chapter 12: homeostasis Flashcards
what is homeostasis?
- the maintenance of a constant internal environment
with a stable environment, homeostasis allows…
an organism to be independent from changes in the external environment
why do body temperatures have to be kept constant?
- enzymes in our body may only work in a certain range of temperature
> changes in temp can cause enzymes to be inactive or denatured
> high fevers can be fatal
why must tissue fluid be kept at a constant pH and water potential?
- drastic changes in the pH value may affect enzymes reactions in cells and harm your body
- water potential also affects cells
describe the negative feedback process.
- if the system is disturbed
- your body reacts to bring about an opposite effect to the changes detected
>it sets in motion a sequence of events that tends to restore the system to its original state
in a negative feedback loop, there must be:
- a norm to be mantained
- a stimulus: a change in the internal environment
- a receptor: to detect the stimulus and sends signal to the control centre
- a corrective mechanism: bring about the reverse effect of the stimulus
- a feedback to the receptor when the set point is reached which causes the corrective mechanism to stop
what are the examples of homeostasis in humans?
(pg 244-246)
- regulating body temperature
-regulating blood glucose concentration
-regulating water potential
what happens when blood glucose level rises above the normal level?
(pg 244)
blood transports insulin to the liver and muscles
- stimulus- the blood glucose conc rises above normal
- receptor- the islets of Langerhans in the pancreas are stimulated
- corrective mechanism: islets of Langerhans secrete insulin into the bloodstream
- blood transports insulin to liver and muscles
* insulin increases the permeability of the cell surface membrane to glucose
> glucose absorbed into the cells more quickly
*insulin causes liver and muscles to convert excess glucose into glycogen and is stored in the liver and muscles - blood glucose conc decreases
> provides a feedback to the receptor to
> reduce insulin production (corrective mechanism stops)
> back to the normal set point
what happens when blood glucose level fall below normal level?
- stimulus: the blood glucose conc falls below normal level
- receptor: the islets of langerhans (in pancreas) are stimulated
- corrective mechanism: the islets of langerhans secrete glucagon into the bloodstream
- blood transfers glucagon to the liver and muscles
>converts stored glucagon back into glucose
- from the liver, glucose enters the bloodstream - blood glucose conc increases
> provides feedback to the receptor to decrease the glucagon production
> back to normal
what happens when the water potential of blood is higher than normal?/
- stimulus: water potential of blood increases
- receptor: the hypothalamus is stimulated
- corrective mechanism:
- less ADH is released by the pituitary gland into the bloodstream
- less ADH is transported to the kidneys
- the cells in the walls of the collecting ducts becomes less permeable to water
- less water reabsorbed into the bloodstream
- more water excreted
- urine is more diluted
- more urine produced - water potential decreases
> feedback to the recepter
> back to normal!
describe what the blood vessels ( capillaries and arterioles) do.
( structures involved in temperature regulation)
- blood vessels are present in the dermis
- CONSTRICTION and DILATION of arterioles is caused by the contraction muscles in the arteriole walls
> which help to regulate body temp - dilation of arterioles > VASODILATION
> more blood is sent to the capillaries in your skin
[ more heat is loss from convection, conduction and radiation] - constriction of arterioles> VASOCONSTRICTION
> reduces the amount of blood flowing through the capillaries in the skin
describe the formation of hair.
( structures involved in temperature regulation)
- hairs are produced by the epidermis and are embedded in the dermis
- the malpighian layer of the epidermis sinks into the dermis to form a hollow tube called the HAIR FOLLICLE
> each hair grows inside the hair follicle - at the base of the hair follicle is the mass of tissue called
> HAIR PAPILLA
> which contains blood capillaries and nerves
> it is covered with epidermal cells that constantly divide, pushing new cells outwards
> cells pushed outwards gradually die and harden to form hair
-hair erector muscles are attached to the hair follicles and when the muscles contract
> hairs stand on their ends
what are sweat glands?
( structures involved in temperature regulation)
- each sweat gland is a coiled tube formed by the downgrowth of the epidermis
> forms a tight knot in the dermis and is surrounded by many blood capillaries - secreted sweat flows through the sweat DUCT to a sweat PORE that opens at the skin surface
> secreted sweat is made up of water and contains dissolved salts and small amounts of urea
> skin considered an excretory organ
what are sensory receptors?
( structures involved in temperature regulation)
- the structure in the body that detect changes in the environment
- nerve endings in the skin are sensory receptors
> enable us to sense pain, pressure and temperature changes in the external environment - receptors that detect temperature changes are called
> THERMORECEPTORS
how does your body produce and gain heat?
(temperature regulation)
- metabolic activities (eg. cellular respiration) produces heat
- high levels of cellular respiration takes place in liver and muscles
> a large amount of heat is released in these organs
> heat distributed around the body via the bloodstream
body can gain extra heat through:
- vigorous muscular exercise
- the consumption of hot food
- being in warm environments
how does your body lose heat?
- through skin by radiation, convection and conduction (limited extent)
- by the evaporation of water in sweat from the surface of your skin
- in the faeces and urine
- in the air that is exhaled
what are shunt vessels? and how do they work?
- connect skin arterioles with skin venules
> control the amount of blood flowing through the skin capillaries
> affect the heat loss through skin surface - when shunt vessels constrict, more blood flows to the skin surface
> greater heat loss - when shunt vessels dilate, less blood flows to the skin surface
> less heat loss
what are the changes to the human body when the temperature rises?
the rise in blood temperature is detected by the hypothalamus causing it to send out nerve impulses to the relevant body parts to bring out changes:
-dilation of arterioles in the skin and the constriction of the shunt vessels
> allow more blood to flow through blood capillaries in your skin
> allows more heat to be lost through your skin by radiation, convection and conduction
- sweat glands become more active > more sweat produced
- more water evaporated from the surface of your skin, more latent heat of vaporisation is lost from your body
- decreased metabolic rate to reduce the amount of heat released within your body
what are the changes in the human body when the temperature falls?
the drop in blood temperature is detected by the hypothalamus causing it to send out nerve impulses to the relevant body parts to bring out changes:
- constriction of your skin arterioles and dilation of shunt vessels so that less blood flows through the blood capillaries
> reduces the heat loss by radiation, convection and conduction - sweat glands become less active > less sweat produced
- less water in sweat evaporates from the surface of your skin
> less latent heat of vaporisation is lost from body - increased metabolic rate to increase the amount of heat released within your body
when the reactions are not sufficient:
- shivering ( a reflex contraction of body muscles) occurs
- this SPASMODIC contraction of the skeletal muscles increases the amount of heat released and helps to raise your body temp to normal
