Chapter 14

• Endocrine gland


  group of cells specialised to secrete hormones
• Hormone


  chemical messenger that is transported in the blood
• How are hormones transported?

  • diffuse out of blood & bind to specific receptors called target cells
  • once bound to their receptors the hormones stimulate the target cells to produce a response
• Chemistry of a steroid hormone

  lipid-soluble
• How does a steroid hormone affect target cells?

  • diffuses through cell surface membrane & bind to steroid hormone receptors (in cytoplasm or nucleus) - form hormone-receptor complex
  • hormone-receptor complex acts as a transcription factor which promotes or inhibits transcription of a specific gene
• Example of a steroid hormone

  oestrogen
• Chemistry of a non-steroid hormone

  hydrophilic (can't pass directly through cell membrane)
• How do non-steroid hormones affect target cells?

  • bind to receptors on cell surface membrane of the target cell
  • triggers a cascade reaction mediated by chemicals called second messengers which activates a transcription factor
• Example of a non-steroid hormone

  adrenaline
• Hormonal system vs Nervous system

  • communication is by hormones/ communication is by nerve impulses
  • transmission is by blood system/ transmission by neurones
  • transmission is slow/ transmission is very rapid
  • hormones travel to all parts of body, but only target organs respond/ nerve impulses travel to specific parts of body
  • response is widespread/ response is localised
  • response is slow/ response is rapid
  • response is long-lasting/ response is short-lived
  • effect may be permanent & irreversible/ effect is temporary & reversible
• Why are hormones a slower & less specific form of communication?

  they are not released directly onto their target cells
• Why do hormones have a longer-lasting & widespread effect?

  they are not broken down as quickly as neurotransmitters
• Adrenal glands

  • adrenal cortex - outer region of glands - produces hormones vital to life - production of hormones controlled by hormones released from the pituitary gland
  • adrenal medulla - inner region of glands - produces non-essential hormones - hormones released when sympathetic nervous system is stimulated - occurs when body stressed

  
• 3 main types of hormones produced by adrenal cortex

  • glucocorticoids
  • mineralocorticoids
  • androgens
• Function of glucocorticoids

  • include cortisol which regulates metabolism by controlling how body converts fats, proteins & carbohydrates to energy - also helps regulate blood pressure & cardiovascular function in response to stress
  • corticosterone - works w cortisol to regulate immune response & suppress inflammatory reactions
  • release of these hormones controlled by the hypothalamus
• Function of mineralocorticoids

  • main one = aldosterone - helps control blood pressure by maintaining balance between salt & water concentrations in the blood & body fluids
  • releases is mediated by signals triggered by kidney
• Androgens

  • small amounts of male & female sex hormones are released
  • impact smaller than larger hormones such as oestrogen & testosterone released by ovaries or testes
  • important especially in women after menopause
• Hormones secreted by the adrenal medulla

  • adrenaline
  • noradrenaline
• Adrenaline

  • increases heart rate sending blood quickly to muscles & brain
  • rapidly raises blood glucose concentration levels by converting glycogen to glucose in liver
• Noradrenaline

  • works w adrenaline in response to stress
  • increases heart rate, widens pupils, widens air passages in lungs, narrows blood vessels in non-essential organs
• Exocrine glands

  produce enzymes & release them via a duct into the duodenum
• Role of the pancreas as an exocrine gland

  • responsible for producing digestive enzymes & pancreatic juice
  • enzymes & juice are secreted from exocrine tissue into ducts which lead to pancreatic duct & from there are released into the duodenum (top part of small intestine)
  • produces amylases, proteases & lipases
• Role of the pancreas as an endocrine gland

  • pancreas is responsible for producing insulin & glucose
  • within exocrine tissue there are small regions of endocrine tissue called islets of Langerhans - cells of the islets of Langerhans produce insulin & glucagon & secrete this hormones into bloodstream
• 2 types of cell in pancreas

  • islets of Langerhans (endocrine)
  • pancreatic acini (exocrine)
• Appearance, shape & function of islets of Langerhans

  • lightly stained (blue/lilac)
  • large, spherical clusters
  • produce & secrete hormones
• Appearance, shape & function of acini

  • darker stained (dark pink/ purple)
  • small, berry-like clusters
  • produce & secrete digestive enzymes
• Types of cell within the islets of Langerhans

  • a (alpha) cells - produce & secrete glucagon
  • b (beta) cells - produce & secrete insulin
  • alpha cells larger & more numerous than beta cells
• What concentration is blood glucose normally maintained at?

  90 mg cm-3
• How does pancreas increase blood glucose concentration?

  • when you eat carbohydrate rich foods, carbohydrates are broken down to release glucose - glucose is absorbed into bloodstream & blood glucose rises
  • glycogenolysis - glycogen in liver is broken down into glucose which is released into bloodstream
  • gluconeogenesis - non-carbohydrate sources (amino acids & lipid) are converted into glucose which is released into bloodstream
• How does the pancreas decrease blood glucose concentration?

  • respiration - glucose in blood is used by cells to release energy. Higher level of activity, higher demand for glucose & greater decrease of blood glucose concentration
  • glycogenesis - excess glucose taken in through diet is converted into glycogen stored in liver
• Where is insulin produced from?

  the β cells of the islets of Langerhans in the pancreas
• Role of insulin 


  • if blood glucose concentration too high, the β cells detect rise & respond by secreting insulin into bloodstream
  • as blood glucose concentration returns to normal, β cells reduce their secretion of insulin
  • (negative feedback)
• How does insulin lower blood glucose concentration?

  • increases rate of absorption of glucose by cells (particularly skeletal muscle cells)
  • increases respiratory rate of cells - increase need & therefore uptake of glucose from blood
  • increases rate of glycogenesis (stimulate liver to convert glucose to glycogen)
  • increases rate of glucose to fat conversion
  • inhibits release of glucagon from α cells of islets of Langerhans
• How does insulin allow glucose to enter cells?

  • most body cells have insulin receptors on cell surface membrane
  • when insulin binds to its glycoprotein receptor it cause a change it tertiary structure of the glucose transport protein channels
  • cause channels to open allowing more glucose to enter the cell
• How often is insulin secreted?

  • is broken down by enzymes in liver cells so has to be constantly secreted to maintain its effect
  • insulin secretion can begin within minutes of food entering body & may continue for several hours after eating
• Where is glucagon produced?


  α cells of the islets of Langerhans in the pancreas
• Role of glucagon

  • when blood glucose concentration is too low, the a cells detect fall & secrete glucagon directly into bloodstream
  • when blood glucose concentration returns to normal this is detected by a cells & when it rises above a set level a cells reduce secretion of glucagon
• How does glucagon increase blood glucose concentration?


  • glycogenolysis - liver breaks down glycogen store into glucose & releases it into bloodstream
  • increases gluconeogenesis - inc conversion of amino acids & glycerol into glucose in liver
  • reduces amount of glucose absorbed by liver cells
• Label the interaction of insulin and glucagon

  A) glucagon

  B) glycogen to glucose

  C) amino acids to glucose

  D) insulin

  E) respiration rate

  F) glucose to glycogen

  G) glucose to fat

  H) glucose into cells

  
• Control of insulin secretion

  • normal blood glucose levels - potassium channels are open & potassium ions diffuse out of cell - potential inside cell = -70mV
  • blood glucose conc rises - glucose enters cell by a glucose transporter
  • glucose is metabolised inside mitochondria - ATP produced
  • ATP binds to ATP-sensitive potassium channels & causes them to close
  • potassium ions can no longer diffuse out of cell - potential reduces to -30mV & depolarisation occurs
  • voltage-gated calcium channels open - calcium ions enter cell & cause secretory vesicles to release insulin they contain by exocytosis