Which of the following statements are TRUE? a. Photoreceptor rods are much more

Question

Which of the following statements are TRUE? a. Photoreceptor rods are much more sensitive to light than photoreceptor cones. b. Cones come in three varieties: blue, green, & red - named for the specific light wavelength they are sensitive to. c. The Fovea centralis in the macula lutea contains a high density of only cones and is the "spot" of greatest visual acuity exactly at the posterior pole eyeball opposite the pupil & lens. d. All of the above e. Only a & b The most common blood cell is ___. a. Neutrophils B. Basophils c. Erythrocytes d. Leukocytes e. Lymphocytes Please place in the correct chronological sequence the following events in the creation/secretion/action of Thyroid Hormones (T_3, T_4). 1. Follicular cells phagocytose a portion of colloid containing DITs, MITs, T_3 & T_4. 2. Thryoid follicle cells increase production of thryoglobulin protein and secrete it into the colloid in response to TSH from adenohypophysis. 3. Lysosomal enzymes cleave or free thyroid hormones from the colloid and these pass the membrane and into the blood. Any remaining MITs & DITs are colloid. 4. Iodide (I-) ions are actively taken up by follicular cells, oxidized to Iodine (I_2) molecules that are also secreted into the colloid. 5. The much more numerous or common T_4 molecules immediately bind to Thyroxine-Binding Globulin proteins in the blood and are transported throughout the body to target tissues. 6. In the colloid, iodine seeks out and binds tyrosine residues. If one iodine and molecule binds, the species is MIT. If two iodine molecules bind, a DIT results. 7. At target tissues, de-iodination occurs and T_3 binds to receptors with greater affinity and causes more pronounced effects, however, it is quickly cleared from blood and is lost. 8. Iodinated tyrosine residues are coupled together to produced triiodothyronine (T_3) and tetraiodothyronine (T_4 or Thyroxine). a. 1, 3, 5, 7, 2, 4, 6, 8 b. 2, 4, 6, 8, 1, 3, 5, 7 c. 1, 2, 3, 4, 5, 6, 7, 8 d. 2, 8, 3, 7, 1, 6, 4, 5 e. 2, 5, 1, 4, 3, 6, 8, 7 Autocrine secretion is defined as ___. a. "a hormone feeding back and affecting the very cell that secreted if' b. "a hormone diffusing a small distance away and affecting neighboring cells" c. "a hormone entering the blood and affecting distant tissues" d. all of the above e. cannot be determined from the information given

Explanation / Answer

72. A) Photoreceptor rods are much more sensitive than photoreceptor cones.

b) Cones come in three varieties: blue, green, and red- named for the specific wavelength they are sensitive to.

c) The fovea centralis in the centre of macula lutea contains a high density of only cones and is the spot of your greatest visual acuity exactly at the posterior pole of the eyeball opposite the pupil and lens. It is false as macula lutea is situated lateral to posterior pole.

Therefore, option e is correct.

73. Erythrocytes also known as red blood cells are the most common types of cells present in blood.

Therefore, option c (erythrocytes) is correct.

74. Chronological sequence of events in the creation/secretion/actions of thyroid hormones:

1) Thyroid follicle cells increase the production of thyroglobulin protein and secrete it into the colloid in response to TSH from adenohypophysis.

2) Iodide ions are actively taken up by follicular cells, oxidized to iodine molecules that are also secreted into the colloid.

3) In the colloid, iodine seeks out and bids to tyrosine residues. If one iodine molecule binds, the species is MIT. If two iodine molecules bind, DIT is formed.

4) Iodinated tyrosine residues are coupled together to produce triiodothyronine (T3) and tetraiodothyronine (T4) or thyroxine.

5) Follicular cells phagocytose a portion of colloid containing MITs, DITs, T3 and T4.

6) Lysosomal enzymes cleave or free thyroid hormones from the colloid and these pass through the membrane and into the blood. Any remaining DITs or MITs are returned to the colloid.

7) The much more numerous or common T4 molecules immediately bind to thyroxine- binding globulin proteins in the blood and are transported throughout the body to the target tissues.

8) At target tissues, de-iodination occurs and T3 binds to receptors with great affinity and causes more pronounced effects. However, it is quickly cleared from the blood and is lost.

Therefore, option b (2, 4, 6, 8, 1, 3, 5, and 7) is correct.

75. Autocrine secretion is defined as “a hormone feeding back and affecting the very cell that secreted it."

Endocrine secretions are transported through blood.

Paracrine secretions are transported through interstitial fluid.

Therefore, option a is correct.

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