● `color{violet}("Hormones")` are also secreted by some `color{violet}("tissues")` which are not `color{violet}("endocrine glands")`.

● For example, the `color{violet}("atrial wall")` of our heart secretes a very important peptide hormone called `color{brown}("atrial natriuretic factor")` (ANF), which decreases `color{violet}("blood pressure.")`

● When `color{violet}("blood pressure")` is increased, ANF is secreted which causes dilation of the `color{violet}("blood vessels")`.

● This reduces the `color{violet}("blood pressure.")`

● The `color{violet}("juxtaglomerular cells")` of kidney produce a peptide hormone called `color{brown}("erythropoietin")` which stimulates `color{violet}("erythropoiesis")` (formation of RBC).

● `color{violet}("Endocrine cells")` present in different parts of the `color{violet}("gastro-intestinal")` tract secrete four major peptide hormones, namely `color{brown}("gastrin, secretin, cholecystokinin")` (CCK) and `color{brown}("gastric inhibitory peptide")` (GIP).

● `color{violet}("Gastrin acts ")` on the `color{violet}("gastric glands")` and stimulates the secretion of `color{violet}("hydrochloric acid ")` and `color{violet}("pepsinogen. ")`

● Secretin acts on the `color{violet}("exocrine pancreas")` and stimulates secretion of `color{violet}("water and bicarbonate ions")`.

● CCK acts on both pancreas and `color{violet}("gall bladder")` and stimulates the secretion of `color{violet}("pancreatic enzymes")` and bile juice, respectively.

● GIP inhibits `color{violet}("gastric secretion")` and `color{violet}("motility.")`

● Several other `color{violet}("non-endocrine tissues")` secrete hormones called `color{brown}("growth factors.")`

● These `color{violet}("factors")` are essential for the `color{violet}("normal growth of tissues")` and their repairing/regeneration.

● `color{violet}("Hormones")` produce their effects on target `color{violet}("tissues")` by binding to specific proteins called `color{brown}("hormone receptors")` located in the target `color{violet}("tissues")` only.

● `color{violet}("Hormone")` receptors present on the `color{violet}("cell membrane")` of the target cells are called `color{violet}("membrane-bound receptors")` and the receptors present inside the target cell are called `color{violet}("intracellular receptors, mostly nuclear receptors")` (present in the nucleus).

● `color{violet}("Binding of a hormone")` to its receptor leads to the formation of a `color{brown}("hormone-receptor complex")`.

● Each receptor is specific to one hormone only and hence `color{violet}("receptors")` are specific.

● `color{violet}("Hormone-Receptor complex")` formation leads to certain `color{violet}("biochemical changes")` in the target tissue.

● `color{violet}("Hormones")` produce their effects on target tissues by `color{violet}("binding")` to specific proteins called hormone receptors located in the target tissues only.

● `color{violet}("Hormone receptors")` present on the cell membrane of the target cells are called `color{violet}("membrane-bound receptors")` and the `color{violet}("receptors present")` inside the target cell are called `color{violet}("intracellular receptors, mostly nuclear receptors")` (present in the nucleus).

● `color{violet}("Binding of a hormone")` to its receptor leads to the formation of a `color{violet}("hormone-receptor complex")`.

● Each receptor is specific to one `color{violet}("hormone")` only and hence receptors are specific.

● `color{violet}("Hormone-Receptor complex")` formation leads to certain `color{violet}("biochemical changes")` in the target tissue.

● Target tissue metabolism and hence `color{violet}("physiological functions")` are regulated by hormones.

● On the basis of their `color{violet}("chemical nature, hormones")` can be divided into groups:

(i) `color{brown}("Peptide, polypeptide, protein hormones")` (e.g., insulin, glucagon, pituitary hormones, hypothalamic hormones, etc.)

(ii) `color{brown}("Steroids")` (e.g., cortisol, testosterone, estradiol and progesterone)

(iii) `color{brown}("Iodothyronines")` (thyroid hormones)

(iv) `color{brown}("Amino-acid derivatives")` (e.g., epinephrine).

● `color{violet}("Hormones")` which interact with `color{violet}("membrane-bound receptors")` normally do not enter the target cell, but generate second messengers (e.g., cyclic `AMP, IP_3, Ca^(++)` etc) which in turn regulate cellular `color{violet}("metabolism.")`

● `color{violet}("Hormones ")` which interact with `color{violet}("intracellular receptors")` (e.g., steroid hormones, iodothyronines, etc.) mostly regulate gene expression or `color{violet}("chromosome function")` by the interaction of hormone-receptor complex
with the `color{violet}("genome. ")`

● `color{violet}("Cumulative biochemical")` actions result in `color{violet}("physiological and developmental")` effects.