3. Homeostasis Flashcards
Homeostasis
Definition
Homeostasis is the maintenance of a constant internal environment within tolerable limits.
Importance of Homeostasis
Homeostasis is required to achieve a certain degree of independence from the external environment, so that the internal environment is maintained in an optimal condition and a state of maximum efficiency.
It is important for optimal functioning of physiological processes as well as component cells, tissues, organs, and organ systems.
5 Factors Controlled by Homeostasis
- Temperature
- Blood water potential, water content in urine
- Blood pressure
- Blood pH, blood CO2 concentration
- Blood glucose concentration
These are only some of the factors controlled by homeostasis.
Negative Feedback
Describe
When normal conditions are restored, a negative feedback is sent back to the control centre to prevent further corrective actions.
Negative Feedback Mechanism
- Stimulus - change from normal conditions in the internal/external environment
- Receptor detects the stimulus and sends signal to the control centre
- Control centre coodinates information from receptors and sends out signals to effectors to correct the deviation
- Corrective mechanism brings out the reverse effect of the stimulus
- Negative feedback is sent to the control centre when the normal condition is restored
- Stops corrective mechanism
Mnemonic: “sneaky rabbits chew carrots non stop”
Describe how the hypothalamus coordinates the maintenance of a constant body temperature.
- When there is a change in external/internal temperature beyond the normal conditions (stimulus),
- thermoreceptors in the skin/hypothalamus detect the stimulus, and send nerve impulses to the hypothalamus, the control centre.
- The hypothalamus sends nerve impulses to effectors such as liver, arterioles in the skin, sweat glands, skeletal muscles, and hair erector muscles,
- to carry out corrective actions to counteract the change.
- Once body temperature returns to normal, thermoreceptors in the hypothalamus detects this, and sends a negative feedback to the hypothalamus to
- stop further corrective actions.
Mnemonic: “sneaky rabbits chew carrots non stop”
Describe the changes that occur when there is an increase in internal temperature.
- Metabolic rate decreases by decreasing rate of aerobic respiration by mitochondria, releasing less heat (in liver).
- Arterioles in the skin dilate (Vasodilation), increasing blood flow to capillaries near the skin surface, increasing heat loss to surroundings through conduction, convection and radiation.
- Sweat glands become more active, causing sweat production to increase. More water in sweat evaporates, hence more latent heat of vaporisation is removed from body.
- (no shivering)
- Hair erector muscles relax, hair shafts flatten and allow free circulation of air over hairs. Moving air conducts heat away from body. (not significant in humans)
Mnemonic: “MASS”
Describe the changes that occur when there is a decrease in internal temperature.
- Metabolic rate increases by increasing rate of aerobic respiration by mitochondria, releasing more heat (in liver).
- Arterioles in the skin constrict (Vasoconstriction), reducing blood flow to capillaries near the skin surface, decreasing heat loss to surroundings through conduction, convection and radiation.
- Sweat glands become less active, causing sweat production to decrease, less water in sweat evaporates, hence less latent heat of vaporisation is removed from body.
- Shivering, the spasmodic contraction of skeletal muscles, further increases rate of aerobic respiration due to muscle respiration, releasing more heat energy.
- Hair erector muscles contract, hair shafts become perpendicular to skin surface, trapping air. Trapped air is a poor conductor of heat so heat is retained to keep the skin warm. (not significant in humans)
Mnemonic: “MASS”
Cross-Section of Skin
Describe
Layer 1: Epidermis
Layer 2: Dermis
- Arterioles, capillaries, venules
- Hair follicles containing hair shaft, sebaceous gland, hair erector muscles
- Sweat glands connected to sweat ducts
- Thermoreceptors connected to sensory neurones
Layer 3: Subcutaneous
- Adipose tissue
