Week 12 The Endocrine System PDF

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Week 12: The Endocrine System and Homeostasis Two systems coordinate communication throughout the body: – the nervous system (electrical impulses) – the endocrine system (communication network in the body) **Both systems control how the body responds to stimuli**

The Endocrine System OBJECTIVES: 1. Define hormone and describe the role and mode of action of these chemical substances. 2. Define endocrine gland and describe the endocrine system of vertebrates, including the location of glands, using humans as an example. 3. Distinguish between endocrine and exocrine glands. 4. Compare and contrast the actions of the endocrine system and nervous system in coordinating the body’s responses to stimuli. 5. Using examples, describe how the hypothalamus interacts with the anterior and posterior pituitary gland to regulate body function. 6. Identify the main hormones produced by the pancreas, thyroid and adrenal glands and describe their main function(s). READING OBJECTIVES: *1. Provide examples of how the action of hormones can alter growth patterns in plants and animals. (Ch. 39, 45.) What are Hormones

Diff between endocrine and exocrine glands Describe the endocrine system and its function in humans  major glands  hormones and their functions Overview of Endocrine System • A network of specialized glands which transmit chemical messages from one part of the body to another. • Together with the nervous system (electrical impulses), they coordinate responses to internal and external stimuli. (changes in body temp and blood pressure) • Secrete hormones from endocrine gland into the circulatory system. Where the messages are transmitted from one part of the body to another • Regulate important internal body functions like metabolism, growth rates and reproductive cycles. Need to know the position of: Hypothalamus, pituitary gland, thyroid gland, adrenal gland(2), pancreas, ovaries, testes

Hormones • Hormones are chemical messenger molecules. – Found in both plants and animals and communicate regulatory messages within the body. – In animals, hormones are produced by endocrine glands and secreted into the circulatory system. • Three major classes of molecules function as hormones in vertebrates: (many originate from kinds of proteins) – Polypeptides (proteins and peptides) – Amines derived from amino acids – Steroid hormones e.g., testosterone Endocrine Signaling • Endocrine glands secrete hormones in response to a stimulus. • Hormones travel through the bloodstream to all parts of the body. • Only the body cells that have protein receptors for that particular hormone will be affected. These are called target cells. All other body cells are unaffected by these hormones • When hormones bind to the protein receptors on target cells it changes the activity of the target cells (response). Brings about changes in how these cells respond. Hormones are very specific to particular body cells – these are called target cells. • Hormones regulate important body processes and functions like growth, development, reproduction and body temperature. E.g. Insect metamorphosis is regulated by hormones. – caterpillar to butterfly Endocrine vs Exocrine Glands • An endocrine gland (secrete their body fluid within an organism) consists of tissue containing specialized secretory cells which produce hormones. Endocrine glands have no ducts and secrete hormones directly into surrounding fluid e.g., thyroid gland. • Exocrine glands have ducts and secrete chemical substances onto body surfaces or into cavities like the digestive system. They DO NOT produce hormones. E.g., salivary glands. • Similarity: They are both glands – made up of specialized cells that excrete hormones. • Differences: Endocrine gland secrete hormones, where exocrine do not secrete hormones. Instead, they secrete chemical substances (different types, example: saliva that has digestive enzymes, but they are not hormones). • Difference: Exocrine (do have ducts for excretion) excretes chemical substances onto body surfaces like sweat on our skin, or into body cavities like our stomachs, where Endocrine (do not have ducts or tubes)excretes chemical messages directly into body fluids. Comparison of Endocrine and Nervous system • Like the nervous system, the endocrine system sends signals to effectors in order to bring about a response to a stimulus. • The nervous system is mostly associated with external stimuli detected by our senses.

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The endocrine system is mostly associated with internal stimuli e.g. changes in blood sugar levels. What types of communication signals do these two systems use and how fast are their responses? Endocrine is chemical, nervous system is primarily electrical. Speed of response: hormone circulating around blood stream is slower and more sustained than the nervous system that is very rapid with a short duration.

Endocrine Pathway A Simple Endocrine Pathway: • The acid needs to be neutralized to protect body organs • The release of acidic contents of the stomach into the duodenum stimulates endocrine cells to secrete the hormone secretin. • This hormone secretin causes target cells in the pancreas to release a chemical which neutralizes the acid in the duodenum. • balances the pH. Negative Feedback 1. Low pH in the duodenum (Stimulus, when food first enters it is acidic) 2. Acid is detected by tissues in the duodenum called S cells, they secrete the hormone secretin 3. Secretin enters the bloodstream/circulatory system 4. Target Cells, with the right hormone receptors, located in the Pancreas 5. When secretin f=binds to target cells in Pancreas, changes the behaviour of those cells 6. These cells start secreting Bicarbonate which travels into the duct that goes into the duodenum 7. Neutralizes the acid 8. Acidity is controlled by the hormone secretin Negative Feedback mechanism: Ø 1. Detect some sort of change in the environment 2. Initiate responses that counteract the initial change that is observed Ø A regulatory system which detects a change in the (internal) environment and initiates a response to counteract the change. Essential for maintaining homeostasis. Ø Negative feedback systems involve the nervous and/or the endocrine system that detects changes in set point and brings about responses that will return the body to set point. Ø Main components: (Stimulus, Sensor, Control Center, Effector, Response) Start with Homeostasis 1. Stimulus: Change in one of the body conditions (increase in blood glucose levels) starting point 2. Sensor: a) detect stimulus/change b) sends message to control center to let it know what happened. Sends messages by endocrine or nervous system

3. Control Center: Makes the decision about what is going to happen, how to response to the stimulus. Sends messages to one or many effectors by endocrine or nervous system. Changes the activity of the effector. Often glands or muscles, but it depends on the stimulus 4. Effector: Activity is changed, counteracts the initial stimulus (this represents the actual response to the stimulus) 5. Response, returns the body to homeostasis Coordination of Endocrine and Nervous Systems in Vertebrates • The hypothalamus receives information from the nervous system and initiates responses through the endocrine system. • Attached to the hypothalamus is the pituitary gland composed of the posterior pituitary and anterior pituitary. • The posterior pituitary stores and secretes hormones that are produced in the hypothalamus. • The anterior pituitary produces and releases hormones under regulation of the hypothalamus. Hypothalamus: Horomones released from the posterior pituitrary and horomones that regulate the anterior pituitary Posterior Pituitary • Only stores hormones, does not produce any • The two hormones stored and then released from the posterior pituitary, act directly on non-endocrine tissues: – Oxytocin (stimulates contractions to bring about child birth)controls milk secretion by the mammary glands and uterine muscle contractions via positive feedback. – Antidiuretic hormone(ADH) (allows more water to be absorbed from the kidney tubules) regulates kidney function (conserves water). – These hormones are transported along the neurosecretory cells of the hypothalamus • Note: Both hormones are produced by the hypothalamus. Anterior Pituitary • Produces quite a few different hormones. (Prolactin, TSH(target organ is the thyroid gland), FSH and LH, ACTH, MSH, GH) • Hormone production in the anterior pituitary is controlled by hormones from the hypothalamus. • Hormones released into circ system to eventually get to the endocrine cells of the anterior pituitary, different from posterior pituitary What is the Interaction between the hypothalamus and Anterior pituitary:

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Thyrotropin releasing hormone (TRH) from the hypothalamus stimulates the anterior pituitary to secrete thyroid stimulating hormone (TSH), which controls secretion of thyroxin from the thyroid gland.

Homeostasis: OBJECTIVES: 1. Define homeostasis in relation to oscillations of a body condition around a set point. 2. Describe the following components of a negative feedback system and explain the significance of their role in maintaining homeostasis: (a) stimulus (b) sensor (c) control centre (d) effector (e) response (f) communication links. 3. Explain the negative feedback mechanism involved in the homeostatic regulation of blood glucose levels. 4. Explain the negative feedback mechanism involved in regulating body temperature in humans. 5. Evaluate the relative importance of the endocrine system and nervous system in maintaining homeostasis. READING OBJECTIVES: 1. Relate body size and complexity to the ability of an organism to maintain homeostasis. (Ch. 40.) 2. Compare and contrast ectotherms and endotherms in terms of their ability to maintain

Homeostasis: Ø Organisms have a set of optimum internal body conditions at which they function most efficiently. E.g., enzymes that control biochemical reactions work best within a narrow range of temperature and pH values. The enzymes are greatly affected by changes in temperature and blood pH. Ø Definition: The maintenance of a stable internal environment of an organism to ensure that body conditions remain within a narrow range of values around set point, despite fluctuations in the external environment. (Do not use the word constant) Ø When internal body conditions like temperature and blood pH vary from their optimum value, enzymes do not function as effectively. Ø If these body conditions vary too much, enzymes may cease to function, and the organism may die. This is why homeostasis is so important. Oscillations and Set Points Ø The ideal level or value of a body condition (e.g. blood sugar level or body temperature (37°C) a target value) is called the ‘set point’. It represents the target value for achieving homeostasis for this particular body condition. Ø Body conditions, never constant and keep changing, often vary above and below the set point but within a limited range. Increase in energy will cause the body temp to increase or vice versa. Ø These cyclic variations (fluctuations) that occur within a narrow range of values from the set point are called oscillations. Control of Homeostasis

Ø How are oscillations in body conditions controlled in order to achieve homeostasis? Negative feedback. What body systems are involved ? endocrine and nervous systems Ø The dynamic equilibrium of homeostasis is maintained by negative feedback, which helps to return a variable to a normal range Ø Most homeostatic control systems function by negative feedback mechanisms. These mechanisms are able to detect changes and help return the body condition to set point. Ø Positive feedback amplifies a stimulus and does not usually contribute to homeostasis in animals Controlling Blood Glucose Levels Ø The negative feedback system controlling blood glucose levels involves the endocrine system. The nervous system has no significant role to play. Ø The endocrine gland involved is the pancreas which contains different groups of endocrine cells. Ø One group contains alpha cells that produce the hormone glucagon. Another group contains beta cells that produce the hormone insulin. Both of these hormones are chemical messages. Ø These hormones target specific effectors causing them to change their activity. Controlling Body Temp Ø Thermoregulation is the process by which animals maintain an internal temperature within a tolerable range despite changes that may occur in their environment Ø 2 groups of animals regarding production of heat Ø Endothermic animals control body temperature by generating heat from metabolism. Birds and mammals are endotherms. Ø Ectothermic animals rely on heat from their environment to regulate their body temperature. Ectotherms include most invertebrates, fishes, amphibians, and non-avian reptiles like lizards. Ø The main advantage of being endothermic is that it allows animals to remain active at a greater range of external temperatures compared to ectothermic animals. Very efficient at maintaining homeostasis Ø This allows them to live in places where other animals are less likely to survive. Ø The main disadvantage of being endothermic is that it requires more energy to remain active. Ø Thus, endotherms require more food to survive compared to ectotherms. Temp Control in Humans Ø The control of body temperature is critical for humans to function normally. A change of just 1 degree in core body temperature makes it difficult for us to perform normal activities. (fever) Ø Body temperature is controlled by a negative feedback system involving both the nervous system and endocrine system. Can you identify the role played by each system and evaluate their relative importance?

Discussion: Compare and contrast the role of the endocrine system and nervous system in maintaining homeostasis in regard to a. Blood glucose levels b. Body temperature Ectotherms vs Endotherms: both are able to regulate body temp to achieve homeostasis (thermoregulation) Ø Ectotherms - Lower rate of metabolism compared to endotherms - Less able to maintain body temperature independently from its environment - Lower ability to achieve homeostasis compared to endotherms. Ø Endotherms - Higher rate of metabolism compared to ectotherms - More able to maintain stable body temperature independently from its environment - Greater ability to achieve homeostasis compared to ectotherms. Structural Adaptations Ø Insulation is a major thermoregulatory adaptation in mammals and birds. Ø Skin, feathers, fur, and blubber (endotherms) reduce heat flow between an animal and its environment. Ø Insulation is especially important in marine mammals such as whales and walruses. Ø Size matters Ø small animals gain and lose heat more rapidly than large animals. Ø in cold climates, large animals spend less energy to maintain a stable body temperature compared to small animals. Ø large animals are more efficient at maintaining homeostasis compared to small animals Ø smaller limbs can also mean less heat loss to the environment, heat loss in a large animal is more efficient/gains and loses it less rapidly Ø being large in a cold environment is more advantageous Physiological Adaptations Ø Regulation of blood flow near the body surface significantly affects thermoregulation. Ø Many endotherms and some ectotherms can alter the amount of blood flowing between the body core and the skin. Ø In vasodilation, blood flow in the skin increases, facilitating heat loss. Ø In vasoconstriction, blood flow in the skin decreases, lowering heat loss.

Ø Many types of animals lose heat through evaporation of water from their skin (perspiration/sweating). Behavioural Adaptations Ø Both endotherms and ectotherms use behavioral responses to control body temperature. Ø Some terrestrial invertebrates have postures that minimize or maximize absorption of solar heat. Ø Sitting in shade or sun when hot or cold is a behavioral response to help us thermoregulate Ø Amphibians are not cold-blooded, they are ectotherms! (they can absorb heart by Convection (air), conduction (the warm rock they are sitting on), or radiation (from the sun)...