COURTNEY LLINARES & BRENDA YIK

COURTNEY LLINARES & BRENDA YIK

Hormones and theEndocrine System

THE ENDOCRINE SYSTEM AND HORMONES

What are hormones? Molecules that are diffused throughout the body to communicate

various regulatory messages to specific target cells

What is the endocrine system? One of two major bodily communication systems (the other being

the nervous system)

TYPES OF CELLULAR COMMUNICATIONS

Intercellular communications: different ways signals are sent between animal cells

Types of intercellular communications are endocrine, paracrine, autocrine synaptic, and neuroendocrine sigaling

Extracellular communications: Pheromones

Intercellular communication by secreted molecules

Bloodvessel Response

Response

Response

Response

(a) Endocrine signaling

(b) Paracrine signaling

(c) Autocrine signaling

(d) Synaptic signaling

Neuron

Neurosecretorycell

(e) Neuroendocrine signaling

Bloodvessel

Synapse

Response

EARLY ENDOCRINE/HORMONAL SYSTEMSCNIDARIANS: HYDRA Endocrine system was not yet developed,

but evidence has shown neurohormones in effect

Contains neuropeptides that stimulate processes

EARLY HORMONES/ENDOCRINE SYSTEM ANNELIDS: NEREIS

Marine worm Long ventral nerve cord with a segmented

ganglion Produces the peptide hormone neredine, in

the ganglion (early brain)

EARLY HORMONES/ENDOCRINE SYSTEMARTHROPODS: BUTTERFLY

Has an endocrine system and hormones for molting, development, and more

A brain hormone stimulates release of ecdysone from the prothoracic glands

HORMONES/ENDOCRINE SYSTEM MAMMALS: HUMANS

Have fully developed endocrine system with a variety of functional hormones

The endocrine systems is made of eight functional glands:• Hypothalamus• Pituitary• Thyroid• Parathyroids• Thymus • Adrenals • Gonads

Major endocrine glands:

Adrenalglands

Hypothalamus

Pineal gland

Pituitary gland

Thyroid gland

Parathyroid glands

Pancreas

Kidney

Ovaries

Testes

Organs containingendocrine cells:

Thymus

Heart

Liver

Stomach

Kidney

Smallintestine

CHEMICAL CLASSES OF HORMONES Three classes of hormones: 1. Polypeptides

2. Steroids

3. Amines

Hormones vary in solubility in aqueous and lipid environments

Water soluble hormones: polypeptides and most amines Lipid soluble hormones: steroids

Hormones differ in form and solubility

Water-soluble Lipid-soluble

Steroid:Cortisol

Polypeptide:Insulin

Amine:Epinephrine

Amine:Thyroxine

0.8 nm

EFFECTS OF HORMONES

Many hormones cause more than one type of cellular response

• Example: Epinephrine triggers glycogen breakdown in the liver, increases blood flow to many skeletal muscles, and more simultaneously

• Signaling by local regulators: local regulators are molecules that send chemical signals in seconds unlike hormones, but have the same pathways as hormones

Ex: Growth factors, and nitric oxide

FEEDBACK REGULATION

In simple endocrine pathways cells responds directly to and internal or environmental stimulus by secreting certain hormones

These responses link back to deduce the initial stimulus (negative feedback) or enhance the initial stimulus (positive feedback)

Signal Transduction Pathway Example

Stimulus Low blood glucose

Pancreas alpha cells secretes glucagon Endocrine

cell

Bloodvessel

LiverTargetcells

ResponseGlycogen breakdown,glucose release into blood

Neg

ativ

e fe

edb

ack

–

ANTAGONISTIC HORMONES AND DIABETES

Insulin and glucagon are antagonistic hormones that help maintain homeostasis in blood glucose levels

Diabetes mellitus: disorder caused by insulin level or response abnormalities

Treatment involves insulin injections, lifestyle changes, or medication

COORDINATION OF ENDOCRINE AND NERVOUS SYSTEMS

Hypothalamus connects the nervous and endocrine systems

Pituitary gland receives signals from the hypothalamus for various hormone excretions

Endocrine glands in the human brain

Spinal cord

Posteriorpituitary

Cerebellum

Pinealgland

Anteriorpituitary

Hypothalamus

Pituitarygland

Hypothalamus = brain

Thalamus

Cerebrum

THYROID REGULATION

In thyroid regulation a hormone cascade pathway occurs where a hormone stimulates the release many other hormones

The last of the secreted hormones activates a nonendocrine target cell

A hormonecasadepathway

Cold

Pathway

Stimulus

Hypothalamus secretesthyrotropin-releasinghormone (TRH )

Neg

ativ

e fe

edb

ack

Example

Sensoryneuron

Neurosecretorycell

Bloodvessel

Anterior pituitary secretes thyroid-stimulatinghormone (TSHor thyrotropin )

Targetcells

Response

Body tissues

Increased cellularmetabolism

–

Thyroid gland secretes thyroid hormone (T3 and T4 )

–

Disorders of Thyroid Function Hypothyroidism occurs when there is low secretion

of thyroid hormones

-Treatment:

-Levothyroxine medication commonly used to replace lacking thyroid hormone

Disorders of Thyroid Function Continued In humans, hyperthyroidism is condition in

which thyroid gland produces excessive amount of thyroid hormone

Treatment:-Antithyroid medications-Radioactive iodine

TROPIC AND NONTROPIC HORMONES

Tropic hormones: regulate the function of other endocrine cells or glands

Examples:

-TSH (thyroid-stimulating hormones) regulate the thyroid gland

-Follicle-stimulation hormone

Growth hormones: stimulates growth through tropic and nontropic effects

PARATHYROID HORMONE AND VITAMIN D

Parathyroid glands release the parathyroid hormone (PTH)

• Maintains homeostatic control of blood calcium levels directly and indirectly

• PTH synthesizes Vitamin D in the kidneys which acts directly by activating the release of Ca² ⁺

• calcitonin is a hormone that inhibits bone absorption and enhances calcium release by the kidney

COORDINATION OF THE ENDOCRINE AND REPRODUCTIVE SYSTEM

Gonadal sex hormones: affect growth, development, reproductive cycles, and sexual behavior

-The gonads produce and secrete three major categories of steroid hormones

(androgens, estrogens, and progestins)

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