General Characteristics
• Cell communication using hormones• Endocrine glands regulate body metabolism• Endocrine glands
o Lack ductso Secrete products into the interstitial fluid
Function• Maintain Internal Homeostasis • Support Cell Growth • Coordinate Development • Coordinate Reproduction • Facilitate Responses to External Stimuli
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
HormonesChemicals that are broadcast
throughout the body which induce physiological changes in specific
target cells.
Types of Receptors
Endocrine Glands
• 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
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
Thyroid Gland• Produces two groups
of hormoneso 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
Some Effects of Thyroid Hormone
• Increases the basal metabolic rateo 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 areo Protein synthesiso Bone growtho Neuronal maturationo Cell differentiation
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
The Parathyroid Glands
• Most people have four• On posterior surface of thyroid
gland(sometimes embedded)
23
Parathyroids(two types of
cells)• Rare chief cells• Abundant oxyphil cells
• Chief cells produce PTH o Parathyroid hormone, or
parathormoneo A small protein hormone
24
Function of PTH
• Increases blood Ca++ (calcium) concentration when it gets too low
• Mechanism of raising blood calcium1. Stimulates osteoclasts to release more Ca++
from bone2. Decreases secretion of Ca++ by kidney3. Activates Vitamin D, which stimulates the
uptake of Ca++ from the intestine
Adrenal Gland
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) rhythmo Complicated feedback via retina’s visual input
The PancreasExocrine and endocrine cells
• Acinar cells (forming most of the pancreas)o Exocrine functiono Secrete digestive enzymes
• Islet cells (of Langerhans)o Endocrine function
Different Types of Insulin Duration
The Gonads (testes and ovaries) main source of the steroid sex hormones
• Testeso Interstitial cells secrete androgenso Primary androgen is testosterone
• Maintains secondary sex characteristics• Helps promote sperm formation
• Ovarieso Androgens secreted by thecal folliculi
• Directly converted to estrogens by follicular granulosa cellso Granulosa cells also produce progesteroneo Corpus luteum also secretes estrogen and
progesterone
© Kenneth L. Campbell, 1997. All rights reserved.
Endocrine cells in various organs• The heart: atrial natriuretic peptide (ANP)
o Stimulates kidney to secrete more sodiumo 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, progesteroneo CRHo HCG
• The kidneyso Juxtaglomerular cells secrete renin
• Renin indirectly signals adrenal cortex to secrete aldosteroneo Erythropoietin: signals bone marrow to increase RBC production
• The skino Modified cholesterol with uv exposure becomes Vitamin D
precursoro Vitamin D necessary for calcium metabolism: signals intestine to
absorb CA++
Top Related