Question

Are you able to describe and classify the structural and functional properties if exocrine and endocrine glands??

Answer 1

Glands : A group of cells which secreate chemical substances called hormones.Glands are classified as Exocrine and Endocrine.

Exocrine glands:Glands which secreate hormones through ducts.

Endocrine glands:Glands which secreate hormones directly to blood steam. They are ductless.

Exocrine glands

Structural Classification of Exocrine glands

Structurally they are classified into 2: a) Unicellular b) Multicellular

a) Unicellular Exocrine Glands

Made up of one cell layer.Eg:Goblet cells:They secrete mucus and are found in the epithelial lining of the respiratory, urinary, digestive, and reproductive systems.

b) Multicellular Exocrine Glands

Made up of more than one layer of cells.They are of 2 types based on their shape of secretory parts and by the arrangement of their ducts.

Simple ducts:A gland with one duct is a "simple,".The secretory portions of simple glands can be straight tubular, coiled tubular, acinar, or alveolar (flask-like).

Compound ducts: Gland with a branched duct is a "compound" gland. The secretory portions of compound glands can be tubular, acinar, or a combination: tubulo-acinar.

Functional Classification of Exocrine glands

Based on how they secrete their products there are three categories of functional classification: holocrine glands, merocrine (or eccrine) glands, and apocrine glands.

1)Holocrine glands: Holocrine glands accumulate their secretions in each cell's cytoplasm and release the whole cell into the duct. This destroys the cell, which is replaced by a new growth cell.
e.g. sebaceous glands: meibomian and zeis glands.

2)merocrine (or eccrine) glands:Here,secretions produced are released it into the duct by a process called Exocytosis, causing no damage to the cell.

e.g. max sweat gland of humans, goblet cells, salivary gland, tear gland and intestinal glands

3) :The secretions of apocrine cells accumulate in one part, called the apical region. This part breaks off from the rest of the cell along with some cytoplasm, releasing its product into the duct. The cells repair themselves quickly and soon repeat the process.

Eg: glands in the mammary glands and the arm pits and groin.

Based on the type of secretory product, exocrine glands may be classified into 3:

1)Serous glands :secrete a watery, often protein-rich, fluid-like product, e.g. sweat glands.

2)Mucous glands: secrete a viscous product, rich in carbohydrates (such as glycoproteins), e.g. goblet cells.

3)Sebaceous glands: secrete a lipid product. These glands are also known as oil glands, e.g. Fordyce spots and meibomian glands.

Endocrine glands

The glands of the endocrine system include: pituitary, Hypothalamus,thyroid, parathyroids, thymus, pancreas, pineal, adrenals, and ovaries or testes.

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Classification of Endocrine Glands:

Vertebrate endocrine glands can be divided into different categories, like

1. On the Basis of Location:

a) Cranial endocrine glands:

These endocrine glands are located in the head region.

e.g., Pituitary gland, Pineal gland, Hypothalamus.

(b) Pharyngeal endocrine glands:

These glands are found in pharyngeal or neck region.

e.g. Thyroid gland, Parathyroid gland.

(c) Abdominal endocrine glands:

These glands are located in the abdominal region.

e.g. Pancreas, Adrenal, Testis, Ovary.

2. On the Basis of Number:

(a) Unilateral endocrine glands:

These endocrine glands are single in num­ber.

e.g. Pituitary, Pineal gland, Pancreas.

(b) Bilateral endocrine glands:

These endocrine glands are paired .

e.g. Thyroid, Adrenal, Parathyroid gland.

3. On the Basis of Secretion:

(a) Telecrine glands:

Hormones are re­leased by specialised endocrine cells into the extracellular space and are thence carried by blood to the dis­tant target cells.

e.g. Thyroid gland, Adrenal gland, Pituitary gland etc.

(b) Paracrine glands:

Hormones diffuse locally through the interstitial fluid from the secretory cells to the adja­cent target cells

e.g. In islets of Langerhans, soma­tostatin is secreted from δ-cells, that reacts on adjacent α and β cells.

Function of endocrine glands is to secrete various endocrine hormones.

Endocrine glands and their secreations

Hypothalamus: Thyrotropin releasing hormone,Dopamine ,Growth hormone releasing hormone, Somatostatin, Gonadotropin Releasing Hormone, Corticotropin Releasing Hoprmone, Vasopressin.

Pineal gland: Melatonin

Pituitary Gland

Anterior pituitary:Growth hormone, Thyroid stimulating Hormone,Adrenocorticotropic hormone,Follicle Stimulating Hormone,Leiutinising Hormone,Prolactin

Posterior Pituitary:Oxytocin and Vasopressin

Intermediate pituitary:Melanocyte Stimulating Hormone

Thyroid: Tri iodothyronin,Thyroxine,Calcitonin

pancreas:Insulin,Glucagon

adrenals:Glucocorticoids, Mineralocorticoids

ovaries :Progesteron,Oestrogens

testes.:Androgens