The Endocrine System Flashcards
What is the circadian rhythm?
A biological rhythm which keeps the body on a 24 hour cycle, which gets its ques from environmental stimulus.
Describe the negative feedback cycle which keeps blood osmolality under control.
The concentration of blood is detected by osmoreceptors in the hypothalamus. If the blood osmolality is high, so water needs to be consevered, the posterior pituarity secretes ADH which means more water is reabsorbed in the collecting ducts of the kidney. If blood osmolaity is low (too much water) the posterior pituarity gland secretes less ADH and less water is absorbed in the collecting ducts of the kidney, so lots of urine of low concentration is produced.
What is a hormone?
A chemical signal produced in endocrine glands that travel in the bloodstream to produce an affect on target tissues.
What are the different mechanisms of communication using hormones?
Endocrine, having affects on a tissue a long way away, autocrine where the hormone acts of the cell of origin, neurocrine, hormone is transported down an axon before being realised in the blood stream and paracrine, where the hormone signal works on adjacent cells.
What are the different classes of hormone?
Steroid hormones, peptide hormones, amino acid derivatives and glycoproteins.
How can hormones be transported?
In solution or attached to a specific protein.
How does being attached to a specific protein affect hormone transport?
There is a dynamic equibilbrum between bound and non bound hormones, and only the non-bound free forms are biologically active.
What is the role of a carrier protein?
Increase the solubility of a hormone, increase the half life of a hormone.
How do water soluble hormones have an effect on target cells?
There is a g protein couple, and then assoication of a g protein subunit, activation of a protein inside the cell such as cAMP and formation of a secondary messenger, and activation of a protein kinase and phosphorylation of the target protein.
How does a lipid soluble protein have an effect on target cells?
These diffuse across the plasma membrane, in type 1 the hormone binds to a cytoplasmic receptor and the receptor hormone complex enters the nucleus and binds DNA. Type II enters nucleus and binds to a pre-receptor on DNA, which binds to a specific DNA sequence called a hormone responder element.
What does the hypothalamic pituarity axis consist of?
Posterior and the anterior piturity gland.
What is the relationship between the hypothalamus and the posterior pituarity gland?
The hypothalamus is physically connected to the posterior pituitary gland, and it has a neurocrine function where hormones travel down from the hypothalamus and then are reales from the posterior pituarity gland, such as ADH and oxytocin.
What is the function is the anterior pitaurity gland?
Hormones are synthesised in the hypothalamus, transported down axons, released into the hypothalamus capillary system and then used to stimulate the endocrine cells of the anterior pitaurity gland to produce hormones.
What is negative feedback?
The response is to reverse the direction of change.
Where is appetite controlled from?
The arcuate nucleus in the hypothalamus, at the appetite and satiety centre of the hypothalamus.
What are the two sets of neurones involved in controlling appetite?
Inhibitory neurones, which inhibit appetite and contain hormones such as POMC which yields several hormones such as a-MSH and b-endorphin. There are also stimulatory neurones, which yeild hormones such as neuropeptide Y (npy) and augoti folded peptide AGRp which promote hunger.
What is the action of ghrelin?
This is a peptide hormone released from the stomach wall when hungry, and it stimulates the excitatory primary neurones in the acurate nucleus.
What is the function of PYY (peptide tryosine tyrosine)
It is a short peptide released by cells in the colon and ileum in response to feeding, and it inhibits excitatory primary neurones and stimulates inhibitory primary neurones.
What is the action of the hormone leptin?
This is a peptide hormone released by adipocytes that inhibits excitatory hormones and stimulates inhibitory neurones.
What is the action of amylin?
This is a peptide hormone secreted by B cells in the pancreas, mechanism not understood but it does suppress appetite. Has been used as a drug to treat type two diabetes.
Define metabolic syndrome:
The cluster of most recognisable risk factors associated with cardiovascular disease, such as disilpidemia, abdominal obesity, high blood pressure, insulin resistance, raised fasting glucose.
What are the some of the key features of the islets of langerhans?
Endocrine region of the pancreas, about 0.25mm in size, containing 6,000 cells (the pancreas contains about 1000 islets of langerhans). The major cells are b-cells that contain about 75% of the total cell number and secrete insulin, the secondary cells are a-cells which produce glucagon.
What are the features of a and b cells in the islets of langerhans?
Extensive rough er, well defined Golgi apparatus, many mitochondria and well defined mircotubules and mircofiliaments.
What are the key features of the structure of insulin?
Contains 2 polypeptide chains, an a and b chain. The two chains are connected by two disuphide bonds between cysteine residues and there is a 3rd disuphide bond within the a chain.
