The Endocrine System Flashcards
1
Q
What are endocrine glands?
A
- Ductless organs that secrete hormones into the bloodstream
- They all have an extensive distribution of blood vessels
- Function to communicate signals throughout the body to maintain homeostasis
2
Q
What are hormones?
A
- Hormones are chemical messenger molecules
- They can only affect target cells or target organs that have receptors for that specific hormone
- Cells that do not possess the right receptors will not respond to that hormone
- 3 chemical classes of hormones
- Protein hormones: chains of amino acids… smaller chains are called peptide hormones
- Steroid hormones: type of lipid derived from cholesterol
- Biogenic amines: small molecules made by altering the structure of an amino acid
- Hormone secretion is regulated by a self-adjusting mechanism called a feedback loop (negative and positive loop types)
3
Q
What is a negative feedback loop?
A
- Where a stimulus starts the process, but a hormone causes the process to slow down or stop
- An example is blood glucose regulation: eating a meal increases blood glucose, in response insulin is secreted, insulin decreases blood glucose levels
4
Q
What is a positive feedback loop?
A
- Accelerates the original process started by a stimulus to ensure it continues or is sped up
- Occurs less frequently than negative feedback loops
- An example is milk release from the mammary glands: baby suckling stimulates oxytocin release, oxytocin stimulates milk release, continuous suckling keeps the release going
5
Q
What does the hypothalamus do for the endocrine system?
A
- Is the control center
- Secretes regulatory hormones that control the release of anterior pituitary hormones
- Secretes releasing and inhibiting hormones
- Produces oxytocin (OT) and antidiuretic (ADH) hormones which are stored and released from the posterior pituitary gland
- Controls the stimulation of the adrenal medulla: by exciting the sympathetic nervous system, it stimulates the adrenal gland to secrete hormones
6
Q
What is the pituitary gland?
A
- Also called the hypophysis
- Located just inferior to the hypothalamus, connected by infundibulum (stalk)
- Housed in sella turcica of the sphenoid bone
- Divided into anterior and posterior lobes
7
Q
What is the anterior pituitary?
A
- Also known as andenophophysis
- Divided into 3 areas
- Pars distalis: large anterior part
- Pars intermedia: scant part between the other 2 areas
- Pars tuberalis: wrapping around infundibulum
- Controlled by regulatory hormones secreted by the hypothalamus: travel through a blood vessel network called the hypothalamo-hypophyseal portal system
- Hypothalamus has a primary plexus network drained by hypophyseal portal veins
- Within anterior pituitary, the portal veins disperse into secondary plexus of capillaries (hypothalamic hormones exit blood and access anterior pituitary cells)
- Blood from anterior pituitary enters systemic circulation via anterior hypophyseal veins
8
Q
What are the hormones secreted by the anterior pituitary?
A
- Secretes several tropic hormones that stimulate other glands to release other hormones
- Thyrotropic cells of pars distalis secrete thyroid-stimulating hormone(TSH)
- Mammotropic cells in pars distalis secrete prolactin (PRL)
- Gonadotropic cells in pars distalis secrete follicle stimulating hormone (FSH) and luteinizing hormone (LH)
- Corticotropic cells in pars distalis secrete adrenocorticotropic hormone (ACTH)
- Somatotropic cells in pars distalis secrete growth hormone (GH)
- Anterior pituitary pars intermedia secretes melanocyte stimulating hormone (MSH)
9
Q
What is the posterior pituitary?
A
- The neutral part of the pituitary gland
- Comprise of pars nervosa and infundibular stalk
- Neural connection between hypothalamus and posterior
pituitary is the hypothalamo-hypophyseal tract - Neurosecretory cells in hypothalamus have unmyelinated axons in tract: when they fire impulses they release hormones (ADH and OT) from their terminals in posterior pituitary to bloodstream
- Hypothalamic nuclei contain cell bodies of neurons that extend into posterior pituitary (supraoptic nucleus and paraventricular nucleus)
10
Q
What is the thyroid gland?
A
- Is the largest gland that is primarily devoted to endocrine activities
- Located inferior to thyroid cartilage and anterior to the trachea
- Is a butterfly shape with left and right lobes connected by a midline isthmus
- Composed of spherical structures called thyroid follicles containing colloid fluid
- Cuboidal follicular cells produce and secrete thyroglobulin (TGB)
- Iodine molecules are combined with TGB to make thyroid hormone precursors that are stored in colloid
- When needed for secretion, follicular cells take up TGB and convert it to thyroid hormone (TH)
11
Q
What is the thyroid and pituitary gland negative feedback loop?
A
- Low body temp signals hypothalamus to thyroptin-releasing hormone (TRH)
- TRH causes the anterior pituitary to release thyroid-stimulating hormone (TSH)
- TSH stimulates thyroid follicular cells to release the thyroid hormone (TH)
- TH stimulates many cells to increase metabolic rate , which raises body temp
- Increased temp inhibits TRH release
- TH inhibits release of TRH and TSH
12
Q
What are parafollicular cells?
A
- Large endocrine cells located between thyroid follicles
- Secrete calcitonin in response to elevated blood calcium
- Calcitonin reduces blood calcium by inhibiting osteoclasts and increasing calcium loss in urine
13
Q
What are parathyroid glands?
A
- Small glands on the posterior surface of the thyroid gland (usually 4 per person)
- Have 2 types of cells
- Chief cells: Secrete parathyroid hormone (PTH)
• PTH raises blood calcium levels by stimulating osteoclasts (free calcium from bone); stimulating calcitriol synthesis (promotes calcium absorption from food); and preventing calcium loss through urine - Oxyphil cells: function unknown
14
Q
What are adrenal glands?
A
- Paired glands that sit on the superior borders of the kidneys
- Each gland has an outer adrenal cortex and an inner adrenal medulla, with each region secreting different hormones
15
Q
What is the adrenal cortex?
A
- The glands outer cortex
- Has 3 layers, each of which secrete different corticosteroid hormones
- Zona glomerulosa: Produces mineralocorticoids such as aldosterone
- Zona fasciculata: Produces glucocorticoids such as cortisol and corticosterone
- Zona reticularis: Produces gonadocorticoids including androgens
