Download Chp.18 Endocrine Glands

Chp. 18Endocrine System
Functions:
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Metabolism and tissue maturation
Ion regulation
Water balance
Immune system regulation
Heart rate and blood pressure regulation
Control of blood glucose and other nutrients
Control of reproductive functions
Uterine contractions and milk release
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Pituitary Gland and
Hypothalamus
• Where nervous and
endocrine systems interact
• Hypothalamus regulates
secretions of anterior
pituitary
• Posterior pituitary is an
extension of the
hypothalamus
• Anterior pituitary produces
nine major hormones that
– Regulate body functions
– Regulate the secretions of
other endocrine glands
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Hypothalamus, Anterior Pituitary,
and Target Tissues
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Releasing and Inhibiting Hormones
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Tropins or tropic hormones: hormones that regulate the hormone
secretions of target endocrine tissues. All anterior pituitary hormones
are tropins.
Releasing hormones:
– GHRH. Growth hormone-releasing hormone. Causes the
anterior pituitary to release growth hormone.
– TRH. Thyrotropin-releasing hormone. Causes the anterior
pituitary to release thyroid-stimulating hormone (TSH).
– CRH. Corticotropin-releasing hormone. Causes anterior
pituitary to produce adrenocorticotropic hormone.
– GnRH. Gonadotropin-releasing hormone. Causes anterior
pituitary to produce FSH (follicle stimulating hormone) and LH
(luteinizing hormone).
– PRH. Prolactin-releasing hormone. Causes the anterior pituitary
to release prolactin.
Inhibiting hormones:
– GHIH. Growth hormone-inhibiting hormone, somatostatin.
Causes the anterior pituitary to decrease release of growth
hormone.
– PIH. Prolactin-inhibiting hormone. Causes the anterior pituitary
to decrease release of prolactin.
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Hypothalamus, Posterior Pituitary,
and Target Tissues
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Hormones of Posterior Pituitary: ADH
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Antidiuretic hormone (ADH). Also called vasopressin.
A. Osmoreceptors (specialized neurons of
hypothalamus monitor changes in intercellular
osmolality (relative concentrations of electrolytes and
water). If the concentration of electrolytes increases
or if the concentration of water decreases, then ADH
secretion is stimulated.
B. Baroreceptors (specialized neurons found in walls of
atria of heart, large veins, carotid arteries, aortic arch)
sense changes in blood pressure (BP). If BP
decreases, then ADH secretion is stimulated.
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Control of ADH Secretion
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Control of Oxytocin Secretion
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Anterior Pituitary Hormones
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Growth hormone (GH) or somatotropin
Thyroid-stimulating hormone (TSH)
Adrenocorticotropic hormone (ACTH)
Melanocyte-stimulating hormone (MSH)
Beta endorphins
Lipotropins
Luteinizing hormone (LH)
Follicle-stimulating hormone (FSH)
Prolactin
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Growth Hormone
(GH or somatotropin)
• Stimulates uptake of amino acids; protein
synthesis
• Stimulates breakdown of fats to be used as
an energy source but stimulates synthesis of
glycogen: glucose sparing
• Promotes bone and cartilage growth
• Regulates blood levels of nutrients after a
meal and during periods of fasting
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Thyroid Gland
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One of largest endocrine glands; Highly vascular. Iodine enters follicular cells
by active transport. Only gland that stores hormone.
Histology
– Composed of follicles: follicular cells surrounding thyroglobulin/thyroid
hormones
– Parafollicular cells: between follicles
Physiology
–Follicular cells secrete thyroglobulin into
lumen of follicle. Iodine and tyrosine
necessary for production of T3 and T4.
Hormones stored here attached to the
thyroglobulin then absorbed into follicular
cells; hormones detached from
thyroglobulin and released into circulation.
–Parafollicular cells. Secrete calcitonin
which reduces [Ca2+] in body fluids when
Ca levels are elevated.
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Biosynthesis of Thyroid
Hormones
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Regulation of
Calcitonin Secretion
• Produced by parafollicular cells
• Secretion triggered by high Ca2+ concentration in
blood; acts to decrease Ca2+ concentration
• Primary target tissue: bone. Decreases osteoclast
activity, lengthens life span of osteoblasts.
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Parathyroid Glands
• Embedded in thyroid
• Two glands on each side
• Secrete PTH: target tissues are bone,
kidneys and intestines.
– Increases blood calcium and phosphate
levels
– Stimulates osteoclasts
– Promotes calcium reabsorption by
kidneys and PO4 excretion
– Increases synthesis of vitamin D which,
in turn, increases absorption of Ca and
PO4 by intestines. Net loss of PO4 under
influence of PTH.
• Regulation depends on calcium
levels.
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Adrenocorticotrophic Hormone (ACTH)
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CRH from hypothalamus causes release of
ACTH from anterior pituitary which
– Causes cortisol secretion from the adrenal
cortex (a glucocorticoid from the zona
fasciculata)
– Causes aldosterone secretion from the
adrenal cortex (a mineralocorticoid from
the zona glomerulosa)
– Binds directly to melanocytes of the skin;
causes increase in production of melanin.
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Adrenal Glands
• Near superior poles of
kidneys; retroperitoneal
• Inner medulla; outer
cortex
• Medulla: formed from
neural crest; sympathetic.
Secretes epinephrine and
norepinephrine
• Cortex: three zones from
superficial to deep
– Zona glomerulosa
– Zona fasciculata
– Zona reticularis
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Pancreas
• Located along small intestine and
stomach; retroperitoneal
• Exocrine gland
– Produces pancreatic digestive juices
• Endocrine gland
– Consists of pancreatic islets
– Composed of
• Alpha cells; secrete glucagon
• Beta cells; secrete insulin
• Delta cells; secrete somatostatin
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Insulin and Glucagon
Insulin
• Target tissues: liver,
adipose tissue, muscle,
and satiety center of
hypothalamus
• Increases uptake of
glucose and amino
acids by cells
Glucagon
• Target tissue is liver
• Causes breakdown of
glycogen and fats for
energy
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Hormones of the Reproductive System
Male: Testes
• Testosterone
– Regulates production of
sperm cells and development
and maintenance of male
reproductive organs and
secondary sex characteristics
• Inhibin
– Inhibits FSH secretion
Female: Ovaries
• Estrogen and
Progesterone
– Uterine and mammary
gland development and
function, external genitalia
structure, secondary sex
characteristics, menstrual
cycle
• Inhibin
– Inhibits FSH secretion
• Relaxin
– Increases flexibility of
symphysis pubis
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LH, FSH, Prolactin
• Gonadotropins: glycoprotein hormones that promote
growth and function of the gonads
• LH and FSH
– Both hormones regulate production of gametes and
reproductive hormones
• Testosterone in males
• Estrogen and progesterone in females
• GnRH from hypothalamus stimulates LH and FSH
secretion
• Prolactin: role in milk production
– Regulation of secretion: prolactin-releasing hormone (PRH)
and prolactin-inhibiting hormones (PIH)
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Melanocyte Stimulating Hormone,
Endorphins, and Lipotropins
• ACTH, MSH, endorphins and lipotropins all
derived from the same large precursor molecule
when stimulated by CRH
• MSH causes melanocytes to produce more
melanin
• Endorphins act as an analgesic; produced during
times of stress.
• Lipotropins cause adipose cells to catabolize fat
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Pineal Body
• In epithalamus; produces melatonin and arginine
vasotocin
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Thymus Gland, GI Tract
• Thymosin. Development of the immune
system.
• GI tract: several hormones regulate
digestion and enzyme secretion. Studied
with digestive system.
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Hormone-like Substances
• Autocrines: chemical signals released by a cell
and the substance affects that same cell.
– Chemical mediators of inflammation which are
modified fatty acids: eicosanoids such as
prostaglandins, thromboxanes, prostacyclins, and
leukotrienes
• Paracrines: chemical signals released into
intercellular fluid and affecting nearby cells.
– Endorphins and enkephalins modulate sensation of pain
– Several growth factors
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Effects of Aging on
Endocrine System
• Gradual decrease in secretory activity of some
glands
– GH as people age except in people who exercise
regularly
– Melatonin
– Thyroid hormones
– Kidneys secrete less renin
• Familial tendency to develop type II diabetes
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