Lect13 Endocrine

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Endocrine System - 1

Lecture 13

Hypophysis

Pineal


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ENDOCRINE SYSTEM I

I. General Introduction to the Endocrine System:1. The Endrocrine system is an integrator of

body functions; and together with the CNS,

maintains homeostasis. The nervous system

brings about rapid localized responses

(directly via neural connections).

The endocrine system causes slower, oftenmore wide spread, responses (indirectly via

hormone release).

2. Characteristics

Clusters of Cells

Ductless Glands

Scattered Single Cells (APUD cells)

3. Endocrine organs develop from all three germ

layers.


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Hormones may be:

proteins or peptides: water soluble;insulin, glucagon, FSH

modified amino acids: water soluble;

thyroxine and epinephrine

Steroids: lipid soluble; progesterone

Clinically monitor hormone levels

*Carrier proteins may be produced and secreted along with

the hormones.

Hormones are normally present in the plasma and interstitial tissue

at concentrations in the range of 10-7 M to 10-10 M.


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IV. What you should learn about endocrine organs/cells:

1. Identify the organ.

2. What are the unique anatomical characteristics of organ or cells.

3. What are the anatomic relationships within the organ and of the

organ with adjacent structures.

4. What hormone (or hormones) is produced and what is the general

chemical class of the hormone.

5. Name the target organ of the hormone and the general action on it

Thyroid

Gland

Thyroid Follicle

Releases T3 & T4

which act on most

cells to upregulate

protein synthesis


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Hypophysis

(Pituitary)

central in endocrine functions

controlled by the CNS and feedback

from target organs

structurally and functionally integratedwith hypothalamus

Structurally complex


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Class Notes

page 110

Hypothalamo-

Hypophysial tract


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Hypophysis has two structurally and

functionally distinct parts:

1) Neurohypophysis (diencephelon)2) Adenohypophysis (pharynx-ectoderm)

Adenohypophysis

Neurohypophysis


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Neurohypophysis:

outgrowth from

hypothalamus3 parts:

Median eminence-

surroundsinfundibular recess

Infundibular stalk-

a nerve tract

Neural lobe =

Posterior lobe =

Pars nervosa

DiencephalonVentricle III

Neural Lobe

Infundibular Recess

of 3rd Ventricle


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median

eminence:1. Contains axons going

from paraventricular

and supraoptic N. to

neural lobe

2. Contains hypophysial

portal system

[Releasing Factors-->

capillary bed-->portal

system--> capillary bed-->

target cells in pars distalis]

infundibular

stalk

neural lobe

Neurohypophysis


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median

eminence

infundibular

stalk- contains

the hypothalamo-hypophysial tract

running from the

supraoptic and

paraventricular

nuclei to the neurallobe

neural lobe

Neurohypophysis


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Infundibular

Stalk

Hypothalamo-

hypophysial Tract

3rd

ventricle

3rd

ventricle

Paraventricular N

Immuno for Oxytocin


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Neurohypophysismedian eminence

infundibular stalk

neural lobe or

posterior lobe:1. axon

terminals of the

hypothalamo-

hypophysial

tract and

2. pituicytes


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Axon terminals

(hypothalamohypophysial

tract)

Pituicytes = glial cells,

they release taurine in

response to hyper-osmotic

stimuli--> increases ADH

release

ADH and oxytocin areattached to a carrier protein,

Neurophysin, also released

Into the neural lobe from

axon terminals of the hypo-

thalamohypophysial tract.

Release ADH and

Oxytocin that were

Produced by the

Supraoptic and

Paraventricular nuclei


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Secretion at Axon

Terminals in the

Neural LobeOxytocin-

paraventricular n.;

Targets mammary

gland and uterine

smooth muscle

Antidiuretic

hormone (ADH)-supraoptic n.;

target: collecting

duct, kidney


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Axon dilatations

Pituicytes


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Outgrowth of pharynx;

3 parts:

pars tuberalis-Surrounds theinfundibular stalk &

medium eminence

pars

intermedia-located between

hypophysial cavity &

the neural lobe;

contains Wulzens

cone in ruminants

pars distalis-largest part of

pituitary-many cell

typesWulzens Cone

Adenohypophysis


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Hypophysial

Portal System

Primary capillaries-located in the median

eminence, take up and

transport releasing and

inhibiting factors

Secondary capillaries-in pars distalis, where

releasing and inhibiting

factors diffuse to target

cells

Venules

This is a

Venous portal system

Neurohypophysis

Pars

Distalis


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Paraventricular

hypothalamic neurons

(parvicellular area)

Hypothalamic hormones

(releasing and inhibiting

Factors, i.e. CRF, )

enter primary capillaries

carried via portal venules

Leave secondary capillaries

act on cells of pars distalis


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Adenohypophysis

pars distalis

Parenchyma:clusters or cords of epitheloid cells

at least 5 cell types-->8 hormones

Stroma-sparse CT, highly vascular

Secretion is regulated by

hypothalamic releasing and

inhibiting hormones.

Carried via portal system from axon

terminals in median eminence

secretory cells contain membrane

bound granuleshormones are proteins, peptides

or glycoproteins

Adenohypophysis and hypothalamus are a functional unit.

Most hormone secreting cells in the pars distalis are chromophils


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Classification of Pars Distalis Secretory Cells (Chromophils)

Acidophilsprotein hormones

2. Lactotropes or mammotropes-solitary

round cells with eccentric nuclei (20-50%)

Secrete: Prolactin

very large granules (stain red)

1. Somatotropes-large cells in clusters

growth hormone (somatotropin)

large granules (stain orange)


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Basophilsglycoprotein hormones

small granules

Thyrotropes-large, pale, polyhedral cells

Thyrotropin (TSH)

Corticotropes-pale cells with slight basophilia

ACTH (adrenocorticotropin)-lipotropin

-endorphin

Gonadotropes-small round to oval cells, very

basophilic

Follitropin (FSH)Lutropin (LH)

Chromophobes

reserve

degranulated

Spherical, Ovoid

or Stellate in shape

Irregular or

angular in

shape


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Classification of Pars Distalis Secretory Cells (Chromophils)

Acidophilsprotein hormones

Growth hormone (Somatotropes)

general anabolic effects-maintains normallipid, carbohydrate and protein metabolism

Regulates epiphyseal plate closure-stature

Absence--> decreased bone and muscle mass

Excess-->gigantism in young; acromegaly

in adults-->increased soft tissue mass,

prominent skin folds & abdominal enlargement;

see increased serum GH levels.

Clinical Note: GH given to increase milk

production & meat production

Prolactin (Lactotropes)stimulates lactation and spermatogenesis

triggers parental behavior - nest building,

cleaning & nursing of young

Dopamine agonists-->suppress prolactin secretion-->luteolysis &

termination of pregnancy [used in dogs in Europe]


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Basophilsglycoprotein hormones, small granules

Thyrotropin or TSH (Thyrotropes)

regulates thyroid function-->increases secretion of major thyroidhormones triiodothyronine (T3) and thyroxin (T4)

Corticotropes-->Pro-opiomelanocortin

ACTH - 39 amino acid peptide that stimulates the adrenal cortex

to secrete glucocorticoids (cortisol) which affect nearly every

tissue in the body-stimulate appetite, help control blood glucoseNote: Excess causes adrenal cortical hyperplasia Cushings Disease-

increased appetite and thirst, pot belly, hair loss, lethargy; in 85-90% of

Dogs with hyperadrenocorticism, there is excess ACTH production;

treat animals with Mitotane, a chemical derivative of the pesticide DDT,

which destroys the cells of the Adrenal Zona Fasciculata that produce

Cortisol.-lipotropin - fat release from adipocytes

-endorphin - endogenous morphine

Gonadotropes

Follitropin (FSH) - stimulates early follicle devel & spermatogenesis

Lutropin (LH)- stimulates late follicle maturation& spermatogenesis


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Lactotropes

Corticotropes

Somatotropes


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Adenohypophysis

pars tuberalissite of portal venules

contains some pars distalis

type cells (thyrotropes &

gonadotropes) and a light

basophilic staining cell type

that is unique to the parstuberalis

high density of

melatonin receptors

assumed important inseasonal breeding cycles

Melatonin-->melatonin receptors

-->pars tuberalis cells-->secrete

a factor, tuberalin-->controls

prolactin release from pars

distalis lactotropes


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Adenohypophysis

pars intermediabetween hyophysial cavity

and neural lobe

controlled by directhypothalamic innervation

Contains:

1) Melanotropes (pale basophils)

POMC is further cleaved to:melanocyte stimulating

hormone (MSH)

Corticotropin-like

intermediate lobe peptide

MSH has roles in:stress adjustment

memory

learning

2) Corticotropes (ACTH and -LPH)


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Pars Intermedia: In large ruminants it contains Wulzens cone-an area of pars distalis cells within the pars intermedia

Wulzens cone

Neural Lobe

Hypophysial cavity

Pars

Intermedia

Pars Distalis


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VI. Pineal GlandNeuroectodermal

Out growth from

diencephalon.A part of the

epithalamus

Capsule formed dorsally by pia

mater and ventrally by ependyma

Pineal tumors impede vasculardrainage in the nearby dural

sinuses


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Capillary

Neuroendocrine Cellacidophilic

many processes

leptochromatic

nuclei

Serotonin

2. Parenchyma:

Pinealocytes

Secrete

melatonin

Melatonin sets

daily cycles &

influences

seasonal cycles

Melatonin

Synthesis


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Pinealocytes

Glial Cells

3. Stroma consists of glial cells- small cells with dark nuclei


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Corpora arenacea

Corpora arenacea = brain sand, concretions of calcium phosphates


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Horned Lizard

Function: In lower vertebrates the Pineal acts as a photoreceptor

(third eye)


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Light Information:

indirectly from Retina

via suprachiasmatic n.or

Indirectly via cranialCervical ganglion

(sympathetic fibers.)

In amphibians melatonin

causes aggregation of

pigment granules-->

lightens skin color.

Melatonin-->circadian& season effects on

breeding, etc. [levels

rise during the night

& fall during the day

Length of dark period

sets seasonal cycles

Regulates

Functions:

Injections of melatonin alter circadian rhythms

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Lect13 Endocrine