[BIO] Chapter 10 - Homeostasis

© Hee Xin Wei (Copyrighted) Topic 10: Homeostasis

Chapter Analysis FOCUS EXAM WEIGHTAGE •Constitute to around 4% in Paper 2 in the past 5 years •commonly tested in MCQ and structured questions •tested twice in section B in the past 5 years •straightforward chapter •very much linked to hormones and excretion

homeostasis negative feedback Key Concept

homeostasis Homeostasis is the dynamic maintenance of a constant internal environment. •Internal Environment refers to conditions within the body of the organism such as body temperature (this chapter), blood glucose level (hormone chapter), water potential of blood (excretion chapter) •Homeostasis allows an organism to be independent from changes in the external environment. Stimulus a change in internal environment deviating from normal range Receptor detect the stimulus and sends signal to the control center Effector Bring about corrective mechanism Response Condition decreases or increases to return to normal Negative feedback Negative feedback is the corrective mechanism where the body reacts to bring about an opposite effect to the changes detected and restore the normal conditions of the internal environment. •stimulus: body temperature increases above normal •receptor: thermoreceptor sensed the increase •effector: body reacts to decrease body temperature •response: body temperature successfully decrease and back to normal •negative feedback: Thermoreceptor receives feedback that the temperature is back to normal. This causes the corrective mechanism to stop.

skin thermoregulation Key Concept

structure of skin Epidermis outermost layer which forms a waterproof and protective covering Dermis Inner later containing hair follicles, sweat glands, sebaceous glands, blood vessels, sensory receptors Sensory receptors detect changes in the environment, eg enable us to sense pain (pain receptors), pressure (mechanorecptors) and temperature changes (thermoreceptors) Hair folliclesEach hair grows inside a hair follicle Hair erector muscles When these muscles contract, the hairs are raised and when the skin around the hair is raised, “goose bumps” are produced Sebaceous glands Produce Sebum Sweat glands A coiled tube Secrete sweat through a sweat duct. sweat contains water, sodium chloride and small amounts of urea Subcutaneous Tissue / Hypodermis This layer consists of adipose tissue. Adipose cells store fat. This layer serves as insulation to reduce heat loss and padding.

structure of skin blood vessels in skins blood capillaries right below skin Arterioles The arterioles leading to the blood capillaries in the dermis are controlled by nerves. They respond to stimulation by undergoing vasoconstriction and vasodilation. •Vasoconstriction is the contraction of smooth muscles in the arteriole walls. It decreases the diameter of the blood vessels, reducing blood flow. •Vasodilation is the relaxation of smooth muscles in the arteriole walls. It increases the diameter of the blood vessels, increasing blood flow. Shunt Vessel •A blood vessel that links an artery directly to a vein, allowing the blood to bypass the blood capillaries. •Shunt vessels can control blood flow by constriction and dilation. shunt vessel

thermoregulation body temperature increases beyond normal Stimulus Body temperature increases beyond normal e.g. vigorous exercise, consumption of hot food, being in warm environment Receptor •Thermoreceptors in our skin which detects increase in temperature from the environment •Thermoreceptors in the hypothalamus which detect increase in temperature of the blood •They send signals to the control centre, hypothalamus in brain Effector Hypothalamus thus send signals to 1.Stimulate vasodilation of arterioles in our skin and constriction of shunt vessels. This increases blood flow in capillaries in skin so more heat is lost through conduction, convection and radiation. 2.Sweat glands become more active and increase sweat production. When water in sweat evaporates, it removes latent heat of vaporisation from the body 3.Decreased in metabolic rate to reduce amount of heat produced by our body Response Temperature decreases

thermoregulation body temperature decreases beyond normal Stimulus Body temperature decreases beyond normal e.g. being in cold environment Receptor •Thermoreceptors in our skin which detects decrease in temperature from the environment •Thermoreceptors in the hypothalamus which detect decrease in temperature of the blood •They send signals to the control centre, hypothalamus in brain Effector Hypothalamus thus send signals to 1.Stimulate vasoconstriction of arterioles in our skin and dilation of shunt vessels. This decreases blood flow in capillaries in skin so less heat is lost through conduction, convection and radiation. 2.Sweat glands become less active and decrease sweat production. Less latent heat of vaporisation is removed 3.Increased metabolic rate to increase the amount of heat released by our bodies. 4.Shivering which is a involuntary contraction of muscles will lead to cellular respiration of muscle cells thus increase heat released Response Temperature increases

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