Endocrine 1 Flashcards
What are the functions of the endocrine system?
- Maintain Internal Homeostasis
- metabolism
- osmoregulation - Regulate growth and morphological change
- Coordinate development
- Coordinate reproduction
- Facilitate behavioural and social interactions
Tropic and Releasing hormones
Primary function is to stimulate release of other hormones
Bilaterians
Animals with bilateral symmetry, including nematodes, insects and vertebrates who developed the internal communication system known as the endocrine system.
Locations of different endocrine glands
- Hypothalamus
- Pituitary
- Target endocrine glands (thyroid, adrenal, gonads, other tissue)
- Others (parathyroids, pancreas, adipose, others)
Starling’s definition of hormone
Chemical messengers which have to be carried from the organ where they are produced to the organ which they affect by means of the blood stream
Early description of diabetes
Describes the discharge of excessive amounts of urine
First description of the hypothalamus and pituitary
The draining route and receptacle, respectively, for mucus passing from the brain to the naopharynx
Berthold’s experiment
In one of the first endocrine experiments ever recorded, Professor Arnold A. Berthold of Gottingen that a rooster’s comb is an androgendependent structure (ca. 1849).
• Following castration, the comb atrophies, aggressive male behavior disappears, and interest in the hens is lost.
• Importantly, Berthold also found that these castration-induced changes could be reversed by administration of a crude testicular extract (or prevented by transplantation of the testes).
Brown-Sequard’s experiment
On June 1, 1889, Brown Sequard reported to Sociète de Biologic in Paris that he had increased his physical strength, mental abilities and appetite by self-injection with an extract derived from the testicles of dogs and guinea pigs
• Although never substantiated, this claim prompted huge interest the field of organotherapy, which still persists today
Claude Bernard
Claude Bernard stated that the endocrine system regulates the internal milieu of an animal. The “internal secretions” were liberated by one part of the body, traveled via the bloodstream to distant targets cells.
Starling on the mechanism of pancreatic secretion
In an anaesthetized dog, a loop of jejunum was tied at both ends and the nerves supplying it dissected out and divided so that it was connected with the rest of the body only by its blood vessels. On the introduction of some weak HCl into the duodenum, secretion from the pancreas occurred and continued for some minutes. After this had subsided a few cubic centimetres of acid were introduced into the enervated loop of jejunum. A similarly marked secretion was produced - Starling: “Then it must be a chemical reflex.” Rapidly. After a few moments the pancreas responded by a much greater secretion then cutting off a further piece of jejunum he rubbed its mucous membrane with sand in weak HCl, filtered, and injected it into the jugular vein of the animald occurred before.
Hormones
Chemical signaling molecules produced by the endocrine glands and secreted into the bloodstream. Travel in the blood to target cells close by or far away from the point of secretion.
Compare and contrast the endocrine system and the nervous system.
Both use chemical secretion to conduct information.
Mode and specificity of delivery to intended receiver greatly differ.
Nervous system: signal goes straight from sender to reciever along closed lines (axons) - rapid.
Endocrine system: signal generally in the bloodstream, only recievers with the proper reciever can recieve it. Slower.
What major players are there in the endocrine system
Endocrine glands, hormones, binding globulins, target tissues. receptors
Do endocrine glands have ducts
No
Do endocrine glands have a rich blood supply
Yes
Hormone receptors
Specific binding sites or ar in the target cell, which transduce the hormonal signal
Classical endocrine signaling
Endocrine cell releases hormones, transported in blood, recieved by target cell.
Neuroendocrine signaling
Neuroendocrine cell releases neurohormone which is transported in blood, recieved by target cell.
Autocrine regulation
Hormone released from a cell, diffuses through interstitial fluid and is received by target cell.
Paracrine regulation
Hormone released from a cell, diffuses through interstitial fluid and is received by itself.
Lactocrine regulation
Hormone in mother’s milk transported in blood and is received by target cell.
Concentration at which most hormones are present in blood and urine
10^-6 to 10^-12 M/L (million-fold range!)
Ablation
The surgical removal of tissue
Early endocrinology research
-ablation and replacement formed the basis of early bioassays
-prolactin - pigeon crop sac assay
-Gonadotropins - ovulation in rodents (the rabbit test)
-adrenal hormones - survival in addrenaliectomized animals
Problems - tedious, slow, insensitive, variable
Radioimmunoassay
Turning point in endocrine reasearch, based on competition for antibody binding by radioactive and non-radioactive hormone. Fast, inexpensive, accurate, reproducible.
Based on serendipitous observation that diabetics receiving insulin injections developed antibodies against insulin.
Rosalyn Yellow
Reaction of insulin with antibodies developed tool for measuring circulating insulin.
Hypophysectomy
Removal of pituitary
Cortin
An adrenal extract containing corticosterone
Adrenotropic
A pituitary extract containing ACTH
Experiment establishing basic principles of hypothalamic-pituitary-adrenal axis without measurement of hormone levels
Normal - no food restriction = normal combined weights of adrenal glands
Normal - food intake restricted = slightly below normal combined weights of adrenal glands
Hypophysectomy - untreated - moderatly lower combined weights of adrenal glands
Normal with 10cc cortin daily - moderately lower combined weights of adrenal glands
Adrenotropic and hypophysectomy with cortin - normal weights of adrenal glands
Adrenotropic and hypophysectomy without cortin - normal weights.
Typical RIA standard curve
As concentration of non-radioactive hormone increases, the bound:free ratio exponentially decreases. Use curve to find out the ratio knowing the bound/free ratio to figure out the displacement caused by the unlabelled sample, and figure out the conentration of non-radioactive hormone.
Solid Phase Immunometric assay
antibodies are labeled with radioisotopes which are used to bind antigens present in the specimen. When a positive sample is added to the tubes, radioactively labeled (labeled with I125 or I131 radioisotopes) antibodies bind to the free epitopes of antigens and form an antigen-antibody complex. Unbound labeled antibodies are removed by a second reaction with a solid phase antigen. The amount of radioactive remaining in the solution is direct function of the antigen concentration.
Pregnancy tests
Rely on the use of antibodies to detect the “hormone of pregnancy”, or hCG.
Western blotting advantage
Can detect
multiple isoforms of a
hormone, separated by
molecular weight
Immunocytochemistry advantage
Can localize distribution
of a hormone at tissue
and cellular level
Does phosphoylation affect antibodies?
Yes, antibodies can detect changes in phosphorylation state of the particular target protein.
Immuno-purification
The use of immunological techniques to purify proteins, antigens etc. Immobilized antibodies can be used for this.
Radioreceptor assays
Uses cognate receptor in place of antibody for detection of hormone in blood or cell lysates. Labeled hormone competes with unlabeled hormone or unknown samples for binding receptors on cell monolayers or in cell lysates. Labeled hormone (radioactive or other label; eg biotin) incubated with cell monolayers or cell homogenates, allowed to bind to receptors. Chemically cross-link to form covalent bonds.
