The endocrine system

Its control over body functions

What is an endocrine gland?

• Secretory structure

• Secretes into interstitial fluid, then blood

• Secretion rates are extremely low

• All are highly vascularized

• What ARE the endocrine glands?– Pituitary, thyroid, parathyroid, adrenal pineal– Many other organs and tissues have

endocrine function

What is a hormone?

• Small molecule: protein, glycoprotein or lipid (steroid or eicosanoid)

• Released into blood

• Binds to specific receptors– Receptors can be blocked– Hormones can be synthesized– Cells may vary the number of receptors

Overview of the endocrine system

Important endocrine glands

• Structure and location

• Hormones produced

• Target cells

• Function

• Effects of insufficiency or overproduction

Hypothalamus/pituitary gland

Two lobes to (adult) pituitary

• Anterior (adenohyphosis)– Pars distalis (anterior), pars tuberalis

(posterior)– Secretes hormones that regulate many body

functions– Is itself regulated by releasing and inhibiting

hormones– Portal system delivers the hormones

Hormones secreted by anterior pituitary cells

• Human growth hormone (somatotrophs)

• Thyroid-stimulating hormone (thyrotrophs)

• Follicle-stimulating hormone; luteinizing hormone (gondaotrophs)

• Prolactin (lactotrophs)

• ACTH (adrenocorticotropic hormone) and MSH (melanocyte-stimulating hormone)

Posterior pituitary

• Neurosecretory cells– Oxytocin– Antidiuretic hormone

(ADH)– Transported out of

axons, into posterior hypophyseal veins

Summary of pituitary activity

The thyroid gland

Thyroid hormone affects metabolic rate

Disorders are common

Parathyroid glands

• Regulate blood calcium levels, along with C cells of thyroid

• Stimulates osteoclast activity

• Promotes calcium retention at kidney

• Stimulates production of calcitrol at kidney

Adrenal glands

• Paired glands lie superior to kidneys• Cortex (outer part) and medulla (inner part)

derive from different tissues• Cortex produces “stress hormones”; can’t live

without them!– Zona glomerulosa (mineralocorticoids)– Zona fasciculata (glucocorticoids)– Zona reticularis (androgens)

• Medulla produces epinephrine and norepinephrine

Location, blood supply, histology of adrenal glands

Pancreas is an endocrine and exocrine gland

99% of tissue

A cells- glucagonB cells- insulinD cells- somatostatinF cells- pancreatic

polypeptide

Responds to eating or fasting

Pineal gland

• Part of epithalamus

• Melatonin helps regulate biorhythms

• May regulate reproductive function

• Other tissues have endocrine function but primary role may be different (digestive system, heart, kidneys, etc.)

Endocrine functions of other organs

• Kidneys– EPO, renin, calcitrol

• Heart

• ANP and BNP suppress ADH

• Digestive organs- secretion of digestive enzymes

• Reproductive organs to be discussed

Summary

• Endocrine organs are distributed over the body

• Some are regulated by hypothalamus and pituitary, some by negative feedback

• Exert effects by releasing hormones that activate specific cells

• Abnormal levels of hormone secretion or activity can cause complex disorders