Specialised tissues Flashcards
State the function of hair
-Protection -Sensation -Thermoregulation
Outline the differences between lanugo, terminal and vellus hair
LANUGO >fine and long, foetus at 20 weeks >shed before birth >premature babies and anorexics TERMINAL >long, thick dark >scalp, brows/lashes, pubic, axillary, beard >begin as vellus, differentiation triggered by androgens during puberty VELLUS >short, fine, light >covers body
Describe the structure of a hair follicle
What is the development of hair throughout life?
- Anagen = Growth, 85% of hair, higly vascularised and energy intensive
- Catagen = Cell division slows/stops, end of shaft keratinises +forms club shape, dermal papilla/club moves towards base of muscle insertion
- Telogen = Shedding hair, club hair takes 4-6 weeks to be released
- Anagen begins again
ACT!!
How does testosterone effect hair follicles?
Changes vellus into terminal hair
Pubic/axillary, then beard and chest, then (in elderly) nose and ear.
Scalp has androgen sensitive hair = determines balding pattern
What are the functions of nails?
- Protection
- Touch
- Communication
Outline the structure of nails
Longitudinal ridging
Grow from germinal matrix
Describe the growth of the nail plate
- Nail produced by proximal nailbed
- grows out due to adhesion
- Top of plate = produced by proximal portion of matrix
* can grow up to 1 week post-mortem*
List the cells of the nervous system (BUMP)
BIPOLAR = 2 axonal projections from the cell body
UNIPOLAR = 1 axonal projection
MULTIPOLAR = Pyramidal - pyramid shaped cell body, Purkinje, GABA neurons in the cerebellum, Golgi - GABA neurons in the cerebellum
PSEUDOUNIPOLAR = 1 axonal projection that divides in 2
Recall the main components of a neurone
Cell body/soma
>Nucleus and ribosomes
>Neurofilaments for transport and structure
Dendrites
>Non-myelinated
>receives signals + highly branched
Axon
>Origionats from axon hillock at soma
>covered in myelin
>can branch into collaterals
Terminal buttons
Myelin sheath
State some cells of the central nervous system
Astrocytes = Most abundant cell, repair/homeostasis/immunity proliferation
Oligodendrocyte = Myelinates many axons
Schwann cell = Myelinates 1 axon (peripheral nerves)
Microglial cells = immunological surveillance of the CNS
Ependymal cells = line fluid-filled ventricles, regulation and production of CSF
How is the resting potential maintained?
Transportation of ions in regulated by channels and pumps.
Describe the creation of an action potential
RMP = voltage-gated channels closed
Depolarisation = Na+ channel opens, influx
Repolarisation = K+ opens at slower rate, efflux from cell
Explain what happens at a synapse and the 2 fates of neurotransmitters
- action potential reaches the presynaptic terminal
- Ca2+ channel opens
- Neuro vesicles exocytosis
- Bind to post-synaptic receptors
FATE OF NEUROTRANSMITTER: enzyme metabolism, recycled by transporter protein
Recall the ultrastructure of skeletal muscle
Z line = made up of a-actinin and CapZ
Explain the process of excitation-contraction coupling
- Action potential prpagates along sarcolemma and T-tubules
- Depolarisation activates DHPR (Dihydropyridine receptors = conformational changes
- change is transmitted to RyR (ryanodine receptors) on sarcoplasmic reticulum
- Opening of RyR and Ca2+ release = depolarisation = increase in Ca2+
What are the components of myofibres?
T-tubules = membrane invaginations that contactwith extrcellular fluid
Sarcoplasmic reticulum = Network of Ca2+ stores surrounding myofibrils
Outline the components of a sarcomere
z line = lateral boundaries of sarcomere
Actin = polymeric thin filaments composed of 2 twisted a helices (displays polarity)
Myosin = Thick filaments, motor proteins with globular heads
Titin = spring-like filaments anchoring myosin to z line
Nebulin = large filaments associated with actin
Tropomyosin = elongated protein bound to actin
Capz(+) and tropomodulin(-) charged ends of actin
Describe the cellular mechanism of a contraction (sliding filament theory)
IN THE PRESENCE OF Ca2+
- Movement of troponin exposes myosin binding site on actin chain
- charged myosin headbinds to site
- Powerstroke due to binding and discharge of ADP. Pull actin towards the centre of sarcomere
- ATP binds = release of myosin head
- ATP hydrolysis = energy for myosin head
Explain the function of skeletal muscle
Interaction with external environment
Antagonist pairs have flexor and extensor
myofibre bundles (cylindrical and multimucleated)
Isotonic contraction: change length, tension is the same
>Concentric = shortening
>Eccentric = Lengthening
Isometric contraction: Increase tension, length is unchanged
Explain the structure and function of cardiac muscle
- Pumps blood around the body
- composed of cardiomyocytes (striated muscle)
>Intercalated disks: specialised regions connecting cardiomyocytes. Gap junctions to allow AP to spread
>Sarcomeres: contractile units of cardiomyocytes, contraction is the same as skeletal muscle
Describe cardiac excitation-contraction coupling
- AP propagates along scarcolemma and t-tubules
- Depolarisation opens VGCC = Ca2+ influx
- Ca2+ = depolarisation - initiate contraction by binding to troponin - CICR (Ca2+ induced Ca2+ release) by binding to RyR on SR
- Depolarisation = increase in intracellular Ca2+ = contract
Explain the structure and E-C coupling of smooth muscle
- Spindle shaped cells
- Irregular arrangment of actin/myosin
- Present in walls of hollow organs (blood vessels, GI tract)
1. Depolarisation activates VGCC
2. CaM complex = activates myosin light chain kinase (MLCK)
3. MLCK phosphorylates myosin light chains (MLC20)
4. Cross-bridges with actin filaments = contraction
Summarise the functions of the skin
- Protection against injury and pathogenic organisms
- waterproofing and fluid conservation
- Thermoregulation
- Protection agaisnt radiation, sbsorption or UV and vit D production
- Surface for grip
- Sensory organ
