Hormones and the Endocrine System

By Elizabeth Chapman, Alec Smith, and Niki Williams

Hormones and the Endocrine System

Key Points of Focus:

• Nervous system relationship

• Maintenance of homeostasis

• Types of hormones/effects on vertebrates

• Effect on invertebrates

Review and Overview

• The Endocrine System is composed of all of the body's hormone secreting cells

 • Hormones are chemical signals carried by the circulatory

system that communicate regulatory messages through the body • One hormone can elicit a variety different responses from

different target cells • There are 3 simple hormonal pathways

1.Simple endocrine2.Simple neurohormone3.Simple neuroendocrine

The Three Simple Pathways

Review of Hormonal Signaling

• Hormonal signaling occurs through the binding of a receptor protein to a target cell:

1.Water-soluble hormones bind to plasma membrane, triggering a signal transduction pathway

2. Lipid-soluble hormones bind to an intracellular receptor (Either the cytoplasm or nucleus), where it acts as a transcription factor

   

Review of Hormone Signaling

Water-Soluble Hormone

Hormone binds to receptor on plasma

membrane

Triggers signal transduction

pathway; leads to response

Lipid-Soluble Hormone

Signal-receptor complex acts as a transcription factor

Hormone binds to intracellular receptor either in the nucleus (as shown) or the cytoplasm

Anterior and Posterior Pituitary 

anterior pituitary:•  synthesizes/secretes

hormones;• four are tropic (regulate

function of other endocrine organs)

• others nontropic• growth hormone

posterior pituitary:•  stores/secretes two

hormones made by hypothalamus1. ADH2. Oxytocin

Anterior Posterior Hormones

Growth Hormones• release insulin-like growth factors which circulate in the blood

to stimulate bone/cartilage growth

• hypersecretion leads to gigantism

• hyposecretion leads to dwarfism 

Thyroid Gland

• Two lobes on trachea

• Maintain homeostasis (blood pressure, heart rate, muscle tone, and digestion)

• Affected by iodine in diet

Control of Blood GlucosePancreas:• produces bicarbonate ions and digestive enzymes• carried to small intestine via pancreatic duct

Exocrine: tissues and glands that discharge secretions into ducts

Islets of Langerhans: clusters of endocrine cells (in exocrine tissue of pancreas

Blood glucose regulated by glucagon and insulin

Glucagon• Raises Blood Glucose Levels

• From alpha cells

• Promotes liver's glycogen breakdown and release of glucose

• Only liver cells are responsive to glucagon

• Fat cells convert sugars to fats

• Skeletal muscles use released glucose  for use in exercise

COOKIES

Insulin

• Lowers Blood Glucose Levels

• From beta cells • Slows liver's glycogen breakdown

• Inhibits conversion of amino acids and glycerol to glucose 

• Promotes uptake of glucose by most somatic cells and synthesis and storage

Glucose Homeostasis (blood glucose regulation)

When blood glucose is too HIGH insulin is released to lower blood sugar concentration

When blood glucose is too LOW>glucagon is released to increase blood glucose concentration

Diabetes MellitusType 1: Insulin Dependent (usually children)• Immune system destroys pancreas's beta cells which produce insulin

Type 2: Non Insulin Dependent  (anyone, yet obese susceptible)• deficiency of insulin or reduced responsiveness of target cells from change in insulin receptors 

Calcium Homeostasis

Too much calcium:thyroid gland releases calcitonin which is deposited in bones; reduces kidney absorption

Too little calcium:parathyroid glands (on thyroid) release PTH, take calcium from bones, increase absorption from kidneys

 

   

Adrenal Hormones: Response to Stress

Adrenal Cortex: (outer)-made of true endocrine cells Adrenal Medulla: (center)made of secretory cells-secretes catecholamines

Catecholamines: act directly on target tissues for a bioenergetic boost

 

Catecholamines: Epinephrine and Norepinephrine

Positive or negative stress: catecholamines released by adrenal medulla

Epinephrine(adrenaline)- heart and metabolic rates Norepinephrine(noradrenaline) - sustains blood pressure     

Functions:    -increase rate of liver's glycogen breakdown    -promote glucose release by liver cells    -stimulate release of fatty acids from fat cells

Effects on Respiratory and Cardiovascular System    -increased rate of heart beat    -dilated bronchiloes in lungs, more oxygen to body    -smooth muscles contract, other relax, blood goes to heart brain and skeletal muscles

Steroid Hormones from Adrenal Cortex

Adrenal cortex: endocrine signals cause hypothalamus to secrete releasing hormone that stimulates anterior pituitary gland to release tropic hormone ACTH, causes release of steroids

Corticosteroids: Mineralocortecoids-act on salt/water balanceie:aldosteronestimulates kidney cells to reabsorb salt ions and water, raising blood pressure and volume

  Glucocortecoids-breakdown of muscle proteins-helps body with longterm environmental changes-anti-inflammatory, supresses immune system-carbon skeletons go to liver and kidneys, converted to glucose, released

Gonadal Sex Hormones

Androgens: (testosterone)-stimulates development of male reproductive system-can determine gender of fetus-PUBERTY

Estrogen:(estradiol)-maintenance of female reproduction system-female secondary sex characteristics

Progestins(progesterone)-prepares and maintains uterus

Melatonin and Biorhythms

Pineal gland: small mass of tissue near center of brain-sometimes has light sensitive cells  that control secretory activity-synthesizes and secretes MELATONINMelatonin regulates light/season changing /day length related functions(ie: reproduction)

Invertebrate Regulatory System- Insects

Brain Hormone: made by neurosecretory cells in brain-stimulates release of ecdysone

Ecdysone: promotes molting and development of adult characteristics Balanced out by: Juvenile Hormone: promotes larval characteristics

 

Overlap of Endocrine and Nervous Systems

• Specialized nerve cells called neurosecretory cells release hormones into the blood via the extracellular fluid

 • Some chemicals serve as both

o hormones in the endocrine systemo chemical signals in the nervous system

 • Nervous system plays a role in regulating the secretion of certain

endocrine glands in certain sustained responses like the reproductive cycles of many animals

Quick Note About Local Regulators

• Local regulators convey messages between neighboring cells- paracrine signaling

• Elicit quicker responses than long-distance endocrine signaling by hormones

• The binding of a local regulator triggers events within the target cell that are similar to those elicited by hormones

• Includes neurotransmitters, the key local • regulators of the nervous system, growth factors, • prostaglandins, and nitric oxide

Group Activity

• Get one set of notecards

• Use notecards to answer questions asked by Alec, Elizabeth, or Niki

• First person to put up the correct notecard wins a point

• Group that wins gets a random bag of stuff