Introduction to the Endocrine System

Question 1

What is the Endocrine System

Answer 1

A collection of specialized glands that synthesis
and secrete chemical messengers (i.e., hormones)
directly into the blood system, to be transported,
(bound or unbound) towards the distant target
cells/organs.

Question 2

What is the Exocrine System

Answer 2

A system of glands called exocrine glands which that secrete chemical substances but not into the bloodstream, instead they secrete them through ducts that carry them to nearby body surfaces

Question 3

Endocrine glands (ductless glands)

Answer 3

Hormones travel to target cells/organs that contain binding

receptors, for specific hormones (lock and key mechanism)

Question 4

Exocrine glands

Answer 4

Examples include, sweat, tears, saliva, and digestive juices)
into excretory ducts for transport to the outside.

Question 5

Endocrine Hormone Facts

Answer 5

Act slowly

Question 6

Chemical Messengers

Answer 6

1. Extracellular chemical messengers bring about
   cell responses primarily by signal transduction-Process by which incoming signals are conveyed to
   target cell’s interior.
2. Binding of extracellular messenger (first
   messenger) to matching receptor brings about
   desired intracellular response by either:

2.1 Opening or closing channels

2. 2Activating second-messenger systems:
   - Activated by first messenger

-Relays message to intracellular proteins that carry out
dictated response

Question 7

Define a Hormone

Answer 7

Chemical messengers that produced by one gland or
organ of the body, secreted directly into the
bloodstream, and transported to target cells/organs of
the body where they exert their regulatory functions.

Question 8

Local Hormone

Answer 8

Hormone that acts on nearby target cells/organs.

Question 9

Paracrine hormones

Answer 9

Secreted by cells into the extracellular fluid and

affect neighboring target cells of a different type.

Question 10

Autocrine hormones

Answer 10

Secreted by cells into the extracellular fluid and

affect the function of the same cells that produced.

Question 11

Circulating hormones

Answer 11

Hormone that acts on a distant target cells/organs

Question 12

Endocrine hormones

Answer 12

Are secreted in very small amounts (µg/ml blood) by
endocrine glands into the circulating blood and influence the function of target cells/organs at
another location in the body.

Question 13

Neurohormones

Answer 13

Secreted by neurons into the circulating blood and
influence the function of target cells/organs at another
location in the body.

Question 14

Cytokines

Answer 14

Peptides secreted by cells into the extracellular fluid and can function as autocrine, paracrine, or endocrine
hormones (i.e., act on both local and distant targets).

Question 15

Mention the Principal Endocrine Glands

Answer 15

Hypothalamus (neuroendocrine)

Pituitary Gland

Pineal Gland

Thyroid Gland

Parathyroid Glands

Adrenal Glands-Adrenal Cortex/Adrenal Medulla

Pancreas (both exo/endocrine function)

Thymus (both exo/endocrine function)

Gonads (both exo/endocrine function)-Testes (males)/Ovaries (female)

Question 16

General Hormone Functions

Answer 16

Regulate metabolism.

Regulate H2O and electrolyte balance.

Induce adaptive changes to help the body cope
with stressful situations (behaviour).

Promote growth and development (cellular synthesis, secretion, and mitosis).

Control reproduction.

Regulate blood pressure and circulation.

Regulate nutrient circulation, digestion and absorption of food (carbohydrates, lipids, and proteins).

Question 17

Chemical classification of Hormones

Answer 17

Amines

Peptides/Polypeptides/Glycoproteins

Steroids

Question 18

Amine

Answer 18

Hormones derived from tryptophan and tyrosine
Tyrosine:

• Catecholamines (epinephrine and norepinephrine)
• Thyroid hormones (thyroxine and triiodothyronine)

Tryptophan:

-Melatonin

Question 19

Peptides/Polypeptides/Glycoproteins

Answer 19

Hormones composed of chains of amino acids (variable length)

Hypothalamic, pituitary gland, parathyroid gland, pancreatic glands

Question 20

Steroids

Answer 20

Hormones derived from cholesterol

Hormones secreted by the testes, ovaries, placenta and adrenal cortex.

Question 21

Hormone Interactions

Answer 21

A hormone can influence the activity of another hormone at given target cell in one of three ways:

1.Two hormones are synergistic if they work together to
produce a larger effect together, than their individual effects added together (complementary action).

2. A hormone has permissive effect if it enhances the
   responsiveness of a target cell to a second hormone.

Example: hormone A must be present in adequate
amounts for hormone B to fully exert its.

3. If the action of hormone A inhibits the effect of
   hormone B, the effect is antagonistic – the
   effectiveness of a second hormone is reduced.