BIOLOGY 5 Marks Questions

1. Two types of receptors are:

1. Membrane bound extracellular receptors.
2. Intracellular receptors.

2. The hormones which cannot enter the target cell, need membrane bound (extracellular) receptors and the hormones which can enter the target cell, need intracellular (mostly nuclear) receptors.
3. Second messengers are those chemicals, which are generated in the target cells, by those hormones which cannot enter the cells, to bring about the biochemical changes, e.g., Inositol Triphosphate (IP₃) Eyclic Adenosine Monophosphate (CAMP).
4. Lakshita is worried about her studies and has capability to understand things in a better and scientific way, she takes initiative to solve the problem so has problem solving skills.

1. The hypothalamus and pituitary function as an integrated and coordinated system because both of them are connected at the base of the brain.

They interact to each other in two ways:

1. By the hypophyseal portal system, which is a system of blood vessels that connects part of hypothalamus to the anterior lobe of pituitary gland. Hypothalamus secretes hormones into this portal system and the hormones act on the anterior pituitary, triggering the synthesis/ secretion of pituitary hormone.
2. The other is that they have direct anatomical connection between the hypothalamus and the posterior lobe of pituitary (posterior pituitary is actually are extension of hypothalamus). Thus, it is said that hormones released through posterior pituitary are actually released from the hypothalamus.

2. Puberty is the phenomenon of physical changes by which child's body matures into an adult male, capable of sexual reproduction to enable fertilisation. It is initiated by the hormonal signals from the brain to the gonads, i.e., testes in a male. In response to the signals, gonads produce hormones that in turn stimulates libido and the growth, function and transformation of the brain, muscles, blood, hair, sexual organs, etc. An androgen called as testosterone in males, functions as principal sex hormone, producing all changes in male and related to growth and development at puberty.

1. The hormones which are derivatives of proteins, amino acids or polypeptides are called peptide hormones.
2. These hormones being insoluble in lipids cannot enter the target cell.
3. They act as primary messengers on the surface of the target cell and bind to the receptors present on the outer surface of the plasma membrane to form a hormone-receptor complex.
4. The enzyme Adenylyl cyclase is activated by this complex.
5. On the inner surface of the plasma membrane, Adenylyl cyclase catalyzes the conversion of ATP to cyclic AMP.
6. Cyclic AMP (cAMP) acts as the secondary messenger which delivers the information to the inside of the target cell.
7. This activates an appropriate cellular enzyme system by means of cascade effect.
8. cAMP is short-lived and rapidly degraded by cAMP phosphodiesterase.
9. Thus, peptide hormones are quick acting hormones and produce an immediate effect through cAMP.

1. Hyperthyroidism is increased levels of thyroid hormones whereas hypothyroidism is decreased levels of thyroid hormones.
2. Hyperthyroidism can lead to thyrotoxicosis and grave’s disease whereas hypothyroidism does not produce those diseases.
3. There is faster metabolism in hyperthyroidism while there is a slow   metabolism in hypothyroidism.
4. Hypothyroidism is treated by supplements of thyroid hormones and hyperthyroidism is treated by anti-thyroid drugs.
5. Hypothyroidism shows decreased levels of T₃ and T₄ and increased levels of TSH whereas in hyperthyroidism, there is an increased levels of T₃ and T₄ and a decreased level in TSH.

1. Increased alertness.
2. Dilation of pupils.
3. Piloerection.
4. Increased heart beat.
5. Increased strength of heart contraction.
6. Increased rate of respiration.
7. Glycogenolysis and increased blood glucose level.
8. Lipolysis and proteolysis.

1. Steroid hormones: These hormones are manufactured by endocrine cells from cholesterol, an important type of lipid in the human body. Examples include cortisol, aldosterone, oestrogen, progesterone and testosterone.
   
2. Amino acid derivatives: The thyroid hormones (T₃ and T₄) are synthesised from the amino acid tyrosine and iodide, respectively. Adrenaline (also known as epinephrine) and noradrenaline (also known as norepinephrine) are produced by the medulla of the adrenal gland, are also derived from tyrosine. Melatonin is synthesised from the amino acid tryptophan.
   
3. Protein hormones: These hormones are long, folded chains of amino acids. Included among these hormones are insulin, glucagons, parathyroid hormone, growth hormone, prolactin, etc.
   
4. Peptide hormones: Hormones such as oxytocin and antidiuretic hormone are smaller than protein hormone. They are made up of a short chain of amino acids.
   

1. Adrenocorticotropic Releasing Hormone (ARH) or Corticotrophin Releasing Hormone – It stimulates the anterior lobe of the pituitary gland to secrete its adrenocorticotropic hormone (ACTH).
2. Thyrotrophic Releasing Hormone (TRH)- It stimulates the anterior lobe of the pituitary gland to secrete its thyroid stimulating hormone (TSH). or thyrotrophic.
3. Growth Hormone-Releasing Hormone (GHRH)- It stimulates the anterior lobe of the pituitary gland to release its growth hormone (GH) or somatotrophin.
4. Growth Hormone-Inhibitory Hormone (GHIH)- This hormone is also called somatostatin (SS). It inhibits the secretion of growth hormone from the anterior lobe of the pituitary gland.
5. Gonadotropin Releasing Hormone (GnRH)- It stimulates the anterior lobe of the pituitary gland to secrete two gonadotropic hormones : Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH)).
6. Prolactin Releasing hormone (PRH)- It stimulates the anterior lobe of the pituitary gland to secrete its prolactin hormone.
7. Prolactin Inhibitory Hormone (PIH)- It inhibits the secretion of prolactin from the anterior lobe of pituitary gland.
8. MSH Releasing Hormone (MSHRH)- It stimulates the intermediate lobe of the pituitary gland to secrete its melanocyte stimulating hormone (MSH).
9. MSH Inhibitory Hormone (MSHIH)- It inhibits the secretion of melanocytes stimulating hormone from the intermediate lobe of the pituitary gland.

1. Growth hormone (GH): Over-secretion of GH stimulates abnormal growth of the body leading to gigantism and low secretion of GH results in stunted growth resulting in pituitary dwarfism.

2. Prolactin (PRL): Prolactin regulates the growth of the mammary glands and formation of milk in them.

3. Thyroid stimulating hormone (TSH): TSH stimulates the synthesis and secretion of thyroid hormones from the thyroid gland.

4. Adrenocorticotrophic hormone (ACTH): ACTH stimulates the synthesis and secretion of steroid hormones called glucocorticoids from the adrenal cortex.

5. Luteinizing hormone (LH): LH and FSH stimulate gonadal activity and hence are called gonadotrophins. In males, LH stimulates the synthesis and secretion of hormones called androgens from testis. In females, LH induces ovulation of fully mature follicles (graafian follicles) and maintains the corpus luteum, formed from the remnants of the graafian follicles after ovulation.

6. Follicle stimulating hormone (FSH): In males, FSH and androgens regulate spermatogenesis. FSH stimulates growth and development of the ovarian follicles in females. MSH acts on the melanocytes (melanin containing cells) and regulates pigmentation of the skin.

Pars intermedia secretes only one hormone called melanocyte stimulating hormone (MSH). However, in humans, the pars intermedia is almost merged with pars distalis.

Neurohypophysis (pars nervosa) also known as posterior pituitary, stores and releases two hormones called oxytocin and vasopressin, which are actually synthesised by the hypothalamus and are transported axonally to neurohypophysis. Oxytocin acts on the smooth muscles of our body and stimulates their contraction. In females, it stimulates a vigorous contraction of uterus at the time of child birth, and milk ejection from the mammary gland. Vasopressin acts mainly at the kidney and stimulates re-absorption of water and electrolytes by the distal tubules and thereby reduces loss of water through urine (diuresis).

Hence, it is also called as anti-diuretic hormone (ADH).

1. Growth hormone (GH): It regulates the growth of the body, its excess secretion leads to gigantism and low secretion causes dwarfism.
   
2. Adrenocorticotropic hormone (ACTH): It stimulates the synthesis and secretion of hormones from adrenal cortex.
   
3. Thyroid stimulating hormone (TSH): It stimulates the thyroid gland to synthesise and secrete thyroid hormones.
   
4. Follicle stimulating hormone (FSH):
   

• Along with the androgens, it regulates spermatogenesis in mole.
• In females, it stimulates the growth and development of ovarian follicles and secretion of FSH from them.

5. Luteinising hormone (LH):

• In males, it acts on the Leydig cells of testes and stimulates the synthesis and secretion of androgens, mainly testosterone.
• In females, it stimulates ovulation, formation of corpus luteum and secretion of progesterone from it.

6. Prolactin (PRL): It regulates the growth of mammary glands and formation of milk in them during pregnancy.

1. 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 mobilizes the release of calcium into the blood from bones. PTH increases calcium reabsorption by the body organs like intestine and kidneys.
2. 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.

1. Protein hormones:

• The protein hormones like FSH, insulin, etc. interact with the membrane-bound (extracellular) receptors and form hormone receptor complex.
• They do not enter the cell, but stimulate the cell to produce second messengers like cyclic AmP, IP₃ or Ca²⁺ ions.
• The second messengers regulate the cell metabolism.

2. Steroid hormones:

• The steroid hormones enter the cell.
• They interact/ bind with the intracellular receptor (mostly nuclear receptors).
• The hormone-receptor complex binds to the chromosome and regulate gene expression, i.e. synthesis of mRNA and proteins.
• The biochemical reactions result in physiological and developmental effects.