Justify the following:

1.  ANF affects natriuresis and diuresis.

ANF is a humoral substance which regulates volume overload by inhibiting, reabsorption by the renal tubules, thereby promoting natriuresis and diuresis. ANF affects diuresis and natriuresis by several physiological functions:

1. It inhibits aldosterone production by the adrenal glomerulus cells.
2. It inhibits the release of renin (which indirectly stimulates aldosterone secretion).
3. It inhibits vasopressin secretion from the pituitary as well as the action of vasopressin at the level of kidney.
4. It causes relaxation of blood vessels (possibly by antagonizing the vasoconstrictor actions of AII).

All these ANF actions effectively reduce the retention of Na+ and water and therefore, decreased volume expansion.

2.  If the neural connection between the hypothalamus and pituitary were severed then secretion of some pituitary hormones area affected.

Since the secretion of the pituitary principles of the pars distalia and pars intermedia is under the control of hypothalamic releasing and inhibitory hormones. So if the neural connection between the hypothalamus and pituitary are severed then some hormones will not be secreted or synthesized. For e.g., the cell bodies for the hormone vasopressin and oxytocin originate within the hypothalamus and secreted through the posterior lobe of pituitary and when the connection is severed several hormones might not be there which are required by the human body.

3.  Catecholamines can produce prolonged hyperglycemia.

Epinephrine increase both the force and rate of the heartbeat through stimulation of cardiac muscle beta-adrenergic. There are no other examples known where beta-adrenergic induce muscle contraction. The particular distribution of vascular smooth muscle ARs provide a mechanism for shunting of blood to various body compartments during stress. For e.g., blood is shunted from the skin, mucosa, connective tissue and kidneys; vascular smooth muscles of these organs possess alpha-ARs. In contrast, smooth muscle of coronary arteries as well as skeletal muscle possess beta-ARs. If dominant alpha-ARs were present, blood flow to these vital organs would be diminished when these organs were maximally active. The decreased blood flow to the kidneys reduces glucose clearance from the circulation, and this reduced clearance may be primarily responsible for the prolonged hyperglycemia induced by catecholamines.

4.  PDGF can play an important role in the development of atherosclerosis.

Platelets also release one or more chemical messengers that stimulate contraction of the injured vessels to prevent further loss of blood. At the site of injury platelets release PDGF in response to thrombin. Its role is to induce proliferation of smooth muscle cells within the arterial wall. Although PDGF serves an important role in the healing process of the vascular system, it may play a dominant part in the development of atherosclerosis as PDGF is a potent vasoconstrictor, and it is possible that this peptide may be responsible for the increased vasoreactivity that occurs primarily at the site of arthrosclerosis lesions. One of the main causes for atherosclerosis is smooth muscle proliferation which is done by PDGF.

5.  A male athlete taking large amount of an androgenic steroid hormones becomes sterile.

When using steroids, users try to maximize the anabolic (tissues growth stimulatory) effect and minimize the androgenic (male type) effect. These steroids have a significant effect on gonadal function. The effects are individual specific in some users sperm production ceases totally and in other the changes are minor.

The functioning of the testicles is controlled by hypophysis. Androgenic steroids prevent the normal functioning of the hypophysis. The testicles own testosterone production and concentration decreases and as consequences, sperm production decreases and may cease totally. These steroids also have an effect on structure of sperm cells. Since they decrease testosterone concentration in blood circulation which is insufficient normal libido and the hormone imbalances cease sexual apathy.

6.  Tissue responsiveness towards a hormone does not remain constant.

Yes, it is true that tissue responsiveness towards a hormone does not remain constant. Some hormones can simultaneously stimulate a number of different tissues which implies that each of these diverse tissues possess receptors for the hormones. Insulin stimulates glucose uptake by hepatocytes, fat cells and certain muscle cells and interact with many other cell types. Thus, insulin is able to rapidly lower extracellular glucose levels, which is one of its functions. If more than one tissue responds to a particular hormone at one time, it is often the case that all these different physiological responses would complement the physiological process being regulated. For e.g., parathyroid hormone (PTH) elevates serum Ca2+ levels by releasing Ca2+ from bone, stimulating calcium uptake from the gut and preventing Ca2+ loss from the kidney. Each of these individual responses to PTH is important in elevating Ca2+ levels.

Tissue responses to a hormone are determined by the presence of specific receptors. If each type of all possessed all of the specific hormone receptors then all cells might be expected to respond to all chemical messengers. If this were the case, all the cells would response and this would result in uncoordinated muscle contraction. and relaxation and an uncontrolled secretion of numerous cellular products. Therefore, cells do not possess receptors for all hormones and the magnitude for an individual tissue's response to a particular hormone is determined in large part by the numbers of receptors for the hormone that are present in those target cells.