Introductory Physiology I - Wellspring University - PDF

Wellspring University, Benin City, Nigeria. COURSE TITLE: INTRODUCTORY PHYSIOLOGY I COURSE CODE: PHS 211 For 200 Level Nursing and Medical Laboratory Science Students Lecture Notes compiled by course lecturer: Dr. O. B. Uhuonrenren (Human Physiologist) MODULE 1: Definitions, History of developme...

Wellspring University, Benin City, Nigeria. COURSE TITLE: INTRODUCTORY PHYSIOLOGY I COURSE CODE: PHS 211 For 200 Level Nursing and Medical Laboratory Science Students Lecture Notes compiled by course lecturer: Dr. O. B. Uhuonrenren (Human Physiologist) MODULE 1: Definitions, History of development of PHYSIOLOGY The study of physiology traces its roots back to ancient India and Egypt. As a medical discipline, it goes back at least as far as the time of Hippocrates, the famous “father of medicine” – around 420 BC. Hippocrates coined the theory of the four humors, stating that the body contains four distinct bodily fluids: black bile, phlegm, blood, and yellow bile. Any disturbance in their ratios, as the theory goes, causes ill health. Claudius Galenus (c.130-200 AD), also known as Galen, modified Hippocrates’ theory and was the first to use experimentation to derive information about the systems of the body. He is widely referred to as the founder of experimental physiology. It was Jean Fernel (1497-1558), a French physician, who first introduced the term “physiology,” from Ancient Greek, meaning “study of nature, origins.” Fernel was also the first to describe the spinal canal (the space in the spine where the spinal cord passes through). He has a crater on the moon named after him for his efforts – it is called Fernelius. Another leap forward in physiological knowledge came with the publication of William Harvey’s book titled An Anatomical Dissertation Upon the Movement of the Heart and Blood in Animals in 1628. Harvey was the first to describe systemic circulation and blood’s journey through the brain and body, propelled by the heart. Perhaps surprisingly, much medical practice was based on the four humors until well into the 1800s (bloodletting, for instance). In 1838, a shift in thought occurred when the cell theory of Matthias Schleiden and Theodor Schwann arrived on the scene, theorizing that the body was made up of tiny individual cells. From here on in, the field of physiology opened up, and progress was made quickly: Joseph Lister, 1858 – initially studied coagulation and inflammation following injury, he went on to discover and utilize lifesaving antiseptics. Ivan Pavlov, 1891 – conditioned physiological responses in dogs. August Krogh, 1910 – won the Nobel Prize for discovering how blood flow is regulated in capillaries. Andrew Huxley and Alan Hodgkin, 1952 – discovered the ionic mechanism by which nerve impulses are transmitted. Andrew Huxley and Hugh Huxley, 1954 – made advances in the study of muscles with the discovery of sliding filaments in skeletal muscle. Biological systems The major systems covered in the study of human physiology are as follows: Circulatory system – including the heart, the blood vessels, properties of the blood, and how circulation works in sickness and health. Digestive/excretory system – charting the movement of solids from the mouth to the anus; this includes study of the spleen, liver, and pancreas, the conversion of food into fuel and its final exit from the body. Endocrine system – the study of endocrine hormones that carry signals throughout the organism, helping it to respond in concert. The principal endocrine glands – the pituitary,  thyroid, adrenals, pancreas, parathyroids, and gonads – are a major focus, but nearly all organs release endocrine hormones. Immune system – the body’s natural defense system is comprised of white blood cells, the thymus, and lymph systems. A complex array of receptors and molecules combine to protect the host from attacks by pathogens. Molecules such as antibodies and cytokines feature heavily. Integumentary system – the skin, hair, nails, sweat glands, and sebaceous glands (secreting an oily or waxy substance). Musculoskeletal system – the skeleton and muscles, tendons, ligaments, and cartilage. Bone marrow – where red blood cells are made – and how bones store calcium and phosphate are included. Nervous system – the central nervous system (brain and spinal cord) and the peripheral nervous system. Study of the nervous system includes research into the senses, memory, emotion, movement, and thought. Renal/urinary system – including the kidneys, ureters, bladder, and urethra, this system removes water from the blood, produces urine, and carries away waste. Reproductive system – consisting of the gonads and the sex organs. Study of this system also includes investigating the way a fetus is created and nurtured for 9 months. Respiratory system – consisting of the nose, nasopharynx, trachea, and lungs. This system brings in oxygen and expels carbon dioxide and water. Branches There are a great number of disciplines that use the word physiology in their title. Below are some examples: Cell physiology – studying the way cells work and interact; cell physiology mostly concentrates on membrane transport and neuron transmission. Systems physiology – this focuses on the computational and mathematical modeling of complex biological systems. It tries to describe the way individual  cells or components of a system converge to respond as a whole. They often investigate metabolic networks and cell signaling. Evolutionary physiology – studying the way systems, or parts of systems, have adapted and changed over multiple generations. Research topics cover a lot of ground including the role of behavior in evolution, sexual selection, and physiological changes in relation to geographic variation. Defense physiology – changes that occur as a reaction to a potential threat, such as preparation for the fight-or-flight response. Exercise physiology – as the name suggests, this is the study of the physiology of physical exercise. This includes research into bioenergetics, biochemistry, cardiopulmonary function, biomechanics, hematology, skeletal muscle physiology, neuroendocrine function, and nervous system function. The topics mentioned above are just a small selection of the available physiologies. The field of physiology is as essential as it is vast. THE CELL Cell, in physiology, the basic membrane-bound unit that contains the fundamental molecules of life and of which all living things are composed. A single cell is often a complete organism in itself, such as a bacterium or yeast. Other cells acquire specialized functions as they mature. These cells cooperate with other specialized cells and become the building blocks of large multicellular organisms, such as humans and other animals. Although cells are much larger than atoms, they are still very small. The smallest known cells are a group of tiny bacteria called mycoplasmas; some of these single-celled organisms are spheres as small as 0.2 μm in diameter (1μm = about 0.000039 inch), with a total mass of 10−14 gram—equal to that of 8,000,000,000 hydrogen atoms. Cells of humans typically have a mass 400,000 times larger than the mass of a single mycoplasma bacterium, but even human cells are only about 20 μm across. It would require a sheet of about 10,000 human cells to cover the head of a pin, and each human organism is composed of more than 30,000,000,000,000 cells. similarities and differences between cells See all videos for this article This article discusses the cell both as an individual unit and as a contributing part of a larger organism. As an individual unit, the cell is capable of metabolizing its own nutrients, synthesizing many types of molecules, providing its own energy, and replicating itself in order to produce succeeding generations. It can be viewed as an enclosed vessel, within which innumerable chemical reactions take place simultaneously. These reactions are under very precise control so that they contribute to the life and procreation of the cell. In a multicellular organism, cells become specialized to perform different functions through the process of differentiation. In order to do this, each cell keeps in constant communication with its neighbours. As it receives nutrients from and expels wastes into its surroundings, it adheres to and cooperates with other cells. Cooperative assemblies of similar cells form tissues, and a cooperation between tissues in turn forms organs, which carry out the functions necessary to sustain the life of an organism. Consider how a single-celled organism contains the necessary structures to eat, grow, and reproduce The nature and function of cells cells A cell is enclosed by a plasma membrane, which forms a selective barrier that allows nutrients to enter and waste products to leave. The interior of the cell is organized into many specialized compartments, or organelles, each surrounded by a separate membrane. One major organelle, the nucleus, contains the genetic information necessary for cell growth and reproduction. Each cell contains only one nucleus, whereas other types of organelles are present in multiple copies in the cellular contents, or cytoplasm. Organelles include mitochondria, which are responsible for the energy transactions necessary for cell survival; lysosomes, which digest unwanted materials within the cell; and the endoplasmic reticulum and the Golgi apparatus, which play important roles in the internal organization of the cell by synthesizing selected molecules and then processing, sorting, and directing them to their proper locations. In addition, plant cells contain chloroplasts, which are responsible for photosynthesis, whereby the energy of sunlight is used to convert molecules of carbon dioxide (CO2) and water (H2O) into carbohydrates. Between all these organelles is the space in the cytoplasm called the cytosol. The cytosol contains an organized framework of fibrous molecules that constitute the cytoskeleton, which gives a cell its shape, enables organelles to move within the cell, and provides a mechanism by which the cell itself can move. The cytosol also contains more than 10,000 different kinds of molecules that are involved in cellular biosynthesis, the process of making large biological molecules from small ones. Britannica Quiz eukaryotic cell Specialized organelles are a characteristic of cells of organisms known as eukaryotes. In contrast, cells of organisms known as prokaryotes do not contain organelles and are generally smaller than eukaryotic cells. However, all cells share strong similarities in biochemical function. The molecules of cells Cells contain a special collection of molecules that are enclosed by a membrane. These molecules give cells the ability to grow and reproduce. The overall process of cellular reproduction occurs in two steps: cell growth and cell division. During cell growth, the cell ingests certain molecules from its surroundings by selectively carrying them through its cell membrane. Once inside the cell, these molecules are subjected to the action of highly specialized, large, elaborately folded molecules called enzymes. Enzymes act as catalysts by binding to ingested molecules and regulating the rate at which they are chemically altered. These chemical alterations make the molecules more useful to the cell. Unlike the ingested molecules, catalysts are not chemically altered themselves during the reaction, allowing one catalyst to regulate a specific chemical reaction in many molecules. Biological catalysts create chains of reactions. In other words, a molecule chemically transformed by one catalyst serves as the starting material, or substrate, of a second catalyst and so on. In this way, catalysts use the small molecules brought into the cell from the outside environment to create increasingly complex reaction products. These products are used for cell growth and the replication of genetic material. Once the genetic material has been copied and there are sufficient molecules to support cell division, the cell divides to create two daughter cells. Through many such cycles of cell growth and division, each parent cell can give rise to millions of daughter cells, in the process converting large amounts of inanimate matter into biologically active molecules. Mammalian cell biology In 1839, two German scientists, Matthias Jakob Schleiden and Theodor Schwann, introduced the “cell theory,” the proposal that all higher organisms are made up of a single fundamental unit as a building block. In 1855, Rudolf Virchow extended this cell theory with a suggestion that was highly controversial at the time: “Omnis cellulae e celula” (all living cells arise from pre-existing cells). This statement has become known as the “biogenic law.” The cell theory is now accepted to include a number of principles: 1. All known living things are made up of cells. 2. The cell is the structural and functional unit of all living things. 3. All cells come from pre-existing cells by division (spontaneous generation does not occur). 4. Cells contain hereditary information that is transmitted from cell to cell during cell division. 5. The chemical composition of all cells is basically the same. 6. The energy flow (metabolism and biochemistry) of life occurs within cells. Although these features are common to all cells, the expression and repression of genes dictates individual variation, resulting in a large number of different types of variegated but highly organized cells, with convoluted intracellular structures and interconnected elements. The average size of a somatic cell is around 20 µm; the oocyte is the largest cell in the body, with a diameter of approximately 120 µm in its final stages of growth. The basic elements and organelles in an individual cell vary in distribution and number according to the cell type. Bacterial cells differ from mammalian cells in that they have no distinct nucleus, mitochondria or endoplasmic reticulum. Their cell membrane has numerous attachments, and their ribosomes are scattered throughout the cytoplasm. Cell membranes They are made up of a bimolecular layer of polar lipids, coated on both sides with protein films. Some proteins are buried in the matrix, others float independently of each other in or on the membrane surface, forming a fluid mosaic of different functional units that are highly selective and specialized in different cells. Cells contain many different types of membrane, and each one encloses a space that defines an organelle, or a part of an organelle. The function of each organelle is determined largely by the types of protein in the membranes and the contents of the enclosed space. Membranes are important in the control of selective permeability, active and passive transport of ions and nutrients, contractile properties of the cell, and recognition of/association with other cells. Cellular membranes always arise from pre-existing membranes, and the process of assembling new membranes is carried out by the endoplasmic reticulum (ER, see below). The synthesis and metabolism of fatty acids and cholesterol is important in membrane composition, and fatty acid oxidation (e.g., by the action of reactive oxygen species, ROS) can cause the membranes to lose their fluidity, as well as have an effect on transport mechanisms. Microvilli They are extensions of the plasma membrane that increase the cell surface area; they are abundant in cells with a highly absorptive capacity, such as the brush border of the intestinal lumen. Microvilli are present on the surface of oocytes, zygotes and early cleavage stage embryos in many species, and in some species (but not humans) their distribution is thought to be important in determining the site of sperm entry. Cell cytoplasm This is a fluid space, containing water, enzymes, nutrients and macromolecules; the cytoplasm is permeated by the cell’s architectural support, the cytoskeleton. Microtubules They are hollow polymer tubes made up of alpha-beta dimers of the protein tubulin. They are part of the cytoskeletal structure, and are involved in intracellular transport, for example, the movement of mitochondria. Specialized structures such as centrioles, basal bodies, cilia and flagella are made up of microtubules. During prophase of mitosis or meiosis, microtubules form the spindle for chromosome attachment and movement. Microfilaments They are threads of actin protein, usually found in bundles just beneath the cell surface; they play a role in cell motility, and in endo- and exocytosis. Centrioles They are a pair of hollow tubes at right angles to each other, just outside the nucleus. These structures organize the nuclear spindle in preparation for the separation of chromatids during nuclear division. When the cell is about to divide, one of the centrioles migrates to the other side of the nucleus so that one lies at each end. The microtubule fibers in the spindle are contractile, and they pull the chromosomes apart during cell division. The nucleus The Nucleus of each cell is surrounded by a layered membrane, with a thickness of 7.5 nm. The outer layer of this membrane is connected to the ER, and the outer and inner layers are connected by “press studs,” creating pores in the nuclear membrane that allow the passage of ions, RNA and other macromolecules between the nucleus and the cell cytoplasm. These pores have an active role in the regulation of DNA synthesis, since they control the passage of DNA precursors and thus allow only a single duplication of the pre-existing DNA during each cell cycle. The inner surface of the membrane has nuclear lamina, a regular network of three proteins that separate the membrane from peripheral chromatin. DNA is distributed throughout the nucleoplasm wound around spherical clusters of histones to form nucleosomes, which are strung along the DNA like beads. These are then further aggregated into the chromatin fibers of approximately 30 nm diameter. The nucleosomes are supercoiled within the fibers in a cylindrical or solenoidal structure to form chromatin, and the nuclear lamina provide anchoring points for chromosomes during interphase ( Figure 1.2 ): Active chromatin = euchromatin – less condensed Inactive (turned off ) = heterochromatin – more condensed Before and during cell division, chromatin becomes organized into chromosomes. Three types of cell lose their nuclei as part of normal differentiation, and their nuclear contents are broken down and recycled: Red blood cells (RBCs) Squamous epithelial cells Platelets. Other cells may be multinuclear: syncytia in muscle and giant cells (macrophages), syncytiotrophoblast. Nuclear RNA is concentrated in nucleoli, which form dense, spherical particles within the nucleoplasm (Figure 1.3 ); these are the sites where ribosome subunits, ribosomal RNA and transfer RNA are manufactured. RNA polymerase I rapidly transcribes the genes for ribosomal RNA from large loops of DNA, and the product is packed in situ with ribosomal proteins to generate new ribosomes (RNP: ribonucleoprotein particles). Mitochondria They are the site of aerobic respiration. Each cell contains 40–1000 mitochondria, and they are most abundant in cells that are physically and metabolically active. They are elliptical, 0.5–1 µm in size, with a smooth outer membrane, an intermembranous space, and a highly organized inner membrane which forms cristae (crests) with elementary particles attached to them, “F1-F0 lollipops,” which act as molecular dynamos. The cristae are packed with proteins, some in large complexes: the more active the tissue, the more cristae in the mitochondria. Cristae are the site of intracellular energy production and transduction, via the Krebs (TCA) cycle, as well as processes of oxidation, dehydrogenation, fatty acid oxidation, peroxidation, electron transport chains and oxidative phosphorylation. They also act as a Ca 2+ store, and are important in calcium regulation. Mitochondria contain their own doublestranded DNA that can replicate independently of the cell, but the information for their assembly is coded for by nuclear genes that direct the synthesis of mitochondrial constituents in the cytoplasm. These are transported into the mitochondria for integration into its structures. A number of rare diseases are caused by mutations in mitochondrial DNA, and the tissues primarily affected are those that most rely on respiration, i.e., the brain and nervous system, muscles, kidneys and the liver. All the mitochondria in the developing human embryo come from the oocyte, and therefore all mitochondrial diseases are maternally inherited, transmitted exclusively from mother to child. In the sperm, mitochondria are located in the midpiece, providing the metabolic energy required for motility; there are no mitochondria in the sperm head. Oocytes contain 100 000–1 000 000 mitochondria. Sperm contain 70–100 mitochondria, in the midpiece of each sperm. These are incorporated into the oocyte cytoplasm, but do not contribute to the zygote mitochondrial population – they are eliminated at the four- to eight-cell stage. All of the mitochondria of an individual are descendants of the mitochondria of the zygote, which contains mainly oocyte mitochondria. The human mitochondrial genome The sequence of human mitochondrial DNA was published by Fred Sanger in 1981, who shared the 1980 Nobel Prize in Chemistry with Paul Berg and Walter The sequence of human mitochondrial DNA was published by Fred Sanger in 1981, who shared the 1980 Nobel Prize in Chemistry with Paul Berg and Walte