Transcript Organs of the Endocrine System and Their Products

Organs of the Endocrine System and
Their Products
• The following major glands
will be covered one at a
time with their products:
1. Pituitary gland /
Hypothalamus
2. Thyroid gland
3. Parathyroid gland
4. Adrenal gland
5. Pancreas (also has exocrine
function)
6. Gonadal hormones
(ovaries and testes)
7. Thymus
•
•
1. Pituitary Gland (Hypophysis)
located in sella turcica of sphenoid bone (in cranial
cavity), inferior to hypothalamus
consists of two lobes:
A. neurohypophysis (~ posterior pituitary)
•
attached to hypothalamus by infundibulum
•
contains axons and axon terminals of
neurosecretory cells whose cell bodies are in
hypothalamic nuclei
B. adenohypophysis (~ anterior pituitary)
•
consists of glandular epithelium
http://www.usc.edu/hsc/dental/ghisto/end/c_1.html
A. Neurohypophysis
(Posterior Pituitary)
• consists of nerve fibers (axons of neurosecretory cells with cell
bodies in hypothalamus) and pituicytes (glial cells that support
nerve fibers)
• acts primarily as a storage and releasing area for hormones
actually made in hypothalamic nuclei
• hormones released in response to impulses from hypothalamus
(neural control)
• hormones are short amino acid chains (peptides)
– oxytocin
– antidiuretic hormone (ADH or “vasopressin”)
A. Neurohypophysis:
Oxytocin (OT)
• action, in pregnant or nursing women:
– stimulates contraction of smooth muscle of
uterine wall during labor and delivery
– stimulates ejection of milk in lactating mothers
• action, in men and non-pregnant women,
may be involved in sexual arousal and orgasm
A. Neurohypophysis:
Oxytocin (OT)
• control:
– during labor/delivery, positive feedback: stretching of
uterus/cervix --> sensory impulses to hypothalamus -->
increased secretion of OT --> increased contraction
– suckling: sucking of infant on breast --> sensory to
hypothalamus --> oxytocin release --> release of milk
A. Neurohypophysis:
Antidiuretic Hormone (ADH)
• action: antidiuretic hormone (ADH) directly affects blood
pressure - acts as powerful vasoconstrictor --> increases
blood pressure (hence name “vasopressin”)
* action: affects water balance (indirect affect on blood
pressure) - acts on tubules of kidney to increase
reabsorption of water  less water lost in urine
A. Neurohypophysis: ADH
• disorders:
– hyposecretion due to damage of hypothalamic nucleus or
neurohypophysis--> diabetes insipidus - excessive urine
production (polyuria) and thirst
– hypersecretion --> SIADH (syndrome of inappropriate ADH
secretion) - water retention, headache, cerebral edema,
weight gain, hypoosmolarity
Antidiuretic Hormone (ADH):
Control
• neural control: increased electrolyte (NaCl) concentration -> affects (supraoptic) nucleus in hypothalamus --> impulse
to neurohypophysis --> release of ADH --> increased water
reabsorption --> decrease in electrolyte concentration
• other stimuli: pain, low BP, morphine, barbiturates, nicotine,
aldosterone (hormone from adrenal cortex - hormonal
control)
• inhibition: alcohol (results in more urine production and,
potentially, dehydration)
• diuretic drugs - some act to supress ADH secretion; used to
treat hypertension and congestive heart failure
B. Adenohypophysis
(Anterior Pituitary)
• linked to hypothalamus via hypophyseal portal system
(capillary networks and small veins)
– carries regulatory hormones from hypothalamus to
pituitary
• releasing hormones stimulate secretion of pituitary
hormones
• inhibitory hormones inhibit secretion
• consists of epithelial cells
• all hormones produced are proteins
* tropic hormones - affect some endocrine glands or
provide maintenance oversight for other organs
B. Adenohypophysis:
Growth Hormone (GH)
• highest levels during evening and sleep
• action: stimulates increased rate of protein synthesis leading
to cell growth and division
– bones and skeletal muscle respond more than other body
cells
• action: stimulates use of fat as energy source and decreases
rate of glucose uptake and glucose metabolism (diabetogenic
effect – “spares” glucose)
• control:
– release stimulated by GHRH (growth hormone releasing
hormone) from hypothalamus
– inhibited by GHIH (from hypothalamus) and
somatomedins (produced by liver under GH stimulation)
Growth Hormone (GH): Disorders
Disorders:
• hypersecretion
– gigantism (in children)
• up to 8’ tall, normal body proportions
– acromegaly (after epiphyseal plates close)
• enlargement of extremities and face, thickening of soft
tissue
• hyposecretion
– pituitary dwarfism - in children, up to 4’ tall
– progeria - premature aging, atrophy of body tissues
Growth Hormone Excess
in childhood leads to GIGANTISM
Growth Hormone Excess
in adulthood leads to ACROMEGALY
B. Adenohypophysis: Prolactin
(PRL)
• action:
* stimulates milk production in mammary glands;
– helps stimulate development of mammary glands
(along with other hormones);
– in males, may help regulate testosterone production
• control:
– stimulation: PRH (prolactin-releasing hormone from
hypothalamus), high estrogens, breast-feeding
– inhibition: PIH (hypothalamus), stimulated by rising
PRL levels, low estrogen
B. Adenohypophysis:
Prolactin (PRL)
Disorders
• hyperprolactinemia = hypersecretion due to
adenohypophyseal tumors; results in galactorrhea, lack of
menses and infertility in women, impotence in men
B. Adenohypophysis:
Thyroid-Stimulating Hormone (TSH)
• TSH = thyrotropin
– action:
• stimulates secretion of hormones from thyroid
gland (T4 and T3); also stimulates development of
thyroid in youth
– control:
• release stimulated by TRH (thyroid releasing
hormone from hypothalamus)
• inhibited by rising levels of thyroid hormones and
by GHIH
B. Adenohypophysis:
Adrenocorticotropic hormone (ACTH)
• ACTH=corticotropin
• action: stimulates release of hormones from adrenal
cortex
• control:
– release stimulated by CRH (corticotropin-releasing
hormone from hypothalamus)
– release inhibited by rising levels of glucocorticoids
from adrenal cortex
B. Adenohypophysis:
Gonadotropins
• regulate activity and secretion by gonads (testes in males;
ovaries in females)
• control:
– stimulated by GnRH (gonadotropin-releasing hormone
from hypothalamus)
– release of GnRH is inhibited by rising levels of
estrogens, progestins and androgens (testosterone)
• two important hormones
– FSH
– LH
Gonadotropins:
Follicle-Stimulating Hormone (FSH)
• action:
– females (ovaries) - stimulates development of ovarian
follicles and estrogen production
– males (testes) - stimulates sperm production and
development
• inhibited by inhibin and testosterone from testes
(feedback to hypothalamus and anterior pituitary) and
estrogen, progesterone and inhibin from ovaries (feedback
to anterior pituitary)
Gonadotropins:
Luteinizing Hormone (LH)
• LH=lutropin
– action:
• females (ovaries) - induces ovulation; stimulates
secretion of estrogens and progestins (e.g.,
progesterone)
• males (testes) - stimulates production of androgens (e.g.,
testosterone )
– inhibited by estrogen, progesterone and inhibin form ovaries
(feedback to anterior pituitary) and by inhibin and
testosterone from testes (feedback to hypothalamus and
anterior pituitary)