Introduction to microscopic anatomy (Anatomy) Flashcards
Recognise the microscopic structure and function of a variety of types of tissue including: epithelium, glands, and connective tissue
Describe the process of autophagy and pathological effect of lysosomal disorders
Outline different rates of renewal for epithelia and identify diseases involving epithelium
- Epithelial tissue is characterised by high cell turn-over → tissue renewal, e.g. epidermis, small intestine.
- Epithelial tissue self-renewal depends on the activity of tissue specific stem or progenitor cells (their characterisation has been studied and described to great detail but some gaps in knowledge remain).
Examples:
- Intestinal Stem Cells characterised by the protein Lgr5
- Hair follicle cells
- Lung epithelium
Epithelium diseases
- The ability of epithelial tissue to renew carries a “risk”.
- Emergence of benign tumours (adenomas)
- Malignant transformation and the emergence of cancers, e.g. carcinomas or adenocarcinomas.
- Damage of the epithelium (faster than renewal capability) and impaired organ function, e.g. celiac disease due to an autoimmune response.
- Celiac disease in the intestinal system: micro-damage in the epithelium when immune response is mounted against gluten over time lead to irreparable damage
What are the types of human tissues?
Epithelial tissue
Connective tissue
Muscle tissue
Nervous tissue
3 types of epithelium
Squamous (flat)
- hearts, lungs, blood vessels (endothelium), membranes (mesothelium)
- functions: diffusion, filtration or secretion
Cuboidal (cube like)
- glands, kidney tubules
- functions: secretion, absorption
Columnar (rectangular)
- gastrointestinal tract, uterine tubes
- absorption, secretion
Simple (single layer)
- squamous; heart, lungs, blood vessels, membranes; diffusion, filtration, secretion
- cuboidal
Stratified (+ layers)
- Keratinised (K) squamous; skin; protects against injury. Includes a keratin layer, which is produced by keratinocytes. Makes the tissue impervious and waterproof
- Non-keratinised squamous (NK); Mouth; protects against injury
Pseudostratified (false appearance of multiple layers)
- ciliated; treachea, repiratory tract; propels mucous particles
- Cilia: an apical specialisation of epithelial cells. These are long, fine, hair-like, motile projections of the apical surface of epithelial cells. They contain a core of microtubules/contractile elements and beat synchronously. They are located in the upper respiratory tract.
- Microvilli: these are fine, finger-like projections on the surface of epithelial cells. They contain a core of microfilaments and increase the apical surface area of epithelial cells for absorption. They can be found in the gut.
Transitional (variable number of cell layers varies)
- Urinary system, bladder & urethra; allows stretching of lining
Types of muscle tissue
Muscle tissues are contractile cells
-
Skeletal muscle: limbs, abdominal wall, thoracic wall
parallel muscle cells (also called muscle fibers or myocytes) with multiple nuclei and striated appearance due to actin and myosin filaments - Smooth muscle: internal organs, e.g. gastrointestinal tract, blood vessels, uterus outer layer of internal organs, no striation and elongated nuclei
- Cardiac muscle: heart
Describe connective tissue
Connects and protects
- Bone, cartilage: strength, stability, repair
- Adipose tissue (fat tissue): provides protection for internal organs, insulation and acts as energy store
- Fibrous connective tissue (e.g. tendon): consists of fibroblast and protein fibres, e.g. collagen, repair
Characterised by the presence of defined extracellular, gaps between cells, filled by proteins
Fibrous connective tissue:
- Dense regular connective tissue (ligaments, tendons)
- Dense irregular connective tissue (glands, dermis), not parallel; more tangled
- Loose connective tissue - found beneath the skin, around blood vessels, muscles & nerves. Sparse fibers and elastic fibres
Specialised connective tissue:
- bone
- Adipose tissue
- cartilage
- Fluid connective tissue:**
Describe collagen
Type 1
- Large fibres, found in skin, tendon, bone, ligaments
Type 2
- small fibres; found in cartilage (collagens IX, X, XI )
Type 3
- Small fibres; found in blood vessels, parachymal organs, bone marrow, lymphoid tissues
Type 4
- Sheet like layer; found in basement membranes
Type 5
- Thin fibrils; basement membranes (smooth, skeletal muscle)
Blood as connective tissues
Blood plasma - non-cellular component of blood is essential for the transport of nutrients and molecules to different tissues and cells in the body.
WBC - defence
RBC - oxygen transport
- proteins
- fibers (fibrin); haemostasis
Nervous tissue
Neurons and glial cells (astrocytes, oligodendrocytes)
Highly specialised tissue
Glands
Are “constructed” from epithelial cells including specially adapted secretory epithelial cells.
Can be divided into exocrine and endocrine (ductless glands that releases secretions directly into the blood.)
Can be unicellular (one cell, goblet cells in intestinal and respiratory epithelium) or multicellular (many cells) that secrete through a duct on the surface of the epithelium, salivary glands, sebaceous glands, sweat glands.
mode and type of secretion
Autophagy (self-eating)
- Digestion of cytosol, molecules (proteins) and worn-out organelles.
- Completed thought the action of lysosomes.
- Autophagy can be non-selective, employed in times of starvation or selective, employed in order to remove cell components during periods of cell growth or differentiation or the removal of organelles such as mitochondria, peroxisomes, ribosomes which are either worn out or surplus.
- Autophagy is important in innate immunity as a response to infection.
Lysosomes
- Contain digestive enzymes, acid hydrolases that can break down biomolecules (proteins, nucleic acids, lipids, sugars)
- Low pH environment
- Heterogenous organelles
- A special category of lysosomes are melanosomes, which are found in melanocytes and hold melanin pigments. The melanosomes secrete melanin by exocytosis, contributing to skin pigmentation.
Function
- A portion of the cytoplasm is surrounded by a double membrane creating an autophagosome
- The autophagosome fuses with a lysosome leading to biomolecule or organelle degradation.
- Autophagosome formation is tightly controlled.
- Cell metabolism signalling pathways are also involved in the formation of an autophagosome.
- Damaged mitochondria are removed through mitophagy.
For biomolecules or entities that enter a cell by endocytosis, endosomes fuse with lysosomes creating endolysosomes
Disorders
- An impairment of the autophagy process can lead to the accumulation of molecules in lysosomes, e.g. in neurodegenerative disorders the accumulation of tau proteins has been attributed to a decline in the autophagic removal of these molecules.
- Impaired mitophagy (mitochondria degradation through autophagy) is linked to a form of early onset Parkinson’s disease
- Lysosomal storage diseases lead to accumulation of undigested biomolecules and have a genetic cause.
- During aging, autophagy gradually declines.
