This document summarizes key hormones and their roles in homeostasis: - Insulin and glucagon regulate blood glucose levels, while thyroxine regulates metabolism and body temperature. Leptin inhibits appetite and is secreted by adipose tissue. Melatonin controls circadian rhythms and is secreted by the pineal gland. - Testosterone and estrogen influence sexual development and characteristics. The menstrual cycle is regulated by feedback between ovarian and pituitary hormones. - Examples of clinical applications include diabetes treatment, obesity research, and assisted reproduction techniques. Historical studies on deer reproduction are also mentioned.

1. Hormones and Homoeostasis

2. 6.6
• Insulin and glucagon are secreted by β and α cells of the pancreas
respectively to control blood glucose concentration.
• Thyroxin is secreted by the thyroid gland to regulate the metabolic rate and
help control body temperature.
• Leptin is secreted by cells in adipose tissue and acts on the hypothalamus of
the brain to inhibit appetite.
• Melatonin is secreted by the pineal gland to control circadian rhythms.
• Testosterone causes pre-natal development of male genitalia and both
sperm production and development of male secondary sexual
characteristics during puberty.
• Oestrogen and progesterone cause pre-natal development of female
reproductive organs and female secondary sexual characteristics during
puberty.
• The menstrual cycle is controlled by negative and positive feedback
mechanisms involving ovarian and pituitary hormones.

3. Applications:
• Causes and treatment of Type I and Type II diabetes.
• Testing of leptin on patients with clinical obesity and reasons for the
failure to control the disease.
• Causes of jet lag and use of melatonin to alleviate it.
• The use in IVF of drugs to suspend the normal secretion of hormones,
followed by the use of artificial doses of hormones to induce
superovulation and establish a pregnancy.
• William Harvey’s investigation of sexual reproduction in deer.

9. Thyroxin: Key Points
• Secreted by the thyroid gland .
• Regulates metabolic rate
• Helps control body temperature.
Correct functioning of the thyroid
requires IODINE in the diet.
Lack of dietary iodine causes GOITRE
Lack of thyroxin causes:
• lack of energy
• Depression
• Weight gain despite appetite
loss
• Feeling cold

10. Click for animation

11. Leptin: Key Points
• Secreted by the adipose tissue cells.
• Acts on the hypothalamus
• Inhibits appetite
Leptin is a protein hormone that targets the appetite
centre of the hypothalamus.
Food intake triggers Leptin
secretion which in turn inhibits
appetite which reduces food
intake.
This is an example of negative
feedback.

12. Spot the mouse
treated with
Leptin blockers.
Leptin and
Obesity: should
GM Leptin be
made available
as a treatment
for obesity?

13. Melatonin: Key Points
• Secreted by the pineal gland .
• Helps control circadian rhythms.
High levels of MELATONIN cause feeling
of drowsiness and promote sleep.
Falling melatonin levels encourage waking
at the end of the night.
Melatonin also promotes a drop in core
temperature and probably causes the
night time body temperature drop.
Melatonin is sometimes
advertised as a treatment
for Jet Lag why do you think
it might work?

14. Functions of Oestrogen
Oestrogen and progesterone
cause pre-natal development of female
reproductive organs and female
secondary sexual characteristics during
puberty.
The menstrual cycle is controlled
by negative and positive feedback
mechanisms involving ovarian and
pituitary hormones.

15. Complete Q16 from the workbook.

18. Text pages 162-3 and complete Q 20 in the workbook

19. William Harvey and Sexual Reproduction
“Omne vivum ex ovo” All life comes from the egg.
• In 1651 he asserted that
all life developed from
the egg
• Harvey was right in some
ways but was limited by
his observations as the
microscope was not
invented until 17 years
after his death.

20. Further information:
Three of the best sites for
IB-specific Biology
information. The top link
takes you to the PPT by
Stephen Taylor