Download Lab 10 Special Senses and Endocrine System

Lecture 5-7
Thyroid , Parathyroid
Thyroid Embryology
 Derived from
endodermal tissue at
base of tongue
 Embryonal remnants
form Thyroglossal duct;
pyramidal lobe; lingual
thyroid
 Fuse with C-cells (neural
crest origin), derived
from the the 5th
branchial arch
 C-cells scattered through
Thyroid Gland
Parathyroid
Glands
Thyroid Gland
Trachea
Thyroid
Thyroid
Esophagus
Thyroid Gland
calcitonin = thyrocalcitonin
THYROID GLAND HISTOLOGY
http://arbl.cvmbs.colostate.edu/hbooks/pathphys/endocrine/thyroid/anatomy.html
Thyroid Gland
Histology of Parathyroid Gland
• Principal (Chief) cells produce
parathyroid
hormone (PTH);
more numerous
• Oxyphil cell function is
unknown
Thyroid & Parathyroid, 400x
Actions of thyroid hormones:
T3 and T4 have the following effects:
1- General metabolism: Thyroid hormones increase the metabolic
rate and O2 consumption of all tissues of the body except the
adult brain, lungs, lymphoid tissues, retina and anterior pituitary
gland.
2- Protein metabolism: Normal levels of thyroid hormones stimulate
protein synthesis (anabolic effect) whilst excess Thyroid
hormones secretions cause protein catabolism (breakdown of
protein molecules).
3- Carbohydrate metabolism: Thyroid hormones stimulate glucose
uptake and utilization by tissues, insulin hormone secretion, liver
glycogenolysis and intestinal absorption of glucose.
4- Lipid metabolism: Thyroid hormones decrease the level of lipid
and cholesterol in the blood (i.e. increased cholesterol
catabolism than lipogenesis)
Actions of thyroid hormones (Continued)
5- Vitamin metabolism: Thyroid hormones are essential for hepatic
conversion of carotene (in green vegetable and carrot) into vitamin A.
6- Growth and maturation: Thyroid hormones are essential for physical,
mental and sexual growth.
7- Cardiovascular manifestations:

Tachycardia (i.e. increased heart rate).

The strength of myocardial muscle is increased.

Increased cardiac output.

Increased systolic blood pressure with a concomitant decrease in
diastolic blood pressure. So, pulse pressure is increased.
8- Respiratory system: Thyroid hormones cause an increase in rate and depth
of breathing to increase body metabolism.
9- Gastrointestinal tract: Thyroid hormones increase appetite, digestive juice
secretion, intestinal motility and absorption.
10- Hemopoietic system: Thyroid hormones stimulate erythropioesis by
increasing the rate of metabolism in the bone marrow and enhance
absorption of vitamin B12 from terminal ileum.
Thyroid Hormones
 The thyroid produces T3 and T4
 T4 ( Tetraiodothyronine )
 T3 ( Triiodothyronine ) , Reverse T3
T4
T3
Calcitonin
• Peptide hormone, acts opposing to
PTH
• Secreted by parafollicular or C cells of
thyroid gland
• Function : Decrease plasma
concentration of calcium
• Acts on bone & kidney
• Regulation of secretion – plasma Ca
concentration
Thyroid hormone synthesis
Functions of
thyroid
hormones
• Generally cause
increased BMR
• It increases
transcription of
large number of
genes
• Thyroid hormone
receptors are either
attached to DNA or
located near to it
http://fig.cox.miami.edu/~cmallery/150/memb/c11x10hormone-receptors2.jpg
SPECIFIC ACTIONS OF THYROID
HORMONE: METABOLIC
• Regulates of Basal Metabolic Rate (BMR).
• Increases oxygen consumption in most
target tissues.
• Permissive actions: TH increases
sensitivity of target tissues to
catecholamines, thereby elevating
lipolysis, glycogenolysis, and
gluconeogenesis.
Thyroid (cont)
•
•
•
•
•
•
•
Regulates basal metabolic rate
Improves cardiac contractility
Increases the gain of catecholamines
Increases bowel motility
Increases speed of muscle contraction
Decreases cholesterol (LDL)
Required for proper fetal neural growth
Regulation of PTH Secretion
Calcium Regulation
• Calcium homeostasis
Total blood calcium is usually 10 mg/dl
PTH and Calcium Feedback Loop
BASICS OF THYROID HORMONE
ACTION IN THE CELL
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Calcium Homeostasis
Endocrine regulation of
Calcium & phosphate
metabolism
• Hormones
– Parathyroid hormone
(PTH)
– Calcitonin (CT)
– Vitamin D3
• Target organs
– Bone
– Intestinal tract
– Kidney
15.3 Thyroid and parathyroid glands
Thyroid abnormalities
Thyroid & parathyroid pathophysiology
– Hypothyroidism
• During childhood = cretinism (“cretins”)
• During adulthood = myxedema
– Goiter (abnormal thyroid growth)
• Endemic = inadequate iodine intake
• Grave’s disease
Goiter
Goiter
Goiter is an enlargement of thyroid gland. It may be
accompanied with normal, hypo function or
hyper function of the thyroid.
Types of goiter
1.
Simple (non – toxic) goiter:
•
It is non – inflammatory, non – neoplastic (not
tumor) enlargement of the thyroid gland, that is
not initially associated with hypo or hyper
secretion of thyroid hormones
(hyperthyroidism). The thyroid gland enlarged
with normal thyroid function (i.e. euthyroidism).
It is due to insufficient iodine in water and soil
for food stuffs.
It may occur physiologically with the increase
demand of the body to thyroid hormones e.g. at
puberty and during pregnancy.
•
•
- cretinism: A type of mental retardation and
bodily malformation caused by severe,
uncorrected thyroid deficiency in infancy and
early childhood.

Hyperthroidism
- Grave’s disease: Grave’s disease is an
autoimmune disease in which the immune
system produces antibodies which stimulate
the TSH receptors of the thyroid gland,
resulting in overproduction of thyroid
hormones. Symptoms: increased pulse rate,
increased sweating, heat intolerance, hair
loss, inflammation of the eyes, swelling of
the tissues around the eyes, and protrusion
of the eyes.
Myxedema
Physical Findings for Myxedema
• Comatose or semi
comatose
• Dry coarse skin
• Hoarse voice
• Thin dry hair
• Delayed reflex
relaxation time
• Hypothermia
• Pericardial, pleural
effusions, ascites
Periorbital Myxoedema
•
Disorders of thyroid function

Hypothyroidism
- Myxedema - Hypothyroidism occurring in
adulthood. Clinical features include lethargy, cold
intolerance, decreased sweating, bradycardia,
tongue enlargement, and non-pitting edema of
the skin due to infiltration of the subcutaneous
tissues by metachromatic proteoglycans.
Myxedema causing
puffiness of the face in
an adult with
hypothyroidism.
EXAMPLES OF THYROID DISEASES
1° Hypothyroidism
Hyperthyroidism
www.hsc.missouri.edu/~daveg/thyroid/thy_dis.html
Disorders of thyroid gland
A- Hypothyroidism
Hypothyroidism is a syndrome resulted from a decrease in the secretion
of thyroid hormones T3 & T4 or inability of the tissues to use the
secreted hormones.
Hypofunction of the thyroid gland during childhood is called '‘Cretinism''
and if occurs during adulthood, it is called '' Myxoedema''.
Cretinism
Cretinism is a hypothyroidism in children. The child who is hypothyroid
since birth is called ''Cretin''
Causes of cretinism:
a) Congenital absence of the thyroid
b) Iodine deficiency during pregnancy.
EXAMPLES OF THYROID DISEASES
Juvenile Hypothyroidism
Congenital Hypothyroidism
www.hsc.missouri.edu/~daveg/thyroid/thy_dis.html