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Transcript
AHS C&T2 11/1/12 C&T2 — Homeostasis/Cellular Function Outline — Homeostasis Definition(s) Significance — key concept External and internal environments Physiological variables – regulated Outline — Cells Organelles Plasma membrane Nucleus Endoplasmic reticulum Golgi apparatus Mitochondrion Cytoskeleton Feedback mechanisms Protein synthesis. Homeostasis KEY CONCEPT" Defined as maintenance of a relatively stable internal environment It does not mean that composition, temperature, and other characteristics are absolutely unchanging Essential for survival and function of all cells Each cell contributes to maintenance of a relatively stable internal environment 1 AHS C&T2 11/1/12 Homeostasis Definitions ‘Homeostasis is essential for the survival of each cell, and each cell, through its specialized activities, contributes as a part of a body system to the maintenance of the internal environment shared by all such cells.’ [Sherwood] ‘dynamic constancy of interstitial fluid composition’ Physiological Variables Mean arterial BP (systolic) 120 mmHg (range 105-150) Red blood cell concentration Male 5.4 x 106/microlitre (4.5-6.5) Female 4.8 x 106/microlitre (3.9-5.6) Variation by physiological state Gender, age, fasted/fed, exercise etc. In other words: The composition of the body fluids is a key element of homeostasis Key concept Negative Feedback Acts to counteract the change in the controlled variable Components 1. Controlled variable 2. Sensor 3. Integrator 4. Effector 5. Compensatory response. Sherwood 1-7" 2 AHS C&T2 11/1/12 Negative Feedback NB ‘set point’ Sherwood Fig. 1-7 1. Controlled variable — body temperature 2. Sensor — nerve cells 3. Integrator — temperature control centre 4. Effectors — skeletal muscle (etc) 5. Compensatory mechanism — heat production. Positive Feedback reinforces the change in the controlled variable Contraction of the uterus at birth cervix Oxytocin —> contraction of uterine smooth muscle —> moves baby lower —> pressure on cervix —> oxytocin release Other examples Clotting Propagation of action potential in a neuron 3 AHS C&T2 11/1/12 Pathophysiology ‘ … a state in which normal function at any organizational level is disrupted to the extent that normal regulatory and compensatory mechanisms cannot maintain homeostasis.’ [Davis et al.] Cells Exchange materials (eg. nutrients, oxygen, carbon dioxide, wastes) with surrounding environment Perform chemical reactions that provide energy for the cell Synthesize cellular components Sense and respond to changes in surrounding environment (receptors) Reproduce (divide) Cell physiology, biochemistry and molecular biology allows us to further assess function of subcellular organelles, proteins etc. 4 AHS C&T2 11/1/12 Cells are structurally specialised for function Humans are very different from single-celled or simple multicellular organisms! Neuron Cardiac muscle cell Gamete Plasma Membrane Controls passage of materials Has embedded proteins and molecules (not shown here) Receptors, carriers, recognition, etc etc. 5 AHS C&T2 11/1/12 Nucleus DNA (genetic) Pores (selective) Nucleolus Ribosomal RNA synthesis A crucial stage in protein synthesis. Endoplasmic reticulum (ER) Membrane " encloses space (lumen)" Continuous with nuclear envelope" ‘Rough’ ER — ribosomes" Protein synthesis" Smooth ER" Lipids (NB steroids)" Ca2+ store (muscle)" Detox (liver)." 6 AHS C&T2 11/1/12 Golgi Apparatus Flattened sacs (green in picture) Between ER and cell membrane Processes and packages molecules into vesicles for transport. Stanfield & Germann 2.19" Proteins — roles Within cell S&G 2.9 " e.g. enzymes, signalling, structure Cell membrane e.g. transporters, structure Proteins are chains of amino acids (AA) & may take very complex forms eg haemoglobin" Outside cell e.g. digestive enzymes, hormones. 7 AHS C&T2 11/1/12 Transcription/Genetic Code A triplet codes for one amino acid (AA) Or start/stop Bases (GTCA) are complementary Forms mRNA mRNA to cytoplasm Translation by ribosomes Addition of AA — peptide. Read more: Germann & Stanfield pp46-50" Protein Synthesis & Sorting Pathway (radiolabel expt) Uptake of amino acids in RER (synthesis) Golgi (packaging) Vacuoles (storage) Cell membrane (release) Further packaging into vesicles takes place in Golgi and ER Sorting " AGA Inst. www.gastroslides.org AGA Inst. www.gastroslides.org" Leader sequence determines fate. 8 AHS C&T2 11/1/12 The Mitochondrion Energy production From glucose Generates ATP ADP + Pi + energy ! ATP 1 mole glucose yields ~38 moles of ATP (40% efficient; rest is heat)" Most ATP synthesis is in the cristae." Cytoskeleton Dynamic array of filaments Confer shape Allow movement 1. Microfilaments 2. Intermediate filaments 3. Microtubules. 9 AHS C&T2 11/1/12 Cytoskeleton Microfilaments (8 nm) Two helices of F-actin (fibrous) Formed from G-actin (globular) Actin is most common Movement: amoeboid; cell division Support for microvilli. Intermediate filaments (10 nm) Stronger & more stable Keratin (skin & hair) Myosin (muscle) Microtubules (25nm) Strength Cell division Movement Cilia and flagellae e.g. respiratory tract, spermatozoa. Cilium" Learning Outcomes Homeostasis To be able to: Cells 1. outline the structure and function of mammalian cell organelles (i.e. 1. give clear physiological examples of nucleus, membrane, mitochondria, homeostasis ribosomes, endoplasmic reticulum, cytoskeleton, and golgi) 2. give a physiological example of positive and negative feedback 2. the cellular events involved in 3. give an example of a change exceeding the body’s capacity to rectify it (pathophysiology) protein synthesis. 10