6.6 Hormones, Homeostasis & Reproduction

Understanding

Applications & skills

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

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)

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

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

Hormones Some common hormone releasing organs

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

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

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”

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

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)

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

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

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

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

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

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

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

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)

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

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

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.