BL Session 2 - Integrating Cells Into Tissues Flashcards
Outline the arrangement of cells together on a basement membrane.
- Cells sit on a basement membrane.
- The basement membrane is the structural site for overlying cells and underlying connective tissue.
- Cells attach to the basement membrane by either:
I. Hemidesmosomes – found in tissues subject to abrasion, such as skin, epithelium of oral cavity.
II. Focal adhesions – that anchor intracellular actin filaments to the basement membrane. They play a prominent role in cell movement such as migration of epithelial cells in wound repair.
Outline the structure and function of integrins.
- Integrins are transmembrane proteins that function mechanically, by attaching the cell cytoskeleton to the extracellular matrix (ECM), and biochemically, by sensing whether adhesion has occurred.
- Integrins have two main functions:
I. Attachment of the cell to the ECM
II. Signal transduction from the ECM to the cell.
Identify the different types of cellular communication
- Direct contact communication: through gap junctions
- Autocrine communication
- Paracrine communication
- Endocrine communication
- Synaptic communication
- Neurocrine communication
Outline cell renewal in the living body.
- Static – CNS, cardiac and skeletal muscle cells
- Stable – fibroblasts, endothelium, smooth muscle cells
- Renewing – blood, skin epithelium, gut epithelium
There is a relationship between cell renewal rate and the propensity to develop cancer.
What is the endosymbiotic theory?
- Endosymbiotic theory: At some stage an aerobic bacterium was taken into an anaerobic eukaryote and formed an organelle which later became a mitochondrion – cells and complex life could develop.
- Based on this information, scientists believe that mitochondria and chloroplasts used to be prokaryotes. Early anaerobic eukaryotes engulfed them and they now live in endosymbiosis.
What are the 4 basic tissue types?
- Epithelial
- Muscle
- Nerve
- Connective tissue (general connective tissue / connective tissue proper)
What are the specialised connective tissues?
- Adipose
- Lymphatic
- Blood
- Haemopoietic
- Cartilage
- Bone
Explain what is meant by the term epithelium.
- Epithelium: A tissue composed of cells that covers the exterior body surface and lines internal closed cavities and body tubes that communicate with the exterior.
- Epithelium also forms the secretory portion of glands and lines their ducts.
- In addition, specialised epithelium functions as receptors for the special senses (smell, taste, hearing and vision).
Most epithelial cells have a free surface and exhibit ‘polarity’. Identify the relevant domains.
- Apical domain
- Lateral domain
- Basal domain
Provide examples of the epithelium apical domain.
- Microvilli, cytoplasmic processes that extend from the cell surface. Examples are intestine and kidney tubule.
- Stereovilli, particularly long microvilli limited to epididymis and sensory hair cells of the ear.
- Cilia, motile cytoplasmic processes that can beat in synchrony with a rapid forward movement called the effective stroke and a slower return recovery stroke. Examples are the tracheobronchial tree and the oviducts
Compare and contrast necrosis and apoptosis,
- Necrosis is a form of cell injury which results in the premature death of cells in living tissue by autolysis.
- It is caused by factors external to the cell or tissue, such as infection, toxins, or trauma which result in the unregulated digestion of cell components.
- Necrotic cells swell and burst because of failure of action of Na, K ATPase.
- In contrast, apoptosis is a naturally occurring programmed and targeted cause of cellular death.
- While apoptosis often provides beneficial effects to the organism, necrosis is almost always detrimental and can be fatal.
- Cellular death due to necrosis does not follow the apoptotic signal transduction pathway, but rather various receptors are activated, and result in the loss of cell membrane integrity and an uncontrolled release of products of cell death into the extracellular space.
Define osmosis.
Osmosis, is the spontaneous net movement of solvent molecules through a semi-permeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides.
Define oncotic pressure.
Oncotic pressure, or colloid osmotic pressure, is a form of osmotic pressure exerted by proteins, notably albumin, in a blood vessel’s plasma (blood/liquid) that usually tends to pull water into the circulatory system.
What is osmolality?
- It is a function of the concentration of particles in solution. For this reason, it is expressed in osmoles or milliosmoles (mOsm/kg).
- For glucose or urea, the osmotic pressure is a function of the number of molecules present. For a solute that ionises, such as NaCl which forms Na+ and Cl- then each mole in solution would provide 2 Osm.
- For practical purposes in medical use the terms osmolarity and osmolality are interchangeable. Osmolality is used in clinical practice.
- Serum/urine osmolality is measure using a freezing point depression technique
- Normal plasma osmolality is 290 mOsmol/kg as measured by freezing point depression. The range is 285-295 mOsmol/kg
What needs to be maintained in homeostasis?
- Concentration of oxygen, carbon dioxide, salt and other electrolytes
- Concentration of nutrients, waste products
- pH of internal environment
- Temperature of internal environment
- Volume and pressure of body fluid compartments
Outline abnormal pH due to shock.
- Abnormal plasma pH nearly always results from major organ dysfunction. The common organs that lead to pH abnormality are lungs, kidneys and liver. However, the other common cause of a low pH is poor tissue perfusion – shock
- When tissues are poorly perfused anaerobic glycolysis leads to lactic acid production and lactic acidosis which lowers pH. This acidosis itself impairs cardiac function – a vicious downwards spiral!
- Normal plasma lactate is less than 1.6 mMol/L
I. 2.0 – 4.0 reflects a significant underlying illness
II. >4.0 – reflects a very serious underlying illness
What are the general functions of connective tissue?
- Connects cells to form tissues, connects tissues to form organs and connects organs to form the body. Some tissues provide support as well as connecting (cartilage and bone)
- Defence against infection (blood, lymph, fixed and wandering cells)
- Wound healing (macrophages, fibroblasts, myofibroblasts)
- Protection – provide a cushion between tissues and organs and provides insulation (adipose tissue)
- Storage – adipose tissue
- Transportation – provide a medium for diffusion of nutrients and wastes
Outline the structure and function of ground substance in connective tissue.
- Ground substance is a viscous, clear substance with a slippery feel. It has a high water content. Composed of proteoglycans.
- A proteoglycan is a large macromolecule consisting of a core protein to which glycosaminoglycans (GAGs) are covalently bound.
- GAGs attract water to form a hydrated gel that permits rapid diffusion but also resists compression.
Outline the structure, function, location and examples of loose connective tissue.
- Loose connective tissue is primarily:
I. Located beneath epithelia (to facilitate diffusion)
II. Associated with epithelium of glands
III. Located around small blood vessels
- All of the above, are sites where pathogens, such as bacteria that have breached an epithelial surface, can be challenged and destroyed by the cells of the immune system. During these reactions, loose connective tissue can undergo considerable swelling.
- Examples:
I. The superficial layer of the dermis in the skin consists of loose connective tissue
II. The submucosa of the colon consists of loose connective tissue
Outline the dense regular connective tissue of the tendon.
Dense regular connective tissue of the tendon – In tendons that connect muscles to bones, the collagen bundles lie in a parallel, densely packed formation in line with the tensile force exerted by the muscle.
Describe the structure of ligaments.
- Connect bone to bone
- The collagen bundles are densely packed in parallel arrangement, but undulate and are arranged in fascicles, separated by loose connective tissue.
What is an aponeurosis?
Aponeurosis: Means a flat sheet of regular CT with bundles of fibres in one layer often arranged at 90° angle to those in adjacent layers.
Outline how the structure of the dermis is suited to its function.
- The dermis is a dense irregular connective tissue.
- The bundles of collagen are densely packed but irregularly arranged, such that they are orientated in multiple directions. The skin can thus resist forces in multiple directions to prevent tearing.
- The elastic fibres allow a degree of stretch and a restoration to the original shape after the skin is bent or folded.
Outline how the structure of the fibroblast (and myofibroblast) is suited to its function.
- Fibroblasts synthesise and secrete both ground substance and the fibres that lie within the ground substance.
- They are very important in wound healing and are the cells primarily responsible for the formation of scar tissue
- Myofibroblasts are modified fibroblasts that contain actin. They are responsible for wound contraction when tissue loss has occurred.
Outline the function of macrophages.
- Macrophages are derived from blood monocytes which move into loose connective tissue, especially when there is local inflammation.
- Macrophages are phagocytic and can degrade foreign organisms and cell debris.
- Macrophages are professional APC’s
Outline the structure and function of a mast cell.
- Mast cells are small resting lymphocytes that look like blood basophils but are not derived from them.
- They are found in connective tissue near blood vessels, but are absent from the CNS to avoid damaging effects of oedema there.
- Mast cell cytoplasm contains abundant granules. These granules contain:
I. Histamine (increases blood vessel wall permeability)
II. Heparin (an anticoagulant)
III. Substances that attract eosinophils and neutrophils
- Mast cells become coated in IgE - molecules which specifically bind allergens. When an allergen cross-links these surface-bound igE molecules, the contents of the granules are all rapidly released from the cell.
- The secretions of the granules can result in immediate hypersensitivity reactions; allergy and anaphylaxis
Outline the significance of Vitamin C.
- Fibroblasts secrete procollagen that is converted to collagen molecules outside the cell. The collagen molecules are then aggregated to form the final collagen fibrils
- Note that Vitamin C is required for the intracellular production of procollagen.
- Vitamin C deficiency leads to scurvy which include poor wound healing and impaired bone formation.
- Osteogenesis imperfecta is due to abnormal Type 1 collagen.
Describe reticular fibres in a lymph node.
- The lymph node’s capsule contains collagen bundles.
- A trabecula extends from the capsule into the node.
- Reticular fibres consist of Collagen type III
- Reticular fibres form an irregular anastomising network throughout the node
- Lymphocytes are densely packed in the spaces between the fibres.
Describe the structure and function of elastic fibres.
- Elastin is the primary component of elastic fibres, but itself enfolds and is surrounded by microfibrils called fibrillin.
- It occurs in most connective tissues but to widely varying degrees.
- Amongst the sites at which elastic fibres have an important role are the dermis, artery walls, lungs and those sites bearing elastic cartilage.
Describe the structure of white adipose tissue cells?
- Most adipose tissue in the body is white fat.
- In a typical H&E stained, wax-embedded preparations, the cells look empty. They are empty because thee toluene and xylene, used in tissue preparation, have dissolved away the lipid.
- Adipose tissue contains fat, a fuel reserve, but also has a role in thermal insulation and in shock-absorption.
- Unilocular adipose cells are almost completely filled by a single fat droplet. The cytoplasm is displaced to the rim of the cell and the nucleus is displaced to the periphery of each adipocyte,
Outline the structure and function of brown adipose tissue cells.
- Brown fat cells (multilocular adipose cells) each contain many lipid droplets and a central nucleus.
- These cells are found close to the scapula, sternum and axillae, especially in the newborn. They are also present in the upper chest and neck of adults.
- The brown colour is due to the rich vascular supply and abundant mitochondria. There is thus a high respiratory capacity for the generation of heat
- ‘Non-shivering thermogenesis’ is important for babies and for hibernating animals
