Behavioral Biology Lecture 10: The Endocrine System (Part 2) PDF

Behavioural Biology Lecture 10 The Endocrine System (Part 2) Endocrine Glands and Tissues we will cover: 1. Pineal Gland 2. Pituitary Gland (anterior and posterior) 3.Thyroid Gland 4.Adrenal Glands 5.Pancreas 6.Gonads (testes and ovaries) Read Textbook Chapter 10 3. T...

Behavioural Biology Lecture 10 The Endocrine System (Part 2) Endocrine Glands and Tissues we will cover: 1. Pineal Gland 2. Pituitary Gland (anterior and posterior) 3.Thyroid Gland 4.Adrenal Glands 5.Pancreas 6.Gonads (testes and ovaries) Read Textbook Chapter 10 3. Thyroid Gland A butterfly shaped gland that lies in front of the trachea just below the voice box (larynx). The thyroid gland releases 2 hormones: 1. Thyroid hormone (TH), regulates metabolic rate 2. Calcitonin, regulates calcium levels in blood. Note: smaller parathyroid glands on backside of thyroid also help regulate blood calcium levels. We will not be covering this topic. Thyroid Hormone (TH) TH (2 forms T3 and T4) regulates our metabolic rate and production of heat. Most body cells are target cells. TH revs up our usage of energy stores, glucose and lipids, to make cellular energy (ATP) in mitochondria and also promotes the making of proteins within cells. Control of TH release TRH and TSH are tropic hormones. TH Ultimate control of our metabolic rate is from the hypothalamus. Thyroid Hormone (T3 and T4) Has 2 forms both of which are hydrophobic: T4 & T3 They only differ in the number of iodine atoms in the molecule (4 vs. 3). Iodine from our diet is required to make it. Salt is often iodized for this reason. Thyroid Hormone Mechanism of Action Being hydrophobic, T3 and T4 are transported in blood plasma bound to plasma proteins. Released T3/T4 can exit bloodstream and enter cells. Most cells in your body contain intracellular thyroid hormone receptors making almost every cell in the body a target for thyroid hormone. T3 binds to intracellular receptors and triggers a nuclear response. Which gene is turned on by T3 entirely depends on the receptor and the target cell Regulation of TH Secretion TH levels are maintained within homeostatic levels by a negative feedback mechanism. When the concentration of T3 is elevated within the blood it inhibits the secretion of thyroid releasing hormone (TRH) from the hypothalamus and the secretion of thyroid stimulating hormone (TSH) by the anterior Diagnostically, levels of all 3 hormones pituitary. are checked (TRH, TSH & TH) when metabolic imbalance is suspected. Thyroid Disorders When TH is not produced in normal levels it affects metabolic rate, and many other aspects of health. Disorders caused by abnormal TH levels including: Hypothyroidism (metabolism to slow) Hyperthyroidism (metabolism to fast) Hypothyroidism Reduced levels of TH released into blood. Causes of hypothyroidism are varied and can be the result of disturbance in any part of the TH regulation pathway. For example: TRH release from hypothalamus TSH release from anterior pituitary TH release from the thyroid gland Lower levels of TH cause a slower metabolic rate, therefore less energy is available to your body to perform its normal homeostatic functions. Hashimoto’s Disease Most prevalent cause of hypothyroidism. An autoimmune disorder. Immune system targets and destroys cells in the thyroid gland decreasing its ability to produce and release T3 and T4. Treatable with administration of synthetic TH (Synthroid®). Hyperthyroidism Elevated levels of TH released into blood. Causes of hyperthyroidism are varied and can be the result of disturbance in any part of the TH regulation pathway. Could be a dysfunction of: TRH release from hypothalamus TSH release from anterior pituitary TH release from the thyroid gland Higher levels of TH cause a faster metabolic rate, therefore organs are more active than required for homeostasis and less energy is stored in the body. Graves’ Disease An autoimmune disorder that is the most common cause of hyperthyroidism. Antibodies ae produced that mimic TSH, they can bind to TSH receptors on cells in the thyroid gland and cause them to release more TH than is necessary. Note: Inhibitory effects of TH on release of TRH & TSH still in place so patients with Graves’ disease will have low levels of TRH & TSH while having elevated Antibodies also bindTH. to TSH receptors on connective tissue cells in eye orbits triggering increased tissue mass around the eyes causing them to protrude, a hallmark characteristic of the disease. Treatment of Grave’s Disease include antithyroid drugs or thyroidectomy. 4. Adrenal Glands Small glands that sit on top of each kidney. The gland has 2 different regions with different functions: 1. Adrenal cortex makes 20 different steroid (hydrophobic) hormones including male and female sex hormones. Some related to long-term (chronic) stress response (e.g. Cortisol) 2. Adrenal medulla Makes short-term stress Stress Responses Enable our body to adapt by: Mobilizing nutrients and increasing metabolic rates Increasing nutrient and O2 delivery to cells (↑BP & RR) Suppressing any bodily functions that are not useful in dealing with the stressor (e.g. decreasing digestive and immune activity) Cortisol Cortisol is released on a daily basis as morning approaches in response to variations in melatonin hormone. Melatonin levels decline as daylight begins and the hypothalamus stimulates cortisol release from the adrenal cortex. This is a circadian rhythm. Cortisol prepares the body to start a new day of activity. Cortisol is also part of our long-term stress response. It is released when we experience Target cells of sustained physical, cortisol physiological, and/or psychological stress. Cortisol Effects The goal of cortisol is to mobilize stored nutrients (carbs, fats and proteins) in the body to use as energy sources. Cortisol also suppresses Breakdown and release your immune system of stored carbohydrates, function. proteins and fat Nighttime Cortisol levels low, melatonin is high. Restoration and repair of tissues and heightened immune function. Morning Cortisol levels high, melatonin low. Mobilization of nutrients for boost in energy to start the day and suppressed immune function. Chronic stress (weeks/months) diminishes the body’s immune response, leaving a person prone to infection. E, NE and the Short Term Stress Response (Fight or Flight) Short-term stress (exercise, excitement, fear, panic) activates the sympathetic nervous system which quickly stimulates our fight or flight response. Sympathetic motor neurons directly innervate the adrenal medulla. During a fight or flight response it is stimulated to release E and NE released as hormones: -Increase heart rate & respiratory epinephrine (E) and rate norepinephrine (NE) into -Increase skeletal muscle readiness the blood. -Increase oxygen and glucose to the brain and muscles 5. Pancreas The pancreas rests on the backside of the stomach. It produces and releases 2 hormones which have antagonistic effects on blood glucose level: 1. Glucagon (increases blood glucose levels) 2. Insulin (decreases blood glucose levels) Glucose is the most common fuel for cellular respiration, the process that creates cellular energy (ATP). Therefore, regulating glucose levels in the blood is a critical homeostatic process to maintain health. Glucagon and Insulin are Antagonistic hormones Glucagon increases blood glucose levels by: Stimulating target cells in the liver to convert stored glycogen into glucose and release it into the blood stream. Insulin decreases blood glucose levels by: Inhibiting the liver from breaking down stored glycogen. Stimulating muscle cells to take in and use glucose. Stimulating adipose cells to take in glucose and Diabetes Mellitus People with diabetes have high levels of glucose in their blood (hyperglycemic). Causes: They are insulin deficient. Their body has become insensitive to insulin. Type I Diabetes: Type II Diabetes: Early onset (under 25) Later onset (over 45, but An autoimmune disease increasingly younger cases that destroys the cells in the occurring) pancreas that make insulin. Insulin must be taken by Body becomes less responsive to injection. insulin. Poor diet, sedentary lifestyle and obesity make an individual more susceptible. Treatment includes strict diet, Diabetic symptoms Type I diabetes: Symptoms severe and sudden Extreme thirst and hunger, frequent urination, unexplained weight loss, fatigue, blurred vision, nausea/vomiting. Type II diabetes: Symptoms develop gradually over a course of years High blood pressure, increased hunger and thirst, frequent urination, blurred vision Complications of diabetes: Unregulated or poorly managed diabetes results in chronic high levels of glucose in the blood. This leads to high blood pressure which damages blood vessels over time. As the person ages they are increasingly at risk of developing heart disease, kidney dysfunction (failure), loss of sensation in the extremities and blindness. 6. Gonads (Testes and Ovaries) The testes in males and the ovaries in females in addition to making our gametes produce and release sex hormones. The Hypothalamus, Pituitary, Gonad (HPG) Axis Gonadotropin releasing hormone (GnRH) from the hypothalamus stimulates the anterior pituitary to release 2 gonadotropins: Luteinizing hormone (LH) and Follicle stimulating hormone (FSH). They target the gonads affecting sperm/egg & sex hormone (testosterone &  Testosterone - Produced in both sexes, but in much higher quantities in males from the testes. - Important for sperm production. - Important for development of male characteristics: Formation of male genitals during embryonic development. Maintenance of male reproductive structures. Secondary sex characteristics at puberty (deep voice, increased muscle mass, facial and chest hair) In both sexes, testosterone is responsible for sex drive. Estrogen Found in both sexes, but in much higher levels in females from the ovaries. Important for: Menstrual cycle. Development and maintenance of female reproductive structures. Development of female secondary sex characteristics (breasts, pubic hair, widened hips). Helps prepare for implantation of an embryo by thickening the endometrial lining of the uterus. Estrogen Beyond the development and maintenance of the female reproductive system, estrogen has many other effects. Helps with regulating body temperature and memory function Regulates cholesterol production, so reduces risk of atherosclerosis. Helps maintain bone density After menopause, estrogen levels drop affecting body temp, concentration, increasing risk of