Introduction to endocrine system and pituitary gland

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•DR. Hanan A. Mubarak, B.M.B.ch, M.Sc., M.D
•Professor, Faculty of medicine, Cairo university

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Introduction
• Endocrine glands are ductless glands. the
y secret hormones directly into the bloo
d
Function of hormones:
• (1) Regulation of biochemical reaction
(metabolic).
• (2) Regulation of body processes e.g. growth
maturation, regeneration, reproduction,
pigmentation.

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Endocrine glands
• They are glands that secrete hormones directly
into blood:
• Pituitary
• Pineal gland (secrete melatonin)
• Thyroid
• Parathyroid
• Suprarenal (cortex & medulla)
• Islets of Langerhans (endocrine pancreas)
• Gonads (ovaries and testes).

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Endocrine glands

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Nervous & Endocrine interrelation
• The hypothalamus controls endocrinal activity by hypothalamic
hypophyseal system.
• In the hypothalamus, there are neurosecretory cells which:
synthesize & secrete neurohormones.
Hypothalamic hypophyseal system is:
(1) Hypothalamic - hypophyseal tract:
• Nervous connection
• Transports ADH & oxytocin hormones from hypothalamus to the
posterior lobe of pituitary gland.
(2) Hypothalamic - hypophyseal portal circulation:
• Vascular connection.
• Transports releasing or inhibitory factors from
hypothalamus to anterior lobe of pituitary gland.

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Hormones
• Definition: Chemical substances that are secreted by spe
cial cells & affect distant organs.
Chemical nature
(1) Simple amino acids (2) Protein, (3) Steroid
(tyrosine derivatives) polypeptide hormones
& glycoprotein
● Thyroid hormones ● Adrenal
● Catecholamines ● Hypothalamic releasing cortical
& inhibitory factors hormones
● Pituitary hormones ● Gonadal
● Parathyroid hormones hormones
● Pancreatic hormones ● Vitamin D
● Thyrocalcitonin derivatives

9. Physiological Properties of Hormones
• 1. They are produced in small amounts (milligrams to
nanograms).
• 2. Their rate of secretion is determined by the body
needs.
• 3. They may have an effect on various tissues of the
body (e.g. insulin) or they may act on specific target
organs (e.g. sex hormones).
• 4. They initiate biochemical reactions that persist after the
disappearance of the hormone.
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10. Physiological Properties of Hormones
• 5. Some hormones antagonize the effect of others, and
the signal, which causes the release of one
hormone, inhibits the release of the other (e.g.
insulin and glucagon).
• 6. Rhythm - secretion: The secretion of some
hormones is further controlled by a circadian rhythm
(i.e., a 24 hour rhythm), where the secretion
increases and decreases at certain hours of the day,
e.g. ACTH, others are controlled by a monthly
rhythm, e.g. female gonadotropic hormone.

11. Mechanism of Action of Hormones
• The end result of a hormone action on its target
cells is a change in the rate.
• This is achieved by combination of the hormone
to its specific receptor.
• The receptor may be present
• On the membrane of the target cell or
• Inside the target cell (in cytoplasm or nucleus)
• Usually the combination of the hormone and its
receptor increases the activity of a certain
enzyme.

12. Mechanism of Action of Hormones
A. Mechanism of action of protein and
polypeptide hormones:
• Protein and polypeptide hormones change
the rate of enzyme activity and do not affect
enzyme or protein synthesis.
• The receptors for such hormones are present
on the cell membrane of target cell.

13. Mechanism of Action of Hormones
• Hormones are called "primary messengers“
• Leading to the formation of hormone-receptor
complex ll resulting in the release of
"second messengers“ (e.g. cAMP or
intracellular Ca++, DAG, IP3).
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15. Mechanism of Action of Hormones
B. Steroid hormones:
• They produce their effects through stimulation of protein
synthesis in their target cells. Therefore their action is
slow.
• Being lipid soluble, steroid hormones pass easily through
the cell membrane.
• The receptors for these hormones are present in the
cytoplasm of their target cells.
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16. • Combination of steroid hormones with their receptors
results in the formation of a "hormone-receptor
complex" (H-R complex).
• The H-R complex moves to the nucleus and binds to
the DNA of chromosomes. This causes the
transcription of specific mRNA, which then diffuses to
the cytoplasm, where it initiates protein synthesis.

17. Mechanism of Action of Hormones
C. Thyroid hormones:
• These hormones also act through protein
synthesis.
• Therefore their action is slow.
• Thyroid hormones combine with their specific
receptors inside the nucleus, forming H-R
complexes.
• H-R complexes then bind to DNA causing
increased or decreased synthesis of certain
enzymes that regulate cell function.
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18. Regulation of Hormone Secretion
• The secretion of hormones is regulated by many factors.
• 1. Nervous control e.g. vagus nerve increase insulin
secretion)
• 2. Hormonal control e.g. Releasing and inhibiting factors
released from the hypothalamus
(hypothalamic hormones).
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19. • 3. Feedback control:
The concentration of a target hormone, substrate or
mineral may influence the secretion of hormones.
Accordingly there are 3 types of feedback control:
• Hormone-hormone feed-back
• Substrate-hormone feed-back
• Mineral-hormone feedback

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Regulation of Hormone Secretion

21. The feedback control is important to:
• 1. Prevent over stimulation of the target glands.
• 2. Maintain the normal level of target hormones
in the blood.
• 3. Adjust the rate of secretion of endocrine
glands according to the body needs.
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The Pituitary Gland
• Located at
the base of
the skull.
• Anterior and
Posterior lobe
s.

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Pituitary Gland (Hypophysis)
• Small gland 1 cm in diameter that lies
inside the skull .
• It is connected with the hypothalamus.
• It is divided into:
1- Anterior pituitary
2- Posterior pituitary

25. Anterior Lobe
secretes
Posterior
Lobe
secretes
Growth hormone (GH) Vasopressin
(ADH)
Prolactin hormone oxytocin
Thyroid stimulating hormone (TSH)
Adrenocorticotrophic hormone(ACTH)
Gondadotrophins
Follicle stimulating hormone (FSH) &
Luteinizing hormone (LH)

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Hypothalamo-pituitary-end organ axis

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Hypothalamo-pituitary-organ axis

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Growth Hormone
• GH Chemistry: polypeptide
• Origin: anterior pituitary
• Functions of GH:
[1] Action on Growth:
• On viscera: It increases size and number of
cells. So, there is increase size of viscera.
• On skeleton: It stimulates growth of the epip
hyseal cartilage & elongation of bone (increas
e stature). After puberty, it increases thicknes
s of all bones.

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GH

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Growth Hormone
Functions of GH:
[2] On protein metabolism: Anabolic
i.e. increases protein synthesis
• Mechanism of its anabolic effect:
1) increases uptake of amino acids by cells
2) increases formation RNA

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Growth Hormone
Functions of GH:
[3] On carbohydrate metabolism:
• GH is diabetogenic, it raises blood glucose
level by: Stimulating glycogenolysis
[4] On fat metabolism:
• GH increases lipolysis & fatty acid release
from adipose tissue.

32. Regulation of GH secretion
A. GH secretion is increased by:
• GHRH (growth hormone releasing hormone secreted
by the hypothalamus).
• Low blood glucose and FFA level, e.g. in exercise, fa
sting, malnutrition
• Increased amino acids in blood.
• Stress, e.g. operations.
• Deep sleep.
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33. Regulation of GH secretion
B. GH secretion is decreased by:
• Somatostatin (SS: GHIH: growth hormone inh
ibiting hormone secreted by the hypothalamu
s)
• Increased blood glucose and FFA level.
• Treatment with corticosteroids (cortisone)
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Disorders of GH secretion
[1] Deficiency of GH : Pituitary Dwarfism
• It is caused by decreased GH secretion before puberty
• Characters & features:
1) Decreased growth
A- Arrested skeletal growth.
B- Symmetrical growth retardation: the height = span &
the distance from crown to symphysis = distance
from symphysis to toes
C- Retardation of soft tissue growth
2) No mental retardation : dwarf may be very intelligent.
3) Sexually normal

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Pituitary Dwarfism

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Disorders of GH secretion
[2] Gigantism:
• Increase GH before the closure of epiphysis of long
bone (before puberty)
• Features:
Overgrowth of all bones leading to tall individual (2 – 2.1
meter long):
growing period is lengthened, giant may continue to gro
w till time of death..
Overgrowth of soft tissue: Visceromegaly
Hypogonadism due to pressure on cells that secrete gonadotropi
ns .
Hyperglycemia: pituitary diabetes.

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• If too little is secreted
, dwarfism occurs; if
too much, gigantism
is the result. It

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Disorders of GH secretion
[3] Acromegalv:
• Increase GH after closure of epiphysis (after puberty). Features:
Overgrowth of bones: the bones become more thicker.
a- Overgrowth of bones of hands & feet.
b- Overgrowth of vertebrae → bowing of spines or kyphosis
c- Overgrowth of skull: large & elongated.
- Supra-orbital ridges are prominent
- Nasal bones: thick
- Overgrowth of mandible → protrusion of
mandible → separation of teeth.
Overgrowth of soft tissues (organomegaly) & muscles
Hyperglycemia and diabetes mellitus
Vision disturbances

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• In the photographs, we see a wom
an at 16, 33 and 52 years of age
who has a condition caused by ex
cessive secretion of growth hormo
ne during adulthood. This conditio
n is characterized by disproportion
ate growth in the jaw, hands and n
ose

46. Actions of ADH
1. On kidneys:
• The principal effect of ADH is to increase the p
ermeability of collecting ducts of the kidney to
water (increase water reabsorption), leading to
retention of water by the kidneys (antidiuretic e
ffect).
2. On blood vessels:
When the hormone is secreted in large amount
s, it directly causes constriction of arterioles, re
sulting in elevation of the arterial blood pressur
e (presser effect). 46

47. Regulation of ADH Secretion
A. ADH secretion is increased by:
• Increased osmotic pressure of extra-cellular fluid (ECF):
It causes dehydration of osmoreceptors in the hypothal
amus.
• Decreased blood volume (Hypovolemia), e.g. in hemorrh
age.
• Morphine and nicotine.
B. ADH secretion is decreased by:
• A decrease in osmotic pressure of ECF.
• Hypervolemia
• Ethanol
• Cortisol

48. Diabetes Insipidus
Deficiency of ADH secretion leads to a condition
known as diabetes insipidus" in which there is:
• Polyuria (excretion of large volume of dilute uri
ne)
• Polydepsia (drinking of large amounts of water
).
• loss of water soluble vitamins.

49. Oxytocin
Actions of Oxytocin:
1. Uterine contractions during delivery.
2. Milk ejection from breast : it causes contract
ion of myoepithelial cells in the breast, causi
ng of milk ejection from breast.

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