The Endocrine System

THE ENDOCRINE SYSTEM 1
THE ENDOCRINE SYSTEM
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THE ENDOCRINE SYSTEM 2
TASK
Question 1
Control of secretion Hormone Principal Actions
Hormonal.
Hormonal control of secretion
means the release of a
hormone in response to
another hormone acting as the
stimuli triggering the release.
This happens in the case of
hypothalamus releasing
secretory or inhibitory
hormones that stimulate the
anterior pituitary to either
increase or lower the
secretion of various
hormones.
1.Thyroxine. Thyroxine is
secreted by the thyroid gland
when stimulated by thyroid
stimulating hormone from the
anterior pituitary gland.
2.Growth Hormone. Secreted
by the anterior pituitary after
stimulation by the growth
hormone releasing hormone
from the hypothalamus.
1.Increases basal metabolic
rate through increased oxygen
consumption in the tissues.
Tissues not affected by this
action include brain,
gonads,spleen,lungs and
retina. Thyroxine induces the
synthesis and activity of Na+-
K+ ATPase.
2. Has diabetogenic effect
causing insulin resistance and
by decreasing glucose uptake
and its utilization by the
target tissues such as the
muscle.
Neural.
In neural control of hormonal
1.Epinephrine. Released from
the adrenal medulla
1. Increases the systolic blood
pressure through increasing

THE ENDOCRINE SYSTEM 3
secretion the nervous system
is directly involved as the
stimuli that causes the
endocrine glands to release
the hormones. The
hypothalamus stimulates the
posterior pituitary through
neural mechanisms to release
its stored hormones. Adrenal
medulla is stimulated by
sympathetic nervous system
to produce catecholamines.
chromaffin cells upon
stimulation by the
sympathetic nervous system.
2. Antidiuretic hormone.
Synthesized by the
hypothalamus and stored in
posterior lobe of the pituitary
gland.
the force of contraction of the
heart and the cardiac output.
Reduces the total peripheral
resistance hence a decrease in
diastolic pressure.This effects
are due to interaction with
theadrenergic receptors found
in this tissues.
2.Acts on the kidneys to
cause water retention by
increasing reabsorption of
water in the distal convoluted
tubule and the collecting duct.
Question 2
Cortisol which is a steroid hormone released by the adrenal cortex has intracellular receptors
which are located inside the target cells, in the nucleus or in the cytoplasm and acts to alter the
gene expression of the target cell. These steroid receptors are a large group of molecules that
function as transcription factors and signal transducers (Agely et al., 2019). Cortisol enters a
target cell by simple diffusion across the cell membrane because it’s a lipid. Once inside the
target cell it binds to its receptor that is either in the cytoplasm or in the nucleus causing
conformational changes in the receptor making it viable for binding DNA termed as receptor

THE ENDOCRINE SYSTEM 4
activation. The hormone-receptor complex functions as a ligand-dependent transcription factor
that binds to the promoter region of responsive genes to stimulate or inhibit the transcription of
these genes.
Insulin binds to its receptor on the cell membrane which is a tetramer composed of two alpha
subunits and two beta subunits. The alpha subunit lies in the extracellular domain while the beta
subunit spans across the cell membrane. Insulin first binds to the alpha subunit causing a
conformational change in the receptor activating tyrosine kinase in the beta subunit which
phosphorylase themselves in presence of ATP (Cara and Rosenfield,2009). The activated
tyrosine kinase then phosphorylates other proteins involved in physiologic actions of insulin. The
insulin receptor complex is then taken into the target cell by endocytosis. The insulin receptor is
then degraded by intracellular proteases, stored or recycled to the cell membrane for re-use.
Target cells have receptors specific to a given hormone and activated by either lipid soluble
which are permeable to plasma membrane or water soluble which bind to cell surface receptor.
Insulin which is a water soluble hormone means it is lipophobic and has to bind to a receptor on
or within the plasma membrane to initiate intracellular signaling cascade. Cortisol which is
lopophilic passes through the plasma membrane and binds to an intracellular receptor and
changes gene expression (Fink, Pfaff & Levine , 2012).
TASK 2
QUESTION 1
The pituitary gland also called hypophysis lies in the Sella turcica at the base of the brain and it
is connected to the hypothalamus by the pituitary or hypophysial stalk and has two lobes,
anterior and posterior lobes. Anterior pituitary also called adenohypophysis acts as the engine of
the endocrine system under the influence of the hypothalamus. Hypothalamus controls the