CH 17 - The Endocrine System

endocrine system interacts closely with

the nervous system

organs of the endocrine system

• are a disperse group ductless glands

• secrete “messenger molecules” called hormones

hormone -

chemical substance that is produced and released by endocrine cells, carried throughout the body in the blood

hormones exerts

regulatory influences on other, distant cells

hormones influence only specific tissue cells

target cells

• can have different effects on different target cells

  • effective at very low concentrations

hormone classes

1. amino acid-based hormones (amines, peptides, proteins(

2. steroids - derived from cholesterol

pure endocrine organs

• pituitary, pineal gland

• thyroid and parathyroid glands

• adrenal glands (adrenal cortex and medulla)

organs containing large proportion of endocrine cells

• pancreas, thymus, gonads

• hypothalamus - a neuroendocrine organs

organs containing some endocrine cells

heart, digestive tract, kidneys, skin

endocrine cells are of

epithelial origin

gonads are

the main source of sex hormones

• large proportion of endocrine cells

males gonads - interstitial cells within

testes secrete androgens

male androgens

primarily testosterone; promotes formation of sperm and maintains secondary sex characteristics

female gonads are

in ovaries

female androgens

are secretes and directly converted into estrogens by ovarian follicle cells

estrogens maintain

reproductive organs and secondary female sex characteristics

secretion of hormones is triggered by one of three major stimuli

humoral, neural, and hormonal

humoral secretion is the

simplest of endocrine control mechanisms

humoral secretion - secretion in direct response to

changing ion or nutrient levels in the blood

humoral secretion - parathyroid gland

monitors calcium

• responds to decline by secreting hormone to reverse decline

humoral secretion - stimulus

low concentration of Ca2+ in capillary blood

humoral secretion - response

parathyroid gland secrete parathyroid hormone (PTH), which increases Ca2+ blood

neural secretion - symapathetic nerve fibers

stimulate cells in the adrenal medulla

neural secretion induces

release of epinephrine and norepinephrine

neural secretion stimulus

action potentials in preganglionic sympathetic fibers ro adrenal medulla

neural secretion response

adrenal medulla cell secrete epinephrine and norepinephrine

hormonal secretion stimuli received from

other glands

hormonal secretion - certain hormones signal

secretion of other hormones

• hypothalamus secretes hormones → stimulates pituitary → stimulates other glands

hormonal secretion stimulus

hormones form hypothalamus

hormonal secretion response

anterior pituitary gland secretes hormones that stimulate other endocrine glands to secrete hormones

hormone secretion always controlled by

feedback loops

blood concentration declines below a minimum →

more hormone is secreted

blood concentration exceeds maximum →

hormone production is halted

the pituitary gland lies in

the hypophyseal fossa in the sella tunica of the sphenoid bone

pituitary gland secretes

9 major hormones

pituitary gland attached to

the hypothalamus by the infundibulum

pituitary gland divisions

anterior lobe (adenohypohysis) and posterior lobe (neurohypophysis)

pituitary gland - anterior lobe

• pars tuberalis

• pars intermedia

• pars distalis

pituitary gland - posterior

infundibulum and pars nervosa

pars distalis

largest division of the anterior lobe

pars distalis contains

5 different endocrine cells that make and secrete 7 different hormones

trophic hormones have other

endocrine glands as their target

hypothalamus controls

secretion of anterior lobe hormone by secreting

• releasing hormones and inhibiting hormones

releasing hormones

prompt anterior lobe to release hormones

inhibiting hormones

turn off secretion of anterior lobe hormones

hypothalamic hormones released into special blood vessels control

the release of anterior pituitary hormones

hypothalamic neurons synthesize

releasing and inhibiting hormones

when appropriately stimulated, hypothalamic neurons secrete

releasing or inhibiting hormones into the primary capillary plexus

hypophyseal portal system

primary capillary plexus and secondary capillary plexus

hypothalamic hormones travel through

portal veins to the anterior pituitary when they stimulate of inhibit release of hormones made in the anterior pituitary

in response to releasing hormones, the anterior pituitary secretes homes into

the secondary capillary plexus

• this is turn emptys into the general circulation

anterior lobe hormones

Growth Hormone (GH)

Prolactin (PRL)

Thyroid-Stimulating Hormone (TSH)

Luteinizing Hormone (LH)

Adrenocorticotropic Hormone (ACTH)

Follicle-Stimulating Hormone (FSH)

posterior lobe

does not make hormones; stores and releases them

• Is structurally part of the brain

hypothalamophypophyseal tract

asrises from neuronal cell bodies in the supraoptic and paraventricular nuclei in the hypothalamus

posterior lobe stores and releases hormones made in

the hypothalamus

• releases 2 “peptide hormones” (antidiuretic hormone (ADH) and oxytocin)

posterior pituitary - nerve impulses travel down the axons of

hypothalamic neurons, causing hormone release from their axon terminals in the PP

hypothalamic neurons synthesize

oxytocin or ADH

oxytocin and ADH are transported down the axons of

hypothalamohypophyseal tract to the PP

oxytocin and ADH are stores in

neurosecretoary bodies in the PP

when associated hypothalamic neurons fire, nerve impulses arriving at the neurosecretory bodies cause

oxytocin or ADH to be released into the blood

gigantism -

hyper secretion of growth hormones (GH) in children

pituitary dwarfism

hypo secretion of GH

diabetes insipidus

passing of dilute urine

• paras nervosa does not make enough antidiuretic hormone (ADH)

thyroid gland (pure organ) located

in the anterior neck

thyroid gland (pure organ)

largest endocrine gland

thyroid gland (pure organ) composed of

follicles and areolar CT

thyroid gland (pure organ) produces

2 hormones

• thryoid normoen(TH) and calcitonin

thyroid hormone (TH)

regulates metabolism

calcitonin

calcium regulation

graves’ disease

most common type of hyperthyroidism

• immune system makes abnormal antibodies → stimulates the overseretion of TH by follicle cells

• leads to nervousness, weight loss, sweating, and rapid heart rate

endemic goiter

irregular growth of thyroid gland

• due to lack of iodine in the diet

cretinism

hypothyroidism in children

• short, disproportionate body; thick tongue, and mental retardation

myxedema (mucous swelling

• adult hypothyroidism (not enough)

• antibodies attack and Destry thyroid tissue

• low metabolic rate and weight gain are common symptoms

• buildup of mucopolysaccharides (a type of gel-like substance) in the skin, soft tissues, and organ

parathyroid gland lie on

the posterior surface of the thyroid gland

parathryoid glands contain

2 types of endocrine cells

• chief cells and oxyphil cells

chief cells

produce parathyroid hormone (PTH) → increases blood concentration of Ca2+

oxyphil cells

calcium-sensing, secretory properties, and PTH synthesis

adrenal glands - 2 endocrine glands in one

1. adrenal medulla

2. adrenal cortex (3 layers)

adrenal medulla

a cluster of neurons

• secretes amine hormones epinephrine and norepinephrine into the blood to enhance the fight-or-flight response

adrenal cortex

• forms the bulk of the gland

• secretes a variety of hormones → corticosteroids

• zone glomerulosa, zona fasciculata, zona reticularis adre

adrenal corticosteroids

mineralcortiicoids and glucocorticoids

mineralocorticoids

regulate salt and water balance

• aldosterone - secreted by the zona glomerulosa

  • secreted in response to decline in blood volume or BP

glucocorticoids

stress response → cortisol is the main type

• secreted by the zona fasciculate and zona reticular

  • helps body deal with stressful situations

the adrenal gland responses to both

short-term and prolonged stress

adrenal short-term stress response

• heart rate, blood pressure increases

• bronchioles dilate

• liver converts glycogen to glucose and releases glucose to blood

• blow flow changes, reducing digestive system activity and rise output

• metabolic rate increases

prolonged stress

release CRH → goes to anterior pituitary and stimulates ACTH → stimulates adrenal cortex

adrenal gland long-term stress response - mineralocorticoids

• kidneys retain sodium and water

• blood volume and blood pressure rise

adrenal gland long-term stress response - glucocorticoids

• proteins and fats converted to glucose or broken down for energy

• blood glucose increases

• immune system suppressed

Cushing’s syndrome

• caused by hyper secretion of glucocorticoid hormones (carb. metabolism) - usually caused by a pituitary hormone

• can cause facial roundness, weight gain around the middle body and upper back, thinning of the arms and legs, easy bruising and stretch marks

addison’s diease

• hyposecreoty disorder of the adrenal cortex

• deficiencies of both mineraloxortcoids (ex. aldosterone; salt balance and glucocorticoids pin

pineal gland

• located on roof of diencephalon

• small-pinecone shapes gland

  • secrete melatonin → regualtes circadian rhythms

pancreas

located in the posterior abdominal wall; contains endocrine and exocrine cells

pancreas - exocrine cells (ducts)

acinar cells

acinar cells

secrete digestive enzymes

pancreas - endocrine cells (without ducts)

• pancreatic islets → pancreatic cells that produce hormones

glucagon -

stimulates the liver to release stored glucose into the bloodstream, increasing blood sugar levels

pancreas - alpha cells

secrete glucagon

• signal liver to release glucose from glycogen

• raise blood sugar

pancreas - beta cells

secrete insulin

• Signal most body cells to take up glucose from the blood

• Promote storage of glucose as glycogen in liver

• Signal most body cells to take up

pancreatic islets - delta cells

secrete somatostatin

• inhibit secretion of insulin and glucagon

pancreatic islets - (PP) cells

secrete pancreatic polypeptide

• may inhibit exocrine activity of the pancreas