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THE ENDOCRINE SYSTEM
• Lecture 2; Holes, Chapter 13
THE PITUITARY GLAND
Secretes 9 hormones
Divided into 2 parts: Anterior lobePosterior lobe
Posterior: nervous tissue(neurohypophysis)
Pituicytes (type of glial cell).Secretes neurohormones from hypothalamus
Essential for normal bone and nerve development and reproductive development.
Thyroxine (T4) - secreted by follicle cells
Triiodothyronine (T3) - converted from T4 at target cells
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TRANSPORT OF THYROID HORMONE (TH)
T4 & T3 are bound to transport proteins Both forms can bind to receptors; T3 much more readily Peripheral tissues have enzymes to convert T4 to T3 T4 & T3 both act like steroids and act in the nucleus
Regulation:
If T4 blood levels fall, thyroid-stimulating hormone (TSH) is released.
T4 is released from gland to increase blood levels
TSH levels fall, T4 release is slowed
(Can be over-ridden is times of need: cold temperature, pregnancy)
HypothalamusThyrotropin-releasing
hormone
Anterior Pit.GlandThyroid Stimulating
Hormone
Thyroid glandThyroid hormone
TARGET CELLS
DISORDERS OF THYROID HORMONE (TH)
Hypersecretion:
Grave’s disease Autoimmune disease - constant stimulation of thyroid to release TH. High metabolic rate, nervousness, weight
CALCITONIN Produced by parafollicular cells (or C cells) Released when blood Ca++ is high Lowers blood Calcium. Inhibits ________ activity, stimulates ________ activity Increases Ca++ excretion by the kidney Humoral stimulus (raised Ca++ levels)
Fast, but short acting response.
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PARATHYROID GLAND
Gland made up of:
Chief cells - PTH Oxyphil cells - ?
Four small glands
Posterior surface of the thyroid gland
Vary in number and position
PARATHYROID HORMONE
PTH release stimulated by falling blood Ca++
Raises falling Ca++ levels.
Stimulates, bone, kidney and intestine.
Activates Vitamin D - precursor of calcitrol
DISORDERS OF PARATHYROID HORMONE
Hypersecretion
Hyperparathyroidism (rare, cancer)Bones are broken down
Raised Ca++ : Depression of Nervous
System Muscle weakness Kidney stones Metastatic calcification