[W1] The endocrine system Flashcards
what are the 2 internal communication systems?
- nervous system (rapid with physical connections)
- endocrine system (slower, more precise system)
what does ‘endo’ mean?
within
what does ‘crine’ mean?
secrete
what does endocrine mean?
signalling system utilising the bloodstream to transport chemical messages collectively known as ‘hormones’
what are the 6 major endocrine glands?
- hypothalamus
- pituitary gland
- pineal gland
- thyroid gland
- parathyroid glands
- adrenal gland
what are the other 11 organs with endocrine function?
- Skin
- Thymus
- Heart
- Liver
- Stomach
- Pancreas
- Small intestine
- Adipose tissue
- Kidneys
- Testes (male)
- Ovaries (female)
give a brief overview of the endocrine system
consists of glands spread around the body that secrete hormones to provide slow(er) but very precise homeostasis
what is the function of the endocrine system?
These processes regulate and modify the internal environment allowing for coordinated cellular responses to changes in the internal and external environment, facilitating reproduction, growth and development
what are hormones?
Chemical messengers secreted by specific cells / tissues that travel (often in blood) to act on specific high affinity receptors on/in a target cell.
what is a ligand?
any molecule or atom/ion which binds reversibly to a protein. [Hormones are ligands]
what are hormone receptors?
A cell protein that binds a specific hormone.
The hormone receptor may be on the surface of the cell or inside the cell. Many changes take place in a cell after a hormone binds to its receptor.
what is a signalling cascade?
what happens after hormone:receptor interaction
what is autocrine action?
occurs when a cell secretes a factor which then acts on the same cell to elicit a response
what is paracrine action?
Paracrine signaling is a cell to cell signaling method in which factors that are released from one cell act upon another nearby cell
what are the 3 classes of hormones?
- steriod hormones
- biogenic amines
- proteins
what are the 2 types of hormone receptors?
- intracellular receptors
- extracellular receptors
what are intracellular receptors used for?
for hydrophobic / lipid soluble hormones (pass through cell membrane unaided)
what are extracellular receptors for?
- Extracellular receptors are required for hydrophilic hormones
true of false:
hydrophobic hormones can be stored easily?
false
cannot be stored easily – usually ‘made to order’. Can pass through cell membranes. Interacts with an intracellular receptor of target cells. Excreted whole - not easily broken down.
true or false:
hydrophilic hormones can be stored easily
true
can be stored within the cells if they are attached to carrier proteins. Released on demand. Require an extracellular receptor for signalling to the target cells. Easily broken down.
what are steroids?
Steroids are any of a large class of organic compounds with a characteristic molecular structure containing four rings of carbon atoms (three six-membered and one five).
- They include many hormones, alkaloids, and vitamins.
how are steriod hormones excreted?
excreated unchanged via urine
what do steriod hormones bind to?
intracellular receptors
what are steriod hormones bound to to increase the half-life?
bound to plasma proteins
are steroid hormones hydrophilic or hydrophobic?
hydrophobic
where are steriod hormones produced?
adrenal cortex or the gonads
what are biogenic amine hormones?
Also known as ‘monoamines’ – modified amino acids (e.g. tyrosine modifications)
are biogenic amines hydrophilic or hydrophobic?
hydrophilic
(except for thyroid hormone)
how does a biogenic amine signal?
via an extracellular receptor
can biogenic hormones be stored?
yes
why is thyroid hormone hydrophobic?
because it has a non-polar ring structure
what are the 2 forms of thyroid hormone?
T3 and T4
where is thyroid hormone stored? how?
Stored within thyroid gland - attached to thyroglobulin (a colloidal binding protein)
what are most hormones?
proteins in various forms: Small peptides, polypeptides or glycoproteins.
are protein hormones hydrophilic or hydrophobic?
all hydrophilic (water soluble)
are protein hormones soluble (free) in blood? what does that mean?
yes, they have a shorter half-life
can protein hormones be stored within a cell?
yes and released rapidly ‘on demand’
what are local hormones?
Chemicals produced by ‘non-glands’ that act on local tissues
what are 3 examples of local hormones?
- histamine (causes an inflamatory response)
- serotonin (causes platelet activation, acts as an anti-depressant)
- prostaglandins (potent wide-ranging effects: inflammatory, fever, regulating BP, ect.)
what are eicosanoids?
Signalling molecules formed from fatty acids derived from phospholipids on the cell membrane.
how is homeostasis regulated?
feedback systems
what are the 2 types of feedback systems?
- negative feedback
- positive feedback
what are negative feedback systems?
effector system opposes the initiating stimuli
what is a positive feedback system?
Effector system reinforces or amplifies the initiating stimuli
what feedback system is the most common?
negative feedback system
what are the 2 ways in which the hypothalamus communicates with the pituitary gland?
- portal bloodstream (anterior)
- direct nerve connections (posterior)
give 4 functions of the hypothalamus
- Autonomic Nervous System responses
- Appetite and satiety
- Thirst and water balance
- Body temperature control
- Emotional reactions
- Sexual behaviours
- Child rearing behaviours
- Sleep and wake cycles
why is the hypothalamus known as the master endocrine gland?
has direct control over the release of stimulating and inhibiting hormones from the pituitary gland
where does the hypothalamus have indirect control over the hormone release from?
- The thyroid gland
- The adrenal glands
- The liver
- The testes
- The ovaries
where is the pituitary gland found?
- Sits in a bony dip of the sphenoid bone below the hypothalamus, which it is attached to by a pituitary stalk.
how large is the pituitary gland?
pea-sized
what are the 2 components of the pituitary gland?
anterior and posterior
what is the proportional of mass of the anterior pituitary?
3/4 total mass
what tissue does the anterior pituitary contain?
- Glandular tissue
what is the proportional of mass of the posterior pituitary?
1/4 total mass
what tissue is the posterior pituitary gland made up of?
neural tissue from the hypothalamus
how is the anterior pituitary connected to the hypothalamus?
Connected to hypothalamus by pituitary portal system (blood)
what regulates the anterior and posterior pituitary hormones?
the hypothalamus
what are the 6 hormones released by the anterior pituitary?
- follicle stimulating hormone (FSH)
- luteinising hormone (LH)
- thyroid-stimulating hormone (TSH)
- prolactin (PRL)
- growth hormone (GH)
- adrenocorticotrophic hormone (ACTH)
what 2 hormones does the posterior pituitary stire?
- antidiuretic hormone
- oxytocin
what is the alternative name for antiduiretic hormone?
vasopressin
what are the 2 main roles of oxytocin?
- parturition (childbirth)
- lactation (breast milk ‘let down’ reflex)
what is the main function of ADH?
- Primary involvement in water conservation by the kidney
- Act on the kidney tubules/collecting ducts to increase water reabsorption from filtrate back into blood, thus concentrating urine
what other effects does oxytocin have on the body?
- Sexual arousal, pair bonding, parental behaviour, pain tolerance, social memory and reducing stress/anxiety
- Increased with hugging, massage / touch and trusting behaviour
- Increases monogamy?
is oxytocin a positive or negative feedback system?
positive feedback system
how is the blood supplied to the pituitary gland?
Highly vascularised, supplied via Internal Carotid Arteries
what is the pineal gland?
- A small endocrine gland attached by a short stalk to the roof of the 3rd ventricle in the brain
- Contains many nerve endings that go to the hypothalamus
what is the function of the pineal gland?
produces melatonin
what are the effects of melatonin in the body?
- Fine tunes the body’s circadian and diurnal rhythms (including information to the hypothalamus)
- Inhibits sexual development before puberty
- Melatonin is Pleiotropic (Additional effects):
- Anti-oxidant (cell protective)
- Anti-inflammatory
- Anti-hypertensive
- Anti-thrombotic
- Anti-lipidaemic
what is the structure of the thyroid gland?
- butterfly shaped
- 2 lobes joined by a narrow ishthmus
- highly vascular, surrounded by a fibrous capsule
where is the thyroid gland situated?
from C5 to T1
what are the associated structures with the thyroid gland anteriorly, posteriorly, superiorly and laterally?
- Anteriorly: Skin, blood vessels
- Posteriorly: Larynx and trachea
- Superiorly: Thyroid cartilage
- Laterally: Common carotid arteries
- Medially/posterior: Recurrent laryngeal nerves - lie very close to inferior thyroid arteries
what hormones are produced by the thyroid gland?
- thyroid hormone (T3 and T4)
- calcitonin
what is the thyroid gland composed of?
spherical hollow follicles formed from circles of cuboidal epithelium
what is the function of collide?
stores iodine and the thyroid hormones
what secretes calcitonin?
Between follicles are parafollicular cells (C-cells) which secrete calcitonin
how are Tri-iodothyronine (T3) and Thyroxine (T4) produced?
tyrosine residues bind iodine atoms
what stimulates T3 and T4 release?
TSH (thyroid stimulating hormone)
what happens when T3 and T4 are stimulated by TSH?
they are released from inside the follicular cells and these diffuse into the blood
which thyroid hormone is more physiologically active?
T3
which thyroid hormone is more abundant?
T4
T3 (15%) and T4 (85%)
most __ is converted to __ inside target cell
most T4 is converted to T3 inside target cells
how much iodine can the thyroid gland store?
4-months worth
what foods is iodine found in?
- seafood
- seaweed
- some fruit/veg
- iodinated table salt
what does a deficiency of iodine cause?
increases TSH secretion causing enlargement of the thyroid gland (goitre)
what are the 3 main functions of thyroid hormone?
- Increase the Basal Metabolic Rate and heat production
- Regulates metabolism of carbohydrates, proteins and fats
- Increases the effects of other hormones such as adrenaline and noradrenaline
where in the body does thyroid hormone act?
acts on most cells of the body
what stimulates the secretion of thyroid hormones?
- sleep
- exercise
- stress
- malnutrition
- low blood glucose
what is the chain of hormones released to regulate thyroid hormones?
TRH –> TSH –> T4 & T3
what is the regulation of thyroid hormones controlled by?
negative feedback to the hypothalamus and anterior pituitary
what are the conditions caused by abnormal levels of thyroid hormones?
hyperthyroidism / hypothyroidism
what is an example of a hyperthyroidism condition?
Graves disease
what is an example of a hypothyroidism condition?
Hashimotos thyroiditis
what are some symptoms of hyperthyroidism?
- Increased BMR
- feel too warm
- sweaty
- weight loss
- increased appetite
- diarrhoea
- anxiety
- restlessness
- tachycardia
- palpitations
- (exophthalmos)
what are some symptoms of hypothyroidism?
- Decreased BMR
- cold
- dry skin
- weight gain
- decreased appetite
- constipation
- depression
- lethargy
- bradycardia
how do you test thyroid function?
test serum levels of all three hormones: TSH, T3 and T4
which results from a thyroid function test would indicate primary hypothyroidism?
- Increased TSH
- decreased T3
- decreased T4
which results from a thyroid function test would indicate secondary hypothyroidism?
- Decreased TSH
- decreased T3
- decreased T4
what is the cause of primary hypothyroidism?
thyroid gland problem
what is the cause of secondary hypothyroidism?
hypothalamus / anterior pituitary problem
what produces and secretes calcitonin?
the parafollicular cells (C-cells) of the thyroid gland
what are the 4 function of calcitonin?
Calcitonin lowers blood calcium by:
- Promoting calcium entry to bone - bone storage of calcium
- Inhibits kidney reabsorption of calcium
- [Thus, increases calcium excretion in urine]
how many parathyroid glands are there and where are they found?
4 small parathyroid glands are on the posterior surface of the thyroid gland
what hormone do parathyroid hormone produce?
parathyroid hormone
what are the parathyroid glands encased in?
connective tissue capsule
what is the function of parathyroid hormone?
calcium homeostasis
what is the most abundant mineral in the body?
calcium
where is most of the bodies calcium stored?
within the skeleton
what 3 hormones control the blood calcium concentration?
- calcitonin
- parathyroid hormone
- calcitriol
how does parathyroid hormone increase blood calcium? (3 points)
- Increasing calcium absorption in the small intestine
- Increasing reabsorption of calcium by the kidneys
- Stimulating osteoclasts to break down bone and release calcium
what 2 arteries supply the thyroid and parathyroid glands?
Superior and inferior thyroid arteries
what are the superior thyroid arteries?
branches of the external carotid arteries
what are the inferior thyroid arteries?
branches of the subclavian arteries
where do the thyroid veins drain?
into the R&L internal julular veins
what is the nerve supply to the thyroid and parathyroid glands?
Sympathetic supply: Cervical ganglia (~C1-8) – causes vasoconstriction limiting blood supply to thyroid / parathyroid glands.
what is the adrenal cortex made up of?
glandular tissue
what hoemones are produced by the adrenal cortex?
group of steroid hormones called corticosteroids
what is the adrenal medulla made up of?
Embryologically nervous tissue
what is the function of the adrenal medulla?
Functions as part of the sympathetic nervous system
is the arenal cortex essential to life?
yes
is the adrenal medulla essential to life?
no
how is the zona glomerulosa in the adrenal glands regulated?
negative feedback system:
- Blood pressure in the kidney regulates the renin-angiotensin-aldosterone system
- Potassium levels regulate aldosterone secretion by the adrenal cortex
- Circadian rhythm: renin, angiotensin and aldosterone all peak at night ( urine production)
what are the 4 zones of the adrenal glands? what are there functions?
- zona glomerulosa: salt
- zona fasciculata: sugar, chronic stress
- zona reticularis: sex
- zona fasciculata & zona reticu
what is the HPA axis?
a communication system between three organs:
- hypothalamus
- pituitary
- adrenal
what does the HPA axis regulate?
corticosteriod production
how is the HPA axis regulated?
by negative feedback system
what is the main glucocorticoid?
cortisol
what do cortisol and ATCH secretion show?
a marked circadian rhythm, lowest between midnight and 3am, peaking between 4am and 8am.
what causes cushing’s syndrome?
systemic effects of high cortisol
what do androgens cause?
male secondary sexual characteristics (present in females in lower amounts)
what is the main androgen secreted by the adrenal glands?
testosterone
what is the percentage split of testosterone production of the adrenal glands and testes?
andrenal glands: 5%
testes: 95%
production rates of androgens are dependent on what?
sleep-dependant
what is DHEA?
- Dehydroepiandrosterone (DHEA)
- The most abundant endogenous circulating steroid hormone
where is DHEA produced?
Produced in the adrenal cortex (and testes/ovaries)
what is DHEA metabolised into?
Metabolised into androgens (testosterone) and oestrogens
what body system is the adrenal medulla part of?
sympathetic nervous system
the hormones produced by the adrenal medulla help prolong the effects of what?
effects of fight or flight response
what hormones are released by the adrenal medulla?
adrenaline and noradrenaline
what supplies blood to the adrenal glands?
Branches of the abdominal aorta, renal arteries & suprarenal arteries
what drains blood from the adrenal arteries?
Via suprarenal veins:
- Right gland drains into inferior vena cava
- Left gland drains into left renal vein then the inferior vena cava
what is the nerve supply to the adrenal glands?
Coeliac ganglion (~T8) – stimulates secretion of adrenaline from adrenal medulla.(No parasympathetic innervation to adrenal glands)
how is the adrenal cortex function regulated?
hormonally regulated not via nerves
what is the pancreas and where is it found?
A 12-15cm organ occupying epigastric and left hypochondriac regions
what are the 3 regions of the pancreas?
- Broad head (in curve of duodenum)
- Body (behind stomach)
- Tail (in front of left kidney, reaches spleen)
what are the endocrine pancreatic cells called?
Pancreatic Islets of Langerhans.
what are the 3 types of Pancreatic Islets of Langerhans and what are there functions?
- alpha cells - secrete glucagon
- beta cells - secrete insulin
- (delta cells - secrete GHRIH (somatostatin))
what 2 hormones are used to regulate blood sugars in the body?
glucagon and insulin
what is a healthy blood glucose concentration?
4 -7 mmol/L
what are some symptoms of hypoglycaemia?
- drowsiness
- confusion
- speech difficulties
- sweating
- trembling
- anxiety
- tachycardia
what are some symptoms of hyperglycaemia?
- damages delicate blood vessels such as those in the retina, kidney, heart.
- Neuropathy (reduced sensation esp feet). Infection risk increases.
how does insulin lower blood sugars?
- Promotes Uptake of glucose by muscle and connective tissue
- Promotes Glycogenesis (production of glycogen) in liver and muscle
- Promotes Uptake of amino acids and synthesis of protein
- Promotes Lipogenesis (synthesis of fatty acids) and storage of fat in adipose tissue
- Reduces glycogenolysis (breakdown of glycogen)
- Prevents gluconeogenesis (formation of new sugar from eg. protein)
- Prevents proteolysis and lipolysis (breakdown of protein and fat)
how is insulin regulated?
Insulin secretion by beta cells in the pancreas is stimulated by:
- Parasympathetic nervous system (rest and digest)
- High blood glucose / amino acid / fatty acid levels (post prandial)
- Gastrointestinal hormones eg. Gastrin, secretin, cholecystokinin
Insulin secretion is inhibited by
- Sympathetic stimulation (fight/flight, stress)
- Other hormones: Glucagon, adrenaline, cortisol, GHRIH (somatostatin)
how does glucagon raise blood sugars?
- Promotes Glycogenolysis (breakdown of glycogen to glucose) in the liver and muscle
- Promotes Gluconeogenesis (formation of new sugars eg. from protein) in the liver/muscle
how is glucagon regulated?
Glucagon secretion is stimulated by
- Low blood glucose (fasting)
- Exercise
Glucagon secretion is reduced by
- Insulin and GHRIH (somatostatin)
what is GHRIH or somatostatin?
Growth Hormone Release Inhibiting Hormone
what is the function of GHRIH?
Hypothalmic GHRIH inhibits secretion of GH by anterior pituitary
what supplies blood to the pancreas?
Splenic artery and mesenteric arteries
what is the nurve supply to the pancreas?
- Parasympathetic: CNX (vagus) – secretion of pancreatic juice and insulin
- Sympathetic: Coeliac ganglia (~T7) – inhibits pancreatic secretion and insulin
