Differences between hypothyroidism and hyperthyroidism are as follows
| Hypothyroidiswm | Hyperthyroidism |
|---|---|
| It is the insufficient secretion of thyroid hormones causing cretinism in children and myxoedema in adults | This syndrome arises as the body tissues and are exposed to excessive levels of $T_3$ and $T_4$. The main effects are due to increased metabolic rate. The gland enlarges and may develop single or multiple hormone secreting cells such as in Grave's disease and toxic nodular goitre |
| Cretinism is associated with the retarded mental and physical development. The child receives hormones from the mother before birth, so appears normal at first, but within a few weeks or months, it becomes evident that physical and mental development is retarded. Symptoms are disproportionately short limbs, a large protruding tongue, coarse dry skin, poor abdominal muscle tone and an umbilical harnia. |
Exophthalmic goitre (Grave's disease) is the most common cause solid of thyrotoxicosis in adults. It affects, women more commonly than men. High levels of thyroxine are secreted, which are not subjected to the normal secretion of TRH from the hypothalamus and TSH from the anterior pituitary. Exophthalamus (Protrusion of the eyeballs) due to the deposition of excess fat and fibrous tissue behind the eyes, is often present in Grave's disease. In severe cases, the eyelids may not completely cover the eyes during blinking of the conjuctiva and thus, predisposed to infection. |
| Myxoedema (Gull's disease), this conditions is common in adults and five times more common in females than in males. It results in an abnormally low metabolic rate and lack of response to demand for increased energy, by muscles, during exercise. Mental and physical processes become slower, skin become coarse, the hair lacks lustre, becomes brittle and tends to fall out. |
Toxic nodular goitre (Plummer's disease) is associated with excess secretion of thyroxine leading to the general effects of increased metabolic rate. |
Suckling by the calf creates a neuroendocrine reflex which results in increase of oxytocin from the neurohypophysis. Oxytocin is synthesised in the hypothalamus in specific nuclei, the paraventricular nucleus and the supra optic nucleus (a cluster of nerve cells in the brain is often called a nucleus).
Neurons in this region (hypothalamic nuclei) synthesise the oxytocin precursor and package it into vesicles. The oxytocin concentration in the blood normally, gets increased within 1-2 min, after the udder stimulation.
It brings about contraction of smooth muscles of the udder resulting in the milk flow. A direct intra-udder function of oxytocin like hormone would do the same function.
It can be summarised as follows
Udder (suckling stimulus) $\rightarrow$ Brain (hypothalamus) $\rightarrow$ Neurohypophysis $\rightarrow$ Blood (oxytocin) $\rightarrow$ Udder (smooth muscles) $\rightarrow$ Milk flow.
A sample of urine was diagnosed to contain high content of glucose and ketone bodies. Based on this observation, answer the following
(a) which endocrine gland and hormone is related to this condition?
(b) name the cells on which this hormone acts
(c) what is the condition called and how can it rectified?
(a) The pancreas is associated with this condition and the related hormone is insulin. The pancreas consists of 'islets of Langerhans. The two main type of cells in islets of Langerhans are $\alpha$-cells and $\beta$-cells. $\alpha$-cells secrete glucagon while $\beta$-cell secrete insulin.
Insulin is a peptide hormone, which plays a major role in the regulation of glucose homeostasis. It decreases the level of glucose in blood by increasing the rate at which glucose is transported out of blood and into the cell.
When insulin is dysfunctional or not produced adequately glucose uptake is hampered" and hence glucose appear in urine along with ketone bodies.
(b) Insulin hormone mainly acts on hepatocytes (liver cells) and adipocytes (cells of adipose tissue) and enhances cellular glucose up take and utilisation.
(c) Prolonged hyperglycemic condition leads to a complex disorder called diabetes mellitus which is associated with loss of glucose through urine and formation of harmful compounds known as ketone bodies due to protein metabolism.
Diabetic patients are successfully treated with insulin therapy. It lowers the blood glucose levels and give relief to the patients.
The endocrine glands and hormones that are responsible for maintaining calcium homeostasis, are thyroid and parathyroid glands and their associated hormones are calcitonin and Parathyroid Hormone (PTH).
(i) Parathyroid glands are the glands developed from the endoderm of the embryo. The cells of parathyroid glands are of two types, i.e., chief cells and oxyphil cells. The chief cells of the parathyroid glands secrete parathyroid hormone (PTH).
This hormone (PTH) is involved in regulating calcium and phosphate balance between the blood and other tissue. It mobilises the release of calcium into the blood from bones. PTH increases calcium reabsorption by the body organs like intestine and kidneys.
(ii) Thyroid gland is the largest endocrine gland located anterior to the thyroid cartilage of the larynx in the neck. This gland plays a vital role in maintaining calcium homeostasis. It releases thyrocalcitonin hormone produced by the parafollicular cells, also called ' $C$ ' cells.
This hormone is secreted when the calcium level in blood gets high. It is a 32 amino acid peptide hormone that lowers the calcium level by suppressing release of calcium ions from the bones. Thus, calcitonin has an action opposite to that of the parathyroid hormone on calcium homeostasis.
