Co-ordination & Response in Humans

Question 1

describe the structure of the eye as seen in front view

Answer 1

1. iris
2. conjunctiva
3. pupil
4. eyelashes
5. tear gland
6. eyelids

Question 2

Structure of eye as seen in horizontal section

Answer 2

1. Ciliary body
2. Suspensory ligament
3. Cornea
4. Choroid
5. Vitreous chamber
6. Fovea or yellow spot
7. Optic nerve
8. Blind spot
9. Retina
10. Lens
11. Aqueous chamber

Question 3

Focusing on a distant object

Answer 3

• light rays reflecting off the obj is almost parallel to e/o when they reach the eye
  1. Ciliary muscles relax, pulling on the suspensory ligament
  2. Suspensory ligament becomes taut, pulling on the edge of lens
  3. Lens become thinner & less convex, increasing its focal length
  4. Light rays from distant obj are sharply focused on retina
  5. Photoreceptors stimulated
  6. Nerve mpulses produced are trasnmitted by optic nerve to the brain. Brain interprets the impulses & the person sees the distant obj

Question 4

Focusing on a near object

Answer 4

• diverging light rays from near obj
  1. Ciliary muscles contract, relaxing their pull on SL
  2. SL slacken, relaxing their pull on lens
  3. Lens, being elastic, become thicker & more convex, decreasing its focal length
  4. Light rays from near obj are sharply focused on retina
  5. Photoreceptors stimulated
  6. Nerve mpulses produced are trasnmitted by optic nerve to the brain. Brain interprets the impulses & the person sees the near obj

Question 5

describe the pupil reflex in response to bright light

Answer 5

1. In bright light, retina is stimulated. Nerve impulses are produced.
2. The impulses are transmitted along sensory neurone in optic nerve to the brain, across a synapse to relay neurone
3. RN transmit the impulses across another synapse to motor neurone
4. MN then transmit the impulses to the iris (effector)
5. The radial muscles in iris relax while the circular muscles in iris contract. This pupil constriction allows less light to enter

Question 6

describe the pupil reflex in response to dim light

Answer 6

1. In dim light, retina is stimulated. Nerve impulses are produced.
2. The impulses are transmitted along sensory neurone in optic nerve to the brain, across a synapse to relay neurone
3. RN transmit the impulses across another synapse to motor neurone
4. MN then transmit the impulses to the iris (effector)
5. The radial muscles in iris contract while the circular muscles in iris relax. This pupil dilation allows more light to enter

Question 7

define a hormone

Answer 7

A hormone is a chemical substance produced in minute quantities by an endocrine gland. It is transported in the bloodstream to target organ(s) where it exerts its effect(s). After hormones have performed their functions, they are eventually destroyed by the liver.

Question 8

explain what is meant by an endocrine gland, with reference to the islets of Langerhans in the pancreas

Answer 8

• An endocrine gland is a ductless gland which produces hormone(s) that is secreted directly ito the bloodstream, which then distributes the hormone around the body
• Islets of Langerhans in pancreas secrete hormones insulin & glucagon into the bloodstream

Question 9

role of the hormone adrenaline in boosting blood glucose levels and give examples of situations in
which this may occur

Answer 9

• stimulates liver to convert glycogen to glucose so that more glucose is available for muscle contraction
• Increases blood glucose level, eg when more glucose is released from liver into bloodstream

Eg, during state of emergency or ‘flight or fight’ response

Question 10

explain how the blood glucose concentration is regulated by insulin and glucagon as a homeostatic
mechanism

Answer 10

When BGC increases above norm, islets of Langerhans in pancreas increase secretion of insulin. Insulin decreases BGC by:
- increasing permeability of cell membranse to glucose, thereby increasing rate of glucose uptake by cells
- stimulating liver & muscle cells to convert glucose into glycogen for storage
- increasing oxidation of glucose during tissure respiration

When BGC decreases below norm, islets of Langerhans secrete glucagon which increases BGC by stimulating:
- conversion of glycogen into glucose, &
- conversion of fats & AAs into glucose

Both glucagon & insulin regulate the BGC.

Question 11

Diabetes mellitus

signs+treatment

Answer 11

Signs:
- a persistently high blood glucose level
- presence of glucose in urine after a meal
- healing of wounds is slow or difficult

Treatment:
Inject insulin regularly. Ensure that they have a supply of sugary food (eg, glucose sweets) as their blood glucose can drop too low if they use too musch insulin, exercise too much or eat too little. A low blood glucose may cause them to go into a coma.