Lecture 22: Homeostasis & The Endocrine System Flashcards
Define homeostasis
Maintaining a relatively constant internal environment that differs to the external environment and remains constant even when there are environmental changes
What is the negative feedback system and what are the components?
A mechanism by which animals that regulate internal environments achieve homeostasis
It is a loop that detects a change that triggers a response to REDUCE the stimulus
- set point
- stimulus
- sensor
- control center
- effector
- response
Describe the set point of a negative feedback system
a variable maintained near a particular value
ex. body temperature at 37 degrees celsius
Describe the stimulus of a negative feedback system
anything that fluctuates the variable above or below the set point
ex. a change in salinity
Describe the sensor/receptor of a negative feedback system
Recognizes the stimulus and sends information to the control centre
Describe the control centre of a negative feedback system
Triggers a response
ex. the hypothalamus
Describe the effector of a negative feedback system
Carries out a response
ex. muscles or capillaries
Describe the response of a negative feedback system
Whatever activity brings the variable back to the set point –> reduces the stimulus
ex. sweating to cool body temperature down
Define thermoregulation
The process by which animals maintain an internal temperature within an optimum range that can differ from the external environment
Define endotherms and ectotherms - give examples of animals
endotherms: use internal metabolism to produce heat to maintain body temperature
- ex. birds and mammals
ectotherms: have body temperatures that are determined by external conditions
- ex. amphibians, reptiles (not birds), most fish, invertebrates
Describe the steps of the negative feedback loop of thermoregulation for body temperature increase
- set point/homeostasis: internal body temperature around 37 degrees C
- stimulus: body temperature increases above set point
- sensor/receptor: warm temperature receipts detect stimulus and signal the thermostat in the hypothalamus
- control centre: hypothalamus triggers a response in the effectors
- effectors:
- blood vessels/capillaries in skin dilate to fill with blood and bring to skin surface so heat can radiate out of body
- sweat glands secrete sweat to evaporate out of body –> cools body - response: sweating and heat loss reduce body temperature (stimulus) back to the set point and stops the loop
Describe the steps of the negative feedback loop of thermoregulation for a body temperature decrease
- set point/homeostasis: body temperature around 37 degrees C
- stimulus: body temperature decreases below set point
- receptors: temperature receptors detect stimulus and signal thermostat in hypothalamus
- control centre: hypothalamus activates warming mechanisms in the effectors
- effectors:
- skeletal muscles contract rapidly to cause shivering and generate heat
- blood vessels in skin contract to reduce heat loss through surface - responses: muscle contractions and capillary contractions reduces stimulus by increasing body temperature to set point and stopping the loop
Describe the endocrine system
A system that regulates the body by short- and long-distance CHEMICAL signalling between cells and organs
define hormone
Molecules that function as chemical signals that are secreted by the endocrine system (usually an endocrine gland) that circulate throughout the body in the blood in order to trigger a response
define target cells
cells that have the specific receptor molecules to which a hormone binds and can respond to the signal
some target cells can have receptors for multiple hormones
define endocrine gland and distinguish it to an exocrine gland
Endocrine glands are DUCTLESS glands that secrete hormones directly into interstitial fluid surrounding cells.
- ex. adrenal glands, pituitary glands
Whereas,
Exocrine glands have ducts and secrete substances OUT of the body (through digestive tract or surface).
- ex. sweat glands, salivary glands, mammary glands, the pancreas
How does the hypothalamus interact with the anterior and poster pituitary glands
The hypothalamus receives information from nerves throughout the body and responds by initiating appropriate endocrine signals that travel to the pituitary gland
What is the posterior pituitary glands role?
the PPG is an extension of the hypothalamus that stores hormones produced by the hypothalamus
It receives hormones from neurosecretory cells of the hypothalamus that trigger the PPG to secrete the stored hormones in response to a nerve (electrical) impulse sent from the hypothalamus
Which 2 hormones are released from the posterior pituitary gland?
Antidiuretic Hormone: sent to the kidneys
Oxytocin: sent to the mammary glands and uterine muscles
What is the anterior pituitary glands role?
synthesizes and secretes its own hormones in response to a hormonal signal from the hypothalamus.
Many of the hormones synthesized by the APG regulate the function of other endocrine glands or cells
Describe the function of the pancreas, what are the main hormones produced by it?
The pancreas is an endocrine gland that functions in GLUCOSE HOMEOSTASIS by responding to blood glucose levels by releasing a hormone into the blood
- insulin
- glucagon
Describe the function of the thyroid glands
releases hormones regulating - blood pressure
- heart rate
- muscle tone
- digestive functions
- reproductive functions
describe the function of the adrenal glands, what are the main hormones produced by it?
releases stress hormones (epinephrine and norepinephrine)
to trigger fight or flight responses (related to the sympathetic nervous system)
Describe the role of ADH
released by the Posterior pituitary gland in response to high salt concentration in the bloodstream via an electrical signal from the hypothalamus. This occurs when there is too much water loss and a high salt concentration in the blood. It is sent to the collecting duct of the kidney to increase the permeability of the collecting duct to reabsorb more water and reduce further water loss.
Describe the role of oxytocin
A hormone secreted by the posterior pituitary gland when the hypothalamus releases an electrical impulse to send it to the mammary glands to produce milk when a baby suckles the nipple
- also sent to the uterine muscles to contract during child birth
- works on a positive feedback system –> more suckling = more milk
Describe how the negative feedback system works for an increase of blood glucose levels
stimulus: blood-glucose levels increases above the set point (high blood glucose levels)
receptor/control centre: the pancreas receives the information and releases the hormone signal
hormone signal: insulin is released by the pancreas into the bloodstream to bind to a target cell
effectors:
large cells in the liver trigger a response
response: the liver takes up glucose and converts it into glycogen to be stored in the liver
the blood glucose levels will drop back to set point and reduce the stimulus and stop the feedback loop.
Describe how the negative feedback system works for an decrease of blood glucose levels
stimulus: blood glucose levels decrease below set point (low blood glucose levels)
receptor/control centre: the pancreas receives the information of stimulus and releases the hormone signal
hormone signal: glucagon released by the pancreas into the bloodstream
glucagon binds to target cells in the liver (effector) to trigger a response
response: the liver breaks down the stored glycogen into glucose and releases it into the blood stream to increase blood glucose levels –> decreasing the stimulus and stopping the feedback loop.
What happens to human blood if the blood-glucose levels are too high?
Glucose can coat the red blood cells, creating a thick viscous liquid, and damage the blood vessels
What happens to humans if blood-glucose levels are too low?
Cells do not receive enough sugar to do cellular respiration and produce ATP so they cannot function properly to produce energy for work
Describe glucose and glycogen
Glucose is the sugar molecule that circulates in the bloodstream
Glycogen is a collection of sugar molecules bonded together by the liver and stored in the liver when there is sufficient glucose in the bloodstream
What is the liver’s function in blood glucose level regulation
The liver interconverts glucose and glycogen when triggered by the pancreas to do so
Glucose too high:
glucose –> glycogen –> stored in liver
Glucose too low:
glycogen –> glucose –> circulates in blood
Describe glucagon and insulin
Insulin is a hormone released by the pancreas to trigger the liver to take up glucose and convert it into glycogen
glucagon is a hormone released by the pancreas to trigger the liver to break down glycogen into glucose
