Lesson nine

Endocrine glands and reproduction

1. What are the endocrine glands?

The pituitary, thyroid, thymus, adrenals, pancreas, ovaries and testes are the endocrine glandswhich regulate some of the most important function of the body.

2. What is characteristic of these hormonal or endocrine glands?

They are transformed atavistic organs. In contrast to ordinary glands they do not send their  product through ducts into the surrounding areas. Instead, the hormones from endocrine glands

directly enter the blood stream and, through the blood, all parts of the body. Therefore they are

called the glands of internal secretion or the ductless glands. Being minute they are difficult todetect. Those who chose to work with sex hormones made contracts with slaughterhouses for the

sex glands of thousands of lambs and steers. Three drops of hormone were finally extracted from

a hecatomb of steers, not as a sacrifice for Olympian Jove but for the Goddess of Science.

3. What is the subject of endocrinology?

The study of the structures and the secretions of the ductless gland along with the effects of their secretion on organ and animal behaviour constitute the subject of endocrinology.

4. What is the master gland of the body?

The pituitary gland (also called the hypophysis) is the master gland of the body. It consists of two lobes: the anterior (the glandular) lobe and the posterior (the neural) lobe. It is situated at the

 base of the brain. It is about the size of a pea, weighing approximately 0.5 g and produces the

largest number of hormones, some of which control the other endocrine glands of the body. For example the hormone ACTH stimulates the functioning of the adrenal cortex. The hormone

known as TSH stimulates the thyroid gland.

a) How many hormonal agents are recognized?Present-day workers in the filed of hormone physiology recognize six distinct hormonal

agents, these being the somatotrophic, follicle-stimulating luteinizing, lactogenic, thyrotropic and

adrenocorticotrophic hormones.

 b) What is the growth hormone responsible for?

The growth hormone is responsible for a normal growth.

Gigantism and dwarfism are symptoms related to disorders in the secretory activity of somatotrophin. Tom Thumb is P.T. Branum’s most famous human curiosity; the pituitary dwarf 

is of extremely small stature but of normal body proportions, having normal mental

development. He is readily differentiated from the cretin dwarf. Acromegaly is characterized byabnormal enlargements, especially of the jaw, nose, hands and feet.

c) What induces labour?

 

A pituitary hormone secreted by the posterior lobe commands the uterus of a pregnant

woman to start those rhythmic movements called labour that will help her to expel her child. The

notice it sends out is: the child is ripe for birth.

d) What is responsible for a milk ejection from the mammary gland of the normally

lactating female?Another posterior-pituitary hormone activates the breast of the mother to produce milk.

e) Do other hormones of the pituitary gland serve the sex functions?One of them, the gonadotropic hormone, ripens the gonads or sex-cells, the spermatozoa

of the male and the ovules of the female.

5. What hormonal gland is located beside the larynx?The thyroid gland consists of two bodies which have a total weight of about 25 g; they are

connected by an isthmus and are located immediately below the larynx.

a) What are the functional units of the thyroid?

The follicles are the functional units of the thyroid; they are composed of a lining of 

cuboidal epithelial cells surrounding a central mass of colloidal material. The colloid is a viscous protein secretion, iodothyroglobulin, produced by the epithelial cells, apparently a storage depot

for thyroid hormone. Thyroid secretion plays an important role in metabolism as well as in

development.

 b) Are there any thyroid deficiencies?

Yes, there are two disturbances: hypothyroidism and hyperthyroidism.

6. What do the parathyroid glands regulate?

They regulate the metabolism of phosphorus and calcium in the body through the parathyroid

hormone. Calcium in the blood is necessary for normal nerve function but when the bloodcalcium rises too high, nerves react sluggishly to stimuli.

7. What is known about thymus?The thymus gland was a mystery until recently. It is necessary in the late stages of embryonic

development and in early infancy to develop the immunity mechanisms of man and animals. The

thymus sends young lymph cells and probably a hormone to the lymph nodes and spleen. As a

result, lymph nodes and spleen become capable of producing antibodies – the method by whichthe organism combats infection.

8. What is characteristic of the islets of the pancreas?In the course of say billion years hormonal tissues immigrated in small groups into the

 pancreas, the big digestive gland behind the stomach. There they became islets of hormonal

tissue producing insulin, which controls the burning of sugar in the cells for the production of energy. A shortage of insulin may bring about diabetes. The most easily detectable sign of 

diabetes is sugar in the urine.

9. What are the adrenal glands?

 

They are double organs with a nervous core and a glandular cortex. The cortex produces a

series of steroids, the corticosteroids, which have wide-ranging effects. The core or medulla

functions in cooperation with the sympathetic nerve system, regulating the blood pressure, theheart action and other activities of the body through the secretion of adrenalin and noradrenalin.

A failure in the adrenal cortex may lead to Addison’s disease. The patient is treated with

corticosteroid.

10. What are the testes and the ovaries?

Each testis is a compound tubular gland enclosed in a fibrous capsule called the tunicaalbuginea. Other cells scattered between the seminiferous tubules in the lobules of the testes

called the interstitial cells (cells of Leydig). These are responsible for production of the male sex

hormone testosterone.

In the follicular fluid of the ovarian follicle is a hormone called estradiol, which is also asterol closely related in chemical structure to the male sex hormones. It is produced by the cells

surrounding the follicle. Estrone (theelin), which is found in urine, is similar in action to estradiol

 but only about 20 per cent as potent. Estradiol and estrone are collectively referred to asestrogens. Progesterone is the hormone produced by the cells surrounding the follicular cavity

after the follicle ruptures. Progesterone is the pregnancy hormone, preparing the uterus still

further for the reception of the egg after the necessary “priming” action of estradiol.

11. What happens with the egg after fertilization?

It begins subdividing and multiplying and floats into the cavity of the uterus. The glands of the mucous membrane of the uterus become active, increasing in size and the membrane is

described as “blooming”. The blastocyst, the inner mass of cells, receives nourishment from the

uterine mucosa. The placenta that feeds the embryo is formed.