The endocrine system regulates bodily functions through hormones secreted into the bloodstream. Hormones are chemicals that induce physiological changes in target cells. The major endocrine glands include the pituitary, thyroid, parathyroid, adrenal, pancreas, gonads and pineal glands. These glands secrete hormones like thyroid hormones, insulin, estrogen and testosterone to maintain homeostasis, support growth, coordinate reproduction and facilitate responses to stimuli. Hormones bind to receptor proteins on target cells and trigger cellular responses through a series of biochemical reactions.

2. General Characteristics
• Cell communication using hormones
• Endocrine glands regulate body metabolism
• Endocrine glands
o Lack ducts
o Secrete products into the interstitial fluid

3. Function
• Maintain Internal Homeostasis
• Support Cell Growth
• Coordinate Development
• Coordinate Reproduction
• Facilitate Responses to External Stimuli

4. Elements
• Sender = Sending Cell
• Signal = Hormone
• Nondestructive Medium = Serum & Hormone
Binders
• Selective Receiver = Receptor Protein
• Transducer = Transducer Proteins & Messengers
• Amplifier = Transducer/Effector Enzymes
• Effector = Effector Proteins
• Response = Cellular Response

5. Hormones
Chemicals that are broadcast
throughout the body which induce
physiological changes in specific
target cells.

8. Types of Receptors

12. Endocrine Glands

14. • Releasing hormones from the hypothalamus control
the secretions of the anterior pituitary.
• The releasing hormones are carried in the
bloodstream directly to the anterior pituitary by
hypophyseal portal veins.

16. 16
Mechanisms of
hormone release
(a) Humoral: in response to changing
levels of ions or nutrients in the blood
(b) Neural: stimulation by nerves
(c) Hormonal: stimulation received from
other hormones

17. Thyroid Gland
• Produces two groups
of hormones
o Thyroid hormones
Thyroxine (T4) and
triiodothyronine (T3) -
Increase metabolic rate
and body heat production
o Calcitonin
o increases bone matrix
formation and Ca2+
secretion from kidneys
• reduces blood Ca2+
levels

19. Some Effects of Thyroid Hormone
• Increases the basal metabolic rate
o The rate at which the body uses oxygen to
transform nutrients (carbohydrates, fats and
proteins) into energy
• Affects many target cells throughout the
body; some effects are
o Protein synthesis
o Bone growth
o Neuronal maturation
o Cell differentiation

20. The Effects of Calcitonin
• Secreted from thyroid parafollicular (C) cells when
blood calcium levels are high
• Calcitonin lowers Ca++ by slowing the calcium-
releasing activity of osteoclasts in bone and
increasing calcium secretion by the kidney
• Acts mostly during childhood

22. 22
The Parathyroid
Glands
• Most people have four
• On posterior surface of thyroid
gland
(sometimes embedded)

23. 23
Parathyroids
(two types of cells)
• Rare chief cells
• Abundant oxyphil cells
• Chief cells produce PTH
o Parathyroid hormone, or
parathormone
o A small protein hormone

24. 24
Function of PTH
• Increases blood Ca++ (calcium)
concentration when it gets too low
• Mechanism of raising blood calcium
1. Stimulates osteoclasts to release more Ca++
from bone
2. Decreases secretion of Ca++ by kidney
3. Activates Vitamin D, which stimulates the
uptake of Ca++ from the intestine

25. Adrenal Gland

28. The Pineal Gland
• At the end of a short stalk on the roof of the
diencephalon
• Pinealocytes with dense calcium particles
• Can be seen on x-ray (because of Ca++)
• Melatonin helps regulate the circadium rhythm
o The biological clock of the diurnal (night/day) rhythm
o Complicated feedback via retina’s visual input

29. The Pancreas
Exocrine and endocrine cells
• Acinar cells (forming most of the pancreas)
o Exocrine function
o Secrete digestive enzymes
• Islet cells (of Langerhans)
o Endocrine function

33. Different Types of Insulin Duration

36. The Gonads (testes and ovaries)
main source of the steroid sex hormones
• Testes
o Interstitial cells secrete androgens
o Primary androgen is testosterone
• Maintains secondary sex characteristics
• Helps promote sperm formation
• Ovaries
o Androgens secreted by thecal folliculi
• Directly converted to estrogens by follicular granulosa cells
o Granulosa cells also produce progesterone
o Corpus luteum also secretes estrogen and
progesterone

39. © Kenneth L. Campbell, 1997. All rights reserved.

40. Endocrine cells in various organs
• The heart: atrial natriuretic peptide (ANP)
o Stimulates kidney to secrete more sodium
o Thereby decreases excess blood volume, high BP and high blood
sodium concentration
• GI tract & derivatives: Diffuse neuroendocrine system (DNES)
• The placenta secretes steroid and protein hormones
o Estrogens, progesterone
o CRH
o HCG
• The kidneys
o Juxtaglomerular cells secrete renin
• Renin indirectly signals adrenal cortex to secrete aldosterone
o Erythropoietin: signals bone marrow to increase RBC production
• The skin
o Modified cholesterol with uv exposure becomes Vitamin D precursor
o Vitamin D necessary for calcium metabolism: signals intestine to
absorb CA++