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
