Nervous system: Glands and Their Role for Competitive Exams

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Thyroid Gland

Type, Location and Lobes

  • Very vascular organ and is located in the neck.

  • Consists of two parts/ lobes, one on each side of the trachea, just below the larynx or voice box.

  • These two lobes are connected by a narrow band of tissue, called the ‘isthmus’.

  • This gland consists of follicles, which produce thyroxin and triiodothyronine hormones.

  • These hormones contain iodine--- about 95% of most functioning hormone is thyroxin and the remaining 5% is triiodothyronine__ both require iodine for their synthesis.

  • Secretion is regulated by a negative feedback mechanism.

Calcitonin

  • Secreted by Para follicular cells of the thyroid gland.

  • Opposes the action of the parathyroid glands by reducing the calcium level in the blood.

  • If calcium level in the blood becomes too high, calcitonin is secreted until calcium ion levels decreases to normal.

Iodine Deficiency

  • Thyroid enlargement is called “goiter” or “iodine deficiency goiter”.

  • If there is a deficiency of iodine in the body, then thyroid produce insufficient hormones required by the body__ causing the thyroid- stimulating hormone of the pituitary gland (anterior lobe) to secrete its hormone.

  • This results in the increase in size of the thyroid gland but it is unable to make enough hormones, because it is lacking the raw material for production i.e. iodine.

Parathyroid Gland

Location, Type, Amount, Hormone

  • Parathyroid gland consists of four small masses of epithelial tissue that are embedded in the connective tissue capsule, on the posterior side of the thyroid glands.

  • Secretes ‘parathyroid hormone’ or ‘parathormone’.

  • Most important regulator of blood calcium levels, secreted in response to low blood calcium levels, and its function is to increase calcium levels in the body.

Deficiency/ Insufficient Secretion of Parathyroid Gland

  • Insufficient secretion of parathyroid hormone ‘hyperparathyroidism’s’, leads to increased nerve excitability.

  • Low blood calcium level in the body triggers spontaneous and continuous nerve impulses, which in turn stimulate muscle contraction.

Pancreas--- Islets of Langerhans

A long, soft organ that lies transversely along the posterior abdominal wall, posterior to the stomach, and extends from the region of the duodenum to the spleen.

A. Exocrine portion of this hormone secretes digestive enzymes that are carried by a duct to the duodenum

B. The endocrine portion consists of the pancreatic islets.

C. secretes glucagons and insulin.

Alpha Cells in Pancreatic Islets

Secrete hormone called ‘glucagons’ when there is a low concentration of glucose in the blood.

Beta Cells in the Pancreatic Islets

After the alpha cells, beta cells secrete hormone called ‘insulin’ as a result of high concentration of glucose in the blood.

Adrenal Gland

Synthesis and Location

  • Developed from different embryonic tissues, it secretes various hormones.

  • The adrenal/ suprarenal is a paired gland and located near the upper portion of each kidney.

Division of Adrenal Gland

  • Each gland is divided into two parts:

    • An outer cortex and

    • An inner medulla

  • The cortex and medulla of the adrenal gland are just like the anterior and posterior lobes of the pituitary gland.

  • The adrenal cortex is essential to life because it has very important functions to perform, but the medulla may be removed with no life-threatening effects.

  • Hypothalamus effects and influences both portions of the adrenal gland but it involves different mechanisms i.e. adrenal cortex is regulated by negative feedback which involves hypothalamus and adrenocorticotropic hormone.

  • Medulla is regulated by nerve impulses of hypothalamus.

Hormones of the Adrenal Cortex

  • The adrenal cortex consists of three different portions/ regions, each region produce different type of hormones.

  • Chemically, all these cortical hormones are steroid.

a. Mineral corticoids

  • Secreted by the outermost region of the adrenal cortex.

  • The main/ principal hormone of mineralocorticoid is aldosterone, which acts to store/ conserve sodium ions and water in the body.

b. Glucocorticoids

  • Secreted by the middle region of the adrenal cortex.

  • The main/ principal hormone of glucocorticoid is cortisol, which increases blood glucose/ sugar level in the body.

c. Gonad corticoids

  • Also known as the sex hormones.

  • These are secreted by the innermost region of the adrenal cortex.

  • Adrenal cortex hormones, androgens (male hormones) and estrogens (female hormones), are secreted in minimal amounts in both sexes, but their effect is usually influenced by the hormones from the testes and ovaries.

  • In females, the masculinization effect may become more evident after menopause. This occurs because the estrogen levels from the ovaries decrease.

  • Hormones of Adrenal Medulla

  • Develops from neural tissues.

  • Secretes two types of hormones,

    • Epinephrine and

    • Nor epinephrine

  • These are secreted in response to stimulation by sympathetic nerve, especially during stressful situations.

  • Lack of hormones from the adrenal medulla produces no significant effects,

  • Hyper secretion, e.g., in case of a tumor, results in prolonged or continual sympathetic responses.

Gonads

  • Primary reproductive organs are testes in the male and the ovaries in the female.

  • These organs are responsible for producing the sperm and ova, but they also secrete other hormones, and that is why they are considered to be endocrine glands.

Testes

  • Male sex hormones (as groups) are called androgens of which the most important and influential is ‘testosterone’; secreted by the testes.

  • Small amount is also produced by the adrenal cortex.

  • Production of testosterone begins before birth. i.e. during fetal development that continues for a short time after birth, nearly ceases during childhood, and then resumes at puberty.

  • This steroid hormone is responsible for:

    • The growth and development of the male reproductive organs.

    • Increase in the size of skeleton and muscular growth.

    • Larynx enlargement, accompanied by voice changes.

    • Growth and distribution of body hair.

    • Increased male sexual drive.

    • It’s secretion is controlled and regulated by a negative feedback system and involves release of hormones from the hypothalamus and gonadotropins from the anterior pituitary.

Ovaries

  • Two groups of female sex hormones are produced in the ovaries i.e.

    • Estrogens and

    • Progesterone

  • Contribute to the development and function of the female reproductive organs and sex characteristics:

    • Estrogen

    • Estrogen (on the onset of puberty) activates/ promotes:

      • Development of female bodily characteristics.

      • Distribution of fats in the body.

      • Maturation of reproductive organs.

    • Progesterone: causes the uterine lining to become thick, preparing uterus for pregnancy.

  • Together both progesterone and estrogen are responsible for a number of changes occurring in the uterus.

  • Other Endocrine Glands

  • In addition to the major endocrine glands and their system, there are various other organs, which are involved, in some hormonal activity or function. These include:

    • Thymus

    • Stomach

    • Small intestines

    • Heart, and

    • Placenta

  • Hormone produced by the thymus gland, which has an important role in the development of the body's immune system.

Gastrin

  • Gastric mucosa (lining of the stomach) produces a hormone, called gastrin that is secreted when the food is present in the stomach.

  • Stimulates the production of ‘hydrochloric acid’ and the enzyme ‘pepsin’, which are involved in the digestion of food.

  • Secretin and Cholecystokinin: The mucosa of the small intestine secretes these hormones.

  • Secretin stimulates the pancreas to produce a neutralizing agent__ bicarbonate-rich fluid that neutralizes the stomach acid.

Cholecystokinin

  • Stimulates contraction of the gallbladder, which result in the releases of bile.

  • Also activate the pancreas to secrete digestive enzyme.

  • Atrial Natriuretic Hormone, or Atriopeptin

  • Heart also function as an endocrine organ

  • In addition to its major role of pumping blood, has special cells in the wall of the upper chambers of the heart ‘atria’, secretes hormone called atrial natriuretic hormone, or atriopeptin.

Placenta

  • Develops in the pregnant female

  • It is a source of nourishment and gaseous exchange for the developing fetus

  • Also serves as a temporary endocrine gland

  • Chorionic gonadotropin: One hormone that placenta secretes in human beings.

Diseases Resulting from Abnormal Secretion of Endocrine Glands

  • Too much or too less secretions of endocrine glands can be harmful for the body.

  • These secretions can be treated by controlling the over production, providing the essentials for production, or replacing hormones.

  • Some of such abnormalities are:

Diabetes

Type 1 Diabetes

  • Develops when pancreas fails to produce enough insulin.

  • Symptoms include excessive:

    • Thirst

    • Hunger

    • Urination, and

    • weight loss

  • In children and teens, the condition is usually an ‘autoimmune disorder”___ specific immune system cells and antibodies produced by the child's immune system that attack and destroy the cells of the pancreas that produces insulin.

  • Can cause long-term complications such as:

    • Kidney problems

    • Nerve damage

    • Blindness

    • And early coronary heart disease and stroke

Treatment

In order to control blood sugar levels and reduce the risk of developing diabetes complications, children with this condition need regular injections of insulin

Type 2 diabetes

  • In this, the body is unable to respond to insulin normally, like in type 1 diabetes

  • Children and teens with this condition are overweight.

  • It is also believed that excess body fat plays a role in the insulin resistance that characterizes the disease.

  • In recent years the rising prevalence of this type of diabetes in children played a crucial role in increasing rates of obesity among children and teens.

  • The symptoms and possible complications of type 2 are the same as those of type 1.

  • Some children and teens can control their blood sugar level with:

    • Dietary changes

    • Exercise

    • Oral medications

    • But many have need to take insulin injections like patients with type 1 diabetes.