CHAPTER 1
Endocrinology, Brain and Pituitary Gland
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FIGURE 1-1 ENDOCRINE
AND PARACRINE REGULATION.
TARGET
CELLS FOR
HORMONES AND PARACRINES MUST HAVE SPECIFIC RECEPTORS ON THEIR CELL
MEMBRANE OR IN THEIR CYTOPLASM OR NUCLEUS TO RESPOND TO A PARTICULAR LIGAND.
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FIGURE 1-2 MAJOR COMPONENTS
PLACENTA IS NOT SHOWN.
OF THE ENDOCRINE SYSTEM (SHOWN IN RED).
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THE
FIGURE 1-3 REPRESENTATION OF A CELL SURFACE RECEPTOR MOLECULE SHOWING
THE LIGANDBINDING DOMAIN (GREEN) AS A PORTION OF THE EXTRACELLULAR DOMAIN.
THE TRANSMEMBRANE DOMAIN SPANS THE PLASMA MEMBRANE OF THE CELL, AND THE
INTRACELLULAR DOMAIN EXTENDS INTO THE CYTOPLASM.
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FIGURE 1-4 MECHANISM OF ACTION OF A PEPTIDE HORMONE. THE LIGAND BINDS TO A
CELL SURFACE RECEPTOR. THE SIGNAL IS TRANSDUCED TO THE CELL INTERIOR, WHERE IT
MODIFIES THE ACTIVITY OF CYTOPLASMIC ENZYMES
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FIGURE 1-5 MECHANISM
OF ACTION OF A STEROID HORMONE.
LIPID-SOLUBLE
STEROIDS ENTER THE CELL CYTOPLASM BY DIFFUSION AND BIND TO RECEPTORS IN THE
CYTOPLASM OR NUCLEUS.
REGIONS OF
THE STEROID/RECEPTOR
DNA, AFFECTING
COMPLEX BINDS TO REGULATORY
THE EXPRESSION OF SPECIFIC STEROID-RESPONSIVE GENES.
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FIGURE 1-6 SECTION THROUGH THE MIDDLE OF THE BRAIN SHOWING THE PITUITARY
GLAND, HYPOTHALAMUS, AND PINEAL GLAND. NOTE THAT THE PITUITARY GLAND
(HYPOPHYSIS) RESTS IN A DEPRESSION IN THE SPHENOID BONE AND IS CONNECTED TO THE
HYPOTHALAMUS BY THE PITUITARY STALK.
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FIGURE 1-7 MAJOR SUBDIVISIONS
OF THE HUMAN HYPOPHYSIS (THE
NEUROHYPOPHYSIS AND THE ADENOHYPOPHYSIS) AND THEIR RELATIONSHIP TO THE
BRAIN.
THE PARS TUBERALIS, PARS DISTALIS, AND PARS INTERMEDIA ALL ARE PART OF THE
ADENOHYPOPHYSIS. IN ADULT HUMANS, THE PARS INTERMEDIA IS OFTEN ABSENT. OC,
OPTIC CHIASMA (NERVES FROM THE EYES). ANTERIOR IS TO THE LEFT.
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FIGURE 1-8 A REGULAR NEURON (A) AND A NEUROSECRETORY NEURON (B).
DENDRITES CARRY NERVE IMPULSES TOWARD THE CELL BODY, WHEREAS AXONS CARRY
NERVE IMPULSES AWAY FROM THE CELL BODY. NEUROTRANSMITTERS ARE SECRETED BY
THE AXON ENDINGS OF REGULAR NEURONS, WHEREAS NEUROHORMONES (DARK DOTS IN B)
ARE RELEASED FROM THE AXON ENDINGS OF NEUROSECRETORY NEURONS.
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FIGURE 1-9 REGIONS
OF THE HYPOTHALAMUS INVOLVED IN THE FUNCTION OF THE
HYPOPHYSIS
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FIGURE 1-10 THE PITUITARY, CONNECTED TO THE HYPOTHALAMUS AT THE BASE OF THE BRAIN, HAS TWO
LOBES. THE NEUROHYPOPHYSIS STORES AND RELEASES TWO HORMONES MADE IN THE HYPOTHALAMUS: OXYTOCIN
AND VASOPRESSIN. OXYTOCIN CAUSES CONTRACTION OF SMOOTH MUSCLEIN THE UTERUS, BREAST, AND MALE
REPRODUCTIVE TRACT. VASOPRESSIN ACTS ON THE KIDNEYS TO CAUSE WATER RETENTION. THE
ADENOHYPOPHYSIS SECRETES NINE OTHER HORMONES: GROWTH HORMONE (GH) PROMOTES GROWTH;
CORTICOTROPIN (ACTH) CAUSES THE ADRENAL CORTEX TO SECRETE CORTICOSTEROID HORMONES; FOLLICLESTIMULATING HORMONE (FSH) AND LUTEINIZING HORMONE (LH) INTERACT TO REGULATE THE FUNCTION OF THE
GONADS; PROLACTIN (PRL) CAUSES MILK SYNTHESIS IN THE MAMMARY GLANDS; THYROTROPIC HORMONE (TSH)
STIMULATES THE THYROID GLAND TO SECRETE THYROXINE; LIPOTROPIN (LPH) AFFECTS FAT METABOLISM;
MELANOPHORE-STIMULATING HORMONE (MSH) STIMULATES MELANIN SYNTHESIS IN PIGMENT CELLS; AND
OPIOIDS (ENDORPHINS AND ENKEPHALINS) REDUCE PAIN
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FIGURE 1-11 THE HYPOTHALAMO–HYPOPHYSIAL VASCULAR SYSTEM. ARTERIAL BLOOD ENTERS THE
MEDIAN EMINENCE AND THE NEUROHYPOPHYSIS VIA THE SUPERIOR HYPOPHYSIAL AND INFERIOR HYPOPHYSIAL
ARTERIES, RESPECTIVELY. BOTH OF THESE ARTERIES ARE BRANCHES OF THE INTERNAL CAROTID ARTERIES,
MAJOR VESSELS SUPPLYING THE BRAIN. NEUROHORMONES SECRETED INTO THE MEDIAN EMINENCE REGION
ENTER THE BLOOD IN THE PRIMARY CAPILLARY PLEXUS. THEY PASS DOWN THE HYPOPHYSIAL PORTAL VEINS TO
THE SECONDARY CAPILLARY PLEXUS IN THE PARS DISTALIS.
THEN THEY LEAVE THE BLOOD AND CAUSE THE PARS
DISTALIS CELLS TO SECRETE OR STOP SECRETING HORMONES. WHEN HORMONES ARE SECRETED BY THE PARS
DISTALIS, THEY LEAVE THE HYPOPHYSIS IN THE INFERIOR HYPOPHYSIAL VEINS, WHICH DRAIN INTO A LARGE
VESSEL, THE CAVERNOUS SINUS. NEUROHYPOPHYSIAL HORMONES ENTER CAPILLARIES IN THE
NEUROHYPOPHYSIS, WHICH ALSO DRAIN INTO THE CAVERNOUS SINUS. SMALL BLOOD VESSELS CONNECT THE
CAPILLARIES OF THE PARS DISTALIS AND NEUROHYPOPHYSIS.
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FIGURE 1-12 WHEN A SINGLE INJECTION OF GNRH (LHRH) IS ADMINISTERED TO
MEN () AND WOMEN (O) AT TIME ZERO, LEVELS OF LH RISE IN THE BLOOD, PEAK AFTER 32
MIN, AND THEN DECLINE. LEVELS OF FSH ALSO RISE AFTER GNRH ADMINISTRATION (NOT
SHOWN), BUT NOT AS HIGH AS LH.
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FIGURE 1-13 COMPONENTS
TO GNRH AND GAP.
OF PREPRO-GNRH, THE LARGE PROTEIN THAT GIVES RISE
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BOX 1: GNRH ANALOGS
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BOX 2: KALLMANN’S SYNDROME
GNRH CELLS
AND THE
EMBRYOLOGICAL ORIGIN
AND
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MIGRATION
OF
FIGURE 1-14 A SIMPLE FEEDBACK SYSTEM. THE RECEPTOR DETECTS THE LEVEL OF A PARTICULAR
COMPONENT OF THE SYSTEM AND TRANSLATES IT INTO A MESSAGE (INPUT) TO THE CONTROLLER CENTER.
THE INPUT IS COMPARED BY THE CONTROLLER CENTER TO ITS PROGRAMMED SET POINT, AND THIS CENTER
COMPUTES WHETHER A REGULATORY RESPONSE IS REQUIRED. IF NECESSARY, THE CONTROLLER CENTER
GENERATES A SIGNAL (OUTPUT) THAT IS TRANSMITTED TO ONE OR MORE EFFECTORS, WHICH RESPOND BY
PRODUCING SOME EFFECT. THIS EFFECT PRODUCES A CHANGE IN THE SYSTEM, WHICH THEN FEEDS BACK
AS A FEEDBACK LOOP ON THE CONTROLLER CENTER AFTER BEING RECEIVED BY THE RECEPTOR. OTHER
CIRCUITS (HIGHER CENTERS) CAN MODIFY THE ACTIVITIES OF THE CONTROLLER CENTER BY TEMPORARILY
ALTERING THE SET POINT OR BY INHIBITING THE OPERATION OF THE CONTROLLER CENTER.
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FIGURE 1-15 SCHEMATIC DIAGRAM OF THE CONTROL OF THE REPRODUCTIVE SYSTEM BY THE BRAIN
AND PITUITARY GLAND AND THE SITES OF FEEDBACK BY GONADAL HORMONES ON THIS CONTROL.
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FIGURE 1-16 THE ACTIONS OF POSITIVE AND NEGATIVE FEEDBACK ON GNRH AND,
THEREFORE, GONADOTROPIN (FSH AND LH) SECRETION IN FEMALES AND MALES.
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