1. 6.6 Hormones, Homeostasis & Reproduction

2. Understanding

3. Applications & skills

4. Homeostasis
Question: What is homeostasis? Answer: The ability of organisms to maintain a stable internal environment

5. Principles of Homeostasis
In order for an organism to maintain a stable internal environment, there are several things that it needs
Communicators
Communicators
(e.g. brain)
(Sensory Nerves)

6. Principles of Homeostasis
Generally works by using negative feedback
Negative Feedback:
In biology, a system whereby a change elicits a reaction that elicits a return to the original condition
Most systems in the body are controlled this way.
Examples
Temperature regulation
Blood glucose regulation
Appetite control

7. Hormones
What is a Hormone? A chemical substance produced in the body and released into the bloodstream. It controls and regulates the activity of certain cells or organs. A hormone is released from a specific cell or organ and only affects its target cell

8. Hormones
Some common hormone releasing organs

9. Studying hormones
To fully understand a hormone and its effects, you should know the following information about it
Organ of release
Target organ/cells
Effect on target organ/cells
What stimulates it
What inhibits it

10. Study chart Hormone Secreted By Target Effect Stimulated by
Inhibited by
Insulin
Glucagon
Thyroxin
Leptin
Melatonin
Testosterone
Estrogen
Progesterone

11. Blood glucose regulation
Two hormones are responsible
Insulin and glucagon
Both are released from the
pancreas; specifically, they
are released by a section of
the pancreas called the
“Islets of Langerhans”

12. Blood Glucose Regulation
Insulin
Glucagon
Released from β cells in the Islets of Langerhans of the pancreas
Released when blood sugar is high
Increases glucose uptake into cells by making the cell membrane permeable to glucose
Also stimulates glylcogen formation in the liver
Release is inhibited when blood glucose decreases to normal levels
Released by αlpha cells in the Islets of Langerhans of the pancreas
Released when blood sugar is low
Causes glycogen in the liver to break down and get released into bloodstream
Inhibited when blood glucose returns to normal levels

13. Diabetes – When Blood Sugar Is not regulated
Diabetes is a condition where glucose cannot enter the cells. This causes blood glucose to remain high for a long time after a meal.
There are several kinds of diabetes but the two most common are Type I (early onset) and Type II (adult or late onset)

14. Type I vs Type ii TYPE I Diabetes TYPE II Diabetes
Occurs because person cannot make insulin
Usually occurs at a young age and is a lifelong condition
May be caused by the body’s own immune system
attackingand destroying Beta cells in the pancreas
Can be treated with insulin injection or islet cell transplants
Person can make insulin but it is not effective in getting glucose into cells
Usually occurs in overweight adults
Often occurs because person eats too much food that is high in sugar. This causes insulin levels to be high all the time. Eventually, the cells become insulin resistant and lose their sensitivity to it
Can be treated with diet and exercise

15. Regulating Metabolism
Thyroxin is released from the thyroid gland in the lower part of the neck
It regulates metabolic rate
It stimulates energy metabolism so you have more energy,
burn more calories and release more body heat
Its release mechanism is complex but it can be stimulated
by low body temperature
Many people are unable to properly regulate their metabolism so they have too much or too little

16. Thyroid Disorders High energy; hyper May find it difficult to focus
Hyperthyroidism
(too much)
Hypothyroidism
(too little)
High energy; hyper
May find it difficult to focus
Rapid heartbeat
Very thin even though they may eat a lot
Feeling hot
Hair loss
Increased sweating
Lack of energy; sluggishness
Depression and forgetfulness
Slow heartbeat
Gain weight very easily
Feeling cold
Puffy face

17. Leptin – The Appetite Hormone
Where is leptin secreted from?
Adipose (fat) cells
What does it do?
Suppresses your appetite.
How does it do this?
Leptin acts on special cells in
the hypothalamus of the
brain and causes apetite
to decrease

18. How does Leptin Work
Leptin is often called a “Master Hormone”. That is, it controls and affects things by stimulating or inhibiting other hormones.
How Does Leptin Suppress Your Appetite?
Several ways:
It counteracts the effects of a feeding stimulant released in the gut called neuropeptide Y
Counteracts the effects of a neurotransmitter called adandamide which stimulates appetite.
Leptin promotes the synthesis of an appetite suppressant called α-melanocyte-stimulating hormone

19. Leptin
What happens if you don’t produce leptin? This is actually a leptin deficient mouse (left) that was treated with leptin

20. What affects leptin levels
Leptin level is
increased by perceived emotional stress
decreased by increases in testosterone levels
increased by increases in estrogen levels
chronically reduced by physical exercise training
increased by insulin
paradoxically increased in obesity
Some foods are said to affect leptin levels as well

21. Leptin & obesity
Since leptin is secreted from adipose tissue (fat cells), it is not surprising that obese individuals have more of it.
But it seems a little surprising that a hormone that supresses appetite is higher in obese people. Do obese people eat less than thin people?
Generally, they do not. While obese people have more leptin, most have developed a condition known as leptin resistance.
This is a condition where leptin no
longer affects the hypothalamus to
the same degree that it used to
This is a common occurrence in
living things; when levels of some-
thing remain high for too long, the
body gets used to it and stops
responding (see insulin resistance)

22. Melatonin – Sleep/Wake cycle control
Melatonin is the hormone responsible for Circadian Rhythms; the daily cycle of sleep and wakefulness
It is released by the Pineal gland in the brain and controlled by special cells in the hypothalamus called the suprachiasmatic nuclei

23. melatonin What Does Melatonin Do? Makes you drowsy
Lowers your core temperature
When is it Released?

24. Melatonin
What Stimulates/Inhibits It? The SCN seem to have their own timekeeping cycle that ranges from ~24-26 hours (people kept in the dark will develop a sleep wake cycle that is usually a little over 24 hours Nerves in the retina (back of the eye) that are stimulated by light will send impulses to the SCN causing them to inhibit the release of melatonin. So light will decrease melatonin and drowsiness.