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ENDOCRINE SYSTEM - PDF

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ENDOCRINE SYSTEM

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									                               ENDOCRINE SYSTEM
A REGULATORY SYSTEM of body functions:

-      control homeostasis by release of hormones (chemical messengers) into bloodstream.

-                 Target cells all over body.


             COMPARISON OF NERVOUS AND ENDOCRINE SYSTEMS

                                            NERVOUS                       ENDOCRINE
1. Control by                      Electrical Impulses delivered   Release of hormones into
                                   over neurons.                   blood stream
2. Target Cells                    Muscle Cells                    Target cells all over body
                                   Gland Cells
                                   Other neurons
3. Effects                         Muscles contract                Change Metabolic
                                   Gland secrete                   Activities of body tissues
4. Response Time                   A few millisecs                 Can be up to several secs-
                                                                   hours - days
5. Direction of response           Brief                           Longer than effect of nervous
                                                                   stimulation




1.     NEURO-ENDOCRINE SYSTEM

       Consists of Central nervous system cells which secrete Neuro-hormone into body
       fluids → circulatory system → target cells → response (evolved first?).

2.     CLASSICAL ENDOCRINE SYSTEM

       Consists of Glandular cells which secrete hormone into body fluids → circulatory
       system → target cells → response.

       Both endocrine systems are important regulatory systems.

       However, effects are slower and longer term than nervous system regulation.
                                                                                 2


1.   NEURO-ENDOCRINE SYSTEM

     Neurosecretory cells: (Special neurons) neurohormone synthesized in rough
     endoplasmic reticulum, packaged into granules by golgi complex.

                                  ↓

     Transported to axon terminals, stored


                   ↓

     Released by exocytosis.




                                         NEURON CELL BODY




                                                AXON


NEUROHORMONE




                                                              AXON
                                                              TERMINALS




                   CIRCULATORY
                   SYSTEM




                                                              TARGET
                                                              CELL


(TORTORA & GRABOWSKI 8th ed. Fig 12.3 p. 337)
                                                                                       3


Neuro-endocrine regulation is present in all Vertebrates and Invertebrates,

-      more common in INVERTEBRATES

       e.g.    Regulation of:

                      Moulting
                      Metabolism
                      Colour change
                      Reproduction
                      Ion and Osmoregulation

(a)    In Hydrozoans:

       Removal of head of Hydra

               ↓

       Neurosecretory granules migrate to axon terminals

               ↓

       Released into E-C space

               ↓

       Target cells: Regeneration of tentacle and mouth




b)     ANNELIDS

       Well-developed nervous system

       Well-developed circulatory system

       Large coelom

       Well-developed neuro-endocrine cont of growth, metamorphosis, gonadal maturation.
                                                                      4


Neuro-endocrine regulation in VERTEBRATES


In Mammals:

      (a)     HYPOTHALAMUS → POSTERIOR PITUITARY


                                OXYTOCIN

                                                 ANTIDIURETIC
                                                 HORMONE (AI)


(TORTORA & GRABOWSKI 8th ed. Fig 18.10 p. 517)

              NERVE CELL
               BODIES
                                                     HYPOTHALAMUS




              ARTERIOLE


              POSTERIOR                                   ANTERIOR
              PITUITARY                                   PITUITARY




                           OXYTOCIN, ADH
                                                                                        5


    (b)    SYMPATHETIC NERVOUS SYSTEM

           → ADRENAL MEDULLA               → ADRENALINE
            (CHROMAFFIN CELLS)               AND NORADRENALINE




                                                               ADRENAL
                                                               MEDULLA
     SYMP.                                                     (CHROMAFFIN
CELLS)
     NERVE

                                                        ADRENALINE
                                                        AND NORADRENALINE




    Chromaffin cells are modified neurons of sympathetic nervous system and are found
    in the adrenal medulla.


    CLASSICAL ENDOCRINE SYSTEM

    Cells/ductless glands which release hormones into body fluids.

    -      Found in higher Invertebrates and Vertebrates,




                                                        ENDOCRINE CELLS


                                                               HORMONE

           CIRCULATORY
            SYSTEM




                                                               TARGET CELLS
                                                                                       6


VERTEBRATES

-     Endocrine glands have rich blood supply

-     Cell often arranged in cords separate by capillaries/sinusoids (blood spaces).

INVERTEBRATES

-     Endocrine glands bathed in haemolymph

-     e.g. (a) Prothoracid gland (Arthropods) consists of compact masses of Cell

-     Hormones diffuse from inner cells

                     ↓

-     Surfaces of gland


             ↓

-     Haemolymph

             ↓

      Target cells


(b)   INSECTS:

      Connective tissue sheath of viscera and endocrine glands may direct flow on
      hormones towards haemolymph and target cells.

      e.g. Secretions of pericardial cells flow along fine channels to heart

      → control heart rate.
                                                                                        7


                            ENDOCRINE SYSTEM

(TORTORA & GRABOWSKI 8th Ed. Fig. 18.1, p. 502)

                                                                      HYPOTHALAMUS


PINEAL GLAND                                                          PITUITARY GLAND




PARATHYROID                                                           THYROID GLAND
  GLANDS
                                                                      THYMUS GLAND


                                                                      ADRENAL GLANDS


                                                                      PANCREAS




                                                                      OVARIES


                                                                      TESTES


Endocrine glands secrete their products (Hormones) into blood.

Hormones act on target cells to alter their physiological activity.
                                                                                             8


                             ACTION OF HORMONES
Alter physiological activity of their target cells.

1.      Control of Internal environment. (Cell metabolism, electrolyte, H2O and nutrient
        balance).

2.      Respond to changes in environment. (Defence against stressors)

3.      Integrate growth and development.

4.      Involved in reproduction.

5.      Regulate red blood cell production.

6.      Control and Integrate circulation, digestion and absorption of food (with A.N.S.).

        A.N.S. Autonomic Nervous System


CONTROL OF HORMONE SECRETION
(NEGATIVE FEEDBACK)


1.      HORMONAL STIMULI

        e.g.    Releasing       Hormones from hypothalam
                Inhibiting

                                        ↓

                                Anterior Pituitary

                                        ↓

                                Hormones,
                                e.g. Thyroid stim hormone

                                Thyroid gland

                                Thyroid hormone
                                                                            9


2.     HUMORAL STIMULI

       Changing blood levels of ions, nutrient stimulate hormone release.

       e.g. ↑ blood glucose → Islet cells, pancri

                                     ↓

                                 Insulin


       ↓ Blood Ca2+ → Parathyroid glands

                                     ↓

                             Parathyroid Hormone

NEURAL STIMULI

e.g. Symp. Nerves → Adrenal medulla

                             ↓

                      Adrenaline and noradrenaline

       Hypothalamus → Posterior Pituitary

                             ↓

                      Oxytocin, antidiuretic H
                            (ADH)




N.B.   POSITIVE FEED-BACK

       Oxytocin - exception to rule of negative feed-back.
                                                                        10


                 HYPOTHALAMUS-PITUITARY - TARGET CELL

                                   FEED-BACK

(TORTORA & GRABOWSKI 8th Ed. Fig. 18.15, p. 523, Fig. 18.21, p. 531))


                                      C.N.S.


                                      HYPOTHALAMUS




                                               ANT.
                                               PITY




            GROWTH
            HORMONE




                                      A.C.T.H.


                         T.S.H.


      THYROID
      GLAND


                                  ADRENAL
                                  CORTEX

      THYROID
      HORMONES


      T.S.H. = THYROID STIMULATING HORMONE
      A.C.T.H. = ADRENO-CORTICOTROPHIC HORMONE
                                                                                    11


PITUITARY GLAND

-      Attached to Hypothalamus by stalk (Infundibulum).

DIVISIONS

1.     Anterior Lobe (Glandular)

2.     Posterior Lobe (Neural)

[3.    Intermediate Lobe]




ANTERIOR PITUITARY (ADENOHYPOPHYSIS)

Hormone release stimulated or inhibited by regulating factors from Hypothalamus.


BLOOD SUPPLY


                                            HYPOTHALAMUS


                                     HYPOPHYSEAL PORTAL VEINS


                                            ANTERIOR PITUITARY


HORMONES OF ANTERIOR PITUITARY

1.     GROWTH HORMONE

       -      Stimulates body cells to grow (mainly bone and skeletal muscle) via
              somatomedins.

       -      increases rate of protein synthesis

       -      Promotes fat catabolism

       -      stimulates conversion of liver Glycogen → Glucose (ie. B.G.L ↑)

       Regulated by releasing and inhibiting hormone (hypothalamus)
       (↓ B.G.L. Stress, vigorous exercise, sleep)
                                                                                       12


2.    THYROID-STIMULATING HORMONE (T.S.H.)

      -      Stimulates synthesis and secretion of thyroid hormones by thyroid gland

      Regulated by: releasing hormone (Hypothalamus) (↓ Thyroxine ↓B.M.R.)




                   HYPOTHALAMUS AND PITUITARY GLAND

(TORTORA & GRABOWSKI, 8th Ed., Fig. 18.5, p. 510, Fig 18.10, p. 517)

                                                                HYPOTHALAMUS




      POSTERIOR                                           PORTAL SYSTEM
      PITUITARY

                                                          ANTERIOR
                                                          PITUITARY




      OXYTOCIN                                                  GROWTH HORMONE
      ANTIDIURETIC H                                            THYROID STIM. H
                                                                A.C.T.H.
                                                                F.S.H.
                                                                L.H.




                  POSTERIOR PITUITARY (NEUROHYPOPHYSIS)


-     Does not synthesize hormones

-     Contains neural tissue:

      Axon Terminals of secretory cells in hypothalamus
                                                                                   13


                     HYPOTHALAMUS SECRETORY CELLS

                          → HORMONES
                                A
                                X
                                O
                                N
                                S
                     POSTERIOR PITUITARY AXON TERMINALS
                          (HORMONES STORED)


POSTERIOR PITUITARY HORMONES

1.   OXYTOCIN

     (a)    Stimulates contraction of pregnant uterus.

     (b)    Stimulates ejection of milk.


     * N.B. Positive Feedback (Cervical/uterine stretching, suckling at breast).


2.   ANTIDIURETIC HORMONE (A.D.H.) (VASOPRESSIN)

     (a)    Kidneys: ↑ H2O Reabsorption →

                                   ↓

                            Urine Volume

     (b)    Sweat Glands: ↓ Sweat secretion.

     (c)    Arterioles: Constrict → ↑ B.P.


     Regulated by:


                     DEHYDRATION, ↓ BLOOD VOLUME


                                           ↓
                                                              14


                      OSMORECEPTORS (HYPOTHALAMUS)


                               ↓

                          ↑ A.D.H. RELEASE




       N.B.     ALCOHOL - INHIBITS A.D.H. SECRETION RELEASE

                                     ↓

                          ↑ URINE VOLUME


THYROID GLAND

R and L Lobes

Location: below larynx

* Rich blood supply
                                                                                      15


THYROID FOLLICLES:

(a)   Follicular cells

      (Thyroxine T4)                            Thyroid
      (Tri-iodothyronine T3)                    Hormones


(b)   Parafollicular cells

      * Calcitonin

(TORTORA & GRABOWSKI, 8th Ed., Fig. 18.13c, p. 521)

FOLLICULAR CELLS                                                     PARAFOLLICULAR
                                                                          CELLS


                                                                     BLOOD
                                                                     CAPILLARY




BASEMENT                                                             THYROID
MEMBRANE                                                                 COLLOID




                         Thyroid gland actively takes up I- from blood

                                                ↓


                                        I2 + Tyrosine


                                                ↓

                                Thyroid Hormones (T4 and T3)

                                (stored in lumen of follicles)
                                                                   16


Functions of thyroid hormones

1.    Regulation of metabolism (↑ B.M.R.)

2.    Regulation of growth and development (N.B, Nervous system)

3.    Regulation of activity of nervous system (Sympath.)

SECRETION OF THYROID HORMONES:

STIMULATED BY:

1.    Low blood thyroid hormone level

2.    Cold environment - Increased energy needs

3.    Pregnancy     “      “      “        “

                                  HYPOTHALAMUS

                                           ↓

                                  RELEASING HORMONE

      STIMULUS

                                           ↓


                                  A.N.T. PITUITARY

                                           ↓

                                  T.S.H.


                                           ↓


                                  THYROID GLAND

                                           ↓

                                  THYROID HORMONES
                                      T3 and T4
                                                                                  17


PANCREAS

1.     Exocrine

2.     Endocrine




(TORTORA & GRABOWSKI, 8th Ed., Fig. 18.23, p. 535)


               LIVER

                                                               SPLEEN

GALL BLADDER
                                                               TAIL OF PANCREAS




DUODENUM                                                       BODY OF PANCREAS




                               HEAD OF PANCREAS




       POSITION:       TRANSVERSE
                       POSTERIOR PART OF UPPER ABDOMEN


ENDOCRINE PANCREAS

Endocrine tissue - islets of langerhans

(alpha) α cells        secrete glucagon                 Regulate
(beta) β cells         secrete insulin                  Blood
(delta) δ cells        secrete somatostatin             Glucose
        PP cells       secrete pancreatic polypeptide
                                                                                             18


(TORTORA & GRABOWSKI, 8th Ed., Fig. 18.23, p. 523)

       ACINI


                                                                    α CELL

                                                                    β CELL

                                                                    δ CELL


BLOOD CAPILLARY


METABOLISM

Glucose               Fuel for cellular metabolism
Fats                  Energy reservoir
Proteins              Source of glucose for brain during fasting

*      The liver and pancreatic hormones insulin and glucagon, control body’s fuel supply.

*      Secretion of Insulin and Glucagon is regulated by blood glucose level.


↑ Blood glucose → insulin release
   (meal)

↓ Blood glucose → glucagon release
 (fasting)


PANCREAS → INSULIN/GLUCAGON → PORTAL CIRC.

                                                    ↓

                                                    LIVER

                                                    ↓

                                     AFFECT BLOOD GLUCOSE LEVELS
                                                                          19


ACTION OF INSULIN

Lowers Blood Glucose Level:

(a)    ↑ Transport of glucose into cells
             (Esp. skeletal, adipose)

(b)    Converts glucose → glycogen

(c)    Decreases glycogen breakdown and gluconeogenesis.

(d)    Increases lipogenesis

(e)    Increases lipogenesis

(f)    Stimulates protein synthesis


N.B.   Brain                                     Do not require insulin
       Exercising skeletal muscles               for entry of glucose
       Liver

ACTIONS OF GLUCAGON

Increases Blood Glucose Level:

(a)    ↑ Glycogen → glucose in liver

(b)    ↑ Conversion other nutrients

              → glucose

(c)    Liver releases glucose → blood

(d)    ↑ Fat breakdown

(e)    ↑ Protein breakdown


N.B. * Actions of Insulin and Glucagon are opposed.

								
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