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The Endocrine System
Anatomy and Physiology
Endocrine System
• Endocrine organs secrete hormones directly into body fluids (blood)
• Hormones are chemical messengers that only affect target cells that have a special receptor on the cell surface
Hormones…
• Are of two types: steroid and nonsteroid, usually peptide (protein)
• Steroid hormones may enter the cell through the cell membrane, but nonsteroid hormones cannot
Nonsteroid hormones
• These hormones, usually proteins, cannot get through the cell membrane.
• They must attach to a receptor on the outside of the membrane
• They use a 2nd messenger system to get the message into the cell, to achieve the desired response
Pass it on!
2nd messenger system
A chain reaction
Endocrine Glands
Control of Hormones
• Most often controlled by negative feedback
• This means a gland or system is sensitive to the concentration of the substance it secretes, or a product it controls
Control of Hormones
• If high levels of a hormone or product are detected, then the gland is inhibited (shut off)
• If low levels are detected, more must be needed, so the gland is not inhibited (allowed to turn on)
Control of Hormones
• What turns on and off each gland varies
• Some have many steps involved, like a chain reaction
Control of Hormones
Control of Hormones
Growth hormone is controlled by a releasing and an inhibiting hormone. Which one is secreted in greater concentration determines whether GH is released or not.
Control of Hormones
Hypothalamus controls Pituitary
Hypothalamus controls Pituitary
Hormones of the Pituitary
Master gland
Growth Hormone
• Stimulates cell growth and division
• Under-secretion can be dwarfism, with correct proportions and normal mental development
• Over-secretion can be gigantism
Twelve years old: 6’5”
6’1” normal male’s hand
Twelve year old’s hand
Gigantism
Hypopituitary Dwarfism
Posterior Pituitary
Vasopressin is also called ADH: antidiruetic hormone
Thyroid Gland
• Secretes three hormones
• Thyroxine (T4), Triiodothyronine (T3)
• Calcitonin
Thyroid Hormones
• T3 and T4 control metabolism
• Undersecretion in childhood could cause cretinism; in adults called myxedema with sluggishness, obesity
• Oversecretion can be Grave’s disease
Grave’s disease
Cretinism
Goiter
• Enlarged thyroid gland
• Caused by lack of iodine
• Iodine is required to make T4, and if not present, the thyroid keeps working to the point of enlargement, yet cannot make T4
Thyroid Control
• TRH (TRF) from hypothalamus to pituitary
• TSH from pituitary to thyroid
• T3 and T4 (thyroxine) from thyroid
• Negative feedback
Parathyroid
• Parathyroid gland secretes parathyroid hormone (PTH)
• PTH increases blood calcium and decreases blood phosphate
• Parathyroid gland can sense level of calcium in the blood
Parathyroid
• Osteoblasts are cells that build bone• Osteoclasts are cells that break down bone to
release calcium• If calcium is low in the blood, PTH stimulates
osteoclasts• If calcium is high in the blood, PTH inhibits
osteoclasts• Controlled by the parathyroid glands, sensing the
amount of blood calcium
Parathyroid
Parathyroid
• Your body sacrifices bone tissue to maintain correct levels of calcium in the blood.
Thyroid helps with calcium
• The thyroid gland also helps with calcium regulation
• It secretes calcitonin, which decreases level of blood calcium by encouraging the kidney to excrete calcium and inhibiting osteoclasts
• PTH and calcitonin are opposites
Adrenal Hormones
• Adrenal glands on each kidney
• Inner part is called medulla
• Outer part is called cortex
• Each section produces different hormones
Adrenal Hormones
• Cortex produces cortisol (hydrocortisone)
• Stimulates carbohydrate metabolism
• Reduces inflammation• Stimulates muscle
growth
Cortisol from Adrenal cortex
• Undersecretion leads to Addison disease, can be fatal by disturbing electrolyte balance
• Oversecretion is Cushing syndrome, alters carbohydrate and protein metabolism, and electrolyte balance
Adrenal Hormones
• Cortex also produces aldosterone
• Acts on kidney to increase uptake of sodium
• Essential for survival because of its role in water and solute balance
Adrenal Hormones
• Medulla produces epinephrine, also called adrenaline
• “Fight or Flight”• Increases heart rate,
blood pressure, glucose level, and blood flow to heart and lungs
Pancreas
• Functions as both endocrine and exocrine gland
• Endocrine: hormones are insulin and glucagon
• Exocrine: digestive enzymes
Pancreas
Pancreas
• Special clusters of cells called the Islets of Langerhans secrete hormones
• Alpha cells secrete glucagon
• Beta cells secrete insulin
Pancreas
• Glucagon stimulates the liver to break down glycogen into glucose
• Stimulated by low blood sugar
Pancreas
• Insulin stimulates the liver to form glycogen and promotes the absorption of glucose into cells
• Lowers blood sugar• Stimulated by high
blood sugar
Diabetes Mellitus
• Lack of insulin• Cells are starving;
cannot get glucose into the cell without insulin, thus weight loss is a symptom
• Kidneys try to get rid of excess sugar, increasing urine output and thirst
Diabetes Mellitus
Diabetes Mellitus
High blood sugar damages blood vessels, leading to complications
Complications include:coronary artery disease, retinal damage, kidney damage, and problems from poor circulation in the peripheral areas