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PITUTARY GLAND
page 1
AC Brown
A6k
INTRODUCTION
A. Hormones/Endocrines
Hormones are substances secreted into the blood by specialized
glands (endocrine glands) or specialized cells in other tissue.
Note: there are two types of glands: endocrine glands (described
above) and exocrine glands. Exocrine gland secrete their products
either onto the surface of the body (e.g. sweat glands) or into the
alimentary tract (e.g. salivary glands of the oral cavity, acid-secreting
glands of the stomach).
Note: There are several types of cell-to-cell chemical
communication: gap junctions, synaptic transmission,
paracrine/autocrine, and endocrine
Gap Junctions
Synaptic
Chemical
transmission
Site of action
Direct from cellto-cell
Adjacent cells
Diffuse across
synaptic cleft
Postsynaptic cell
Specificity due to
Anatomic
location
Anatomic location & receptors
Paracrine &
Autocrine
Diffusion through
interstitial fluid
Nearby cells (P)
or same cell (A)
Receptors
B. Characteristics of Hormones
1. Hormones circulate in the blood either in free form (dissolved) or
bound to carrier proteins
2. Hormones have their effect by binding to receptors on their
target organs or tissues.
Note: Trophic hormones are hormones whose target is another
endocrine gland
3. Hormones are either peptides, proteins, steroids, or amines
C. Major Endocrine Glands
1.
2.
3.
4.
5.
6.
7.
Pituitary gland: multiple hormones
Thyroid gland: thyroxine and triiodothyronine, calcitonin
Parathyroid gland: parathyroid hormone
Pancreas: insulin and glucagon
Adrenal medulla: epinephrine and norepinephrine
Adrenal cortex: aldosterone, cortisol
Gonads (testis and ovary): androgens (testosterone), estrogens
Endocrine
Transport by the
circulation
General (target
tissue)
Receptors
PITUTARY GLAND
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INTRODUCTION (continued)
D. Other Endocrine Secreting Structures include
1. Kidney: Renin and Erythropoietin (control of red cell production)
2. Heart: Natriuretic Peptide
3. Pineal Gland: Melatonin (entrainment of circadian rhythms,
sleep-wake cycle)
PITUITARY(also called the "Hypophysis")
A. Structure
1. Small gland at the base of the brain
2. Divided into the anterior pituitary (also called the
adenohypophysis) and posterior pituitary (also called the
neurohypophyssis); there also is an intermediate region
(intermediate lobe)
3. Attached to the hypothalamus by the infundibulum or
hypothalamo-hypophyseal stalk, which contains
a. nerve axons of neurons originating in the hypothalamus and
terminating in the posterior pituitary
b. blood vessels originating in capillary beds in the
hypothalamus and terminating in capillary beds in the
anterior pituitary (portal system)
AC Brown
A6k
PITUTARY GLAND
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AC Brown
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PITUITARY(continued)
B. Pituitary Hormones
Hormone
Anterior Pituitary
Growth hormone (GH, GRH, somatotropin, STH)
Adrenocorticotropic hormone (ACTH,
corticotrophin)
Thyroid-stimulating hormone (TSH, thyrotropin)
Luteinizing hormone (LH) (gonadotropin)
Follicle-stimulating hormone (FSH)
(gonadotropin)
Prolactin (PRL)
Posterior Pituitary
Antidiuretic hormone (ADH, Vasopressin)
Oxytocin
Actions
Promotes body growth
Promotes secretion of cortisol and related
glucocoricoids from the adrenal cortex
Promotes synthesis and release of thyroid
hormones and growth of the thyroid
Females: promotes ovulation and
luteinization of ovarian follicles
Males: promotes testosterone secretion
Females: promotes follicle growth
Males: promotes spermatogenesis
Females: stimulates milk secretion
Promotes water retention in the kidney
Causes uterine contraction in pregnancy;
promotes milk ejection
C. Control of Anterior Pituitary Secretion
1. Hypothalamic releasing and inhibiting hormones
a. synthesized in the hypothalamus
b. released into capillaries in the hypothalamus
c. transported by hypothalamo-hypophyseal blood vessels to
the anterior pituitary capillary bed (portal system)
d. diffuse from the anterior pituitary capillaries to the pituitary secretory cells
e. either stimulate (releasing hormones) or inhibit secretion of
specific anterior pituitary hormones
2. Feedback
a. short loop feedback: feedback from
the pituitary hormone to the
hypothalamus
b. long-loop feedback: feedback from
target tissue secretions to the
hypothalamus and/or the pituitary
PITUTARY GLAND
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AC Brown
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GROWTH HORMONE AND BONE GROWTH
A. Bone Structure of Growing Bone
1. Diaphysis: bone shaft
2. Epiphysis: bone ends
3. Epiphyseal plate: plate of cartilage
between the diaphysis and epiphysis
B. Bone Growth
Bone growth occurs as the epiphyseal
plate lays down new bone at the end of the
shaft. During development, the epiphyseal
plate narrows and eventually disappears;
this occurs in an orderly sequence at
different times for different bones and
permits determination of "bone age".
When the plate disappears, bone
elongation is no longer possible.
C. Effect on Bone Development of Growth
Hormone
1. Before epiphyseal closure: elongation
of long bones either by the direct effect
of GH on bone or by GH's stimulation
of release of somatomedin medators
from the liver
2. After epiphyseal closure: thickening of
bone
D. Pathophysiology
1. Inadequate GH secretion or defective
GH receptors during bone
development: Dwarfism
2. Excess GH during bone development:
Giantism
3. Excess GH after epiphyseal closure:
Acromegaly, enlargement of the hands
and feet, growth of facial bones,
protrusion of the jaw
Acromegaly