicle stimulating hormone (FSH) – stimulates follicle development and estrogen secretion in females and
sperm production in males
Luteinizing hormone (LH) causes ovulation and progestin production in females and androgen production in
males
Gonadotropin releasing hormone (GNRH) from Hypothalamus promotes the release of FSH and LH
Prolactin (PH) – stimulates the development of mammary glands and milk production
Prolactin releasing hormone from Hypothalamus promotes the release of PH
Growth hormone (GH or somatotropin) – stimulates cell growth and replication
Growth hormone releasing hormone from Hypothalamus promotes the release of FSH and LH
Melanocyte stimulating hormone (MSH) – stimulates melanocytes to produce melanin
Posterior Pituitary
Structurally part of the brain
Contains axons of hypothalamic nerves where
hormones are manufactured
Releases antidiuretic hormone (ADH)
Decreases the amount of water lost at
the kidneys
Elevates blood pressure
Releases oxytocin
Stimulates contractile cells in mammary
glands
Stimulates smooth muscle cells in
uterus
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Feedback Control of Endocrine Secretion
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Negative Feedback Controls: Long & Short Loop Reflexes
Negative Feedback Controls: Long & Short Loop Reflexes
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Thyroid
Lies near the thyroid cartilage of the larynx
Thyroid Follicles and Thyroid Hormones
Thyroid gland contains numerous follicles
Release several hormones such as thyroxine (T4) and triiodothyronine (T3) that regulate metabolism
increases protein synthesis
promotes glycolysis, gluconeogenesis, glucose uptake
C cells produce calcitonin - helps regulate calcium concentration in body fluids
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The Thyroid Follicles
Thyroid hormones
Held in storage
Bound to mitochondria, thereby increasing ATP production
Bound to receptors activating genes that control energy utilization
Exert a calorigenic effect
C cells produce calcitonin - helps regulate calcium concentration in body fluids
Four Parathyroid Glands
Embedded in the posterior surface of the thyroid gland
Chief cells produce parathyroid hormone (PTH) in response to lower than normal calcium concentrations
Parathyroid hormones are regulators of calcium levels in healthy adults
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Homeostatic Regulation of Calcium Ion Concentrations
Adrenal Cortex
Synthesizes and releases steroid hormones called corticosteroids
Different corticosteroids are produced in each of the three layers:
Zona glomerulosa – mineralocorticoids (chiefly aldosterone)
Zona fasciculata – glucocorticoids (chiefly cortisol)
Zona reticularis – gonadocorticoids (chiefly androgens)
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Adrenal Cortex
Secretes over 30 different steroid hormones (corticosteroids):
Mineralocorticoids
Aldosterone – maintains electrolyte balance
Glucocorticoids
Cortisol:
Stimulates gluconeogenesis
Mobilization of free fatty acids
Glucose sparing
Anti-inflammatory agent
Gonadocorticoids
Testosterone, estrogen, & progesterone
Mineralocorticoids
Regulate the electrolyte concentrations of extracellular fluids
Aldosterone – most important mineralocorticoid
Maintains Na+ balance by reducing excretion of sodium from the body
Stimulates reabsorption of Na+ by the kidneys
Aldosterone secretion is stimulated by:
Rising blood levels of K+
Low blood Na+
Decreasing blood volume or pressure
Glucocorticoids (Cortisol)
Help the body resist stress by:
Keeping blood sugar levels relatively constant
Maintaining blood volume and preventing water shift into tissue
Cortisol provokes:
Gluconeogenesis (formation of glucose from non-carbohydrates)
Rises in blood glucose, fatty acids, and amino acids
Gonadocorticoids (Sex Hormones)
Most gonadocorticoids secreted are androgens (male sex hormones), and the most important one is
testosterone
Androgens contribute to:
The onset of puberty
The appearance of secondary sex characteristics
Sex drive in females
Androgens can be converted into estrogens after menopause
Pancreatic Islets
Clusters of endocrine cells within the pancreas called Islets of Langerhans or pancreatic islets
Alpha cells secrete glucagons
Beta cells secrete insulin
Delta cells secrete GH-IH
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Insulin and Glucagon
Insulin lowers blood glucose by increasing the rate of glucose uptake and utilization
Glucagon raises blood glucose by increasing the rates of glycogen breakdown and glucose manufacture by the
liver
Regulation of Blood Glucose Concentrations
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