18 - Endocrine System Flashcards
What are the chemicals that the endocrine system uses called?
Hormones
What are the three classes of hormones?
Steroids
Hormones Derived from Amino Acids
Peptides and Protein Hormones
Define Steroids as a Hormone Class
- synthesized from cholesterol (lipid soluble)
- e.g. testosterone, estrogen, vitamin D
What are some Hormones Derived from Amino Acids
- e.g. derived from tyrosine
a) thyroxine /T4- a thyroid hormone
- lipid soluble
- controls cellular metabolism, growth, development
b) epinephrine + norepinephrine (catecholamines) - adrenal medulla hormones
- water soluble
- short term stress - part of fight-or-flight response
Describe Peptides and Proteins Hormones
- chains of amino acids held together by peptide bonds
- water soluble
- e.g. oxytocin, antidiuretic hormone (ADH), growth hormone (GH), insulin
List the endocrine glands
Pituitary Gland
Thyroid Gland
Parathyroid Gland
Adrenal Glands
List the endocrine tissues
Pancreatic Islets of Langerhans
Hypothalamus
Gonads
Others
Describe the structure and location of the pituitary gland
- suspended from hypothalamus
- lies in sella turcica of sphenoid bone
- 2 lobes:
- Anterior Pituitary
- Posterior Pituitary
Describe the Anterior Pituitary
- epithelial tissue
- anterior pituitary hormone secretion regulated by hormones released from the hypothalamus
- metabolism hormones:
i) Growth Hormone – promotes growth + metabolism
ii) Thyroid Stimulating Hormone (TSH) - stimulates activity of thyroid gland
iii) Adrenocorticotropic Hormone (ACTH) - stimulates secretion of adrenal steroids (adrenal cortex)
- reproductive hormones:
i) Luteinizing Hormone (LH)
ii) Follicle Stimulating Hormone (FSH)
iii) Prolactin (PRL) - stimulates milk formation
Describe the Posterior Pituitary
- nervous tissue
- extension of hypothalamus
- hormones produced in hypothalamus, stored and secreted from post pituitary:
i) Oxytocin- stimulates uterine contraction and milk ejection
ii) Antidiuretic Hormone (ADH) - water reabsorption in the kidney
- stimulates uterine contraction and milk ejection
Describe the Thyroid Gland
- on anterior surface of superior part of trachea
- butterfly shaped
- thyroid histology:
a) follicles - walls = epithelial (follicular) cells
- produce mainly T4
- activated in other tissues to T3
b) parafollicular cells - between follicles
- secrete calcitonin
- increases Ca++ uptake into bone (bone formation), which lowers blood Ca++
Describe the Parathyroid glands
- 4 (usually) glands embedded in posterior thyroid
- secrete parathyroid hormone (PTH)
- increases blood Ca++ by:
a) ↑ Ca++ release from bone (= bone resorption) - activates osteoclasts
b) ↓ Ca++ loss in urine (kidney)
c) ↑ vitamin D activation (kidney) - vitamin D then ⇑ Ca++ absorption at the small intestine
Describe the Adrenal Glands
- superior surface of each kidney
- 2 parts
a) adrenal cortex (outer) - epithelial tissue
- secretes steroids only
- 3 layers (1 hormone type secreted by each):
i) zona glomerulosa
- secretes mineralocorticoids (mainly aldosterone)- salt balance
ii) zona fasciculata- secretes glucocorticoids (mainly cortisol)
- long-term stress hormone
- carbohydrate metabolism
iii) zona reticularis- secretes androgens (a small amount of testosterone)
- women - sex drive
- some converted in other tissues (e.g. fat) to estrogens
- salt balance
b) adrenal medulla (inner)
- nervous tissue
- 2 hormones:
i) epinephrine (80%)
ii) norepinephrine (20%)
Describe the Pancreatic Islets of Langerhans
- 4 cell types (we will cover 2):
a) α cells - produce glucagon
- ⇑ blood glucose
b) β cells - produce insulin
- ⇓ blood glucose
Describe the hypothalamus as an endocrine tissue
- regulates anterior pituitary via e.g.:
a) GHRH = growth hormone releasing hormone
b) GHIH = growth hormone release-inhibiting hormone
c) GnRH = gonadotropin releasing hormone (for LH, FSH) - synthesizes posterior pituitary hormones
