1. Adrenal. Thyroid. Parathyroid.

2. Adrenal Glands
 Paired organs that cap the superior borders of the kidneys
 Each consists of:
 Adrenal cortex (outer)
– derived from neural crest ectoderm
– does not receive neural innervation so it must be stimulated
hormonally
- Consists of three zones: zona glomerulosa, zona fasciculata
and zona reticularis
 Adrenal medulla (inner)
– derived from mesoderm
– innervated by preganglionic sympathetic nerve fibers

3. Structure of Adrenal Gland

4. Functions of Adrenal Cortex
 Secretes steroid hormones (corticosteroids or
corticoids)
 Mineralocorticoids – regulate Na+ and K+ balance
 Glucocorticoids – regulate the metabolism of glucose
and other organic molecules
 Sex steroids – weak androgens
(dehydroepiandrosterone or DHEA)

5. Aldosterone
 Most potent mineralocorticoid
 Secreted by the zona glomerulosa
 Stimulate the kidneys to retain NaCl and water while
excreting K+ in the urine
 These actions help to increase the blood volume and
pressure and to regulate blood electrolyte balance

6. Cortisol
 Predominant glucocorticoid
 Secreted by zona fasciculata and perhaps also the
zona reticularis
 Secretion is stimulated by the ACTH from the
anterior pituitary gland
 have effects on metabolism:
 Stimulate gluconeogenesis
 Inhibit glucose utilization
 Promote lipolysis and consequent release of free fatty
acids into the blood

7. Exogenous Glucocorticoids
 Taken as pills, injections, sprays and topical creams
 Used medically to suppress the immune response
 Very useful in treating inflammatory diseases (asthma,
rheumatoid arthritis)
 Side effects:
 Hyperglycemia
 Decreased glucose tolerance
 Decrease synthesis of collagen and other extracellular
matrix proteins and increased bone resorption
(osteoporosis)

8. Cushing’s Syndrome
 Hypersecretion of ACTH (glucocorticoid)
 Can also result from a tumor of the adrenal cortex
 Characterized by:
 Changes in carbohydrate and protein metabolism
 Hyperglycemia
 Hypertension
 Muscular weakness

9. Functions of Adrenal Medulla
 Secrete epinephrine and norepinephrine
 Effects of catecholamine hormones secreted by the
medulla:
 Increase cardiac output
 Dilate coronary blood vessels
 Increase mental alertness
 Increase respiratory rate
 Elevates metabolic rate
 Supported by the metabolic actions of E and NE:
 Rise in blood glucose (due to stimulation of hepatic
glycogenolysis)
 Rise in blood fatty acids (due to lipolysis)

10. Stress and the Adrenal Gland
 1936 – Hans Selye discovered that injections of cattle
ovary extract into rats:
1. stimulated growth of the adrenal cortex
2. caused the atrophy of the lymphoid tissue of the
spleen, lymph nodes and thymus, and
3. produced bleeding peptic ulcers
 Same things happened when he subjected the rats to
cold environment and when he dropped them into
water and made them swim until they were exhausted

11. Stress and the Adrenal Gland
 Stress – reaction of the organism to stimuli
(stressors) which may produce damaging effects
 Stressors stimulate the pituitary-adrenal axis
 Under stressful conditions, there is a increased
secretion of ACTH therefore there is the increased
secretion of glucocorticoids

12. Stress and the Adrenal Gland
 There is a nonspecific response of the body to readjust
itself following any demand made upon it
 A rise in the plasma glucocorticoid level results from
the demands of the stressors (General Adaptation
Syndrome or GAS)
 3 stages in response to stress:
 Alarm reaction (adrenal glands are activated)
 Stage of resistance (readjustment occurs)
 Stage of exhaustion (if readjustment is not complete –
this leads to sickness and possibly, death)

13. Thyroid Gland
 Located just below the larynx
 Two lobes are positioned on either side of the trachea
and are connected anteriorly by a medial mass of the
thyroid tissue (isthmus)
 Largest pure endocrine gland (20-25 grams in wt.)

14. Thyroid Gland

15. Thyroid Gland
 Consists of numerous spherical hollow sacs (thyroid
follicles) lined with simple cuboidal epithelium
composed of follicular cells (secrete thyroxin)
 The interior of follicles contain colloid (protein-rich
fluid)
 Also contains parafollicular cells (secrete calcitonin
or thyrocalcitonin)

16. Thyroid Gland

17. Production and Action of Thyroid
Hormones
 Thyroid follicles actively accumulate iodide (I-) from
the blood and secrete it into the colloid
 Iodide will be oxidized to form iodine once it enters
the colloid then it will be attached to amino acids
(tyrosines) within the polypeptide chain of protein
(called thyroglobulin)
 The attachment of:
 One iodine to tyrosine => monoiodotyrosine (MIT)
 Two iodines => diiodotyrosine (DIT)

18. Production and Action of Thyroid
Hormones
 Within the colloid, enzymes modify the structure of
MIT and DIT and couple them together
 Tetraiodothyronine (T4) or thyroxine – produced
when two DIT molecules that are appropriately
modified are coupled together
 Triiodothyronine (T3) – combination of one MIT
with one DIT
 Upon stimulation of TSH, the cells of the follicle take
up a small volume of colloid by pinocytosis, hydrolyze
the T3 and T4 from the thyroglobulin, and secrete free
hormones into the blood

19. Production and Action of Thyroid
Hormones
 Through the activation of genes, thyroid hormones:
 Stimulate protein synthesis
 Promote maturation of the nervous system
 Increase the rate of cell respiration
 Through this, thyroxin elevates the basal metabolic rate (the
resting state of calorie expenditure by the body)
 Calcitonin
– works with parathyroid hormones to regulate calcium levels
of the blood
- Inhibits dissolution of the calcium phosphate crystals of
bone and stimulates the excretion of calcium in the urine
by the kidneys

20. Hyperthyroidism
 Iodine-deficiency (endemic) Goiter
– abnormal growth of the thyroid gland
– due to the absence of the dietary iodine, the thyroid
cannot produce adequate amounts of T4 and T3
– the resulting lack of negative feedback inhibition
causes hypersecretion of TSH that stimulates
abnormality

21. Hypothyroidism
 Condition of people who have inadequate secretion of
the thyroid hormone
 People who have hypothyroidism have an abnormally
low basal metabolic rate and they experience weight
gain and lethargy
 In adults, it causes:
 Myxedema
– accumulation of mucoproteins and fluid in
subcutaneous connective tissues
– symptoms: swelling of the hands, face, feet and tissues
around the eyes

22. Hypothyroidism
 Can also be caused by insufficient thyrotropin-
releasing hormone (TRH) secretion from the
hypothalamus, or insufficient secretion of TSH from
the anterior pituitary or insufficient iodine in the diet

23. Parathyroid Glands
 Small flattened glands that are embedded in the
posterior surfaces of the lateral lobes of the thyroid
gland

24. Parathyroid Glands

25. Parathyroid hormone
 Only hormone secreted by the parathyroid glands
 Important in the control of calcium levels of the blood
 Promotes rise in blood calcium levels by acting on the
bones, kidneys and intestine