Homeostasis and the Organization of the Animal Body

1. Homeostasis and the Organization of the Animal Body Chapter 31 pages 604 - 618

2. Hierarchy of Structures • Tissues are composed of similar cells that perform a specific function • Organs perform complex functions and include two or more interacting tissue types • Organ systems consist of two or more interacting organs that function in a coordinated manner

3. Cells, Tissues, Organs, Organ Systems

4. How Is the Animal Body Organized? • Animal tissues are composed of similar cells that perform a specific function • There are four categories of animal tissues • Epithelial tissue • Connective tissue • Muscle tissue • Nerve tissue

5. Epithelial Tissue • Covers the body, lines cavities, and forms glands • All body surfaces — skin, digestive, respiratory, and urinary tracts, and circulatory system • Epithelial tissue is sheets of cells firmly attached to one another by connections such as desmosomes and tight junctions • Attached to an underlying layer of fibrous proteins or basement membrane - provides support, flexibility, and strength • Cells are continuously lost and replaced

6. Types of Epithelium • Simple epithelium is one cell thick and lines the respiratory, urinary, reproductive, and circulatory systems • Stratified epithelium is found in the skin and just inside body openings that are continuous with the skin (mouth and anus) and are continuously lost and replaced • Several cells thick and can withstand considerable wear and tear

7. Epithelial Tissue flattened cells basement membrane (a) Lining of the lungs (simple epithelium) cilia mucus basement membrane mucus- producing cells (b) Lining of the trachea (simple epithelium)

8. Skin - Epithelial Tissue dead cells flattened dying cells differentiating cells dividing cells basement membrane (c) Skin epidermis (stratified epithelium)

9. Glands • Glands are cells or groups of cells specialized to secrete large quantities of substances outside the cell • Two categories • Exocrine glands secrete substances into a body cavity or onto the body surface, usually through a duct • Sweat glands, mammary glands, salivary glands, and glands that secrete digestive enzymes • Endocrine glands lack ducts, and release hormones into the extracellular fluid, diffuses into capillaries • Hormones are chemicals produced in small quantities and transported thru the bloodstream to regulate the activity of other cells

10. Connective Tissues • Diverse structures and functions • Support and strengthen other tissues, binding the cells of other tissues into coherent structures, such as skin or muscle • They consist of fluid containing proteins, especially collagen • Three categories of connective tissue • Loose connective tissue • Dense connective tissue • Specialized connective tissue

11. Loose Connective Tissue • The most abundant form of connective tissue, consisting of a thick fluid containing scattered cells that secrete protein • Flexible tissue connects, supports, and surrounds other tissue types, forming a framework for organs such as the liver

12. Dense Connective Tissue • Packed with collagen fibers that provide flexibility and strength, but only in the direction in which the collagen fibers are arranged • Tendons, which connect bones to muscles • Ligaments, which connect bones to bones

13. Specialized connective tissues • Diverse functions and structures • Cartilage • Bone • Fat (adipose tissue) • Blood • Lymph

14. Cartilage • Widely spaced cells surrounded by thick, nonliving matrix composed of collagen • It covers the ends of bones at joints, provides the supporting framework for the respiratory passages, supports the ear and nose, and forms shock-absorbing pads between the vertebrae • Flexible, but can break if bent too far

15. Bone • Bone resembles cartilage, but its matrix is hardened by deposits of calcium phosphate • It forms in concentric rings around a central canal, which contain blood vessels

16. Adipose • Adipose tissue is made up of fat cells that are modified for long-term energy storage • Can serve as insulation for animals living in a cold environment

17. Blood and Lymph • Blood and lymph are specialized forms of connective tissue because they are composed largely of extracellular fluids in which proteins are suspended • The cellular portion of blood - • Red blood cells transport oxygen • White blood cells fight infection • Platelets are cell fragments that aid in blood clotting • The blood cells are suspended in a fluid called plasma

18. Lymph • Lymph is fluid that has leaked out of blood capillaries, it enters the lymph vessels and is carried back to the circulatory system

19. Muscle Tissue • Have the ability to contract • The long, thin cells of muscle tissue contract when stimulated and then relax when the stimulation stops • There are three types of muscle tissue • Skeletal muscle • Cardiac muscle • Smooth muscle

20. Skeletal Muscle • Skeletal muscle is stimulated by the nervous system and is under voluntary, or conscious, control • Its main function is to move the skeleton

21. Cardiac Muscle • Cardiac muscle spontaneously active, not under conscious control • Interconnected by gap junctions, through which electrical signals spread, stimulating cardiac muscles cells to contract in a coordinated fashion

22. Smooth Muscle • Found throughout the body, in the walls of the digestive and respiratory tracts, uterus, bladder, and larger blood vessels • Produces slow, sustained, involuntary contractions that are stimulated by the nervous system, by stretch, or by hormones or other chemicals

23. Nervous Tissue • Specialized to produce and conduct electrical signals • Brain, spinal cord, and nerve cells (neurons) • Neurons are specialized to generate electrical signals and conduct signals to other neurons, muscles, or glands • Glialcells surround, support, insulate, and protect neurons

24. How Is the Animal Body Organized? • Organs are formed from at least two types of tissues that function together; most consist of all four tissue types • Function as part of an organ system • The skin illustrates the properties of organs • Outer layer of epithelial cells underlain by connective tissue that contains a blood, nerve supply, muscle, and glandular structures derived from the epithelium

25. Structural Components of Skin • Epidermis, or outer layer, is specialized stratified epithelial tissue • Immediately beneath the epidermis lies a layer of loose connective tissue, the dermis, which contains blood vessels • Specialized epithelial cells dip down from the epidermis into the dermis, forming hair follicles • Below the dermis is a layer of adipose tissue

26. Skin is an Organ hair shaft pore sebaceous gland capillary bed epidermis dead cell layer living epidermal cells dermis sensory nerve endings subdermal connective and adipose tissue hair follicle arterioles venules lymph vessels muscle (pulls hair upright) sweat gland

27. Organ Systems • Two or more interacting organs, located in different regions of the body, that work together to perform a common function • Digestive system - in which the mouth, esophagus, stomach, intestines, liver and pancreas, all function together to convert food into nutrient molecules that can be absorbed into the bloodstream

30. Homeostasis • Animal cells need a narrow range of conditions to survive • Homeostasis is the process by which an organism maintains its internal environment, within that narrow range

31. How does it work? • The internal environment is maintained in a state of dynamic constancy • The internal environment is in a state of dynamic constancy • The body adjusts to ongoing internal and external changes to maintain constant conditions

32. Examples of Regulated Conditions • Temperature • Water and salt concentrations • Glucose concentrations • pH (acid-base balance) • Oxygen and carbon dioxide concentrations

33. Why is this Important? • Animal cells are constantly generating and using large quantities of ATP to sustain life processes • Continuous supplies of high-energy molecules and O2 are required to carry out the reactions that generate ATP • Energy production helps explain the importance of glucose and oxygen levels

34. Each of the reactions for producing ATP is catalyzed by a protein whose ability to function depends on its three-dimensional structure • This structure is maintained by hydrogen bonds, which can be disrupted if the environment is too hot, salty, acidic, or basic • The need to maintain these bonds helps explain the requirement for a narrow range of temperature, pH, and salt

35. Animals vary in their homeostatic abilities • Birds and mammals are efficient at maintaining homeostasis for all the internal conditions listed above • Other animals have reduced or absent homeostasis for one or more aspects of their internal environment • For example, many marine invertebrates, including snails, crabs, and worms, cannot regulate the overall concentration of their bodily fluids

36. Classification • Scientists classify animals according to their major source of body warmth • Endotherms generate heat through metabolic reactions - birds and mammals • Warm blooded • Ectotherms derive body heat from the environment, and maintain it by occupying a constant environment or by behavioral activities - reptiles, amphibians, fishes, and invertebrates • Cold blooded

37. Warm-Blooded or Cold-Blooded?

38. Regulation • Feedback systems regulate internal conditions • Homeostatic mechanisms that maintain internal constancy are called feedback systems • Two types • Negative feedback - counteracts the effects of changes in the internal environment to maintain homeostasis • Positive feedback, - drives rapid, self-limiting changes, such as those that occur when a mother gives birth

39. Negative Feedback • Works by reversing the effect of a change • The most important feedback mechanism • A change in the environment causes responses that “feed back” to counteract the change • The overall result of negative feedback is a return to the original condition • Three components • A sensor detects the current condition • A control center compares that condition to the desired state, called the set point • An effector produces an output that restores the desired condition

40. Animation: Elements of a Feedback System

41. Home temperature is regulated by negative feedback • Negative feedback systems that control body temperature are similar to those used to heat a home • The sensor is a thermometer, the control center is a thermostat, and the effector is the heater • The thermometer detects the room temperature and sends that information to the thermostat, where it is compared to the set point of the desired temperature • If the temperature is below the set point, the thermostat signals the heater to turn on and generate heat • The heater warms the room, restoring the temperature to the set point, causing the thermostat to turn off the heater

42. Animation: Temperature Control in Your House

43. Negative feedback maintains body temperature • The temperature control center is located in the hypothalamus, a part of the brain • Set point is between 97º- 99º F • Nerve endings act as temperature sensors and transmit information to the hypothalamus • If the body temperature falls below the set point, the hypothalamus activates effector mechanisms that raise body temperature • Shivering, blood vessel constriction, increased metabolic rate • When body temperature is restored, the sensors signal the hypothalamus to switch off these actions

44. Negative Feedback Maintains Homeostasis

45. The body’s temperature controls system can also act to reduce body temperature if rises above set point • Blood vessels leading to the skin to dilate, allowing warm blood to flow to the skin, where heat can be radiated into the air • Sweat glands secrete fluid, cooling the body as it evaporates from the skin • Fatigue and discomfort cause the body to slow down, so the body generates less heat

46. Animation: The Control of Body Temperature

47. Positive Feedback • Positive feedback enhances the effects of changes • A change produces a response that intensifies the initial change • Positive feedback is relatively rare in biological systems, but occurs during childbirth and blood clotting

48. Childbirth • Labor contractions force the baby’s head against the cervix at the base of the uterus, causing it to stretch and open • Stretch-receptor neurons in the cervix signal the hypothalamus • The hypothalamus releases oxytocin, a hormone which stimulates more and stronger contractions • Stronger contractions cause the baby’s head to stretch the cervix even more, causing the release of more oxytocin • Delivery of the baby relieves the pressure on the cervix, halting the positive feedback cycle

49. Animation: The Control of Labor