Lab 18: Endocrine System Notes
INTRODUCTION
Endocrine Sys- plays role in maintaining homeostasis by regulating activities of organs,
tissues, and cells
Organs
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Endocrine glands- secrete hormones directly into blood stream
o Hormones- chemical messengers
 Carried by bloodstream to their target organ, tissues, cells
 Adjust activities of these organs to match current needs of body
 Very powerful chemicals capable of altering activity of organs
o Hypersecretion- gland secretes too much hormone which causes target
to overreact
o Hyposecretion- gland secretes too little hormone which causes target to
not be active enough
o Negative feedback loops- used to adjust secretion of endocrine glands
ORGANS OF THE ENDOCRINE SYSTEM
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Include pituitary gland, thyroid gland, parathyroid gland, adrenal gland,
pancreas, pineal gland, thymus gland, ovaries, testes
Pituitary gland (hypophysis)
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Located inferior to the hypothalamus
Infundibulum- narrow stalk of tissue that connects pituitary gland to the
hypothalamus
Two lobes- anterior lobe, posterior lobe function independently of another
o Anterior lobe- adenohypophysis
 Composed of glandular tissue
 Regulated by hypothalamus
o Posterior lobe- neurohypophysis
 Composed of neurons that originate in hypothalamus
Plays important role in regulating activity of other endocrine glands
Hormones (anterior pituitary)
o Growth hormone
 Target- bones, muscles, other tissues
 Action- stimulates cell growth + division
o Adrenocorticotrophic hormone (ACTH)
 Target- adrenal cortex
 Action- stimulates release of adrenal cortex hormones
o Thyroid stimulating hormone (TSH)
 Target- thyroid gland
 Action- stimulates release of thyroid hormones
o Follicle stimulating hormone (FSH)
 Target- gonads
 Action- stimulates dev of ova and sperm
o Luteinizing hormone (LH)
 Target- gonads
 Action- stimulates secretion of sex hormones
o Prolactin (PRL)
 Target- mammary glands
 Action- stimulates milk production
o Melanocyte stimulating hormone (MSH)
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 Target- melanocytes
 Action- stimulates melanin production
Hormones (posterior pituitary)
o Antidiuretic hormone (ADH)
 Target- renal tubules
 Action- stimulates water reabsorption
o Oxytocin (OXT)
 Target- uterus, mammary glands
 Action- stimulates uterine contractions during labor, delivery and
release of milk
Thyroid and Parathyroid Glands
Thyroid gland- butterfly-shaped organ located in anterior neck
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Partially wrapped around trachea just below larynx
Thyroid follicles- spherical, composed of simple cuboidal epithelium
o Colloid- protein material that stores thyroxine and triiodothyronine
synthesized by follicular cells until it is time to be released into
bloodstream
Parafollicular cells (clear, C cells)- found in spaces b/w follicles
o Secrete calcitonin
Hormones
o Thyroxine (T4), triiodothyronine (T3)
 Secreted by- follicle cells
 Target- every cell of body
 Action- regulate O2 utilization and rate of metabolism of cells
o Calcitonin (CT)
 Secreted by- parafollicular cells
 Target- bones, kidneys
 Action- reduces blood Ca2+ levels by causing Ca2+ to be
deposited into bone and excreted by kidneys
Parathyroid gland- 4 pea-like glands found on posterior surface of thyroid gland
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Completely independent of thyroid gland
Chief cells- secrete parathyroid hormone which regulates Ca2+
Oxyphil cells- Lord knows
Hormones
o Parathyroid hormone (PTH)
 Target- bone, kidneys
 Action- raises blood Ca2+ level by causing Ca2+ to be removed
from bone and reabsorbed by kidney
Adrenal glands
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Named for location- one sits above each kidney
Connected to kidney by dense CT capsule
Function independently from the kidneys
Subdivided into two regions w different functions
o Adrenal cortex- produces corticosteroid hormones
o Inner medulla- secretes epi and norE (fight or flight) hormones
Hormones (adrenal cortex)
o Mineralocorticoids (aldosterone)
 Target- kidneys
 Action- increases renal reabsorption of Na+
o Glucocorticoids (cortisol)
 Target- most cells
 Action- affects rate of glucose metabolism
o Androgens
 Target- amount in adults is so small it barely has any effect
 Action- precursor of male and female sex hormones
Hormones (adrenal medulla)
o Epinephrine (EP)
 Target- most cells
 Action- increases cardiac activity, BP, and blood glucose levels
o Norepinephrine (NEP)
 Target- most cells
 Action- increases cardiac activity, BP, and blood glucose levels
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Zone glomerulosa- part of adrenal cortex
o Secretes mineralocorticoids
Zona fasciculata- part of adrenal cortex
o Secretes glucocorticoids
Zona reticularis- part of adrenal cortex
o Secretes androgens
Adrenal medulla- secretes epi, norE
Pancreas
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Located along greater curvature of stomach
Wide head connected to duodenum by pancreatic duct
Narrow tail tapers off on the left side of abdominal cavity
Both an endocrine and exocrine gland
Exocrine cells- arranged into pancreatic acini
 Secrete digestive enzymes + buffers into pancreatic duct that
carries them to the duodenum to aid in digestion of food in intestine
o Endocrine cells- arranged into pancreatic islets
 Secrete insulin and glucagon
Pancreatic islet- aka islets of langerhans
o Contains endocrine cells
o Appears as lighter area surrounded by darker acinar cells on a slide
o Beta cells- secrete insulin
o Alpha cells- secretes glucagon
Pancreatic acini- exocrine cells
o Composes tissue surrounding pancreatic islets
o Secretes digestive enzymes and buffers
Hormones
o Insulin
 Target- every cell of body
 Action- lowers blood glucose level by stimulating uptake of
glucose from bloodstream by cells of body
o Glucagon
 Target- liver
 Action- raises blood glucose levels by stimulating liver to break
down glycogen and release glucose into bloodstream
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Thymus gland
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Located in superior mediastinum of thoracic cavity posterior to sternum
Large in infants in children but begins to devolve in young adults and virtually
disappears in adults
Secretes thymosin
o Plays role in maturation of T lymphocytes
Pineal gland
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Part of diencephalon
Located on posterior wall of thalamus
Pinealocytes- endocrine cells that secrete melatonin hormone
o Melatonin- regulates circadian rhythm
Testes
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Male gonads- responsible for production of male gametes (sperm)
Interstitial cells- secrete testosterone
o Testosterone stimulates spermatogenesis + dev of male secondary sexual
characteristics beginning at puberty
Ovaries
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Female gonads responsible for production of female gametes (ova)
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Follicular cells- secrete estrogen
o Estrogen is responsible for preparation of endometrium to receive fertilized
ovum and dev of female secondary sexual characteristics
Corpus luteum- secretes progesterone
o Responsible for maintaining endometrium during pregnancy
ENDOCRINE PATHOLOGIES
Negative feedback loops- most common method for monitoring body’s need for
hormone
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Change in condition from status quo (set points) trigger reaction from endocrine
gland that works to move body conditions back to that point
When status quo is reached, trigger for action is gone and gland stops secreting
hormone
Ex. Reaction of pancreas to blood glucose levels
Hypersecretion disorders
o Ex. Endocrine gland tumor that secretes large amounts of hormone
regardless of what body requires
Hyposecretion disorders
o May develop if there is injury to gland from trauma or when body’s own
immune sys attacks it (autoimmune disorder)