8.5.1 Causes of Disorders

Question 1

Structure of Ear

Answer 1

The ear is divided into five major divisions, four in the peripheral mechanism (first four) and one central mechanism (brain).

1. Outer/External Ear - collects sound, localises, resonates, protects
2. Middle Ear - an air-filled cavity that separates the external ear, conducts, protects, transduces and amplifies
3. Inner Ear - converts mechanical sound waves to neural impulses that can be recognised by the brain
4. VIII Cranial Nerve
5. Brain

Question 2

Outer/External Ear

Structure of Ear: Peripheral Mechanism

Answer 2

Pinna - the visible portion that is commonly viewed as ‘the ear’, it localises sound sources to direct the sound into the ear, creating a distinctive imprint on the acoustic wave as it travels into the auditory canal

Auditory Canal/Meatus - extends from the pinna to the tympanic membrane (26mm long and 7mm diameter), protecting the eardrum and resonating the sound (10dB of gain at around 3300 Hz)

• Sounds in the 2000 to 4000 range are amplified by 10-15dB, meaning sensitivity to sounds is most hazardous in this area.

Cerumen (Ear Wax) - repels water, traps particles, moisturises epithelium in the ear canal, discourages insects via odour, cleanses ear canal and has antibiotic/antiviral/antifungal properties

Question 3

Middle Ear

Structure of Ear: Peripheral Mechanism

Answer 3

Tympanic Membrane (Ear Drum) - separates the outer ear and the middle air with a barrier that protects the middle and inner areas from foreign objects

• Its cone shape (17.5mm diameter) allows it to vibrate in response to sound pressure waves but the membrane movement is as little as one-billionth of a centimetre.

Ossicles - composed of the malleus (hammer), incus (anvil), and stapes (stirrup)

Transformer/Amplifier - transforms the vibrating motion of the eardrum into motion of the stapes, enhancing the transfer of acoustical energy

• The area of the eardrum is about 17 times larger than the oval window, increasing the effective pressure.
• The malleus and incus vibrate together and perform a lever action to amplify the pressure and transmit the sound waves to the footplate of the stapes (mechanical energy)
• Without the transformer action, about one-thousandth of acoustic energy would transmit into inner ear fluid (about 30dB loss)

Eustachian Tube - connects the front wall of the middle ear with the nasopharynx, as well as operating like a valve during swallowing and yawning to equalise the pressure on either side of the eardrum for optimal hearing, without which the pressure may cause the eardrum to displace

Question 4

Inner Ear

Structure of Ear: Peripheral Mechanism

Answer 4

Oval Window - a membrane that separates the middle and inner ear

Round Window - situated below and a little behind the oval window, the membrane vibrating with opposite phase to vibrations entering the cochlea through the oval window

Semicircular Canals - involved in balance

Cochlea - a spiral tube (about the size of a pea) that spirals for about 2 3/4 turns around a bony column, divided into three parts and separated by two membranes

• The cochlea includes the organ of Corti, which has hair cells on the basilar membrane that have cilia in touch with another membrane called the tectorial membrane to create an electrochemical message when vibrated.

Question 5

VIII Cranial Nerve

Structure of Ear: Peripheral Mechanism

Answer 5

Auditory Nerve and Processing - the electrochemical message can be sent along the auditory nerve to the brain for processing

Question 6

Brain

Structure of Ear: Central Mechanism

Answer 6

The auditory cortex and several groups of neurons to translate the impulses

Question 7

Hearing Loss

Answer 7

Hearing loss occurs when one or more parts of the ear/brain that make up the hearing pathway do not function and can be caused by many things. The impact on the ability to hear sounds is known as audiometric hearing loss and can range from being mild to profound. It can originate from birth or develop later in life.

The types of hearing loss include:

1. Conductive Hearing Loss
2. Auditory Processing Disorder
3. Sensorineural Hearing Loss

Question 8

Kidney Function

Answer 8

Any accumulation of wastes may be toxic to cells, so metabolic water is removed from the body to maintain homeostasis. If wastes are not continuously removed, their levels in the body will increase and alter the conditions in the internal environment, inhibiting enzyme functioning and prevents cells from undergoing normal metabolic activity.

• The buildup of nitrogenous wastes such as ammonia causes an increase in pH in cells. This results in them becoming more alkaline.
• The buildup of CO2 lowers pH which results in the internal environment becoming more acidic. These changes can slow down or inhibit enzyme functioning in metabolism.

Question 9

Excretory System

Kidney Function

Answer 9

The excretory system works to remove metabolic wastes from the tissues of an organism and expel them to the outside.

Kidneys - the main organ in this system, responsible for the two-way movement to remove nitrogenous wastes by filtering the blood that enters and remove necessary substances from urine to reabsorb in the bloodstream

• Renal Cortex -
• Renal Medulla -
  
  • Loop of Henle - limbs that maintain hypertonic conditions by pumping sodium ions out of the fluid between cells in the medulla
    
    • Ascending Limb - permeable to salts, impermeable to water
    • Descending Limb - permeable to water, impermeable to sodium ions
    • Animals that need to conserve more water have longer loops of Henle

Renal Pelvis -

Nephrons - millions of microscopic tubules that carry out the blood filtration

• Ultrafiltration - filter small molecules through pores in the capillaries at the glomerulus, from the blood into the Bowman’s capsule
  
  • Fenestration - pores between cells in the wall of capillaries that allow fluid, but not blood cells, to escape
  • Basement Membrane - covers and supports the wall of capillaries to prevent plasma proteins from being filtered out
  • Podocytes - forms the inner wall of Bowman’s capsule and prevents small molecules from being filtered out of the blood.
• Selective Reabsorption - glucose, amino acids and salts are reabsorbed back into blood capillaries, actively pumped out of the proximal convoluted tubule with possibly water
  
  • Proximal Convoluted Tubule - selectively reabsorbs useful substances by active transport, including more of the filtrate from glomerulus (all glucose, amino acids, 80% water, sodium and other mineral ions)
• Secretion - toxins and metabolites of drugs are pumped into the distal convoluted tubule to be excreted
• Excretion - Urea, some salts, water, ammonia and toxins are excreted from the collecting duct and ultimately from the body in urine
• Oxygenated blood arrives via the renal artery, carrying nitrogenous wastes. The wastes, water and other solutes are filtered to form urine before the kidney is drained of all fluids through the renal vein (for purified blood) and ureter (for urine)

Question 10

Osmoregulation

Kidney Function: Excretory System

Answer 10

The process of maintaining the water and electrolyte (salt) balance when water is lost during excretion through both active and passive transport.

• Passive is limited by its dependence on the presence of a different concentration in the two regions and its relatively slow rate.
  
  • Brownian Motion - particles continually collide and move randomly in passive transport
• Active mainly more sodium ions, glucose, amino acids and hydrogen ions across the nephron membrane to be reabsorbed into the bloodstream or to add additional wastes to the urine.
  
  • Sodium Pump Mechanism - operates in the tubules to move salt ions from the urine back into the kidney cells to conserve salts and water
• Antidiuretic Hormone (ADH) - increasingly or decreasingly released by the pituitary gland when prompted by the hypothalamus because of unusual water levels in blood to alter the permeability of the distal tubule and collecting duct, allowing water to be reabsorbed from the urine or leave the kidney.

Question 11

Urine

Kidney Function: Excretory System

Answer 11

Urine is the final excretory solution produced by the microscopic tubules of the kidney, draining it out along with the wastes via the ureters (ducts).

• In vertebrates, the ureters lead to the bladder, a urine storage organ. However, in some other vertebrates, the ureters can carry urine directly to the cloaca (a common opening chamber of the urinary, digestive and reproductive tracts) to empty to the outside.

Question 12

Kidney Issues

Answer 12

The presence of glucose in the urine is the main identifying feature of diabetes, where high levels of glucose present in the glomerular filtrate enters the proximal convoluted tubule (PCT).

Kidney Disease: Loss of kidney function occurs when kidneys lose the ability to filter waste from your blood sufficiently.

1. Acute Prerenal Kidney Failure - caused by insufficient blood flow to the kidneys (kidneys cannot filter toxins from the blood without enough blood flow)
2. Acute Intrinsic Kidney Failure - can be caused by direct trauma to the kidneys, such as physical impact or an accident, or indirect, such as toxin overload and ischemia (lack of oxygen)
3. Chronic Prerenal Kidney Failure - caused by a lack of blood flow to the kidneys for an extended period of time, causing them to shrink and lose function
4. Chronic Intrinsic Kidney Failure - caused when there is long-term damage to the kidneys due to intrinsic kidney disease (direct trauma)
5. Chronic Post-Renal Kidney Failure - caused by a long-term blockage of the urinary tract that prevents urination, causing pressure and eventual kidney damage

Question 13

Eye Structure

Answer 13

Sight relies on light entering the eye through the pupil, being detected by photoreceptors, and then nerve impulses being sent to the visual centres of the brain to be interpreted as images.

• Conjunctiva - a layer of clear epithelial cells across the front surface of the eye and continuing inside the upper and lower eyelids to protect the eye
• Cornea - a transparent, collagen protein membrane over the front of the eyeball that protects the eye, blocks short wavelengths and refracts light through the pupil
• Sclera - the white of the eye, and a tough layer continuous with the cornea to hold fluid and keep the spherical shape
• Choroid - the black layer between the sclera and retina with many blood vessels to provide blood supply to the retina
• Aqueous Humour - a clear, thick liquid to lubricate the cornea and lens
• Iris - an extension of the choroid, a coloured, muscular ring that can contract and dilate around the pupil to control light
• Pupil - an opening at the centre of the eye that changes size to control light
• Lens - biconvex, flexible disc responsible for light refraction to all of the adjustment needed to form a retinal image.
  
  • Accommodation is the adjustments made by the lens to form a focused image.
• Ciliary Body - encircles the lens with suspensory ligaments and ciliary muscle to hold the lens in position
• Vitreous Humour - a clear, jelly-like filling in the back of the eyeball to maintain spherical shape, refract light and keep hydrated
• Retina - a sensory layer inside the back of the eyeball to hold cone and rod photoreceptor cells and neurons
  
  • Converts the light stimuli to electrochemical signals
  • Cone cells - three types of conical shaped photoreceptor neurons with photopsin pigments (detect colours)
  • Rod cells - cylindrical-shaped photoreceptors with rhodopsin pigment (detects light intensity through sensitivity to shades of black, grey and white)
• Fovea/Macula - shallow pit in the central area of the retina with the highest density of cone cells
• Optic Nerve - connection between the eye and brain for visual messages (left and right optic nerves go in opposite directions)