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D.Body08 - Physiology& the Human Body Levels of...

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Unformatted text preview: Physiology & the Human Body Levels of Physiological Organization The Body’s Internal Environment An Introduction to Physiology Tissues Primary types: • Epithelial • Connective • Muscle • Nervous Connective Tissue • Cells are suspended in an extracellular matrix. • • • • • Cells Tissues Organs Organ systems Organism Epithelial Tissue • Continuous sheet or layers of cells with direct cellcell junctions Muscle Tissue • Specialized for contraction. – The matrix is often largely composed of collagen fibers. Heyer 1 Physiology & the Human Body Nervous Tissue Organ Systems • Specialized to conduct electrochemical nerve impulses. 11 Organ Systems Bauplan: Ger. “Life Plan” (pl: baupläne) The arrangement, pattern, and development of tissues, organs, and systems unique to a particular type of organism. • Descriptions on p. 66 –67 of Human Biology , 9th ed. Cell Differentiation Cell Differentiation in Development • From one original fertilized egg cell (zygote), mitotic division has produced all your body ’s cells. ~50,000,000,000 cells in your body • Each genetically identical! But >200 cell types of cells • (specialized [differentiated] tissues) • Each type uses only ~20% of the total genes in their nucleus • Even fewer in more specialized cells • Unused genes may be permanently inactivated \ permanently differentiated \ cannot change into a different type of cell Heyer Cell Differentiation Cell Differentiation in Development • Undifferentiated • Totipotent : able to become any cell type • Cells may be separated and each become a new identical embryo • First differentiation: cells separate into layers 1. Inner cell mass 2. Trophoblast • Secretes hormone ( hCG ) • Secretes enzymes fi implant into uterine lining 2 Physiology & the Human Body Cell Differentiation Cell Differentiation Cell Differentiation in Development 2. Extra-embryonic membranes • form the placenta and “bag of waters ” around the embryo Epiblast • Third differentiation stage: Embryonic disc develops into three basic embryonic germ layers 1. Ectoderm 2. Mesoderm • Second stage of differentiation: Inner cell mass divides into: 1. (day 14) Cell Differentiation in Development 3. (day 8) Embryonic disc • becomes the embryo Ectoderm Embryonic disc Mesoderm Endoderm Hypoblast Endoderm Cell migration & specialization to form body organs Neural tube Ectoderm Endoderm Mesoderm (day 12) (day 22) Cell Differentiation Cell Differentiation Cell Differentiation in Development Cell Differentiation in Development • Final differentiation : the three embryonic germ layers differentiate into the primary tissue types and their subtypes. • Final differentiation : the three embryonic germ layers differentiate into the primary tissue types and their subtypes. ECTODERM (day 56) All organs formed. (From now on called a fetus) What about Stem Cells? • Epidermis of skin and its derivatives (including sweat glands, hair follicles) • Epithelial lining of mouth and rectum • Sense receptors in epidermis • Cornea and lens of eye • Nervous system • Adrenal medulla • Tooth enamel • Epithelium or pineal and pituitary glands MESODERM • Notochord • Endoskeletal system • Muscular system • Muscular layer of stomach, intestine, etc. • Excretory system • Circulatory and lymphatic systems • Reproductive system (except germ cells) • Dermis of skin • Lining of body cavity • Adrenal cortex ENDODERM • Epithelial lining of digestive tract • Epithelial lining of respiratory system • Lining of urethra, urinary bladder, and reproductive system • Liver • Pancreas • Thymus • Thyroid and parathyroid glands • Nervous tissue from ectoderm. • Muscle & connective tissues from mesoderm. • Epithelial tissues from all three germ layers. ( Embryonic tissue is epithelial-like.) What about Stem Cells? • Remain partially undifferentiated (embryonic). – Most their genes not permanently deactivated. • Can divide and differentiate on demand to replace specialized tissue cells. Heyer 3 Physiology & the Human Body Bone Marrow Stem Cells Adult Stem Cells • Many organs are known to produce stem cells in adults • Long known to have multipotential hematopoietic stem cells • Recently discovered able to also differentiate into other types of connective tissue – One stem cell has the potential to form any type of blood cell – Adipose, bone, & cartilage Embryonic Stem Cells Embryonic Stem Cell Research • Current research • Preferred because they are pluripotent – More potential to be induced to form any cell type desired “left over ” embryos from in vitro fertilization clinics • Future proposal “human cloning ” Personalized Stem Cells The Promise of Stem Cell Research Nuclear Transfer Method: 1. Remove nucleus from egg cell from donor 2. Replace with the nucleus from your epithelial cell 3. Stimulate egg to develop into embryo – “Hello Dolly ” … a clone ? If the nucleus of epithelial cells is non-differentiated enough to be used to form embryonic stem cells, why cannot epithelial cells be induced directly to become stem cells?? Heyer 4 Physiology & the Human Body The Debate over Embryonic Stem Cell [ESC] Research Funding Current Limitations • • • • Localization Tumor formation Rejection May not address underlying problem PRO • Possible therapy replacement for tissues that don ’t regenerate – Neurons, heart muscle • No embryos created just for stem cells CON • Over-hyped – Actual “cures ” not attained • • – IVF clinics may legally dispose of extra embryos Physiology function and process: why and how Taxpayer subsidies for very lucrative biomedical business Immoral to “destroy one life to prolong another ” – Focus efforts on adult stem cell research Function and process: an example – Teleology = purpose/function = “Why?” – Mechanism = “How?” Important physiological themes • • • • • • Heyer Homeostasis Regulation Compartmentalization Distribution of materials Communication, coordination, & integration Energy flow Observation: red blood cells transport oxygen. • Teleological (function) approach: Why does the system exist? “… because red blood cells deliver oxygen to the cells that need it. ” This answer explains the reason blood cells transport oxygen but says nothing about how the cells transport oxygen. • • Mechanistic approach: How does the system operate? “… because there are hemoglobin molecules that combine reversibly with oxygen molecules. ” This very concrete answer explains exactly how oxygen transport occurs but says nothing about the significance of oxygen transport to the intact animal. One role of physiology is to integrate function and process into a cohesive picture. • • Understanding the processes of life • Physiology incorporates the teleological approach and the mechanistic approach • (modified from Human Physiology: An Integrated Approach, D. U. Silverthorn 3rd ed Homeostasis: maintaining a constant, optimal internal environment 5 Physiology & the Human Body Homeostasis helps us adjust to change Homeo stasis “same” “stay” • Dynamic Constancy (= Dynamic Equilibrium): – Fluctuate around set point. – Set point may be reset for new situations. Homeostatic Mechanisms Negative Feedback Loop •Negative feedback loops ÿIntrinsic — within an organ ÿExtrinsic — integrating multiple organs Negative Feedback: Room Thermostat Antagonistic Effectors Pairs of effectors with opposing actions provide much tighter control. Heyer 6 Physiology & the Human Body Negative Feedback: Body Thermostat Effector Sets Table 1.2 Redundant effectors allow stronger responses to stronger deviations. Homeostasis & Regulation of Blood Glucose BIN DOWN Negative Feedback: Body Glucostat • Pancreas controls blood sugar levels • Glucose is taken up or released by: – liver as glycogen • Glucagon from alpha cells ups it GAC UP • Insulin from beta cells drops it BIN DOWN GAC UP Heyer 7 Physiology & the Human Body Body-Fluid Compartments Life is dynamic • 65-75% of total body weight is H20. • Intracellular compartment: – Fluid inside the cell. • 2/3 of H 20. • Extracellular compartment: – 2 Subdivisions: • Blood plasma. • Interstitial fluid. • 1/3 H 20. • Constant exchange between internal and external environments Energy Flow Heyer The Body’s Internal Environment 8 ...
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