Chapter 5.1 Homeostasis ✓ Flashcards
Define Homeostasis
The process of keeping the environment inside the body fairly constant
What aspects of the internal environment that the body needs to regulate to maintain homeostasis?
-Core body temperature
-pH and concentrations of dissolved substances in the body fluids
-Concentration of glucose in the blood
-Concentration of oxygen and carbon dioxide in the blood and other body fluids
-Blood pressure
-Concentration of metabolic wastes
Define feedback loop
A circular situation in which the body responds to a change, or stimulus, with the response altering the original stimulus and thus providing feedback.
What are the two types of feedback loops?
Positive
Negative
Define stimulus
Any change, internal or external, that causes a response
Define receptor
A structure that detects a stimulus
Define modulator
A control centre responsible for processing information received from a receptor and for sending information to the effector.
Define effector
The effector carries out a response counteracting or enhancing the effect of the stimulus
In order, draw a feedback loop
-Stimulus: A change occurs in the environment
-Receptor: The stimulus is detected by sensory cells
-Message: Sensory cells generate a message in the form of a nerve impulse or hormone
-Modulator: A control centre processes the message received from the receptor
-Message: A new message is sent out by the modulator
-Effector: Muscles or glands receive the message from the modulator
-Response: The effector organs bring about an appropriate reaction
-Feedback: The response changes the original stimulus
What systems control homeostatic mechanisms?
Endocrine system and the Nervous system
Define negative feedback
Feedback that reduces the effect of, or eliminates, the original stimulus
What is another word for homeostasis?
Steady state
What is another word for negative feedback system?
Steady state control system
Define dynamic equilibrium
A state reached when the rates of the forward and reverse changes are equal
Define set point
In a feedback system, the level at which a variable is to be maintained
Define tolerance limit
The limit of factors such as temperature and fluid balance which the body malfunctions
Define positive feedback
Feedback that reinforces the original stimulus
Does positive feedback have a role in homeostasis?
no
What are examples of positive feedback?
Childbirth
Blood clotting
Describe how childbirth is positive feedback and describe the positive feedback system for childbirth
-Childbirth is positive feedback because it is a process that must be completed quickly to avoid stress and injury to the mother and child
-Labour is initiated by the secretion of the hormone oxytocin for the posterior lobe of the pituitary gland.
-Oxytocin causes contractions of the uterus
-The contractions push the baby’s head against the mothers cervix
-Stimulation of the cervix causes it to send nerve impulses to the brain, which responds by instructing the pituitary gland to secrete more oxytocin
-The increased oxytocin makes the uterus contract more strongly
-These contractions push the baby’s head more forcibly against the cervix, which sends even more impulses to the brain, and so the uterine contractions are increasingly intensified.
-Once the baby is delivered, the cervix is no longer stretched; it ceases sending nerve impulses to the brain and the positive feedback cycle stops.
Explain why a positive feedback system would not achieve homeostasis?
-It would not achieve homeostasis because it amplifies changes in the internal environment instead of counteracting them.
-Positive feedback moves the system further away from the set point
Explain the difference between set point and tolerance limit
Set point is the ideal or normal value that the body tries to maintain for a specific variable (e.g. temp)
Tolerance limits is the range of values around the set point which the body can still function normally
Draw a flow chart when you are over hydrated
Stimulus
-Increase in water concentration (decrease in blood osmolarity)
Receptor
-Osmoreceptors in hypothalamus detect the decreasing osmolarity.
-Baroreceptors in blood vessels detect an increase in blood pressure (blood volume increases with an increase in water concentration
Message
-Hypothalamus send a nerve impulse to the posterior pituitary gland to control ADH
-Baroreceptors sends signals to the adrenal cortex
Modulator
-ADH (antidiuretic hormone) decreases which reduced water reabsorption at kidneys
-Aldosterone decrease which decrease Na+ Reabsorption
Effector
-Collecting ducts are less permeable
-Distal convoluted tubules excrete Na+ and water
Response
-More dilute urine is produced
-Blood volume and pressure decreases
Feedback
-Negative feedback to decrease the water concentration
-ADH and aldosterone levels return to normal
Draw a flow chart when you are dehydrated
Stimulus
-Decrease in water concentration (increase in blood osmolarity)
Receptor
-Osmoreceptors in hypothalamus detect an increase in osmolarity
-Baroreceptors in blood vessels detect a decrease in blood pressure (blood volume decreases with decreased water concentration)
Message
-Hypothalamus sends nerve impulse to the posterior pituitary gland to control ADH (antidiuretic hormone)
-Baroreceptors sends signals to adrenal cortex
Modulator
-Posterior pituitary gland increases the secretion of ADH
-Adrenal cortex increases the secretion of aldosterone
Message
-ADH increases water absorption at kidneys
-Aldosterone increases which increases Na+ reabsorption
Effector
-Collecting ducts are more permeable
-Distal convoluted tubules reduced Na+ and water loss
Responce
-More concentrated urine is produced
-Blood volume and pressure increases
Feedback
-Negative feedback to increase water concentration
-ADH and aldosterone levels return to normal
