The Endocrine System Flashcards
Draw a diagram to explain thermoregulation
What are the benefits of an increase in body temp?
Pyrogens change the set point to a higher level resulting in fever. This:
– Inhibits bacterial growth
– Speeds up metabolic reactions
– Increases delivery of wbcs to infection sites
Draw a diagram to show the homeostatic control of blood pressure
To increase BP, HR increases and vasoconstriction occurs
To decrease BP, HR decreases and vasodilation occurs.
In hypertension, the sensitivity of the baroreceptors are reset
Draw a diagram to show cortisol concentration control
Cortisol wakes us up in the morning and its levels decrease at night- so its controlled by circadian rhythm (body clock)
Stress also alters the set point to produce more cortisol
How is uterine contractions during Labour an example of positive feedback?
In labour oxytocin is released from posterior pituitary network
stimulates contraction of uterine muscles
Cervix dilates and activate stretch receptors
Action potentials signal to hypothalamus. This stimulates further release of oxytocin
Give the major endocrine glands and their secretions
HYPOTHALAMUS: Releasing & inhibiting hormones
PITUITARY GLAND: works w hypothalamus in concert
Anterior lobe: trophic hormones
Posterior lobe:oxytocin & vasopressin (ADH)
THYROID GLAND: Thyroxine, tri-iodothyronine
PARATHYROID GLAND - Parathyroid hormone
ADRENAL GLAND
Cortex: Cortisol, aldosterone
Medulla: Adrenaline/noradrenaline
GONADS - Oestrogens, androgens, progestagens
PANCREAS - Insulin, glucagon
Describe the types of signalling mechanisms in the endocrine system
Define four major classes of hormone
peptide hormones- eg pituitary and hypothalamic hormones. Fast acting- half life is in mins. Does not need to bind to plasma proteins unlike the other hormone types Steroid hormones (derived from cholesterol) eg cortisol aa derivatives (tyrosine/tryptophan) eg Adrenaline, NA Fatty acid derivatives- eg prostaglandins
What are neurosecretory cells?
Neurosecretory cells: nerve cells that produce and secrete hormones eg:
Magnocellular neurones in the hypothalamus synthesise and release posterior pituitary hormones
Other neurosecretory cells in the hypothalamus inc parvicellular hormones
Draw a diagram to explain Glands controlled by the hypothalmic-pituitary axis
TSH, ACTH, LH, FSH are all peptide hormones. Peptide hormones will signal to other endocrine glands and endocrine cells which produce steroid hormones
Disorders of the endocrine system arise due to…
Excess or deficiency
Impaired synthesis
Transport and metabolism of hormones
Resistance to hormone action- eg malfunctioning receptor
How are peptide and protein hormones formed?
Peptides and proteins are water soluble, made from large precursor molecules (prohormones)
Transcription of DNA to RNA
Post-transcriptional processing: RNA forms mature RNA. Hay changes to 3’ and 5’ ends, excision of introns
Translation of mRNA into protein
Post-translational processing: cleavage of large pre-prohormone, protein folding, glycosylation
Synthesis of large precursor proteins forms active hormone. What is the difference between a pre prohormone and a prohormone?
Synthesis of large precursor proteins forms active hormone
How are steroid hormones synthesised from cholesterol?
Cholesterol bound to sterol carrier protein is transported to mitochondria. StAR protein transports cholesterol to inner mitochondrial membrane
Cholesterol forms pregnenolone by side chain cleavage enzyme, P450scc
Between mitochondria and sER steroids synthesised by hydroxylase enzymes
Draw a diagram to demonstrate simplified steroid synthesis
Describe and explain the synthesis of thyroid hormones
- Active uptake of iodide into follicular cell
- Oxidation of iodide to iodinating intermediate by thyroid peroxidase which is activated by H2O2
- Iodination of tyrosine residues of thyroglobulin and apical-colloid interface
- Storage of T3 and T4 in colloid in the follicular cell
- Uptake of thyroglobulin droplets into follicle cell
- Release and secretion of T3 and T4 stimulated by TSH
Describe the hormone action of peptide hormones
Peptide and protein hormones
Water soluble so act on cell surface receptors
Activate second messengers and/or enzymes
Cytoplasmic and nuclear effects
Signalling pathways for receptors with tyrosine kinase activity= Raf/MEK ERK pathway. PI3-Kinase/Akt pathway. JAK STAT pathway
Describe the hormone action of steroid hormones
Steroid and thyroid hormones
Lipophilic so act on intracellular receptors in cytoplasm
or nucleus. Receptors are transcription factors
Describe steroid and thyroid hormone receptors
Steroid and thyroid hormones cross cell membranes and act on intracellular receptors
Steroid hormone receptors= family of transcription factors
Different functional regions of the receptor are defined as domains - A-F
C domain=DNA binding region and is highly conserved
Both the A/B domains and E/F domains have transcriptional activity (AF-1/AF-2)
What is the C domain?
How else can hormones affect transcription?
Hormone crosses cell membrane
Heat shock protein dissociates from receptor
Hormone binds to receptor and dimerization occurs
Dimerized receptors translocate to the nucleus and to the hormone response element on the DNA
Along with other transcription factors transcription is initiated
Some receptors located within the nucleus, not the cytoplasm
Describe a disorder of protein signalling that is can be associated with obesity
Type 1 diabetes – autoimmune destruction of the pancreatic islets: absolute insulin deficiency
Type 2 – saturation of insulin receptors, insulin resistance, partial loss of insulin production (insulinopaenia) – often associated with obesity
What is metabolic syndrome?
A clustering of metabolic abnormalities –central obesity, dyslipidaemia (changes to both the HDL and LDL low density lipoprotein), insulin resistance and hypertension
What is testotoxicosis?
Activating mutation of the LH receptor – also a G-protein coupled receptor. If you have an activating mutation, you’ll have continuous activation even in the absence of a ligand
Testotoxicosis: High levels of testosterone stimulate penile growth and growth of pubic hair
Give another disorder of peptide receptor signalling
Describe disorders of steroid hormone signalling
Abnormalities in steroid synthesis. Can cause:
Aromatase deficiency in men- can’t synthesise oestrogens from androgens, no epiphyseal closure, long stature
In women: Virilisation of XX fetuses. Clitoromegaly- increased clitoral size. Ambiguous genitalia
Girls develop male-type characteristics and boys show early sexual development due to excess androgens
Describe Disorders of steroid receptor signalling
Resistance to hormone action: when you cannot respond to steroid hormones
Inactivating mutations of steroid receptors e.g. Androgen receptor (nuclear receptor)
Androgen insensitivity syndrome (AIS): when a XY genotype is resistant to male hormones (androgens). They thus have physical traits of a woman
Describe disorders of thyroid hormone signalling
Goitre – enlargement of thyroid gland, caused by hyper/hypothyroidism.
Lack of iodine in the diet leads to deficiency in T3 and T4 (hypothyroidism)
Graves’ Disease/hyperthyroidism:
Autoantibodies to the TSH receptor act on the thyroid gland, stimulating excess thyroid hormones. Can cause eye disease
OR activating mutation of the TSH G-protein coupled receptor
