University of Jordan
Faculty of Medicine
Physiology || for Pharmacy
L11 –Dr. Loai
Endocrine-System
Note:
1) Make sure you understand everything, exams questions will be based on
understanding NOT memorizing alone
2) Anything between *** was not mentioned during the lecture (only for your
knowledge)
3) make sure you go through the slides for the endocrine system by Dr.loai
----------------------------------------------------------------------------------------------------------The thyroid gland
***The thyroid gland is an endocrine gland in the neck, consisting of two lobes
connected by an isthmus. It is found at the front of the neck, below the Adam's
apple***
Tissue of the thyroid gland from the inside
cells that surrounds follicles and these
follicles are called thyroid follicles
Cells that surrounds the follicle directly 
follicular cells  which produces the main
hormone (Thyroid hormoneone of its main
contents is iodine)
These cells take iodine from our blood 
binds it to a protein  and store it inside the
follicle
 The highest amount of iodine in our body is stored in the thyroid gland
Cells that are far from the follicle  Parafollicular cells
The thyroid gland actually secretes two types of hormones:
1) T3 (triiodothyronine)
2) T4 (Thyroxine)
 Secretion of thyroid hormone is 90% T4 and 10% T3
 Note: T3 has a higher and stronger effect on receptor than T4  usually at
target tissue T4 is converted to T3
If we had high T4 But no effect  hypo-responsiveness
T4 & T3 has the same receptor same effect (general effect is to increase
metabolic rate increase energy consumption  increase body temp)
We get energy from many sources:
1) Fats
2) Proteins
3) Glucose(sugar)
Recall that the thyroid hormones main function is to increase energy
consumption and proteins are molecules that are responsible for the breakdown
and energy production of fats and glucose
So we cannot consume glucose without enzymes (proteins) so the thyroid
hormone’s main effect is to preserve the enzyme (protein) and to burn fats and
glucose (stimulates protein synthesis & breakdown of ATP)
One of the most important proteins that produced to breakdown about 1/3 ATP in
our body  Na-K pump
 Q: what happens when we increase the number of Na-K pumps?
Resting membrane potential
So thyroid hormones will affect many parts of our body mainly:
1) On the nervous system and muscles (will affects the function of cells
directly)
2) Permissive effect (synergetic) with the sympathetic system

1)
2)
3)
4)
5)
As a conclusion the effects of thyroid hormones on the body are:
Increase rate of metabolism
Stimulates increment in amount of Na-K pump
Increase body temp
Stimulates proteins synthesis
Increase lipolysis of glucose production of ATP through glucose and fats
breakdown
6) Potentiate sympathetic system
 Thyroid hormones are regulated by (negative feedback) :
1) Level of thyroid hormone
2) Pituitary hormones and hypothalamus secretes hormones that work as
a chronotropic hormones that might increase or decrease secretion of
thyroid hormones
 For example:
If we had lower levels of thyroid in our body  lower protein synthesis
lower production of energy  low body temp bad skin in addition to
bad resting membrane potential that will lead to fatigue and muscle
weakness  bad mental status
And also it will result in imbalance in body proteins  which will lead into
edema (buffy face)
This usually happens for elderly people
But if it happened in early stage of life  it will affect the activity of the
nervous system  and it will lead to mental retardation (Cretinism) *** is a
condition of severely stunted physical and mental growth owing to
untreated congenital deficiency of thyroid hormone ***

Another example:
If we had higher levels of thyroid in our body  Grave’s disease
It usually affects females more than males and is common around
the age 40.
 Hyperthyroidism will lead to enlargement of the thyroid gland
(Goiter) that can be seen!
Reasons of thyroid gland enlargement:
1) Too many orders to secrete thyroid hormones
2) No enough iodine
3) Not able to produce extra hormones
Goiters can happen due to: 1- hyperthyroidism 2-euthyrodism 3-hypothyroidism
As we mentioned there are perifollicular cells  they don’t access to follicles
They produce a hormone called calcitonin  regulates Ca+ in blood
Most of Calcium in our body is stored in bones  so if we need calcium it will be
taken from our bones
Calcitonin is responsible for decreasing amount of Ca+ in blood by storing it in
our bones.
Parathyroid Gland
Secretes parathyroid hormone (PTH)  which is a major regulator for Calcium,
magnesium and phosphate ion in the blood
PTH  increases calcium in blood
While calcitonin  decreases calcium in blood
The parathyroid glands are small endocrine glands in the neck of humans and
other tetrapods that produce parathyroid hormone. Humans usually have four
parathyroid glands, variably located on the back of the thyroid gland
PTH  regulates calcium in blood by:
1)
2)
3)
4)
preventing calcium from entering the urine
taking it up from bones
Increase number of cells that breaks down bone tissue  Osteoclasts
Increase calcium absorption from the small intestine
So the target tissues for PTH are:
-Bone  directly by receptors
-Intestine no direct effect  so it have to activate Vitamin D in the
kidney  the kidney will secrete vitamin D  that will increase the
absorption of calcium
-Kidney  directly by receptors
 Q: can we consider PTH as a chronotropic hormone?
Yes, it is a chronotropic hormone to the kidney

Example :
-If the patient had hypoparathyroid  this means lower amounts of
Calcium in blood (calcium is important in neurotransmitters release
& activity of nervous system & muscles)  this will effect
contractions of muscle  it will result in tetany (read about it in the
slides –S02 slide number 16)
-If the patient has hyperparathyroid  this means higher amounts
of Calcium in blood  excessive absorption from bone matrix and
will cause Osteoporosis  and also it will deposits in the kidney
and will cause kidney stones (read about it in the slides –S02 slide
number 16)
Adrenal Gland is a small gland on the top of the kidney
From anatomical view, it has 3 parts:
1) Capsule  does not have hormones
2) Cortex
3) Medulla
Internally, the adrenal medulla which secretes sympathetic hormones
such as epinephrine and norepinephrine (adrenaline and noradrenaline).
Adrenal cortex is the main part of the gland secretes several types of
hormones:
1) Mineralocorticoids  affects mainly Na+ & K+
It has many types of hormones; the most popular one is Aldosterone
(95% of hormonal activity)
It
Na+ & Cl- in blood And K+ & H+ (regulated by the kidney) and
as a result it will affect balance of water in the body & acidity in the
blood
It also activates renin-Ang ll mechanism Increases water and
contraction of blood vessels ( blood pressure) without changing
osmolarity.
2) Glucocorticoids  affects glucose homeostasis and cortisol
Regulation of synthesis and breakdown of glucose
When a person is in a stressful situation  it will maintain high levels
of glucose in blood and allow breakdown of proteins and lipids while
preventing glucose from breaking down
So as a side effect 
It will increase level of glucose in blood and it will increase blood
pressure & heart rate
It ignores wound healing or any bacteria that enters the body (lowers
immunity)
Cortisol is one of the common glucocorticoids that is used as a
medication and it is about 95% from total glucocorticoids
3) Androgens  male sex hormones
Note: Ach is the neurotransmitter that will increase adrenal hormones
secretions
Adrenal disorders
-Hypersecretion of glucocorticoids lowering proteins (increase
breakdown)  edema low regulation for blood pressure in addition
to hypertension  will results in buffy face or buffalo hump
(Cushing’s syndrome)
Also increases glucose levels  might cause diabetic effect
And elevated levels of cortisol  might cause osteoporosis
-Hyposecretion of Glucocorticoids will result in Addison’s disease 
 due to stress blood pressure will remain low  imbalance between
Na-K  will affect resting membrane potential and also the nervous
system  it will affect muscles (specially the heart muscle) and might
cause arrhythmias.
Done by:
Rahaf Mihyar