introduction Flashcards
compare between endocrine&exocrine gland
Endocrine glands
- They are ductless glands that release hormones into tissue fluids. They have dense
capillary networks to distribute hormones.
- They produce intracellular effects, e.g. altering target cell metabolism.
> Exocrine glands
- They are characterized by ducts that carry secretion to body surface or organ cavity.
- They produce extracellular effects e.g. GIT secretions that help food digestion.
Mention Other Endocrine Organs or Tissues, and examples of the hormones secreted
1- Heart: Atrial natriuretic peptide (ANP).
2- Gastro-intestinal tract: Enteric hormones coordinate digestive motility and secretion.
3- Placenta: Hormones that influence pregnancy and mammary glands (estrogen,
progesterone and others).
4- Liver: Erythropoietin, Somatomedins.
5- Kidneys: Calcitriol (active vitamin D), Erythropoietin, renin.
6- Skin (cholecalciferol, precursor of vitamin D).
7- Adipose tissue: Numerous hormones such as Leptin which is a satiety hormone that helps
to regulate energy balance.
What are Mode of Hormone Delivery
a- Autocrine hormones: (self-acting)
- Hormone released feeds-back on the cell of origin again without entering blood
circulation. e.g. prostaglandins.
b- Paracrine hormones: (nearby acting)
- Hormone released diffuses to its target cells through immediate extracellular space
(neighboring cells) e.g. histamine which is released by injured cells, causes local
capillary walls to become more permeable, allowing more white blood cells and fluid
to leak into injured area.
- Blood is not directly involved in the delivery.
c- Neurohormones:
- Hormones released by neurons into the blood for action at distant targets.
- Example: vasopressin, a hormone produced by nerve cells in the brain that promotes
water conservation by the kidneys during urine formation.
d- Endocrine hormones: ;
- Hormones secreted by endocrine tissues or glands delivered to target cells by blood.
- Example: Insulin, from pancreatic beta cells
1.hormones that are Amino acid derivatives ……………………………
2.Lipid derivatives …………………………………
3.Proteins, peptides, glycoproteins ……………………..
1.Thyroid hormones, Catecholamines, and melatonin.
2.(steroids and eicosanoids): e.g. Adrenal cortical hormones, some
placental hormones and Sex hormones e.g. testosterone, estrogen.
3.Growth hormone and Insulin.
Classification of Hormones
According to solubility
a) Hydrophilic (water soluble & fat insoluble): Protein, peptide and glycoprotein
hormones, Catecholamines, and melatonin.
b) Lipophilic (fat soluble & water insoluble): All Steroid Hormones, Thyroid hormones.
1/protein and peptide hormones are stored in ……………………………….
2/Steroid hormones are formed from …………………what about storage
1/cytoplasmic vesicles and secreted on
stimulation (exocytosis).
2/cholesterol by a series of enzymatic reactions. They are
not stored and are secreted according to the rate of synthesis.
The strength of the response to hormone will depend on:
1……………………
2……………………
3……………………
I- Blood levels of the hormone.
II- The relative numbers of receptors for that hormone on or in the target cells (up & down
regulation).
Ill- The affinity (or strength of interactions) of the hormone and the receptor.
- Receptors are constantly being synthesized and broken down.
- “Lock and Key” approach describes the interaction between the hormone and its specific
receptor.
what are mechanism of Action of Hormones
I- Ion channel activation
2. Direct activation of transcription
3.Action through “ second messenger”:
4.activation of tyrosine kinase enzyme.
how can A hormone influence the activity of another hormone at a given target cell
~ Permissiveness:
One hormone must be present in adequate amounts to permit another hormone to exert its full effect. For example, thyroid hormone increases the number of receptors for epinephrine in epinephrine’s target cells, increasing the effectiveness of epinephrine. 2- Synergism:
Occurs when the actions of several hormones are complementary, and their combined effect is greater than the sum of their separate effects. An example is the synergistic action of follicle-stimulating hormone and testosterone, both of which are needed to maintain the normal rate of sperm production.
3- Antagonism:
Results when one hormone causes the loss of other hormone receptors, reducing the effectiveness of the second hormone. For example, progesterone decreases uterine responsiveness to estrogen during pregnancy by causing loss of estrogen receptors on uterine smooth muscles.
what is Neuroendocrine reflex
Hormonal secretion is controlled by neuroendocrine reflexes, which include neural as well
as hormonal components. The purpose of such reflexes is to produce a sudden increase in
hormone secretion in response to a specific stimulus.
Circadian rhythms mean…………..
The master biological clock …………….
1.Hormone secretion rates fluctuate cyclically over a 24-hour period (circadian is Latin
for “around a day”).
2.suprachiasmatic nucleus (SCN).
