11-1: Hormones as Master Regulators

Question 1

Functions and the importance of the endocrine system

Answer 1

• Endocrine glands -> hormones -> blood stream -> target
cells
• Often very effective when present even in small
concentrations
• The production of the hormones is tightly regulated by input from the nervous system and by other hormones
• Hormones coordinate the activities of cells in 3 general
situations:
1) Environmental changes (short-term and long-term stress)
2) Growth, development and reproduction (promoting cell
division, increasing overall body size, promoting sexual
differentiation)
3) Homeostasis (calcium, glucose, water and electrolyte balance, reproduction)

Question 2

Multiple effects of some hormones

Answer 2

• Some hormones have multiple effects, depending on the
target cells and their receptors:
• Adrenaline -> beta receptors in liver cells -> breaking down
glycogen -> releasing glucose into the blood
• Adrenaline -> beta receptors in blood vessels of skeletal
muscles -> vessels relax
• Adrenaline -> alpha receptors in blood vessels in the intestine
-> vessels constrict

Question 3

Regulation of hormone production

Answer 3

• The main regulatory mechanism of hormone
production is the feedback regulation.
• Feedback regulation works in two different ways:
• Negative feedback (the response reduces the initial
signal)
• Positive feedback (it reinforces a stimulus, leading to an even greater response)

Question 4

The hypothalamus and the posterior pituitary

gland

Answer 4

• An extension of the
hypothalamus;
• Does not make its own
hormones;
• Stores/releases hormones
made in the hypothalamus
• ADH and oxytocin are
transported into the posterior
pituitary gland by axons.
• ADH and oxytocin are released
from the posterior pituitary
gland into the blood.

Question 5

Anterior pituitary gland

Answer 5

The hypothalamus:
• releasing hormones
(they stimulate releasing of the anterior pituitary hormones)
• inhibiting hormones (inhibiting release of pituitary hormones).
Tropic hormones (e.g., ACTH, FSH, LH, TSH) target other endocrine glands in the body.
-Prolactin (PRL) and growth hormone target non-endocrine cells and tissues in your body.

Question 6

Thyroid and parathyroid glands

Answer 6

-Thyroid gland produces:
• Triiodothyronine (or T3)
• Thyroxine (T4)
• Calcitonin 
-Parathyroid glands produce:
• Parathyroid hormone (PTH) 
-Calcitonin reduces calcium levels in the blood.
-PTH raises the level of calcium ions in the blood.

Question 7

Functions of T3 and T4 hormones

Answer 7

-Play a crucial role in vertebrate development and maturity
-Also important for homeostatic regulation:
• In maintaining blood pressure
• Heart rate
• Muscle tone
• Digestion
• Reproductive functions
• Regulation of calcium levels in the blood

Question 8

Hyperthyroidism (Graves’ disease)

Answer 8

-Autoimmune disease
(releasing abnormal
antibodies that mimic
TSH, thus fooling the
thyroid gland to
produce more of its
hormones) -> overactivity of the thyroid
gland

Question 9

Hypothyroidism

Answer 9

Retarded skeletal
growth and poor
mental development

Question 10

An enlargement of the thyroid gland

Answer 10

-Reason #1: It occurs due to
hypothyroidism, when there is
not enough T4 to turn off TSH
production
-Reason #2: It also occurs when
the negative feedback
mechanism fails to turn off T4
production – in
hyperthyroidism.

Question 11

Adrenal glands

Answer 11

Both are individually composed of 2 glands:
1. Adrenal cortex secretes:
• mineralocorticoids (such as aldosterone)
• glucocorticoids (such as cortisol)
• small amounts of sex hormones, particularly male
androgens (affecting both males and females).
• The adrenal cortex responds to endocrine signals (ACTH).
2. Adrenal medulla (short term response) secretes:
• epinephrine (adrenaline)
• norepinephrine (noradrenaline).
• The adrenal medulla responds to nervous input.

Question 12

Adrenal cortex hormones

Answer 12

• glucocorticoids
• cortisol
• mineralocorticoids

Question 13

gulcocortucoids

Answer 13

primary effect on glucose metabolism; also have anti- inflammatory effect

Question 14

cortisol

Answer 14

(a glucocorticoid) acts on skeletal muscle, causing the
breakdown of muscle proteins (when body needs more glucose)
• If introduced in high concentrations to the body, it suppresses certain
components of the body’s immune system (when treating arthritis)

Question 15

mineralocorticoids

Answer 15

- aldosteron - act mainly in maintaining salt and
water balance (although cortisol does this too)

Question 16

Adrenaline and noradrenaline

Answer 16

• Allow acute stress response (“fight-or-flight”) • Increase the availability of energy sources • Affect the cardiovascular system • Dilate the bronchioles in the lungs • Raise the rate of oxygen delivery to body cells • Alter blood flow • Affect heart and metabolic rates (adrenaline) • Modulate blood pressure (noradrenaline)

Question 17

Gonads: testes and ovaries

Answer 17

• The gonads produce and secrete 3 major categories of
hormones:
• Androgens
• Estrogens
• Progestins
• The testes primarily synthesize androgens, the main one
being testosterone.
• The ovaries mostly synthesize estrogens and progestins.

Question 18

Functions of gonadal hormones

Answer 18

-Androgens and estrogens are mainly responsible for the:
• development and maintenance of male and female
reproductive systems
• sexual development
• testosterone helps maintain muscle and bone mass in
women, and contributes to their sex drive
-Progestins have roles in:
• supporting the growth and development of embryo(s) while
in the uterus
• progesterone in men increases levels of testosterone in the
body and enhances its effects, at the same time reducing
estrogen and antagonizing its effect