Tissues 2 Flashcards
Name the 4 cerebral hemispheres and locate them
Frontal, Temporal, Parietal, Occipital
Name the convoluted ridges of the brain
Gyri are the ridges
Sulci are the grooves
What is the brainstem composed of
Midbrain, pons and medulla
What is the function of the brainstem
Target source of all cranial nerves with numerous functions
Locate the cerebellum and give its function
Hindbrain attached to the brainstem
Motor coordination, balance and posture
What is the function of the spinal cord
Conduit for neural transmission
Co-ordinates some reflex actions
Outline the following: Unipolar Pseudo-unipolar Bipolar Multipolar
Unipolar - 1 axonal projection (Rare)
Pseudo-unipolar - single axonal projection dividing into 2
Bipolar - 2 projections from the cell body
Multipolar - numerous projections from the cell body (only 1 axon)
Give 3 examples of multipolar neurones
pyramidal
Purkinje
Golgi
Describe astrocytes
Most abundant in the CNS
Able to proliferate
Neuroglial
What are the functions of astrocytes
Structure
Cell repair
Immune cells
Neurotransmitter release and re-uptake
Describe an oligodendrocyte
Variable morphology and function
Numerous projections that form internodes of myelin
Myelinates axons
What is the function of Schwann cells
Produces myelin for peripheral nerves
What is the function of Microglial cells
Immune functions in the CNS
What is the function of ependymal cells and where is it found
Regulates the production and movement of cerebrospinal fluid. Found lining fluid filled ventricles
Explain the process of intracellular communication through a synapse
- AP propagates along the axon
- AP opens voltage-gated channels at the presynaptic terminal
- influx causes vesicle exocytosis
- NT binds to receptors on the post synaptic membrane to activate them for post-synaptic activity
- NT dissociates from the receptor and is metabolised by enzymes in the synaptic cleft or is recycled by transporter proteins
Give some common features of neurones
Soma - contains nucleus and ribosomes
Axons - originates from the soma at the axon hillock and branch off into collaterals (myelinated)
Dendrites - highly branched endnote covered in myelin, receiving signals from other cells
What are the 4 major physiological ions for RMP
potassium, sodium, chloride, calcium
How is resting membrane potential generated in neurones
Cell membranes are impermeable to some ions so transportation is regulated by channels and pumps which cause uneven ion distribution. Differences in concentration produces the potential difference
Describe the process of action potential generation in neurones
- sodium channels open to induce sodium influx
- depolarisation
- potassium channels open at a slower rate
- depolarisation of the cell
- sodium potassium ATPase restores the gradient
What is the function of myelin
Prevents AP propagation
What is the function of nodes of Ranvier
Provides small gaps that the AP can jump across for faster transmission
What is the function of skeletal muscle
Produces movement relative to the external environment
What do antagonist muscle pairs consist of
Flexor (bicep)
Extensor (tricep)
What is isotonic contraction ands what are the two types
Muscle changes length while tension remains the same
concentric - shortening
eccentric - lengthening
muscle tension > force exerted by load
What is isometric contraction
tension develops but muscle does not change in length e.g. carrying a bag
muscle tension = force exerted by load
myosin heads reattach to the same point on the actin chain
Describe the ultrastructure of skeletal muscle myofibres
Consists of myofibres (bundles) large and cyclindrical multinucleated packed with myofibrils sarcoplasmic reticulum - calcium stores T-tubules
Describe the structure of a sarcomere
Z-line - Lateral boundaries
Actin - Polymeric thin filament composed of two twisted 𝛼-helices - displays polarity
Myosin - Thick filaments with globular heads that interact with actin
Titin - Very large springy 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 sliding filament theory
- Ca2+ release -> movement of troponin from tropomyosin
- Exposure of the myosin binding site on the actin chain
- Charged myosin heads bind to the exposed sites
- Binding + ADP discharge causes the myosin head to pivot (power stroke), pulling the actin filament towards the centre of the sarcomere
- ATP binding releases myosin head from the actin chain
ATP hydrolysis provides energy to recharge the myosin head
Explain the process of excitation in skeletal muscle
- Action potential propagates along the myofibre membrane (sarcolemma) 7 T-tubules
- Depolarisation activates dihydropyridine receptors (DHPR)
- Conformational change in DHPR
- Transmission to ryanodine receptors (RyR) on sarcoplasmic reticulum
- Opening of RyR & release of Ca2+ from intracellular stores
- Depolarisation -> increase in intracellular Ca2+
What are the pacemaker cells of the heart
SA node : small empty spindle shaped cells that are spontaneously active
AV node: spindle shaped network of cells at the base of the right atrium
What are the conducting fibres of the heart
Bundle of His: fast conducting cells adjoining AV node and Purkinje fibres
Purkinje fibres: large cells for rapid conduction
What are intercalated disks in cardiac muscle
specialised regions connecting individual cardiomyocytes
contains numerous gap junctions for APs to spread
Describe excitation contraction coupling in cardiomyocytes
Same as skeletal muscle
depolarisation opens voltage-gated calcium channels
What effects does calcium have in cardiac muscle
Ca2+ induced Ca2+ release by binding to RyR on SR
Initiate contraction binding to troponin
Further depolarisation
Describe the structure of smooth muscle
in walls of hollow organs e.g. blood vessels and the GI tract
doesn’t have the regular arrangement of actin and myosin
Explain the process of excitation contraction coupling in smooth muscle
- Depolarisation activates voltage gated Ca2+ channels
- Ca2+-CaM complex activates myosin light chain kinase
- MLCK phosphorylates myosin light chains
- Cross -bridges form with actin filaments -> contraction
Why do cells communicate
process information, self preservation, voluntary movement, homeostasis
Describe endocrine signalling and give an example
hormone travels via blood vessels to act on a distant target cell
Glucagon is secreted from the pancreas travels in the blood stimulates glycogenolysis and gluconeogenesis in the liver
others: insulin acting on liver, muscle cells and adipose tissues
adrenaline from glands acting on the trachea
Describe paracrine signalling and give an example
Hormone acts on an adjacent cell
insulin released by beta cells inhibits glucagon secretion in adjacent alpha cells (+endocrine)
others: NO in endothelial cells in blood vessels
Osteoclast activating factor produced by adjacent osteoblasts
Describe aubocrine signalling and give an example
Signalling molecule acts on the same cell
Activated TCR initiates a cascade of reactions in the cell, expressing interleukin 2 receptor. Secretion of IL-2 also binds to IL-2 receptor on the same cell
other: acetycholine
growth factors e.g. TGFB form tumour cells
Describe signalling by membrane attached proteins and give an example
plasma membrane proteins on adjacent cells interacting
APCs presenting parts of the pathogen through MHC I
circulating T cells engage with MHC molecules through TCR
others: HIV GP120 glycoprotein
bacterial cell wall components
Describe ionotropic receptors
Ligand binding opens an ion permeable pore leading to a signal transduction event
- ligand binds to receptor
- change in conformation of channel
- pore opens
- movement of ions according to gradient
Give an example of ionotropic receptor action
nicotinic acetylcholine
Acetylcholine causing muscle contraction in skeletal muscle
GABAa (gamma amino butyric acid) causes a decreases in neuronal excitability in neurones
Describe G-protein coupled receptors
Ligand binds to activate an intracellular G-protein
1. 7-TM receptor + heterotrimeric G-protein are inactive
2. Ligand binds changing conformation of the receptor
3. G-protein binds to the receptor
4. GDP exchanged for GTP
5. G-protein dissociates into 2 active units (alpha & gamma+beta)
6. units bind
7. GTPase dephosphorylates GTP to GDP
8. alpha subunit dissociates and becomes active
Receptor is active as long as the ligand is bound
What are the 3 types of G-protein coupled receptors and what are their functions (+examples)
Gs - stimulates adenyl cyclase
ATP -> cyclic AMP -> Activated protein kinase A
e.g. beta adrenergic receptor to increase heart rate
Gi - inhibits adenylyl cyclase
reduces PKA levels
e.g. Muscarinic receptor to decrease heart rate
Gq - stimulates phospholipase C
PIP2 -> IP3 + DAG -> calcium release + PKA activation
e.g. angiotensin receptor to vasoconstrict
Describe enzyme-linked receptors
Ligand binds to cause clustering of receptors
- ligand binds
- receptors cluster to activate enzymes
- enzymes phosphorylate the receptor
- signal proteins bind to cytoplasmic domain
- recruit other signal proteins to generate the signal
Give an example of enzyme-linked receptors
insulin receptor (CD220) insulin causes glucose uptake
ErbB
Epidermal growth factor causing cell growth and proliferation
Guanylyl-cyclase
Atrial natriuretic peptide causes vasodilation to decrease blood pressure
Ser/Thr-kinase
Transforming growth factor beta causes apoptosis
Describe type 1 signal transduction
cytoplasmic
association with chaperone molecules (heat shock proteins)
1. hormone binds to receptor
2. HSP dissociates
3. 2 hormone-bound receptors -> homodimer
4. translocates -> nucleus + binds to DNA
Describe type 2 signal transduction
nuclear
- hormone ligand binds
- transcriptional regulation
Give an example of signal transduction
glucocorticoid
cortisol/corticosterone causes a decrease in immune response and an increase in gluconeogenesis
Thyroid hormone
T4 and T3 cause growth and development
Give 3 common skin diseases
acne
eczema
psoriasis
Give some functions of skin
Protection against injury and pathogenic organisms
Waterproofing and fluid conservation
Thermoregulation (~36.8) through blood flow (sympathetic) and sweating
Protection against radiation, absorption of ultra violet radiation and vitamin D production
Surface for grip
Sensory organ
Cosmetic
What are the 4 layers of the epidermis
Keratinocytes Stratum Corneum Stratum granulosum Stratum spinosum Stratum basale
Outline the very basic structure of the skin
Epidermis
Basement membrane
Dermis
Give some other components of the skin
desmosome
sweat glands
hair/ hair follicle
sebaceous glands
Describe the Stratum corneum
corneocytes (flat with no nuclei)
Protective
Filagrin gene mutation leads to eczema
Describe Stratum Spinosum
prickle/spinous cells that produce keratin
Desmosomes
Describe Stratum Basale
Basal cells that connect to eh basement membrane
Keratinocytes found here
Give some other components of the epidermis
Melanocytes (production of melanin) Langerhans cells (antigen presenting) Merkel cels (sensation)
Describe the basement membrane in the skin
Highly specialised region where epidermis meets dermis
via hemidesmosomes, anchoring plaques and proteins
Blisters are common e.g. epidermolysis bullosa
Describe the structure of the basement membrane in skin
hemidesmosomes
tonofilaments
demo-epidermal junctions
anchoring fibrils
Describe the dermis
supportive connective tissues - collagen, elastin, GAG
Thickness varies between 0.1mm and 3mm
contains fibroblasts that synthesises collagen, elastin and GAG
Dendritic cells found here
Describe the subcutaneous layer
Connective tissue and fat
Describe the pilo-sebaceous unit of the skin
Follicle
Hair shaft
Sebaceous gland
Pilo-erecti muscle
What are the two types of sweat glands found in skin
Apocrine - only located in the axillary and groins that produce discus sweat - subject to bacteria and therefore produce odour
Eccrine
What are the components of the dermo-epidermal junction
Lamina lucida Lamina densa Anchoring fibrils Hemidesmosomes Anchoring filaments
Explain the role of melanocytes and their development
Dendritic cells in Stratum Basale
Produces melanin pigment in the melanosome, which is then packed into granules that are transferred to adjacent keratinocytes via phagocytosis
Granules form a protective cap around the nuclei to protect DNA from UV (which stimulates melanin production)
Variation in pigmentation is from no. and size of melanosomes
What are the 3 types of hair
Lanugo
Vellus
Terminal
Describe Lanugo hair
Fine whispy and long hair
Found in the foetus at 20 weeks and in anorexic people
Shed before birth
Describe vellus hair
Short, fine, light hairs that cover the body
Describe terminal hair
Long, thick, dark hair
Scalp, eyebrows, eyelashes, pubic, axillary
Starts at vellus and androgens make it terminal
Describe the hair follicle
Made up of pilo-sebaceous units Hair follicle Hair shaft Erector pili muscle Sebaceous gland Hair bulb- blood from the dermal papilla
What are the 3 stages in hair growth
anagen
catagen
telogen
Describe anagen in hair growth
growth phase (85% cells)
Energy intensive + highly vascularised
Most metabolically active
Rate depends on body site
Describe catagen in hair growth
Cell devision slows and stops
End of shaft keratinises to form a club shape
Dermal papillae and club moves to the base of muscle insertion
Describe telogen in hair growth
Hair is shed actively
Next anagen phase begins
Club hair takes 4-6 weeks
What is synchronicity in hair growth
when a baby is born, all the hair growth cycles are in synchronicity
How does age affect hair growth
Telogen effluvium - the thinning of hair due to early entry to telogen
Due to emotional and physiological stress or hyperthyroidism, sepsis and anaemia
How do sex hormones affect hair growth
testosterone on the follicles
There is a surge during puberty which grows terminal hair
Pubic and axillary, then beard and chest, then nose and ear hair
Androgen sensitivity - balding pattern
What are nails made of
Hard hair keratin
Describe the growth of nails
Nails grow from the Germinal matrix
Describe the structure of the nail
Distal end is the lunula/germinal matrix (critical to growth) - white moon
eponychium - skin cover
hyponychium
onychodermal band - overhang of nail
Describe the growth of nails
Fingernails - 3mm a month
Toenails - 1mm a month
Due to adhesion and nail folds, the nail grows out and not up
Nail surface is produced by the proximal nailbed
