Endocrinology

Endocrinology is the branch of biological science that deals with the study of

Hormones and their receptors. The study of chemical (hormonal) communication systems

that provide the means to control many physiologic processes (integration): i.e., it is a science

that involves chemical integration to maintain homeostasis of the body.

Reproductive Endocrinology

Reproductive endocrinology is a branch of medicine that identifies and treats

infertility in both humans and animals.

Two major categories of glands that secret in the animal body:

1. Exocrine Glands

a. Having ducts: A gland with ducts that are used for secretion.

b. Non-hormonal products are directed to the surfaces of cell membranes: The secretions pass

into a ductal system that leads to the exterior of the body. Example: Salivary glands, Bile-

producing glands (liver), Pancreas: pancreas fluid (duodenum), Sweat glands

2. Endocrine Glands:

Endocrine; Endo: from the Greek “endon”; within and Crine: “Krinein”; to release

• Ductless glands

• Hormonal secretions: Secretes substances into surrounding tissue fluids (in vascular or

lymphatic drainage) that affect cells elsewhere in the body.

• The secretion does not involve loss of tissue or provide energy to the target cells.

Hormones

• Greek verb: to excite, and encompass (to surround or enclose)

• Signalling molecules produced by the endocrine gland (glandular cells)

• Secreted into the internal

• Acts as a catalyst (needs receptors)

• Acts on target cells, tissues, or organs at a place other than where it is produced.

Hormones are chemical substances produced in one part of the body that diffuse or is

transported in another area where it influences activity and tends to integrate component parts

of the organism.

Different cells may respond to the same hormone differently: e.g. Insulin stimulates

muscle and adipose cells to uptake glucose, and the liver to store glucose in the form of

glycogen.

Characteristics of Hormones

(1) Act in minute quantities (10-9

-10-12)

(2) Have short half-lives in general (differs between water-soluble and insoluble)

(3) Bind to specific receptors

(4) Regulate intracellular biochemical reactions

Classification of hormones base on:

A. On the basis of source or origins

B. On the basis of type or functions

C. On the basis of biochemical combination or structure

A. On the basis of source or origins: site of production; glandular origins

1. Hypothalamic hormones: GnRH, oxytocin, neuropeptides

2. Pituitary hormones: FSH, LH, and Prolactin

 Gonads’ hormones: affecting functions of the hypothalamus, pituitary, reproductive

tracts (E2, P4), and 2°sex characteristics

3. Ovary: Relaxin, Inhibin, progesterone, and estrogen.

4. Testes: Testosterone

5. Pineal: Melatonin

6. Uterus: Prostaglandins

7. Placenta: Human chorionic gonadotropins, equine chorionic gonadotropins, Placental

lactogen, protein B.

B. On the basis of type of functions:

1. Primary Hormones of Reproduction: These hormones are directly involved in the

various aspects of reproduction such as Spermatogenesis, sexual behavior, Ovulation,

Fertilization, Implantation, Maintenance of Gestation, Parturition, and Lactation.

Examples of such hormones are FSH, LH, GnRH, Oxytocin, Estrogens, Progesterone,

Testosterone etc.

2. Metabolic Hormones: These hormones are necessary for the general well-being and

metabolic state of the animal. They are necessary for the proper maintenance of the internal

environment to ensure successful reproduction.

In general, Metabolic Hormones influence Growth, Development, and Metabolism.

They maintain the physiologic state of the animal and thus permit the full effect of the primary

Hormones of reproduction. Examples of Metabolic Hormones are STH, thyroxin,

thyrocalcitonin, insulin, and growth hormones, etc.

C. On the basis of biochemical combination or structure:

1. Proteins: hypothalamic, e.g. GnRH, oxytocin, relaxin

2. Glycoproteins: pituitary, gonads e.g. FSH, LH, PMSG, ECG, hCG

3. Steroids: gonadal, adrenal hormones e.g. Estrogen, progesterone, thyroxin, testosterone

4. Fatty acids: many sources, prostaglandins, PGF2α

5. Modified amino acids: thyroid hormones, melatonin

Forms of hormone regulation

Paracrine: secretion acts on neighboring cells (a small distance)

The target cells are close to or next to the signal releasing cell.

(The hormone merely diffuses away from the source cell, and the adjacent target cells

respond to the signal.)

Autocrine a cell utilizes the compound it produces by itself, i.e., the target cell is also the cell

that released the signal.

e.g., when cytokine interleukin-1 (IL-1) is released from monocytes in response to an external

stimuli, the IL-1 can actually bind the cell-surface receptors on the monocyte that produces it

(self-stimulation)

Epicrine: hormones pass through gap junction of adjacent cells without entering extracellular

fluid.

Intracrine: the regulatory molecules remain and effective within the cell

Neurocrine: hormones diffuse through synaptic clefts between neurons (neurotransmitters)

Pheromones

The term "pheromone" was introduced by Peter Karlson and Martin Lüscher in

1959, based on the Greek word pherein (to transport) and hormone (to stimulate). Another

class of substances directly influences reproductive processes. Substances are secreted to the

outside of the body.

They are also sometimes classified as ecto-hormones, and also called “alarm

substances”. These chemical messengers are transported outside of the body and result in a

direct effect on the hormonal levels or behavioral changes.

Volatile and/or non-volatile signals detected by the olfactory system.

Functions: to influence the onset of puberty, the identification of estrus by the males, other

behavioral and physiological traits.