2. • The endocrine system is a chemical messenger system
comprising feedback loops of hormones released by internal
glands of an organism directly into the circulatory system
(ductless glands), regulating distent target organs.
• The study of endocrine system and its disorders is known as
endocrinology. Endocrinology is a branch of internal medicine.
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11. • THE LEVEL OF HORMONE IN THE BLOOD IS VARIABLE AND SELF
REGULATING WITHIN THE NORMAL RANGE. A HORMONE IS RELEASED IN
RESPONSE TO SPECIFIC STIMULUS AND USUALLY ITS ACTIONREVERSE
THE STIMULUS THROUGH A NEGATIVE FEEDBACK.
• THE EFFECT OF A POSITIVE FEEDBACK MECHANISM IS AMPLIFICATION OF
THE STIMULUS AND INCREASEING RELEASE OF THE HORMONE UNTIL A
PARTICULAR PROCESS IS COMPLETE AND THE STIMULUS CEASES i.e.
RELEASE OF OXYTOCIN DURING LABOUR
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16. LOCATION
• THE HYPOTHALAMUS IS LOCATED BELOW THE THALAMUS
AND RIGHT ABOVE THE BRAIN STEM.
• IT FORMS THE ANTERIOR PART OF THE DIENCEPHALON.IT
IS ROUGHLY THE SIZE OF ALMOND.
• ALTHOUGH THE HYPOTHALAMUS IS CLASSIFIED AS A PART
OF THE BRAIN RATHER THAN A ENDOCRINE GLAND,IT
CONTROLS THE PITUITARY GLAND, AND HAS AN INDIRECT
EFFECT ON MANY OTHERS.
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22. • THE ANTERIOR PITUITARY (ADENOHYPOPHYSIS OR PARS ANTERIOR OR
PARS DISTALIS) IS AN UPGROWTH OF GLANDULAR EPITHELIUM FROM THE
PHARYNX AND THE POSTERIOR PITUITARY(NEUROHYPOPHYSIS,PARS
POSTERIOR,PARS NERVOSA) IS A DOWNGROWTH OF NERVOUS TISSUE
FROM THE BRAIN.
• THERE IS A THIN STRIP OF TISSUE IN BETWEEN THESE LOBES CALLED
“INTERMEDIATE LOBE” BUT ITS FUNCTION IN HUMAN BEING IS NOT
KNOWN.
23. BLOOD SUPPLY TO THE PITUITARY
GLAND-
• ARTERIAL BLOOD-This is supplied by branches from the
internal carotid artery. The anterior lobe is supplied indirectly
by blood that has already passed through a capillary bed in the
hypothalamus but the posterior lobe is supplied directly.
• VENOUS DRAINAGE-THIS COMES FROM BOTH LOBES CONTAINING
HORMONES , AND LEAVES THE GLAND IN SHPRT VEINS THAT ENETR
THE VENOUS SINUSES BETWEEN THE LAYERS OF THE DURA MATER.
24. HYPOTHALAMUS AND PITUITARY GLAND
RELATIONSHIP-
The influence of the hypothalamus on the release of
hormones is different in the anterior and posterior lobes of
the pituitary.
Anterior pituitary- The anterior pituitary lobes receives
releasing and inhibiting hormones from the hypothalamus
via a portal vein system known as hypothalamic
hypophyseal portal system.
25. HYPOTHALAMIC HYPOPHYSEAL PORTAL
SYSTEM
• Usually blood passes from the heart through an artery to a capillary to
a vein and back to the heart. But in portal system,blood flows from one
capillary network into a portal vein,and then into second capillary
network before returning to the heart. The name of portal system
indicates the location of the second capillary network. In the
hypophyseal portal system,blood flows from capillaries in the
hypothalamus into portal veins that carry blood to capillaries of the
anterior pituitary.
26. • The Posterior Pituitary- The posterior lobe is composed of neural tissues
and derived from a downgrowth of hypothalamic tissues and maintain its
neural connection with the hypothalamus via a nerve bundle called the
hypothalamic-hypophyseal tract.this tract arises from neurons in the
supraoptic and paraventricular nuclei of the hypothalamus.
• Hormones produced by the cell bodies of the neurosecretory cells are
packaged in the vesicles and these vesicles are called Herring bodies.
• POSTERIOR PITUITARY DOES NOT PRODUCE ITS OWN
HORMONES,BUT ONLY STORES AND RELEASE OXYTOCIN AND
ADH SECRETED BY HYPOTHALAMUS.
29. • 1. GROWTH HORMONE (SOMATOTROPHIN HORMONE)-GH IS
PRODUCED BY CELLS CALLED SOMATOTROPHS ;THE MOST
NUMEROUS CELLS IN THE ANTERIOR PITUITARY. THUS THIS IS
THE MOST ABUNDANT HORMONE SYNTHESIZED BY THE
ANTERIOR PITUITARY.
• UNLIKE THE OTHER HORMONES,GH IS NOT TARGETED TO ANY
ONE OR FEW ORGANS BUT HAS WIDESPREAD EFFECTS ON THE
BODY,ESPECIALLY ON CARTILAGE,BONE,MUSCLES AND FAT.
31. • 1.GROWTH-
• GH STIMULATES THE GROWTH OF ALL TISSUES OF THE BODY.
• THE GENERAL EFFECT OF GH IS TO PROMOTE CELLULAR DIFFERENTIATION
AND THUS TO PROMOTE WIDESPREAD TISSUE GROWTH.
• BODY GROWTH IN RESPONSE TO SECRETION OF GH IS EVIDENT DURING
CHILDHOOD AND ADOLESCENCE AND THEREAFTER SECRETION OF GH
MAINTAINS THE MASS OF BONES AND SKELETAL MUSCLES.
• ALTHOUGH , GH STIMULATES MOST BODY CELLS TO INCREASE IN SIZE AND
DIVIDE ,ITS MAJOR TARGETS ARE THE BONES AND SKELETAL MUSCLES-
STIMULATION OF THE EPIPHYSEAL PLATE LEADS TO LONG BONE GROWTH
STIMULATION OF SKELETAL MUSCLES PROMOTES INCREASED MUSCLES MASS.
32. 2.STIMULATION OF SECRETION OF INSULIN LIKE GROWTH FACTORS-
GH PROMOTES THE SYNTHESIS AND SECRETION OF SMALL PROTEIN HORMONE CALLED
INSULIN LIKE GROWTH FACTORS PRIMARILY INSULIN LIKE GROWTH FACTOR-1 OR
SOMATOMEDIN
THESE GROWTH PROMOTING PROTEIN HORMONES ARE PRIDUCED BY ELIVER, SKELETAL
MUSCLES,BONE,AND OTHER TISSUES IN RESPONSE TO HUMAN GROWTHH HORMONE.THE
FUNCTIONS OF IGFs ARE AS FOLLOWING-
• Stimulate uptake of amino acid from the blood nd their incorporation into cellular protein
throughout the body,accelerating protein synthesis.
• Enhance lipolysis in adipose tissues
• Stimmulate proliferation of chondrocytes resulting in bone growth
33. • 3.GLUCOSE SPARING-
• GH DECREASES THE USE OF GLUCOSE FOR ATP PRODUCTION BY MOST
BODY CELLS .THIS SPARES GLUCOSE SO THAT IT IS AVAILABLE TO NEURON
FOR ATP PRODUCTION IN TIMES OF GLUCOSE SHORTAGE.
• IN THE LIVER,GH ENCOURAGES GLYCOGEN BREAKDOWN AND RELEASE OF
GLUCOSE TO THE BLOOD.
• THIS HORMONE IS ALSO SAID TO HAVE ANTI INSULIN ACTIVITY,BECAUSE IT
SUPPRESSES THE ABILITIES OF INSULIN TO STIMULATE UPTAKE OF
GLUCOSE IN PERIPHERAL TISSUES AND ENHANCE GLUCOSE SYNTHESIS
INN THE LIVER.
34. REGULATION OF SECRETION AND INHIBITION OF
GROWTH HORMONE
• Growth hormone releasing hormone stimulates GH release.
• GHRH release is stimulated by low blood levels of GH and no. of secondary
triggers like hypoglycemia,increases in the blood levels of amino acids,low
levels of fatty acids ,other types of stressors such as vigorous physical
exercise.
• Growth hormone inhibiting hormone also called somtostatin,inhibit GH release.
• GHIH release is trigggerd by the feedback of GH and IGFs.
• GH release is also inhibited by hyperglycemia,hyperlipidemia,obesity.
36. • THYROID STIMULATING HORMONE OR THYROTROPIN IS SECRETED BY
PITUITARY CELLS CALLED THYROTROPHS.
• ITS RELEASE IS STIMULATED BY THYROTOPHIN RELEASING HORMONE(TRH)
FROM THE HYPOTHALAMUS.
• IT STIMULATE THE GROWTH AND CTIVITY OF THE THYROID GLAND,WHICH
SECRETES THE HORMONES THYROXIN (T4) AND TRI-IDOTHYRONINE(T3).
• SECRETION IS REGULATED BY A NEGATIVE FEEDBACK MECHANISM.
• RISING BLOOD LEVELS OF THYROID HORMONES ACT ON BOTH THE
PITUITARY AND THE HYPOTHALAMUS TO INHIBIT TSH SECRETION.
38. • CORTICOTROPHIN RELEASING HORMONE (CRH) FROM THE HYPOTHALAMUS PROMOTE
THE SYNTHESIS AND RELEASE OF THE ACTH BY THE ANTERIOR PITUITARY.
FUNCTIONS-
• 1.ACTH STIMULATES THE ADRENAL CORTEX TO RELEASE CORTICOSTEROID
HORMONES,CHOLESTEROL AND,MOST IMPORTANTLY CORTISOL.
• ACTH PLAY A CENTRAL ROLE IN THE BODY’S RESPNSE TO STRESS.
REGULATION OF SECRETION-
ITS RELEASE IS STIMULATED BY CRH,HAS A DAILY RHYTHM,WITH LEVELS PEAKING IN THE
MORNING,SHORTLY BEFORE AWAKENING.
RISING LEVEL OF GLUCOCORTICOID FEEDBACK AND BLOCK SECRETION OF CRH.
TRIGGERING CRH RELEASE INCLUDE FEVER,HYPOGLYCEMIA AND STRESSORS OF ALL
TYPES.
40. • PROLACTIN IS SECRETD BY LACTOTROPHS(MAMMOTROPES) OF ANTERIOR PITUITARY
,WHICH INCREASE IN SIZE AND NUMBER DURING PREGNANCY.
• THE BLOOD LEVEL OF PROLACTIN IS STIMULATED BY PROLACTIN RELEASING
HORMONE(PRH) RELEASED FROM THE HYPOTHALAMUS AND IS LOWERED BY
PROLACTIN INHIBITING HORMONE AND BY AN INCREASED BLOOD LEVELS OF
PROLACTIN.PIH NOW KNOWN TO BE DOPAMINE PREVENTS PROLACTIN SECRETION.
DECREASED DOPAMINE SECRETION LEADS TO AN INCREASE IN PROLACTIN
SECRETION.
• IN FEMALES, PROLACTIN LEVELS RISE AND FALL IN RHYTHM WITH ESTROGEN BLOOD
LEVELS. ESTROGEN STIMULATES PROLACTIN RELEASE BOTH DIRECTLY AND
INDIRECTLY. A BRIEF RISE IN PROLACTIN LEVELS JUST BEFORE THE MENSTRUAL
PERIOD PARTIALLY ACCOUNTS FROM THE BREAST SWELLING AND TENDERNESS SOME
WOMEN EXPERIENCE ATBTHAT TIME,BUT BECAUSE THIS PRL STIMUALTION IS SO
BRIEF,THE BREAST DO NOT PRODUCE MILK.
43. MSH STIMULATES MELANOCYTES TO INCREASE SYNTHESIS OF MELANIN
PIGMENT WHICH INFLUENCES PIGMENTATION OF SKIN AND HAIR BUT THIS
IS NOT AN IMPORTANT FUNCTION OF MSH IN HUMAN.THERE IS A LITTLE
CIRCULATING MSH IN HUMANS.
ITS EXACT ROLE IN HUMAN IS UNKNOWN.
EXCESSIVE LEVELS OF CRH CAN STIMULATE MSH RELEASE,DOPAMINE
INHIBITS MSH RELEASE.
45. • FOLLICLE STIMULATING HORMONE AND LUTEINIZING
HORMONE REFERRED COLLECTIVELY AS
GONADOTROPINS,ARE SECRETED BY PITUITARY CELLS
CALLED GONADOTROHS.AT PUBERTY SECRETION
INCREASES,FURTHER ENABLING NORMAL ADULT
FUCTIONING OF THE REPRODUCTIVE ORGANS, IN BOTH
MALES AND FEMALES.
46. • LUTEINIZING HORMONE
• IN FEMALES LH TRIGGERS OVULATION,THE RELEASE OF A SECONDARY
OOCYTES BY AN OVARY.LH STIMULATES FORMATION OF THE CORPUS
LUTEAM IN THE OVARY AND THE SECRETION OF PROGESTERONE BY
THE CORPUS LUTEUM.
• IN MALES, LH STIMULATES CELLS IN THE TESTES TO SECRETE
TESTOSTERONE. SECRETION OF LH LIKE THAT OF FSH IS CONTROLLED
BY GONADOTROPINN-RELEASING HORMONE.
47. • FSH-
• IN FEMALES THE OVARIES ARE THE TARGETS FOR FSH.EACH MONTHS FSH
INITIATES THE DEVELOPMENT OF SEVERAL OVARIAN FOLLICLES .FSH ALSO
STIMULATES FOLLICULAR CELLS TO SECRET ESTROGEN(FEMALE SEX
HORMONE)
• IN MALES,FSH STIMULATES SPERM PRODUCTION IN THE TESTES.
• GONADOTROPHIN RELEASING HORMONE FROM THE HYPOTHALAMUS
STIMULATES FSH RELEASE.RELEASE OF GnRH AND FSH IS SUPPRESSED BY
ESTROGEN IN FEMALE AND TESTOSTERON IN MALE THROUGH NEGATIVE
FEEDBACK SYSTEM.THERE IS NO GONADOTROPIN INHIBINTING HORMONE.
49. • OXYTOCIN-OXYTOCIN STIMULATES TWO TARGET TISSUES DURING AND AFTER
CHILD BIRTH(PARTURITION):UTERINE SMOOTH MUSCLES AND THE MUSCLE CELLS
OF THE LACTATING BREAST.
• DURING CHILD BIRTH-
• IN CHILDBIRTH,,IT STIMULATES SMOOTH MUSCLES OF THE UTERUS TO
CONTRACT,THUS CONTRIBUTING TO THE LABOUR CONTRACTIONS THAT EXPEL
THE CHILD.THIS IS AN EXAMPLE OF POSITIVE FEEDBACK MECHANISM.
• A STRONG STIMULANT OF UTERINE CONRACTION,OXYTOCIN IS RELEASED IN
SIGNIFICANTLY HIGHER AMOUNTS DURING CHILD BIRTH AND IN LACTATING
WOMEN.
• THE NO. OF OXYTOCIN RECEPTORS IN THE UTERUS PEAKS NEAR THE END OF
PREGNANCY AND UTERINE SMOOTH MUSCLE BECOMES MORE AND MORE
SENSITIVES TO THE HORMONE’S STIMULATORY EFFECTS.
50. • DURING LACTATION-
OXYTOCIN ALSO ACT AS THE HORMONAL TRIGGOR FOR MILK
EJECTION(THE LETDOWN REFLEX) IN LACTIATING WOMEN WHOSE
BREASTS ARE PRODUCING MILK IN RESPONSE TO PROLACTIN.
SUCKELING CAUSES A REFLEX INTIATED RELEASE OF OXYTOCIN,WHICH
TARGETS SPECIALIZED MYO-EPITHELIAL CELLS SURROUNDING THE MILK
PRODUCING GLANDS.AS THESE CELLS CONTRACT,MILK IS FORCED FROM
THE BREAST INTO THE INFANT’S MOUTH.
SUCKELING ALSO INHIBITS RELEASE OF PROLACTIN SECRETION AND
LACTATION.
51. • SEXUAL FUNCTION :
IN BOTH SEXES ,OXYTOCIN SECRETION INCREASES DURING
SEXUAL AROUSAL AND ORGASM.THE ROLE OF THIS HORMONE
IN MALES AND NON LACTATING WOMEN REMAONS UNCLEAR.
53. • ADH ALSO CALLED AS VASOPRESSIN BECAUSE IT CAUSES
VASOCONSTRICTION AT HIGH CONCENTRATION,FOR EXAMPLE AFTER
SEVERE BLOOD LOSS ,ADH CAUSES SMOOTH MUSCLES
CONTRACTION,ESPECIALLY VASOCONSTRICTION IN SMALL ARTERIES.
• THE MAIN EFFECT OF ADH IS TO REDUCE URINE OUTPUT(DIURESIS IS THE
PRODUCTION OF LARGE VOLUME OF URINE)
• ADH ACT ON DCT AND COLLECTING DUCTS OF THE NEPHRONS AND AS A
RESULT OF WATER FROM THE GLOMERULAR FILTRATE IS INCREASED.
• THE AMOUNT OS ADH SECRETED IS DETERMINED BY THE OSMOTIC
PRESSURE OF THE BLOOD CIRCULATING TO THE OSMORECEPTORS IN THE
HYPOTHALAMUS.
54. • AS THE OSMOTIC PRESURE RISES, FOR EXAMLE AS A RESULT