Endocrine glands Flashcards
Name 3 endocrine glands in the brain
hypothalamus, pituitary gland and pineal gland
Location of hypothalamus
superior to pituitary gland (hypothalamus-pituitary axis)
What is the name of the connection between the hypothalamus and pituitary gland?
infundibulum
How is the pituitary gland divided?
anterior and posterior pituitary gland
Functions of the hypothalamus
thermoregulation, hormone secretion, regulates circadian rhythm, motivation (thirst, hunger, sexual), emotions
Why can obesity be considered a metabolic disorder?
Damage to the hypothalamus (e.g. in mice by injecting MSG) can affect hunger
What are the 2 categories of hormones secreted by the hypothalamus?
primary hormones and trophic hormones
What are primary hormones?
hormones that act directly on the target
What are trophic hormones?
Hormones that stimulate another gland to produce a different hormone. Aka releasing hormones
Name of the system that enables thermoregulation/homeostasis
negative feedback system
What happens if there is a decrease in the core body temperature?
Decrease is detected by thermoreceptors in the hypothalamus and compared to the ‘set point’. Effectors increase heat production and decrease heat loss. This raises the body temperature.
Example of when a set point may change
during the night core body temperature has a lower set point (regulated by circadian rhythm - hypothalamus)
What is the name of the anterior pituitary gland?
Adenohypophysis
What does the prefix adeno- mean?
relating to a gland
Which cells in the hypothalamus release hormones targeting the adenohypophysis?
hypothalamic neurosecretory cells
What type of hormones are released by hypothalamic neurosecretory cells?
trophic/releasing hormones
How do the hormones from the hypothalamus reach the adenohypophysis?
via hypothalamic-pituitary portal vessels (hormones released into blood vessels)
What is the posterior pituitary gland called?
neurohypophysis
Where are the hormones that travel to the neurohypophysis produced?
in the supraoptic nucleus and paraventricular nucleus of the hypothalamus
How are the hormones from the hypothalamus transported to the neurohypophysis?
hormones are transported as neurotransmitters via axons
Where are the cell bodies of the neurones that transport hormones to the neurohypophysis located?
within the supraoptic and paraventricular nuclei
What happens to the hormones once they reach the neurohypophysis?
they are released into circulation in the posterior pituitary gland / neurohypophysis
What are the hypothalamic hormones?
corticotropin releasing hormone (CRH), gonadotrophin RH, thyrotropin RH, growth hormone RH, somatostatin (SS), prolactin RH (PLRH), dopamine (DA, also PLIH)
Which hormone inhibits growth hormone?
somatostatin
What are the anterior pituitary hormones?
adrenocorticotropic hormone (ACTH), follicle stimulating hormone (FSH), luteinising hormone (LH), thyroid stimulating hormone (TSH), growth hormone (GH), prolactin (PL)
How can hormone secretion be regulated?
by negative feedback - hormone 2 or 3 can inhibit the release of a hormone earlier on in the sequence (e.g. from the hypothalamus or pituitary gland)
What hormones are released during stress?
corticotropin RH is secreted from hypothalamus, stimulating the release of ACTH from the adenohypophysis, which triggers cortisol to be released from the adrenal cortex.
Effects of cortisol
stress hormone. can act on hypothalamus and pituitary gland to inhibit the release of CRH and ACTH respectively
What medication can affect the stress response?
corticosteroids
Effect of gonadotrophin RH being secreted from the hypothalamus
triggers the release of FSH and LH from the anterior pituitary gland
Effect of FSH on ovaries
ovum maturation and oestrogen production
Effect of LH on ovaries
ovulation, production of oestrogen and progesterone
Effect of FSH on testes
sperm production
Effect of LH on testes
testosterone production
What happens when thyrotropin RH is secreted from the hypothalamus?
triggers the anterior pituitary gland to release thyroid stimulating hormone. This stimulates the thyroid to release thyroid hormones.
-trophin meaning
used as a suffix for hormones that affect growth/function
What determines the quantity of growth hormone released from the anterior pituitary gland?
the balance between GHRH and GHIH (SS) released from the hypothalamus (depends on stimulus)
Function of prolactin
breast development and milk production
What factors determine how much prolactin is released from the anterior pituitary gland?
the balance of prolactin RH and PLIH released from the anterior pituitary gland (depends on stimulus)
Which hormones are released from the posterior pituitary gland / neurohypophysis?
antidiuretic hormone (ADH) and oxytocin
Where are ADH and oxytocin produced?
by neurones in the hypothalamus (in supraoptic and paraventricular nuclei). Hormones passed along axons to neurohypophysis
Where is oxytocin produced?
Supraoptic nucleus
Where is ADH produced?
paraventricular nucleus
Function of ADH
water reabsorption in collecting ducts
Sequence of release of ADH
ADH is released from the hypothalamus (paraventricular nucleus) and travels down axons to the posterior pituitary gland where ADH is released into blood plasma and is transported to the kidneys.
Function of oxytocin
contraction of uterus (parturition) or milk ejection (depending on stimuli)
What happens in the endocrine system when an infant sucks on breast?
hypothalamus (supraoptic nuclei) releases oxytocin which travels down axons to posterior pituitary gland where oxytocin is released into blood plasma. Actions milk ejection.
Example of positive feedback in endocrine system
during parturition the stretch of the uterus causes oxytocin to be released which triggers contraction of the uterus, hence leading to more stretching and more oxytocin being released
What are the other endocrine glands in the body?
thyroid gland. parathyroid glands, islets of Langerhans in the pancreas, andrenal/suprarenal glands, gonads (ovaries/testes), placenta
Location of thyroid gland
anterior to trachea in the neck
Which hormones are secreted by the thyroid gland?
thyroid hormones (T3 and T4) and calcitonin
Function of calcitonin
Decreases/regulates calcium levels
Where does the thyroid gland originate from?
foramen caecum of the tongue
Where are the thyroid hormones released from?
follicular cells in the thyroid gland
Where is calcitonin produced?
by parafollicular C cells in the thyroid gland
What is T3?
tri-iodo-thyronine
What is T4?
tetra-iodo-thyronine (thyroxine)
Which is more potent, T3 or T4?
T3 is more potent
Which precedes the other, T3 or T4?
T4 is a precursor for T3
Why is T4 (thyroxine) used in pharmacology, not T3?
T4 is more stable and has a longer half life
Functions of thyroid hormones (T3 and T4)
increase metabolic rate of all cells, determines basal metabolic rate, normal fetal and child growth
How can thyroid hormones impact response to adrenaline?
thyroid hormones have a permissive effect on adrenaline action because they upregulate adrenoreceptors
Why is it important for dentists to be aware of conditions affecting the thyroid gland?
Hypersecretion can make patients more sensitive to adrenaline which is found in LA
What disorders are associated with under secretion of thyroid hormones?
hypothyroidism, cretinism (congenital), myxoedema (adult)
What disorders are associated with over secretion of thyroid hormones?
hyperthyroidism, Grave’s disease
Characteristics of congenital hypothyroidism
tongue is enlarged and sticks out
Why is it important to detect congenital hypothyroidism early?
the effects cannot be reversed
How is hypothyroidism treated?
injection of thyroid hormone (thyroxine)
Effects of congenital hypothyroidism
restricted mental development
What is the difference between congenital and adult (myxoedema) hypothyroidism?
the effects of adult hypothyroidism can be recovered with thyroxine
What is thyroid swelling called?
simple goitre
Cause of simple goitre
iodine deficiency (means T3 and T4 are not produced as they need to be iodised first)
What happens if there are low levels of thyroxine?
thyrotropin releasing hormone (TRH) is secreted from the hypothalamus which causes an increased secretion of thyroid stimulating hormone (TSH) from posterior pituitary gland.
Treatment for simple goitre
add iodine to salt
Characteristic of over secretion of thyroid hormones
exophthalmos (eyes bulging - sensitivity to adrenaline is apparent)
Where are parathyroid glands located?
deep / posterior surface of thyroid gland
How many parathyroid glands are there in the thyroid?
4-5
Function of parathyroid glands
produce parathyroid hormone
Function of parathyroid hormone
regulates blood calcium levels (increases Ca)
What glands are found in the pancreas?
endocrine and exocrine glands
Name of the endocrine portion of the pancreas
islets of Langerhans
What percentage of the pancreas is occupied by islets of Langerhans?
1-2%
What hormones are produced by the islets of Langerhans?
Insulin, glucagon, somatostatin
Which staining technique is used to visualise the different cell types (alpha, beta, delta) in the pancreatic islets?
Immunocytochemistry
How does immunocytochemistry work?
fluorescent antibodies are used which bind to the specific antigen on the cell type to be visualised
Which cells produce insulin?
Beta cells
Which cells produce glucagon?
Alpha cells
Which cells produce somatostatin?
Delta cells
What does immunocytochemistry of pancreatic islets reveal?
alpha and delta cells are found to be in close proximity to each other (colocalization) which suggests the hormones/cells closely interact
What factors promote insulin secretion?
increased blood glucose, increased blood amino acids, glucose-dependent insulinotropic peptide (GIP), vagus nerve activity
Function of insulin
lower blood glucose
How does insulin lower blood glucose?
promotes glucose uptake by muscle cells and adipocytes (not hepatocytes), and promotes formation of glycogen (glycogenolysis) and triglycerides, and facilitates glucose synthesis
What factors inhibit insulin secretion?
adrenaline, sympathetic nerves (to keep high blood glucose), and somatostatin
When is glucagon released?
when blood glucose concentration is low
Function of glucagon
increase blood glucose
How does glucagon act to increase blood glucose?
stimulates glycogenolysis and gluconeogenesis in liver, and lipolysis and ketone synthesis
What factors promote glucagon secretion?
low blood glucose, high blood amino acids (other elements are being produced using aa leading to low blood glucose), cholecystokinin, autonomic nerve activity
What factors inhibit glucagon secretion?
Only inhibited by hormones - insulin and somatostatin
What are the 2 types of diabetes?
Diabetes mellitus and diabetes insipidus (reduced ADH)
What does diabetes mellitus literally mean?
passing through a large volume of urine sweet like honey
What is the name of the disease that causes elevated blood glucose concentration?
diabetes mellitus
Why does diabetes mellitus cause elevated blood glucose concentration?
due to a decreased glucose uptake by cells - either due to lack of insulin or ineffective glucose uptake
What metabolic changes occur due to diabetes mellitus?
gluconeogenesis and lipolysis increases (to try to compensate for lack of sugar in cells)
What are the clinical features of diabetes mellitus?
polyuria, polydipsia (increased fluid intake/thirst), glycosuria (glucose in urine), diabetic neuropathy, skin and oral diseases
Oral diseases associated with diabetes mellitus
periodontitis and xerostomia
Which type of diabetes mellitus is insulin-dependent?
type 1
Cause of type 1 diabetes mellitus
autoimmune destruction of beta cells which decreases insulin secretion
What percentage of diabetes mellitus patients have type 1?
10%
Which type of diabetes mellitus is early onset?
type 1 (type 2 is late onset)
What is the treatment of type 1 diabetes mellitus?
Insulin injections (or pumps), diet control, transplant of islets of Langerhans
cause of type 2 diabetes mellitus
reduced target cell responsiveness to insulin despite normal insulin levels
Why may type 2 diabetic patients sometimes be insulin-dependent?
after a long period, beta cells can be destroyed
Which health conditions are related to development of type 2 diabetes mellitus?
overweight
Treatment for type 2 diabetes
diet, oral hypoglycaemic agents (and products to increase insulin secretion)
Which patients are at risk of becoming hypoglycaemic?
type 1 diabetics (and possibly insulin-dependent type 2) - important to check whether insulin-dependent
Why may a hypoglycaemic crisis occur?
If the patient takes insulin without having a meal
Location of adrenal glands
superior to kidneys (suprarenal)
What is the general term for hormones released from the adrenal cortex?
corticosteroids
What are the cortex hormones?
aldosterone, cortisol, androgens
Why is the adrenal medulla classified as a modified sympathetic ganglion?
Because it is controlled by pre-ganglionic sympathetic nerves (part of sympathetic NS)
Name of hormone released from adrenal medulla
adrenaline (epinephrine)
Importance of cholesterol
component of phospholipid bilayer and produces steroid hormones (e.g. aldosterone, glucocorticoids)
What are the zones of the adrenal cortex?
zona glomerulosa, zona fasciculata, zona reticularis
What class of corticosteroids does cortisol belong in?
glucocorticoid hormone
Where is cortisol produced from?
Zona fasciculata of adrenal cortex
How is cortisol release controlled?
cortisol secretion is controlled by ACTH (adrenocorticotropic hormone) from the anterior pituitary gland
Effects of cortisol
metabolic effects (increase), permissive effects (activate receptors), anti-inflammatory and immunosuppressant
What are corticosteroid drugs used for?
Anti-inflammatory and immunosuppressant drugs
What group of corticosteroids does aldosterone belong to?
mineralocorticoid
Where is aldosterone produced from?
zona glomerulosa of adrenal cortex
What controls the release of aldosterone?
renin-angiotensin system
What are the actions of aldosterone?
promotes reabsorption of Na+ and water from DCT of kidneys, increases excretion of H+ and K+
Describe the steps of the renin-angiotensin-aldosterone system
the juxta-glomerular apparatus recognises a stimulus (decreased Na+ and BP) and releases renin. Renin converts angiotensinogen to angiotensin I which is converted to Angiotensin II by ACE. Angiotensin II stimulates the release of aldosterone from the adrenal cortex. Aldosterone acts to increase Na+ reabsorption in cortical collecting ducts.
What is ACE?
Angiotensin converting enzyme (ACE) converts angiotensin I to angiotensin II
What is ACE inhibitor a treatment for?
High blood pressure (inhibits conversion into angiotensin II which reduces aldosterone release, reducing Na+ reabsorption)
What group of corticosteroids do androgens belong to?
gonadocorticoids
Where are gonadocorticoids (androgens) released from?
zona fasciculata and zona reticularis of the adrenal cortex
Function of androgens
growth (pubertal growth spurt) and sexual characteristics
Name of the disease when caused by excess glucocorticoid (e.g. corticosteroids for medical reasons)
Cushing’s syndrome
Name of genetic condition involving over production of androgens
adreno-genital syndrome
Effects of adreno-genital syndrome / excess androgens
precocious puberty, rapid growth which stops at a shorter than average height (epiphyseal plate becomes sealed)
Name of the disease that is due to adrenal insufficiency
Addison’s disease
Cause of Addison’s disease
Decreased adrenal function and reduced levels of glucocorticoids (cortisol) and mineralocorticoids (aldosterone)
