the endocrine system Flashcards
direct cell communication
gap junctions, ions, small solutes and lipid-soluble
paracrine cell communication
extracellular fluid
- cell to cell communication
endocrine cell communication
through the bloodstream
synaptic cell communication
across synaptic clefts
endocrine glands
secrete directly into the blood
exocrine glands
secrete products into ducts, carrying them from outside the body i.e sweat glands
endocrine tissues
- thyroid glands
- parathyroid glands
- thymus
- adrenal glands
- pineal glands
- hypothalamus
- pituitary glands
What are hormones?
chemicals that encode a message and help maintain homeostasis.
auto cell signalling
self cell
pheromones
can signal between organisms
How do hormones send messages?
- Hormone molecule bind to receptor
- Receptor will change conformation
- Change in conformation allows other intracellular components to interact.
Cells expressing recptors = target cells
Role pf hormone receptors
- regulate cell sensitivity to hormone signal
- constantly synthesized and broken down
- increases the sensitivity of target cell to hormone
- decrease sensitivity as people could become drug dependant.
what happens when a hormone reaches its target?
Lipid soluble = hormone receptors inside of cell and trigger response within the cell.
Water-soluble = Hormone receptors on outside surface cell and trigger response inside of the cell.
role pf lipid-soluble hormone
- transcription
- intracellular
role of the water-soluble hormone
- circulate free
- second messenger = activation of intracellular components and signal amplification
how a target cell responds to a hormone is based on ?
- hormones concentration in blood
- # of hormone receptors on the target cells
- influences exerted by other hormones
- some hormones are more effective in presence of a second assisting hormone
- some hormones oppose the action of other
The response of target cells of hormone
- synthesis of new molecules
- changing permeability of the cell membrane
- stimulating transport of a substance into or out of the cell
- altering the rate of metabolic actions
hormone interactions (antagonistic)
- opposite hormones interact = weaker effect than those produced by the singular opposing hormone
Additive interaction
greater effect combining than if the hormone acted alone
permissive interaction
the first hormone is needed for the second to produce an effect
integrative interactions
different and complementary effects
Humoural stimuli
changes in circulating ions and molecules stimulate hormone secretion - e.g. glucose in negative feedback
neural stimuli
nerve impulses stimulate hormone release
hormonal stimuli
endocrine glands can be regulated by other hormones. - neg. feedback - releasing and stimulating hormones
Role of hypothalamus
- link between nervous and endocrine systems
- produces 9 hormones = regulating stimulation/inhibition of release if other hormones
- ADH and oxytocin
Posterior pituitary glands
- neural tissue connected to the hypothalamus
- stores and secretes ADH (water balance) and Oxytocin (pregnancy).
Anterior pituitary glands
- regulated by hypothalamic hormones
- releasing hormones in response (stimulating hormones)
Thyroid-stimulating hormone (TSH)
stimulates the production of thyroid hormones
ACTH
stimulates the adrenal cortex to release cortisol
FSH + LH
stimulates gonads to produce sex cells and sex steroids
prolactin
mammary glands to develop and produce milk
MSH
cause skin cells to produce melanin
promotes skeletal and muscular growth
promotes skeletal and muscular growth
Human growth hormone
- hypothalamus
- targets all body cells
- increases cell division and growth by increasing their intake of amino acids and synthesis of proteins
- stimulate lipolysis in adipose so fatty acids are used for ATP.
regulation of HGH
- low blood sugar stimulate the release of GHRH from the hypothalamus = more glycogen broken down into glucose by liver cells.
- high blood sugar stimulates the release of GHIH from the hypothalamus = glycogen does not break down into glucose.
thyroid gland
- large gland close to trachea and larynx
- requires iodine for the production of thyroid hormones
- produces T3 and T4: regulate metabolism
- produces calcitonin lowers circulating calcium concentrations by stimulating deposition in bone.
Released in response to TSH.
Thyroid hormone production
T3 and T4 = a protein that has one or two iodine ions attached.
- The more t4 produced, t3 more active
- Most t4 cells are converted into t3 in cell
- lipid-soluble = circulates bound to thyroid hormones
actions of thyroid hormone
- increases BMR
- increase the use of o2 + glucose for ATP
- increase cellular metabolism
- increase body temp
- increase the synthesis of proteins and breakdown of fats
- increase heat production
- increase action of adrenaline
Thyroid abnormalities
- Hypothyroidism = low blood levels of thyroid hormone (thyroid doesn’t develop properly)
- Hyperthyroidism = excess thyroid hormone in the gland
large thyroid gland.
Parathyroid glands
- small glands on posterior surfaces of the thyroid glands
- secrete PTH = causes Ca concentration to rise by promoting osteoclast activity.
Stimulates Ca reabsorption at the kidneys
PTH opposes the effects of calcitonin
regulation of parathyroid hormone
- low ca - secretion
- high ca - inhibition of secretion
- calcitriol increases ca absorption from the digestive tract
adrenal glands
- glands superior to kidneys
- adrenal medulla: controlled by the nervous system
- adrenal cortex: partly controlled by ACTH secretion from the anterior pituitary
Adrenal medulla
- hypothalamus initiates stimulation of hormone secretion
- innervated by the sympathetic nervous system (fast stimulation)
- produces hormones that allow short term alarm (fight and flight response)
Adrenal cortex
- outer portion of the adrenal glands
- produces hormones that provide a long-term response to stress
Cushing syndrome
- hypertension of cortisol
- hyperglycaemia
- water and salt retention
- redistribution of fat
Addison disease
- hyposecretion of glucocorticoids and mineralocorticoids
- hypoglycemia
- severe dehydration and hypotension due to decrease sodium in the blood.
pancreas
- exocrine pancreas: secretes and produces digestive juices
- endocrine pancreas: priduces and secretes hormones
insulin = secreted when glucose concentration is high, stimulates glucose uptake in cells.
Glucagon: secreted when glucose concentration is low - stimulates glycogenesis.
Diabetes
- inability to control blood glucose levels
symptoms of diabetes
hyperglycaemia
- frequent urination
- change in weight
- thirst/hunger
type 1 diabetes
- heredity
- pancreatic cells are attached and cannot produce insulin
- need insulin injections
type 2 diabetes
- due to lifestyle choices
- cells don’t respond to insulin
- exercise and a good diet needed
Testes
- produce testosterone
- secondary sex characteristics e.g. facial
- causes larynx and vocal cords to enlarge
Ovaries
- produce oestragen and progesterone =
stimulate the growth of the uterus and vagina
responsible for secondary sex characteristics
regulates uterine cycle
thymus gland
- lies beneath the sternum
- this gland is the largest and most active in childhood
- T lymphocytes mature here
Role of the autonomic system
Input: autonomic sensory neurons - monitor the internal environment in the body e.g. blood pressure, blood o2 levels).
Output: autonomic motor neurons
regulate activity in effector tissues - cardiac, smooth muscles
sympathetic response
fight or flight response
autonomic motor pathways
2 pathways
1. Preganglionic neuron
located within the CNS
The myelinated axon from this neuron extends into an autonomic ganglion
- postganglionic
within the autonomic
the unmyelinated axon from this neuron extends to the effector
what do preganglionic neurons?
- AcH
postganglionic neurons release?
- Noradrenalin and Ach
organs innervated by the sympathetic nervous system?
- spinal cord
- skin
- heart
- lungs
- blood vessels
organs innervated by the parasympathetic?
- brain
- heart
- larynx
- liver
- stomach
sympathetic nervous system activation
- during exercise, emotional stress and arousal
- reduces body functions that lead to storage of energy in fear and excitement
- fight or flight response
parasympathetic nervous system activation
- during quiet intervals between exercise, stress or arousal
- promote the conservation and storage of energy reserves
- stimulates SLUDD (salivation, lacrimation, urination, digestion, defection). = lowers heart rate.
autonomic nervous system activation
role in reflexes and homeostasis
- receptor
- sensory neuron
- integrating centre
- motor neuron
- effector neuron
adrenal cortex
- outer portion of the adrenal glands
- produces hormones that provide a long-term resoinse to stress
3 layers
1. zona glomeruli
2. zona fasciculata
3. zoa reticularis
Glucocorticoids (2nd layer)
95% of hormonal activity to due to cortisol
- regulates metabolism
- increase rate of protein catabolism and lipolysis
- conversion of amino acids to glucose
- stimulate lipolysis
adrenal cortex regulation
- low cortisol detected at the hypothalamus
- CRH secreted + ACTH released in response
- ## cortisol secreted in circulation
mineralocorticoids (aldosterone) - renal system
- 95% of hormonal activity due to aldosterone
- increase reabsorption of NA and Cl bicarbonate + H20
promotes excretion of K+ and H+ - prevents drops in blood volume and blood pressure
- secretion in response to low plasma (Na+) and high plasma (k+)
