Copyright 2009, John Wiley & Sons, Inc. Pancreas.

Copyright 2009, John Wiley & Sons, Inc.

Pancreas


Pancreatic Islets

Both exocrine and endocrine gland Roughly 99% of cells produce digestive enzymes Pancreatic islets or islets of Langerhans

Alpha or A cells secrete glucagon – raises blood sugar Beta or B cells secrete insulin – lowers blood sugar Delta or D cells secrete somatostatin – inhibits both insulin

and glucagon F cells secrete pancreatic polypeptide – inhibits

somatostatin, gallbladder contraction, and secretion of pancreatic digestive enzymes

18-3

Cell Types in the Pancreatic Islets

Alpha cells (20%) produce glucagon Beta cells (70%) produce insulin Delta cells (5%) produce somatostatin F cells produce pancreatic polypeptide

Low blood glucose(hypoglycemia)stimulates alphacells to secrete

1

GLUCAGON

Glucagon acts onhepatocytes(liver cells) to:

• convert glycogen into glucose (glycogenolysis)• form glucose from lactic acid and certain amino acids (gluconeogenesis)


GLUCAGON

1

2 Glucagon acts onhepatocytes(liver cells) to:


Glucose releasedby hepatocytesraises blood glucoselevel to normal


GLUCAGON

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2

3




If blood glucosecontinues to rise,hyperglycemia inhibitsrelease of glucagon


GLUCAGON

1

2

3

4






High blood glucose(hyperglycemia)stimulates beta cellsto secrete

GLUCAGON

1 5

2

3

4

INSULIN

Insulin acts on variousbody cells to:

• accelerate facilitated diffusion of glucose into cells• speed conversion of glucose into glycogen (glycogenesis)• increase uptake of amino acids and increase protein synthesis• speed synthesis of fatty acids (lipogenesis)• slow glycogenolysis• slow gluconeogenesis







INSULINGLUCAGON

1 5

2

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6 Insulin acts on variousbody cells to:


Blood glucose level falls







INSULINGLUCAGON

1 5

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Insulin acts on variousbody cells to:


If blood glucose continuesto fall, hypoglycemiainhibits release ofinsulin

Blood glucose level falls







INSULINGLUCAGON

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Pineal Gland


Pineal Gland

Attached to roof of 3rd ventricle of brain at midline

Masses of neuroglia and pinealocytes Melatonin – amine hormone derived from

serotonin Appears to contribute to setting biological

clock More melatonin liberated during darkness

than light

SCN lesioning

Tau mutant with period of ~20h

Wild type animal with period of ~24h

Transplanting SCN of donor with ~20-h period

Wild type animal acquiresperiod of donor (~20h)

SCN lesioning abolishes circadian rhythm

A

B

C

SCN and sleep

Modified from Ralph and Lehman, Trends Neuro 1991

Melatonin: Produced by pineal gland, released at night-inhibited during the day (circadian regulation); initiates and maintain sleep; treat symptoms of jet lag and insomnia

Hypothalamus and Pituitary Gland


Anterior pituitary

Release of hormones stimulated by releasing and inhibiting hormones from the hypothalamus

Also regulated by negative feedback Hypothalamic hormones made by

neurosecretory cells transported by hypophyseal portal system

Anterior pituitary hormones that act on other endocrine systems called tropic hormones


Hormones of the Anterior Pituitary1. Human growth hormone (hGH) or somatotropin

Stimulates secretion of insulin-like growth factors (IGFs) that promote growth, protein synthesis

2. Thyroid-stimulating hormone (TSH) or thyrotropin Stimulates synthesis and secretion of thyroid hormones by

thyroid

3. Follicle-stimulating hormone (FSH) Ovaries initiates development of oocytes, testes stimulates

testosterone production

4. Luteinizing hormone (LH) Ovaries stimulates ovulation, testes stimulates testosterone

production


Hormones of the Anterior Pituitary5. Prolactin (PRL)

Promotes milk secretion by mammary glands

6. Adrenocorticotropic hormone (ACTH) or corticotropin

Stimulates glucocorticoid secretion by adrenal cortex

7. Melanocyte-stimulating Hormone (MSH)


Function of Anterior Pituitary Hormones

18-15

1) Human Growth Hormone Increases synthesis of insulin-like growth factors

“(IGFs) or somatomedins” at target cells target cells are liver, skeletal muscle, cartilage

and bone. IGF will work locally or enter bloodstream and they will lead to: increases cell growth & cell division Increases cell uptake of amino acids & synthesis of

proteins stimulate lipolysis in adipose so fatty acids used for

ATP retard use of glucose for ATP production so blood

glucose levels remain high enough to supply brain

18-16

Regulation of hGH Low blood sugar stimulates

release of GNRH from hypothalamus anterior pituitary releases

more hGH, more glycogen broken down into glucose by liver cells

High blood sugar stimulates release of GHIH from hypothalamus less hGH from anterior

pituitary, glycogen does not breakdown into glucose

18-17

Diabetogenic Effect of Human Growth Hormone Excess of growth hormone

raises blood glucose concentration pancreas releases insulin continually beta-cell burnout

Diabetogenic effect causes diabetes mellitis

18-18

2) Thyroid Stimulating Hormone (TSH)

Hypothalamus regulates the production of Thyroid Stimulating Hormone (TSH)

TSH stimulates the synthesis & secretion of T3 and T4 at thyroid gland

Metabolic rate stimulated

18-19

3) Follicle Stimulating Hormone (FSH)

FSH functions initiates the formation of follicles within the ovary stimulates follicle cells to secrete estrogen stimulates sperm production in testes

18-20

4) Luteinizing Hormone (LH)

In females, LH stimulates secretion of estrogen(with FSH) ovulation of secondary oocyte from ovary formation of corpus luteum secretion of progesterone

In males, stimulates interstitial cells to secrete testosterone

5) Prolactin (PRL)

Under right conditions, prolactin causes milk production

Suckling reduces cause prolactin levels rise along with milk production

Nursing ceases & milk production slows

18-22

6) Adrenocorticotrophic Hormone

ACTH stimulates cells of the adrenal cortex that produce glucocorticoids

18-23

7) Melanocyte-Stimulating Hormone Releasing hormone from hypothalamus

increases its release From the anterior pituitary

Function not certain in humans (increase skin pigmentation in frogs )


Regulation of Ant. Pitutary Hormone Secretion

negative feedback

Hypothalamus

Hypothalamus Hypothalamus is a section of

brain above where pituitary gland is suspended from by infundibulum or stalk

Functions of hypothalamus

• Endocrine function

• Caloric balance

• Osmolarity balance

• Thermal regulation

• Autonomic balance

• Sleep

• Affective behavior

• Memory

• Somatic movements


Hypothalamus Hypothalamus is a section of brain above

where pituitary gland is suspended from by infundibulum or stalk

Hypothalamus is a major link between nervous and endocrine system

It receives input from cortex, thalamus, limbic system & internal organs

Is influenced by emotions and the metabolic state of the individual

Hypothalamus Releasing Hormones: Secretion Synthesizes hormones in cell bodies of neurons

Hormones are transported down the axon and stored in the nerve endings



Delivered to the anterior pituitary via the hypothalamic-hypophyseal portal system

Usually initiates a three-hormone sequence Hypothalamus controls pituitary gland with 7

different releasing & inhibiting hormones

Hypothalamus and anterior pituitary

18-33

Flow of Blood to Anterior Pituitary

Controlling hormones enter blood Travel through portal veins Enter anterior pituitary at capillaries

Hypothalamic control of anterior pituitary secretions

Endocrine Control: Three Levels of Integration

Figure 7-13: Hormones of the hypothalamic-anterior pituitary pathway

Hypothalamic control of anterior pituitary

Effect on Ant Pituitary

Hormones

(+) TSH & Prolactin Thyrotropin-releasing hormone (TRH)

1.

(+) ACTH Corticotropin-releasing hormone (CRH)

2.

(+) GH Growth hormone releasing hormone (GHRH)

3.

(+) Prolactin Prolactin releasing hormone (PRH) 4.

(+) Gonadotropic hormones

(LH, & FSH)

Gonadotropin-releasing hormone (GnRH)

5.

(-) Prolactin Prolactin inhibitory hormone (PIH)“Dopamine”

6.

(-) GH(-) TSH

Growth hormone inhibitory hormone (GHIH) “Somatostatin (SS)”

7.

Hypothalamic hormones


Hypothalamus

FSH & LH GH

Anterior Pituitary

GHIH/SSGHRHGnRH TRH PRIH PRH CRH

TSH Prolactin ACTH+ - -+ + + - + +


Regulation of Ant. Pitutary Hormone Secretion

negative feedback

Hypothalamus


Negative Feedback Regulation

Low blood glucose(hypoglycemia)stimulates release of

GHRH

1 Low blood glucose(hypoglycemia)stimulates release of

hGH

GHRH stimulatessecretionof hGH bysomatotrophs

GHRH

1

2


hGH


GHRH

hGH and IGFs speedup breakdown of liverglycogen into glucose,which enters the bloodmore rapidly

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3

2


hGH


GHRH


Blood glucose levelrises to normal(about 90 mg/100 mL)

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2


hGH


GHRH



If blood glucosecontinues to increase,hyperglycemia inhibitsrelease of GHRH

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3

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2

Anteriorpituitary


High blood glucose(hyperglycemia)stimulates release of

hGH


GHIHGHRH




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2

Anteriorpituitary

GHIH inhibitssecretion ofhGH bysomatotrophs



hGH


GHIHGHRH




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2 GHIH inhibitssecretion ofhGH bysomatotrophs



Anteriorpituitary

hGH


GHIHGHRH

A low level of hGH andIGFs decreases the rateof glycogen breakdownin the liver and glucoseenters the blood moreslowly




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Anteriorpituitary

hGH


GHIHGHRH


Blood glucose levelfalls to normal(about 90 mg/100 mL)




1 6

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Anteriorpituitary

hGH


GHIHGHRH


Blood glucose levelfalls to normal(about 90 mg/100 mL)




If blood glucosecontinues to decrease,hypoglycemia inhibitsrelease of GHIH

1 6

7

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3

4

5

2

Copyright 2009, John Wiley & Sons, Inc. Pancreas.

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Transcript of Copyright 2009, John Wiley & Sons, Inc. Pancreas.