Endocrine System

MajorHormone Secreting Structures

General Information• Integrates and coordinates activities of body

cells. • Maintains homeostasis by regulating:

1. metabolism and energy balance2. water, electrolyte & nutrient balance3. reproduction, growth and development4. mobilization of body against stressors

• Hormones are secreted into interstitial fluid diffusing into blood or lymph fluid.

• Hormones act upon specific target cells.

Regulation & Communication• Two systems for regulation:

– endocrine system • ductless glandular epithelium

– secrete hormones directly into blood– chemical travels to target tissue– target cells have receptor proteins– slow, long-lasting response

– nervous system• system of neurons

– transmits “electrical” signal & release neurotransmitters to target tissue

– fast, short-lasting response

Regulation by chemical messengers• Neurotransmitters released by neurons• Hormones release by endocrine glands

axon

endocrine gland

receptor proteins

target cell

receptor proteins

hormone carried by blood

neurotransmitter

Lock & Keysystem

Classes of Hormones• Protein-based hormones

– polypeptides• small proteins: insulin, ADH

– glycoproteins• large proteins + carbohydrate: FSH, LH

– amines• modified amino acids: epinephrine, melatonin

• Lipid-based hormones– steroids

• modified cholesterol: sex hormones, aldosterone

insulin

Steroid HormonesSteroid Hormones• Lipid soluble (hydrophobic) • Synthesized from

cholesterol• Transported by a protein in

bloodstream.• Diffuses inside, binds with

DNA to transcribe gene.• Full effect could be minutes

to days.

Animation – Intracellular Receptor Model

Protein HormonesProtein Hormones• Water soluble (hydrophilic) • Binds to receptors on target cell

membranes. No diffusion!• Causes second messengers

(cAMP) to be activated inside cell.

• Cascading effect: a single molecule can activate hundreds of second messengers each which activates thousands of reactions.

• Rapid response• Multiplier effect! Animation – Second Messenge

r cAMP

AP Biology

Benefits of a 2° messenger system

Amplification!

signal

receptor proteinActivated adenylyl cyclase

amplification

amplification

amplification

amplification

GTP G protein

product

enzyme

protein kinase

cAMP

Not yetactivated

1

2

4

35

6

7

FAST response!

amplification

Cascade multiplier!

Specificity of Hormones

• Target cells only respond to a specific hormone by having a unique receptor just for that

hormone.

• EX: Insulin receptors only respond to insulin not thyroxine.

Control of Hormone Secretion

Hormone RegulationHormone Regulation• Hormone secretion is controlled by:

1. Neural stimuli 2. Humoral stimuli (blood chemistry)3. Hormonal stimuli

• Process used to regulate:FEEDBACK LOOPS!

Homeostasis of Blood Glucose

liver

pancreas

liver

Regulation of Blood Sugar

blood sugar level(90mg/100ml)

insulin

body cells takeup sugar

from blood

liver storesglycogen

reducesappetite

glucagon

pancreas

liver releasesglucose

triggershunger

high

low

FeedbackEndocrine System Control

islets of Langerhans beta islet cells

islets of Langerhansalpha islet cells

Gland A secretes a hormone that stimulates

gland B to increase secretion of another

hormone. The hormone from gland B alters its

target cells and inhibits activity of gland A.

Target CellsTarget Cells Responsiveness can depend on:

1. Hormone concentration2. Amount of receptors a. up-regulation (increasing # of receptors)

b. down-regulation (decreasing # of receptors)

3. Influence of other hormones

Synergistic effect vs. Antagonistic effect(Glucagon + epinephrine) (Insulin and Glucagon)

Nervous & Endocrine systems linked• Hypothalamus = “master nerve control center”

– nervous system– receives information from nerves around body about

internal conditions – releasing hormones: regulates release of hormones from

pituitary

• Pituitary gland = “master gland”– endocrine system– secretes broad range

of “tropic” hormones regulating other glands in body

hypothalamus

pituitary

posterior

anterior

Hormone DisordersHormone Disorders

• Most involve the HYPOSECRETION or HYPERSECRETION of a hormone.

• Hypersecretion most likely due to a tumor on the gland.

• Few cases involve faulty hormone receptors or reduction of receptors.

Grave’s DiseaseHyperthyroidism

Symptoms:

Intolerance to heat

Heart palpitations

Sensitivity to light

Weight loss

Appetite increase

Easily agitated

Protruding eyes

Hypothyroidism or MyxedemaEarly symptoms:Being more sensitive to cold Constipation Depression Fatigue or feeling slowed down Heavier menstrual periods Joint or muscle pain Paleness or dry skin Thin, brittle hair or fingernails Weakness Weight gain (unintentional)

Late symptoms, if left untreated:Decreased taste and smell Hoarseness Puffy face, hands, and feet Slow speech Thickening of the skin Thinning of eyebrows

Cretinism – lack of thyroxine during fetal life

AP Biology

GoiterIodine deficiency causes thyroid to enlarge as it tries to produce thyroxine

thyroxines

tyrosine+

iodine ✗✗

+

Acromegaly

• hypersecretion of GH during adulthood, usually a pituitary tumor.

Only certain bony regions in face, feet and hands are affected by excessive bone deposition.

Gigantism

Hypersecretion of GH during childhoodIf left untreated, acromegaly will occur.

Pituitary Dwarfism

• Hyposecretion of GH, can be corrected by giving GH hormone

• Must be diagnosed before growth plates have closed.

• Can be tumor related

Gigantism vs. Dwarfism

Adrenal Gland DisordersCushing’s

• Excess Cortisol• Weight gain• Rounded moon face• Fatty hump on back• Fatigue

Addison’s• Hyposecretion of

glucocorticoids and mineralcorticoids

• Mouth lesions• Hypoglycemia• Strange skin

pigmentation• Salt craving

Diabetes

D. Insipidus• “tasteless”• Hyposecretion of ADH• Extreme thirst• Dehydration• Excessive urination

D. Mellitus• “Sweet tasting”• Hyposecretion of insulin

(type 1)• Blood glucose build up• Weight loss• Excessive urination• Sweet smelling breath

Adipose and Leptin• Leptin is hormone that

causes you to feel full.• Obesity may be due to no

leptin or not enough or hypothalamus becomes leptin resistant.