Homeostasis And Endocrine System Flashcards
What is the role of the control centre in a control system?
In a control system, the control centre is responsible for setting a limit for which a variable must be maintained within, and then sending signals to effector organs to maintain this.
What is the afferent pathway?
This is the pathway from stimulus to control centre.
In a control system, what is the name of the pathway from control centre to effector organ?
Efferent.
What is a circadian rhythm?
This is the 24 hour pattern of a control system as its parameters vary with time.
What nucleus is the biological clock in the brain?
Superachiasmalic
Name the five zeitgebers which help to keep our biological clock:
Light, temp, social interaction, eating, exercise.
Name the hormone which maintains the biological clock.
Melatonin.
What are the three main compartments of water in the body?
Extracellular fluid, intracellular fluid, blood plasma.
Where is osmotic pressure of the blood measured?
It is measured by osmoreceptors in the hypothalamus.
What is the difference between osmolality and osmolarity?
The first is the number of moles in a litre of solution and the second is the number of moles in a kilo of solution.
What hormone is used to control blood osmolarity and where does this act?
ADH. This is secreted by the pituitary and acts on the kidneys to increase or decrease reabsorption.
How does the body respond if blood osmolarity is high?
If blood osmolarity is high this is detected by osmoreceptors in the hypothalamus. This sends a signal to the pituitary to secrete ADH which leads to increased reabsorption of water in the kidneys. Osmoreceptors also stimulate thirst.
Explain why someone may have very dilute urine.
If someone has low blood osmolarity, then osmoreceptors in the hypothalamus will send a signal to the pituitary to decrease ADH secretion. This means that less water will be reabsorbed in the kidney and so urine is dilute.
What is the endocrine system?
This is a collection of glands throughout the body which secrete hormones into the blood stream to effect other tissues.
What is it called when a hormone signal acts upon the cell it was secreted from?
Autocrine
What does paracrine mean?
Paracrine is when a hormone signal acts on a cell after traveling a short distance through interstitial fluid.
What is neurocrine?
This is where a signal is carried down an axon into the bloodstream
How are nervous signals conveyed?
Via axons and synapses.
How does the speed of endocrine and nervous signals vary?
Endocrine signals are slow and nervous signals are fast.
What are the four different types of hormones?
Polypeptide, amino acid derivatives, steroids and glycoproteins.
Give examples of glycoprotein hormones.
LH, FSH, TSH. These are large, water soluble protein molecules with carbohydrate side chains.
What type of hormone are Insulin, Glugacon and Growth Hormone?
These are polypeptide hormones. They are water soluble and made from short amino acid chains.
Are amino acid derivatives hormones soluble?
Some are. They are all derived from tyrosine. Adrenaline and noradrenaline from the adrenal medulla are both water soluble, whilst thyroid hormones are lipid soluble.
What is a steroid hormone derived from?
Cholestrol.
Explain what a biologically active hormone is?
This is a hormone which is in its free (unbound) form in the blood and not bound to a carrier protein.
State three useful properties of carrier proteins.
They increase hormone solubility in plasma, they increase half life and they allow a hormone reserve to be maintained.
State what factors can affect hormone concentration in the blood.
Rate of hormone synthesis/secretion, rate of delivery and rate of degradation.
Name the two water soluble hormone cell surface receptors.
G protein coupled receptor, tyrosine kinase.
Explain the action at a G protein coupled receptor.
The alpha subunit dissociates which leads to activation of the effector protein and a second messenger leads to protein kinase activation. This phosphorylates the target protein and activates a cellular response.
How does tyrosine kinase cause a cellular response?
Dimerisation followed by auto phosphorylation of specific tyrosines. Adapter proteins and the signalling complex are recruited leading to protein kinase activation. Phosphorylation of target protein activates cellular response.
Where can lipid soluble hormones act?
Lipid soluble hormones can cross the plasma membrane so these act within the cell, either in the cytoplasm or in the nucleus.
What happens when a lipid soluble hormone binds to a cytoplasmic receptor?
This forms a complex which enters the nucleus and binds to DNA.
What do lipid soluble hormones bind to when they enter the nucleus?
They bind to pre bound receptor on DNA. This relieves the repression in transcription. Receptors are generally found in promoter regions for different genes.
Which part of the pituitary gland is connected to the hypothalamus?
Posterior.
What hormones are produced in the hypothalamus but then pass down neurones to the posterior pituitary?
Oxytocin (milk let down and uterus contractions)
Antidiuretic hormone. ADH responsible for osmotic balance.
What is meant by the neurocrine function of the posterior pituitary?
Hormones synthesised in the hypothalamus pass down axons to the posterior pituitary where they are stored and then released to act on target tissues.
How are cells of the anterior pituitary stimulated?
Neurocrine signals from the hypothalamus.
What is the hypophyseal portal system?
This is a series of blood vessels which hormones produced in the hypothalamus pass through to stimulate the anterior pituitary.
What type of hormone secretion occurs in the anterior pituitary?
Endocrine cells secrete hormones into the blood stream, but also Autocrine and paracrine secretion occurs which affects neighbouring cells.
What is a tropic hormone?
These are produced in the hypothalamus and act on the anterior pituitary.
What is the name of the hormone released from the hypothalamus to stimulate release of TSH from the pituitary?
TRH thyrotropin releasing hormone.
What does Corticotropin releasing hormone (CRH) leads to release of from the pituitary? Where does this act?
ACTH which leads to secretion of cortisol from the adrenal gland.
What is the name of the hormone which controls lactation of the mammary glands?
Prolactin, secreted by the pituitary. This is activated by PRH from hypothalamus and inhibited by PRIH.
What two hormones secreted by the hypothalamus act on the pituitary to control growth hormone release?
GHRH, GHIH.
What is the function of GnRH (Gonadotropin releasing hormone)?
This is released from the hypothalamus and acts on the pituitary to control release of FSH and LH.
What are the two possible forms of communication in a control system?
Nervous or Endocrine.
