Medical Physiology
Endocrine system
• Endocrine glands (7)
Pituitary gland
Thyroid gland
Suprarenal cortex
Gonads (testis &
ovaries).
Parathyroid glands
Suprarenal medulla
Pancreas.
The master gland
Under control of pituitary
Not under pituitary control
All endocrine glands are
important for body
function but the:
√ Anterior pituitary
√ Adrenal cortex
√ Parathyroid
….. Are essential
to life
Pituitary Gland (hypophysis)
Pituitary stalk
Pituitary gland
Pituitary gland
The pituitary gland is divisible into two
distinct portions:
• small posterior lobe (neurohypophysis)
• large anterior lobe (adenohypophysis)
• Intermediate lobe; is located at the junction of
the two lobes, almost absent in human
Hormones secreted by the pituitary gland
- Six hormones are secreted by the anterior pituitary.
- Two hormones are secreted by the posterior pituitary.
Hormones secreted by the anterior pituitary
1- Growth hormone (GH)
2- Adreno-cortico-tropin (corticotrophin) ACTH →
Adrenal cortex
3- Thyroid-stimulating hormone (thyrotropin) TSH →
Thyroid gland
4- Prolactin
5- & 6 - Two gonadotropic hormones
a. follicle-stimulating hormone (FSH)
b. luteinizing hormone (LH)
“ They control growth of the ovaries and testes, as well
as their hormonal and reproductive activities”
Hormones secreted by the posterior pituitary
1- Antidiuretic hormone (vasopressin) ADH
2- Oxytocin
Growth hormone (somatotropin)
• It has 2 main actions:
1- Metabolic action
2- Growth
1- Metabolic action of growth hormone
1- On protein metabolism:
a. an anabolic hormone: increasing protein synthesis all
over the body, so there is increase in size and number of
the cells.
2- on carbohydrate metabolism:
a. GH decreases carbohydrate utilization. (anti-insulin
effect)
b. Diabetogenic (hyperglycemic) hormone so it
increases blood glucose level
3- on fat metabolism
a. It is a lipolytic & Ketogenic hormone.
b. Growth hormone enhances fat utilization for energy
production.
2- Growth
1- Soft Tissues:
a. GH stimulates the growth of All soft tissues:
increases size of tissues & organs (kidney, liver,
spleen, …)
2- Bone growth stimulation:
a. before closure of epiphysis
√ increase length of long bones:
→ The shaft of long bones will elongate
and stature is increased (linear growth).
b. After closure of epiphysis:
√ increase in the thickness of membranous
bone.
Disturbances in GH function
These either:
√ hypofunction
√ hyperfunction.
1- Hypofunction (Pituitary dwarfism)
Child growth is arrested
- Decrease in the
size of the trunk
and all extremities,
and they are well
proportioned
Span = height
vertex to symphysis =
symphysis to heel
2- Hyperfunction:
Before adolescence
(Gigantism)
After adolescence
(Acromegaly)
Posterior pituitary hormones
1- Oxytocin
2- Antidiuretic hormone (ADH) =(vasopressin)
Oxytocin
During labour:
It causes strong contractions of the uterus to expel the baby &
placenta.
Antidiuretic hormone (ADH) =
vasopressin
1- Renal effects:
A- In the tubular system
Decreased urine volume (anti-diuresis).
B- In the renal vascular system
ADH → local production of a vasodilator (PG E2), to
antagonizes the ADH renal vasoconstrictor effect and maintains
renal perfusion
ADH
2- Extra-renal effects:
A- In the vascular system:
induces intense vasoconstriction →
raises the arterial blood pressure in cases of
hemorrhage (vasopressor effect).
B- In cases of stress: as pain & trauma
ADH → increases cortisol secretion from
adrenal cortex (antistress)
Disturbance of ADH
• Diabetes insipidus (DI)
It is characterized by producing large volume of urine (diabetes),
very dilute & tasteless (insipidus)
Thyroid gland
Hormones secreted from thyroid gland
1- Thyroid hormones
(secreted from thyroid
follicles)
a. Thyroxine (T4)
b. Triiodothyronine (T3)
2- Thyrocalcitonin H:
(secreted from parafollicular
cells)
Effects of thyroid hormones
1- Effects on metabolism
2- Effects on growth
3- Effects on body systems
A- Effects on metabolism
Calorigenic effect: stimulate oxygen
consumption & metabolism of all body tissues.
1- Effects on carbohydrate metabolism:
a. Increases glucose absorption and glucose uptake
by the cells
b. Increases gluconeogenesis → increase blood
glucose level
2- Effect on fat metabolism:
a. T3 & T4 stimulate all aspects of fat metabolism
b. Mobilization of lipids (depletion of fat stores),
increases free fatty acid in plasma & it increases
FFAs oxidation.
3- Effect on protein metabolism:
a. T3 & T4 are anabolic hormones (increases protein
synthesis all over the body)
4- Effects on plasma lipids: Thyroid
hormones decreases plasma cholesterol
5- Effect on basal metabolic rate (BMR)
a. Thyroid hormones (normal level) are
responsible for normal BMR & normal body
weight.
B- Effects on growth:
• Responsible for Normal Mental & Physical and
Sexual growth
C- Effects on body systems:
T3 & T4 stimulate most body systems
• In SUMMARY: the thyroid hormones are
essential for:
• Normal development: physical, mental &
sexual in young
• Normal functions: physical, mental and
sexual in adults
Disturbances in thyroid hormones
• Hypothyroidism
• Hyperthyroidism
Hypothyroidism
Cretinism
Myxedema
In children since birth or
during early childhood
In adults
Hyperthyroidism
Thyrotoxicosis
Parathyroid gland
• They secrete
parathyroid hormone
(parathormone)
(PTH)
Functions of PTH:
1- Hypercalcaemia (increase the plasma calcium
level)
2- Decrease phosphate in blood
(Hypophosphataemia)
3- Increasing the phosphate excretion in urine
(Phosphaturic action).
PTH acts on Bone & kidneys and intestine
Tetany
It is a clinical state of
increased
neuromuscular
excitability, caused by a
decrease in the plasma
level of ionized calcium.
Calcitonin hormone
• Secreted from parafollicular cells of thyroid gland.
• It is Hypocalcaemic hormone:
Antagonistic to PTH as regards Ca++, but similar effects on
phosphate.
Decrease reabsorption of both calcium & phosphate from
urine = increase both calcium& phosphate excretion