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