Chapter 13
Endocrine System
• Endocrine glands
are ductless
• Exocrine glands
have ducts
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Endocrine System
• composed of cells, tissues and organs that secrete
substances into the internal environment
•Hormones - chemicals secreted by the endocrine
system that diffuses from the interstitial fluid into
the bloodstream and eventually act on target cells
2
Endocrine System Functions
•Endocrine glands and their hormones:
•help regulate metabolic processes
•control the rate of certain chemical reactions
•aid in transporting substances through
membranes
•help regulate water balance, electrolyte balance
and blood pressure
•play vital roles in reproduction, development and
growth
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1
Gland Secretions
Paracrine secretions
Endocrine secretions
• act locally
• release hormones
• affect only neighboring cells
• hormones travel
through blood to target
cells
Autocrine secretions
• affect only the secreting cell
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Comparison of Nervous System
and Endocrine System
• Neurons release
neurotransmitters into
a synapse, affecting
postsynaptic cells
• Glands release
hormones into the
bloodstream
• Only target cells of
hormone responds
5
Comparison of Nervous System
and Endocrine System
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2
Chemistry of Hormones
Steroid or Steroid-Like
Hormones
• lipids that include
complex rings of C
and H atoms derived
from cholesterol
• sex hormones
• adrenal cortex
hormones
Nonsteroid Hormones
• amines
• proteins
• peptides
• glycoproteins
• most hormones
7
Actions of Steroid Hormones
• hormone crosses membranes
• hormone combines with
receptor in nucleus
• synthesis of mRNA
activated
• mRNA enters cytoplasm to
direct synthesis of protein
8
Actions of
Non-steroid Hormones
• hormone binds to receptor on cell
membrane
• adenylate cyclase activated
• ATP converted to cAMP
• cAMP promotes a series of
reactions leading to cellular
changes
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3
Prostaglandins
• paracrine substances
• act locally
• very potent in small amounts
• regulate cellular responses to hormones
• can activate or inhibit adenylate cyclase
• controls cAMP production
• alters cell’s response to hormones
• wide variety of functions
10
Control of Hormonal
Secretions
• primarily controlled by negative feedback mechanism
Tropic hormones
Nervous system
humoral
11
Major Endocrine Glands
12
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13
Pituitary Gland
Attached to the hypothalamus by the infundibulum
Two distinct portions
• anterior pituitary
(adenohypophysis)
• posterior pituitary
(neurohypophysis)
14
Pituitary Gland Control
• Hypothalamic releasing hormones stimulate cells of anterior
pituitary to release hormones
• Nerve impulses from hypothalamus stimulate nerve endings
in the posterior pituitary gland to release hormones
15
5
Hypothalamic Hormones
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Hormones of the Pituitary Gland
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Clinical Application
Growth Hormone Ups and Downs
• Gigantism - hypersecretion of GH in children
• Acromegaly – hypersecretion of GH in adults
• Dwarfism – hyposecretion of GH in children
Figure shows oversecretion of GH in adulthood as changes occur in the
same person at ages (a) nine, (b) sixteen, (c) thirty-three, and (4) fifty-two
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6
Thyroid Gland
• Made up of two lobes
connected by an isthmus
• stucture
• Connective tissue
capsule covers gland
• secretory parts are
called follicles
• Extra follicular cells
are cells outside the
follicle that also
secrete hormones
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Thyroid Gland Hormones
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Disorders of the Thyroid Gland
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7
Disorders of the Thyroid Gland
Graves Disease
• Hyperthyroidism
Cretinism
• Infantile hypothyroidism
22
Parathyroid Glands
•Located on the
posterior side of the
thyroid gland
23
Parathyroid Hormone
• secrete parathyroid hormone (PTH) or
parathormone
• increases blood calcium concentration and
decreases blood potassium concentration
through action in the bones, kidneys and
intestines
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8
Disorders of the Parathyroid
Glands
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Adrenal Glands
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Hormones of the Adrenal Medulla
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9
Hormones of the Adrenal Cortex
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Pancreas
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Hormones of the Pancreatic Islets
30
10
Other Endocrine Glands
Pineal Gland
• located deep between the cerebral hemispheres
• secretes melatonin
• regulates circadian rhythms
Thymus Gland
• located above the heart
•Shinks with age
• secretes thymosins
• promotes development of certain lymphocytes
• important in role of immunity
31
Other Endocrine Glands
Reproductive
• ovaries produce estrogens and progesterone
• testes produce testosterone
• placenta produces estrogens, progesterone, and
gonadotropins
32
Life-Span Changes
• endocrine glands decrease in size
• muscular strength decreases as GH levels decrease
• ADH levels increase due to slower break down in liver
and kidneys
• calcitonin levels decrease; increase risk of osteoporosis
• PTH level changes contribute to risk of osteoporosis
• insulin resistance may develop
• changes in melatonin secretion affect the body clock
• thymosin production declines increasing risk of
infections
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