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Endocrine System

Bio 250Human Anatomy &

Physiology

Endocrine vs. Exocrine

Endocrine glands secrete their products called hormones into body fluids (the internal environment)Exocrine glands secrete their products into ducts that lead to the outside of the body

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The endocrine system is generally very reliableThe endocrine system controls metabolic processes that do not require rapid onset but that may continue for long periods of timethat may continue for long periods of time.When malfunctions do occur, they are often very dramaticThe particular effects may be quite different depending on whether they occur in children or adults

Endocrine System???

Most body systems possess anatomical continuityEndocrine system consists of many glands y y gscattered around the bodyEndocrine glands are only loosely connected by way of the blood stream

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Neuro-Endocrine Comparison

Hormone Action

As a group, endocrine glands regulate metabolic processesEndocrine glands secrete hormones that ff t t t ll i ifiaffect target cells possessing specific

receptorsHormones are typically carried from gland to target in the blood streamHormones are extremely potent chemicals

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Hormones Grouped by Function-Not StructureChemicals like proteins, carbohydrates and lipids are grouped by their common structure

Proteins are composed of chains of amino acidsProteins may function as enzymes, structural

l l tmolecules, etc

Hormones are grouped by common functionHormones may be proteins, lipids, steroids, modified amino acids, etcHormones are all chemical messengers controlling metabolic activities

Steroid Hormones

Steroid hormones enter target cells and combine with receptors to form complexesTh l ti t ifiThese complexes activate specific genesDirect synthesis of specific proteinsDegree of cellular response proportional to number of hormone-receptor complexes formed

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Nonsteroid Hormones

Nonsteroid hormones combine with receptors in the target cell membraneHormone-receptor stimulates membrane proteins to induce second messenger moleculesto induce second messenger moleculesA second messenger activates protein kinasesProtein kinases activate protein substrate molecules which change cell processesNonsteroid response is amplified by large number of second messengers formed

Control of Hormonal Secretions

Hormones are regulated by feedback control systems

Negative feedback systems typically maintain hormones at nearly constant levels (Common)Positive feedback systems increases effects of hormone action. (Not very common)

Some endocrine glands are controlled by nerve impulsesSome glands are auto-regulated Some glands are controlled by releasing or inhibiting hormones from the hypothalamus

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Pituitary Gland (Hypophysis)

The pituitary is attached to the base of the brain by the infundibulumConsists of an anterior lobe ord h h i dadenohypophysis and

Posterior lobe or neurohypophysisLobes have different embryological origins, different types of hormones and different controls

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Anterior Lobe

Forms from the roof of the embryo’s mouthSecretes several protein hormonespControlled by releasing and inhibiting hormones from the hypothalamusHypothalamic hormones delivered via hypophyseal portal system

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Posterior Lobe

Consists of glial cells and fibers of neurons whose cell bodies are in the hypothalamusT h t d b t iTwo hormones are secreted by posterior lobe but are made in the hypothalamus

ADH or Antidiuretic hormone causes kidneys to reduce the amount of water they excreteOxytocin stimulates the pregnant uterus to contract and causes milk let-down in the lactating breast in response to suckling

Hormones of the Anterior LobeSTH, GH or Growth Hormone

stimulates body ycells to grow and reproduceGH-RH and somatostatin(GH-IH) control GH secretion

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Pituitary Dwarf Giantism

Acromegaly

Hormones of the Anterior Lobe

Prolactin or PRLpromotes breast development and stimulates milk productionPRL-IH restrains secretionPRL-IH restrains secretionPRL-RH promotes secretion

TSH or Thyroid Stimulating HormoneControls secretions from the thyroid glandTSH is controlled by TSH-RH from the hypothalamus

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Hormones of the Anterior Lobe

ACTH or Adrenocorticotropic HormoneControls secretion of certain hormones fromControls secretion of certain hormones from the adrenal cortexACTH is controlled by C-RH from the hypothalamus

Hormones of the Anterior Lobe (Gonadotropins)

FSH or Follicle Stimulating HormoneStimulates development of follicles containing egg cells in the ovaryStimulates development of sperm in the p pseminiferous tubules of the testicle (GSH)

LH or Luteinizing HormoneStimulates ovulation of the egg and conversion of ruptured follicle into a corpus luteum in ovaryStimulates Interstitial Cells to secrete testosterone in the testicle (ICSH)

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Thyroid Gland

Located in the neck and has two lobesThyroid gland consists of fluid filled secretory parts called folliclesFollicles store the hormones the follicle cells secreteThyroid Hormones called Thyroxine (T4) (80%) and triiodothyronine (T3) (20%)

T3 is about 3x more active than T4

Stimulate rate of metabolismEnhance protein synthesis & lipid breakdownNeeded for normal growth, development and maturation of the nervous system

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Woman with endemic goiterdue to iodine deficiency.

Map showing area of glaciation and deposition of iodine poor soil

Thyroid GlandThyroid Gland––CalcitoninCalcitonin

CalcitoninCalcitonin lowers blood calcium and lowers blood calcium and phosphate ion concentrationsphosphate ion concentrationsPrevents prolonged elevation of calcium Prevents prolonged elevation of calcium p gp gion after a mealion after a mealStimulates osteoblast activity in bones to Stimulates osteoblast activity in bones to store excess calcium and phosphate in store excess calcium and phosphate in bone tissuebone tissue

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Parathyroid Glands

Located on the posterior surface of thyroidTypically 2 pair of small glandsSecrete Parathyroid hormone (PTH)Increases blood calcium ion concentrationIncreases blood calcium ion concentration

Causes osteoclasts to resorb bone calcium ionsInhibits osteoblasts from storing calcium ionsCauses kidneys to conserve calcium ionStimulates increased absorption from GI tract

Autoregulated by negative feedback control

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Adrenal Glands

Glands sit on top kidneys (suprarenal)Gland consists of cortex and medullaRemember, adrenal medulla is part of the , psympathetic function secreting epinephrine or nor-epinephrineAdrenal medulla consists of post-ganglionic fibers of the sympathetic nervous system

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Adrenal Glands

Gland consists of cortex and medullaAdrenal cortex secretes several steroids

MineralocorticoidsMineralocorticoidsGlucocorticoidsSex Hormones

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Adrenal Cortex

Mineralocorticoids (e.g. aldosterone)Causes kidney to conserve sodium ions and water and excrete potassium ionsSecretion autoregulated in response to low bloodSecretion autoregulated in response to low blood sodium ions, increased blood potassium ions or presence of angiotensin IIHelps to maintain normal blood volume and normal blood pressure

Produced by the zona glomerulosa

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Adrenal CortexGlucocorticoids (e.g. cortisol)

Inhibits protein synthesis, releases stored fatty acids and stimulates gluconeogenesisAnti-inflammatory propertiesAnti allergic propertiesAnti-allergic propertiesAids in bodies reaction to stressControlled by negative feedback loop involving the hypothalamus, anterior pituitary and adrenal cortex (C-RH ---->ACTH --->glucocorticoids)

Produced by the zona fasciculata

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Adrenal Cortex

Adrenal sex hormonesThese hormones are primarily male type in both sexes but can be converted into female hormonesThey supplement sex hormones made by the gonadsHypersecretion in fetus can caused adrenogenital syndrome: can masculinize female fetus.

Pancreas

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Pancreas

Exocrine gland producing digestive enzymes and endocrine gland producing hormonesEndocrine portion called Islets of Langerhans which secretes insulin glucagon (2 8%)which secretes insulin, glucagon (2-8%)Insulin moves glucose through cell membranes, stimulates its storage, promotes protein synthesis and stimulates fat storageNerve cells lack insulin receptors and are depend on diffusion for glucose supply

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Pancreas

Endocrine portion called Islets of Langerhans which secretes insulin, glucagonGl ti l t li t dGlucagon stimulates liver to produce glucose, increasing blood glucose level

Pineal GlandAttached to the thalamus above the third ventricleSecretes melatonin which inhibits secretion of gonadotropins (FSH & LH) from anterior pituitaryfrom anterior pituitaryMay help regulate circadian rhythms (daily or 24 hour rhythms)May help regulate onset of pubertyMay help regulate female reproductive cycleSeasonal Affective Disorder (SAD)

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Thymus Gland

Lies posterior to sternum and between lungs (i.e. in the mediastinum)Size and activity varies with age (reaches

i i j t b f b t thmaximum size just before puberty, then regresses)Secretes thymosin which affects production of certain lymphocytes (T-cells) and helps provide immunity

Reproductive Glands

Ovaries secrete estrogens (female hormones) and progesteronePlacenta secretes estrogens, g ,progesterone, a growth hormone and a gonadotropinTestes (testicles) secrete androgens (male hormones) e.g. testosterone

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Other Hormones Producers

Digestive glands several hormones that help regulate digestion, e.g. gastrinHeart and kidneys produce hormones, y p ,e.g. renin, erythropoietinMost of the cells in the body secrete some kind of chemical messenger, but most only affect the cells nearby.