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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