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The Endocrine System

The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

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Page 1: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

The Endocrine System

Page 2: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

Endocrine system: characteristics• Endocrine system is mostly

controlled by the nervous system

• Endocrine system controls most of the processes occurring in the body

• Divided into cranial & extracranial endocrine glands– Cranial = hypothalamus, pituitary

& pineal glands– Extracranial = thyroid,

parathyroid, thymus, pancreas, adrenals, gonads, GI tract & placenta

Page 3: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

Cranial endocrine glands• Hypothalamus:

– Many “nuclei” within this region to control various aspects of homeostasis• Exhibits control over pituitary

gland

– Blood supply / blood flow pattern is important for control• “portal system”: capillaries in

hypothalamus drain into “portal venules” (veins) that connect to capillaries in the pituitary gland (capillary-vein-capillary)

• Hypothalamic neurons will release “releasing hormones” or “inhibiting hormones” into these capillaries/portal veins to eventually target the pituitary gland

Page 4: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of
Page 5: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

Pituitary gland - Hypophysis• Known as “the conductor” or

“master gland” but is itself under control of the hypothalamus

• Inferior region of the brain, nestled within the sella turnica of the spenoid bone

• 2 regions (visibly different)• Adenohypophysis (anterior lobe)

– Most of the hormones are produced here

• Neurohypophysis (posterior lobe)– More “neural” area, 2 hormones

Page 6: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

Pituitary gland (hypophysis)• Anterior lobe (adenohypophysis)

– Derived from ectodermal glandular tissue– Linked to hypothalamus via the infundibulum which

has the hypophysial portal vascular system (vascular communication)

– Body = anterior pituitary proper – secretes 5 different hormones, prolactin (PL), growth hormone (GH), thyroid stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), Follicle stimulating hormone (FSH) and luteinizing hormone (LH)

• Posterior lobe (neurohypophysis)– Derived from nervous tissue– “extension of the brain”– Releases 2 hormones (which are synthesized in the

brain but stored in the posterior pituitary), oxytocin and vasopressin (or antiduiretic hormone (ADH))

• Intermediate lobe: – Thin, sandwiched between the 2 above layers– secretes a minor hormone (melanin-stimulating

hormone=MSH)

Page 7: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of
Page 8: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

Pineal gland

• roof of the 3rd ventricle)• Larger in children than adults• Secretes melatonin: involved in

circadian rhythm

Page 9: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

Extracranial endocrine glandsThyroid gland

• Thyroid gland– Below larynx, bi-lobed lateral

to the trachea– Largest endocrine gland– Bloodflow via external carotid

& subclavian arteries– Simple cuboidal epithelia

(heavily reliant on iodine)– Follicular cells secrete

thyroxine (T4), Tri-iodo-thyronine (T3) , parafollicular cell or C cells secrete calcitonin

Page 10: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

Parathyroid glands

• Posterior to the thyroid gland (para = around)– 4 distinct glandular

formations• Secretes parathyroid hormone (=

parathormone = PTH)

Page 11: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

Pancreas• Has BOTH endocrine & exocrine

functions• Endocrine = Endocrine cells

grouped into the “Islets” (Islets of Langerhans).

• 3 types of cells:– Alpha cells: secrete glucagon– Beta cells secrete insulin– Delta cells secrete

somatostatin

Page 12: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

Minor gastrointestinal endocrine glands

• GI tract (gastrointestinal tract)– Numerous endocrine cells

distributed throughout GI tract (often single cells)

• Additional endocrine glands:– Salivary glands– Brunner’s glands

(duodenum)

Page 13: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

Adrenal glands• Located on the top of the

kidneys• Composed of 2 major parts:

– Adrenal cortex: 3 layers• Zona glomerulosa secretes

mineralocorticoids• Zona fasciculata secretes

glucocorticoids• Zona reticularis secretes sex

hormones– Adrenal medulla: is an

extension of the sympathetic autonomic nervous system (specialized 2nd motor neurons which secrete adrenaline)

Page 14: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

Gonads• Testicles: Contains the

seminiferous tubules where sperm is made. In between the tubules, the Leydig cells secretes testosterone

• Ovaries: The developing follicle secretes estrogen and progesterone

Page 15: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

Placenta• Transfers waste from fetus to mother and

nutrients from mother to fetus• Secretes estrogen & progesterone• Also secretes human chorionic gonadotrophin

(hCG)…what’s used to change color of pregnancy test sticks

Page 16: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

Pituitary pathophysiology• Panhypopituitarism: reduced

pituitary activity or total loss of pituitary function

• Abnormal growth hormone: • Inadequate during childhood =

pituitary dwarfism• Inadequate during adulthood =

Simmond’s disease– Premature aging

• Oversecretion during childhood = gigantism

• Oversecretion during adulthood = acromegaly– Bones thicken, soft tissues grow

inappropriately

Page 17: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

Acromegaly Gigantism

Occurs during adulthood Begins during childhood

WHY are patients who suffer gigantism taller than those who suffer acromegaly?

Page 18: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

Thyroid & parathyroid pathophysiology

– Hypothyroidism• During childhood = cretinism (“cretins”)• During adulthood = myxedema

– Goiter (abnormal thyroid growth)• Endemic = inadequate iodine intake• Grave’s disease

Page 19: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

Pancreatic pathophysiology– Diabetes mellitus• Type I diabetes: insulin

dependent due to autoimmune destruction of pancreatic beta cells (loss of insulin production)• Type II diabetes: insulin

insensitive due to reduced responsiveness to insulin (metabolic obesity)

Page 20: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

Adrenal pathophysiology

– Pheochromatocytomas: chromaffin cell tumor• Excessive norepinephrine secretion = resembles ANS

overstimulation

– Addison’s disease: decreased mineralcorticoid & glucocorticoid secretion• Constant hypoglycemia, electrolyte imbalances

– Cushing’s syndrome: increased glucocorticoid secretion (Zona fasciculata)• Altered metabolism and physical changes indicative of

edema

Page 21: The Endocrine System. Endocrine system: characteristics Endocrine system is mostly controlled by the nervous system Endocrine system controls most of

Pediatric Cushing’s syndrome