IC1 Flashcards
Define hormone
Hormones are substances secreted by endocrine glands and transported throughout the bloodstream to target tissues where they act to regulate specific functions.
Can hormones exert its effect at very low concentrations? (Y/N)
Yes
Exocrine vs Endocrine glands
- Exocrine glands produces non-hormonal substances and contains ducts that carry these substances to a membrane surface e.g. sweat and saliva glands
- Endocrine glands produces hormones which is released into surrounding tissue fluid (lacks ducts)
2 types of endocrine glands + examples
- Central - pituitary glands, hypothalamus
- Peripheral - thyroid gland, adrenal gland, pancreas, ovary, testes
Consequences of disrupting oestrogen (e.g. due to synthetic hormones)
- Female: Increased incidence of breast tumour
- Male: Reduced sperm count, cryptorchidism (undescended testis)
- Animal: gender bending
Characteristics of hormones bound to cell surface Vs intracellular receptors
Cell membrane receptors are usually bound to water-soluble, hydrophilic hormones Vs intracellular receptors are bound to lipid-soluble, hydrophobic hormones
What could cause hormonal imbalances?
- Excessive/ decreased secretion of hormones
- Excessive/ decreased target cell responsiveness
Intracellular events after binding hormones with a receptor
- Alters channel permeability by acting on pre-existing channel forming proteins
- Acts through second messenger system to alter activity of pre-existing proteins
- Activates specific genes to cause formation of new proteins
Where is the thyroid gland located?
Located in the neck, on the anterior surface of trachea, immediately below larynx
Where is the thyroid gland located?
Located in the neck, on the anterior surface of trachea, immediately below larynx
What are the two thyroid lobes connected by?
Isthmus
Role of follicle cells, thyroid follicle & colloid
- Follicle cells: Synthesises thyroglobulin and secrete it into the colloid of the thyroid follicles
- Thyroid follicle: Functional unit for thyroid hormone production
- Colloid: Extracellular space that stores thyroglobulin with attached iodine atoms
Role of parafollicular cells (AKA C cells)
Secrete calcitonin
Basic ingredients of thyroid
- Tyrosine aa (synthesised in body)
- Iodine (obtained from diet and reduced to I- prior to absorption by small intestine)
Key points of thyroid synthesis
- Iodide trapping
- Iodination
- Coupling
- Colloid resorption
- Thyroglobin proteolysis
___ is the major biologically active form of TH at the cellular level (10 times more potent than T4)
T3
T4 (thyroxine) can get broken down into T3 (liver, kidney, pituitary) or inactive metabolite (liver, kidney) by ______.
5-deiodinase
Physiological effects of T3 and T4
- Controls rate of metabolism (BMR & thus heat production)
- Sympathomimetic effect (Increased proliferation of catecholaminereceptor thus increased target cell responsiveness to catecholamines)
- Cardiovascular effect (Increased heart responsiveness to catecholamines thus increased HR, force of contraction & CO)
- Essential for normal bone growth and maturation
- Crucial role in normal development of nervous system, especially the brain during childhood, and normal CNS activity in adults
- Increased synthesis and degradation (metabolism) of proteins, lipids & carbohydrates
Causes of hypothyroidism
- Primary failure of thyroid gland
- Secondary to deficiency of TSH, TRH or both
- Inadequate supply of dietary iodine
Key signs and symptoms of hypothyroidism
Intolerance to cold, weight gain, brittle nails & hair, constipation, dull-blank expression & extreme fatigue
Key signs and symptoms of hypothyroidism
Intolerance to cold, weight gain, brittle nails & hair, constipation, dull-blank expression & extreme fatigue
Causes of hyperthyroidism
- Production of TSI
- Secondary to excess of TSH, TRH or both
- Hypersecreting thyroid tumour
Key signs & symptoms of hyperthyroidism
Intolerance to heat, bulging eyes, enlarged thyroid, increased systolic BP, weight loss, muscle wasting, increased tremors & diarrhoea
What is graves disease?
An autoimmune disease which causes body to erroneously secrete thyroid stimulating immunoglobulin (TSI). TSI binds to TSH receptor on thyroid cells and mimic the action of TSH –> leads to both secretion and growth of thyroid.
What causes bulging of eyeball in graves disease?
Abnormal fluid retention behind eyeballs cause them to bulge forward (TSI stimulates release of cytokines, causing inflammation and oedema(?))
Is TSI subjected to negative feedback inhibition by thyroid hormone? What is the consequence?
Unlike TSH, TSI is not subject to negative feedback inhibition by thyroid hormone –> thyroid secretion and growth remains unchecked
Possible treatment options for hyperthyroidism
- Anti-thyroid drugs that interfere with TH production (drugs that block I- uptake or inhibit TPO)
- Surgical removal of a portion of hypersecreting thyroid gland
- Administration of radioactive iodine
What is goiter and its causes?
Enlarged thyroid gland; developed when thyroid gland is overstimulated by increased TSI / TSH
1. Hyperthyroidism: Increased TSH-TSI receptor activation
2. Hypothyroidism: Increased TSH but low iodine -> low TH synthesis -> high TSH remains -> thyroid growth
Brief description of thyroid synthesis
The thyroid gland produces thyroid hormones by a process of concentration of iodine in the thyroid, iodination of tyrosine residues of Tg in the colloid space of the follicle, and endocytosis of colloid followed by proteolytic release of thyroid hormones T4 and T3.
Pancreas is made up of an exocrine and endocrine portion (Y/N)
Yes
Which cell secrete insulin and glucagon?
- alpha cells of islets of Langerhans of pancreas secrete glucagon
- beta cells of islets of Langerhans of pancreas secrete insulin
Biggest risk factor for type 2 diabetes
Obesity
3Ps of acute consequences in insulin deficiency
- Polyuria (excessive urine production)
- Polydipsia (extreme thirst)
- Polyphagia (excessive appetite/ eating)
Example of microvascular complications in DM
Retinopathy, kidney failure, nerve damage
Example of macrovascular complications in DM
Stroke, heart attack, reduced blood circulation
Role of thyroperoxidase
- Catalyses oxidation of Iodide to ‘active’ iodide
- Attaches iodine to a tyrosine within Tg molecule
Is MIT/ DIT of any endocrine value? (Y/N)
No
What happens after endocytosis of colloid?
Lysosomes attack the engulfed vesicle and split the iodinated products from Tg
Role of iodinase
Removes iodine from worthless MIT and DIT, allowing the freed iodide to be recycled for synthesis of more hormone
Acute consequences of insulin deficiency
- Increased hepatic glucose output
- Decreased glucose uptake by cells
- Decreased TG synthesis
- Increased lipolysis
5, Decreased aa uptake by cells - Increased protein degradation
3 consequences of dehydration caused by insulin deficiency
- Polydipsia (excessive thirst)
- Cellular shrinkage -> nervous system malfunction
- Reduced blood volume -> peripheral circulatory failure -> low cerebral flow & renal failure -> death
