Endocrine System LO Flashcards
Define homeostasis and explain its importance
- homeostatic mechanisms act to counteract changes in the internal environment
- variables regulate so that internal conditions remain stable and relatively constant
- homeostasis is not a steady state but a dynamic equilibrium. Failure in homeostasis leads to disease
Name the major endocrine glands
1) hypothalamus
2) pineal gland
3) pituitary gland
4) parathyroid gland
5) thyroid gland
6) thymus
7) adrenal gland
8) pancreas
9) ovary/testes
Define the chemical classes of hormones
1) Peptide/polypeptide
- largest group
- short chains of amino acids
- e.g. insulin, glucagon, growth hormone
- all water soluble
2) amino acid derivatives
- synthesised from aromatic amino acids
- e.g. adrenaline, noradrenaline, thyroid hormones, melatonin
- adrenal medulla hormones = water soluble, thyroid hormones = lipid soluble
3) glycoproteins
- large protein molecules
- often made of subunits
- carbohydrate side chain
- e.g. LH, FSH< thyroid stimulating hormone
- all water soluble
4) steroids
- all derived from cholesterol
- steroidgenic tissues convert cholesterol to different hormones
- e.g. cortisol, aldosterone, testosterone
- all lipid soluble
Understand the concepts of positive and negative feedback
Positive - response in a way so as to change the variable even more in the direction of the change
Negative - response in a way to reverse the direction of change
Describe how hormones are transported
- some hormones travel in blood, peptides + adrenaline
- most hormones bind to specific proteins, thyroid hormones
- dynamic equilibrium between bound and free forms of hormone in plasma
- only free form is biologically active
Describe how hormones act on cells
- hormones exert their effects by binding to specific receptors
- water soluble hormones bind to cell surface receptors
- lipid soluble hormones bind to intracellular receptors
Understand the relationship between the hypothalamus and the pituitary gland
The hypothalamic pituitary axis
- the hypothalamus and the pituitary gland form a complex functional unit that serves as the major link between the endocrine and nervous system.
- Processes they modulate:
1) body growth
2) reproduction
3) adrenal gland function
4) water homeostasis
5) milk secretion
6) lactation
7) thyroid gland function
8) puberty
Name the 2 hormones produced by the hypothalamus for release from the posterior pituitary and briefly state there’re biological roles
1) OT, oxytocin - milk let down and contraction of the uterus during birth
2) ADH, antidiuretic hormone - regulation of body water volume
Name the 6 tropic hormones produced by the hypothalamus and briefly state their biological role
1) TRH, thyrotropin releasing hormone - PRH, prolactin releasing hormone - regulates thyroid gland growth and function
2) PIH, prolactin release-inhibiting hormone (dopamine) - inhibits the release of prolactin
3) CRH, corticotropin releasing hormone - regulator of the hypothalamic-pituitary-adrenal axis which is the main organiser of the body’s response to stress
4) GnRH, gonadotropin releasing hormone - causes pituitary gland to make and secrete LH and FSH
5) GHRH, growth hormone releasing hormone - stimulate pituitary gland to produce and release growth hormone into the bloodstream
6) GHIH, growth hormone-inhibiting hormone (somatostatin - acts as neurotransmitter in the nervous system) - inhibit secretion of other types of hormones
Name the 6 tropic hormones produced by the anterior pituitary gland and briefly state their biological roles
1) GH, growth hormone - regulates metabolism and promotes tissue growth, especially of bones and muscles
2) TSH, thyroid stimulating hormone - stimulates growth and activity of the thyroid gland and secretion of T3 and T4
3) ACTH, adrenocorticotrophic hormone - stimulates the adrenal cortex to release glucocorticoids
4) PRL, prolactin - stimulates growth of breast tissue and milk production
5) FSH, follicle stimulating hormone - stimulates production of sperm in the testes, stimulates secretion of oestrogen by the ovaries, maturation of ovarian follicles, ovulation
6) LH, luteinising hormone - stimulates secretion of testosterone by the testes, stimulates secretion of progesterone by the corpus luteum
Describe the anatomical divisions of the adrenal gland and the hormones produced
Capsule
Cortex
- zona glomerulosa - mineralocorticoids e.g. aldosterone
- zona fasiculata - glucocorticoids e.g. cortisol
- zona reticularis - glucocorticoids + small amounts of androgens
Medulla - chromaffin cells e.g. adrenaline (80%) and noradrenaline (20%)
Describe the components and overall function of the renin angiotensin aldosterone system
- comprised of three hormones: renin, angiotensin II and aldosterone
- regulates blood pressure by modulating blood volume, sodium reabsorption, potassium secretion, water reabsorption and vascular tone
Describe the location, structure and control of the thyroid gland
Location
- against and around front of larynx + trachea
- below thyroid cartilage
- isthmus extends from 2nd to 3rd rings of the trachea
Structure
- 2 lobes joined by isthmus
- “bow tie” shape and location
- parathyroid and thyroid are distinct glands
Control
- regulation of thyroid hormone starts in the hypothalamus
- hypothalamus secretes thyrotropin-releasing hormone into the anterior pituitary
- thyrotropin cells in the anterior pituitary stimulates release of TSH
Outline the overall structure of T3 and T4 and the mechanisms of their production, storage and secretion
- produced in the thyroid gland
- T4 works with TRH and TSH to maintain proper feedback mechanisms and homeostasis
