Specialised tissues Flashcards
Explain the classification of epithelia (cell shape vs cell stratification)
Shape;
- squamous (flattened)
- cuboidal
- columnar
Layering;
- single layer (single epithilium)
- multi layered (stratified epithilium)
Simple squamous; Lung alveolar, mesothelium, endothelium
Simple cuboidal; Kidney collecting duct
Simple columnar; Enterocytes
Stratified squamous; Epidermis (keratinising), lining of mouth/anus/cervix/vagina (non-keratinising)
Pseudostratified; Upper airway (bronchi) epithelium
Recognise how epithelial function (including absorption, secretion, fluid transport and protection) is determined by the type and organisation of epithelial cells and summarise patterns of cell division found in different epithelia
Epithelia function; must be directional
Polarity is required to give directionality to the epithelium
Belt functions can segregate the epithelial plasma into apical and basolateral domains (different lipid and protein composition and distinct function)
Transport;
- Plasma membrane contains high concentration of ion transporters (can be found in the proximal convulated tubule of the loop of Henle)
- there is extensive basal membrane infolding resulting in a higher number of mitochondria and increases the amount of water and ion molecules that are pumped
Absorptive;
- Found on brush-border membranes – enterocytes, kidney PCT cells
- Secretory cells interspersed through absorptive cells
- similar to the transporting cells
Secretory;
- Exocrine/endocrine (ex pancreas)
- Constitutive – secretory vesicles move directly to plasma membrane (hepatocytes)
- Stimulated – vesicles stored in cytoplasm and released after signal
- solutes like glucose are pumped across cell layers against the concentration gradient –> why arent these concentrations lost by back diffusion ?
- it is because of tight junctions
Protective;
- Usually stratified-squamous – skin, lining of oesophagus
- forms thick layer that protects underlying tissues from various physical adn chemical insults ( heat, cold, solvents, abrasion)
- Keratinising and non-keratinising
Patterens of cell division;
cell turnover; a balance between cell profileration and cell death, it is key in maintaning the architecture of tissues
- the rate at which cells die and are replaeced varies considerably between tissues.
- Lining of the gut ; 3-10 days
- fat, heart muscle and bone; 8-10 years
- neuronal cells; are not replaced
- In intestinal vili new cells are produced by the crypt stem cells and are lost from the villus tip
Inhibition of intestinal crypt cell proliferation results in flattening of intestinal wall
- cell loss = cell production -> steady state
- cell loss > cell production -> reduction in tissue mass
- cell loss < cell production -> increased tissue mass
in case of chemeotherapy cell division is stopped, slows down.
- vili shortens and the villus tip but is not replaced at thje from the crypt stem cells
Adenoma; which is non-malignant tumor is the result of exessive cell profileration
Infectious cells can affect turnover epidermis; human papillima virus can increase profileration adn cause hard skin/corns
Another example
- is the cyclic production and loss of the endometrial epithelial lining of the uterus in the menestrual cycle
- the large increase during pregnancy in the number and size of the epithelial glands of the breast and their loss after weaning (stopping breast feeding)
Explain the structure and function of the skin, explain the mechanisms by which integrity is maintained
Functions;
- Protection against injury
- Protection against pathogenic organisms
- Waterproofing and fluid conservation
- Thermoregulation
- Protection against radiation, absorption of ultra violet radiation and vitamin D production
- Surface for grip
- Sensory organ
Structure;
(1)Epidermis:
-
Stratum Corneum;
- Corneocytes, flat cells with no nuclei
- Protective
- Defects lead to eczema due to filagrin gene mutation
- Stratum Granulosum
-
Stratum Spinosum
- Prickle (spinous) cells- keratin producing epidermal cells
- Desmosomes
-
Stratum Basale
- Basal cells (connect to basement membrane)
- Keratinocytes mainly found here
- Stratum Lucidum
(2)Dermis:
- supportive connective tissue matrix
- Collagen (70%), elastin, glycosaminoglycans (GAGs)
- Fibroblasts
- Immune cells
- Blood vessels, lymphatics
Dermo-epidermal junction
Components;
- Lamina lucida
- Lamina densa
- Anchoring fibrils
- Hemidesmosomes
- Anchoring filaments
Clinical conditions;
- •Bullous Pemphigoid
- •Epidermolysis Bullosa
Recall the development, function and control of melanocytes
- Melanocytes originate from the neural crest
- Melanocyte surround keratinocyte in stratum basale of epidermis
- 1 melanocyte+ 36 keratinocytes
- Melanocytes –> melanin –> melanosomes in nearby keratinocytes to shield the nucleus
Eumelanin;
- dark pigment that predominates in black/brown hair
- there are two different types of eumelanin (brown eumelanin and black eumelanin)
- A small amount of brown eumelanin in the absence of other pigments causes blond hair
Pheomelanin;
- lighter pigment found in red hair, and is concentrated in lips
- Because people with red hair are less able to make the dark eumelanin pigment, their skin is generally quite pale and burns easily with sun exposure.
Summarise the structure and function of hair, recall the development and structure of the hair follicle
Function;
- Protection
- Sensation
- thermoregulation
Types;
- Lanugo;
- fine, long, it is formed in 20 weeks foetus
- shed before birth
- seen in pre-mature babies and anorexics
- Terminal
- Long, thick, dark hair
- scalp, eyebrows, eyelashes, pubic, axillary and beard region
- Start off as vellus, differentiation in puberty triggered by androgens
- Vellus;
- Short, fine, light hair
- covers the body
Development and structure;
- Hair made up of pilosebaceous units
- Hair follicle- invagination of the epidermis
- hair shaft
- Sebaceous gand
- Arrector pili muscle (isthmus)
- Dermal papilla- vasculature, sensitive to androgens
- Hair bulb- fed blood by dermal papilla; germinative cells (in pigmented hair there are melanocytes)
Summarise the regulation of hair growth
- Anagen
- Growth
- 85% of hair
- Highly vascularised, energy intensive
- Catagen
- Cell division slows and stops
- End of shaft keratinises + forms club shape
- Dermal papilla and club moves towards base of muscle insertion
- Telogen
- Hair is shed actively and the next anagen phase begins.
- The club hair can take 4-6 weeks to be released
( we go from Telogen to Anagen)
Telogen Effluvium;
- thinning of hair due to early entry of hair into telogen phase.
- Aetiologies include emotional as well as physiological stress (hypothyroidism, sepsis and anemia).
Effects of age; (in the scalp)
- 2-3 weeks–> Catagen
- 2-3 months–> Telogen
- 2-6 years–> anagen
Effects of sex hormones
Testosterone surge in beginning of puberty changes vellus to terminal hair
- Pubic hair and axillary hair grows first
- Then beard and chest
- In elderly, nose and ear hair
- In the scalp there is androgen sensitive hair- determines balding pattern
- This is known as androgenic alopecia
Summarise the functions, structure and growth of nails
Function;
- Protection
- Touch
- communication
Structure;
- Alpha keratin, little Ca2+
- Longitudinal ridging
- Proximal to distal curvature
Growth;
- Nail grows from germinal matrix
- Distal end is called lunula clubbing
- nail surface is produced by proximal nailbed
- Nail grows out because of adhesion
- Top of nail plate is produced by the most proximal portion of matrix
- Nail can grow up to 1 week post-mortem
List cell types within the nervous system, recall their functions
Nervous system;
-
Brainstem ;
- midbrain, pons, medulla (in desending order)
- target source of all cranial nerves
-
Cerebellum;
- attached at the back of the brainstem
- responisble for motor co-ordination; balance+posture
-
Spinal cord
- extend down from medulla
- neural transmition and reflexes
-
Cerebral hemispheres
- higly convulated surface of ridges(gyri) and valleys(sulci)
- 4 functional regions
- frontal
- parietal
- occupital
- temporal
Gyrus; fold between two clefts on a cerebral hemisphere, which is surrounded by a sulcus (gyrus=hill, sulcus=valley)
- Development starts from the prenatally and antenatally form the neural tube.
- Disorders in sulci/gyri formation is associated with architectural disturbances of the cortex, often presenting as epilepsy.
Cells of the nervous system ;
-
Unipolar
- 1 axonal projection
-
pseudounipolar
- 1 axonal projection + divides into 2
-
bipolar
- 2 axonal proections from the cell body
-
multipolar
- Pyramidal- pyramid-shaped cell body
- Purkinje- GABA neurons found in the cerebellum
- Golgi- GABA neurons found in the cerebellum
Recall the components of a neuron
-
SOMA
- Nucleus and ribosomes
- Neurofilaments for transport and structure
-
AXON
- Originates from axon hillock at soma
- Covered in myelin
- Can branch off into collaterals
-
DENDRITE
- Highly branched
- Non-myelinated
- Receive signals from other neurons
Other cells of the CNS
Astrocytes
- most abudant cell type in the CNS
- provides repair, homeostasis, synapse formatio, neuronal maturation, plasticity and immunity
Oligodendrocyte
- numerous projections that form internodes of myelin
- variable morphology and function
Schwan cells
- myelinates 1 axon only
- produces myelin for peripheral cells
Microglial cells
- immune functions, specialized cells–> similar to macrophages
Epemdymal cells
- line fluid filled vesicles
- regulation and production of Cerebrospinal fluid (9CFS)
Intracellular communication, resting membrane potential and action potential
Major physiological ions;
- potassium (K+)
- sodium (Na+)
- chloride (Cl-)
- calcium (Ca2+)
- Cell membrane is impermeable to such ions and transport is done by pumps and channels
- This causes an uneven ion distribution: (extracellular positive and intracellular negative)
High extracellular - Na+ & Cl-
Low extracellular - K+
High concentration gradient for Ca2+
For neuronal cells
- Negative charge inside compared to outside
- RMP of between -40 to -90mV
Action potential;
-
Resting membrane potential
- Voltage-gated Na+ channels (VGSCs) & voltage-gated K+ channels (VGKCs) are close d
- Membrane depolirization; opening of VGSC ® Na+ influx causing further depolarisation
- Membrane re-polarization; VGKCs opens at a slower rate and causes efflux of K+ from cell
-
Saltatory conduction; AP spreads across the axon by “cable transmition”
- Myelin prevents AP from spreading –> high resistance
- Nodes of Ranvier; small gaps along the axon –> AP jumps between nodes
-
Synapse;
- Action potential reaches presynaptic terminal
- Opens Ca2+ channel; Ca2+ influx and vesicle exocytosis
- Neurotransmitter released & binds to post-synaptic receptors to elicit a response
- Two fates of Neurotransmitters
- Enzyme metabolism
- Recycled by transporter protein
Recall the ultrastructure of skeletal muscle, list functional characteristics
Consists of :
a bundle of myofibers;
- large and cylindrial
- many nucleous
- consist of 4 structures;
- A-Band
- Dark band, intersected by a darker region called H-Zone
- I-Line
- Light bands, intersected by a dark line called Z-line
- Z-Line
- Made up of a-actinin CapZ
- Sarcomere
- Functional unit between two adjacent Z-Lines
- A-Band
A-lines and I-Lines give the striated colours to muscle fibres
Explain the process of excitation-contraction coupling
Myofibres have:
- T-tubules: Membrane invaginations that contact the extracellular fluid
- Sarcoplasmic reticulum (SR): extensive network of Ca2+-stores surrounding each myofibril
Excitation-contraction (E-C) coupling
- Action potential (AP) propagates along myofibre membrane (sarcolemma) & T-tubules
- Depolarisation activates dihydropyridine receptors (DHPR) ® conformational change in DHPR
- The conformational change is transmitted to ryanodine receptors (RyR) on SR ® opening of RyR & Ca2+ release from intracellular stores
- Thus depolarisation leads in an Increase in intracellular Ca2+
Draw a sarcomere (7components)
- Z-line - Defines lateral boundaries of sarcomere
- Actin - Polymeric thin filament composed of two twisted a-helices - displays polarity
- Myosin - Thick filaments ® ‘motor proteins’. Contain numerous ‘globular heads’ that interact with actin
- Titin - Very large ‘spring-like’ filaments anchoring myosin to the Z-line
- Nebulin - Large filaments associated with actin
- Tropomyosin - Elongated protein bound to actin
- CapZ & Tropomodulin - associated with +ve & –ve ends of actin, respectively
Explain the cellular mechanisms resulting in contraction
- In the presence of Ca2+ there is a movement of troponin from tropomyosin chain
- Movement exposes myosin binding site on surface of actin chain
- ‘Charged’ myosin heads bind to exposed site on actin filament
- Binding and the stimultaneous discharge of ADP causes the ‘power stroke’ pulling actin filament towards centre of sarcomere
- ATP binding releases myosin head from actin chain
- ATP hydrolysis provides energy to ‘recharge’ the myosin head
