The Endocrine system Flashcards
neuroendocrine
due to shared functions of the nervous and endocrine systems, together they are often described as ‘neuroendocrine system’. the nervous and endocrine systems coordinate their activities and together are considered the control or regulatory systems of the body.
eg hypothalamus = responsible for the regulation of hunger, thirst and body temperature, serves both the nervous and endocrine systems
primary functions of endocrine system
- integration and regulation of bodily systems
- repair of bodily tissues
- physical and psychological stress management
- stabilisation of the body’s internal environment (homeostasis)
- production, combination and activation of enzymes to regulate metabolism
homeostasis
a state of internal biological equilibrium and balance. Via a series of chemical, electrical and mechanical processes, the body is able to create a stable environment in which all energy releasing, consuming and storing reactions and processes can occur at a rate appropriate to sustain life.
these reactions can only occur in a very narrow range of temperatures and lower levels of acidity; the body must therefore continually make subtle changes to its internal environment in order to ensure that the environment is suitable for these reactions to occur.
structure of the endocrine system
hormones are transported throughout the body in the blood plasma to their ‘target organ’ where they bring about the desired physiological response. the transportation delays the response time which is why the endocrine system is generally lower than the nervous system at inducing changes.
classification of hormones
steroids
peptides
peptide hormones
synthesised from amino acids and are transported throughout the body in the blood plasma. Generally faster acting than steroid hormones, insulin, glucagon, growth hormone and leptin are examples of peptide hormones.
steroid hormones
generally synthesised from cholesterol and are fat soluble.
they are therefore usually transported throughout the body, attached to other hormones until they pass through the cell membrane of their target organ. Because these hormones interact with the DNA of the cell, they are usually slower to react. eg testosterone and cortisol
where are hormones secreted from
generally from glands, although in some cases hormones are actually secreted from organs containing areas of endocrine tissue like the pancreas, adipose tissue and small intestine. Glands can be classified as ‘endocrine’ or ‘exocrine’ depending on their structure and function.
Endocrine glands are ductless and secrete their hormones into space around gland
exocrine glands contain ducts which secrete hormones directly to a specific surface or area of body the hormone is required
lock and key theory
each organ contains specialised cells known as ‘receptors’ which detect the concentration of specific hormones within and around their cellular environment. when the organ receives a chemical signal from the hormone, its receptors trigger a response within the organ to increase or decrease its activity.
An organs’ receptors are only compatible with specific hormones to ensure that only the target organs are affected. this principle is referred to as the ‘lock and key theory’ because the receptors act as the lock and the hormones act as the key. when the key and the lock interact, the target organ is stimulated or suppressed in order to elicit the desired physiological change within the body.
adrenal glands
tiny organs that rest on top of each kidney.
they assist the sympathetic nervous system and play an important role in growth, stress management, kidney function and metabolism.
the adrenal glands control the heart rate, blood pressure, breathing rate and the mobilisation of fat from adipose tissue.
the adrenal glands perform these functions by releasing adrenaline and noradrenaline (catecholamines)
hormone secretion
hormone secretion is not constant - varies depending on body’s needs.
‘half-life’
describes the time required to reduce the concentration of a particular hormone by 50% of its secreted concentration.
provides a good indication as to how long a hormone will continue to elicit its affects in the body.
eg. the activity of insulin has a half-life of 5-7 minutes and must be constantly secreted when blood sugar levels are high in order to prevent hyperglycaemia
pancreas
lies just below duodenum of the small intestine.
primary role is to regulate blood glucose levels to ensure that the bodily tissues have sufficient energy.
the pancreas achieves this aim by secreting the hormones ‘insulin’ and ‘glucagon’.
beta cells = triggered in high blood sugar levels
alpha cells = triggered when blood sugars are low
testes
male sex glands.
located behind penis in lower pelvic region.
produce testosterone which is responsible for promoting masculinisation - why testosterone is referred to as an ‘adrogenic hormone’
women have it too but higher in men
it is an anabolic (building) hormone which increases muscle mass, reduces body fat and increases the volume of red blood cells within circulatory system
adrenaline
sometimes called ‘epinephrine’
primary hormone utilised in body’s fight or flight
when facing fear, the adrenal glands secrete large amounts of adrenaline. this sympathetic action is intended to increase the volume of oxygen entering the body and the stimulate the metabolism of glucose, proteins and fats from their stored sources of glycogen, lean tissue and adipose tissue.
noradrenaline
sometimes called ‘norepinephrine’
works in collaboration with adrenaline to support the body’s sympathetic responses.
while the release of noradrenaline typically results in the same outcome as the release of adrenaline, they bind with different receptors to accelerate the desired action.
cortisol
emotional stress, trauma, physical exertion, infection and surgery (emotional or physical stress) cause the adrenal glands to secrete cortisol.
it is a steroid hormone that reduces the transportation of amino acids into the body’s cells, inhibiting protein synthesis.
when glycogen is low, cortisol breaks down amino acids into glucose, via gluconeogenesis. = CNS has ready supply of energy
cortisol also is believed to exert a more potent effect on the type 2 muscle fibres, because they have greater concentration of protein than type 1 fibres.
glucocorticoid hormones
especially cortisol are classically thought to be catabolic hormones, they also serve as essential signal hormones for the metabolism of carbohydrates.
ovaries
female sex glands
located in the lower lateral region of the pelvis (both sides)
secrete the female sex hormone, oestrogen and progesterone, which are responsible for the feminisation of women and the development of the physical characteristics during and after puberty.
ovaries control the growth of breast tissue, the decreased growth of bodily hair and increase level of body fat.
also produce small quantities of testosterone which has the same effect in females as in males, albeit to a lesser degree.
anabolism
the component of metabolism that is responsible for the building and formation of new cells. Examples of anabolic reactions include the hypertrophy of type 2 skeletal muscles following strength training, or the capillarisation that occurs around type 1 fibres following endurance training.
testosterone and growth hormone are anabolic hormones
catabolism
degradation and breakdown of the body’s tissues during metabolism, usually with the goal of generating energy.
egs include the metabolism of fatty acids, proteins and glucose during exercise or the loss of lean muscle tissue associated with stress.
parathyroid and cortisol are catabolic hormones.
hypothalamus
- located in base of brain
- acts with the pituitary gland as a control unit for a variety of physiological responses
- linked with regulation of autonomic nervous system, appetite and satiety, thirst and fluid balance, body temp, emotional responses, sexual behaviour and biological clocks
pituitary gland
- size of a pea
- below the hypothalamus
- comprises of an anterior, posterior and intermediate division
- controlled largely by the hypothalamus
- secretes growth hormone and trophic hormones.
growth hormone
most abundant hormone produced by anterior division of the pituitary gland and stimulates all anaerobic processes including the development of body cells (esp those in musculoskeletal system).
also plays important role in regulating metabolism, protein synthesis, breaking down fats and increasing blood glucose.
trophic hormones
are in a group of hormones which are released largely from the anterior pituitary gland and which have another endocrine gland as their target
eg. thyroid stimulating hormone is released from the anterior pituitary gland and stimulates the growth and activity of the thyroid gland.
thyroid gland
- in the neck
- anterior to the larynx and pharynx
- between the 5th cervical vertebra and 1st thoracic vertebra
- contained within a fibrous capsule
- consists of 2 lobes
- primarily secretes the hormone thyroxine
- thyroxine performs a variety of metabolic processes including increasing basal metabolic rate, heat production and the breakdown of carbs, fats and proteins
- most other bodily organs are also affected by the thyroid hormones.
parathyroid gland
- located in neck posterior to thyroid gland
- primarily secretes the parathyroid hormone which regulates the levels of calcium within the blood.
- calcium is essential for muscle contractions, nerve impulse transmission and blood clotting
feedback control
- the mechanism by which hormone secretion is regulated
- occurs from the constant interaction between the CNS, the hormone receptors of the target organ and the secreting gland(s) in order to maintain homeostasis
afferent nerves (part of feedback control)
feedback to the CNS information about changes in the cellular environment
efferent nerves (part of feedback control)
stimulate the endocrine glands to secret their hormone
positive feedback loops
- usually used to increase the output of a process above what is considered normal eg when bodily tissues are damaged or ruptured, a set of chemicals are released from the damaged tissues in order to increase the production and concentration of platelets - help thicken blood and form blood clots
- used to a lesser extent to regular homeostasis and accelerate physiological process that have already begun
negative feedback loops
- most commonly used mechanism by which homeostasis is maintained
- normally used to reverse a physiological state
- usually the result of 2 equal and opposite reactions which seek to maintain hormone concentrations within very fine limits.
eg when blood glucose levels rise, the pancreas secretes insulin. the secretion of insulin reverses the increasing blood glucose levels = negative feedback
fight or flight
the physiological response to either a ‘perceived’ or ‘actual’ threat has the same effect because the body unable to determine the difference between something that is actually experienced or vividly imagined.
physiological responses to a threat
1) activation of the sympathetic nervous system
2) rapid release of adrenaline and noradrenaline
3) vasodilation of the blood vessels supplying skeletal muscles
4) vasoconstriction of the blood vessels to non-active tissue (e.g. digestive system)
5) increased heart rate and blood pressure
6) increased respiration
7) increased testosterone secretion
8) increased perspiration/sweating
9) increased metabolic enzyme activity
blood glucose regulation
- largely controlled by the action insulin and glucagon
- these hormones typically act in opposition to maintain blood glucose between the healthy 4-8mmol/l range
- if blood glucose is not maintained within these narrow limits, homeostasis is disrupted and other bodily systems/organs will be placed under and increased level of stress
hypoglycaemia
(low blood glucose)
- can occur during prolonged exercises, or several hours later due to the insulin-like effects of exercise
- can also present when insufficient carbs are consumed
- common symptoms = hunger, slurred speech, fatigue, tiredness, drowsiness and unexplained mood changes
hyperglycaemia
(high blood glucose)
- often occurs in diabetics because the body has either become resistant to the effects of insulin or it cannot produce enough
- mild hyperglycaemia symptoms can be observed in children who consume large quantities of sugar, and their tiny bodies are unable to produce sufficient insulin to transport this into muscle cells for storage
- common symptoms of high blood sugar include increased thirst, reduced appetite, frequent urination, eratic behaviour, difficulty concentrating, headaches
blood glucose and food consumption
following ingestion of food, blood glucose levels rise, which necessitates an increase in insulin secretion from the B-cells of the pancreas in order to shuttle the digested glucose into the muscle and liver for storage as glycogen.
the effect of insulin in healthy individuals
insulin exerts a potent effect on the muscles, liver and adipose tissue to transport and store excess glucose in the form of glycogen, and fats when these stores are already full
low glucose levels in healthy individuals
- glucagon is secreted from the a-cells of the pancreas, which in turn releases glucose from the liver in order to elevate blood glucose concentration
- adrenaline and cortisol are also released by the adrenal glands during this period in order to help increase the circulating levels of blood glucose. this serves to spare the body’s diminishing glycogen stores.
growth hormone
- an anabolic peptide hormone that is responsible for the growth, repair and reproduction of cells throughout the human body
- particularly important in the integration and combination of amino acids to build new protein cells
- the hypothalamus secretes growth hormone-releasing factor which stimulates the anterior pituitary gland to release growth hormone into blood
- anterior pituitary gland produces growth hormone, but the rate it is produced is controlled by hypothalamus
growth hormone and exercise
- the release of growth hormone reduces the rate at which carbs are used for energy and increases the metabolism of fats
- those who engage in frequent bouts of exercise/activity experience a sharp spike in the circulating levels of growth hormone
- when greater levels of growth hormone are secreted, higher levels of fat can be metabolised, even at rest
- exercise/physical activity also increases the half-life of growth hormone which extends the action of the hormone on the target organs
- overtraining = impaired growth hormone response
posterior pituitary
hormones and training responses
hormone = oxytocin
thyroid gland
hormones and training responses
hormone = thyroxin
training responses = reduced concentration during exercise - increased ‘free thyroxine’ concentration at rest
adrenal gland
hormones and training responses
hormone = adrenaline, noradrenaline, cortisol
training responses = decreased secretion during repeat bouts of exercise at same intensity, impaired response if overtrained, decreased secretion at rest, slight elevation during exercise (stress response)
pancreas
hormones and training responses
hormone = insulin, glucagon
training responses = increased sensitivity to insulin (need less insulin secretion to manage blood glucose), decreased insulin concentration during exercise to promote a greater uptake of glucose, slight increase during exercise, greater production post exercise
anterior pituitary gland (brain)
hormones, target organs, physiological functions
hormones = growth hormone, melatonin
target organ = several unknown
physiological functions =
growth hormone = increases bone and soft tissue growth, stimulates the metabolism of carbs, proteins and fats
melatonin = stimulates ovulation in females and testosterone production in males, controls circadian rhythms
posterior pituitary gland
hormones, target organs, physiological functions
hormone = oxytocin
target organs = breast and uterus
physiological functions = stimulates uterine contractions during childbirth, decreases urine output of kidneys, milk production and secretion of mammary glands, promotes arteriole constrition
thyroid gland (anterior neck) hormones, target organs, physiological functions
hormones = thyroxin, calcitonin
target organs = several
physiological functions = stimulates cell growth and metabolism (esp those involving the aerobic energy system), promotes calcium deposition in bone and lowers blood calcium levels (reducing osteoclasts)
parathyroid gland (posterior neck) hormones, target organs, physiological functions
hormones = parathyroid hormone or parathyrin
target organs = bone and kidneys
physiological functions = increases calcium concentration in the blood by stimulating osteoclasts activity, stimulates vitamin D synthesis
pineal gland
hormones, target organs, physiological functions
hormones = melatonin
target organs = many
physiological functions = helps maintain sleep rhythm and regulate reproductive hormones
hypothalamus
hormones, target organs, physiological functions
hormones = growth hormones, trophic hormones
target organs = anterior pituitary gland
physiological functions = release or inhibit hormones secreted from the anterior pituitary gland
pancreas
hormones, target organs, physiological functions
hormones = insulin, glucagon
target organs = many
physiological functions = shuttles glucose into the muscles and liver for storage as glycogen to reduce blood sugar levels, promotes protein, fat and glycogen synthesis
adrenal glands (kidney) hormones, target organs, physiological functions
hormones = adrenaline, noradrenaline, cortisol
target organs = many
physiological functions =
adrenaline = increases cardiac output, increases metabolism of glucose, adipose tissue and proteins
noradrenaline = same properties as adrenaline but is also able to constrict blood vessels
cortisol = released as a response to stress and results in a lowered immune system and the metabolism of carbs, fats and proteins, also signals carb metabolism
ovaries
hormones, target organs, physiological functions
hormones = oestrogen, progesterone
target organs = oestrogen ~ many
progesterone ~ uterus
physiological functions = development of the female sex characteristics and increases body fat levels, development of female sex characteristics and helps to create and maintain a stable and healthy pregnancy
testes
hormones, target organs, physiological functions
hormones = testosterone
target organs = many
physiological functions = stimulates tissue growth, masculinisation and reduces body fat levels, produces sperm and maintains male sex characteristics
