anatomy of the endocrine system and hormones presented to December 2016 midwifery class.

1. THE ENDOCRINE SYSTEM
AND HORMONES
MR. ABDOU PANNEH
(RM ,FWACN,DHAF,NT, RN)

2. INTRODUCTION
• The endocrine system is part of the chemical
communication system of the body and
complements the nervous system.
• The nervous system evokes rapid but short-term
responses whereas the former (endocrine
system) causes slower and more sustained
effects.
• The endocrine system consists of glands widely
separated from each other with no direct
anatomical links.

3. • They are commonly referred to as the ductless
glands because the hormones they secrete pass
directly into the blood stream.
• A hormone is a chemical messenger which,
having been formed in one organ or gland, is
carried in the blood to another organ (target
organ) or tissue, probably quite distant, where it
influences activity, growth, nutrition, etc.

5. HYPOTHALAMUS AND PITUITARY
GLAND
• Although the hypothalamus is classified as a
part of the brain and not as an endocrine
gland, it has a direct controlling effect on the
pituitary gland and an indirect controlling
effect on many others.
• The pituitary gland (master gland) and the
hypothalamus act as a unit, regulating the
activity of most of the other endocrine glands.

6. • The pituitary gland is located just below the
hypothalamus, to which it is attached by a
stalk. The pituitary gland consists of two main
parts:
The adenohypophysis (anterior lobe) is an up
growth of tissues from the pharynx.
The neurohypophysis (posterior lobe) is a
down growth from the brain.

9. Adenohypophysis
• There are several hormones secreted by the
adenohypophysis:
Growth hormone (GH)
• GH is synthesised by the anterior pituitary
gland.
• Its release is stimulated by GHRH (growth
hormone releasing factor) secreted by the
hypothalamus.

10. • GH promotes growth of the skeleton, muscles,
connective tissue and organs such as kidneys,
liver, adrenal glands, intestines, pancreas, etc.
Increased secretion is stimulated by exercise,
anxiety, sleep and hypoglycaemia.
• It stimulates growth and activity of the thyroid
gland which secretes the hormones thyroxin
(T4) and triiodothyronine (T3).

11. Thyroid Stimulating Hormone
(TSH)
• This hormone is synthesised by the anterior
pituitary gland and its release is stimulated by
thyroid releasing hormone (TRH).
• Secretion is also regulated by a negative
feedback mechanism. When the blood level of
thyroid hormones is high secretion of TSH is
reduced and vice versa.

12. Adrenocorticotrophic Hormone (ACTH)
• Corticotrophin releasing factor (CRF) from the
hypothalamus promotes the synthesis and
release of ACTH by the anterior pituitary.
• This stimulates the flow of blood to the
adrenal cortex, increases the concentration of
cholesterol and steroids within the gland and
increases the output of steroid hormones,
especially cortisol.

13. Prolactin
• This hormone has a direct effect on the
breasts immediately after parturition.
• Suckling stimulates prolactin secretion and the
resultant high blood level is a factor in
reducing the incidence of conception during
lactation.

14. Gonadotrophic hormones
• The anterior lobe secretes two gonadotrophic or
sex hormones in females and males:
Female gonadotrophic hormones
• Follicle-stimulating hormone stimulates the
development and ripening of the ovarian follicle.
• During its development the ovarian follicle
secretes its own hormone, oestrogen. As the
level of oestrogen increases in the blood so FSH
secretion is reduced.

15. • Luteinising hormone promotes the final
maturation of the ovarian follicle and
ovulation (discharge of the mature ovum).
• Its main function is to promote the formation
of the corpus luteum which secretes the
second ovarian hormone, progesterone.
• As the level of progesterone in the blood
increases there is a gradual reduction in the
production of the Luteinising hormone.

16. Male gonadotrophic hormones
• Follicle-stimulating hormone stimulates the
epithelial tissues of the seminiferous tubules
in the testes to produce spermatozoa.
• Luteinising hormone stimulates the interstitial
cells in the testes to secrete the hormone
testosterone.

18. Neurohypophysis
• The posterior lobe of the pituitary gland
releases the hormones oxytocin and
antidiuretic hormone (ADH).
• These two hormones are synthesized by the
cells of the hypothalamus and migrate along
nerve fibres to the posterior pituitary where
they are stored in nerve endings.
• Each hormone is released in response to a
different stimulus.

19. Oxytocin
• Oxytocin promotes contraction of uterine
muscle and contraction of the myoepithelial
cells of the lactating breast, squeezing milk into
the large ducts behind the nipple.
• In late pregnancy the uterus becomes very
sensitive to oxytocin. The amount secreted is
increased just before and during labour and by
the suckling baby.
Antidiuretic hormone/ vasopressin
• This hormone has two main functions:

20. • Antidiuretic effect – this hormone stimulates
the kidneys to reabsorb more water.
• The amount of ADH secreted is influenced by
the osmotic pressure of the blood circulating
to the osmoreceptors in the hypothalamus.
• As the osmotic pressure rises the secretion of
ADH increases and more water is reabsorbed.
• Conversely, when the osmotic pressure of the
blood is low, the secretion of ADH is reduced,
less water is reabsorbed and more urine is
produced.

21. • The blood level of ADH is increased in
dehydration and following haemorrhage.
• Pressor effect – In pharmacological doses,
ADH stimulates contraction of smooth muscle,
especially in blood vessel walls of the skin and
abdominal organs, raising the blood pressure.
• It is not clear whether physiological amounts
have a significant pressor effect.

23. THYROID GLAND
• The thyroid gland, which is situated at the
front of the neck, partially surrounding the
trachea, plays an important role in regulating
the body’s metabolism.
• It consists of two lobes, one on either side of
the thyroid cartilage. The lobes are joined by a
narrow isthmus, lying in front of the trachea.
• The lobes are roughly cone-shaped, about
5cm long and 3cm wide.

25. Function of the thyroid hormones
• Iodine is essential for the formation of the
thyroid hormones, thyroxin (T4) and
triiodothyronine (T3).
• It is ingested in food and most of it is taken up
by the gland and used in hormone formation.
• The release of thyroid hormones is regulated
by thyroid releasing hormone (TRH) from the
hypothalamus.

26. • Thyroid releasing hormone stimulates the
anterior pituitary gland to secrete thyroid
stimulating hormone (TSH) which in turn acts
on the thyroid to secrete its hormones.
• The hormones produced by the thyroid gland
act on cells to control the body’s metabolism,
including the use of energy.
• They are also associated with the growth and
development of tissues, especially the
nervous system.

27. • Increased levels of T3 and T4 decrease thyroid
stimulating hormone secretion and vice versa.
• When the supply of iodine is deficient, excess
TSH is secreted and there is proliferation of
thyroid gland cells and enlargement of the
gland.
• Secretion of T3 and T4 begins about the 3rd
month of fetal life and is increased at puberty
and in women during the reproductive years,
especially during pregnancy.

28. • Calcitonin is secreted by the C-cells in the
thyroid. It acts on bone and the kidneys to
reduce the blood calcium level.
PARATHYROID GLANDS
• There are four small parathyroid glands, two
embedded in the posterior surface of each
lobe of the thyroid gland.
• The function of the parathyroid glands is to
secrete the hormone parathryn (PTH).

30. Function of parathryn
• Secretion of PTH is regulated by the blood
level of calcium. When this falls, secretion of
PTH is increased and vice versa.
• The main function of PTH is to maintain the
blood concentration of calcium within normal
limits.
• This is achieved by influencing the amount of
calcium absorbed from the small intestines
and reabsorbed from the renal tubules.

31. ADRENAL/SUPRARENAL GLANDS
• There are two adrenal glands, one situated on
the upper pole of each kidney enclosed within
the renal fascia. They are about 4 cm long and
3cm thick.
• The glands are composed of two parts which
differ both anatomically and physiologically.
• The outer part is the cortex and the inner part,
the medulla. The cortex is essential to life but
the medulla is not.

34. Adrenal cortex
• The adrenal cortex produces three groups of
hormones:
a. Glucocorticoids
b. Mineralocorticoids
c. Androgens (sex hormones)
Glucocorticoids
• Cortisol (hydrocortisone) and corticosterone
are the main glucocorticoids.

35. • Secretion of glucocorticoids is stimulated by
adrenocorticotrophic hormone (ACTH) from
the anterior pituitary and by stress.
• Glucocorticoids have widespread effects on
body systems. The main functions include:
Regulation of carbohydrate metabolism
Promotion of the formation and storage of
glycogen.
Gluconeogenesis from protein, raising the
blood glucose level.

36. Promotion of sodium and water reabsorption
from the renal tubules
In pathological and pharmacological
quantities glucocorticoids have an
antinflammatory action and suppress the
response of the tissues to injury, delaying
healing.
Mineralocorticoids
• Aldosterone is the main mineralocorticoid. Its
function is associated with the maintenance of
the electrolyte balance in the body.

37. • It stimulates the reabsorption of sodium by
the renal tubules and when the amount of
sodium reabsorbed is increased the amount of
potassium excreted is increased.
• Aldosterone increases the reabsorption of
water and sodium and the excretion of
potassium by the kidneys.
• The amount of aldosterone produced is
influenced by the sodium level in the blood. If
there is a fall in the blood sodium level more
aldosterone is secreted and more sodium
reabsorbed.

38. Adrenal medulla
• The medulla is completely surrounded by the
cortex. It produces the hormones adrenaline
and noradrenaline.
• The adrenal medulla is not essential to life but
its hormones greatly assist the body in its
response to adverse environmental
conditions.
• The main function of noradrenalin is
maintenance of blood pressure by causing
generalized vasoconstriction, except of the
coronary arteries.

39. • Adrenaline is associated with potentiating the
conditions needed for ‘fight or flight’, e.g.:
Constricting skin blood vessels
Dilating blood vessels of muscles, heart and
brain
Converting glycogen to glucose
Increasing the metabolic rate
Dilating the pupils
Dilating the bronchioles, allowing an increase
in air intake

40. ISLETS OF LANGERHANS
• The cells which make up the islets of
Langerhans are found in clusters irregularly
distributed throughout the substance of the
pancreas.
• Their secretion passes directly into the
pancreatic veins and circulates throughout the
body.
• There are three main types of cells in the islets
of Langerhans:

42. • Alpha cells that secrete glucagon,
• β (beta) cells that secrete insulin,
• and delta cells that secrete somatostatin
• Insulin and glucagon influence the level of
glucose in the blood, each balancing the
effects of the other.
• Glucagon tends to raise the blood glucose
level and insulin reduces it.

44. • The normal blood glucose level is between
2.5and 5.3mmol/litre (45 to 95mg/100ml).
• When there has been excessive exercise or an
insufficient intake of carbohydrate foods it
may fall to the low end of the normal range or
below.
• When this happens glucagon has the effect of
raising the blood glucose level by mobilising
the glycogen stores in the liver.
• Insulin acts on all cell membranes, stimulating
the uptake of glucose, amino acids and fats.

45. • In addition it is associated with:
Conversion of glucose to glycogen
in the liver and muscles
Synthesis of DNA and RNA
Storage of fat as adipose tissue
Prevention of gluconeogenesis and
the breakdown of protein and fat

46. QUESTIONS,
CONTRIBUTIONS,
CLARIFICATIONS
&
CONSTRUCTIVE
CRITICISMS????
?