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Hormonal Communication

  • -  2 types of hormone

    • -  Protein and Steroid

    • -  Protein are not soluble in the phospholipid membrane so do not enter the cell (act via receptors)

    • -  Steroid hormones are lipid soluble so can diffuse into a cell and have a direct effect of DNA

  • -  Key in the endocrine system which uses hormones as signalling molecules and the hormones are transported in the blood

  • -  Hormones released directly into the blood via endocrine glands which are ductless and are associated with numerous capillaries

  • -  Target cells receive a signal and can be grouped together or in isolation

  • -  For non-steroid hormones the receptor on the target cell must have a complementary

    shape to that of the hormone

  • -  The fact that some of the cells will have receptors that are non-complementary means

    that the hormone can be carried in the blood without causing an effect to all cells nd only

    affecting those with the required receptor

  • -  Method of Action:

    • -  Non-steroid hormones are first messengers, this is because they bind to the receptor initiating a response from a second messenger which can lead to numerous other changes in the cell and finally the desired change

    • -  Many act via a G protein in the membrane.

    • -  When the non-steroid hormone binds to the complementary receptor the G

      protein within the cell activates an effector molecule

- The effector molecule will usually be an enzyme that converts an inactive

molecule into an active molecule so it can act as a secondary messenger

(such as cAMP which we can use as an example)

  • -  The effector molecule in many cells is Adenyl Cyclase

  • -  Adenyl Cyclase converts ATP to cyclic AMP (cAMP) and it is this cAMP that then

    acts as a secondary messenger within the cell

  • -  This secondary messenger may act directly on another protein or initiate an

    enzyme cascade whereby numerous enzyme controlled reactions occur altering

    the activity of the cell and leading to a desired effect

  • -  The action on another protein could be the opening or closing of ion channels etc

    Adrenal Glands:

  • -  Found just above the Kidneys

  • -  Each gland is divided into the outer adrenal cortex and the inner adrenal medulla

  • -  Both regions are supplied well with blood and secrete hormones directly into the blood

  • -  Adrenal Cortex:

    • -  Zona Glomerulosa (outermost) - mineralocorticoids e.g aldosterone

    • -  Zona Fasciculata (middle) - glucocorticoids e.g. cortisol

    • -  Zona Reticularis (inner) - precursor sex molecules ot produce the sex hormones

    • -  THINK: (GO FIND RELIGION [from out to in])

  • -  Adrenal Medulla - Secretes Adrenaline and Noradrenaline (Link to neuronal and animal responses)

  • -  Hormones produced: - Cortex:

    • -  Uses cholesterol for many of the hormones produced and so are steroid based and can enter cells directly and the hormone can have a direct effect on the nucleus

    • -  They have numerous roles:

    • -  Mineralocorticoids: help control sodium and potassium level in the blood

      and thus contribute to maintaining blood pressure. Aldosterone specifically, acts on the distal tubules and collecting ducts of the kidney in order to increase absorption of sodium ions, decrease absorption of potassium ions and increase overall water retention

    • -  Glucocorticoids: aid control of carbohydrate, lipid and fat metabolism in the liver. Cortisol is released in response to stress or as a result of low blood glucose concentration and stimulates glucose production from stored compounds

    • -  Note: cortisol can be released from the zona reticularis but if the correct enzymes are not present for cortisol then precursor androgens will be released which ar taken up by the testes or ovaries and converted to sex hormones

      - Medulla:

    • -  Adrenaline is polar (link to biological molecules) and so cannot enter the

      cell as it cannot pass the plasma cell membrane and so has to interact

      with complementary receptors on the cell surface membrane

    • -  Many cells have the receptors and so the effects of adrenaline can be

      vast

    • -  They include (Link to animal responses)

      • -  Relaxing smooth muscles in bronchioles

      • -  Increasing heart STROKE VOLUME

      • -  Increasing heart rate

      • -  Vasoconstriction to cause a raise in blood pressure

      • -  Stimulating glycogen to glucose

      • -  Dilate pupils

      • -  Increase mental awareness

      • -  Inhibit gut action

      • -  Causing body hair to erect

        Pancreas:

  • -  Has both exocrine and endocrine function

  • -  2 main products are pancreatic juices secreted into the small intestine and hormones

    secreted from the Islets of Langerhans

  • -  Exocrine:

    • -  Substances secreted into a duct

    • -  The exocrine function is that of the production of digestive enzymes

  • -  Cells that secrete the enzymes are packed in small groups surrounding small tubules called acini (acinus for many)

  • -  All the acinus tubules connect to form intralobular ducts which combine and form the pancreatic duct which carries the enzymes (in a fluid medium) to the duodenum

  • -  The enzymes include:

    • -  Pancreatic amylase - carbohydrate digests amylose to maltose

    • -  Trypsinogen - converted to trypsin which catalyses peptide bond

      hydrolysis

    • -  Lipase - digests lipid molecules

    • -  Fluid medium will have sodium hydrogencarbonate to aid the

      neutralisation of the content of the stomach

      - Endocrine:

  • -  Islets of Langerhans are found in patches in between clusters of acini

  • -  Islets of Langerhans are composed of alpha and beta cells

  • -  Alpha cells - secrete glucagon

  • -  Beta cells - secrete insulin

  • -  Release of insulin: mechanism

    • -  Cell membrane of beta cells have calcium and potassium ion channels

    • -  Potassium ion channels are normally open and the calcium ion channels closed which acts to make the inside of the cell more negative in relation

      to the outside (resting potential of -70 mV)

    • -  When glucose conc outside the cell is high glucose will diffuse in

    • -  Glucose is metabolised in the cell and produces ATP (using glucokinase)

    • -  The extra ATP causes the K+ ion channels to close

    • -  As a result the potassium can no longer diffuse out and this alters the

      potential difference across the cell membrane so it becomes less neg

    • -  The change in potential difference causes the Ca2+ ion channels to open

      and due to the conc grad calcium ions diffuse in rapidly

    • -  The calcium ions cause the vesicles of insulin to move to and fuse with

      the cell membrane and release insulin via exocytosis (caused possibly by

      binding to outside as in neuronal communication an synaptic cleft)

  • -  Blood Glucose:

- If blood glucose drops too low this is hypoglycemia → inadequate delivery of glucose to body tissue and brain

- Can cause irritability, tiredness or if sever then impairment of brian function and confusion which can lead to unconsciousness or death

  • -  If blood glucose too high this is hyperglycemia which can lead to diabetes mellitus and a variety of problems

  • -  Islets fo Langerhans monitor using aforementioned mechanism, if too high → insulin, if too low → glucagon

- Can act on hepatic tissue causing the storage of glucose as glycogen thus reducing blood glucose conc or the inverse to increase

  • -  Insulin: Mechanism

    • -  Target: hepatic cells, muscle & more

    • -  Binds to receptor activating tyrosin kinase

    • -  This causes phosphorylation of inactive enzymes

    • -  This causes an enzyme cascade

    • -  They also interact with a vesicle of glucose transporter proteins

      which can insert glucose transporter channels in the plasma cell

      membrane

    • -  More glucose enter the cell and is converted to glycogen

      (glycogenesis) or fats or used in aerobic respiration (link to

      respiration)

  • -  Glucagon: Mechanism

Targets hepatic cells
Glucagon binds to receptor
Stimulates a G protein which activated adenyl cyclase
ATP → cAMP
Enzyme controlled reaction cascade
Causes glycogenolysis (glycogen to glucose) usin phosphorylase enzyme
Also causes respiration of fatty acids and an increase in gluconeogenesis where amino acids and fats are converted to glucose
mechanism is an example of negative feedback

- - - - - -

-

Diabetes:

  • -  Body no longer able to produce sufficient Insulin to control blood glucose so

    hyperglycaemia for a long period of time or even hypoglycaemia after intense exercise

    etc.

  • -  2 types

- T1: insulin-dependent, sufficient insulin cannot be synthesised so prolonged hypoglycemia and a variety of issues to do with fatigue, tiredness etc.

- Treatment is insulin injections and blood glucose concentration must be monitored. There are also treatments such as islet cell transplantation from stem cells or heathy individuals and pancreatic transplants, or a insulin pump (permanent insulin injection which monitors for you)

- T2: non-insulin dependent produces insulin but cells not as responsive and major organs and circulation can be damaged. Caused by certain factors such as obesity, lack of regular exercise, diet high in sugar etc.

- Treatment is primarily surrounding lifestyle changes such as losing weight and having a healthy diet etc. If sever insulin may be given

  • -  This feedback

  • -  Insulin and glucagon are antagonistic hormones

- Source of Insulin: (LINK to cloning and biotechnology & manipulating genomes)

  • -  Often extracted from the pancreas of animals such as pigs (matches human

    insulin closely)

  • -  Bacteria have now undergone genetic modification to manufacture human insulin

  • -  Poses benefits: exact copy so more effective, less chance of developing

    tolerance and of rejecting (immune system), lower infection risk, cheaper and greater quantities, less ethically problematic

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