Here is the transcription and translation of the lecture chunk:
Welcome back after the break. Where were we, Niraj ji?
Glucagon is a peptide hormone and plays an important role in maintaining normal blood glucose levels. Glucagon acts mainly on liver cells, which are hepatocytes, and stimulates glycogenolysis, resulting in increased blood sugar, which is a hyperglycemic condition.
In addition, the hormone stimulates the process of gluconeogenesis, which also contributes to hyperglycemia. Glucagon reduces cellular glucose uptake and utilization. Thus, glucagon is a hyperglycemic hormone. Such questions are very common, so remember this.
Just as PTH, parathyroid hormone, was hypocalcemic, glucagon is hyperglycemic. Right? Yes.
What does it do? It breaks down glycogen into glucose, leading to glycogenolysis. Secondly, gluconeogenesis, meaning it will produce glucose from sources other than glycogen, like fats and proteins. And insulin is a peptide hormone, again, which plays a major role in the regulation of glucose homeostasis. Insulin acts mainly on hepatocytes and adipocytes, liver cells, and fat cells, and enhances cellular glucose uptake and utilization.
As a result, there is a rapid movement of glucose from the blood to hepatocytes and adipocytes, resulting in decreased blood glucose levels, which is hypoglycemia. Insulin also stimulates the conversion of glucose to glycogen. The glucose homeostasis in the blood is thus maintained jointly by both insulin and glucagon, which is why they are considered antagonistic to each other.
Prolonged hyperglycemia leads to a complex disorder called diabetes mellitus, which is associated with the loss of glucose through urine and the formation of harmful compounds known as ketone bodies. This is a very, very, very important point. Right?
Diabetic patients are successfully treated with insulin therapy. I have already explained its physiological mechanism, but let me recall it.
Insulin binds to receptors present on the cell membrane. These are insulin receptors. Insulin binds here. And as a result, GLUT4, remember? This is insulin-dependent. So, this insulin-dependent GLUT4 will reach the membrane, and it will transport glucose from the blood into the cell. If there is sufficient insulin. If there is insulin deficiency, then blood glucose levels will rise, which will then go into the urine, as discussed.
Now, testes and ovaries. A pair of testes is present in the scrotum, outside the abdomen, in males. It is important to know that in humans, testes and ovaries are made of the same type of tissue, called bipotential gonads. When there are XX chromosomes, ovaries develop from the bipotential gonad, and when there are XY, testes develop. I will explain in detail later about Wolffian ducts and Mullerian ducts.
A pair of testes is present in the scrotum, outside the abdomen, of the male individual. The testis performs a dual function as a primary sex organ as well as an endocrine gland. Testes are composed of seminiferous tubules and stromal or interstitial cells. You might recall, we called them Leydig cells, which are present in the intertubular space. They produce a group of hormones called androgens, primarily testosterone. Androgens regulate the development, maturation, and function of the male accessory sex organs like epididymis, vas deferens, seminal vesicle, prostate gland, and urethra.
These hormones stimulate muscular growth, the growth of facial and axillary hair, aggressiveness, and a low pitch of voice, meaning a deep voice. Androgens play a major stimulatory role in the process of spermatogenesis, which is the formation of spermatozoa.
Androgens act on the central nervous system and influence male sexual behavior, known as libido. These hormones produce anabolic, synthetic effects on protein and carbohydrate metabolism. Synthetic, meaning they play a constructive role in it. This is an important point.
We are presented with an excellent, not just a good, but a great question today. This is a 'greatest of all time' question from NCERT.
The question is: How androgens produce an anabolic effect on protein and carbohydrate metabolism? This means, how do androgens help in preserving protein and carbohydrates? Metabolism involves breakdown and synthesis. So, this question asks how androgens prevent their breakdown, meaning they conserve sugar and amino acids, and thereby conserve protein.
If sugar and protein are conserved, they will be utilized within the cell. Either amino acids or proteins will remain within the cell, leading to muscle building. This is why bodybuilders often use androgens or steroids. While not a good practice, in normal metabolism, they enhance this process.
How do they enhance it? Let's summarize some important points. Firstly, how do they have a positive role in protein metabolism? Steroids enter the cell directly. They don't work through cyclic AMP or other secondary messengers from the outside. They enter the cell and enhance gene transcription, which is the process of DNA transcribing into RNA. When transcription increases, protein synthesis will naturally increase. They also increase the uptake of amino acids by the cell, meaning the cell starts capturing more amino acids from the bloodstream.
Furthermore, they block the effects of glucocorticoids, like cortisol. If you recall, glucocorticoids promote lipolysis and proteolysis. Androgens counteract these effects. When their catabolic effects are blocked, protein remains in the cell in larger quantities.
How do they have a positive role in carbohydrate metabolism? They increase the expression of GLUT4, which is a glucose transporter. This means the cell will receive a larger amount of glucose. They also enhance glycogenesis, meaning when glucose enters the cell, it triggers the formation of glycogen. Glycogen will be stored in the muscles, and it will be available for muscle contraction when needed. Additionally, they increase insulin sensitivity. When skeletal muscles become more sensitive to insulin, more glucose and nutrients reach the cells, allowing them to function more effectively.
So, the question of how androgens contribute positively to carbohydrate and protein metabolism is now clear.
There was also a hypothesis, which I thought about presenting to aspiring doctors: If androgens or testosterone are reduced, for instance, due to statins (which block cholesterol synthesis), could this lead to reduced glucose uptake by cells (because GULT4 expression might not be enhanced) and thus increase blood glucose levels?
When we researched this extensively, reading books, consulting various sources, our hypothesis wasn't entirely correct in its initial form. We didn't find strong evidence that statins directly affect testosterone. However, we did find that while they may not directly impact androgens, statins do inhibit the HMG-CoA reductase enzyme, which is crucial for cholesterol synthesis. This inhibition indirectly affects the availability of precursors or signaling pathways, potentially leading to reduced glucose availability to cells or decreased GLUT4 function. As a result, glucose might remain in the bloodstream, increasing blood glucose levels.
This was quite an interesting part of the lecture.
The amount of which increases. So, you can say that statin-induced diabetes can occur. Statin's link with androgen is weak, but its link with diabetes exists; there is no doubt about it. It was interesting to understand and know this entire matter.
Now we are moving on to the ovary. Females have a pair of ovaries located in the abdomen. The ovary is the primary female sex organ which produces an ovum during the menstrual cycle. In addition, the ovary also produces two groups of steroids called estrogen and progesterone. The ovary is composed of ovarian follicles and stromal tissue. Estrogen is synthesized and secreted mainly by the growing ovarian follicle. After ovulation, the ruptured follicle is converted into a structure called corpus luteum.
The word 'luteum' means yellow, right? The 'albicans' – corpus albicans will also be discussed – that is white. So these are the terms. Albinism indicates white, and luteum indicates yellow. They secrete mainly progesterone.
So what happens? How are estrogen and progesterone coming from the ovary? The ovary is made up of ovarian follicles and stromal tissue. Estrogen is produced by the growing ovarian follicle. When the ovary ruptures, and ovulation occurs, on the 14th day of the cycle, the corpus luteum forms and then produces progesterone. I will teach you this in great detail, my child, when I teach human reproduction; I will provide a lot of detail there.
Estrogen produces wide-ranging actions such as the stimulation of growth and activities of female secondary sex organs. It also leads to the development of growing ovarian follicles. The appearance of female secondary sex characteristics, such as a high pitch of voice and mammary gland development. Estrogen also regulates female sexual behavior. Over there, we referred to male sexual behavior as 'libido'. Here, estrogen is regulating female sexual behavior.
On the other hand, progesterone supports pregnancy. Progesterone also acts on the mammary gland and stimulates the formation of alveoli, which are sac-like structures that store milk and facilitate milk secretion. Got it?
Now we have arrived at section 19.3: Hormones of the Heart, Kidney, and GI Tract. Now you know about the endocrine glands and their hormones. However, as mentioned earlier, hormones are also secreted by some tissues which are not endocrine glands. For example, the atrial wall of our heart secretes a very important peptide hormone called atrial natriuretic factor. I had also taught you this, my child, if you remember, when I taught about the kidney, I had already discussed this. So, atrial natriuretic factor (ANF) decreases blood pressure. This is very important.
Because when our renin-angiotensin-aldosterone system was working, this hormone works in opposition to it, remember? That system had increased the pressure. This one, because if pressure increases, it will impact the heart. So its job is to serve its master, and its master is the heart. Thus, it serves its master and lowers the blood pressure for it. When blood pressure is increased, ANF is secreted, which causes dilation of blood vessels. This reduces the blood pressure.
The JG cells, that is, juxtaglomerular cells of the kidney, produce a peptide hormone called erythropoietin, which stimulates erythropoiesis, the formation of RBCs. Endocrine cells of different parts of the GI tract secrete four major peptide hormones, namely gastrin. This happens when you feel hungry, right? For example, if I talk to you about food, and just thinking about food makes you feel hungry, then gastrin is released at that time.
So gastrin is that initial hormone which starts your digestive process or all the processes that occur when you feel hungry. Secretin, CCK (Cholecystokinin), and gastric inhibitory hormone. My child, I will teach this further; we will also study digestion, where I will teach you about the harmony of two hormones: secretin and CCK. This old name for CCK is very useful: CCK-PZ, Cholecystokinin-pancreozymin. That will help you learn how these two hormones work; it will be very interesting.
Both these hormones act on the gallbladder, liver, and pancreas, but their roles are different. I will teach you which one releases enzymes and which one releases some other specific things from there. So remember, remind me, we need to learn about the harmony of secretin and CCK. And gastric inhibitory peptide. Gastrin acts on gastric glands and stimulates the secretion of HCl and pepsinogen. Secretin acts on the exocrine pancreas and stimulates the secretion of water and bicarbonate ions. CCK acts on both the pancreas and gallbladder, as I just told you, and stimulates the secretion of pancreatic enzymes and bile juice. Let me finish this.
What is secretin causing to be released from the pancreas? Bicarbonate. Where? In the exocrine part of the pancreas, right? There is no discussion of the endocrine part yet; it happens through the gland. And the main function of CCK is that it releases from the pancreas the pancreatic...
This lecture chunk discusses hormones and their functions. It begins by explaining that certain enzymes are released by the pancreas. Then, it touches upon secretin, which is secreted by the gallbladder or liver to produce bile.
The discussion then shifts to Cholecystokinin (CCK), also known as pancreozymin. CCK's primary role is to stimulate the gallbladder to contract and release bile, and also to stimulate the pancreas to release pancreatic enzymes.
The lecture then elaborates on the functions of CCK. It stimulates the secretion of pancreatic enzymes and also promotes the contraction of the gallbladder. The name "cholecystokinin" itself signifies its function: "cholecysto" refers to the gallbladder, and "kinin" means to cause movement or contraction.
Gastric Inhibitory Peptide (GIP) is also mentioned. It inhibits gastric secretion and motility. The lecture notes that several other non-endocrine tissues secrete hormones called growth factors, which are crucial for the normal growth, repair, and regeneration of tissues.
The final part of the lecture focuses on the mechanism of hormone action. Hormones exert their effects by binding to specific proteins called hormone receptors, located on target tissues. Receptors on the cell membrane are called membrane-bound receptors, while those inside the cell are intracellular receptors, mostly nuclear receptors.
The binding of a hormone to its receptor forms a hormone-receptor complex, which then triggers specific biochemical changes within the target tissue. These changes alter the target tissue's metabolism and, consequently, its physiological functions.
Hormones are classified into four main groups based on their chemical nature: peptide hormones (like insulin and glucagon), steroid hormones (like cortisol and testosterone), iodothyronines (like thyroid hormones), and amino acid derivatives (like epinephrine).
Hormones that interact with membrane-bound receptors typically don't enter the target cell but generate secondary messengers, such as cyclic AMP (cAMP), IP3, and calcium. These secondary messengers then regulate cellular metabolism.
The lecture then asks a question about Inositol triphosphate (IP3), defining it as a secondary messenger. It clarifies that primary messengers are the hormones themselves.
Hormones that interact with intracellular receptors, like steroid hormones and iodothyronines, primarily regulate gene expression and chromosomal function by interacting with the hormone-receptor complex and the genome. The cumulative biochemical actions result in physiological and developmental effects.
The lecture concludes by summarizing the role of these hormones and mechanisms, and thanks the audience. It also hints at future discussions covering the entire NCERT syllabus.