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.

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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

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The Parathyroid Glands

• Most people have four• On posterior surface of thyroid

gland(sometimes embedded)

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Parathyroids(two types of

cells)• Rare chief cells• Abundant oxyphil cells

• Chief cells produce PTH o Parathyroid hormone, or

parathormoneo A small protein hormone

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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++