6.6 – Hormones, homeostasis and reproduction

Essential Idea: Hormones are used when signals need to be widely distributed. 6.6 Hormones, Homeostasis and Reproduction Understandings: Insulin and glucagon are secreted by beta and alpha cells of the pancreas respectively to control blood glucose concentrations   Thyroxin is secreted by the thyroid gland to regulate the metabolic rate and help control body temp Leptin is secreted by cells in adipose tissues and acts on the hypothalamus of the brain to inhibit appetite Melatonin is secreted by the pineal gland to control circadian rhythms A gene on the Y chromosome causes embryonic gonads to develop as testes and secrete testosterone Testosterone causes pre-natal development of male genitalia and both sperm production and development of male secondary sexual characteristics during puberty Estrogen 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 Applications: Causes and treatments of Type I and 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 Skill: Annotate diagrams of the male and female reproductive system to show names of structures and their functions.

Homeostasis Keeping the body within certain physiological limits pH, CO2 and glucose concentrations of blood, water balance, and body temperature Much energy in your body is used to maintain homeostasis

3. Negative feedback mechanisms – work like a thermostat a 3. Negative feedback mechanisms – work like a thermostat a. If certain limit is reached, triggers a response to bring body back within normal range

4. Nervous and endocrine systems work together to maintain homeostasis a. Autonomic nervous system triggers glands to release hormones which travel through blood to target cells

5. Positive Feedback

Hormones and their functions A. Thyroxin – amino acid and iodine 1. Thyroid – butterfly shaped gland in neck 2. 2 forms – T3 and T4 (# of iodines) 3. Target cells – most all in body 4. Transcription regulator (stimulates) 5. Increases metabolism in cell -> requires more energy -> requires more O2 6. Also helps regulate body temp (increased activity increases temp)

Leptin Produced by adipose tissue More fat -> more leptin produced Target cells = hypothalamus Function is to decrease appetite (since there is enough supply in reserves) Obesity – desensitized to leptin, tend to have higher levels, but does not suppress appetite

Melatonin Produced by pineal gland in brain Regulates circadian rhythms Produced mostly at night Production disrupted by exposure to light at irregular times

III. Diabetes A. Insulin – produced by beta cells in pancreas – decreases blood sugar 1. Opens protein channels on cell membranes so that glucose goes into the cell (and out of the blood) 2. Stimulates hepatocytes (liver cells) to convert glucose to glycogen B. Glucagon produced by alpha cells in pancreas – increases blood sugar 1. Stimulates liver to break down glycogen into glucose

Hyperglycemia (high blood sugar) Type I – beta cells don’t produce enough insulin a. Genetic, auto-immune, unknown b. Controlled with insulin injections Type II – body cell receptors don’t respond to insulin (insulin-resistance) a. Genetic, over-consumption of sugar, obesity b. Treated with diet and various medications

Effects 1. Blindness 2. Kidney failure 3. Nerve damage 4. High risk of cardiovascular disease 5. Poor wound healing