L1 Basics in Endocrinology

Question 1

What is The main function of the endocrine system ?

Answer 1

is to maintain the homeostasis of the internal environment

Question 2

What are the sources of endocrine cells ?

Answer 2

1. cells of endocrine glands (ductless glands)

2. tissues that regulate the activity of other cells in the body

Question 3

What are the primary endocrine glands and their hormones ?

Answer 3

1. Anterior pituitary gland: ACTH (corticotrophin), FSH, LH, PRL, TSH (thyrotropin), GH(somatotrophin)
2. Posterior pituitary gland (stored & secreted only): oxytocin and ADH
3. Thyroid gland: T4, T3 and calcitonin
4. Parathyroid gland: parathyroid hormone (parathormone)
5. Adrenal glands:
   • Cortex: cortisol, aldosterone and sex hormones
   • Medulla: epinephrine and norepinephrine
6. Pancreas: insulin, glucagon and somatostatin (GHIH)
7. Ovaries: estrogens, progesterone, inhibin and relaxin
8. Testes: androgens, inhibin and anti-mullerian hormone (fetus)
9. Pineal gland: melatonin ( for sleep )
10. Thymus gland: thymosine (thymopoeitin)

Question 4

What is the Classification of Hormones in Terms of the Cells they Target ?

Answer 4

1. Autocrine:
   - hormone that is secreted by the cell and acts on the same cell
2. Paracrine:
   - hormone secreted by a cell but acts on a nearby cell without entering the main bloodstream (but can enter local circulation)
3. Endocrine:
   - acting on cells or organs at distant sites, to which they are carried in the bloodstream, or through another aqueous ducting system, such as the lymph
4. Neurocrine/neuroendocrine:
   - paracrine or endocrine, except that the hormones are synthesized in a nerve cell which releases the hormone either into:
   • the bloodstream (endocrine)
   • or adjacent to the target cell (paracrine)

Question 5

What are the hormonal rhythms ?

Answer 5

1. Circadian (sleep/wakefulness cycle) or diurnal rhythms (when the rhythm is synchronized with the day/night cycle):
   - pulsatile, have a 24-hour cycle
   - e.g. PRL, GH and cortisol
2. Ultradian rhythms:
   - pulsatile, with usually a ½ to 2 hr period (< 24hrs)
   - e.g. LH, FSH and testosterone
3. Infradian rhythms:
   - pulsatile, periodicity > 24 hrs
   - e.g. menstruation or seasonal breeding in animals

Question 6

How diurnal /circadian rhythm is regulated ?

Answer 6

Having a biological clock in suprachiasmatic nucleas that have multiple connections with hypothalamus that will be affected by light and darkness
It will ensure that melatonin is only secreted at night

Question 7

What is the importance of hormonal rhythms ? What can disrupt it ?

Answer 7

Hormonal rhythm is important for normal hormonal functions
It can be disrupted by :
* jet lag
* work shift 
* old age 
* it is usually absent in disease sates

Question 8

What is the effects of disrupting the rhythms ?

Answer 8

Disruption of the clock detrimentally affects our :

• well-being
• mental and physical performance

Question 9

Give examples of Control Mechanisms: Positive and Negative Feedback Mechanisms

Answer 9

1. Positive feedback:
   - some consequence of hormonal secretion acts on the secretory cells to provide augmented drive for secretion
   - oxytocin and prostaglandins
2. Negative feedback:
   - some consequence of hormone secretion (or the hormone itself) acts directly or indirectly on the secretory cell in a negative way to inhibit further secretion; regulates secretion of most hormones; long, short and ultrashort loop systems
   - insulin and glucagon

Question 10

How can Anterior Pituitary Hormone Secretion controlled by Hypothalamus ?

Answer 10

1. CRH > releasing ACRH
2. GnRH > releasing LH and FSH
3. dopamine ( PIH )
   - inhibiting prolactin release ( main )
   - releasing GH
4. PRH > releasing prolactin
5. TRH ( general stimulator )
   - releasing TSH ( main )
   - releasing GH
   - releasing prolactin
6. GHRH > releasing GH
7. Somatostatin ( general inhibitor )
   - inhibiting GH
   - inhibiting TSH

Question 11

What are the Endocrine Hyper-function Disorders ?

Answer 11

1. Due to tumor, hyperplasia or autoimmune stimulation of endocrine gland:
   - hyperplasia of parathyroid gland with renal failure
   - hyperplasia of thyroid gland (may be due to autoimmune stimulation of gland)
2. Ectopic production of hormones by tumors of tissues that do not produce the hormones
   - ACTH, vasopressin & calcitonin produced by lung carcinomas

Question 12

What are the Endocrine hypo-function Disorders ?

Answer 12

1. Destruction of the gland mostly due to autoimmune disease
   - IDDM
   - hypothyroidism ( Hashimoto disease )
2. Damage to gland as a result of infection or hemorrhage
3. Tissue insensitivity ( resistance )
   - insulin
   - vasopressin
4. Failure to convert to active product by organs other than endocrine glands
   - testosterone
   - 25-hydroxyvitamin D 3

Question 13

What is primary, secondary, tertiary endocrine disorder ?

Answer 13

1. Primary endocrine disorder:
   - Target gland itself (e.g. thyroid, adrenal or ovary) isn’t functioning normally
2. Secondary endocrine disorder:
   - When the initial disorder is in the pituitary and the problem in target organ is secondary to the pituitary disorder
3. Tertiary endocrine disorder:
   - In which the problem originates in the hypothalamus