BIO211 Weekly Guide #1
ENDOCRINE
SYSTEM
After completing this laboratory you should be able to:
1) Identify the endocrine organs in models and histological section
2) Name and chemically characterize the major hormone products of each endocrine gland
3) Identify the primary target tissues and organs of each hormone
4) Describe the cellular and systemic effects of each hormone
5) Diagram the functional control loops for each hormonal system
6) Relate each hormonal loop to the physiological, developmental, kinetic, and/or behavioral processes which it regulates
Guide to Gross Anatomy Guide to Histology Guide to Physiology
Outline
I. General Features of Endocrine Glands and Hormones {FAP 18-1, 18-2}
A. Epithelial
B. Ductless - secrete to blood
C. Hormones
chemical classes: amines, peptides, steroids, other {FAP Spotlight 18-2}
effects: metabolic, trophic, kinetic, behavioral
cellular mechanisms (2nd messenger) {FAP Spotlight 18-3, 18-4}
D. Target organs
E. Homeostasis
F. Feedback control systems:
v--------------------------------------\
1) gland hormone > target organ effect >
v----------------------------------------------------------------\
2) hypothalamus releasing hormone>anterior pituitary hormone>target organ effect >
v------------------------v-----------------------------------\
3) hypothal releas horm.>ant. pit.trophic horm.>gland hormone>target organ effect>
II. Hypophysis (Pituitary) {FAP 18-3}
A. Location - sella turcica
B. Regions
posterior lobe (neurohypophysis, pars nervosa)
anterior lobe (adenohypophysis, pars distalis)
intermediate lobe (pars intermedia - part of anterior lobe)
C. Posterior lobe
histology - neurosecretory terminals of hypothalamic nuclei
ADH (antidiuretic hormone, vasopressin)
increased water permeability in kidney collecting tubules
vasopressive action
oxytocin
contraction of smooth muscle
uterine contractions
milk ejection
D. Anterior lobe
histology - epithelial tissue from pharynx
hormones:
GH (growth hormone)
LTH (prolactin, luteotrophic hormone)
ACTH (adrenocorticotrophic hormone)
TSH (thyroid stimulating hormone)
FSH (follicle stimulating hormone)
LH (lutenizing hormone)
E. Intermediate lobe
hormone: MSH
F. Pituitary Endocrine Syndromes
pituitary dwarfism
pituitary gigantism/acromegaly
diabetes insipidis
III. Hypothalamus - Neuroendocrine Control {FAP 18-3}
A. Location - diencephalon
B. Histology - nervous tissue - nuclei and fiber tracts
C. "Head ganglion of the visceral nervous system"
D. Secretory functions
some releasing hormones (act on anterior pituitary):
CRH
PIH (dopamine)
GHRH
TRH
LHRH (GnRH)
hypophysial portal system
posterior pituitary nuclei and tracts
IV. Adrenals {FAP 18-6}
A. Location - superior to kidneys (retroperitoneal)
B. Regions:
cortex
medulla
C. Cortex
3 zones:
zona glomerulosa --> aldosterone
zona fasciculata --> cortisol, corticosterone
zona reticulata --> cortisol, corticosterone
D. Medulla
similar to giant sympathetic ganglion
epinephrine (adrenaline)
norepinephrine (noradrenaline)
E. Adrenal Endocrine Syndromes
Addison's syndrome
Cushings's syndrome
V. Thyroid {FAP 18-4}
A. Location - anterior to trachea
B. Structure
bilobed
follicles --> TH (thyroid hormone, thyroxine)
simple cuboidal epithelium
colloid - thyroglobulin
role of iodine
parafollicular "C" cells --> calcitonin
C. Thyroid Endocrine Syndromes
hypothyroidism
hyperthyroidism (Graves' disease)
goiter
VI. Parathyroids {FAP 18-5}
A. Location - typically on dorsal thyroid, but variable
B. 2 cell types:
principal cells --> parathyroid hormone (parathormone)
oxyphils (function unknown)
C. Parathyroid Endocrine Syndromes
hypocalcemia
hypercalcemea
VII. Islets of Langerhans {FAP18-8}
A. Location - "islands" scattered throughout pancreas
B. 2 principal endocrine cell types:
"B" cells --> insulin
"A" cells --> glucagon
C. Insular Endocrine Syndromes
hypoglycemia
diabetes mellitus (Type I and Type II)
VIII. Pineal Gland {FAP 18-7}
A. Location - epithalamus
B. Pinealocytes --> melatonin
C. Pineal sand (psammoma bodies, corpora arenacea)
IX. Other Organs {FAP 18-9}
A. Gonads
B. Placenta
C. Thymus
D. Liver
E. GI tract, kidney, liver, heart, blood vessels, skin, etc.
X. Systemic Physiological Control {FAP 18-10}
A. Interrelationships between hormones
B. Homeostasic regulation
C. Non-homeostatic processes
Growth
Stress
Behavior
Aging
Gross Anatomy List
Endocrine and Neuroendocrine Organs:
hypothalamus
pituitary = hypophysis
posterior lobe = neurohypophysis, pars nervosa
anterior lobe = adenohypophysis, pars adenosa
intermediate lobe = pars intermedia
pituitary stalk = infundibulum
median eminence
pineal = epithalamus
thyroid
parathyroids
adrenals - cortex and medulla
pancreas (Islets of Langerhans)
thymus
liver
ovaries
testes
Key: Know location, hormones, and target organs (for endocrine organs)
Guide to Gross Anatomy
Endocrine Organs {APL Exercise 16-1}
Endocrine organs (glands) are composed of either epithelial cells or neurosecretory cells which secrete their products (hormones) into the blood stream. Because the endocrine system is actually an interrelated set of physiological control systems, this week we will deal more with physiology than with strict anatomical detail. The basic rule for studying the endocrine system in this class is to know the following for each endocrine organ:
The location of the gland (recognize gland in models and charts)
The hormone(s) that the gland produces
The target organ(s) or tissue(s) of the hormone(s)
The effect of each hormone on each target organ or tissue
How hormonal production and release is regulated
You should be able to discuss each hormonal system starting from the gland, the hormone, the target organ, or the hormonal effects. This is what is meant by the phrase "Review the functions of the hormone(s) of the ________" used below. It will probably be helpful to draw yourself lots of flowcharts.
a) Locate the pituitary (hypophysis) and the hypothalamus in the models and in the prepared brain slices (if available). Identify the following regions of the pituitary:
{FAP Fig. 18-5 to 18-9; APL Fig 16.3}
posterior pituitary (pars nervosa, neurohypophysis)
intermediate pituitary (pars intermedia)
anterior pituitary (pars distalis, adenohypophysis)
pituitary stalk (infundibulum)
- The neurohypophysis is essentially an extension of the brain, in that it is composed of nerve terminals from hypothalamic neurons. Review the functions of oxytocin and vasopressin (ADH), the hormones of the neurohypophysis.
- The adenohypophysis develops from an epithelial pouch off of the pharynx. How does the hypothalamus regulate each of the adenohypophyseal hormones? Review the functions of the hormones of the adenohypophysis.
- The hypophyseal portal system is a specialized set of blood vessels which deliver releasing hormones from the hypothalamus to the anterior pituitary. What defines a portal system (think of the hepatic portal system also)? What is the advantage ofw a portal system for hormonal delivery?
- In what bony cradle does the pituitary rest? What cranial bone is this a part of?
b) Locate the adrenal glands in the models and the charts. Locate the suprarenal arteries and veins (if possible). {FAP Fig. 18-14; APL Fig 16.5}
- Note that the adrenal is really two glands. The cortex is composed of epithelial cells which produce the three classes of cortical steroids - the mineralocorticoids, the glucocorticoids, and the sex steroids. Review the functions of each of these hormonal types.
- The medulla is derived from embryonic neural tissue and is essentially a large modified sympathetic ganglion. It produces mostly epinephrine (adrenaline). Review the functions of this hormone.
- What is the significance of the fact that blood reaching the medulla must flow through the cortex first (essentially a portal system)?
c) Locate the thyroid in the models and charts. Review the functions of the two hormones produced by the thyroid gland, thyroxine and calcitonin. {FAP Fig. 18-10; APL Fig 16.4}
- The thyroid is much larger in the newborn than in the adult. What is the functional significance of this?
- What trace ion is incorporated by the thyroid into thyroxine? Is a constant dietary supply of this ion essential? Why or why not?
d) The parathyroids are usually described as a pair of small glands on the posterior surface of each lobe of the thyroid. In fact, parathyroid tissue may occasionally occur in other locations of the neck and superior mediastinum. Review the functions of parathormone (parathyroid hormone). {FAP Fig. 18-12; APL Fig 16.34}
- Note that the effects of parathormone on calcium and phosphate metabolism normally greatly outweigh the effects of calcitonin. What are the effects of hyperparathyroidism (overproduction)? What are the effects of hypoparathyroidism (underproduction)? What other hormone, in addition to parathormone and calcitonin, regulates calcium metabolism?
e) The islets of Langerhans are clumps of cells scattered through the pancreas. The principal endocrine products are insulin and glucagon. Review the opposing functions of these hormones on glucose metabolism. {FAP Fig. 18-16; APL Fig 16.2, 16.6}
- What is the functional significance of the fact that the pancreas empties its hormones into the hepatic portal system?
- What are the effects of insulin deficiency (diabetes mellitus) and insulin excess?
f) Locate the pineal gland in the models and brain slices (if available). It is an extension of the epithalamus of the diencephalon. Its product melatonin is involved in both seasonal and diurnal rhythms in other mammals. In humans it seems to play a major role in regulating the sleep-wake cycle. {FAP Fig. 18-15; APL Fig 16.2}
g) Most organs have at least some endocrine functions. We will deal with many of these over the remaining weeks of this couurse. Some other endocrine organs, their hormones, and actions are:
liver somatomedins growth regulation
kidney erythropoietin RBC production
thymus thymosin lymphoid tissue development
heart auriculin promotes Na+ loss in kidney
GI tract gastrin gastric motility and secretion
secretin pancreatic fluid production
CCK/pancreozymogen gall bladder contraction/pancreatic
enzyme production
Guide to Histology
Endocrine System {APL Exercise 16-2}
For each of these endocrine organs you should be able to state:
1) The location of the gland
2) The hormone(s) produced by the gland
3) The target organ(s) or tissue(s) of the hormone(s)
4) The effect of each hormone on each target organ or tissue
5) How hormonal production and release is regulated
Of course, your study of each endocrine organ should begin with learning to identify it in histological section.
a) Pituitary {FAP Fig. 18-6}
The pituitary is actually two rather distinct glands with different embryological origins, structures, and functions. The anterior pituitary (adenohypophysis, pars distalis) is densely cellular, with three interspersed populations of distinctly staining cells. The posterior pituitary (neurohypophysis, pars nervosa) is composed mostly of fibrous nerve terminals, with sparse cells.
- Distinguish the anterior and posterior pituitary in the pituitary slide(s).
- Review the hormones released from the posterior pituitary. Where are the cell bodies located whose processes form the posterior pituitary?
b) Thyroid and Parathyroid {FAP Fig. 18-10, 18-12; APL Fig 16.7}
The thyroid may be recognized by its unique follicular structure with the multi-hued colloid in the follicular lumens. The white crescents around the periphery of each colloid mass are an artifact of slide preparation, but are nonetheless fairly diagnostic. The parathyroid may be recognized by its proximity to the thyroid, or by the small clusters of orange staining oxyphil cells. Although generally concentrated in four spots adjacent to the lobes of the thyroid, parathyroid tissue can actually occur anywhere in the upper mediastinum.
- Identify the thyroid follicles, with their enclosed colloid masses. Scan the slide to locate the parathyroid tissue embedded in the thyroid's connective tissue capsule.
- Classify the epithelium of the thyroid follicles. How does this epithelium change with the state of activity of the thyroid? What is the function of the colloid (thyroglobulin)? Review the functions of thyroxine, the hormone produced by the follicles.
- Try to identify the interstitial "C" cells of the thyroid. Review the functions of their product calcitonin.
- Identify the parathyroid tissue in the slide. Review the functions of parathyroid hormone (parathormone).
c) Adrenal {FAP Fig. 18-14; APL Fig 16.8}
The adrenal is really two distinct glands; the cortex, which produces steroid hormones, and the medulla, which functions like a giant sympathetic ganglion and produces adrenalin and noradrenalin. The adrenal gland may be recognized by the three distinctly organized zones of the cortex, and the larger, pale, neuron-like cells of the medulla.
- Identify the capsule, cortex, and medulla of the adrenal gland. Try to distinguish the zona glomerulosa, zona fasciculata, and zona reticularis of the adrenal cortex. Review the principal steroid hormones produced in each region.
- Note the similarity in appearance of the medullary cells to those of sympathetic ganglia. Review the actions of adrenalin (epinephrine).
d) Pancreas {FAP Fig. 18-16; APL Fig 16.9}
The pancreas may be recognized by the densely packed islets of endocrine cells, surrounded by a much larger mass of exocrine acini.
- Identify the Islets of Langerhans, the endocrine "islands" scattered throughout the pancreas.
- Review the opposing functions of glucagon and insulin. Note that each islet produces both of these hormones, although they are produced by two different cell types.
- The pancreas provides a good opportunity to review exactly what distinguishes endocrine from exocrine glands.
e) Pineal Gland {FAP Fig. 18-15}
The pineal gland (epithalamus) is a medial structure located dorsal to the thalamus.
- The identifying histological characteristic of the pineal gland is the presence of involuted concretions called pineal sand, corpora aranacea, or psammoma bodies. Try to identify these in the slide.
f) Other Endocrine Organs
You will study some endocrine functions of other organ systems in upcoming weeks. As each organ system is introduced, you should review the origins, functions, and control of the hormones that act on that system.
Guide to Physiology
Endocrine Feedback Loops {APL Exercise 16-3}
Use the five "fill in the blank" examples in Exercise 26-3 in the laboratory text to trace the feedback control loops for blood osmolarity, blood glucose level, blood calcium level, and the stress response.
"Mystery Case" Exercises {APL Exercise 16-4}
Work in groups to complete the following "Mystery Cases" from the laboratory text:
The Cold Colonel
The Bloated Ms. Blanc
The Parched Professor
"Virtual Rat" Exercise
Work in groups to complete the handout for the "Virtual Rat" exercise (adapted by Barb Trask of Weber State University from “Laboratory Exercise Using ‘Virtual Rats’ to Teach Endocrine Physiology” by Odenweller, CM, et al., Advances in Physiology Education 273:S24-40, 1997.)
Additional Histology Resources
Remember that the following resources are available online to help you learn the histology of each organ system:
JayDoc HistoWeb A fairly inclusive library of standard histological images. Some descriptive text is included, but labeling of structural features in the photomicrographs is minimal. The emphasis is on fairly low magnification images and defining structural features of each tissue. Very little useful information on cytology.
Loyola University Medical Education Network (LUMEN) A collection of excellent, mostly high-magnification histology images, including both light and electron micrographs. The emphasis is on comparative cytology. Sample lab practical exam questions (mostly identification) are included.
Michigan State Anatomy 562 Histology Study Guide A very easy to use histological set, organized for efficient review. Each slide is accompanied by a nice descriptive paragraph.
Southern Illinois University School of Medicine (SIU SOM) A complete, self-contained online histology text. Extensive descriptions of very good histological images. The amount of material here makes finding particular topics more difficult that at many other sites, but much more information is included surrounding each image. This site also includes histology methodology, histophysiology, and histopathology.