The Endocrine System Flashcards
Describe the endocrine system
- Consists of endocrine (ductless) glands
- Those that secrete hormones form the endocrine system
- Composed of several separate organs
- The endocrine & nervous systems act together in a single interrelated system
What is a hormone
A chemical secreted into the blood that exerts an action at another site. Hormones in blood will reach all tissues in the body, but only act on specific organs.
Describe the 4 main categories of hormones
1) Steroids
2) Amino acid derivatives
3) Peptides ( chain of <50 amino acids)
4) Proteins ( chain of >50 amino acids)
What is the function of hormones
- Hormones change the rate at which target cells perform an activity
for example contraction of muscle cells & secretion of gland cells - The activity of an enzyme in the cell may be changed
- Enzyme activity may be changed by:
producing more of the enzyme
Inactive forms activated
Increased production & activation
What are hormone receptors
For steroids they are the proteins in the the cytoplasm of cells. Receptors for most non-steroid hormones are in the plasma membranes of the cells
Describe the pituitary
- The pituitary gland lies below the hypothalamus & the brain
- 3 lobes: anterior, intermediate, posterior
- Each acts as a distinct gland
What is the function of the Anterior pituitary gland
Secretes growth hormone, thyroid- stimulating hormone, adrenocorticotropic hormone, prolactin, gonadotropic hormones
Composed of true glandular tissue
What does the posterior pituitary secrete
- Oxytocin (controls milk secretion & uterine motility)
- Antidiuretic hormone
What are the pituitary disorders
Disorders of the growth hormone
1) Overproduction: acromegaly (enlargement of body parts, skin thickening)
2) Underproduction: growth hormone deficiency (growth failure, low bone density)
Disorders of the antidiuretic hormone
1) Overproduction: SIADH (Fluid overload)
2) Underproduction: Diabetes insipidus (thirst, dilute urine)
What does the adrenal cortex secrete
1) Aldosterone (Na & K secretion)
2) Cortisol (stress responses, organic metabolism)
3) Androgens (sex steroids, growth)
What does the adrenal medulla secrete
Epinephrine - organic metabolism, stress response, cardiovascular response
Norepinephrine
(reinforcer of sympathetic activity)
Describe the 2 adrenal disorders
1) Cushing’s syndrome: overproduction of ACTH by the pituitary. Excess stimulation of the adrenal gland. Weight gain in face, excess hair, weakness
2) Addison’s disease: underproduction of glucocorticoids in the cortex. Weakness, nausea, skin darkening
What does the thyroid gland secrete?
Thyroxine, triiodothyronine
Both affect energy, metabolism, growth, development
Both derivatives of amino acids & contain iodine
Describe the structure of the thyroid
- Composed of follicles
- Follicles surrounded by connective tissue embedded with parafollicular cells
- Iodine absorbed from gastrointestinal tracts as iodide
- Follicular cells remove iodide from blood & convert to iodine
- Iodine attached to tyrosyl which are linked together to form thyroid hormones
Describe thyroid disorder
- Iodine supplied by food
- Lack of iodine causes enlargement, to better use whatever iodine is present, regulated by the thyroid stimulating hormone
- Hereditary factors & disease may reduce thyroid secretion
