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Homeostasis (part 2): Examples of homeostasis in Man

Students should be able to:<br>- identify on a diagram of the skin: hairs, sweat glands, temperature receptors, blood vessels and fatty tissue <br>- describe the maintenance of a constant body temperature in humans in terms of insulation and the role of: temperature receptors in the skin, sweating, shivering, blood vessels near the skin surface and the coordinating role of the hypothalamus

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Homeostasis (part 2): Examples of homeostasis in Man

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  1. Examples of homeostasis in Man 1. Blood glucose concentration regulation 2. Blood water potential 3. Temperature regulation

  2. 1) Blood glucose concentration regulation Normal blood glucose (norm) Low blood glucose (stimulus) High blood glucose (stimulus) negative feedback negative feedback Pancreas (receptor) Secretes more glucagon Pancreas (receptor) Secretes more insulin Liver Liver glycogen → glucose glucose → glycogen

  3. 2) Regulation of blood water potential (water Φ) Normal water Φ (norm) water Φ increases water Φ decreases stimulates stimulates negative feedback negative feedback hypothalamus hypothalamus causes causes Pituitary gland (receptor) Pituitary gland (receptor) secretes less ADH secretes more ADH Kidney tubules → reabsorb less water Kidney tubules → reabsorb more water

  4. 3) Temperature regulation

  5. Body hair

  6. Why don’t we look like that?

  7. The fuss about hair… Austin powers Yu Zhenhuan (hairiest man in China)

  8. Advantages: • The advantages are: • It keeps me warm in the winter; • and cool in the summer! • It definitely protects me from sunburn - and I get burnt very easily. • Perhaps being hairy enables me to spend less on clothes, though that could simply be that I dislike clothes shopping

  9. Disadvantages: • The disadvantages are: • You wouldn't believe the size of my shampoo bill! • You wouldn't like my barber's bill either! • I get confused: should I wash my body with soap or shampoo?

  10. Important functions of the skin 1. Produces Vitamin D under UV radiation 2. The sebaceous fat helps to insulate against heat loss 3. Excretes small amounts of urea, salts and water

  11. Structure of skin

  12. Structure of human skin

  13. Quiz

  14. Label the parts below:

  15. 4. 1. 7. 8. 9. 2. 5. 10. 6. 11. 3.

  16. Microscopic skin slides

  17. Microscopic skin slides

  18. A. Epidermis

  19. Outer cornified layer ▪ dead, dry, flat cells ▪ water resistant ▪ prevent uncontrolled water loss by evaporation ▪ protective barrier against germs ▪ constant renewal ▪ Thickest in regions subjected to greater wear and tear

  20. Granular layer ▪ living cells ▪ give rise to cornified layer Innermost Malpighian layer ▪ living cells ▪ usually pigmented (gives characteristic colour + protects skin from harmful UV rays) ▪ undergo cell division

  21. B. Dermis ▪ mainly fibrous connective tissue ▪ upper part thrown into ridges/ papillae

  22. Hair ▪ characteristic feature of mammals ▪ produced by epidermis though embedded in dermis ▪ hair follicle: hollow tube formed by Malpighian layer of epidermis sinking into dermis; hair grows here ▪ hair papillae: mass of tissue at base of follicle containing blood vessels + capillaries; formation of hair here ▪ hair erector muscles: contraction causes hair to “stand on end” →responsible for goose bumps

  23. *Sebaceous glands ▪ Secretes sebum (oily substance into hair follicle) →lubricates hair + keeps skin smooth & soft →Prevents dehydration + has antiseptic action (prevents bacteria growth) ▪ at least 2 open into each hair follicle

  24. *Sweat glands ▪ characteristic feature of mammals ▪ coiled tube ▪ forms tight knot in dermis; surrounded by blood capillaries ▪ sweat secreted (from blood capillaries) flows through sweat duct + sweat pore to skin surface ▪ sweat = mainly water + inorganic salts (NaCl) + metabolic waste product (urea) ▪ sweat evaporation helps in temperature regulation

  25. *Sense receptors ▪ consists of nerve endings ▪ sense pain, pressure/ temperature changes in external environment

  26. Blood vessels ▪ Numerous capillaries ▪ Arterioles supplying capillaries controlled by vasomotor nerves ▪ *Nerves bring about vasodilation and vasoconstriction (helps regulate body temperature) ▪ Vasodilation – increased blood flow to skin surface helps to lose heat to the surroundings by conduction, convection and radiation ▪ Vasoconstriction – decreased blood flow to skin surface limits the amount of heat lost to the surroundings by conduction, convection and radiation

  27. C. Sub-cutaneous fat ▪ several layers of adipose tissues ▪ fat in cells serve as insulating layer ▪ adipose tissue known as fat storage + insulating tissue

  28. Structure of human skin - vasomotor nerves bring about vasodilation and vasoconstriction (helps regulate body temperature) - secretes sebum (oily substance into hair follicle) 1) lubricates hair + keeps skin smooth & soft 2) prevents dehydration + has antiseptic action (prevents bacteria growth) - consists of nerve endings - sense pain, pressure/ temperature changes in external environment - contraction causes hair to “stand on end” → responsible for goose bumps - sweat = mainly water + inorganic salts (NaCl) + metabolic waste product (urea) - sweat evaporation helps in temperature regulation (known as fat storage + insulating tissue)

  29. Temperature Regulation

  30. How do these mammals survive the cold?

  31. 3) Temperature regulation – hot day High body temperature Hypothalamus activated 1) Vasodilation 4) rapid breathing 3) ↑ sweat production 5) metabolic rate ↓ 2) constriction of shunt vessels negative feedback Restore to normal temperature

  32. 3) Temperature regulation – cold day Low body temperature Temperature receptors in skin activated Hypothalamus activated 1) vasoconstriction 4) shivering 3) ↓ sweat production 5) metabolic rate ↑ 2) Dilation of of shunt vessels negative feedback Restore to normal temperature

  33. Temperature regulation (summary) Normal body temperature hot Detected by temp. receptors (skin) cold Send nerve impulses to brain 6) Breathing rate increases? 7) Shivering? Brain sends impulses to relevant body parts 2) Shunt vessels (Constrict/ Dilate) 1) Blood vessels 3) Sweat glands (active?) 5) Hair erector muscles (relax/contract) 4) Metabolic rate (↑ or ↓) (constrict/dilate) negative feedback

  34. Discuss as a group what you think would be some advantages of our bodies having a constant temperature

  35. Advantages of constant temperature 1. Can remain active throughout year 2. Optimum temperature for enzymes 3. No hibernation 4. Able to exploit and colonise area with different climates

  36. Essay questions D86 2B 9 (a) How does the skin of mammals help them to maintain a constant body temperature? (b) How may an excess of heat be gotten rid of by a mammal (other than Man) in conditions which tend to cause overheating?

  37. Essay questions J90 2B 8(a)(i) Explain how the humidity of air affects temperature regulation in Man.

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