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?
- Connective tissue (general connective tissue / connective tissue proper)
What are the specialised connective tissues?
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.
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
What does Connective Tissue Proper consist of?
- Ground substance
Identify the fibres in connective tissue.
- Collagen – flexible with high tensile strength
- Reticular – provide a supporting framework/sponge
- Elastin – allows tissues to recoil after stretch or distension
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.
What is the extracellular matrix?
Extracellular matrix – a term used to describe a complex extracellular structural network that consists of ground substance and fibres.
Briefly, compare and contrast loose and dense connective tissue.
I. Many cells
II. Sparse collagen fibres
III. Abundant ground substance
IV. Viscous, gel-like consistency
V. Important role in transport (by diffusion)
I. Few cells, nearly all fibroblasts
II. Many collagen fibres
III. Little ground substance
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.
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 structure and location of regular dense connective tissue.
- Collagen fibres are arranged in parallel bundles and are densely packed. Between the bundles are fibroblasts.
- Designed to withstand stress in a single direction.
- Seen in tendons, ligaments and aponeuroses.
Outline the structure and location of irregular dense connective tissue.
I. Collagen fibres are arranged in bundles orientated in various directions. Between the bundles are fibroblasts.
II. Designed to withstand stress in multiple directions.
III. Examples are submucosa of intestine and deep layers of dermis.
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.
Identify the fixed cells in connective tissue.
- Fibroblasts (and myofibroblasts)
- Mast cells
- Mesenchymal ‘stem cells’