Endocrinology - Lecture 2 Flashcards
What are the 2 different tissues of the pituitary gland?
adenohypophysis and neurohypophysis
What is the adenohypophysis tissue also known as?
anterior pituitary
What is the neurohypophysis tissue also known as?
posterior pituitary
What kind of tissue is the anterior pituitary?
endocrine tissue
What kind of tissue is the posterior pituitary?
neural tissue
What 2 hormones does the posterior pituitary produce?
vasopressin and oxytocin
What 6 hormones does the anterior pituitary produce?
- TRH
- GnRH
- somatostatin
- GRH
- PIH
- CRH
What 2 nuclei synthesize oxytocin and vasopressin?
supraoptic nucleus and paraventricular nucleus
Where do the supraoptic and paraventricular nuclei run and terminate?
run: down the pituitary stalk
terminate: in the posterior pituitary close to capillary blood vessels
What are processed in secretory granules during axonal transport of supraoptic and paraventricular nuclei?
prohormones
What is the name of the mature hormones liberated from the carrier molecules produced in the posterior pituitary?
neurophysins
What are the circulating half lives of the neurophysins produced by the posterior pituitary?
1-3 minutes
What are the 3 functions of oxytocin in females?
- parturition
- milk ejection
- behavioural effects
How is oxytocin important in parturition?
dilation of uterine cervix by fetal head causes release of oxytocin -> uterine contraction, which assists the expulsion of fetus and then placenta.
How is oxytocin important in milk ejection?
it causes milk filled ducts to contract and squeeze milk out
What are the behavioural effects of oxytocin in females and males?
it reduces anxiety and enhances bonding, pro-social behaviour
What are the 2 functions of oxytocin in males?
- ejaculation
- behavioural effects
How is oxytocin important in ejaculation?
there is a surge of oxytocin during sexual activity which assists in epididimal passage of sperm and ejaculation
What is the major component of the thyroid gland?
thyroglobulin
What hormones are present in the thyroid gland?
T4 and T3
What controls the synthesis of thyroglobulin?
TSH of pituitary gland
What does thyroglobulin provide for T4 and T3 prior to release?
storage
What is the mass of the thyroid gland and what does its size vary with?
15 to 20g, varies size with sex, age, diet, reproductive state
The thyroid gland is larger in ___ than in ___.
females, males
How many grams of healthy thyroid are needed to maintain euthyroid state?
3 g
What element do thyroid hormones contain?
iodine
Which kinds of cells are able to trap iodide and transport it across the cell against a chemical gradient?
thyroid follicular cells
What is iodine used for?
iodination of tyrosine residues of thyroglobulin
What does thyroglobulin produce after it becomes iodinized?
monoiodotyrosine and diiodotyrosine
Oxidative coupling of how many DIT forms T4?
2
Oxidative coupling of how many MIT and DIT forms T3?
1 of each
What is the synthesis of thyroid hormones stimulated by?
TSH
Without ___, thyroid has very low turnover of thyroid hormones.
TSH
What is the synthesis and release of TSH controlled by?
hypothalamic thyrotropin releasing hormone TRH
What happens to the release of TRH and TSH when T4 and T3 in blood increases?
it decreases
What happens to the synthesis of thyroid hormones when the supply of iodide is deficient?
it decreases
What happens to TSH when there is an iodine deficiency?
it increases and the thyroid follicular cells are constantly stimulated
What happens to the thyroid gland when there is iodine deficiency?
it enlarges and may form a visible lump (goiter)
What happens to cardiac output, oxygenation of blood and rate of breathing when thyroid hormones stimulate the calorigenesis in most cells?
cardiac output: increases
oxygenation of blood: increases
rate of breating: increases
How can thyroid hormones effect carbohydrate metabolism?
Increased lipid synthesis; Increased lipid mobilization; Increased lipid oxidation
How can thyroid hormones effect protein metabolism?
it stimulates protein synthesis
How can thyroid hormones promote normal growth?
they promote neural branching and myelination of nerves, maturation of nervous sytem, stimulate bone growth
What do thyroid hormones T3 and T4 increase?
BMR
What does absence of thyroid hormones at early stages of development lead to?
irreversible mental retardation
What growth factor do thyroid hormones stimulate?
nerve growth factor NGF
What does NGF induce?
dendritogenesis and regeneration of sympathetic neurons
How are thyroid hormones analogous to the mechanism of action of steroid hormones?
T3 and T4 enter target cell nucleus, bind to their cognate nuclear receptor. Alters the transcription of specific genes, and thus levels of encoded proteins.
What do thyroid hormones interact with to induce some effects?
plasma membrane and mitochondria
Where is a specific receptor for T4/T3 located in the mitochondria?
in the inner mitochondrial membrane
What can T4/T3 hormones increase the uptake of?
amino acids
What are the 4 kinds of hypothyroidism?
primary, secondary, tertiary and infantile
What is primary hypothyroidism at the level of?
the thyroid gland
What is primary hypothyroidism?
inability to synthesize active thyroid hormones
What sex is primary hypothyroidism more common in?
females
What are the 3 main causes of primary hypothyroidism?
- Atrophy of the thyroid .
- Autoimmune Thyroiditis
A.K.A. autoimmune thyroiditis or Hashimoto’s disease. More common in women. - Goitrous Hypothyroidism or Non-Toxic Goitre
What is autoimmune thyroiditis?
destruction by antibodies against cellular components of thyroid
What is goitrous hypothyroidism or non-toxic goitre?
blockage in a step of T4/T3 synthesis.
What is secondary hypothyroidism at the level of?
pituitary
What is secondary hypothyroidism?
synthesis of little or no thyroid stimulating hormone TSH
What is tertiary hypothyroidism at the level of?
hypothalamus
What is tertiary hypothyroidism?
synthesis of little or no thyrotropin releasing hormone TRH
What is infantile hypothyroidism?
absence of thyroid gland or incomplete development of thyroid gland at birth
Why is early treatment of infantile hypothyroidism important?
because otherwise the child will have dwarfism and mental retardation will be associated with cretinism
How can all types of hypothyroidism be effectively treated?
with thyroid hormones
What are the 3 kinds of hyperthyroidism?
primary, secondary and tertiary
What are the 2 kinds of primary hyperthyroidism?
- toxic diffuse goiter (graves disease)
- thyroid adenoma or thyroid cancer
What is primary hyperthyroidism at the level of?
the thyroid gland
What is Graves Disease?
presence of LATS that are constantly stimulated which increases mass of thyroid leading to the formation of goitre synthesizes biologically active T4/T3; known as toxic goitre.
What is LATS?
long acting thyroid stimulator, an antibody that mimics the action of TSH and stimulating release of T3 and T4
What is thyroid adenoma?
synthesis of thyroid hormones is independent of TSH stimulation
What is secondary hyperthyroidism at the level of?
anterior pituitary gland
What is secondary hyperthyroidism?
no negative feedback from increased levels of T3/T4 and synthesize autonomously thyroid stimulating hormone (TSH).
What often causes secondary hyperthyroidism?
pituitary tumour
What is tertiary hyperthyroidism at the level of?
hypothalamus
What is tertiary hyperthyroidism?
no negative feedback of high T3/T4 to decrease synthesis of thyrotropin releasing hormone (TRH)
What often causes tertiary hyperthyroidism?
hypothalamic tumour
What are the 3 treatments for hyperthyroidism?
- surgery plus replacement therapy
- administration of radioactive iodide
- administration of antithyroid drugs like propylthiouracil
What is radioactive iodide administered to those with hyperthyroidism?
because the radioactive iodide concentrates in the cells of the thyroid follicles and destroys them
What is the function of propylthiouracil to treat hyperthyroidism?
it blocks the addition of iodine to thyroglobulin
What is the function of calcium?
-essential structural component of the skeleton.
- important in normal blood clotting.
- with Na+ and K+ helps maintain transmembrane potential of cells.
-important in excitability of nervous tissue
-important in contraction of muscles
-important in release of hormones and neurotransmitters.
What is the concentration of calcium in cellular and ECF?
10mg/100 mL
How is calcium in the circulation?
50% free 50% bound to albumin
About 99% of the body’s calcium is in ___.
bone
How do hormones control calcium?
- maintenance of plasma calcium is achieved mainly by exchange between bone and plasma under influence of hormones.
- hormones also affect intestinal absorption of calcium and excretion of by kidneys.
What 3 hormones are important in controlling calcium levels?
- parathyroid hormone PTH
- calcitonin
- vitamin D
Does PTH increase or decrease calcium levels?
increases
Does calcitonin increase or decrease calcium levels?
decreases
Does vitamin D increase or decrease calcium levels?
increases
Where is calcium absorbed in the digestive tract?
the duodenum and upper jejunum
What is calcium absorption increased by?
vitamin D and PTH
What increases calcium deposition in bone?
calcitonin
Where can calcium go?
- through the kidney and into the urin
- deposited in bone
What does PTH stimulate the reabsorption and removal of when plasma concentration of calcium is below 10mg/100 mL?
reabsorption: of calcium from the kidney
removal: of calcium from the bone
