The Endocrine System

Around age 12, as they enter puberty, boys and girls start to develop striking differences in physical appearance and behavior. Chemical messages originating from the brain and pituitary gland markedly increase the synthesis of new messenger molecules, the sex hormones, from the gonads. In girls, fatty tissue starts to accumulate in the breasts and hips. In boys, muscle mass builds and they develop a deeper voice. These changes provide just a few examples of the powerful influence of secretions from endocrine glands.

Contents:1. Endocrine Glands:

a)Hypothalamusg) Ovary

b)Pituitaryh) Testes

c)Thyroidi) Pineal

d)Parathyroidj) Thymus

e)Adrenalk) Heart

f)Pancreasl) Kidney

Functions:

  1. Maintain homeostasis in body fluids
  2. Salt balance, glucose balance, calcium balance
  1. Regulate metabolic rate
  2. Rate of protein synthesis
  3. Rate of bone modeling
  1. Regulate growth and onset of puberty and menopause

4. Regulate gametogenesis

5.Regulate pregnancy, childbirth and milk production

1

  1. Endocrine glands vs. exocrine glands

All glands of the body derive from embryonic extoderm

exocrine:

Glands secrete into a duct  onto surface of skin or into a hollow organ.

Ex) sweat gland, oil gland, salivary gland, tear gland, stomach

acid.

endocrine:

Glands secrete into blood or interstitial fluid. NO DUCT!

Ex) hormones

2. Endocrine regulation vs. nervous regulation

Sometimes, the line separating nervous and endocrine systems is fuzzy.

Ex) some neurons secrete hormones

One endocrine gland is made of neurons

-Often combined into neuro-endocrine system

nervous systemendocrine system

a) Uses electrochemical messagesa) uses chemical messages in

(action potentials) blood (hormones)

b) Fast acting but short-livedb) slow acting but long-lived

c) affects: 3 types of muscles and glandsc) affects: metabolic rate of

cells

3. Hormones

Chemical messengers that are sent from one group of cells through body fluids to influence the activity of a second group of cells.

Another example of a chemical messenger-neurotransmitter

About 50 hormones in the human body

Hormones are powerful chemicals and work in relatively low concentrations

Basal Level = the lowest concentration of a hormone in body fluids

a) chemical types of hormones

1) Steroidex: testosterone

2) polypeptide/ proteinex: insulin

3) biogenic amineex: epinephrine (adrenaline)

4) flcosonoidsex: prostaglandins

b) target cells

Virtually all cells in body are exposed to circulating hormones but only certain cells respond to a given hormone. These are TARGET CELLS.

Target cells have specific receptors. These are located

a)on the surface of cell membranes

b)inside target cells

Once a hormone binds to a receptor, it alters the activity within the target cell.

It alters the rate of an existing metabolic process

Ex: increase/decrease rate of cell division

Ex: increase/decrease synthesis and secretion of a material.

4. Control of endocrine secretion

a) negative feedback

Feedback that causes the original stimulus to decline or end

The response of the target cells reverses the original imbalance back into homeostasis.

Low [Ca] in bloodStimulates the release of travels in blood

imbalanceParathyroid hormone

[Ca] level normalIncreases [Ca] level in bloodTarget Cells: Osteoclasts

homeostasis reestablished(break down bone tissue)

b) nervous stimulation

In most all cases, the ANS controls the release of hormones as a motor response within a reflex arc.

Ex: stimulates adrenal gland to secrete epinephrine and norepinephrine

stimulates kidney to secrete renin

5. Endocrine glands:

a) hypothalamus

a region of the brain within the diencephalon

secretes several hormones whose functions are to control the release of other hormones called RELEASING hormones

Ex: growth hormone releasing hormone

Function: stimulates the release of growth hormone

b) anterior pituitary gland

Pituitary gland is located immediately inferior to the diencephalon.

  • nick-named: master gland
  • Anterior pituitary comprises 75% of entire gland. Secretes 7 hormones
  • Ex: growth hormone. Function: stiumulate growth and increases metabolic rate.
  • Ex: prolactin. Function: initiate milk production during pregnancy.

c) posterior pituitary gland

Posterior pituitary comprises 25% of entire gland.

* neurons secrete these hormones. There are 2.

* Oxytocin. Function: allows milk secretion & contracts smooth muscles of the uterus

* Antidiuretic hormone: Function: decrease urine production to conserve water

(Diaretic – increases urine production)

QUIZ 1

d) thyroid gland

Located in anterior neck just anterior to larynx and trachea. Secretes 2 hormones:

  • thyroxine – regulates rate of general metabolism.
  • calcitonin – decreases calcium level in blood.

e) parathyroid gland

Located on posterior sie of thyroid gland

Consists of 4 small patches of tissue. Secretes 1 hormone.

  • Parathyroid hormone- increases calcium level inblood.

f) adrenal cortex

Adrenal galnd is located at superior end of each kidney

  • outer (superficial) region is the CORTEX.
  • The cortex secretes 5 hormones.
  • Aldosterone – increases Sodium level in blood
  • Cortisol – increases activity of immune system. Increases resistance to stress

g) adrenal medulla

Inner (deep) region of adrenal gland

Made entirely of sympathetic postganglionic neurons.

Secretes 2 hormones

  • epinephrine and norepinephrine
  • Function increase HR, RR, BP, etc…

h) pancreas

Located in abdominal cavity. Contains both endocrine and exocrine cells. Secretes 4 hormones

  • ex: insulin – decrease glucose level in blood.
  • Glucagon – increase glucose level in blood.

i) ovaries

Female reproductive organs that produce gametes via meiosis.

Secretes 4 hormones.

  • estrogen-regulates menstrual cycle & produces secondary sex characteristics
  • progesterone – regulates pregnancy

j) testes

Male reproductive organs that produce gametes via meiosis.

Secrete 2 hormones

  • testosterone – regulates sperm production & produces secondary sex characteristics.
  • Inhibin – inhibits the release of menstrual cycle hormones

k) pineal

A small rounded gland located in midbrain region. Secretes 1 hormone.

  • Melatonin – controls body’s internal clock. Affects: jet lag, insomnia.

l) thymus

A small mass of tissue located anterior to heart. Secretes 4 hormones.

  • thymosin – promotes maturity of T-Cells.

m) heart

A large muscular organ in thoracic cavity. Secretes one hormone.

  • Atrial matriuretic peptide – decreases blood pressure

n) kidneys

2 large bean-shaped organs located on posterior wall of abdominal cavity. Secretes 2 hormones.

  • renin(combined with another hormone) regulates blood pressure
  • erythropoietin – regulates production of new blood cells in red bone marrow.

6. Disorders of the endocrine system

a) diabetes mellitus

A group of related disorders that all result in hyperglycemia (high level of glucose in blood and/or in urine)

Two varieties

Type I - juvenile onset diabetes. Insulin dependant diabetes. Insulin producing cells in pancreas are destroyed by body’s own immune system.

Type II – Adult onset diabetes. Target cells loose ability to respond to insulin.

b) diabetes insipidus

An under-secretion of ADH from posterior pituitary.

Symptoms: production of large volumes of urine, excessive thirst, dehydration. Associated with cases of bed-wetting in children.

Treatment: replace ADH via injection or nasal spray

c) acromegaly

An over-secretion of growth hormone in adulthood.

Symptoms: thickening of facial bones, large hands and feet. Usually caused by tumor of pituitary.

Treatment: Surgical removal of tumor but symptoms not reversible.

d) goiter

A pronounced enlargement of thyroid gland. Increased size due to a lack of iodine in diet.
Iodine needed in assembly line to manufacture thyroxine. Accumulation of intermediary compounds. Treatment: add iodine to diet (iodized salt)

1