Endocrinology Flashcards
What do the endocrine system control and integrate ?
processes such as:
- reproduction
- growth and development
- maintenance of electrolyte, water and nutrient balance of the blood
- regulation of cellular metabolism and energy balance
- mobilisation of body defenses
What is the main signal in the endocrine system?
hormone
What do endocrine glands do?
secrete hormones into the systemic circulation
how are hormones secreted?
via specialised organs called endocrine glands
Where are the hormones secreted to?
the 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 to bring about specfic changes in cellular function.
What are the target cells?
Can be local
referred to as paracrines or autocrines
What are the 2 types which hormones are made of?
Amino acid based
Lipid based- steroid based hormones
What are the amino acid based hormones?
- Polypeptides (large)- long chain
- not able to pass through plasma membrane through diffusion- have to use specialised proteins/channels within plasma membrane
- water soluble - as they are protein based
- most common e.g TRH, TSH, insulin, glucagon
What are the modified amino acid based hormones?
-small
-still cannot pass though plasma membranes by diffusion
water soluble
e.g thyroxine
What are the steroid/lipid based hormones?
- synthesised by cholesterol
- small, fat soluble - can pass through the plasma membrane by diffusion- as they can pass through that hydrophobic region
e. g. cortisol, oestrogen, testosterone
Whta re the stimulus for these hormones to be released to maintain homeostasis?
- 3 types of stimuli- regulating endocrine system
- Humoral stimulus
- Neural stimulus
- hormonal stimulus
What is the humoral stimulus?
- Hormone release caused by altered levels of certain critical ions or nutrients
- these glands are constantly monitoring levels of ions and nutrients in systemic circulation
- endocrine glands sense if the levels are high or low and then will sense 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
What is hormonal stimulation?
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 regulated?
Negative feedback
Example of a negative feedback - homeostasis
hormonal stimulation
Gland A- secrete hormone A in blood stream
Hormone A - have effect on glsnd B
Gland B - release hormone B
-Hormone B - some used by a target organ (where it is neeeded)-Low levels of hormone B
-Again gland A stimulated- REPEAT process
-When too much hormone B- it inhibits secretion of it in gland A
What are the main endocrine glands in the body?
Pineal Pituitary- Growth/lactation/thyroid Thyroid- Metabolism Thymus- T-cell maturation Adrenal-stress response Pancreas-glucose metabolism Ovaries-ovulation Testis-spermatogenesis
What is pineal gland?
- Sits right in the middle of the brain
- regulate sleep wake cycle- info relayed through eyes- in retina have photoreceptor cells - nervous innervation through the retina
- Sends nervous innervation to pineal gland which secretes melatonin- peaks at night- causing drowsiness and lowers body temperature through neural stimulation
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 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 is optic chiasm?
- Bundles of nerves coming from back of eye ( optic nerve)
- cross middle line of brain
- sits directly above the pituitary gland
What is the hypothalamus?
part of CNS
- regulate pituitary and pineal gland- uses neuroendocrine system
- links the CNS to endocrine system
What is the pitutiary gland?
- lies close to optic nerves
- has a bony cup and grows upwards
- have 2 regions:
- anterior lobe
- posterior lobe
What does these 2 regions do?
secrete different hormones
and innervated differently by hypothalamus
What is anterior lobe?
- produce and secrete hormones from the lobe
- lots of different cells - which are responsible in secreting a specific hormone in the body
What are the anterior pituitary cells?
- Somatotrophs- growth hormone
- Lactrotophs- prolactin
- Corticotrophs- ACTH
- Thyrotrophs- TSH
- Gonadotrophs- FSH and LH
What is the posterior lobe?
secretes oxytocin and vasopressin
What is the relationship between neuroendocrine hormones from hypothalamus and the hormones that are then released from the anterior pituitary?
Hypothalamus is the CNS -Are Neurones which secrete special hormones called neuroendocrine hormones in the blood and detected by anterior pituitary
What do the hormones end in?
end in RH- releasing hormone
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?
- Neuroendocrine signals/hormones such as TRH, Gn RH, PIF are secreted in the neurones in the hypothalamic nuclei- into blood stream
- 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
- Hormones then secretion into hypophyseal vein- which takes hormones everywhere in the body
What is GnRH in females?
GnRH- is secreted from the hypothalamus in a cyclical way leading to a cyclical secretion of LH and FSH from the pituitary, which maintains the menstrual cycle.
- LH- acts on the ovarian follicle and it induces ovulation
- FSH- causes development of ovarian follicle and stimulates secretion of oestradiol and progesterone
What is GnRH in males?
- Release in pulsating action- burst
Causes the release of LH and FSH from the anterior pituitary - same as females
-LH - acts on testes to produce testosterone
-less cyclical action
-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.
What is growth hormone?
Come out somatotrophs
- Have a direct affect on organs around the body such as skeletal muscle- growth and protein synthesis
- Liver- regulate IGF- insulin growth factor
- Bone/Chondrocytes- increases axial length- increase cartilage which increases more bone
- Adipose tissue- increase fat oxidation- to make more ATP available for growth protein synthesis- metabolism
What can excess production of growth hormone cause?
gigantism - over elongation of muscles and bones - acromegaly- esp in hands and feet
What is TSH- Thyroid stimulating hormone?
- TSH exerts an effect on the Thyroid gland- in reponse to this secretes thryoid hormones such as thyroxine which can be converted into T3 (Tri iodothyronine)
- Secretion is stimulated by TSH- secreted from the anterior pituitary lobe
Negative feedback- hormonal control for TSH?
in hypothalamus- TRH secreted
- Down portal vein
- Detected in pituitary gland
- TSH- goes down vein into systemic circulation
- goes through capillaries in thyroid gland
- induce to secrete T3 and T4 in systemic circulation- regulate metabolism
- Hyphoseal vein
- When metabolism not needed- T3 and T4 can build up
- An excess of T4 and T3 stimulates the anterior lobe of the pituitary gland to reduce TSH secretion into the bloodstream
- This reduces T4 AND T3 production in the thyroid gland
- as TSJ secretion is also controlled by the hypothalamus
- the hypothalamus secretes thryroptropinRH- TRH
- Excess T4/T3 in the blood will inhibit the production and secretion of TRH by the hypothalamus- so dont over stimulate metablosim- needs to be regulated
What is ACTH?
- This acts on adrenal cortex of adrenal gland
- results in production of cortisol
- regulate in diurnal rhythm- more secretion during day
- stress response
- increase b.p
- increase blood glucose- energy boost
What is prolactin?
Prolactin Inhibitory factor- released by hypothalamus
to Inhibit secretion of prolactin from anterior pituitary gland
-it induces milk production /lactation and mammary growth during pregnancy
-Inhibited by dopamine
What is posterior pituitary ?
Hypothalmus which inervate neurons down to the posterior lobe in pituitary gland via the supra optic or paraventricular nucleus.
- Hypothalamus to posterior pituitary via nervous innervation
- Neruones dont stop and secrete neuroendocrine signals
- they innervate directly down to posterior lobe in pituitary gland
- These neurones coming from supra optic and paraventricular nuclei in hypothalamus- innervate down in posterior lobe
- No cells in posterior lobe which produce and secrete hormones
- hormone stored in nuclei then secreted in blood stream via posterior pituitary into hypophyseal veins
- hormones secreted are oxytocin and vasopessin (ADH)
What is Vasopressin?
ADH
- regulate water of blood
- increase water retention by kidneys (antidiuretic)
- Constricts arterial walls therefore increases BP
- regulated by baroreceptors in atria
- act through humoral stimulus- osmoreceptors also increase ADH release to reserve water
What is oxytocin?
happy hormone
- orgasm
- socialisation
- giving birth- helps mother baby bonding
where is the thyroid and parathyroid gland located?
.the neck
what is the function of the thyroid and parathyroid gland?
. important for calcium homeostasis
. regulate metabolism:
protein synthesis
lipid and carbohydrate metabolism
how many parathyroid glands are there?
. 4 small parathyroid gland which release parathyroid hormone
what are the two types of cells in the thyroid gland?
. thyroid follicular cells
. calcitonin cells
what is the function of thyroid follicular cells?
. produce T3 and T4 hormones
what is the function of calcitonin cells?
. in follicles produce calcitonin which decreases calcium uptake
what do thyroid hormones T3 and T4 require?
. thyroid hormones require iodine
what is the main hormone secreted by thyroid gland?
.T4
.T4 is a precursor to T3 because T3 is more potent
what is the function of T3 ?
. growth
. metabolism increases
. body temperature regulation
. mood
what kind of cells are present in the parathyroid gland?
cells that secrete parathyroid hormone (PTH)
what type of stimuli occurs in the parathyroid glands?
. humoral stimulus
this is because levels of PTH regulated by free calcium in the bloodstream
what does PTH respond to?
PTH respond to low Ca levels
how does PTH retain Calcium?
. increases renal tube absorption of calcium in the kidney
. augments gastrointestinal absorption of Calcium
where are adrenal glands located?
they sit on top of the kidney
what are the three regions in the adrenal glands?
. capsule - holds everything together . medulla - in the centre , which are large blood vessel respond to neural stimulus . cortex - ACTH from pituitary acts here respond to hormonal stimulus
what hormones does cortex release in respond to ACTH ?
. corticosteroids
1. mineral corticosteroids
2. glucocorticoids
. androgens
what is the function of mineral corticoids? ie. aldosterone
. retains water and maintains BP and blood volume , it does this by increasing Na+ retention by the kidney and water.- increases water and na absorption
. electrolyte balance and blood pressure
what is the function of glucocorticoids? ie. cortisol
. increases metabolism of fats/glucose
. increases blood glucose levels through gluconeogensis
. suppresses immune system
. linked to stress
what is the function of androgens?
. precursors to testosterone
. estrogen has effect maintaining male/female characteristics
where are the hormones that the adrenal cortex derive from ?
. the adrenal cortex produces hormones derived from cholesterol as they are steroid based hormones
how is the endocrine system regulated by negative feedback?
. corticosteroids are regulated by ACTH from the anterior pituitary gland
. ACTH secretion is regulated by CRH secretion from the hypothalamus
what is the function of the medulla?
. secretes hormones that help cope with emotional or physical stress
. produces two hormones
1. adrenaline ( epinephrine )
2. noradrenaline ( norepinephrine )
how are the two medulla hormones released by ?
. sympathetic innervation
what two glands make up the pancreas?
the pancreas is both an endocrine and exocrine gland
how is the pancreas act as an endocrine gland ?
. secretes insulin and glucagon to regulate blood glucose levels
how does the pancreas also act as an exocrine gland ?
releases pancreatic enzymes into the duodenum to aid digestion
what are the endocrine cells that make up the pancreas?
the islet of langerhans
what is the structure of islet of langerhans ?
uniformly distributed along fenestrated capillaries with pores to allow easy transfer of hormones in/out the blood ?
how are the islet of langerhans linked?
they linked by bridges/linkages of these cells ?
what are the 5 cell types that make up the islet of langerhans?
- alpha cells 30-40%
- beta cells 50%
- delta cells 10-20%
- F cells
- epsilon cells
what is the function of the function of the 5 types of cells that make up the islet of langerhans?
they secrete hormones
1. alpha cells - secrete glucagon - increase blood sugar level
2. beta cell - secrete insulin - decrease blood sugar level
3. delta cells - somatostatin and gastrin -
gastrin - regulates the exocrine function of pancreas
somatostatin- inhibits gastrin
4. F cells - pancreatic polypeptide - regulate digestive enzyme
5. Epsilon cells - ghrelin- controls hunger
tells you when to eat
function of alpha cells in the pancreas ?
. secrete glucagon
. liver breaks down glycogen to glucose
. glucagon increase blood glucose levels
what is the function of beta cells in the pancreas ?
. secrete insulin
. increase glucose uptake
. insulin decreases blood glucose levels
what is the main metabolic effect of insulin ?
. facilitates uptake of glucose into muscle and adipocytes
. stimulate liver to store glucose as glycogen
. stimulates liver to convert excess glycogen to fatty acids
what happens when insulin secretion goes wrong ?
type 1 diabetes
what is type 1 diabetes ?
is an autoimmune disease that kills off the pancreatic beta cells
what happens when you have type 1 diabetes ?
. less insulin production and secretion
. this leads to a loss of control of blood glucose levels - they increase
what is the function of insulin ?
suppresses glucagon secretion.
what happens when there is no insulin?
glucagon is secreted in excess which increases blood glucose levels further
