Introduction to Endocrine System

Question 1

What are the types of secretions in our body?

Answer 1

a) Endocrine secretion; substance released by cell into blood stream that affects distant cells
b) Exocrine secretion; substance released by cell into a duct that leads to epithelial surface (onto skin or gut) . Action doesn’t depend on receptors in target tissue.

• ** Both endocrine and exocrine secretions are glandular secretions, whereby they come from specialized secretory cells that are clumped together to form a gland.
• ** Secretions may have several sites of action simultaneously

Question 2

What are the communication pathways of hormones?

Answer 2

a) Autocrine; cell produces hormone that stimulates or inhibits itself (acts on itself)
b) Paracrine; cell produces hormone that stimulates or inhibits its neighboring cells (acts on different cells)
c) Juxtacrine; cells sit side by side - one has hormone on surface, another has receptor on surface

Question 3

State the functions of hormones

Answer 3

• stimulate cell function
• inhibit cell function
• maintain normal levels of substance
• stimulate cell differentiation
• stimulate apoptosis (programmed cell death) or protect cells from apoptosis

Question 4

What are the types of hormones (classification of hormones)?

Answer 4

1. Depending upon chemical nature
   a) peptide hormones
   b) steroid hormones
   c) thyroid hormones
2. Depending upon structures
   a) Peptides
   b) Amines
   C) Steroids
3. Depending upon mechanisms of action
   a) Group I hormone; act by binding to intracellular
   receptors and mediate their actions via formation
   of a hormone receptor complex. These include
   steroid, thyroid hormones. These hormones have intracellular receptors
   b) Group II hormone; involve second messenger to mediate their effect. These hormones have cell membrane receptors

Question 5

What are the classifications of hormones according to structure?

Answer 5

a) Steroids
- lipid derived from cholesterol
- secreted by the gonads, adrenal cortex, and placenta

b) Peptides
- peptides are short chains of amino acids

c) Amines
- amines are derived from a.a tyrosine and are secreted from thyroid and adrenal medulla

**Solubility of the hormone classes varies

Question 6

Name the different endocrine glands

Answer 6

a) adrenal glands
b) hypothalamus
c) ovaries and testicles
d) pancreas
e) parathyroid glands
f) pineal body
g) pituitary gland
h) thymus gland
i) thyroid gland

Question 7

Explain the endocrine system regulation and feedback cycles

Answer 7

• The endocrine system uses cycles, negative feedback and antagonistic pairs of hormones to regulate physiological functions
  a) Cycles; maintain homeostasis. Range from hours to months in duration
  b) Negative feedback;
  example; cold temp. -> triggers hypothalamus (releases thyrotropin-releasing hormone) -> triggers anterior pituitary (releases thyrotropin) -> triggers thyroid gland -> secretes thyroxine

** Negative feedback in thyroxine causes reflex

c) antagonistic pairs of hormones; insulin and glucagon