Lec 5 Flashcards
What did A.A Berthold do in 1849?
noted that removing the testes from a developing rooster caused it to become a docile capon.
Capons lack many male-type behaviors and anatomical traits (they look more like hens).
Berthold found that if you put some other testes back into a capon, its male-type behaviors and anatomical traits would return.
Importantly, this worked even though Berthold did not re-connect the nerves. This suggested to him that the testes secreted a substance into the blood
Testosterone
What are hormones?
chemicals secreted by one cell group that travel through the bloodstream to act on targets (other organs, cells)
What are hormones released by?
Endocrine glands release hormones within the body
Exocrine glands use ducts to secrete fluids such as tears and sweat outside the body
What is synaptic/neurocrine signaling?
involves chemical release and diffusion across a synaptic cleft.
What is endocrine signaling?
hormones being released into the bloodstream to act on target tissues
what are the principles of hormone function?
- Hormones act in a gradual fashion
- Hormones act by changing the probability or intensity of a behavior (not like on/off switch)
- The relationship between behavior and hormones is reciprocal
Hormones change behaviours and behaviours change hormone levels - A hormone may have multiple effects and one behavior can be affected by several hormones
- Hormones often have a pulsatile secretion pattern – in bursts
Example: Growth Hormone (GH) shows pulsatile release during the day, higher release at night, and maximum levels during puberty.
Example: estrogen and progesterone show changes over the roughly month long menstrual cycle. - Some hormones are controlled by circadian clocks
- Hormones can interact with other hormones and change their effects
E.g., cortisol can affect levels of luteinizing hormone, ghrelin
How are hormonal and neural signaling the same?
Neurons and endocrine glands produce and store chemicals (neurotransmitters or hormones) and release them upon stimulation.
Neurotransmitters and hormones both bind to receptors to stimulate target cells.
Some chemicals can act as either hormones or neurotransmitters, depending on where they are released.
For example: norepinephrine is a neurotransmitter associated with alertness in the CNS, but it is also a hormone released by the adrenal glands under conditions of stress or anxiety.
How are hormonal and neural signaling different?
Neural communication travels to precise destinations. Hormonal communication spreads throughout the body, and is picked up by cells with the proper receptor
Neural messages are rapid, measured in milliseconds. Hormonal messages are slower, measured in seconds and minutes
Distance traveled varies – the synaptic cleft is small while hormones may travel over a meter
Neural communications are sometimes under voluntary control, while hormones are involuntary
How are hormones classified?
Classified on basis of chemical composition, not function
What are the different classes of hormones?
- Peptide/Protein hormone – a string of amino acids
E.g., Insulin - Monoamine hormones – a modified amino acid, found in brain as neurotransmitters as well
E.g., norepineprine - Steroid hormones – four rings of carbon atoms
E.g., testosterone
How do hormones bind to cells?
Rather than affecting the membrane potential, when hormones bind to their receptors they trigger the release of intracellular second messengers.
Hormones are considered first messengers
These second messengers spread throughout the cell and cause a variety of physiological changes.
Changes in metabolism, hormone release, receptor trafficking, cell growth, etc.
Second messenger mediated effects inside the cell are rapid.
What are the effects of steroid hormones on cells?
Steroid hormones (like testosterone, estrogen, cortisol, etc.,) are all made from cholesterol, a fatty substance. Consequently, steroid hormones are lipophilic and can easily pass through the cell membrane.
Steroid hormone receptors are inside the cell, usually floating freely within the cytoplasm.
The steroid-receptor complex binds to DNA and acts as a transcription factor – controlling gene expression.
Transcription factor mediated mechanisms are slow, however their effects are long-lasting.
These mechanisms usually take hours to kick in.
What are the effects of hormones on organs?
Hormones may promote proliferation, growth and differentiation of cells.
Example: Growth hormone promotes growth of the long bones (during childhood and adolescence).
Hormones may modulate cell activity and metabolism.
Example: Insulin increases glucose uptake by muscle, fat, and liver.
Example: Thyroid hormones increase glucose and fat metabolism in all tissue.
Hormones may modulate hormone secretion from endocrine glands.
Example: ACTH causes the release of cortisol from the adrenal glands.
Example: Negative feedback.
What is the hierarchy of hormones?
- hypothalamus: in response to sensory stimuli and cognitive activity, the hypothalamus produces neurohormones that enter the anterior pituitary through veins and posterior pituitary through axons
- Pituitary gland: on instructions from these releasing hormones, the pituitary sends hormones into the blood stream to target endocrine glands
- Endocrine gland: release their own hormones that stimulate target organs, including the brain
- Target organs and tissues
Hormones affect _____________________
almost every neuron in the brain; Can also influence genetic expression, synthesis of proteins
