Lecture 7 - Endocrine principles Flashcards
Part 1
what is homeostasis and how does it differ from equilibrium
The process of maintaining a constant internal environment despite changing conditions
it is dynamic process
not to be confused with equilibrium
Homeostasis is an active process of maintaining internal stability, requiring energy and regulatory mechanisms.
Equilibrium is a passive state of balance with no net movement or change, often requiring no energy to maintain once achieved
what is the setpoint in homeostasis? what is the normal range of function for setpoints?
the value (for ex. temperature) that is required for the environment to possess for homeostasis
for ex. fish tanks should be at 29 degrees for homeostasis
- there is oscillation around the set point which is known as the normal range of function. if values exceed this +/- range between the setpoint, function can be affected
for ex. fish tanks can be 28-30 degrees (+/- 1 from 29 degrees)
- if it exceeds 30, negative feedback turns response loop off (water is too hot)
- if it drops below 28 degrees, negative feedback turns response loop on (water is too cool)
what is negative vs positive feedback
negative feedback: (stabilizing)
initial stimulus –> response –> stimulus decrease –> loop back to turn on or off the stimulus
- homeostatic
positive feedback: (reinforcing)
initial stimulus –> response –> stimulus increase (outside factor adds + feedback) –> loops back to response to generate more stimulus
- not homeostatic
example of negative feedback with regulation of cortisol secretion
no cortisol/ need to generate more
hypothalamus –> hormone –> anterior pituitary –> hormone –> adrenal cortex –> increase cortisol to the target tissue
if cortisol is increased and reaches sufficient homeostatic level –> cortisol inhibits the release of the two hormones that is used mid process
example of positive feedback loop with oxytocin and the control of uterine contractions
stimulus: baby drops lower in the uterus to initiate labour
–> cervical stretch –> oxytocin release –> uterine contractions –> push baby against cervix –> loops back to more cervical stretch etc. until baby is delivered and the cycle is done.
note this is not homeostatic
to maintain homeostasis and other body functions we require intercellular communication
what are three examples of local control/communication
- Gap junctions
- Small ions and molecules
move through gap junctions (small holes) in connecting cells - Contact dependent
when membrane molecules on cells right next to each other contact and give a signal - Autocrine / Paracrine
- Autocrine acts on same cell that secreted them
- paracrine molecules move through interstitial fluid and diffuse/bind to adjacent cells
to maintain homeostasis and other body functions we require intercellular communication
we also need long distance communication. what are two ways we can communicate with cells from a long distance ?
- nervous system
- neurotransmitters are chemicals secreted by neurons that diffuse across a small gap to a target cell
- neurohormones are chemicals released by neurons into the blood for action at distant targets that have the specific receptor - endocrine system
- hormones are secreted by the endocrine glands or cells into the blood. only target cells with receptors for the hormone respond to the signal.
what are simple and complex reflexes
Reflexes are automatic, rapid responses to stimuli that help protect the body or perform certain functions.
– Simple reflexes are mediated either by the nervous or the endocrine system
– Complex reflexes are mediated by both systems and
go through several integrating systems
* Compare neural and endocrine reflexes
explain how changes of blood pressure can be seen as a local change and a reflex control / long distance change
local change:
- if the blood pressure changes locally, the cells in the vicinity of the change will initiate a local response
long distance change / reflex control:
- stimulus: if there is a systemic change in blood pressure sensed
- integrating center: the brain evaluated the change and initiates a response
- response: reflex response is initiated by cells at a distant site
what are the reflex steps for a feedback loop in order
stimulus
sensor
input signal
integrating center
output signal
target
response
what are two types of sensors
one type has two subsections
- specialized cells or structures that convert various stimuli into electrical signals
a. central receptors are in or close to the brain (eyes, ears, nose, tongue, thermoreceptors etc)
b. peripheral receptors that lie outside the brain (chemoreceptor, osmoreceptor, barorreceptor) - cell membrane or intracellular receptor proteins
what is the reflex pathway:
simple neural reflex
vs.
complex neuroendocrine reflexes
simple neural reflex:
stimulus -> sensor -> sensory neuron -> CNS integrating center -> efferent neuron -> neurotransmitter -> target cell -> response
– uses only neuronal pathway ex. knee jerk reflex
complex neuroendocrine reflex:
stimulus -> sensor -> sensory neuron -> CNS integrating center -> neurohormone -> blood stream -> endocrine cell 1 -> hormone 1 -> endocrine cell 2 -> hormone 2 -> target cell -> response
– uses both pathways ex. in anterior pituitary
what is the difference between a simple neural reflex and a simple endocrine reflex?
in simple neural reflex you have:
- stimulus –> receptor –> input signal –> integrating center –> efferent neuron
in endocrine reflex you have:
- stimulus –> integrating center –> hormone
thus:
simple neural has an efferent neuron output
simple endocrine has a hormone output
ex. of simple endocrine reflex = insulin hormone released when blood glucose increases (stimulus)
why do you need different control systems for neural and endocrine systems?
explain the specificity, nature of the signal, speed, duration of action, and coding for stimulus intensity differences between neural and endocrine reflex.
we need different control systems because we need each system to perform a different task
specificity:
Neural reflex = Each neuron terminates on a single target cell or on a limited number of adjacent target cells.
endocrine reflex = Most cells of the body are exposed to a hormone. The response depends on which cells have receptors for the hormone.
nature of the signal:
Neural reflex = Electrical signal that passes through neuron, then chemical neurotransmitters that carry the signal from cell to cell. In a few cases, signals pass from cell to cell through gap junctions.
endocrine reflex = Chemical signals secreted in the blood for distribution throughout the body.
speed:
Neural reflex = very rapid
endocrine reflex = Distribution of the signal and onset of action are much slower than in neural responses.
duration of action:
Neural reflex = Usually very short. Responses of longer duration are mediated by neuromodulators.
endocrine reflex = Responses usually last longer than neural responses.
coding for stimulus intensity:
Neural reflex = Each signal is identical in strength. Stimulus intensity is correlated with increased frequency of signaling.
endocrine reflex = Stimulus intensity is correlated with amount of hormone secreted.
what are exocrine and endocrine glands and where do they release their substances/hormones to?
- thus which gland is responsible for hormone secretion
- hormones are derived from tissues that can deliver chemicals
- we have different glands in our body like exocrine (out-secrete) and endocrine (in-secrete) glands
- exocrine release their substances externally (into a duct or pore)
- endocrine release their hormones internally (into the bloodstream)
- hormones are secreted into the bloodstream and are thus secreted by endocrine glands
