Endocrinology Flashcards
What are the bodies two main control systems
- Nervous system
- Endocrine system
What do the nervous system and endocrine system control and integrate how are hormones secreted?
Processes such as:
- reproduction
- growth and development i.e. puberty, growth phases
- maintenance of electrolyte, water and nutrient balance of the blood
- regulation of cellular metabolism and energy balance
- mobilisation of body defenses - links immune system
Role of endocrine glands
Secrete hormones into systemic circulation/blood
Dense vascular place - lots of capillaries - red
What are hormones also called
Chemical messengers
What is main signal within the endocrine system
Hormone
How are hormones secreted?
Around body via specialised organs called endocrine glands - travels around body in blood
How are hormones transported and where do they go to
In blood to a tissue where they have a specific action
What is a hormone
A chemical substance which is secreted by specialised endocrine cells directly into the blood to exert an effect on distant target cells
What is the target cell
Local
Only specific target cell receptors around the body are able to identify hormone and respond to it.
What are the local target cells reffered as
Paracrines - Secreting another cell in same area
Autocrines - Having effect back onto themselves
What are the 2 types which hormones are made of?
Amino acid/proteins based
Lipid based- steroid based hormones
What are the 2 types of amino acid based hormones
- Polypeptides
- Modified amino acids
Amino acid based hormones - Polypeptides
- Polypeptides - long chain
- Can not pass through plasma membrane by diffusion- have to use specialised proteins/channels within plasma membrane which bind to receptors
- Water soluble - as they are protein based
- Most common e.g TRH, TSH, GnRH, FSH, insulin, glucagon
Amino acid based hormones - Modified amino acids
- Small
- Still cannot pass though plasma membranes by diffusion because….
- water soluble
e. g thyroxine
- water soluble
What are the lipid based/steroids hormones
- Synthesised by cholesterol - one of constituents of p.membrane - sit in hydrophobic region inside p.membrane
- Small, fat soluble - can pass through the plasma membrane by diffusion- as they can pass through the hydrophobic region
e. g. cortisol, oestrogen, testosterone
What are the 3 types of stimuli to release hormone
-Humoral stimulus
-Neural stimulus
-hormonal stimulus
These stimulate hormone secretion = maintain homeostasis
What is humoral stimulus?
- Hormone release caused by altered levels of certain critical ions or nutrients
- STIMULUS: Low conc of Ca2+ in capillary blood.
- RESPONSE: Parathyroid glands secrete parathyroid hormone ( PTH), which increases blood Ca2+.
- These glands are constantly monitoring levels of ions and nutrients in systemic circulation
- Endocrine glands sense if the levels are high or low and respond by secreting a hormone
- Which will exert an effect on another gland in the body to change the uptake or excrete the ions/nutrients to regulate the level in the blood.
What is neural stimulus?
- Hormone release caused by neural input
- Stimulated by nervous system
- STIMULUS: action potential in preganaglionic sympathetic fibres to adrenal medulla
- RESPONSE- regulate secretion of adrenaline by adrenal medulla cells
- Medulla of adrenal gland - secretes adrenaline - noradrenaline - regualtes fight or flight response - responds to external stimulus - sympathetic fibres coming from one of ganglions - regulate secretions of adrenaline and noradrenalin
What is hormonal stimulus
- Hormone release caused by another hormone
- STIMULUS- hormones from hypothalamus
- endocrine glands regulated by hormones
- RESPONSE- pituitary gland secretes hormones that stimulate other endocrine glands to secrete hormones
How is hormone release regualted
Negative feedback
Example of a negative feedback - homeostasis
hormonal stimulation
- Gland A- secrete hormone A in blood stream
- Hormone A - have effect on endocrine organ - Gland B
- Gland B induced to secrete hormone B back into blood stream
- Hormone B - some used up by a target organ (where it is needed)-Low levels of hormone B in blood stream
- Detected by gland A = secrete more hormone A so more hormone B = keep levels of hormone B constant
- Again gland A stimulated- repeat process
- When hormone B levels in blood build up and too much- it inhibits secretion of hormone A from gland A = not stimulating gland B to secrete hormone B - eventually blood stream levels of Hormone B decreases
What happens if iron levels too high
Can stop secretions of hormones
What are the main endocrine glands in the body?
Pineal - sleep/wake cycle Pituitary- Growth/lactation/thyroid Thyroid- Metabolism Thymus- T-cell maturation - wbc maturation, adolescence Adrenal-stress response Pancreas-glucose metabolism Ovaries-ovulation Testis-spermatogenesis
What does pineal gland cause
Drowsiness
Lowers body temp - at night - direct link between melatonin levels in bloody and body temp
What hormone does pineal gland secrete
Melatonin
What type of stimulus is melatonin
Neural
Where is pineal gland located
Middle of brain - no access to light
What is role of melatonin in pineal gland
Regulate sleep/wake cycle through neural stimulation from eyes back to pineal gland
Neural stimulation through retina - in retina - photoreceptor cells - melatonin cells or IPRG’s - detect levels of moon light in environment - relay most photoreceptors - some of them regulate pineal gland through nervous stimulation - back into through suprachiasmaticc nucleus - sends nervous innervation back to pineal gland - regualtes secretion of hormone called melatonin
When is melatonin secreted
Overnight - when dark - as meltaonin puts body in a state where you can sleep = need high levels of melatonin to sleep
Also regulates metabolism
What does the hypothalamus do?
- Receives input from higher brain centres- limbic system= detect emotional changes
- Receive input from visceral and somatic sense via brain stem (everywhere else in body- respond to physical changes- neural stimulus from touch , temp to brain which relays info)
- The release of hormones from the pituitary is regulated by different stimuli acting on the hypothalamus initially.- interaction into your endocrine system
- sends neurones into pituitary gland
What happens if tumour in pituitary gland
If present and it starts to grow, it cant go down or sidewards, can only go up. As it grows upwards it starts to compress nerves coming from retina to eye where you see and cuts off info from eye to brain = loss of vision
Lot of tumours in brain are in pituitary gland as its in bony cup
What is optic chiasm?
- Bundles of nerves coming from back of eye through optic nerve
- Cross middle line of brain
- Sits directly above the pituitary gland
What does pituitaty gland sit in
Bony cup
Lie close to optic nerve
What is the hypothalamus?
- Part of CNS/brain
- Regulate pituitary and pineal gland- uses neuroendocrine system - main relay point between nervous system and endocrine system
- links the CNS to endocrine system
What is master regulator of hormones in body
Pituitary gland
What are 2 regions of pituitary gland
Anterior lobe - front
Posterior lobe - back
What does these 2 regions do?
Secrete different hormones
and innervated differently by hypothalamus
What is anterior lobe?
- Produce and secrete hormones from cells within the anterior lobe itself into bloodstream
- Lots of different cells types - each type secretes different hormone
What are the anterior pituitary cells?
- Somatotrophs- growth hormone - v.active during childhood
- Lactrotophs- prolactin
- Corticotrophs- ACTH
- Thyrotrophs- TSH
- Gonadotrophs- FSH and LH
What does TSH stand for
Thyroid Stimulating Hormone
Role of posterior lobe
Secretes oxytocin and vasopressin ( ADH)
Role of posterior lobe
Secretes oxytocin and vasopressin ( ADH)
Regulation of Anterior Posterior Lobe
- Neuroendocrine hormones secreted from hypothalamus into blood which is detected by pituitary gland. Neurons can secrete hormones called neuroendocrine hormones
- Relationship between neuroendocrine hormones from hypothalamus and the hormones that are then released from the anterior pituitary
What do the hormones end in?
In RH- releasing hormone = stimulate
End in I- Inhibit release- from the cells in anterior pituitary lobe
How is the neuroendocrine gland signal getting to those cells in anterior pituitary lobe?
- Hypothalamic nuclei to anterior pituitary
- Neuroendocrine signals/hormones such as TRH, Gn RH, PIF are secreted/released in the neurones in the hypothalamic nuclei- have projections into into blood stream/capillaries
- Hormones travel down portal vein- in systemic circulation into capillaries which surround all the cells in the anterior lobe
- Cells respond to stimulus- act on speciifc cells to release their speicific hormones into the blood again - i.e. TSH , PRL , LH .FSH - inhibiting/regulaating secretion in response
- Hormones then secretion into hypophyseal vein- which takes hormones everywhere in the body/blood out through the vein
Role of TRH ( thyrotropin releasing hormone )
Stimulate secretion of TSH from thyrotrophs
Role of PIF ( dopamine )
Inhibits prolactin secreted
Role of GnRH
Stimulate FSH or LH to be secreted
Role of GHRH and GIH ( somatostatin )
Regulate growth hormone production
Role of GHRH and GIH ( somatostatin )
Regulate growth hormone production
What is GnRH in females?
GnRH- is secreted from the hypothalamus in a cyclical way leading to a CYCLICAL secretion ( over a month - consistenly burst of secretions, sudden surges of release of GnRH) of LH and FSH from the pituitary, which maintains the menstrual cycle.
- LH- acts on the ovarian follicle directly and it induces ovulation
- FSH- causes development of ovarian follicle and stimulates secretion of oestradiol and progesterone
What is GnRH in males?
- Release in continously pulsating action- burst on daily basis. Less cyclical action
- Causes the release of LH and FSH from the anterior pituitary - sameas females
- LH - acts on testes to produce testosterone
- FSH- acts on the testes to maintain spermatogenesis
- continuously producing sperm and testosterone - on a slightly short cyclical cycle- less level- get bursts/show more aggression suddenly at a time.