Introduction to Human Physiology PDF

Introduction to Human Physiology Physiology explores the science of life by examining the mechanisms of living organisms. It delves into the functions of cells at the ionic and molecular levels, extends to the coordinated activities of the entire body, and considers the impacts of exter...

Introduction to Human Physiology Physiology explores the science of life by examining the mechanisms of living organisms. It delves into the functions of cells at the ionic and molecular levels, extends to the coordinated activities of the entire body, and considers the impacts of external environmental factors. Multiple organ systems (heart, kidneys, endocrine glands) all have the effect of maintaining body function around a set point as biological systems become more complex we use reductionist methods to isolate particular processes to aid and understanding however we must not neglect a holistic view of the entire system that recognizes the emergent properties that emanate from the synergies among components. All components work together to maintain a relatively constant internal environment, a process known as homeostasis. Homeostasis refers to the dynamic mechanisms that detect and respond to deviations in physiological variables from their set point values, initiating effector responses to restore these variables to their optimal physiological range. Basic organization of tissues and organs within the human body: Cell division and growth → Cell differentiation → Specialized cell types → Tissues → Organ (kidney) → Organ system (urinary system) Cells of the body can be categorized into four main functional groups. Specialized Cell Types and Tissues: Epithelial cell (Epithelial tissue), Connective-tissue cell (Connective tissue), Neuron (Nervous tissue), Muscle cell (Muscle tissue) The cell is the smallest unit capable of maintaining the functions characteristic of life. All cells are remarkably similar in how they exchange materials, obtain energy, synthesize organic molecules, duplicate themselves, and detect and respond to signals in their immediate environment. Cells of an organism all carry the same genome, yet the expression of different parts of this genome leads to cell differentiation, transforming an unspecialized cell into the specialized cells that make up the body. As many as 200 different types of cells can be identified in the body. These cells can be further divided into functional groups, where cells share a common theme but vary in their function from tissue to tissue. Different tissues are combined into organs, which frequently contain cells of all four common themes. Epithelial cells are specialized for selective secretion and absorption of ions and organic molecules and for protection. These cells are characterized and named according to their unique shapes. For example, cuboidal or cube-shaped cells, columnar or elongated cells, squamous or flattened cells, and ciliated cells. Epithelial cells form boundary tissues of either a single cell layer (simple epithelium) or multiple cell layers (stratified epithelium). Epithelial cells can also serve as a protective layer for many organs and have specialized functions depending on where in the body they are found. Epithelial cells rest on an extracellular protein layer called the basement membrane, which anchors the tissue. The cell Introduction to Human Physiology membrane facing the basement membrane is referred to as the basolateral side, and the cell membrane facing the interior or lumen is called the apical or luminal side. A distinguishing feature of these cells is that the two sides perform very different physiological functions. In most tissues, epithelial cells are connected to one another at their lateral surfaces by an extracellular barrier called tight junctions. Tight junctions enable epithelial tissue to form boundaries between body compartments and to function as a selective barrier regulating the passage of materials. For example, glucose is actively removed from the kidney tubule by active transport across the luminal membrane and is passively discharged to the plasma membrane across the basolateral membrane. The tight junctions ensure that glucose does not diffuse back into the renal tubule. Connective tissue cells connect, anchor, and support the structures of the body. Loose connective tissue consists of a loose meshwork of cells and fibers underlying most epithelial layers. Dense connective tissue includes the tough, rigid tissue that makes up tendons and ligaments. Other connective tissues include bone, cartilage, adipose tissue, and blood, which is considered a fluid connective tissue. An important function of some connective tissues is the formation of the extracellular matrix (ECM) around cells. This matrix consists of a mixture of proteins, polysaccharides, and, in some cases, minerals. It surrounds cells and includes the extracellular fluid that bathes body tissues. The ECM first provides a scaffold for cellular attachments and, secondly, transmits information in the form of chemical messengers to the cells to help regulate their activity, migration, growth, and differentiation. Neurons Neurons, a second specialized cell type, are used to initiate and conduct electrical signals, often over great distances. Neurons are a major means of controlling the activities of other cells, whether the other cells are neurons, muscles, or glands. The incredible complexity of connections between neurons underlies phenomena such as consciousness and perception. Collections of neurons form nervous tissue, such as the brain and spinal cord. Many neurons packaged together with connective tissue carry signals from one part of the body to another and are called nerves. Muscle cells are specialized to produce mechanical force that can generate movement. They can be attached to bones to produce movement of limbs, to the skin to produce facial expressions, or surround hollow organs or vessels to regulate the movement of materials and/or flow by changing the diameter of the chamber or vessel. Skeletal muscle is under voluntary control via the somatic nervous system, meaning that contraction and movement are consciously initiated. Cardiac muscle is under involuntary control via the autonomic nervous system and is only found in the heart. Smooth muscle surrounds many tubes of the body and is also under involuntary control, via the autonomic nervous system. Contraction and relaxation of smooth muscle promote or restrict the Introduction to Human Physiology movement of materials through the body’s tubes. Organs are composed of two or more of the four basic tissue types arranged in a pattern conducive to the function of the organ. Many organs contain smaller functional units, where each unit performs the function of the organ. An example would be the kidney, where the functional unit is a nephron, each nephron contributing a portion of the kidney’s overall function (i.e., urine production). Organ systems are collections of organs that all contribute to a common function. In the renal system, the kidney, ureter, bladder, and urethra constitute the renal system, all necessary for the formation and excretion of urine. The body, therefore, consists of a collection of differentiated cells that combine structurally and functionally to carry out the processes necessary for the survival of the entire organism. Key to the survival of all body cells is the internal environment of the body. This fluid, which surrounds cells and exists in the blood, is the environment that most physiological homeostatic mechanisms are designed to modulate. The consistency of this pool is essential for the survival of the cells.