Homeostasis in mammals__igcse
- 1. Made by: TAHIRA PASHA
- 2. Let’s exercise!! • Heart rate before, after and during exercise • Why does heart rate change? • How does your heart rate become normal? • What evidence shows that homeostasis was disturbed in this activity? • Discuss how long it took your heart rate to return to its state of homeostasis. • What might cause differences in the time it took for different people? • Why do athletes typically have a quicker recovery time in their heart rate compared to the average person?
- 3. Examples from daily life • Body temp • Water content • Glucose Conc. • Attack by immune system • The maintenance of healthy blood pressure • Urinating
- 4. Learning objectives • Define homeostasis • Skin structure • Control of body temperature • Homeostasis • Negative feedback
- 5. Definition: Homeostasis is the maintainance of constant internal conditions in the body.
- 6. Skin structure: • In the basal layer some of the cells are continually dividing and pushing the older cells nearer the surface. Here they die and are shed at the same rate as they are replaced. • The basal layer and the cells above it constitute the epidermis. • The basal layer also contributes to the hair follicles. The dividing cells give rise to the hair. The skin and temperature control
- 7. • There are specialized pigment cells in the basal layer and epidermis. Melanin • The thickness of the epidermis and the abundance of hairs vary in different parts of the body • The dermis contains connective tissue with hair follicles, sebaceous glands, sweat glands, blood vessels and nerve endings. • There is usually a layer of adipose tissue
- 8. The structure of human skin
- 9. Epidermis Dermis Outermost layer Middle layer Innermost layer Sweat gland Blood capillaries Subcutaneous fat ReceptorsErector muscle Nerve fibres Sebaceous gland Hair follicle Structure of Mammalian Skin
- 10. Skin function 1. Protection • The outermost layer of dead cells of the epidermis helps to reduce water loss and provides a barrier against bacteria. • The pigment cells protect the skin from damage by the uv rays in sunlight. • Why do white ppl tan? 2. Sensitivity • sense receptors in skin- touch, pressure, heat, cold and pain. ?? 3. Temperature regulation • Help in maintaining body temp by adjusting the flow of blood near the skin surface and by sweating.
- 11. Temperature control • Normal human body temperature?? What if it fluctuates? • Hands, feet, head or internal organs, will be at different temperatures but temp under the tongue, will vary by only 1 or 2 degrees. • Heat is lost from the body surface by conduction, convection, radiation and evaporation. • The amount of heat lost is reduced to an extent due to the insulating properties of adipose (fatty) tissue in the dermis. • Some mammals - whales and seals, have thick layers of blubber to reduce heat loss more effectively. • How much insulation the blubber gives?? Water : fat • Heat is gained, internally, from the process of respiration and, externally, from the surroundings or from the Sun.
- 12. Overheating • - More blood flows near the surface of the skin, • - Sweating – the sweat glands secrete sweat on to the skin surface. When this layer of liquid evaporates, it takes heat (latent heat) from the body and cools it down • Overcooling • Less blood flows near the surface of the skin • Sweat production stops – thus the heat lost by evaporation is reduced. • Shivering –rapid muscular contraction in the limbs release heat as a result of respiration in the muscles. • 37 °C but control our temperature by adding or removing clothing or deliberately taking exercise. • Whether we feel hot or cold depends on the sensory nerve endings in the skin, which respond to heat loss or gain. • No conc control on body temp • The brain detects change in body temp • hypothalamus - thermoregulatory centre - temperature receptors detect temperature changes in the blood and co-ordinate a response to them. • Temperature receptors are also present in the skin. They send information to the brain about temperature changes.
- 13. Homeostasis extended • Enzymes & temperature • The cell membrane controls the substances that enter and leave the cell, but it is the tissue fluid that supplies or removes these substances, so composition of the • Tissue fluid should be maintained. • If the tissue fluid were to become too concentrated? • If the tissue fluid were to become too dilute? • The kidneys, which remove substances that might poison the enzymes. • The kidneys also control the level of salts, water and acids in the blood. • The composition of the blood affects the tissue fluid which, in turn, affects the cells. • Role of liver in maintaining blood glucose in body • Glucose and the brain • The lungs play a part in homeostasis by keeping the concentrations of 02 and carbon CO2 in the blood at the best level for the cells’ chemical reactions, especially respiration. • The skin regulates the temperature of the blood. • If the cells were to get too cold Or If they became too hot? • The brain checks the composition of the blood flowing through it and if it is too warm, too cold, too concentrated or has too little glucose, nerve impulses or hormones are sent to the organs concerned, causing them to make the necessary adjustments.
- 14. • kidneys : – regulate water & mineral salts concentration • skin : – regulate body temperature • liver & pancreas : – regulate blood glucose level Parts of Body involved kidney liver pancreas + skin tissue cells blood
- 15. Homeostasis and negative feedback • Temperature regulation • Maintenance of a constant body temperature important so the reactions do not speed up or slow down when the surrounding temperature changes. • The constant-temperature or homoiothermic (‘warm-blooded’) animals, the birds and mammals, therefore have an advantage over the variable temperature or poikilothermic (‘cold-blooded’) animals. • Poikilotherms such as reptiles and insects can regulate their body temperature to some extent by, for example, basking in the sun or seeking shade. Nevertheless, if their body temperature falls, their vital chemistry slows down and their reactions become more sluggish. They are then more vulnerable to predators. • The ‘price’ that homoiotherms have to pay is the intake of enough food to maintain their body temperature, usually above that of their surroundings.
- 16. Thermoregulation (Regulation of Body Temperature) • poikilotherms (cold-blooded animals) – body temperatures vary with that of the environment – e.g. reptiles, fish, amphibians
- 17. • Homoiotherms (warm-blooded animals) – keep body temperature constant even in winter by increasing metabolic rate – e.g. birds, mammals Thermoregulation (Regulation of Body Temperature)
- 18. • In the hypothalamus- thermoregulatory centre. • temperature receptors in the skin. • A rise in body temperature • vasodilation and sweating. • A fall in body temperature • vasoconstriction and shivering. • Negative feedback.
- 20. Regulation of blood sugar • Role of insulin and glucagon • Insulin increases the uptake of glucose in all cells for use in respiration; it promotes the conversion of carbohydrates to fats and slows down the conversion of protein to carbohydrate. • The level of glucose in the blood to within narrow limits –homeostasis.
- 21. • FBG- between 90 and 100 mg 100 cm−3 blood. • After a meal, 140 mg 100 cm−3 • 2 hours later, 95 mg- why?? • About 100 g glycogen is stored in the liver of a healthy man. • If the concentration of glucose in the blood falls below about 80 mg 100 cm−3 blood? • If the blood sugar level rises above 160 mg 100 cm−3, glucose is excreted by the kidneys. • A blood glucose level below 40 mg 100 cm−3?? • Liver helps in maintaining BGC between 80 and 150 mg, • What if production or function of insulin is not proper?
- 22. Regulation of Blood Glucose Level controlled by Negative feedback mechanism controlled by insulin secreted from the islets of Langerhans in pancreas Diabetes - malfunction of pancreas (does not secrete enough insulin)
- 23. Liver converts glycogen to glucose normal blood glucose level Blood glucose level fallsSoon after a meal Long after a meal Blood glucose level rises normal blood glucose level Too High Too Low Pancreas secretes insulin Pancreas secretes less insulin Liver coverts glucose to glycogen
- 24. Type 1 diabetes • It results from a failure of the islet cells to produce sufficient insulin. • Need regular injections of the hormone • ‘insulin-dependent’ diabetes. • The patient is unable to regulate the level of glucose in the blood- excreted in the urine, or fall so low that result is coma. • feeling tired, feeling very thirsty, frequent urination and weight loss. • Weight loss is experienced because the body starts to break down muscle and fat. • Diabetics need a carefully regulated diet • Need regular blood tests and take regular exercise.
- 25. Temperature control • Skin maintains a constant body temperature. • Dilation or constriction of arteriole blood to flow near the skin surface through the blood capillaries. • Vasodilation – the widening of the arterioles in the dermis allows more warm blood to flow through blood capillaries near the skin surface and so lose more heat • Vasoconstriction – narrowing (constriction) of the arterioles in the skin reduces the amount of warm blood flowing through blood capillaries near the surface
- 26. Control Body Temperature in Hot Conditions
- 27. More sweat is produced by sweat glands – evaporation of sweat takes away heat which produces a cooling effect Vasodilation of skin arterioles – arterioles near the surface of the skin dilates – to let more blood flows near the skin surface – to have more heat lost by conduction & radiation.
- 28. Erector muscles relax – hairs lie flat on the skin – reduce thickness of air trapped among the hairs (not effective in human because human’s hairs are short)
- 29. Develop thinner subcutaneous fat & shed their fur –as long term responses –increase heat loss Decrease metabolic rate & muscle contraction –gain less heat
- 30. Control Body Temperature in Cold Conditions
- 31. Vasoconstriction of skin arterioles – arterioles near the surface of the skin constrict – to let less blood flows near the skin surface – to have less heat lost by conduction & radiation
- 32. Erector muscles contract – pull hairs erect for trapping more air – thicker layer of air acts as a good insulator of heat Less sweat is produced by sweat glands – reduce heat loss by evaporation
- 33. Develop thicker subcutaneous fat & thicker fur – as long term responses – reduce heat loss Increase metabolic rate & muscle contraction – gain more heat
- 34. ~END~