Chapter 18: The Endocrine System

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Chapter 18 The Endocrine System

• BIO 211 Lab
• Instructor Dr. Gollwitzer

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• Today in class we will
• Describe the endocrine system
• Identify the organs and tissues of the endocrine
  system and the locations, associated structures,
  hormones and the functions of those hormones
  secreted by each of those endocrine organs,
• Pineal gland
• Hypothalamus
• Pituitary gland
• Thyroid gland
• Parathyroid glands
• Discuss the hypophyseal portal system

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Endocrine System

• One of the bodys two coordination/communication
  systems
• Nervous system is the other
• Endocrine glands are ductless glands
• Communicate with other cells/organs/ systems
  through release of hormones
• Endocrine cells ? hormone (chemical messenger) ?
  interstitial fluid or circulatory system ? target
  cells ? effect(s)

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Figure 12
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Figure 12
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Endocrine Organs

• Pineal gland
• Hypothalamus
• Pituitary gland
• Thyroid gland
• Parathyroid glands
• Adrenal glands
• Pancreas
• Kidneys
• Reproductive organs (gonads and placenta)
• Other heart, thymus, adipose tissue

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• Fig 18-1

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Pineal Gland

• Location
• In posterior roof of third ventricle
  (epithalamus)
• Contains
• Neurons
• Neuroglia
• Pinealocytes (special neurosecretory cells)
• Pinealocytes ? melatonin

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Pineal Gland

• Functions of melatonin
• Time-keeping hormone, e.g., tells body its time
  for sleep
• Establishes circadian rhythms, e.g., daily
  changes in body temperature, hormone and enzyme
  levels
• Inhibits reproductive function, e.g., decreases
  at puberty
• An antioxidant may protect CNS neurons from free
  radicals
• Inhibits MSH (secreted by anterior pituitary)

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Pineal Gland
Figure 1411a
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Hypothalamus

• Location
• Floor of diencephalon, below thalamus and above
  brainstem (mesencephalon, pons, medulla
  oblongata)
• Extends from
• Area superior to optic chiasm (where optic nerves
  arrive at brain) to
• Posterior margins of mamillary bodies (nuclei in
  floor of hypothalamus control feeding reflexes)
• Infundibulum (slender stalk) connects
  hypothalamus to pituitary gland
• Area adjacent/posterior to infundibulum median
  eminence

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Hypothalamus
Figure 1410a
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3 Endocrine Regions of Hypothalamus

• Supraoptic nuclei ? antidiuretic hormone (ADH)
• Causes water retention at kidneys, increased
  blood pressure
• Transported via axons of neurosecretory cells to
  posterior pituitary for release near fenestrated
  capillaries
• Paraventricular nuclei ? oxytocin (OT)
• Stimulates smooth muscle contraction of
• Uterus, mammary glands, ductus deferens, prostate
  gland
• Transported via axons of neurosecretory cells to
  posterior pituitary for release near fenestrated
  capillaries

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3 Endocrine Regions of Hypothalamus

• Median eminence
• Swelling near attachment of infundibulum
• Where hypothalamic neurons ? regulatory hormones
  (RHs) near fenestrated capillaries
• Transported in blood to anterior pituitary via
  hypophyseal portal system
• Stimulate/inhibit cells that produce/secrete
  hormones

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Fig 18-7
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Portal System

• Blood vessels that link 2 capillary networks
• Capillaries ? veins ? capillaries ? veins ? heart
  
• vs. usual pattern
• Heart ? arteries ? capillaries in organ/tissues ?
  veins ? heart
• Examples
• Hepatic portal system
• From GI tract to liver
• Hypophyseal portal system
• From hypothalamus to anterior pituitary

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Hypophyseal Portal System

• Capillaries from median eminence unite to form
  portal vessels (veins) that travel to anterior
  pituitary capillaries
• RHs enter hypothalamic blood stream quickly due
  to fenestrated capillaries
• Portal system ensures RHs reach pituitary before
  entering general circulation

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Pituitary Gland (Hypophysis)

• Location
• In hypophyseal fossa within sella turcica of
  sphenoid
• Connected to hypothalamus by infundibulum
• Held in position by diaphragma sellae
• Divided into 2 lobes/glands
• Anterior pituitary (adenohypophysis)
• Posterior pituitary (neurohypophysis)

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Pituitary Gland (Hypophysis)
Figure 186
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Pituitary Gland Hormones
Fig 18-9
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Posterior Pituitary (Neurohypophysis, Pars
Nervosa)

• Contains axons of hypothalamic neurons
  (neurosecretory cells)
• Releases 2 peptide hormones produced in the
  hypothalamus
• ADH (antidiuretic hormone)
• OT (oxytocin)

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Anterior Pituitary(Adenohypophysis)

• Has 3 parts (pars)
• Pars distalis
• Largest, most anterior
• Produces/secretes 6 of 7 hormones (not MSH)
• Pars intermedia
• Narrow band bordering posterior pituitary
• Produces/secretes MSH
• Pars tuberalis
• Wraps around infundibulum

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Anterior Pituitary(Adenohypophysis)

• Produces and releases 7 peptide hormones
• ACTH (adrenocorticotropic hormone)
• Stimulates production/secretion of
  glucocorticoids (GCs) by adrenal gland
• TSH (thyroid-stimulating hormone)
• Triggers secretion of thyroid hormones
• GH (growth hormone)
• Stimulates tissue growth
• PRL (prolactin)
• Stimulates mammary gland development and milk
  production

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Anterior Pituitary(Adenohypophysis)

• FSH (follicle-stimulating hormone)
• A gonadotropin
• Stimulates ovarian changes, hormone production
  and egg and sperm development
• LH (luteinizing hormone, aka interstitial cell-
  stimulating hormone, ICSH)
• Another gonadotropin
• Triggers ovulation and corpus luteum (CL)
  development in females
• Hormone production in both sexes
• MSH (melanocyte-stimulating hormone)
• Stimulates melanin production by melanocytes in
  stratum germinativumm of epidermis

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Thyroid Gland

• Location
• Curves across anterior surface of trachea,
  inferior to thyroid cartilage of larynx
• Extensive blood supply gives it red color
• Consists of two lobes united by an isthmus
• Lobes filled with thyroid follicles
• Spheres formed by simple cuboidal epithelium
• Cavity contains viscous colloid (proteinaceous
  fluid)
• Surrounded by capillary network

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Thyroid Gland
Fig 18-10a
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Fig 18-10b
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Thyroid Gland Hormones

• Follicle cells
• Simple cuboidal epithelium
• ? T3 and T4
• Stimulate tissue metabolism, energy utilization,
  growth
• C (clear, parafollicular) cells
• ? Calcitonin
• Decreases serum Ca

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Parathyroid Glands

• 2 pairs of glands embedded in posterior surface
  of thyroid gland
• Contain principal (chief) cells
• ? PTH (parathyroid hormone)
• Increases serum Ca

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Parathyroid Glands
Fig 18-12a
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• Today in class we will
• Identify the following organs and tissues of the
  endocrine system and the locations, associated
  structures, hormones and the functions of those
  hormones secreted by each of those endocrine
  organs,
• Adrenal glands
• Pancreas
• Kidneys
• Reproductive organs (gonads and placenta)
• Other heart, thymus, adipose tissue

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Adrenal Glands

• aka Suprarenal glands
• Location
• On superior surface of kidneys
• 2 regions
• Adrenal cortex
• ? steroid hormones (adrenocortical steroids/
  corticosteroids)
• Adrenal medulla
• ? epinephrine and norepinephrine (E, NE)
• Under ANS control)

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Adrenal Glands
Fig 18-14a
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Fig 18-14b
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Adrenal Cortex3 Zones ? Different Hormones
Fig 18-14c
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Adrenal Cortex 3 Zones

• Zona glomerulosa
• Outer zone, under capsule
• ? mineralocorticoids, e.g., aldosterone
• Zona fasciculata
• Middle zone, largest region
• ? glucocorticoids, e.g., cortisol, cortisone
• Zona reticularis
• Inner zone, adjacent to medulla
• ? androgens, e.g., testosterone

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Pancreas

• Location
• In J-shaped loop between stomach and duodenum of
  small intestine
• Appearance
• Lumpy
• 3 parts
• Head
• Body
• Tail
• Has endocrine and exocrine functions

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Pancreas
Figure 1815
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Endocrine Pancreas

• 1 of volume
• Small groups of cells scattered among exocrine
  cells pancreatic islets (islets of Langerhans)
• Alpha cells ? glucagon ? ? blood glucose
• Beta cells ? insulin ? ? blood glucose

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Exocrine Pancreas

• 99 of volume
• Clusters of gland cells (pancreatic acini) and
  ducts
• Release enzyme-rich digestive juices into small
  intestine

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Kidneys

• Location
• On either side of vertebral column
• Produce hormones
• Calcitriol
• Stimulates calcium and phosphate ion absorption
  from digestive tract
• Erythropoietin (EPO)
• Stimulates RBC production by bone marrow

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Figure 262