Lecture 12 - Endocrine System Flashcards
What is the main function of the endocrine system
Produces and secretes hormones
Recommended reading
Vander’s Human Physiology (Chapter 11) – Widmaier E.P., Raff H. and Strang K.T., The McGraw-Hill Co. ed.
Exercise Physiology (Chapter 5) – Powers S.K. and Howley E.T., The McGraw-Hill Co. ed.
Exercise Physiology (Chapter 20) – McArdle W.D. Katch F.I. and Katch V.L., Lippincott, Williams & Wilkins ed.
Any other Human physiology or Exercise physiology textbooks. Look for the Endocrine/Neuroendocrine system.
What are the two major control and communication systems
Nervous system – rapid responses
Endocrine system – slower and more prolonged responses.
What do endocrine glands and cells do
The endocrine glands and cells release chemical substances, hormones, into the bloodstream, to target specific organs, tissues and cells, and to elicit a response.
What are the major endocrine glands
Hypothalamus
Pineal Gland
Pituitary gland
Thyroid Gland
Parathyroid gland
Adrenal gland
Pancreas
Ovaries
Testes
What are the organs that contain endocrine cells
Thymus
Heart
Liver
Stomach
Kidneys
Small intestine
Adipose Tissue
What are some glands that have both exocrine and endocrine functions
(pancreas, gastro-intestinal tract)
What are the major classes of hormones based on chemical composition
Amine hormones
Peptide and protein hormones
Steroid hormones
What is a hormones “mode of action”
How they interact with the target tissue
What are amine hormones derived from
The amino acid Tyrosine
What are some examples of amine hormones and where they are secreted from
Thyroid hormones (Thyroxine, T4 and Triiodothyronine, T3) secreted by the thyroid gland.
Epinephrine (adrenaline) and norepinephrine (noradrenaline) secreted by the adrenal medulla in the adrenal gland. Also secreted by adrenergic neurons in the synaptic nerve system
What are some examples of Catecholamines
Epinephrine, norepinephrine and dopamine are generically called catecholamines.
What are som key features of peptide and protein hormones
They are usually synthesised as protein prohormones by the ribosomes in the endocrine cells.
Then they are packaged into secretory vesicles, the prohormones are cleaved into peptides (active hormones).
Stored inside the cells.
Secreted/Released in the bloodstream when the cells are stimulated.
What are some examples of peptide and protein hormones
insulin, glucagon, IGF1, growth hormone, leptin, GLP-1
What are steroid hormones derived from
Cholesterol
Where are steroid hormones primarily produced
Adrenal cortex and the testes/ovaries
What is an example of a steroid hormone produced in the kidneys
1,25-dihydroxyvitamin D
Are steroid hormones Hydrophobic or hydrophillic
Very hydrophobic
What its the effect of a hormone directly related to
Concentration of hormone in plasma
What does the concentration of the hormone on the plasma dependent on
The secretion from the endocrine gland. This will depend on the input (stimuli).
The metabolism and excretion of hormones. Major site of metabolic inactivation are the liver and the kidneys.
How they circulate in the blood – free or bound to plasma proteins; plasma volume changes and blood redistribution (during exercise).
The binding to target cells to produce a response.
What are tropic hormones
Hormones which induce the secretion of other hormones
They usually also induce the growth and development of the target gland.
What does the transport of hormones in the blood dependant on
Chemical composition and mainly their water solubiltiy
What are some traits of protein and peptide hormones
water soluble and are transported dissolved in the plasma.
Fast acting
Short half-life (minutes)
Rapidly eliminated
What are some key traits of steroid and thyroid hormones
lipid soluble (hydrophobic) and to be transported via the blood circulation have to bind to plasma transport proteins.
Slower action
Long half-life (hours to days).
Slower elimination
What is the total hormone concentration the sum of
free and bound hormone, (but only the free hormones can interact with target cells and organs.)
What is the concentration of free hormone -which is biologically important
very low micrograms (10-6 g), nanograms (10-9 g) and picograms (10-12 g).
What are the different type of hormone action
Intracrine
Autocrine
Paracrine
Endocrine
Neuroendocrine
What are 2nd messengers
small biologically active molecules such as cyclic AMP (cAMP), inosine tri-phosphate (IP3) or diacylglycerol (DAG) which are produced inside the cell as a result of the peptide hormone biding to its receptor at the cell surface and the activation of signalling pathways.
They magnify/amplify the message from the hormones to trigger a response..
Which tissues respond to a specific hormone§
Tissues that respond have specific receptor proteins ON or IN the target cells.
The location (on or inside the cells) depends again on the water solubility (chemical properties) of the hormones:
Why is the number of receptors essential for the hormone action on the target cell
Because the number of receptors is limited, the hormone action will always reach a saturation point (or plateau).
How do hormones bind to the receptors
Some hormones bind with strong bonds to the receptor – high affinity ligands; some with weaker bonds – low affinity ligands.
How can the number of receptors regulated
The number of receptor could be regulated by the availability of the hormone in the blood plasma.
When the blood concentration is low the number of receptor is low – down-regulation
When the blood concertation increases the number of receptors increases too – up-regulation
Some hormones can regulate the receptors for other hormones too – permissive role
What are the 4 types of endocrine diseases
Hyposecretion – too little hormone is secreted (type 1 diabetes).
Hypersecretion – too much hormone is secreted (usually caused by an endocrine tumour; water retention – hypersecretion of ADH).
Hyporesponsiveness – reduced responsiveness of the target cells to physiological levels of hormones (Insulin resistance in type 2 diabetes).
Hyperresponsiveness – increased responsiveness of the target cells (hyperthyroidism causes increased heart rate because of increased epinephrine receptor numbers).
What is the endocrinic function of the posterior pituitary gland
The posterior pituitary does not synthesize any hormones; it only secretes them. It secretes neuropeptides synthetised in the hypothalamus.
What are some examples of hormones secreted by the posterior pituitary gland
Oxytocin is involved in the milk ejection reflex of nursing mothers and emotional bonding.
Antidiuretic hormone (ADH or Vasopressin) is involved in regulation of water balance and osmolarity
What is FSH
Follicle-stimulating hormone§
What is LH
Luteinizing hormone
What is TSH
Thyroid stimulating hormone
What is ACTH
adrenocorticotropic hormone
What are the main hormones that control growth
Growth hormone and Insulin-like growth factors (IGF)
Thyroid hormones
Insulin
Sex hormones (testosterone, oestrogen).
Cortisol
How is growth determined
Growth is genetically determined, but environmental factors such as nutritional state (amino acid, fatty acids), vitamins or minerals can influence growth.
Exercise can also stimulate growth.
What does GH do
Major stimulus of postnatal growth.
Stimulates liver to secrete Insulin-like growth factor 1 (IGF-1).
Stimulates protein synthesis.
Affects muscle, bones, adipose and liver growth and function.
GH release is stimulated during exercise and this stimulates muscle growth via release of IGF-1 (doping agent)
GH secretion is stimulated during sleep (diurnal cycle)
Slide 33 + google
What is the major stimulus of GH secretion
Exercise
(Different type of exercise will induce different GH responses.
Responses are higher in younger individual compared to early middle-aged men. )
How does the endocrine system respond to stress
The endocrine system responds to stresses on the body such as trauma, infection, pain, sleep deprivation, fright, and other emotional stresses by increasing the release of cortisol from the adrenal cortex and epinephrine (adrenaline) from the adrenal medulla.
What are the physiological functions of cortisol in response to chronic stress
Permits action of epinephrine and norepinephrine on muscles and blood vessels.
Promotes glucose synthesis in the liver during long term fasting and exercise.
Increases lipolysis in the adipose tissue.
Maintains cellular concentrations of metabolic enzymes required to produce glucose and fatty acids between meals.
Decreases events associated with the inflammatory response such as capillary permeability and production of prostaglandins.
Has a strong diurnal cycle – elevated in the morning.
What is the relationship between cortisol and exercise
Cortisol is a catabolic hormone therefore will act in synergy with other hormones to increase the supply of energy to the working muscle
Elite endurance trained athletes have higher levels of cortisol
Resistant and HIIT exercise also increase cortisol secretion but usually after the end of the exercise session.
How does catecholamine secretion aid in a fast response to stress
“Fight or flight” response to stress (neural input) or stimuli (exercise) is mediated by epinephrine (adrenaline) and norepinephrine (noradrenaline) .
Increased availability of energy (glucose and lipids) in the blood.
Increased heart rate, breathing rate and cell metabolism.
Dilation of major blood vessels and constriction of peripheral capillary.
Pupil dilation.
What percentage of the catecholamine secreted by the medulla is epinephrine (adrenaline)
80%
What is norepinephrine a precursor of
Epinephrine
(also a hormone in its own right. Norepinephrine is released mainly by the adrenergic neurones of the sympathetic nervous system)
What do both epinephrine and norepinephrine bind to
Both bind to α- and β-adrenergic receptors at the cell membranes. The receptor type will define the response.
How does the endocrine system regulate glucose homeostasis
Glucose is the major source of energy for the human body.
Many organs depend exclusively on glucose as a source of energy (Brain, Retina).
Maintenance of glucose homeostasis (constant glucose levels) is essential for all physiological processes.
The human body has established a very fine tuned mechanism for maintaining glucose homeostasis.
This mechanism rely on the action of two hormones secreted by the endocrine pancreas: insulin and glucagon.
What are the 2 functions of the pancreas
Exocrine – secretion of pancreatic enzymes (juice) for food digestion in the duodenum.
Endocrine – secretion of insulin and glucagon
What is the endocrine function of the pancreas carried out by
Islets of Langarhans
What percentage of the islets of langerhans do alpha cells make up and what do they secrete
10% - secrete glucagon
What percentage of the islets of langerhans do beta cells make up and what do they secrete
80%
Secrete insulin
What percentage of the islets of langerhans do F cells make up and what do they secrete
<2%
Secrete pancreatic polypeptide (PP)
What percentage of the islets of langerhans do delta cells make up and what do they secrete
3-5%
Secrete somatostatin
What percentage of the islets of langerhans do epsilon cells make up and what do they secrete
<1%
Secrete ghrelin
What is the function of insulin
Decreases blood glucose levels
How does insulin decrease blood glucose levels
Increasing glucose uptake and storage in adipose (lipogenesis) and muscle tissues (glycogenesis).
Increases glucose uptake and storage (glycogen) in the liver and decreases hepatic glucose production.
Increases amino acid uptake and protein synthesis.
Decreases triglyceride breakdown (lipolysis) in adipose tissue.
What is the function of glucagon
it raises the concentration of glucose in the blood by promoting glycogenolysis, which is the breakdown of liver glycogen,
stimulating gluconeogenesis, which is the production of glucose from amino acids and glycerol in the liver.
(acts mainly in the liver)
How is glucose metabolism regulated during exercise
Glucagon secretion increases during exercise to promote liver glycogen breakdown (glycogenolysis)
Epinephrine and Norepinephrine release further increase glycogenolysis.
Cortisol levels also increase to promote protein catabolism for later gluconeogenesis.
Growth hormone levels increase to increase fatty acid oxidation, lipolysis and gluconeogenesis.
Insulin secretion deceases to lower the storage of glucose.
What is Type 1 diabetes
Due to destruction of the β cells of the pancreas.
No insulin is secreted
What is Type 2 diabetes
Environmental factors (sedentary lifestyle and bad nutritional habits) play a major role in the development of the disease.
Obesity is a risk factor for development of type 2 diabetes.
The insulin secretion from the pancreas is normal, but is the action of insulin that is impaired. The adipose and muscle cells do not respond to the action of insulin (insulin resistance).
