Case 8 - Ossobuco PDF

Case 8 - ossobuco Different types of cells Cells can differentiate. Once a cell has differentiated it can not go back. Multipotent cells lose potency but develop specific abilities. - Totipotent → Cells that can develop into any cell type, including all embryonic and extra-embryonic tiss...

Case 8 - ossobuco Different types of cells Cells can differentiate. Once a cell has differentiated it can not go back. Multipotent cells lose potency but develop specific abilities. - Totipotent → Cells that can develop into any cell type, including all embryonic and extra-embryonic tissues (e.g., zygote). - Pluripotent → Cells that can give rise to most cell types but not extra-embryonic tissues (e.g., embryonic stem cells). - Multipotent → Cells that can develop into a limited range of cell types within a specific tissue or organ (e.g., hematopoietic stem cells for blood cells). - Unipotent cells are specialized stem cells that can differentiate into only one specific cell type If you have the right transcription factors you can dedifferentiate a cell into a pluripotent cell. 1. Different types of tissues The organs of the human body are formed from the 4 basic types of tissue. In general, each tissue is built from a special type of cells which are surrounded by more or less extracellular matrix. The four main tissues are: 1. Epithelial tissue (incl. glands) 2. Connective tissue - Connective supporting tissue - Cartilage - Bones - Fat - Blood 3. Muscle tissue 4. Nerve tissue Epithelial Tissue: Covers body surfaces and lines cavities. Its main functions include protection, absorption, secretion, and sensation. It forms the skin and the linings of organs like the intestines. Connective Tissue: Provides support and structure. It includes bone, blood, and fat tissues. It holds organs in place, stores energy, and transports nutrients and waste products. Muscle Tissue: Responsible for movement. There are three types: skeletal (moves bones, you can control), cardiac (pumps the heart), and smooth (controls movements in organs like the stomach). You have voluntary and involuntary contraction Skeletal muscle: has to be synchronized→ Syncytium A syncytium is a single cell with multiple nuclei. The function of a syncytium includes the rapid transfer of information between cells to trigger a coordinated action. A syncytium is a single cell containing multiple nuclei as seen in the skeletal muscle of humans. The smooth muscle in the heart works as a functional syncytium. This means that the individual cells work with adjacent cells for coordinated action. Rapid transmission of electrical impulses transfers between cells to trigger simultaneous contraction of the heart muscle. - Blood vessels have smooth muscle → control of blood flow and pressure Nervous Tissue: Conducts electrical signals throughout the body. It is found in the brain, spinal cord, and nerves and allows for communication between different parts of the body and the environment. Origin of these tissue types - Ectoderm: nerve tissue, epithelial tissue (skin) - Mesoderm: muscle tissue, connective tissue, epithelial tissue (mesothelium and endothelium) - Endoderm: epithelial tissue (mucosal epithelial tissue of the gastrointestinal tract) 2. What are tissues made of (structure)? Epithelial tissue It covers all organs, and the outside of the body. Epithelia can differ in the height of the cells and the number of cell layers. Special invaginations of the epithelial layer form glands such as the sweat glands or the mammary gland. Epithelial cells are always contiguous with each other. Endothelium cells line the organs. There are many types of epithelia, which are defined according to their cell shape as: squamous, cuboidal and columnar. And with respect to the layering as: simple, pseudostratified, stratified, and transitional. - In stratified epithelia only the basal cells are in contact with the basement membrane (BM), followed by connective (supporting) tissue – the lamina propria.  - Pseudostratified is a simple epithelium (all cells contact the basement membrane), but the nuclei are situated at various levels and not all cells reach the apical side (the side that contacts the lumen or the “outside”). - Transitional epithelium is found in places where the underlying tissue can be stretched or relaxed, like in the bladder. In stratified epithelium, the name of the epithelium is determined by the shape of the most apical cell layer. - Have a free surface, apical surface. - Basal side. - Lateral side → what touches the other cells - Cells are polarized - Are typically avascular - Have a lot of tight junctions and gap junctions. - Also desmosomes, hemidesmosome, adherens and focal junctions → can be controlled by the nerve Mucociliary clearance Getting rid of mucus → cilia cells move in one direction to get the mucus to move Skin Stratified squamous epithelium → Top layer of squamous cells is responsible for the name! In skin, this top layer is keratinized. The cells have lost their nuclei. This layer of dead cells can become quite thick (hand palms and foot soles). - Fibroblasts are also present Glands A gland is formed as an indentation of surface epithelium into the underlying connective tissue (lamina propria). The gland can be simple (A, B, D) or branched (C,E,G,H,I). The end of the indentation (purple) transforms into a tubule (eg A) or acinus (eg E) and those cells synthesize and secrete their product. The remaining indentations form the duct (yellow). Such glands are named exocrine. In example (F) there are no ducts anymore; the acini are now named follicles and the product is secreted to the blood; this is an endocrine gland. - Sweat glands - Salivary glands - Digestive glands (pancreas, stomach…) - Endocrine glands (pancreas, thyroid, gonads, adrenal glands…) - Exocrine glands - Merocrine: cell stays intact - Apocrine: portion of cells is secreted - Holocrine: whole cell is secreted The thyroid gland differs from all glands mentioned before, because it lacks a duct. It is a so-called endocrine gland, a gland which secretes its products directly to the blood. Accordingly, the lamina propria surrounding the follicles is richly vascularized. In the case of the thyroid gland, the epithelial cells can also store their product in the follicle lumen, and distribute it to the blood later. The stored thyroid hormone is a colloid (fine dispersion of two phases). When the thyroid gland is active (hormone synthesis or hormone transport to the blood vessels), the epithelium is cuboidal to columnar. Inactive cells are flat (low cuboidal or squamous). Different types There is regular or irregular and loose or dense tissue - Dermis under skin is dense and irregular. - Tendons are dense and regular, arranged in the same directions. Connective (or supporting) tissues Are defined by their extracellular matrix (the substance surrounding the cells), which determines the tissue consistency: elastic, firm or rigid. All supportive tissues are of mesenchymal origin. Some mesenchymal cells undergo further differentiation, for example fat cells (fat storage), erythrocytes (red blood cells, contain no nucleus), leukocytes (white blood cells), monocytes (phagocytosis). The extracellular matrix of blood is plasma. Connective or supporting tissue (both names are found) consists of cells (e.g. fibroblasts) and extracellular matrix. Connective tissue supports and binds other tissues, facilitates transport and cell interaction, protects against microorganisms and has storage functions. The physical properties depend on the extracellular matrix secreted by the fibroblasts. This matrix consists of ground substance and different types of fibers: fibrillar collagen, elastin fibers, and reticular fibers. The ground substance of the bone matrix is an amorphous transparent semi-fluid (jelly-like) material. It consists of glycosaminoglycans (GAGs), proteoglycans (PGs), hyaluronic acid (HA) and water. The fibrous components define the physical properties of the connective tissue. The fibers can be distinguished by specific stains. - Is never exposed to the environment: except if you have a wound Connective tissue: a) supporting tissue Collagen fibers Consist of different polypeptides that form fibers of 2-20 µm (type I). These fibers show high tensile strength and form the supporting tissue of the dermis, tendons and ligaments as well as bones. Putting traction on those fibers does not result in lengthening. - Rich in glycine and proline. It also has 2 unusual amino acids: hydroxyproline, hydroxylysine. It makes a helical structure, 3 collagen strands will wind around each other. Elastic fibers Consist of tropoelastin, which is stretchable, and fibrous fibrillin. Those fibers are often found in membranes. After stretching, these fibers retract to their original form (like a rubber elastic). Elastic fibers are found in the lung, aorta, elastic ligaments, and cartilage. Reticular fibers Are very thin (1 µm) collagen type III fibers with bound glycoproteins. They can be visualized with special stains like PAS and silver. The fibers are slightly stretchable, mainly reinforcing the organs. They form a delicate branched meshwork of highly cellular (low amount of ground substance) organs like liver, bone marrow and lymphoid tissue. They join connective tissue to adjacent tissue. Connective tissue: b) cartilage and bones Cartilage and bones are special forms of connective tissue. Collagen fibers (types I-III) are part of their extracellular matrix. Different fibers result in different physical properties of cartilage. The physical properties of bone tissue are the result of the close interaction of hydroxyapatite (a calcium phosphate of the ground substance) and collagen. During development, a bone template is formed from connective tissue. Subsequently, most of this connective tissue is replaced by cartilage followed by ossification, resulting in the final bone. Cartilage is a semi-rigid tissue containing collagen type I, II and III fibers (only visible with special staining), with intermediate elasticity. The ground substance consists of sulfated GAGs (glucosaminoglycans), yielding the solid, yet flexible, consistency of cartilage. The different amounts and forms of fibers give rise to three main types of cartilage. The main form is hyaline cartilage containing collagen type I (not visible in the light microscope) found in joints. Elastic cartilage is more flexible due to a higher content of elastin fibers (ear). Fibrocartilage provides tensile strength and is found in the intervertebral disks. In the light microscope, the characteristic big chondrocytes are visible. Dividing cells are grouped closely together within the cartilaginous matrix. Bone is a rigid tissue. Calcification (hydroxyapatite crystals, Ca3(PO4)2-Ca(OH)2) of the ground substance is the cause. During mineralization of the bone, the osteoblasts that produce bone extracellular matrix, decrease in size, and are called osteocytes. The extracellular matrix of the mature bone represents 98% of the tissue. Osteoblasts and osteoclasts are special cells that help your bones grow and develop. Osteoblasts form new bones and add growth to existing bone tissue. Osteoclasts dissolve old and damaged bone tissue so it can be replaced with new, healthier cells created by osteoblasts. Connective tissue: c) fat and blood cells Fat cells (adipocytes) and blood cells (erythrocytes and leukocytes) are specialized mesenchymal cells related to the other connective tissue cells. During maturation, these cells develop special properties. Some of these properties are detectable under the light microscope as special cell forms and subcellular structures. Fat cells (adipocytes) are defined by their ability to store fat. As fat is not water soluble it has to be stored in special vacuoles within the cytoplasm. Early in development (embryo) several small vacuoles are visible (plurivacuolar), which merge to end up as one large vacuole in an univacuolar adipocyte. During this process, the cytoplasm gets reduced to a small space harboring the flattened nucleus and (light-microscopically invisible) organelles. During tissue fixation and preparation of the slides, the fat is washed out leaving a seemingly empty, white cell with a nucleus at the outer rim. Blood cells differ in their form and function. In general, one distinguishes red (erythrocytes) and white blood cells (leukocytes). The main histological difference is that mature erythrocytes do not contain a nucleus. Blood cells are replaced regularly by new cells produced within the bone marrow. In the bone marrow, one can also find huge cells called megakaryocytes which produce the platelets (thrombocytes). Platelets are anuclear (no nucleus) like the erythrocytes and play an important role in blood clotting. Leukocytes: macrophages Muscle tissue Can be divided into three subtypes: skeletal, smooth, heart. All of them contain contractile elements (such as actin, myosin), but differ in their ultrastructure. Muscle cells also are of mesenchymal origin. Muscle tissue is yet another tissue originating from mesenchymal precursor cells. Cellular differentiation results in the expression of typical muscle proteins and this defined tissue. Although contractility is an inherent property of nearly all cells of the body, the contractile elements myosin and actin are highly concentrated in muscle cells. In addition, muscle cells contain a special tubular system, the sarcoplasmic reticulum, which stores high amounts of Ca2+. When muscle cells connect in cooperative units, muscle tissue is formed. Three different types of muscle are distinguished: skeletal, smooth and heart muscle. The intracellular organization of actin and myosin, the location of the nucleus and the organization of the cells within the tissue can be used to distinguish those muscle types. Skeletal muscle (voluntary) Cells are syncytia (several cells fused together; diameter 55µm) containing several nuclei per cell. The cigar-shaped nuclei are located at the side of the elongated parallel orientated syncytia. The arrangement of the contractile proteins is responsible for the typical cross striation. Syncytium - cells together - from multiple fusions of uninuclear cells - Mostly fast and short - Moves the skeleton - Generates heat - Guards entrances and exits - Is striated, sarcomere: unit of muscle contraction Visceral striated muscle: movement of the tongue Axon of a motor neuron branches when it reaches the muscle and can innervate very few fibers (delicate movements such as the eye) or several hundreds (back muscles for posture). The neuron endings together with all the fibers it innervates are called a motor unit. Smooth muscle (involuntary) Cells are small (diameter 5µm) and do not show cross striation. Each cell contains one elongated nucleus, located in the middle of the cell. Like skeletal muscle cells, smooth muscle cells lie parallel to each other, forming strings. - Slow and long - Moves material through organs - No syncytium - Nucleus is central - very elongated  - They can behave as a syncytium → through direct contact with neurons or through gap junctions - Smooth muscle can stretch much more as skeletal muscle → through length adaptation Cardiac muscle (involuntary) Cells are ~100 µm long (diameter 15 µm) and branched, forming meshes. They are connected to each other via intercalated discs and gap junctions that allow the transmission of currents. Functionally, they form a syncytium. Heart cells are striated with one nucleus located in the cell center. - Moves blood through the body - Have intercalated disks - Have desmosome, adherens and gap junctions Nerve tissue Forms the central nervous system as well as peripheral nerves. Neurons, a subset of the glial cells and derivatives of sympathetic neurons (melanocytes, adrenal medulla cell) are members of this system. All of them originate from neuronal stem cells. Somatic nervous system Conscious voluntary control: Sensory and motor innervation to all parts of the body, except viscera (organs), smooth and cardiac muscle, and glands Reflex arcs: e.g. patella reflex or reflex retraction when touching something hot Autonomous nervous system Involuntary control: Smooth muscle - change of diameter of hollow tubes Cardiac muscle - innervation of the Purkinje fibers (specialized cardiac muscle cells) Glandular epithelium - synthesis, composition and release of secretions Macroscopy The nervous system is divided into 1) a central part, which includes brain and spinal cord, and 2) a peripheral part, consisting of peripheral nerves and ganglia (2%). Cells - Neuroglia cells: physical support, protection, insulation, repair of injury, supply of nutrients, clearance of neurotransmitters - Neurons: transmit information - large cell body - many dendrites to receive information Neuron The nervous system contains more than one hundred billion neurons (nerve cells). Each neuron has an average of one thousand connections with other neurons. Neurons provide communication within the nervous system, but also to muscles and glands, and receive information from sensors in the body. The communication occurs in two ways: via an electrical impulse (conduction within the neuron) and by chemical impulses for signal transduction at the synapse. Traditionally, scientists classify neurons based on function into three broad types: - Sensory - Motor - Inter Of these, interneurons are the most abundant. - Unipolar neurons: These neurons have a single long axon that is responsible for sending electrical signals. The axon in unipolar neurons is myelinated, which allows for rapid signal transmission. - Multipolar neurons: These neurons can receive impulses from multiple neurons via dendrites. The dendrites transmit the signals through the neuron via an electrical signal that is spread down the axon. - Bipolar neurons: These neurons send signals and receive information from the world. Examples include the neurons in the eye that receive light and then transmit signals to the brain. - Pseudo-unipolar neurons: These neurons relay signals from the skin and muscles to the spinal cord. They are the primary neurons responsible for coordinating the movement of the arms and legs using input from the brain. Construction of a neuron A neuron consists of a perikaryon (soma, cell body), the center of cell metabolism, dendrites, branched extensions which usually receive electrical information, and the axon (neurite) as a single, sometimes very long extension, which conducts electrical impulses away from the perikaryon, starting at the axon hillock. The telodendron (end) is usually branched and ends 88with buttons (end plates), where the electrical impulse is transferred chemically at the synapse by neurotransmitters. The perikaryon has a large nucleus with a clear nucleolus and many RNA-rich (rER) Nissl bodies. The axon is surrounded by a myelin sheath. This is formed by oligodendrocytes within the central nervous system and by Schwann cells in the peripheral nervous system. The tissue containing the glia cells as well as the perikaria of the neurons is called neuropil. 3. How are the tissues organized Tissues are organized into a hierarchy that contributes to the structure and function of the body. The organization follows this pattern: 1. Cells: The basic unit of life. Different cell types perform specific functions, such as muscle cells contracting or nerve cells transmitting signals. 2. Tissues: Groups of similar cells work together to perform a common function. For example, muscle tissue contracts to enable movement, while connective tissue provides support. 3. Organs: Different tissues combine to form organs. Each organ has a specific function and is made up of at least two types of tissue. For instance, the stomach contains epithelial tissue (for lining), muscle tissue (for contraction), and connective tissue (for structure). 4. Organ Systems: Organs work together in systems to carry out complex functions. For example, the digestive system includes the stomach, intestines, and liver, all working together to digest food and absorb nutrients. 5. Organism: All organ systems function in coordination within an organism, like the human body, to maintain homeostasis and support life. This hierarchical organization allows the body to function efficiently and respond to various physiological needs. Here are some open-ended questions based on the content of the document "Case 8 - Ossobuco" that align with a university-level understanding: 1. **Describe the four basic types of tissue found in the human body and explain the primary functions of each type.** 2. **Explain the difference between simple, pseudostratified, and stratified epithelia in terms of structure and function. Provide examples of where each type can be found in the body.** 3. **What are glands, and how are exocrine and endocrine glands structurally and functionally different? Use the thyroid gland as an example in your explanation.** 4. **Discuss the structural differences between collagen, elastic, and reticular fibers in connective tissue, and explain how these differences influence their respective roles in the body.** 5. **Describe the process of bone development from connective tissue, including the role of cartilage and the process of ossification.** 6. **Compare and contrast the three types of muscle tissue (skeletal, smooth, and cardiac) in terms of their structure, function, and location in the body.** 7. **What is the role of fibroblasts in connective tissue, and how do they contribute to the maintenance of the extracellular matrix?** 8. **Explain the function of the sarcoplasmic reticulum in muscle cells and how it contributes to muscle contraction.** 9. **Describe the hierarchical organization of cells, tissues, organs, and organ systems in the human body. Provide specific examples of each level of organization.** 10. **What is the role of the axon hillock in neurons, and how does it contribute to the initiation of electrical impulses?** 11. **Discuss the composition and function of cartilage, including the different types of cartilage and their specific roles in the human body.** 12. **How does the process of mineralization in bone tissue occur, and what role do osteoblasts and hydroxyapatite play in this process?** 13. **Describe the difference between univacuolar and plurivacuolar adipocytes and explain how fat storage evolves during cellular development.** 14. **Explain the process of nerve signal transmission within the nervous system, including the roles of dendrites, axons, and synapses.** 15. **Discuss the importance of the basement membrane in epithelial tissue, and explain how it interacts with the connective tissue below.**