HUMAN PHYSIOLOGY FROM CELLS TO
SYSTEMS ACTUAL EXAM PAPER 2026
QUESTIONS WITH SOLUTIONS GRADED A+
◉ Isthmus. Answer: the thin strip that connects the two lobes of the
thyroid
◉ Follicular Cells. Answer: the major thyroid secretory cells,
collectively called the granulosa and thecal cells; they secrete two
iodine-containing hormones derived from amino acid tyrosine; they are
arranged into hollow spheres, each of which forms afunctional unit
called a follicle
◉ Follicle. Answer: a hollow sphere made up of granulosa and thecal
thyroid cells; they appear as rings of follicular cells that enclose an inner
lumen
◉ Colloid. Answer: the thyroglobulin-containing substance enclosed
within the thyroid follicles; found in an inner lumen; this substance is
extracellular, and not in direct contact with the ECF that surrounds the
follicle
,◉ Thryoglobulin (Tg). Answer: a large complex molecule on which all
steps of thyroid hormone synthesis and storage take place; this molecule
contains within it the thyroid hormones in various stages of synthesis
◉ Tetraiodothyronine. Answer: (also known as T4 or thyroxine), the
most abundant hormone secreted by the thyroid gland; important in the
regulation of overall metabolic rate; most of the secreted T4 is
"activated" by being stripped of one of its iodines outside the thyroid
gland, primarily in the liver and kidneys, thus turning it into its more
potent counterpart, T3
◉ Triiodothyronine (T3). Answer: the most potent hormone secreted by
the thyroid follicular cells; important in the regulation of overall
metabolic rate; it is the major biologically active form of thyroid
hormone at the cellular level
◉ Thyroid Hormone. Answer: collectively, the hormones secreted by the
thyroid follicular cells, namely tetraiodothyronine (thyroxine) and
triiodothyronine; the relative function of these hormones is the same, but
they differ in speed and intensity of action
◉ C Cells. Answer: the thyroid cells interspersed in the interstitial fluid
between the follicles that secrete calcitonin
◉ Thyroid Synthesis. Answer: this process requires tyrosine, an amino
acid, and iodine, taken from dietary intake.
,◉ Step 1 of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: tyrosine-containing thyroglobulin (Tg) produced within the
thyroid follicular cells by the endoplasmic Reticulum-Golgi complex is
transported by exocytosis into the colloid
◉ Step 2 of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: iodide is carried by secondary active transport (via the Na-K
pump) from the blood into the colloid by symporters in the basolateral
membrane of the follicular cells
◉ Step 3 of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: iodide exits the cell through a luminal channel to enter the
colloid
◉ Step 4A of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: catalyzed by thyroperoxidase (TPO), iodide is simultaneously
oxidized to iodine (I0) and attached to tyrosine within the Tg molecule
to yield (monoiodotyrosine (MIT)
◉ Step 4B of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: attachment of two iodines to tyrosine yields diiodotyrosine
(DIT)
◉ Step 5A of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: coupling of one MIT and one DIT yields triiodothyronine (T3)
, ◉ Step 5B of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: coupling of two DITs yields tetraiodothyronine (T4)
◉ Step 6 of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: on appropriate stimulation, the thyroid follicular cells engulf a
portion of Tg-containing colloid by phagocytosis
◉ Step 7 of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: lysosomes attack the engulfed vesicle and split the iodinated
produced from Tg
◉ Step 8A of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: T3 and T4 diffuse into the blood (secretion)
◉ Step 8B of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: MIT and DIT are deiodinated, and the freed iodide is recycled
for synthesizing more hormone
◉ Thyroid Hormone Secretion. Answer: this process essentially involves
the follicular cells "biting off" a piece of colloid, breaking the
thyroglobulin molecule down into its component parts, and "spitting
out" the freed T3 and T4 into the blood; once released into the blood, the
highly lipophilic (water-insoluble) thyroid hormone molecules bind with
several plasma proteins (the binding affinity is 6 times greater for T4
SYSTEMS ACTUAL EXAM PAPER 2026
QUESTIONS WITH SOLUTIONS GRADED A+
◉ Isthmus. Answer: the thin strip that connects the two lobes of the
thyroid
◉ Follicular Cells. Answer: the major thyroid secretory cells,
collectively called the granulosa and thecal cells; they secrete two
iodine-containing hormones derived from amino acid tyrosine; they are
arranged into hollow spheres, each of which forms afunctional unit
called a follicle
◉ Follicle. Answer: a hollow sphere made up of granulosa and thecal
thyroid cells; they appear as rings of follicular cells that enclose an inner
lumen
◉ Colloid. Answer: the thyroglobulin-containing substance enclosed
within the thyroid follicles; found in an inner lumen; this substance is
extracellular, and not in direct contact with the ECF that surrounds the
follicle
,◉ Thryoglobulin (Tg). Answer: a large complex molecule on which all
steps of thyroid hormone synthesis and storage take place; this molecule
contains within it the thyroid hormones in various stages of synthesis
◉ Tetraiodothyronine. Answer: (also known as T4 or thyroxine), the
most abundant hormone secreted by the thyroid gland; important in the
regulation of overall metabolic rate; most of the secreted T4 is
"activated" by being stripped of one of its iodines outside the thyroid
gland, primarily in the liver and kidneys, thus turning it into its more
potent counterpart, T3
◉ Triiodothyronine (T3). Answer: the most potent hormone secreted by
the thyroid follicular cells; important in the regulation of overall
metabolic rate; it is the major biologically active form of thyroid
hormone at the cellular level
◉ Thyroid Hormone. Answer: collectively, the hormones secreted by the
thyroid follicular cells, namely tetraiodothyronine (thyroxine) and
triiodothyronine; the relative function of these hormones is the same, but
they differ in speed and intensity of action
◉ C Cells. Answer: the thyroid cells interspersed in the interstitial fluid
between the follicles that secrete calcitonin
◉ Thyroid Synthesis. Answer: this process requires tyrosine, an amino
acid, and iodine, taken from dietary intake.
,◉ Step 1 of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: tyrosine-containing thyroglobulin (Tg) produced within the
thyroid follicular cells by the endoplasmic Reticulum-Golgi complex is
transported by exocytosis into the colloid
◉ Step 2 of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: iodide is carried by secondary active transport (via the Na-K
pump) from the blood into the colloid by symporters in the basolateral
membrane of the follicular cells
◉ Step 3 of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: iodide exits the cell through a luminal channel to enter the
colloid
◉ Step 4A of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: catalyzed by thyroperoxidase (TPO), iodide is simultaneously
oxidized to iodine (I0) and attached to tyrosine within the Tg molecule
to yield (monoiodotyrosine (MIT)
◉ Step 4B of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: attachment of two iodines to tyrosine yields diiodotyrosine
(DIT)
◉ Step 5A of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: coupling of one MIT and one DIT yields triiodothyronine (T3)
, ◉ Step 5B of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: coupling of two DITs yields tetraiodothyronine (T4)
◉ Step 6 of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: on appropriate stimulation, the thyroid follicular cells engulf a
portion of Tg-containing colloid by phagocytosis
◉ Step 7 of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: lysosomes attack the engulfed vesicle and split the iodinated
produced from Tg
◉ Step 8A of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: T3 and T4 diffuse into the blood (secretion)
◉ Step 8B of Synthesis, Storage, and Secretion of Thyroid Hormone.
Answer: MIT and DIT are deiodinated, and the freed iodide is recycled
for synthesizing more hormone
◉ Thyroid Hormone Secretion. Answer: this process essentially involves
the follicular cells "biting off" a piece of colloid, breaking the
thyroglobulin molecule down into its component parts, and "spitting
out" the freed T3 and T4 into the blood; once released into the blood, the
highly lipophilic (water-insoluble) thyroid hormone molecules bind with
several plasma proteins (the binding affinity is 6 times greater for T4
