Week 11 Flashcards
What is temperature homeostasis controlled by?
the thermoregulatory centre in the hypothalamus
Describe the thermoreceptors
2 sets
receptors in hypothalamus measures temperature of blood passing through brain (core temperature)
receptors in skin measures external temperature
What is the body’s response in there is a low core temperature?
vasoconstriction
increased metabolic rate
shivering
hair raised
What is the body’s response if there is a high core temperature?
vasodilation
decreased metabolic rate
sweating hair lowered
What is pyrexia?
also known as fever
any elevation of the body temperature above normal
Defensive mechanism to fight infection
Describe the mechanism of pyrexia
When bacteria or viruses damage body tissue, WBCs secrete pyrogens
Pyrogens are carried in the blood to the hypothalamus
they inhibit the heat-sensing neurons and excite the cold-sensing neurones
The hypothalamic thermostat “set-point” is raised
What are the high temperatures in pyrexia thought to achieve?
stimulate leukocyte activity
may directly kill or inhibit the growth of some viruses and bacteria
Describe paracetamol
Also known as acetaminophen
small molecule
not NSAID
no anti-inflammatory properties
describe how paracetamol is thought to work?
acts directly on the CNS, increasing pain thresholds by inhibiting cyclooxygenases, COX1, COX2 and COX3 - enzymes involved in prostaglandin synthesis
antipyretic properties due to effects on the heat-regulating centres of the hypothalamus resulting in peripheral vasodilation, sweating and hence heat dissipation
Describe the external ear
Extending from the side of the head is the pinna (auricle)
canal leading inwards is external acoustic meatus
canal covered in epithelium, some of which contain hair and modified sweat glands producing cerumen
Describe the tympanic membrane
separates the external acoustic meatus form the middle ear
Connective tissue core lined with epithelium on the outside and mucous membrane on the inside
Attaches to the malleus and the umbo of the tympanic membrane
Describe the middle ear
malleus, incus, stapes
stapes attached to the lateral wall of the internal ear at the oval window
middle ear muscles
Describe the inner ear
Vestibular apparatus - sensory structures for balance and head movements
cochlea- contains sensory epithelium for hearing, the organ of corti
Describe the amplification of sound that occurs in the ear
pinna acts as directional filter, amplifying sounds from some directions more than others
The pinna and the ear canal increase the sound pressure level by up to 20dB
Since the area of the tympanic membrane is greater than the of the footplate at the oval window sound is further amplified by about 25dB
Describe how vibrations get into the cochlea
oval window faces into the vestibule
vestibule contains sensory epithelia for vestibular apparatus
vestibule leads into the scala vestibuli. Waves of pressure pass through the scala vestibuli to and back out through the scala tympani, terminating at the round window
Describe the scala media
organ of corti - sensory epithelium containing hair cells
stria vascular - regulates ionic and metabolic environment of the scala media
Describe resonant frequency
objects vibrate most strongly at their resonant frequency
the mass and stiffness of an object determines its resonant frequency
resonant frequency goes up with increasing stiffness and down with increasing mass
What mass and stiffness would a high frequency sound resonate best in?
stiff and light
What mass and stiffness would a low frequency sound resonate best in
flexible and bendy
Describe the basilar membrane
stiff and light at one end
flexible and heavy at the other
thus its resonant frequency varies over its length
Populated by “hair cells”
Describe the structure of a hair cell
epithelial origin, resembling the cells that line the stomach
steriocilia form a bundle at the apical pole of the hair cell
What do inner hair cells do?
turn vibrations into neural signals
What do outer hair cells do?
amplify vibrations
Describe outer hair cells
motile
when stimulated, can change their shape and stiffness
Act as amplifiers, increasing the amount of vibration on the basilar membrane
What would happen if outer hair cels were lost?
vibration isn’t significantly amplified
What would happen if inner hair cells were lost?
no signal to the brain
What can damage hair cells?
noise
infections
ageing
certain drugs
wear and tear
Describe the “tonotopic” map
maintained throughout much of the auditory system
Describe otitis media
inflammation of the inner ear
build up of fluid behind the tympanic membrane
usually bacterial
more common in children - more difficult for fluid to drain out through eustachian tube
What are the three types of antibiotic use?
guided therapy
empirical therapy
prophylactic therapy
when is guided therapy used?
mild infections that can wait a few days to be treated
rationalising therapy in patients in patients already on treatment
When is empirical therapy used?
patients with more severe infection
delay in therapy would result in worsening of condition
need to cover all likely causes
When is prophylactic therapy used?
healthy people exposed to surgery, injury, infected material
immunocompromised individuals - HIV, transplantation, splenectomy
What are the ideal characteristics of the target effects of antibiotics?
highly toxic to bacteria causing infection
penetrate the body area affected by infection
limit release of toxins from bacteria
What are the ideal characterises of the co-lateral damage of antibiotics?
non-toxic to patient
limited effect on colonising bacteria
low potential for bacteria to escape treatment through developing resistance
What type of antibiotics are usually used for guided therapy?
narrow spectrum
What type of antibiotics are usually used for empirical therapy?
broad spectrum
Give an example of a bactericidal antibiotic
penicillin
Give an example of a bacteriostatic antibiotic
calrithromyocin
What do bactericidal antibiotics do?
directly kill bacteria
lysis of bacteria can lead to toxin release
What do bacteriostatic antibiotics do?
suppresses growth but doesn’t directly kill bacteria
requires immune mediated killing to clear bacteria
Give examples of cell wall agents
pencillins
glycopeptides
Give examples of antibiotics that target ribosomes
macrolides
aminoglycosides
Give examples of antibiotics that target DNA
Quinolones
Give examples of antibiotics that target cell metabolism
thimethoprim
Describe resistance mechanisms
mutation of target sites
inactivating of enzymes
limit access - reduce permeability, increased efflux
genes mediating resistance can often be easily transferred
What is the innervation of the eye?
optic nerve (CNII)
extra-ocular muscles by cranial nerves III, IV and VI
Describe tear production
From lacrimal gland
function - lubricate movement, remove debris
drains into nose
Describe the nose
warms, humidifies and filters air
rich, superficial blood supply
mucous provides moisture
mucous and hair trap particles
Describe olfaction
olfactory nerve (CNI)
converts chemical signal to electrical
superior surface of nasal cavity
conchae increase surface area
What is the innervation of the tongue?
Lingual nerve (CNV5) and chorda tympani nerve (CNVII) -taste and sensation to anterior 2/3
glossopharyngeal taste and sensation to posterior 1/3
hypoglossal motor control
