THE ENDOCRINE SYSTEM

• Lecture 2; Holes, Chapter 13

THE PITUITARY GLAND

Secretes 9 hormones

Divided into 2 parts: Anterior lobePosterior lobe

Posterior: nervous tissue(neurohypophysis)

Pituicytes (type of glial cell).Secretes neurohormones from hypothalamus

Anterior: glandular tissue.(adenohypophysis)

The Pituitary Gland

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PITUITARY GLAND

Glandular tissue.

Derived from epithelial tissue of oral muscosa.

Makes its own hormones.

Growth hormoneThyroid-stimulating hormone

Adrenocorticotrophic hormone (ACTH)Follicle-stimulating hormone (FSH)

Luteinizing hormoneProlactin

(all use cAMP 2°messenger system)

Anterior lobe (adenohypophysis) Posterior lobe (neurohypophysis)

Pituicytes & Nerve cells.

Actually part of the brain.

Receives hormones from hypothalamus.

OxytocinAntidiuretic hormone (ADH)

POSTERIOR PITUITARY GLAND & THE HYPOTHALAMUS

Hypothalamic-hypophyseal tract

(hormones travel down neurons)

Hypothalamus:Supraoptic nucleus (ADH)

Paraventricular nuclei (Oxytocin)

Posterior Pituitary(hormones released into

capillary beds when neurons fire)

ANTERIOR PITUITARY GLAND & THE HYPOTHALAMUS

Primary capillary plexus

Hypothalamus sends chemical instructions to the Anterior Pit. Gland

Anterior PituitaryEpithelial tissue

5 types of secretory cells

Secondary capillary plexus

Hypophyseal Portal system

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HYPOTHALAMUS: CONDUCTOR OF THE HORMONE ORCHESTRA

Hypothalamus

Posterior Pit. GlandOxytocin

ADH

Hormone releasing chemicals

Anterior Pit. GlandGrowth Hormone

Prolactin(pro-opiomelanocortin)

(melanocyte stimulating hormone)

TSHACTHFSHLH

TARGET ORGAN

Other hormones“Trophins”

GROWTH HORMONE (GH; SOMATOTROPIN)

Made and secreted by somatotropic cells in Anterior Pit. Gland Protein hormone

Promotes growth/division of most cell types:

Major targets: Bone & Muscle (stimulates epiphyseal plate, muscle mass increase) Promotes Anabolic activity Increases Protein Synthesis (amino acid movement) Increases Fat mobilization (alternative fuel to CHO) Conserves carbohydrates

Acts either directly or via Insulin-like growth factor (IGF)IGF produced by liver, muscle, bone & other tissues.

GROWTH HORMONE FUNCTION

Release of IGF (liver, muscle, bone)

Increase Amino Acid

Uptake

Increase sulfur uptake

Increase protein

synthesis

Increase cartilage

production

Increased Fat release and utilization

Stimulation of bone growth

Decrease glucose use

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CONTROL OF GROWTH HORMONE RELEASE

HYPOTHALAMUSGrowth hormone releasing hormone

(GHRH)

Growth hormone released

Other factors: Age Sleep Nutritional statusGH blood

levels rise

GH release decreased

IGF increase

Growth hormone inhibiting hormone(somatostatin)

ANTERIOR PIT. GLAND

GROWTH HORMONE RELEASE

Hypersecretion: Gigantism & Acromegaly

GROWTH HORMONE RELEASE

Hyposecretion: Pituitary dwarfism

Synthetic GH now produced and cases of pituitary dwarfism are reduced

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THYROID STIMULATING HORMONE

Released by thyrotrophin-releasing hormone (hypothalamus)

Stimulates secretions from Thyroid gland

Rising blood levels of TSH inhibit further release of TRH at ant.pit.gland. Also inhibited at hypothalamus.

Also released during pregnancy, emotional stress, cold temperature

THYROID STIMULATING HORMONE

Hypersecretion: Grave’s disease: overactive

thyroid

Hyposecretion: Cretinism (children): retardation

of mental and physical growth Myxedema (adults): lowered

mental awareness, fatigue, weakness.

ADRENOCORTICOTROPHIC HORMONE (ACTH)

ACTH: Secreted by anterior Pit. Gland

Controlled by hypothalamic corticotrophin releasing hormone. (daily rhythm: highest in morning).

ACTH acts on adrenal cortex

Adrenal cortex stimulated to release corticosteriods

Glucocorticoids feedback and inhibit ACTH release

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ADRENOCORTICOTROPHIC HORMONE (ACTH)

Hypersecretion: Cushing’s disease.

Prolonged exposure to elevated corticosteroids: upper body obesity rounded face increased fat around the neck thinning arms and legs

Children tend to be obese with slowed growth rates.

GONADOTROPHINSFollicle-stimulating hormone & Luteinizing hormone

(FSH) Gamete production: eggs, sperm (LH) Controls gonad hormones

FSH & LH cause maturation of egg follicle; LH causes egg release

LH stimulates testes to produce testosterone (male)

FSH & LH - maturation of gonads during puberty

Both released by gonadotrophin-releasing hormone (GnRH) from the hypothalamus

PROLACTIN

Stimulates milk production by the breasts. (increases testosterone in males)

Release controlled by hypothalamus - Prolactin-releasing hormone (serotonin) & Prolactin-inhibiting hormone (dopamine)

PIH and PRH affected by estrogen; increased estrogen causes increase in prolactin.

Prolactin levels rise toward end of pregnancy. Sustained rise results in milk production by breast tissue

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POSTERIOR PITUITARY (HYPOTHALAMIC) HORMONES

Oxytocin and Antidiuretic Hormone.

Posterior Pituitary stores the hormones

Released by neural stimulation from hypothalamus

OXYTOCIN (GR. SWIFT BIRTH)

Number of receptors increase near end of pregnancy

Contractions cause increased release via stimulation of the hypothalamus. (Positive feedback).

Suckling child stimulates ‘letdown’ reflex - release of oxytocin and stimulation of breast to release milk.

Synthetic Oxytocin used to induce labor

Males: plays a role in sexual arousal and nurturing behavior (‘cuddle hormone’)

Causes smooth muscle contractionsuterus wall - childbirthmyoepithelial cells in breast tissue

ANTIDIURETIC HORMONE (ADH)(Diuresis - production of urine)

Dehydration: high salt concentration in blood

Osmoreceptors in hypothalamus start firing

Release of ADH in to bloodstream

Target organ: Kidney

Kidney tubules reabsorb more water

Blood volume rises, urine production slows

Osmoreceptors in stop firing

Blood Salt concentration decreases

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ANTIDIURETIC HORMONE (ADH)

Alcohol: dehydration Drug: antagonist to ADH to induce diuresis In high concentrations, ADH is powerful vasoconstrictor (vasopressin)

Hyposecretion: e.g. Diabetes insipidus - damage to pit.gland or hypothalamus means less ADH, means more urine produced.

Hypersecretion:e.g. meningitis, hypothalamic injury - blood retention, head ache, hypotonic blood.

THE THYROID GLAND

Butterfly shaped glandLargest gland in body

Very high blood supply

Hollow folliclesSquamous/cuboidal epithelium (follicular cells)

Inside lumen:Thyroglobulin + iodine = colloid = precursor to Thyroid hormone

Parafollicular cells: producing calcitonin

THYROID HORMONE (TH)Two forms of the hormone (both amines, both with iodine):

Target cells: everywhere BUT brain, spleen, testes, uterus and thyroid itself.

TH stimulates glucose oxidation (increases metabolism)

Essential for normal bone and nerve development and reproductive development.

Thyroxine (T4) - secreted by follicle cells

Triiodothyronine (T3) - converted from T4 at target cells

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TRANSPORT OF THYROID HORMONE (TH)

T4 & T3 are bound to transport proteins Both forms can bind to receptors; T3 much more readily Peripheral tissues have enzymes to convert T4 to T3 T4 & T3 both act like steroids and act in the nucleus

Regulation:

If T4 blood levels fall, thyroid-stimulating hormone (TSH) is released.

T4 is released from gland to increase blood levels

TSH levels fall, T4 release is slowed

(Can be over-ridden is times of need: cold temperature, pregnancy)

HypothalamusThyrotropin-releasing

hormone

Anterior Pit.GlandThyroid Stimulating

Hormone

Thyroid glandThyroid hormone

TARGET CELLS

DISORDERS OF THYROID HORMONE (TH)

Hypersecretion:

Grave’s disease Autoimmune disease - constant stimulation of thyroid to release TH. High metabolic rate, nervousness, weight

loss, protusion of eyeballs (Exophthalmos)

Hyposecretion:

Endemic - lack of dietary iodine

Cretinism, myxedema - low metabolic rate, chills, mental retardation (children) or sluggishness (adults)

CALCITONIN Produced by parafollicular cells (or C cells) Released when blood Ca++ is high Lowers blood Calcium. Inhibits ________ activity, stimulates ________ activity Increases Ca++ excretion by the kidney Humoral stimulus (raised Ca++ levels)

Fast, but short acting response.

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PARATHYROID GLAND

Gland made up of:

Chief cells - PTH Oxyphil cells - ?

Four small glands

Posterior surface of the thyroid gland

Vary in number and position

PARATHYROID HORMONE

PTH release stimulated by falling blood Ca++

Raises falling Ca++ levels.

Stimulates, bone, kidney and intestine.

Activates Vitamin D - precursor of calcitrol

DISORDERS OF PARATHYROID HORMONE

Hypersecretion

Hyperparathyroidism (rare, cancer)Bones are broken down

Raised Ca++ : Depression of Nervous

System Muscle weakness Kidney stones Metastatic calcification

Hyposecretion

Surgery or trauma

Lower Ca++ : Increased excitability of

neurons Tetany - loss of

sensation, muscle twitches, convulsions Paralysis

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