ORGANS WITH SECONDARY ENDOCRINE FUNCTIONS
HEART
When the body experiences an increase in blood volume or pressure, the cells
of the heart’s atrial wall stretch. In response, specialized cells in the wall of the
atria produce and secrete the peptide hormone atrial natriuretic peptide
(ANP). ANP signals the kidneys to reduce sodium reabsorption, thereby
decreasing the amount of water reabsorbed from the urine filtrate and
reducing blood volume. Other actions of ANP include the inhibition of renin
secretion and the initiation of the renin-angiotensin-aldosterone system
(RAAS) and vasodilation. Therefore, ANP aids in decreasing blood pressure,
blood volume, and blood sodium levels.
GASTROINTESTINAL TRACT
The endocrine cells of the GI tract are located in the mucosa of the stomach
and small intestine. Some of these hormones are secreted in response to
eating a meal and aid in digestion. An example of a hormone secreted by the
stomach cells is gastrin, a peptide hormone secreted in response to stomach
distention that stimulates the release of hydrochloric acid. Secretin is a peptide
hormone secreted by the small intestine as acidic chyme (partially digested
food and fluid) moves from the stomach. It stimulates the release of
bicarbonate from the pancreas, which buffers the acidic chyme, and inhibits
the further secretion of hydrochloric acid by the stomach. Cholecystokinin
(CCK) is another peptide hormone released from the small intestine. It
promotes the secretion of pancreatic enzymes and the release of bile from the
gallbladder, both of which facilitate digestion. Other hormones produced by
the intestinal cells aid in glucose metabolism, such as by stimulating the
pancreatic beta cells to secrete insulin, reducing glucagon secretion from the
alpha cells, or enhancing cellular sensitivity to insulin.
KIDNEYS
The kidneys participate in several complex endocrine pathways and produce
certain hormones. A decline in blood flow to the kidneys stimulates them to
release the enzyme renin, triggering the renin-angiotensin-aldosterone (RAAS)
system, and stimulating the reabsorption of sodium and water. The
reabsorption increases blood flow and blood pressure. The kidneys also play a
role in regulating blood calcium levels through the production of calcitriol from
vitamin D3, which is released in response to the secretion of parathyroid
hormone (PTH). In addition, the kidneys produce the hormone erythropoietin
(EPO) in response to low oxygen levels. EPO stimulates the production of red
blood cells (erythrocytes) in the bone marrow, thereby increasing oxygen
delivery to tissues. You may have heard of EPO as a performance-enhancing
drug (in a synthetic form).
SKELETON
Although bone has long been recognized as a target for hormones, only
recently have researchers recognized that the skeleton itself produces at least
two hormones. Fibroblast growth factor 23 (FGF23) is produced by bone cells
in response to increased blood levels of vitamin D3 or phosphate. It triggers the
kidneys to inhibit the formation of calcitriol from vitamin D3 and to increase
phosphorus excretion. Osteocalcin, produced by osteoblasts, stimulates the
pancreatic beta cells to increase insulin production. It also acts on peripheral
tissues to increase their sensitivity to insulin and their utilization of glucose.
ADIPOSE TISSUE
Adipose tissue produces and secretes several hormones involved in lipid
metabolism and storage. One important example is leptin, a protein
manufactured by adipose cells that circulates in amounts directly proportional
to levels of body fat. Leptin is released in response to food consumption and
acts by binding to brain neurons involved in energy intake and expenditure.
Binding of leptin produces a feeling of satiety after a meal, thereby reducing
appetite. It also appears that the binding of leptin to brain receptors triggers
the sympathetic nervous system to regulate bone metabolism, increasing
deposition of cortical bone. Adiponectin—another hormone synthesized by
adipose cells—appears to reduce cellular insulin resistance and to protect
blood vessels from inflammation and atherosclerosis. Its levels are lower in
people who are obese, and rise following weight loss.
SKIN
The skin functions as an endocrine organ in the production of the inactive form
of vitamin D3, cholecalciferol. When cholesterol present in the epidermis is
exposed to ultraviolet radiation, it is converted to cholecalciferol, which then
enters the blood. In the liver, cholecalciferol is converted to an intermediate
that travels to the kidneys and is further converted to calcitriol, the active form
of vitamin D3. Vitamin D is important in a variety of physiological processes,
including intestinal calcium absorption and immune system function. In some
studies, low levels of vitamin D have been associated with increased risks of
cancer, severe asthma, and multiple sclerosis. Vitamin D deficiency in children
causes rickets, and in adults, osteomalacia—both of which are characterized by
bone deterioration.
THYMUS
The thymus is an organ of the immune system that is larger and more active
during infancy and early childhood, and begins to atrophy as we age. Its
endocrine function is the production of a group of hormones
called thymosins that contribute to the development and differentiation of T
lymphocytes, which are immune cells. Although the role of thymosins is not
yet well understood, it is clear that they contribute to the immune response.
Thymosins have been found in tissues other than the thymus and have a wide
variety of functions, so the thymosins cannot be strictly categorized as thymic
hormones.
LIVER
The liver is responsible for secreting at least four important hormones or
hormone precursors: insulin-like growth factor (somatomedin),
angiotensinogen, thrombopoetin, and hepcidin. Insulin-like growth factor-1 is
the immediate stimulus for growth in the body, especially of the bones.
Angiotensinogen is the precursor to angiotensin, mentioned earlier, which
increases blood pressure. Thrombopoetin stimulates the production of the
blood’s platelets. Hepcidins block the release of iron from cells in the body,
helping to regulate iron homeostasis in our body fluids.
ORGANS
HEART
GASTROINTESTINAL
TRACT
GASTROINTESTINAL
TRACT
KIDNEY
KIDNEY
KIDNEY
SKELETON
MAJOR HORMONES
EFFECT
Atrial natriuretic peptide Reduces blood volume,
(ANP)
blood pressure, and
Na+ concentration
Gastrin, secretin, and
Aid digestion of food and
cholecystokinin
buffering of stomach acids
Glucose-dependent
Stimulate beta cells of the
insulinotropic peptide pancreas to release insulin
(GIP) and glucagon-like
peptide 1 (GLP-1)
Renin
Stimulates release of
aldosterone
Calcitriol
Aids in the absorption of
Ca2+
Erythropoietin
Triggers the formation of
red blood cells in the bone
marrow
FGF23
Inhibits production of
calcitriol and increases
phosphate excretion
SKELETON
Osteocalcin
ADIPOSE TISSUE
Leptin
ADIPOSE TISSUE
SKIN
Adiponectin
Cholecalciferol
THYMUS AND OTHER
ORGAN
Thymosins
LIVER
LIVER
LIVER
Insulin-like growth
factor-1
Angiotensinogen
Thrombopoetin
LIVER
Hepcidin
Increases insulin
production
Promotes satiety signals in
the brain
Reduces insulin resistance
Modified to form vitamin
D
Among other things, aids
in the development of T
lymphocytes of the
immune system
Stimulates bodily growth
Raises blood pressure
Causes increase in
platelets
Blocks release of iron into
body fluids
ARRYTHMIA
Cardiac arrhythmia refers to a group of conditions that cause the heart to beat
irregular, too slowly, or too quickly.
There are several categories of arrhythmia, including:

bradycardia, or a slow heartbeat

tachycardia, or a fast heartbeat

irregular heartbeat, also known as a flutter or fibrillation

early heartbeat, or a premature contraction
TYPES
1. Atrial fibrillation
This is the irregular beating of the atrial chambers, and nearly always involves
tachycardia. Atrial fibrillation (A-fib) is common and mainly develops in
adults over 65 years of age.
Instead of producing a single, strong contraction, the chamber fibrillates, or
quivers, often producing a rapid heartbeat.
2. Atrial flutter
While fibrillation causes many random and different quivers in the atrium,
atrial flutter is usually from one area in the atrium that is not conducting
properly. This produces a consistent pattern in the abnormal heart conduction.
3. Supraventricular tachycardia
The condition known as supraventricular tachycardia (SVT) refers to a rapid but
rhythmically regular heartbeat. An individual can experience a burst of
accelerated heartbeats that can last from a few seconds to a few hours.
4. Ventricular tachycardia
This condition refers to abnormal electrical impulses that start in the ventricles
and cause an abnormally fast heartbeat. This often happens if the heart has a
scar from a previous heart attack.
5. Ventricular fibrillation
This is an irregular heart rhythm consisting of rapid, uncoordinated, and
fluttering contractions of the ventricles. The ventricles do not pump blood.
Ventricular fibrillation can be life threatening and usually has links to heart
disease. A heart attack often triggers it.
What is a normal heartbeat?
Doctors identify a healthy heartbeat by counting the number of times the
heart beats every minute (bpm) during rest. This is known as the resting heart
rate. The range for a healthy resting heart rate varies between individuals, but
the American Heart Association (AHA) suggests that it is usually between 60
and 100 bpm.
The fitter a person is, the lower their resting heart rate becomes. Olympic
athletes, for example, will usually have a resting heart rate of less than 60 bpm,
because their hearts are highly efficient. The heart should beat with a regular
rhythm, consisting of double “ba-bum” beats with even spaces in between
each.
One of these beats is the heart contracting to provide oxygen to blood that has
already circulated, and the other involves the heart pushing oxygenated blood
around the body.A person can measure their heart rate using their pulse. This
is a point at which they can feel the heartbeat through the skin. The best
locations on the body for this are:

the wrists

the insides of the elbows

the side of the neck

the top of the foot
ELECTROCARDIODIAGRAM (ECG)
ATRIAL FIBRILLATION
IN ATTRIAL FIBRILLATION, THE TRACING SHOWN TINY, IRREGULAR FIBRILLATION WAVES
BETWEEN HEARTBEATS. THE RHYTHM IS IRREGULAR AND ERRATIC.
ATRIAL FLUTTER
ATRIAL FLUTTER OCCURS WHEN A “REENTRANT” CIRCUIT IS PRESENT, CAUSING A
REPEATED LOOP OF ELECTRICAL ACTIVITY TO DEPOLARIZE THE ATRIUM AT A RATE OF
ABOUT 250 TO 350 BEATS PER MINUTE; REMEMBER THE ATRIAL RATE IN ATRIAL
FIBRILLATION IS 400 TO 600 BPM. THIS PRODUCES A
CHARACTERISTIC “SAWTOOTH” PATTERN OF THE P WAVES, DIFFERENT FROM ATRIAL
FIBRILLATION, IN WHICH THE ATRIAL RATE IS SO FAST THAT THE P WAVES ARE NOT
IDENTIFIABLE, OR ONLY COARSE FIBRILLATORY WAVES ARE SEEN.
SUPRAVENTRICULAR TACHYCARDIA
ECG features:
P waves are often hidden – being embedded in the QRS complexes.
Pseudo R’ wave may be seen in V1 or V2.
Pseudo S waves may be seen in leads II, III or aVF.
In most cases this results in a ‘typical’ SVT appearance with absent P waves and
tachycardia




TYPE
ATRIAL FIBRILLATION
ECG
BEAT PER
MINUTE
(BPM)
400 – 600
BPM
ATRIAL FLUTTER
250 – 350
BPM
SUPRAVENTRICULAR
TACHYCARDIA
151 – 250
BPM
VENTRICULAR
TACHYCARDIA
MORE THAN
100 BPM
VENTRICULAR
FIBRILLATION
400 – 600
BPM
CAUSES
Any interruption to the electrical impulses that stimulate heart contractions
may result in arrhythmia. Several factors can cause the heart to work
incorrectly, including:

alcohol abuse

diabetes

substance use disorder

drinking too much coffee

heart disease, such as congestive heart failure

high blood pressure

hyperthyroidism, or an overactive thyroid gland

stress

scarring of the heart, often due to a heart attack

smoking

certain dietary and herbal supplements

some medications

structural changes in the heart
A person with good heart health will hardly ever experience long-term
arrhythmia unless they have an external trigger, such as a substance use
disorder or an electric shock. However, an underlying heart problem can mean
that electrical impulses do not travel through the heart correctly. This
increases the risk of arrhythmia.
TREATMENT
How arrhythmia will be treated will depend on whether it is a fast or slow
arrhythmia or heart block. Any underlying causes of your arrhythmia, such as
heart failure, will need to be treated as well.
1. Medication : To stop or prevent an arrhythmia or control the rate of an
arrhythmia

amiodarone (Cordarone, Pacerone)

flecainide (Tambocor)

ibutilide (Corvert), which can only be given through IV

lidocaine (Xylocaine), which can only be given through IV

procainamide (Procan, Procanbid)

propafenone (Rythmol)

quinidine (many brand names)

tocainide (Tonocarid)
2. Cardioversion : A treatment that uses electricity to shock the heart back
into a normal rhythm while you are anaesthetised or sedated
3. Catheter ablation : A keyhole treatment under local or general anaesthetic
that carefully destroys the diseased tissue in your heart that causes the
arrhythmia
4. Pacemaker : A small device containing its own battery that is implanted in
your chest under local anaesthetic, it produces electrical signals to do the
work of the natural pacemaker in your heart to help it beat at a normal
rate.
5. ICD : A device similar to a pacemaker that monitors your heart rhythm and
shocks your heart back into a normal rhythm whenever this is needed
REFERENCE
1.
2.
https://medlineplus.gov/arrhythmia.html
https://www.google.com/search?q=heart+arrhythmias&rlz=1C1SQJL_enMY875MY875&oq=HEA
RT+ARR&aqs=chrome.1.69i57j0l7.4421j0j7&sourceid=chrome&ie=UTF-8
3.
4.
https://www.healthline.com/health/leukocytosis#symptoms
https://www.drugs.com/health-guide/cardiac-arrhythmias.html