The endocrine system coordinates body functions through glands that release hormones directly into the bloodstream. There are three main types of hormones - peptides and proteins, steroids, and amines. Peptide hormones are synthesized in the endoplasmic reticulum and Golgi apparatus and secreted via exocytosis. Steroid hormones are synthesized from cholesterol and diffuse across cell membranes. Amine hormones like thyroid hormones and epinephrine are synthesized from the amino acid tyrosine.

1. 27-Oct-23 Introduction to Endocrine system 1
Endocrine System
By Njiru Njeru- ObGy

2. 27-Oct-23 Introduction to Endocrine system 2
Introduction
 Endocrine system
 One of the system involved in
coordination of body functions
 Systems involved in coodination
of body fnctn include
 Neural system
 Release chemical substances
(neurotransmitters) at axon terminals
 Act locally to control cell function

3. 27-Oct-23 Introduction to Endocrine system 3
Introduction
 Endocrine system
 Glands or specialized cells
 Release chemicals (hormones)
 Into blood
 Have influence on cell function at
another location
 Neuro-endocrine
 Neurons secrete substances
(neurohormone)

4. 27-Oct-23 Introduction to Endocrine system 4
Introduction
 Reach circulating blood
 Influence cell function at another
location
 Paracrine
 Cells secrete substances
 Diffuse in ECF
 Affect neighboring cells

5. 27-Oct-23 Introduction to Endocrine system 5
Introduction
 Autocrine
 Cells secrete substances
 Affect the functioning of the same cell

6. 27-Oct-23 Introduction to Endocrine system 6
Hormones
 Working definition=
 Hormones r chemical substances
 Serve as regulators & coordinators of
Various biologic functions in the
body
 Highly potent, specialized organic
molecules
 Produced by endocrine cells
 In response to specific stimuli

7. 27-Oct-23 Introduction to Endocrine system 7
Hormones
 They exert their actions on specific
target cells
 The target cells are equipped with
 Receptor that bind hormones
 With high affinity & specificity
 When bound, hormones
 Initiate characteristic biological
responses by target cells

8. 27-Oct-23 Introduction to Endocrine system 8
Principal Endocrine
Organs
Organ Hormone
Pituitary gland Tropic hormones (ACTH, GH, prolactin)
Hypothalamus Hypophysiotropic hormones (releasing
hormones, TRH, GnRH)
Thyroid gland Thyroxin , triiodothyronin
Adrenal glands Mineralocorticoids (aldosterone),
glucocorticoids (cortisol), catecholamines
(epinephrine, norepinephrine)
Parathyroid gland Parathtyroid hormone (PTH)
Gonads Testosterone, estrogen, progesterone
Pancreatic islets Insulin, glucagon, somatostatin

9. 27-Oct-23 Introduction to Endocrine system 9
Principal Endocrine
Organs
Other organs Hormone
Heart Atrial natriuretic peptide (ANP)
Kidney 1,25-dihydroxycholecalciferol (calcitriol),
erythropoeitin
Liver 25-hydroxycholecalciferol (calcidiol),
somatomedin
Pineal gland Melatonin
Skin Calciferol (vitamin D)
GIT Gastrin, cholecyctokinin (CCK), secretin,
vasoactive intestinal peptide (VIP) etc

10. 27-Oct-23 Introduction to Endocrine system 10
Structure & Synthesis
3 general classes of hormone
 Protein & polypeptides
 Include hormones secreted by
 Anterior pituitary
 The pancreas (insulin, glucagon)
 Parathyroid gland (PTH)

11. 27-Oct-23 Introduction to Endocrine system 11
Structure & Synthesis
 Steroids, include hormones secreted by
 Adrenal cortex
 Cortisol, aldosterone
 Ovaries
 Oestrogen, progesterone
 Testes
 Testosterone
 Placenta
 Oestrogen, progesterone

12. 27-Oct-23 Introduction to Endocrine system 12
Structure & Synthesis
 Derivatives of amino acid tyrosine
 Thyroid gland
 Thyroxin, tri-iodothyronin
 Adrenal medulla
 Epinephrine & norepinephrine

13. 27-Oct-23 Introduction to Endocrine system 13
Peptide Hormones
 Polypeptides and
protein hormone
 Synthesized on
 Rough endplasmic
reticulum of the
endocrine cells
 Usually synthesized as
preprohormone
 Larger protein
 Has no biological
activity
Preprohormone
Prohormone
Hormone &
Inactive fragments
Synthesis in
RER
Cleaved into
prohormone in
ER
Packaging in
Golgi, cleaved
into active
hormone

14. 27-Oct-23 Introduction to Endocrine system 14
Peptide Hormones
 This is then cleaved
 To a prohormone
 In endoplasmic
reticulum
Preprohormone
Prohormone
Hormone &
Inactive fragments
Synthesis in
RER
Cleaved into
prohormone in
ER
Packaging in
Golgi, cleaved
into active
hormone

15. 27-Oct-23 Introduction to Endocrine system 15
Peptide Hormones
 The prohormone is
then
 Transferred to Golgi
apparatus
 For packaging
 In the process enzymes
cleave it into
 An active hormone &
 A larger inactive
fragment
Preprohormone
Prohormone
Hormone &
Inactive fragments
Synthesis in
RER
Cleaved into
prohormone in
ER
Packaging in
Golgi, cleaved
into active
hormone

16. 27-Oct-23 Introduction to Endocrine system 16
Peptide Hormones
 Secretion of peptide
hormones
 Active hormone &
inactive fragment
 Occur by exocytosis
when
 secretory vesicles
fuse with cell
membrane
 Ca++
Ca++

17. 27-Oct-23 Introduction to Endocrine system 17
Peptide Hormones
 Granular content are then
extruded into
 Interstitial fluid
 Blood stream
 In many cases the
stimulus for the
exocytosis
  Ca++ in cytosol as a
result of
 Depolarization of
plasma membrane
 Ca++
Ca++

18. 27-Oct-23 Introduction to Endocrine system 18
Peptide Hormones
 In other cases
 Stimulation of the
endocrine cell
surface receptors
  cAMP
 Activation of protein
kinase
 Initiate release of the
hormone
 cAMP
Prot kinase
Activation
Receptor

19. 27-Oct-23 Introduction to Endocrine system 19
Peptide Hormones
 Peptide hormone
are water soluble
 Enter the circulatory
system easily
 Carried to target
tissues
 cAMP
Prot kinase
Activation
Receptor

20. 27-Oct-23 Introduction to Endocrine system 20
Steroid Hormones
 Usually synthesized from
cholesterol
 Chemical structure
 Similar to that of cholesterol
 They are lipid soluble,consist of
 3 cyclohexyl ring and
 1 cyclopentyl ring

21. 27-Oct-23 Introduction to Endocrine system 21
Structure of Steroid
Hormones
19
3
2
1
8
7
6
5
4
10
9
15
14
13
12
11
18
17
16
Derivative of cholesterol
Have 3 cyclohexyl rings( A, B, C)
One cyclopentyl ring (D)
A B
C D
Cyclopentanoperhydrophenanthrene

22. 27-Oct-23 Introduction to Endocrine system 22
Steroid Hormones
 There is little hormone stored
 In steroid forming cells
 But there are large stores
 Of cholesterol esters
 Can be rapidly mobilized for steroid
synthesis

23. 27-Oct-23 Introduction to Endocrine system 23
Steroid Hormones
 Most of the cholesterol
 Come from plasma
 But cells have the ability to
synthesize it

24. 27-Oct-23 Introduction to Endocrine system 24
Steroid Hormones
 Steroid hormones are lipid
soluble
 Once they are synthesized
 They diffuse across cell membrane
 Into interstitial fluid

25. 27-Oct-23 Introduction to Endocrine system 25
Amine Hormones
 Derivatives of tyrosine
 From the thyroid & adrenal
medulla glands
 Formed by the action
 Of cytoplasmic enzymes

26. 27-Oct-23 Introduction to Endocrine system 26
Amine Hormones
 Thyroid hormones
 Synthesized and stored in thyroid gland
 Incorporated in thyroglobulin
 Stored in large follicle within the gland
 Secretion occurs when
 The amines are split from thyroglobulin
 Free hormone released in blood
 Bound to thyroxine binding globulin (TBG)
 Which slowly releases the hormone to target
tissues

27. 27-Oct-23 Introduction to Endocrine system 27
Amine Hormones
 Epinephrine & norepinephrine
 Formed in the adrenal medulla
 Secrete 4 times more epinephrine than
norepinephrine
 Stored in vesicles
 Secreted by exocytosis
 In plasma can exist
 Free form or in conjugation with other
substances

28.  Thank You!
27-Oct-23 Introduction to Endocrine system 28