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Chapter 8: The Endocrine System

Chapter 8: The Endocrine System. Hormones...not just for teenagers. You have seen how aldosterone plays an important part in water regulation Most of your body’s processes are regulated by hormones – they are considered to be chemical messengers

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Chapter 8: The Endocrine System

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  1. Chapter 8: The Endocrine System

  2. Hormones...not just for teenagers You have seen how aldosterone plays an important part in water regulation Most of your body’s processes are regulated by hormones – they are considered to be chemical messengers The collective set of these organs that secrete hormones important for homeostatic regulation are known as the ENDOCRINE SYSTEM

  3. Efficient or Inefficient? If you think about the fact that the blood is the primary substance in our body that passes through EVERY organ, it makes sense to use it as a transportation vector Therefore, chemical signals, though inefficient when compared to something like nervous signals in the brain, are useful because very distant parts of the body can communicate with each other However, the complication is that hormones must travel through the WHOLE body before reaching its target organ

  4. Delay This means that most systems controlled by hormones will have lag period of start up and stopping They are also regulated by very tightly monitored feedback loops in order to stop the secretion of the hormone when it is no longer needed Most feedback loops in the endocrine system are negative

  5. Basic set up If you recall the first lecture on homeostasis, a given organ in the endocrine system will follow a basic feedback loop Diagrams are often used to describe the mechanism of action for a given hormone Others are named according to the hormone involved There are usually at least two organs involved; a monitoring organ and a target organ, but axes may include more than one organ

  6. MONITORING ORGAN (-) (+) TARGET ORGAN CHANGE (+) (+) TARGET ORGAN

  7. Types of hormones Hormones can be classified into two types based on their chemical structure: Based on the chemical structures, each type of hormone has slightly different mechanisms of action and can affect cells through different methods

  8. Steroid hormones: welcome in Recall that the cellular membrane is composed of mainly lipids Therefore, the release and absorption of steroid hormones are less well regulated, since they have the capacity to exit and enter cells freely If they can pass through cellular membranes, they can pass through nuclear membranes as well; they are often used to control DNA transcription for this reason

  9. http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter18/animation__mechanism_of_steroid_hormone_action__quiz_1_.htmlhttp://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter18/animation__mechanism_of_steroid_hormone_action__quiz_1_.html

  10. Protein hormones: knock first Protein hormones require more regulation because they cannot easily pass through the cellular membranes to affect cells Protein hormones must interact with cells via receptors on the surface of the cell

  11. http://highered.mcgraw-hill.com/sites/dl/free/0072421975/196644/second_messengers.htmlhttp://highered.mcgraw-hill.com/sites/dl/free/0072421975/196644/second_messengers.html

  12. A noteworthy gland: the pituitary gland One particular gland that is of great importance in the endocrine system is the pituitary gland It is located at the base of your brain, just in front of the brain stem

  13. Nervous control The pituitary gland is a good example of how the brain directly links into the endocrine system The brain not only helps monitor the state of the body, but it also acts to synthesize and release hormones that control other hormones Therefore, the brain itself is an important endocrine organ

  14. Hormone axes The hormone axes we are going to study will include: Glucagon: Hypothalamic-Pituitary-Adrenal axis: Hypothalamic-Pituitary-Thyroid axis: Parathyroid: Hypothalamic-pituitary-testicular axis: Hypothalamic-pituitary-ovarian axis:

  15. 8.2 Glucose regulation

  16. Glucose regulation Because glucose is an essential molecule for cellular survival, its regulation is important A specific concentration of glucose must be kept in the blood in order for cells to access the glucose they need to function

  17. The pancreas Pancreatic tissue contains many different types of cells – each different type is responsible for secreting different substances The cluster of cells that regulate blood sugar form a structure known as the ISLETS OF LANGERHANDS

  18. Glucagon and insulin Insulin and glucagon are antagonistic hormones – they produce opposite effects and work together to balance glucose levels Insulin acts on cells to increase their permeability to glucose by binding to receptors on the cell surface and helping increase the activity of glucose transporters – this decreases the level of glucose in the blood

  19. Time lag Understanding this axis helps us to understand the importance of portion sizes in healthy eating After a meal, glucose floods your bloodstream – if there is more glucose than can be used immediately by cells, it will be put into storage by the liver, who, due to insulin secretion, will be increasing its uptake of glucose, and therefore, creating more glycogen Between meals, your “starvation mode” – glucagon is secreted to break down the glycogen stored earlier

  20. Diabetes Diabetes occurs when insulin production or response to insulin is compromised There are two types of diabetes: Type 1 Diabetes/Juvenile Diabetes/Diabetes Mellitus: Type 2 Diabetes/Adult-Onset Diabetes:

  21. Symptoms of Diabetes Diabetes results: Increased urine production and therefore increased loss of water Increased thirst Increased glucose secretion in urine and therefore increased glucose levels in urine

  22. Long term complications of diabetes Peripheral neuropathy – numbness in the extremeties There is a thought that the heart is also directly affected by the inability to regulate glucose levels

  23. Treatment Type 1 diabetes Type 2 diabetes

  24. Gestational Diabetes Pregnant mothers are also at risk of developing gestational diabetes This results in an increased blood glucose level that can affect the baby

  25. 8.3 Metabolic control

  26. Metabolism Metabolism refers to the sum total of all chemical reactions that maintain a living organism It is most closely associated with those processes that produce and store energy in the body which would include, in simple terms, the making and breaking of chemical bonds

  27. Metabolic control The BASAL METABOLIC RATE refers to the rate at which an organism can process energy This rate refers to the amount of energy that the body uses when at rest BMR is different for everyone – this explains why two people that have the same diet may have very different body masses High BMR usually means that you burn more calories per minute than someone with low BMR

  28. Thyroid gland The thyroid gland is a large endocrine gland on its own, but situated on top of the thyroid are 4 individual glands that collectively make up the parathyroid gland The thyroid gland secretes very powerful steroid hormones that control metabolism

  29. Thyroid gland Two hormones, T3 and T4, are secreted by the thyroid gland – collectively known as Thyroxine The “3” and “4” refer to the positions of iodine which are bound to the molecule

  30. Hypothalamic-Pituitary-Thyroid axis TRH= Thyroid releasing hormone TSH = Thyroid stimulating hormone

  31. Thyroid disorders Because iodine is an essential part of the T3 and T4 molecule, a lack of iodine can lead to the underproduction of these hormones If T3 and T4 are not being secreted, the hypothalamus will not receive negative feedback; therefore, it will continually secrete TRH This will cause the anterior pituitary to continually secrete TSH TSH stimulates the thyroid to secrete T3 and T4 – and to do meet the constant demand, the thyroid will increase in size (by increasing the number of secreting cells)

  32. Hyper and Hypothyroidism An over or undersecretion of thyroxine can lead to a change in BMR Hyperthyroidism refers to an oversecretion of thyroxine which can lead to rapid weight loss, heightened state of agitation and nervousness, difficulty focusing The cause can be a tumour (for example, tumour blocks the exit duct for the hormone) and it is common with aging as cells begin to slow down

  33. Calcium balance The parathyroid glands, along with the thyroid gland, work together to balance calcium levels in the blood Parathyroid hormone (PTH) is secreted by the parathyroid gland and is antagonistic to Calcitonin, secreted by the thyroid gland

  34. Calcitonin and PTH Low levels of blood Ca stimulate the release of PTH PTH increases blood Ca by stimulating the activity of osteoclasts, bone cells that break down bone This will lead to the release of Ca into the blood stream

  35. Problems with Ca balance Improper Ca blood levels can affect bone and muscle If Ca levels cannot be maintained at normal values, this can affect the amount of available Ca to bones for normal development

  36. Human Growth Hormone HGH is an important hormone required for growth in young children Think carefully about what happens to appetite during adolescence: growing children require large amounts of energy in order to fuel muscle, bone and neuronal development

  37. Secretion HGH is secreted by the anterior pituitary Its secretion is controlled by the hypothalamus that secretes GHRH (growth hormone releasing hormone) HGH acts on the liver to secrete hormones such as IGF (Insulin like growth factor) that acts on muscles to increase hypertrophy (increase in size of cells) and hyperplasia (increase in number of cells) of muscle

  38. (-) (-) (-) (-) IGF

  39. Actions GH will also: • Mobilize fat stores by increasing the breakdown of fat • Stimulate the growth of internal organs • Stimulate immune system

  40. Problems with GH Lack of GH secretion has a much more severe effect during childhood than adulthood Low GH levels during development will lead to shorter statures and smaller builds in children This can be a cause of dwarfism – Too much GH secretion during childhood can result in the opposite – gigantism – Oversecretion of GH in adulthood can cause increased body mass and bone thickness which can interfere with normal skeletal movements – creating a condition called acromegaly

  41. 8.4 The stress response

  42. The stress response Human response to stress is a very important evolutionary mechanism that has evolved to keep us alive It is controlled by the hypothalamus Therefore the first cues that a stress response is necessary due to a threat of danger would be processed through the brain, usually via visual information (as primates are reliant heavily on vision as a sense)

  43. If you’re in danger, then what? To understand the mechanism better, it is important to understand what happens physiologically in times of danger This group of symptoms is associated with what biologists refer to as the “flight or fight” response:

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