L-2-cell physiology

1、 CELL AND TISSUE CHARACTERISTICS CELL AND TISSUE CHARACTERISTICS The cell is the smallest functional unit of life. (living thing ) Humans have about 100 trillion cells. a typical cell size is 10 m a typical cell mass is 1 nanogram. Cells tissues body structures and organs. FUNCTIONAL COMPONENTS OF T

2、HE CELL Eukaryotic cells: The nucleus The cytoplasm The cell membrane THE NUCLEUS the control center for the cell. contains most of the cells genetic material: multiple long linear DNA a large variety of proteins (i.e. histones) form chromosomes. The genes within these chromosomes are the cells nucl

3、ear genome. THE NUCLEUS The function of the nucleus: to maintain the integrity of these genes and to control the activities of the cell by regulating gene expression. THE NUCLEUS The nuclear envelope: completely encloses the nucleus and separates the cells genetic material from the surrounding cytop

4、lasm. “nucleoplasm the cytoplasm” Nuclear pores: regulate molecules pass from the cytoplasm to the nucleus and vice versa. i.e. fluids, electrolytes, RNA, some proteins, homones THE NUCLEUS Chromosomes: contains the majority of the cells genetic material, in the form of multiple linear DNA molecules

5、. the DNA-protein complex dispersed in the matrix is Chromatin. a small fraction of the cells genes are located in the mitochondria. THE NUCLEUS Nucleolus: a densely stained structure not surrounded by a membrane These regions are called nuclear organizer region (NOR) The main roles: to synthesize r

6、RNA and assemble ribosomes THE CYTOPLASM AND ITS ORGANELLES most cellular activities occur in cytoplasm, such as many metabolic pathways. i.e. glycolysis, and processes such as cell devision. Organelles: ribosomes, endoplasmic reticulum (ER), Golgi complex, mitochondria, lysosomes, microtubules, and

7、 filaments. Ribosome Structure: non-membraneous, spherical bodies (attached to ER or as free ribosomes) composed of RNA (ribonucleic acid) and protein enzymes. Function - site of protein synthesis Endoplasmic Reticulum (ER) Structure: sheets of unit membrane with ribosome on the outside forms a tubu

8、lar network throughout the cell. Endoplasmic Reticulum (ER) Function: transports chemicals between cells and within cells provides a large surface area for the organization of chemical reactions and synthesis Golgi Apparatus Structure: stacks of flattened sacs of unit membrane vesicles pinch off the

9、 edges Function: modifies chemicals to make them functional secretes chemicals in tiny vesicles stores chemicals may produce endoplasmic reticulum Mitochondrion Structure Structure: composed of modified double unit membrane (protein, lipid) inner membrane infolded to form cristae Function: site of c

10、ellular respiration i.e. the release of chemical energy from food. Glucose + Oxygen - Carbon Dioxide + Water + Energy (ATP) Lysosome Structure: membrane bound bag containing hydrolytic enzymes hydrolytic enzyme = (water split biological catalyst) i.e. using water to split chemical bonds Function: br

11、eak large molecules into small molecules by inserting a molecule of water into the chemical bond Centriole Structure: nine triplets of microtubules form one centriole two centrioles form one centrosome Function: forms spindle fibres to separate chromosomes during cell division CELL MEMBRANES: ” func

12、tion as a selective barrier to the passage of molecules, allowing some molecules to cross while excluding others. Membrane Structure: all consist of a double layer of lipid molecules containning embedded proteins. The major membrane lipids are phospholipids. are amphipathic molecules. Nonpolar fatty

13、 acid chains ( in the middle). The polar regions oriented ( toward the surfaces) Membrane Junctions : Many cells are physically joined along their membranes by specialized types of junctions: desmosomes 2) tight junctions 3) gap junctions Desmosomes : (adhering juntions) 20 nm between two adjacent c

14、ells. have a dense accumulation of protein at the cytoplasmic surface of each membrane. and in the space between the two membranes. Protein fibers (cadherins) are linked from one cell to other. Tight junction: no extracellular space between cells. occurs in a band around the entire circumference of

15、the cell. epithelial cells cover the inner surface of the intestinal tract. organic nutrients are required to pass through the cells, rather than between them. Gap junction: protein channels linking the cytosols of adjacent cells. within 2-4 nm of each other, allows specific proteins from the two me

16、mbranes to join, forming small protein-lined channels linking the two cells. channels (1.5 nm): Pass small molecules and ions: Na+, K+, (Not for large protein MEMBRANE POTENTIALS Self-generated electricity Cell membranes function like batteries. Membrane potential: is the difference in concentration

17、 of ions on opposite sides of a cellular membrane produce a voltage difference called the membrane potential. (Vinterior Vexterior) MEMBRANE POTENTIALS The largest contributions usually come from Na+ and Cl ions which have high concentrations in the extracellular region, and K+ ions, which along wit

18、h large protein anions have high concentrations in the intracellular region. MEMBRANE POTENTIALS Functions: 1) It allows a cell to function as a battery, providing power to operate a variety of molecular devices embedded in the membrane. 2) In electrically excitable cells (i.e. neurons), it is used

19、for transmitting signals between different parts of a cell. Opening or closing of ion channels at one point in the membrane produces a local change in the membrane potential, which causes electric current to flow rapidly to other points in the membrane. RESTING MEMBRANE POTENTIALS In non-excitable c

20、ells, and in excitable cells in their baseline states, the membrane potential is held at a relatively stable value, called the resting potential. low permeability of the membrane to the rapid flow of charged ions. 70 -90 mv less charge on inside of the membrane than on the outside. RESTING MEMBRANE

21、POTENTIALS Factors contribute to the resting membrane potentials: 1) the presence of large numbers of the nondiffusible negatively charged intracellular ions. i.e. protein ions, sulfate ions, and phosphate ions. 2) the selective permeability of the resting membrane to the potassium ions. 3) the Na+-

22、K+ -ATPase pump. RESTING MEMBRANE POTENTIALS permeable to K+ vs. Na+: 50 100 times K+ remain inside: 1) attracted by intracellular anions 2) repelled by the positively changed extracellular Na+ ions Na+/K+ -ATPase pump: extrudes 3 Na+ for 2 K+ that returned to the inside ACTION POTENTIALS is a short

23、-lasting event in which the electrical membrane potential of an excitable cell rapidly rises and falls, following a stereotyped trajectory. ( neurons, muscle cells, and endocrine cells) In neurons, play a central role in cell-to- cell communication. In muscle cells, is the first step in the chain of

24、 events leading to contraction. In bata cells of the pancreas, provoke release of insulin ACTION POTENTIALS Three phases: The resting phase: the period before the action potentiall begins. (large negative potential polarized) Depolarization: the membrane is highly permeable to Na+ ions. ( Na+ gates

25、are open reversial of the membrane potential) The sodium channels close at the peak of the action potential. ACTION POTENTIALS Repolarization: reestablish the polarity of the resting membrane potential. close Na+ channel. open K+ channel: out flow of positively charged K+ return the membrane potenti

26、al to negativity. ACTION POTENTIALS ALTERATIONS IN MEMBRANE EXCITABILY 1) Changes in the resting membrane potential 2) Changes in the permeability of the membrane. Hyperpolarization: the resting membrane potential becomes extrimely negative. Hypopolarization: the resting membrane potential becomes l

27、ess negative. 1) Hypokalemia: serum K+ the resting membrane potential becomes more negative. the nerve and muscle fibers become hyperpolarized they can not be reexcited. (muscle paralysis) 2) Hyperkalemia: serum K+ the resting membrane potential becomes hypopolarized. the action potential is decreas

28、ed because the membranr has not been fully repolarized unexcitable. (Heart) ALTERATIONS IN MEMBRANE EXCITABILY Changes in membrane permeability alters neural excitability. i.e. Local anesthetic agents: (e.g. procaine or cocaine) act directly on neural membranes to decrease their to Na+. CELLULAR ENE

29、RGY METABOLISM Energy metabolism: the process by which the fats, proteins, and carbohydrates are converted in to energy or complex energy source in the cell. Catabolism: breaks down of stored nutrients and body tissues to produce energy. Anabolism: uses energy to construct components of cells such a

30、s protein or nucleic acids CELLULAR ENERGY METABOLISM ATP ANAEROBIC METABOLISM Glycolysis: the process by which the energy is liberated from glucose. a sequence of reactions that converts glucose to pyruvate with the concomitant production of ATP and ADP (+ lactic acids) (2 ATP) inefficient “hypoxia

31、” ANAEROBIC METABOLISM AEROBIC METABOLISM Mitochondria the citric acid cycle (Krebs cycle) and the oxidative phosphoration. ATP + CO2 + water Most efficient AEROBIC METABOLISM BODY TISSUES The cell is the smallest functional unit of life. (living thing ) Humans have about 100 trillion cells. About 2

32、00 distinct kinds of cells (differences in structure and function). Cells tissues body structures and organs. Muscle cell Total organism (human being) Organ system (e.g., urinary system) Epithelial Cell Connective tissue cell Nerve cell Organ (e.g., kidney) Nephron Kidney Ureter Bladder Urethra Func

33、tional Unit (nephron) Tissues Specialized cell types Cell division and growth Cell differentiation Fertilized egg Levels of cellular organization Cell differentiation: The process of transforming an unspecialized cell into a specialized cell. (nerve cell, muscle cell?) Tissues: Specialized cells are

34、 associated with other cells of a similar properties aggregate to form tissues. (nerve tissue, muscle tissue, etc). Organs: four types of tissues combine to form organs (the heart, lungs, kidneys, etc.) Organ systems: a collection of organs that together perform an overall function. Four functional

35、categories of cells Muscle cells are specialized to generate the mechanical forces that produce force and movement. (skeletal, cardiac, and smooth muscle cells) Nerve cells: initiate and conduct electric signals, often over long distances. Epithelial cells: selectively secrete and absorb ions and or

36、ganic molecules. Connective-tissue cells: connect, anchor, 2) it transmits information to the cells, chemical messengers, that helps regulate their migration, growth, and differentiation. Organ Organs are composed of the four kinds of tissues arranged in various proportions and patterns: sheets, tub

37、es, layers, bundles, strips, etc. kidneys: (functional units, 2 million nephrons) 1) small tubes, each composed of a single layer of epithelial cells; 2) blood vessels, whose walls contain varying quantities of smooth muscle and connective tissue; 3) nerve-cell extensions that end near the muscle an

38、d epithelial cells; 4) a network of connective-tissue elements that are interspersed throughout the kidneys and also form enclosing capsules; 5) extracellular fluid and matrix. System Major Organs or Tissues Primary Functions Circulatory Heart, blood vessels, blood Transport of blood throughout the

39、bodys tissues Digestive Mouth, pharynx, esophagus, stomach Digestion and absorption of organic nutrients, intestines, salivary glands, pancreas, salts, and water liver, gallbladder Respiratory Nose, pharynx, larynx, trachea, Exchange of carbon dioxide and oxygen; bronchi, lungs regulation of hydroge

40、n-ion concentration Urinary Kidneys, ureters, bladder, urethra Regulation of plasma composition through controlled excretion of salts, water, and organic wastes Nervous Brain, spinal cord, peripheral nerves and Regulation and coordination of many activities ganglia, special sense organs in the body;

41、 detection of changes in the internal and external environments; states of consciousness; learning; cognition Immune White blood cells, lymph vessels Defense against foreign invaders; return of and nodes, spleen, thymus, extracellular fluid to blood; formation of white and other lymphoid tissues blo

42、od cells Endocrine All glands secreting hormones: Pancreas, Regulation and coordination of many activities testes, ovaries, hypothalamus, kidneys, in the body pituitary, thyroid, parathyroid, adrenal,etc. Musculoskeletal Cartilage, bone, ligaments, Support, protection, and movement of the tendons, j

43、oints, skeletal muscle body; production of blood cells Organ Systems (page 4) The Internal Environment and Homeostasis The human body: a complex society of differentiated cells structurally and functionally combined and interrelated to carry out the functions essential to the survival of the entire

44、organism. Exchanges of matter occur between the external environment and the circulatory system via the digestive, respiratory, and urinary systems. Extracellular fluid (plasma and interstitial fluid) is the internal environment of the body. The external environment is the air surrounding the body.

45、The activities of organ systems is to create an environment in which all cells can survive and function. This fluid environment surrounding each cell is called the internal environment. From this fluid: cells receive oxygen and nutrients & into which they excrete wastes. The relative constancy of th

46、e internal environment is known as homeostasis. Homeostatic control system: a collection of body components that functions to keep a physical or chemical property of the internal environment relatively constant. e.g. Mountaineer high altitude O2 in inspired air PO2 in blood nervous system signals to

47、 the skeletal muscles responsible for breathing breathes more rapidly and deeply The homeostasis is a state of dynamic constancy a given variable e.g. glucose may vary in the short term, but is fairly constant when averaged over the long term. Hemeostatic compensatory mechanism Numerous variables within the body must be maintained hemeostatically. When homeostasis is lost for one variable, it may trigger a series of changes in other variables. e.g. Na+, Ca+, O2, CO2, pH Physiology- homeo