Chapter 25Chapter 25 The Endocrine SystemThe Endocrine System

1.1. Compare the basic organization and function Compare the basic organization and function of the ES and the NSof the ES and the NS

2.2. Describe the structural and functional Describe the structural and functional organization of the hypothalamus and the organization of the hypothalamus and the pituitary and explain their relationshippituitary and explain their relationship

3.3. Discuss the locations and structures of the Discuss the locations and structures of the thyroid, parathyroid, and adrenal glands as thyroid, parathyroid, and adrenal glands as well as the thymus and the endocrine part of well as the thymus and the endocrine part of the pancreas.the pancreas.

4.4. List the hormones (and their function) List the hormones (and their function) produced by these glands. produced by these glands.

5.5. Briefly review examples of abnormal Briefly review examples of abnormal hormone productionhormone production

Endocrine System OverviewEndocrine System Overview

DuctlessDuctless glands produce hormones glands produce hormones Secreted into the Secreted into the bloodstreambloodstream

(endocrine)(endocrine) Except the thyroidExcept the thyroid

Gland may be entire organ:Gland may be entire organ: Pituitary, thyroid, parathyroid, pineal, Pituitary, thyroid, parathyroid, pineal,

adrenaladrenal

or bits of tissue interspersed within or bits of tissue interspersed within an organan organ Gonads, kidneys, many othersGonads, kidneys, many others

Classes of Hormones Classes of Hormones (p 754)(p 754)

Chemical classification of Chemical classification of hormoneshormones Amino Acid DerivativesAmino Acid Derivatives

Proteins (longer)Proteins (longer) Peptides (shorter)Peptides (shorter)

SteroidsSteroids (from cholesterol) (from cholesterol) EicosanoidsEicosanoids (from arachidonic (from arachidonic

acid)acid)

Target tissues are identified by Target tissues are identified by specific receptors (on target specific receptors (on target cells). The effects may be cells). The effects may be stimulatory or inhibitory, stimulatory or inhibitory, depending on the receptors.depending on the receptors.

Control of Hormone SecretionControl of Hormone Secretion

HumoralHumoral BP and the kidney’s JG apparatusBP and the kidney’s JG apparatus

NeuralNeural Recall the adrenal medullaRecall the adrenal medulla Hypothalamic Releasing FactorsHypothalamic Releasing Factors

HormonalHormonal Pituitary Releasing Hormones, e.g., FSHPituitary Releasing Hormones, e.g., FSH

HypothalamusHypothalamus

Control Center for internal environment

Regulates nervous and endocrine systems via 3 mechanisms:

1. ANS centers exert nervous control on adrenal medulla

2. ADH and Oxytocin production

3. Regulatory hormone production (RH and IH) controls pituitary gland directly and all other endocrine glands indirectly

1. These regulatory hormones are released from neurons, thus we have neuroendocrine cells.

Fig 25.3

Pituitary Gland (= Hypophysis) Pituitary Gland (= Hypophysis) p 755p 755

Structure: Located at the base of the brain, Located at the base of the brain,

surrounded by the Circle of Willissurrounded by the Circle of Willis Infundibulum - connection to Infundibulum - connection to

hypothalamus hypothalamus In the sella turcica of the In the sella turcica of the

sphenoid bonesphenoid bone Two parts with separate Two parts with separate

embryonic origins:embryonic origins: Anterior PituitaryAnterior Pituitary Posterior PituitaryPosterior Pituitary

Pituitary Gland (= Hypophysis) Pituitary Gland (= Hypophysis) p 755p 755

Fig 25.3

•Anterior Pituitary (= (= adenohypophysis)adenohypophysis)

•AKA pars distalisAKA pars distalis•production of 7 production of 7 peptide hormonespeptide hormones

•4 are tropic 4 are tropic hormones, hormones, stimulating other stimulating other endocrine glandsendocrine glands

•Pars intermedia and Pars intermedia and pars tuberalis secrete pars tuberalis secrete MSH and some MSH and some gonadotropins.gonadotropins.

Pituitary Gland (= Hypophysis) Pituitary Gland (= Hypophysis) p 755p 755

Fig 25.3

• Posterior PituitaryPosterior Pituitary (= neurohypophysis)(= neurohypophysis)

•AKA pars nervosaAKA pars nervosa•StorageStorage reservoir for reservoir for ADH and Oxytocin ADH and Oxytocin (produced in ?)(produced in ?)

Pituitary Gland (= Hypophysis)Pituitary Gland (= Hypophysis)

Review Table 25.1

Hypophyseal Portal System Hypophyseal Portal System

Review: Three sites of capillary portal systems: liver, kidney, and pituitary

Portal systemsPortal systems:: two two capillary networks in serial capillary networks in serial arrangementarrangement

Portal veinsPortal veins:: blood blood vessels that link two vessels that link two capillary networkscapillary networks

Control of the AdenohypophysisControl of the Adenohypophysis

Hypothalamus has neurons Hypothalamus has neurons that producethat produce Releasing , e.g., GnRH, orReleasing , e.g., GnRH, or Inhibiting HormonesInhibiting Hormones

Into a capillary plexusInto a capillary plexus Down the Down the infundibuluminfundibulum in in

portal veinsportal veins Into a second capillary Into a second capillary

plexusplexus Receptors in pituitaryReceptors in pituitary

Hormones then released into Hormones then released into the circulationthe circulation

Fig 25.4

Neurohypophysis = PPNeurohypophysis = PP

Neurons originate in Neurons originate in the Supraoptic and the Supraoptic and Paraventricular NucleiParaventricular Nuclei

Extend down the Extend down the infundibuluminfundibulum

Release Oxytocin and Release Oxytocin and Antidiuretic Hormone Antidiuretic Hormone (ADH or vasopressin) (ADH or vasopressin) into the circulationinto the circulation

Pituitary MRI, contrast enhanced

Thyroid GlandThyroid Gland

Anterior surface of Anterior surface of trachea just inferior of trachea just inferior of thyroid cartilage (or thyroid cartilage (or Adam’s apple)Adam’s apple)

Two lobes connected Two lobes connected by isthmusby isthmus

Fig 25-7

More ThyroidMore Thyroid Thyroid follicular cells Thyroid follicular cells (simple (simple

cuboidal epithelium) produce and cuboidal epithelium) produce and store thyroglobulin in store thyroglobulin in thyroid folliclesthyroid follicles

Iodine then added to produce Iodine then added to produce thyroxine (Tthyroxine (T44) and triiodothyronine ) and triiodothyronine (T(T33) inside the follicles) inside the follicles

The thyroglobulin is reabsorbed by The thyroglobulin is reabsorbed by the follicular cells, cleaved, and the the follicular cells, cleaved, and the thyroid hormone (T3 and T4) are thyroid hormone (T3 and T4) are released into the bloodstreamreleased into the bloodstream

Note that this is the only extracellular Note that this is the only extracellular storage of hormonesstorage of hormones

C (chief) CellsC (chief) Cells: (AKA parafollicular : (AKA parafollicular cells) produce cells) produce calcitonincalcitonin

Interspersed between thyroid folliclesInterspersed between thyroid follicles Lower blood Calcium Lower blood Calcium

Classic Negative Feedback LoopClassic Negative Feedback Loop

C-Cells

Thyroid DiseaseThyroid Disease Hyper-Hyper-

CardiovascularCardiovascular Increased BPIncreased BP TachycardiaTachycardia PalpitationsPalpitations

NeuromuscularNeuromuscular Emotional labilityEmotional lability InsomniaInsomnia WeaknessWeakness Hand TremorHand Tremor

Hypo-Hypo- WeaknessWeakness Dry, coarse SkinDry, coarse Skin Lethargy, Slow SpeechLethargy, Slow Speech Feel coldFeel cold Less SweatLess Sweat Eyelid and Facial Eyelid and Facial

EdemaEdema

Four Parathyroid Four Parathyroid GlandsGlands

Parathyroid Parathyroid hormone (PTH; hormone (PTH; sometimes also called sometimes also called parathormone)parathormone)

Function: Function:

(raises blood [Ca(raises blood [Ca2+2+])])

antagonist to antagonist to CalcitoninCalcitonin

4 tiny glands embedded in the posterior 4 tiny glands embedded in the posterior aspect of the thyroid (superior and inferior)aspect of the thyroid (superior and inferior)