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Title: Endocrine Physiology
Description: High-end university notes which are suitable for a course with the module 'Human Physiology' such as Biomedical Science or Nutrition. These detailed, yet made simple, super affordable notes target areas in Endocrine System including extra features such as T3 and T4 hormones, Steroid Hormones and Pancreas. With these notes, you will be at the top of your Endocrinology game.
Description: High-end university notes which are suitable for a course with the module 'Human Physiology' such as Biomedical Science or Nutrition. These detailed, yet made simple, super affordable notes target areas in Endocrine System including extra features such as T3 and T4 hormones, Steroid Hormones and Pancreas. With these notes, you will be at the top of your Endocrinology game.
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Advanced Endocrine Physiology (1st Year University notes)
Definitions:
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Hormone is derived from the Greek word Hormao meaning ‘I excite’
Endocrinology is the study of hormones and their effects on the body
The Endocrine system is the collection of glands that produce hormones that regulate metabolism,
growth and development, tissue function, reproduction, sleep and mood among other functions
An Endocrine gland is a gland which secretes hormones in the body which have an effect/s on other
parts of the body
Communication Model:
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Message is initiated and decoded by the Receiver
The message is then encoded as the Feedback/Response
The Response is decoded by the Sender and encoded into a message
This process is a continuous process known as the Communication process
Types of Communication:
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Synaptic communication (Neurotransmitters)
Endocrine communication through bloodstream (Hormones)
Differences between Nervous and Endocrine Systems:
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Nervous system reacts quickly whereas Endocrine system reacts slowly
Reaction stops instantaneously in Nervous system whereas effects may continue for large periods of time in
Endocrine Systems
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Nervous system effects are targeted and specific whereas Endocrine system may have a general, widespread
effects on many organs
Linking Nervous and Endocrine System:
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Brain and Endocrine Glands linked together
The brain secretes nerves whilst Endocrine Glands secrete Hormones to Target Cells
These target cells cause Biological responses
Conveying information to coordinate activity of specific cells
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Help regulate growth and development, reproduction, metabolism many aspects of physiology
A single hormone may affect more than one of these functions and each function may be controlled by
several hormones
Hormone Action and Communication:
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Hormones never act directly as they bind to specific proteins found on surface of cells or in cytoplasm or the
nucleus
They bind onto receptors of the target cells that cause a Biological Response
Hormones communicate their effect by their unique chemical structures recognised by specific proteins in or
on their target cells
Advanced Endocrine Physiology (1st Year University notes)
3 Major Classes of Hormones:
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Polypeptides – Not lipid soluble, bind to receptors on surface of target cells
Amino Acid Derivatives – Most not lipid soluble, bind to receptors on surface of target cells
Steroids – Lipid soluble, often bind to receptors inside target cells
Polypeptide Hormone Synthesis:
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Most protein and peptide hormones require transcription of a single gene
Post-translational modifications of original amino acid sequence
Synthesis of Peptide Hormones:
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Preprohormones – Larger hormones produced on Ribosomes of Endocrine Cells
Prohormones – Cleavage of preprohormones by proteolytic enzymes in rough ER
Prohormones – Packaged into secretory vesicles by Golgi Apparatus
Prohormones – Cleaved to give active hormone and pro- fragments
Polypeptide Hormone Receptors:
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Polypeptide hormones are water soluble and therefore are usually not able to enter the cell
Most common method of entry is for this type of hormone to bind to a receptor site located on plasma
membrane of the cell
Hormone is considered a first messenger
Second messenger is a substance inside the cell
Transient/rapid effects
Steroid Hormone Synthesis:
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Synthesised in the Mitochondria and Endoplasmic Reticulum
Requires presence of specific enzymes converting cholesterol into appropriate steroid
Conversion processes:
Advanced Endocrine Physiology (1st Year University notes)
Cholesterol Synthesis:
Steroid Hormones:
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Lipid soluble; usually able to enter a cell
Bind to specific receptor within nucleus/cytoplasm
Hormone-receptor complex bind to specific sites on cell’s DNA
Activates genes resulting in synthesis of new proteins
Long-term effects
Amino Acid Derivatives:
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Small molecules
Structurally related to Amino Acids
Derived from either single Tyrosine or Tryptophan molecule
Synthesised by sequential action of enzymes
Transport of Hormones in the Blood:
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Peptides and Amines are generally free and unbound and not carried on a plasma protein; bind directly to
receptors, fast onset of effect
Binding proteins for several protein and peptide hormones recognised
May interact with both passive transporters and membrane receptors
Steroids carried on plasma protein to increase hormone half-life; carrier makes steroid more soluble in
plasma
Feedback control:
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Many hormones rely on feedback for secretory control
Once hormones bring out their effects; target cells feedback signals to reduce hormone secretion, cell
response restores homeostasis and rising levels of hormone itself may halt secretion
Advanced Endocrine Physiology (1st Year University notes)
Negative and Positive Feedback:
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Negative – Triggers something to stop or oppose any change on it
Positive – Triggers something to be amplified in effect
Feedback is central for maintaining Homeostasis
----------------------------------------------------------------------------------------------------------------------------------------------------------Endocrine control of Absorptive and Postabsorptive states:
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Control of transition between fed and Postabsorptive states
Primarily achieved by Insulin and Glucagon
Pancreas – A mixed Gland:
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Emptying exocrine secretions into Small Intestine
Endocrine function associated with Pancreatic Islets
Islets of Langerhans:
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Made up of Capillaries as well as Alpha, Beta and Delta Cells
Alpha cells are found on the interior edges
The inside in mostly comprised of Beta Cells
Delta cells are found sparsely but connected the Alpha Cells
A few Capillaries are found within the Beta Cells
Amino Acid Peptide Structure:
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Signal sequence ➔ B Chain ➔ C Chain ➔ A Chain
The A Chain is usually the shortest and found on the inside of the chain
Control of Insulin Secretion:
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Most potent metabolic stimuli to Insulin secretion being Glucose and Amino Acids acting synergistically
Autonomic nerves innervate Islets
The Innervations account for increase in Insulin secretion occurring before entry of food into the
Gastrointestinal tract
Somatostatin from a-cells inhibit release of Insulin and Glucagon
Insulin Secretion:
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There are 2 phases of Insulin Secretion
Potassium channels are open so Potassium ions move out of Beta cell
Glucose enters the Beta Cells and converted into Glucose Phosphate by Glucokinase
Glucose Phosphate metabolises into ATP which is used to close Potassium channels
This causes depolarisation inside the cell
The less –ve charge inside the cell causes Calcium voltage-gated channels to open
Calcium ions rush into the cell
Calcium ions allow vesicles storing Insulin to fuse with cell membrane to secrete the Insulin (Exocytosis)
Advanced Endocrine Physiology (1st Year University notes)
Control of Glucagon Secretion:
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Most potent metabolic stimuli to Glucagon secretion are hypoglycaemia
Autonomic nerves may account for increase in Glucagon secretion occurring during exercise, starvation or
stress
Insulin inhibits release of Glucagon
Gastrointestinal Hormones
Counter-regulatory:
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Glucagon has opposing actions to Insulin
Primary action is on the liver where breakdown of Glycogen to Glucose is stimulated and increases
Gluconeogenesis
Pancreatic Hormones regulating Blood Glucose:
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By either Insulin or Glucagon
Insulin:
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High blood sugar level
Promotes Insulin Release by Beta Cells
Enters Pancreas
Stimulates formation of Glycogen in the Liver
Stimulates Glucose uptake from blood (Tissue cells)
Lowers blood sugar level
Glucagon:
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Low blood sugar level
Promotes Glucagon release by Alpha cells
Enters Pancreas
Stimulates breakdown of Glycogen into Glucose in the Liver
Raises blood sugar level
What could go wrong in Pancreas:
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Diabetes – Beta cells either stop working or become inefficient so not enough Insulin is made
Type 1 Diabetes Mellitus caused when body’s immune system attacks its own cells in the Islets of Langerhans
so the cells cannot produce Insulin
Type 2 Diabetes Mellitus is a metabolic disorder where the body is no longer able to produce adequate
amounts or respond to insulin
Type 2 Diabetes:
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Beta cells of Pancreas produce Insulin but body is unable to use it effectively as cells of the body are Insulin
Resistant
Accounts of 90% of all Diabetes cases
Complications include CVD, Neurological changes, renal failure and blindness
Therapy – Diet and Physical Exercise, Drugs/Insulin
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Advanced Endocrine Physiology (1st Year University notes)
Thyroid Location:
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Under the Cartilage and just above the Trachea
T3 and T4:
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Synthesised from Tyrosine
Gland produces 2 Iodine containing hormones T3 Triiodothronine and T4 Thyroxine
Iodine + Tyrosine ➔ Monoiodothrosine (MIT)
Iodine + Iodine + Thyrosine ➔ Di-iodotyrosine (DIT)
DIT + MIT ➔ Tri-iodothyronine (T3)
DIT + DIT ➔ Thyroxine (T4)
Synthesising location:
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Synthesised on Thyroglobulin
Very large Glycoprotein
Follicle cells of the Thyroid produce Thyroglobulin
Thyroglobulin released into Colloid Space where it is Tyrosine residues are iodinated by Iodine positive ions
Synthesis and Release of Iodine containing thyroid hormones:
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Follicular cell synthesises Enzymes and Thyroglobulin for Colloid
Iodine positive ions co-transported into cell with Sodium ions transported into the Colloid
Enzymes add Iodine to Thyroglobulin to make T3 and T4
Thyroglobulin taken back into the cell
Intracellular enzymes separate T3 and T4 from the protein
Free T3 and T4 enter the circulation
Iodine Requirement:
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Dietary Iodine absorbed in the GI tract then taken up by Thyroid Gland
Transport of Iodine into Follicular cells dependent upon Sodium/Iodine ion co-transport system
Transport of Thyroid Hormones:
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Thyroid hormone-binding Globulin, Transthyretin and Albumin are binding proteins for Thyroid Hormones
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Title: Endocrine Physiology
Description: High-end university notes which are suitable for a course with the module 'Human Physiology' such as Biomedical Science or Nutrition. These detailed, yet made simple, super affordable notes target areas in Endocrine System including extra features such as T3 and T4 hormones, Steroid Hormones and Pancreas. With these notes, you will be at the top of your Endocrinology game.
Description: High-end university notes which are suitable for a course with the module 'Human Physiology' such as Biomedical Science or Nutrition. These detailed, yet made simple, super affordable notes target areas in Endocrine System including extra features such as T3 and T4 hormones, Steroid Hormones and Pancreas. With these notes, you will be at the top of your Endocrinology game.