Homeostasis & hormones
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Homeostasis & hormones






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Homeostasis & hormones Presentation Transcript

  • 1. HOMEOSTASIS & HORMONES “…it is all about a balancing act…”
  • 2. OVERVIEW A) Homeostasis B) Hormones: chemical nature and mode of action C) Hypothalamus and Pituitary gland D) Adrenal glands E) Hormonal regulation of blood sugar levels
  • 3. Homeostasis:  Greek: ‘homoios’ = similar ‘stasis’ = standing still
  • 4. Intracellular fluid (cytoplasm) Homeostasis is the maintenance of a relatively stable internal environment What is the ‘internal’ environment?
  • 5. Are variables absolutely constant? STEADY STATE Low Variable High NO
  • 6. Examples of Physiological conditions requiring homeostasis: O2 and CO2 levels in the body energy requirements glucose level in blood water / ion balance pH temperature
  • 7. fluid surrounding cells where organism lives
  • 8. Living systems are seen to be open systems. What does this mean? Require a continuous exchange of matter between the environment and themselves Oxygen Food Carbon dioxide Heat UreaWater
  • 9. An organism may be thought of as a complex system of chemical processes these processes are:  self-regulating  tend to maintain a steady state even though the external environment changes
  • 10. Why is homeostasis is important? An organism functions more efficiently if conditions are maintained within narrow limits close to optimum conditions To prevent large fluctuations from the optimum What causes these fluctuations? Changes in external and internal environments
  • 11. Internal conditions may be maintained constant within the body by: developing a variety of mechanisms: Structural Physiological Behavioural
  • 12. Fat Fur Feathers Structural
  • 13. Which structure is missing here? May 22, 2002
  • 14. Sweat Increase in heart rate Cardiac arrest in frozen frog Physiological
  • 15. HOT: Seek shade HOT: Seek shade COLD: Bask in the sun Behavioural
  • 16. Three basic components of a control system: 1. Detector / Receptor / Sensor 2. Regulator / Control centre / Co-ordinator / Integrating centre 3. Effector
  • 17. Stimulus (Input) Response (Output) What is the role of each component? Detects deviation from set point Produces response Compares input with set point & determines response
  • 18. Integrating Centre in mammals is: An endocrine gland Brain or spinal cord
  • 19. What is Feedback? Feedback refers to responses made after a change has been detected
  • 20. Time Positive feedback Two forms of feedback: Negative feedback Time EquilibriumDivergence
  • 21. Negative Feedback: refers to the mechanism by which a system responds to a fluctuation in the opposite direction
  • 22. Corrective mechanism: DECREASES body temperature Body temperature: RISES
  • 23. Corrective mechanism: INCREASES body temperature Body temperature: DECREASES
  • 24. Sensor + Regulator: Effector: Blood sugar regulation: Negative feedback
  • 25. In negative feedback (feedback inhibition): the initial stimulus provokes a response which tends to reduce the magnitude of the stimulus as conditions return to their optimum, the corrective processes can be switched off
  • 26. Negative feedback also applies to the regulation of a population size: Death rate increases Birth rate increases
  • 27. Why is negative feedback very common in the body? increases the stability of systems
  • 28. Examples of Negative Feedback Control: O2 and CO2 levels in the body hormone levels, e.g. thyroxine sex hormones metabolic levels e.g. glucose water balance the regulation of pH body temperature
  • 29. Control of thyroxine release as an example of negative feedback
  • 30. TRH (thyroid releasing hormone / thyrotrophin releasing hormone) TSH (thyroid stimulating hormone) TRH TSH
  • 31. Positive feedback:  a disturbance leads to events which increase the disturbance even further  rare in biological systems WHY rare? lead to:  an unstable situation  extreme states
  • 32. Examples of Positive Feedback Control: 1. Blood clotting Activated platelet releases chemicals More platelets are activated A blood clot forms
  • 33. Examples of Positive Feedback Control: 2. Child birth Oxytocin stimulates muscular contractions of the uterus More oxytocin is released
  • 34. 3. The control of ovulation Oestrogen stimulates the secretion of LH (luteinising hormone)
  • 35. 4. Stimulation of a nerve fibre sodium gates open and sodium ions rush into the axon. Cytoplasm Extracellular fluid
  • 36. Na+ Na+
  • 37. K+ K+ Na+ Na+
  • 38. Na+ Na+ Na+ Na+ K+ K+ K+
  • 39. Na+ Na+ K+ K+
  • 40. Does the disturbance ever stop?  in most cases, once the purpose of the feedback loop is completed, counter-signals are released which:  suppress or break the loop Oxytocin level drops once baby is born
  • 41. Essay Title Write an essay on feedback mechanisms and their role in control of biological systems. [SEP, 2001]
  • 42. OVERVIEW A) Homeostasis B) Hormones: chemical nature and mode of action C) Hypothalamus and Pituitary gland D) Adrenal glands E) Hormonal regulation of blood sugar levels
  • 43. A chemical communication system is made up of at least two types of cell: one cell: produces & releases the hormone  message released second cell with receptor: receives message  target cell activated
  • 44. Receptors are SPECIFIC
  • 45. Explain why insulin affects all body cells but ADH only the kidney. Receptors for insulin occur on all body cells but those for ADH only in the kidney. ADH Target: Kidney cell Receptor
  • 46. Hormones are chemicals secreted by: Endocrine cells Nerve signals (arrows) cause release of neurohormones Neurosecretory cells
  • 47. Hormones are classified over distance they operate: Histamine [endocrine only is in syllabus]
  • 48. Endocrine hormones : are released into the bloodstream and interact with distant target cells e.g. adrenaline
  • 49. Where are the receptors located? Position of receptor depends on the solubility of the hormone
  • 50. Lipid-soluble (lipophilic) hormones intracellular receptors Water-soluble hormones: receptors on the cell surface
  • 51. Water-soluble & lipid-soluble hormones act in different ways: Water-soluble hormones: Activate enzymes within the cell
  • 52. Lipid-soluble Hormones: Induce transcription and translation to form enzymes
  • 53. Explain why lipid-soluble hormones are slow acting. Enzymes need to be formed before a reaction occurs.
  • 54. What can you say about the solubility of ‘growth factor’? Explain. Water soluble. Receptor is in plasma membrane as it cannot pass through it.
  • 55. Steroid Model vs. Protein Model • Diffuse through cell membrane • Receptors in cytoplasm • Response has slow onset • Long-lasting • Typically derived from cholesterol • Examples: Testosterone, Oestrogens, Progesterone • Do not diffuse through cell membrane • Receptors on surface of cell • Response has quick onset • Short-lasting • Typically derived from amino acids • Examples: Insulin, Glucagon Steroid Model Protein Model
  • 56. Question: End-of Year SEP, 2010 Use your knowledge of biology to describe the significance of the following. Steroid hormones act by activating genes. (5 marks)
  • 57. Enzymes within the cell are activated when a hormone binds to a receptor in the membrane by the help of a: second messenger e.g. cyclic AMP (cAMP)
  • 58. cAMP forms from ATP The enzyme that catalyzes the formation of cAMP from ATP is: located on cytoplasmic side of plasma membrane called adenylyl cyclase or adenylate cyclase
  • 59. cAMP forms from ATP
  • 60. Formation of cAMP Adenylyl cyclase A B
  • 61. Formation of cAMP G protein receptor signal C Enzymes activated
  • 62. cAMP is a common second messenger What is a second messenger?
  • 63. A second messenger is a substance released in the cytoplasm after the first messenger – the signal – binds its receptor GTP: guanosine triphosphate
  • 64. What is the “first messenger”? Hormone Why is a “second messenger” needed? Hormone cannot enter the cell.
  • 65. Cyclic AMP (cAMP) has many effects on the cell :  including glucose mobilisation for:  energy  muscle contraction Let us study the role of cAMP in the release of glucose from the liver
  • 66. A Cascade of Reactions (part 1) an enzyme cascade is a system for amplifying a biological signal
  • 67. A Cascade of Reactions (part 2)
  • 68. cyclic adenosine monophosphate cAMP b gaGTP adrenaline Gs Inactive protein kinase A Active protein kinase A adenosine triphosphate ATP aGTPGDP G-protein linked receptor adenylate cyclase
  • 69. Why are only a few molecules of the hormone needed to produce many molecules of product? Each enzyme in the cascade can act on many molecules of the next molecule. Amplification occurs through a cascade of reactions.
  • 70. End-of-Year 2012 Adrenaline affects a range of target tissues in the body. Suggest how the adrenaline molecule can cause different effects in different target tissues. Different tissues have different (types of adrenaline) receptors; (causing) cAMP concentration/ second messenger to increase or decrease; Second messenger (may be) different; activates different / other enzymes / enzyme reactions (in different target cells)
  • 71. cAMP is not the only second messenger e.g. nitric oxide (NO)
  • 72. cAMP is not the only second messenger nitric oxide (NO) causes relaxation of blood vessels
  • 73. Calcium can be a second messenger calcium is widely occurring an increase in cytoplasmic Ca2+ concentration will cause: NOTE: the same second messenger is involved in two very different biological actions A muscle cell to contract A salivary gland cell to fluid secrete 1 2
  • 74. Remember: The nature of the biological activity triggered by second messenger is dependent on the cell type The same second messenger is involved in more than one biological action. True of all second messenger pathways:
  • 75. Protein hormones cannot enter the cell. Say why. Question: End-of Year SEP, 2010 Use your knowledge of biology to describe the significance of the following. (5 marks) Protein hormones act by means of a second-messenger system.
  • 76. A Gland is:  a structure which secretes a specific chemical substance or substances
  • 77. A Gland secretes chemicals into: Some other part of the body The bloodstream
  • 78. Glands in the body are: secrete a product into a duct  secrete hormones  have no duct (ductless)  have a rich blood supply Exocrine gland Endocrine gland
  • 79. Why is the pancreas described as both an endocrine and an exocrine gland? Produces both enzymes and hormones.
  • 80. Why is the pancreas richly supplied with blood? Blood is needed to carry hormones towards the target organs.
  • 81. Four different chemical categories of hormones: 1.POLYPEPTIDES hormones composed of less than 100 amino acids  e.g.  Insulin  Glucagon  Oxytocin  Growth hormone  ADH Growth hormone
  • 82. 2. GLYCOPROTEINS hormones composed of a:  polypeptide larger than 100 amino acids  attached to a carbohydrate e.g. FSH, LH Carbohydrate Polypeptide
  • 83. 3. STEROIDS these hormones are lipids derived from cholesterol  e.g. testosterone, oestrogen, progesterone, cortisol Oestrogen
  • 84. 4. AMINES derived from the amino acids tyrosine and tryptophan  include all hormones produced by the:  adrenal medulla  thyroid gland Adrenal glands Kidneys
  • 85. Summary A hormone is a chemical messenger with the following properties: it travels in the blood; it has an effect at a site different from the site where it is made, called the target;
  • 86. Summary it fits precisely into receptor molecules in the target like a key in a lock – it is therefore specific for a particular target; it is a small soluble organic molecule; it is effective in low concentrations.
  • 87. OVERVIEW A) Homeostasis B) Hormones: chemical nature and mode of action C) Hypothalamus and Pituitary gland D) Adrenal glands E) Hormonal regulation of blood sugar levels
  • 88. The Hypothalamus & Pituitary Gland 1. Nervous 2. Endocrine systems  major centres in the body for the coordination of the:
  • 89. Position of Hypothalamus & Pituitary Gland Pituitary gland
  • 90. The Pituitary Gland is a small red-grey gland weighs about 0.5g [size of a pea] hangs from the base of the brain by a short stalk is a link between the nervous system and many endocrine glands
  • 91. Neurosecretory cells end at the Posterior Pituitary
  • 92. The Posterior Pituitary Gland:  does not synthesise any hormones but stores and releases two hormones: ADH (antidiuretic hormone or vasopressin) Oxytocin
  • 93. Mammary glands, uterine muscles Hypothalamus Kidney tubules OxytocinHORMONE TARGET ADH Posterior pituitary Neurosecretory cells of the hypothalamus Axon Anterior pituitary
  • 94. Function of ADH: Increased permeability to water by: Distal convoluted tubule Collecting tubule
  • 95. ADH causes formation of aquaporins in tubule walls
  • 96. Functions of Oxytocin:  contraction of the uterus during birth  ejection of milk from the nipple
  • 97. The Anterior Pituitary is connected to the hypothalamus by a: Portal system: connects two organs, neither of which is the heart
  • 98. Relationship between secretory cells & blood vessels in hypothalamus & pituitary
  • 99. The hypothalamus collects information from: 1. other regions of the brain 2. blood vessels passing through it What does the hypothalamus do with this information?  passes it to the pituitary gland
  • 100. How does the pituitary gland respond? By releasing hormones, which directly or indirectly regulate the activity of all other endocrine glands
  • 101. What parts of the body does the pituitary gland affect?
  • 102. How does the hypothalamus control the anterior pituitary gland? Hypothalamus produces: 1. Releasing hormones 2. Release-inhibiting hormones
  • 103. The pituitary gland is under the influence of the hypothalamus in two ways. How? 1. The anterior pituitary produces hormones or stops producing them when the hypothalamus releases its own hormones. 2. The hormones released from the posterior pituitary are actually secreted by neurosecretory cells in the hypothalamus.
  • 104. Hypothalamus hormone Anterior pituitary hormones Site of action Prolactin-releasing hormone Prolactin release-inhibiting hormone Prolactin Inhibition of prolactin secretion Ovary and mammary gland Gonadotrophin-releasing hormone (GnRH) FSH LH Ovary and testis Thyrotrophin-releasing hormone (TRH) TSH Thyroid gland Adrenocorticotrophin- releasing hormone (CRH) ACTH Adrenal cortex
  • 105. Hormones Released by the Anterior Pituitary:  TSH- Thyroid Stimulating Hormone  ACTH - Adrenocorticotrophic hormone  LH - Luteinising hormone  FSH – Follicle Stimulating Hormone  Prolactin
  • 106. Functions of Anterior Pituitary Hormones: Prolactin – stimulates milk production and secretion FSH - stimulates growth and maturation of eggs in females - stimulates sperm production in males LH – stimulates secretion of sex hormones from ovaries and testes
  • 107. Functions of Anterior Pituitary Hormones: TSH – stimulates secretion of thyroxine from the thyroid gland ACTH – stimulates release of glucocorticoids such as cortisol from adrenal cortex
  • 108. Hormones Released by the Anterior Pituitary:  TSH  ACTH  LH  FSH  Prolactin Tropins or Trophic hormones
  • 109. What is a trophic hormone? A trophic hormone stimulates other endocrine glands to release their hormones Anterior pituitary secretes hormones that stimulate: Gonad (testis) Thyroid gland Adrenal cortex Other glands to secrete hormones
  • 110. The release of the trophic hormones is regulated by negative feedback of hormones from the target glands acting on receptors in the:  hypothalamus  anterior pituitary
  • 111. The Pituitary Gland has often been called “the master gland” of the body
  • 112. The Pituitary Gland has often been called “the master gland” of the body such a term is justified since the anterior and posterior pituitary glands release a battery of hormones that collectively influence all cells and affect virtually all physiologic processes the pituitary gland may be the king, but the power behind the throne is clearly the hypothalamus
  • 113. HOWEVER: the pituitary gland secretes some hormones that are actually produced by neurones in the hypothalamus under the influence of still other brain hormones, it produces a number of its own hormones, which control the activities of various endocrine glands throughout the body
  • 114. Essay Titles: Describe the role of the anterior pituitary gland in the co-ordination of hormonal activity. [SEP, 1996] The pituitary gland is referred to as a “master gland” in the human body. Discuss. [MAY, 2004] Give an account of the role of the hypothalamus and pituitary gland in hormonal control in the human body. [SEP, 2011]
  • 115. OVERVIEW A) Homeostasis B) Hormones: chemical nature and mode of action C) Hypothalamus and Pituitary gland D) Adrenal glands E) Hormonal regulation of blood sugar levels
  • 116. Where are the adrenal glands positioned? Adrenal glands Kidneys
  • 117. Two regions in the adrenal glands: Cortex Medulla
  • 118. Two regions in the adrenal glands: - richly supplied with nerves and blood vessels - cells of the medulla are modified neurones of the sympathetic NS Cortex - forms 80% of the gland - produces steroid hormones Medulla
  • 119. Steroid hormones of the Adrenal Cortex Mineralocorticoids mainly aldosterone (stimulates kidney to conserve sodium and excrete potassium) Glucocorticoids mainly cortisol: (under stress, raises blood glucose concentrations )
  • 120. The Cortex is able to: i) synthesise cholesterol ii) take up cholesterol from the circulation following absorption from the diet Why does the cortex need a supply of cholesterol ? To synthesise steroid hormones.
  • 121. Hormones of the Adrenal Medulla Adrenaline (epinephrine) Noradrenaline (norepinephrine) [not in syllabus]
  • 122. Adrenaline – Blood glucose increases – Blood glycerol and fatty acids increase – Heart rate increases – Blood pressure rises – Breathing rate increases – Air passages dilate – Pupils dilate – Blood flow redistributes, leading to increased alertness and decreased digestive and kidney activity • Causes short term “fight or flight” or alarm stage:
  • 123. Adrenal medulla is closely linked to the nervous system
  • 124. OVERVIEW A) Homeostasis B) Hormones: chemical nature and mode of action C) Hypothalamus and Pituitary gland D) Adrenal glands E) Hormonal regulation of blood sugar levels
  • 125. The Pancreas
  • 126. The Pancreas produces: Pancreatic duct 1. HORMONES 2. PANCREATIC JUICE
  • 127. Is it correct to state that the pancreas is both an endocrine & an exocrine gland? YES. Endocrine: produces hormones Exocrine: produces enzymes.
  • 128. Hormones and Pancreatic juice do not mix Produce hormones Produce enzymes
  • 129. Why is the islet of Langerhans highly vascularised? Hormones produced here must be transported to their target organ via the bloodstream.
  • 130. Beta cells produce insulin Which cell produces which hormone? REMEMBER: BIN Alpha cells produce glucagon
  • 131. When are insulin and glucagon secreted? Insulin Glucagon
  • 132. Islet of Langerhans Beta cell INSULIN Cells become permeable to GLUCOSE
  • 133. How is it possible for insulin to bring an effect inside body cells? Insulin binds to its receptors.
  • 134. How does insulin make cells more permeable to glucose? Glucose transporters are inserted within the plasma membrane.
  • 135. Insulin is: a small protein composed of 51 amino acids released: blood glucose level rises above 90 mg per 100 cm3 blood carried in the plasma bound to b globulin
  • 136. Insulin has an effect on: every organ of the body but main effect is on the: Liver Muscles
  • 137. Glucagon is a protein composed of 29 amino acids  role:- increases blood glucose level  target: liver  effects: 1. Glycogenolysis 2. Gluconeogenesis  glucagon has no effect on muscle glycogen
  • 138. Glycogenolysis: Conversion of glycogen to glucose Glycogenesis: Conversion of glucose to glycogen Gluconeogenesis: Conversion of non carbohydrate sources (proteins, fats and lactic acid) to glucose
  • 139. Question: MAY 2013 The following statements are linked to human physiology. Use your knowledge of biology to write short notes on each of the following. Gluconeogenesis aids in maintaining adequate sugar levels in the blood during strenuous physical exercise. (5 marks)
  • 140. By what type of feedback mechanism is blood sugar controlled? Negative feedback
  • 141. In blood sugar what is the DETECTOR, REGULATOR, EFFECTOR? Muscles & Liver: Effector Pancreas: Detector ; Regulator
  • 142. Maintaining the set-point 90 mg per 100 cm3 of blood
  • 143. Diabetes Mellitus is a metabolic disease: glucose is excreted in urine as it exceeds the maximum which the kidneys can reabsorb
  • 144. Hypoglycaemia: blood glucose level falls Hyperglycaemia: blood glucose level rises Normal blood glucose level [70-100 mg/100 cm3 of blood] Both lead to COMA
  • 145. Two Types of diabetes: Type I Diabetes [Juvenile Onset] Type II Diabetes [Maturity Onset]
  • 146. Type I Diabetes – Juvenile Onset  Decrease in the number of beta cells insulin deficiency Requires daily injections of insulin hormone
  • 147. Type II Diabetes – Maturity Onset Insulin is secreted BUT Body cells lose ability to use insulin WHY? Membrane receptors in the target cells are insensitive to insulin
  • 148. Type II Diabetes
  • 149. Diabetes mellitus makes a person feel thirsty Glucose in urine causes water to be withdrawn from blood This results in diuresis.
  • 150. Diuresis is the condition when: large volumes of dilute urine are produced Diuresis dangerous as it leads to: dehydration of the body
  • 151. Why does a diabetic person lose weight ? The breakdown of glycogen is not inhibited The stores of glycogen are quickly used up Body fats and proteins are then used as respiratory substrates A rapid loss of body mass
  • 152. Time Glucose Concentration Meal eaten Insulin is produced and glucose levels fall to normal again. Glucose levels rise after a meal. Normal
  • 153. Time Glucose Concentration Meal eaten Insulin is not produced so glucose levels stay high Glucose levels rise after a meal. Diabetic
  • 154. Cortisol is an anti-stress hormone:  secreted by the adrenal cortex: in a circadian rhythm [any biological process that displays an endogenous oscillation of about 24 hours] 1 2 Under stress
  • 155. Some effects of cortisol : 1. stimulates cells to:  decrease their use of blood glucose  shift instead to utilise fats and proteins for energy 2. raises blood sugar level 3. blocks the immune system reaction
  • 156. Keep your balance!!