Lecture notes Chapter 1 The Human Body: An Orientation Anatomy - Structure Physiology - Function • The shape of a building should relate to its intended function • We can apply this truism to the Anatomy and Physiology of living cells, tissues and organisms. Form (anatomy) determines function (physiology) Two complementary branches of science—anatomy and physiology—provide the concepts that help us to understand the human body. • Anatomy studies the structure of body parts and their relationships to one another. • Concrete: Structures can be seen, felt, and examined closely. No need to imagine what they look like. • You can memorize • Physiology concerns the function of the body, in other words, how the body parts work and carry out their life-sustaining functions. • Physiology is explainable only in terms of the underlying anatomy. • You really need to understand Complementarity of Structure & Function • Although it is possible to study anatomy and physiology individually, they are really inseparable because function always reflects structure. That is, what a structure can do depends on its specific form. • This key concept is called the principle of complementarity of structure and function. • You can infer function from structure. Scientific Reductionism • Reductionism: an approach to understanding the nature of complex things by reducing them to the interactions of their parts, or to simpler or more fundamental things. • Physiology often focuses on events at the cellular or molecular level because the body’s abilities depend on those of its individual cells, and cells’ abilities ultimately depend on the chemical reactions that go on within them. • In this course, we will be learning about life on small and large scales. • Gross (macroscopic) anatomy is the study of large body structures visible to the naked eye, such as the heart, lungs, and kidneys. • Microscopic anatomy deals with structures too small to be seen with the naked eye. • Try to keep in mind what scales we are dealing with. Structural Organization of the Human Body Atoms < molecules < organelle < smooth muscle cell < smooth muscle tissue < organ level < organ system level < organismal level Cells are the Smallest Unit of Life • Fundamental structural and functional unit of living things • Smallest unit that can maintain and perpetuate life • All cells share common functions but vary widely in size and shape, reflecting their unique functions • New cells can only come from existing cells Cool Facts: • In one square inch of skin there are 4 yards of nerve fibers, 3 yards of blood vessels, 1300 nerve cells, 100 sweat glands, and 3 million cells • In the time it takes me to say this, 50,000 cells in your body will die and be replaced by new cells. Tissues, Organs and Organ Systems • Tissues: Groups of similar cells with a common function – 4 types: epithelial, muscle, connective and nervous • Organs: Discrete structure composed of at least two (usually four) tissue types. Specialized functional center for a specific activity. • Organ systems: Organs that work together to accomplish a common purpose (e.g. Cardiovascular system includes heart and blood vessels) CHAPTER 3 Cells: The living units Review of cell structure, function and organelles Lecture the second Tissue: The Living Fabric (Chapter 4, pages 116-137) Tissues • Unicellular organisms must carry out all activities necessary for life (like a single parent!) • In multicellular organisms, cells are specialized to perform specific tasks (division of labour) – Pro: Allows sophisticated functions – Con: A group of cells may be indispensible – Tissues are groups of cells that are similar in structure, have a common function and are organized into organs. • 4 main tissue types • Histology is the study of tissues How do we study tissue structure? • Fixation or freezing • Cut into thin sections • Stained with dyes (light microscopy) – 1850s • or heavy metals (electron microscopy) – 1950s • or antibodies conjugated to dyes • Preservation induces artifacts • Two-photon excitation microscopy is a fluorescence imaging technique that allows imaging of living tissue up to about one millimeter in depth. Epithelial Tissue • Epithelial tissue (epithelium) is a sheet of cells that covers body surfaces or cavities – Two main forms: – Covering and/or lining epithelia • On external and internal surfaces (example: skin) – Glandular epithelia • Secretory tissue in glands (example: salivary glands) • Functions: protection, absorption, filtration, excretion, secretion, and sensory reception Special Characteristics of Epithelial Tissues Epithelial tissue has five distinguishing characteristics: 1. Polarity 2. Specialized contacts 3. Supported by connective tissues 4. Avascular, but innervated 5. Ability to regenerate Polarity • Epithelial cells have polarity • Apical surface, top, is exposed to surface or cavity (external) – Most apical surfaces are smooth, but some have specialized fingerlike projections called microvilli (function?) • Basal surface, bottom, faces inwards toward body – Attaches to basal lamina, an adhesive sheet that holds basal surface of epithelial cells to underlying cells – Both surfaces differ in structure and function and have specialized proteins • Correct establishment and maintenance of cell polarity are crucial for normal cell physiology and tissue homeostasis. • Loss of cell polarity, tissue disorganization and excessive cell growth are hallmarks of cancer. • Specialized contacts – Epithelial tissues need to fit closely together (barriers) • Many form continuous sheets – Specialized contact points bind adjacent epithelial cells together • Lateral contacts include: • Tight junctions – prevents substances from leaking between cells (can be selectively leaky – regulated) • Desmosomes – prevents cells from pulling apart (in tissues subjected to mechanical stress) • Supported by connective tissues – All epithelial sheets are supported by connective tissue – Reticular lamina • Deep to basal lamina • Consists of network of collagen fibers – Basement membrane • Made up of basal lamina and reticular lamina • Reinforces epithelial sheet • Resists stretching and tearing • Defines epithelial boundary Clinical Relevance • Cancerous epithelial cells are not contained by the basement membrane boundary like other cells • They penetrate the boundary and invade underlying tissues, resulting in spread of cancer (metastasis) • 90% of cancer deaths caused by metastases • Avascular, but innervated – No blood vessels are found in epithelial tissue • Must be nourished by diffusion from underlying connective tissues – Epithelia are supplied by nerve fibers, however • Regeneration – Epithelial cells have high regenerative capacities – Stimulated by loss of apical-basal polarity and broken lateral contacts – Some cells are exposed to friction, some to hostile substances, resulting in damage • Must be replaced • Requires adequate nutrients and cell division Classification of Epithelia • All epithelial tissues have two names – First name indicates number of cell layers – Second name indicates shape of cells • Simple epithelia are a single layer thick • Stratified epithelia are two or more layers thick and involved in protection (example: skin) • Squamous: flattened and scale-like • Latin squama meaning "the scale of a fish or serpent." • We have a lot of squamous cells. – Most of the cells in the outer layer of the skin (epidermis) – Passages of the respiratory and digestive tracts – Linings of hollow organs • Cuboidal: box-like, cube • Columnar: tall, column-like – In stratified epithelia, shape can vary in each layer, so classified according to the shape in apical layer Classification of Epithelia • Simple epithelia – Involved in absorption, secretion, or filtration processes • Two special simple squamous epithelia are based on different locations – Endothelium: • lines the inner surface of the blood vessels, lymphatic vessels, and the heart • derived from ectoderm and endoderm in the early embryo – Mesothelium: • Form serous membranes that surround the pericardium, peritoneum, and pleura and internal reproductive organs (covers the organs' outer surfaces) • derived from mesoderm • Two membranes system with fluid in between (function?) Epithelium: Simple Squamous • Description: Single layer of flattened cells with disc-shaped central nuclei and sparse cytoplasm; the simplest of the epithelia • Function: Allows materials to pass by • diffusion and filtration in sites where protection is not important but rapid diffusion is; secretes lubricating substances in serosae (linings of ventral body cavity). • Location: Kidney glomeruli; air sacs of lungs; lining of heart, blood vessels, and lymphatic vessels; serosae. Epithelium: Simple Cuboidal • Description: Single layer of cube like cells with large, spherical central nuclei. • Function: Secretion and absorption • Location: Kidney tubules; ducts and secretory portions of small glands; ovary surface. Epithelium: Simple Columnar • Description: Single layer of tall, closely packed cells with round to oval nuclei; many cells bear microvilli, some have cilia; layer may contain mucus-secreting unicellular glands (goblet cells). • Function: Absorption; secretion of mucus, enzymes, and other substances; ciliated type propels mucus (or reproductive cells) by ancillary action. • Location: Nonciliated type lines most of the digestive tract (stomach to rectum), gallbladder, and excretory ducts of some glands; ciliated variety lines small bronchi, uterine tubes, and some regions of the uterus. Epithelium: pseudostratified columnar • Description: Single layer of cells of differing heights, some not reaching the free surface; nuclei seen at different levels; may contain mucus-secreting cells and bear cilia. • Function: Secrete substances, particularly mucus; propulsion of mucus by ciliary action. • Location: Ciliated variety lines the trachea and most of the upper respiratory tract; nonciliated type in males’ sperm-carrying ducts and ducts of large glands. Classification of Epithelia: Stratified • Stratified (layered) epithelial tissues – Involve two or more layers of cells – New cells regenerate from below • Basal cells divide and migrate toward surface – More durable than simple epithelia because protection is the major role – Stratified squamous epithelium • Most widespread of stratified epithelia • Free surface is squamous, with deeper cuboidal or columnar layers • Located in areas of high wear and tear (example: skin) • Keratinized cells found in skin; nonkeratinized cells are found in moist linings • Keratinization Slide26