Endocrine System

Biology 2122

Introduction(1) What are hormones?

(2) What are the functions of hormones?

(3) What are the types of hormones?– Amino Acids– Steroids– Eicosanoids

How do Hormones Work?(1) Action on Target Cells – Membrane permeability– Synthesis of proteins or enzymes

• Or inhibits

– Induces secretory activity– Stimulates mitosis

(2) Target-Specific– Target cell receptor sites – “Turns on cell” – “Dynamic”

How do Hormones Work?(3) Half-Life

(4) Interaction – Target Cells– Permissive – Synergistic – Antagonistic

(5) Control of Release – Negative feedback– Endocrine Gland Stimuli

• Humoral stimuli • Neural stimuli• Hormonal stimuli

Plasma Membrane Receptors Plasma Membrane Receptors (1) Second Messenger System – All amino acid hormones (except thyroid)

Plasma Membrane Receptors Plasma Membrane Receptors (2) Intracellular – Direct Gene Activation – Lipid soluble; steroid– Binds to intracellular receptors – Binds to DNA – Activates a gene

(1). Somatotroph cells produce GH

(2). Secretion – GHRH – stimulates release (GHIH) inhibits – Produced in the hypothalamus

(3). Effects– Anabolic – protein synthesis– Targets bones and muscles – Stimulates epiphyseal plates during

development

(4). Disorders – Gigantism and Acromegaly

Anterior Pituitary Hormones-HGHAnterior Pituitary Hormones-HGH

• (1). Also referred to as thyrotropin. – Produced by thyrotroph cells

• (2). Secretion – TRH or thyrotropin releasing hormone stimulates the release

of TSH – Negative feedback – rising levels of thyroid hormones

• ANIMATION

• (3). Effects – Moderates normal thyroid gland activity.

Thyroid-Stimulating HormoneThyroid-Stimulating Hormone

• (1). ACTH – adrenocorticotropic hormone secreted – corticotroph cells

• (2). Stimulation-Secretion– CRH – corticotropin-releasing hormone – hypothalamus

• Levels peak in the morning

– Negative feedback

• (3). Effects – Stimulates the Adrenal gland (cortex) to release Glucocorticoids

• Cortisol (stress hormone)

Adrenocorticotropic Hormones Adrenocorticotropic Hormones

(1). FSH and LH – gonadotrophic cells

(2). Stimulus-Secretion◦ Puberty ◦ GnRH – prompts the anterior pituitary to release hormones◦ ANIMATION

(3). Effects ◦ (a). LH

FSH - maturation of follicle Ovulation Stimulates interstitial cells - testosterone in males

◦ (b). FSH – stimulates gamete production; follicle development.

Gonadotropins Gonadotropins

(1). PRL or prolactin is a protein hormone. – Produced by the lactrotroph cells

(2). Stimulus – Secretion– PRH and PRH – PRH plays dominant role – dopamine prevents secretion

(3). Effects– Stimulate milk production in the breasts

Prolactin

Acromegaly

(1). Production- hypothalamic neurons

(2). ADH or Antidiuretic Hormone – Reabsorption of water – collecting tubules – Release stimulated by – increasing osmolarity

• Diabetes insipidus

(3). Oxytocin– Stimulated release by positive feedback – contractions

during birth– Milk ejection – Synthetic – induce contractions

Posterior Pituitary Gland Hormones

(1). Produces TH or thyroid hormones ◦ T4 or thyroxin; T3 or triiodonthyronine

(2). Stimulus – Secretion◦ Hypothalamus (TRH) - Pituitary (TSH) --

TH ◦ Stress - cold, pregnancy – cause

hypothalamus to produce TRH.

◦ Rising TH levels – negative feedback to hypothalamus-pituitary axis.

(3). Effects ◦ Increases BMR ◦ body heat production (stimulates enzymes

to increase glucose oxidation)

Thyroid Gland

Synthesis of TH

• (1). Myxedema – hypothyroid

• (2). Goiter

• (3). Cretinism – Infant hypothyroidism

• (4). Grave’s Disease – Hyperthyroid

Thyroid Imbalances

(1). Polypeptide hormone – Parafollicular cells of the thyroid – Lowers calcium blood levels– Reabsorption back into the bones

(2). Stimulus for release – 20% above normal levels for calcium blood levels – Lower than normal – inhibitory effect

(3). More important in childhood– Due to developing bones and keeps calcium levels in check

Calcitonin

(1). Cells in the parathyroid gland– Oxyphil and chief cells (secretes ) PTH

(2). Stimulus and Secretion– Hypocalcemia ----- PTH

Parathyroid Hormones

(1). Adrenal gland has two distinct regions◦ (a). Cortex - outer region◦ (b). Medulla - inner region

(2). Hormones produced – corticosteroids

◦ 12 total

(3). Steroid Hormones– Not stored in cells – rate of release depends on productivity

(4). Cortical regions ◦ (a). Zona glomerulosa – mineralocorticoids ◦ (b). Zona fasciculata – glucocorticoids ◦ (c). Zona reticualaris – adrenal sex hormones called

gonadocorticoids.

Adrenal Hormones

(1). Produced in the zona glomerulosa of the cortex◦ Mostly aldosterone◦ Balances ions and water

(2). Stimulus and Secretion◦ Renin-angiotensin mechanism ◦ Elevated K+ levels

(3). Disorders ◦ Aldosteronism ◦ Addison’s disease

Mineralocorticoids

(1). Produced in the zona fasciculata

– Metabolic hormones

(2). Cortisol is the main hormone – Gluconeogenesis; lipolysis;

protein metabolism

(3). Stimulation and secretion– ACTH from the anterior pituitary

(low levels of hormones)

(4). Disorders – Cushing’s syndrome– Addison’s disease

Glucocorticoids

(1). Androgens produced in the zona reticularis– Converted to testosterone and estrogen

(2). Stimulus and secretion– ACTH released from anterior pituitary

(3). Effects – Males – Female libido; pubic and axillary hair in females; estrogen

after menopause

Gonadocorticoids