This MCQ module is based on: Gonads Hormone Action
TOPIC 89 OF 90
Gonads Hormone Action
🎓 Class 11
Biology
CBSE
Theory
Ch 19 – Chemical Coordination and Integration
⏱ ~14 min
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Gonads, Non-glandular Hormones and Mechanism of Hormone Action
This part completes the survey of the endocrine system with the gonads, then turns to hormones produced by organs that are not endocrine glands at all, and finally asks the underlying question: how does a hormone circulating in the blood produce an effect in only a few tissues?
Testis
A pair of testis is present in the scrotal sac (outside abdomen) of male individuals. Testis performs dual functions — as a primary sex organ as well as an endocrine gland.
Testis is composed of seminiferous tubules and stromal or interstitial tissue. The Leydig cells or interstitial cells, which are present in the intertubular spaces, produce a group of hormones called androgens, mainly testosterone.
Actions of androgens:
- regulate the development, maturation and functions of the male accessory sex organs like epididymis, vas deferens, seminal vesicles, prostate gland, urethra etc.;
- stimulate muscular growth, growth of facial and axillary hair, aggressiveness, low pitch of voice etc.;
- play a major stimulatory role in the process of spermatogenesis (formation of spermatozoa);
- act on the central neural system and influence the male sexual behaviour (libido);
- produce anabolic (synthetic) effects on protein and carbohydrate metabolism.
Ovary
Females have a pair of ovaries located in the abdomen. Ovary is the primary female sex organ which produces one ovum during each menstrual cycle. In addition, ovary also produces two groups of steroid hormones called estrogen and progesterone.
Ovary is composed of ovarian follicles and stromal tissues. The estrogen is synthesised and secreted mainly by the growing ovarian follicles. After ovulation, the ruptured follicle is converted to a structure called corpus luteum, which secretes mainly progesterone.
Actions of estrogens:
- stimulation of growth and activities of female secondary sex organs;
- development of growing ovarian follicles;
- appearance of female secondary sex characters (e.g., high pitch of voice, etc.);
- mammary gland development;
- regulation of female sexual behaviour.
Actions of progesterone: Progesterone supports pregnancy. Progesterone also acts on the mammary glands and stimulates the formation of alveoli (sac-like structures which store milk) and milk secretion.
One structure, two hormones, in sequence. The ovarian follicle secretes estrogen while it is growing. After ovulation, the same ruptured follicle becomes the corpus luteum and secretes mainly progesterone. So the switch from estrogen to progesterone is not a switch between two glands but a transformation of one structure — which is why the two hormones dominate different halves of the menstrual cycle.
Hormones of Heart, Kidney and Gastrointestinal Tract
Hormones are also secreted by some tissues which are not endocrine glands.
Heart
The atrial wall of our heart secretes a very important peptide hormone called atrial natriuretic factor (ANF), which decreases blood pressure. When blood pressure is increased, ANF is secreted, which causes dilation of the blood vessels. This reduces the blood pressure.
Kidney
The juxtaglomerular cells of kidney produce a peptide hormone called erythropoietin, which stimulates erythropoiesis (formation of RBC).
Gastro-intestinal tract
Endocrine cells present in different parts of the gastro-intestinal tract secrete four major peptide hormones:
| Hormone | Acts on | Effect |
|---|---|---|
| Gastrin | The gastric glands | Stimulates the secretion of hydrochloric acid and pepsinogen |
| Secretin | The exocrine pancreas | Stimulates secretion of water and bicarbonate ions |
| Cholecystokinin (CCK) | Both pancreas and gall bladder | Stimulates the secretion of pancreatic enzymes and bile juice, respectively |
| Gastric inhibitory peptide (GIP) | The stomach | Inhibits gastric secretion and motility |
Several other non-endocrine tissues secrete hormones called growth factors. These factors are essential for the normal growth of tissues and their repairing/regeneration.
Here is the payoff of the new definition. In Part 1 you learnt that the classical definition — a chemical produced by endocrine glands — was replaced by "non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts". The heart, the kidney and the gut are not endocrine glands, and growth factors come from ordinary tissues. Under the old definition none of these could be called hormones; under the new one they all can.
Mechanism of Hormone Action
Hormones produce their effects on target tissues by binding to specific proteins called hormone receptors, located in the target tissues only.
- Hormone receptors present on the cell membrane of the target cells are called membrane-bound receptors.
- Receptors present inside the target cell are called intracellular receptors, mostly nuclear receptors (present in the nucleus).
Binding of a hormone to its receptor leads to the formation of a hormone-receptor complex. Each receptor is specific to one hormone only, and hence receptors are specific.
Hormone-receptor complex formation leads to certain biochemical changes in the target tissue. Target tissue metabolism, and hence physiological functions, are regulated by hormones.
This answers the central puzzle. A hormone travels in the blood and therefore reaches every tissue. Why then does it act only on a few? Because the receptor, not the hormone, decides: receptors are located in the target tissues only, and each receptor is specific to one hormone. A tissue without the receptor is deaf to the message, however much of the hormone reaches it.
Chemical classes of hormones
On the basis of their chemical nature, hormones can be divided into four groups:
| Group | Examples |
|---|---|
| (i) Peptide, polypeptide, protein hormones | Insulin, glucagon, pituitary hormones, hypothalamic hormones, etc. |
| (ii) Steroids | Cortisol, testosterone, estradiol and progesterone |
| (iii) Iodothyronines | Thyroid hormones |
| (iv) Amino-acid derivatives | Epinephrine |
Two routes of action
Hormones which interact with membrane-bound receptors normally do not enter the target cell, but generate second messengers (e.g., cyclic AMP, IP3, Ca++ etc.) which in turn regulate cellular metabolism.
Hormones which interact with intracellular receptors (e.g., steroid hormones, iodothyronines, etc.) mostly regulate gene expression or chromosome function by the interaction of the hormone-receptor complex with the genome.
In both cases, cumulative biochemical actions result in physiological and developmental effects.
| Feature | Membrane-bound receptor route | Intracellular receptor route |
|---|---|---|
| Receptor location | On the cell membrane of the target cell | Inside the target cell, mostly nuclear receptors |
| Does the hormone enter the cell? | Normally does not enter | Enters the cell |
| Hormone types | Protein and peptide hormones | Steroid hormones, iodothyronines, etc. |
| How the message is carried inside | Generates second messengers (cyclic AMP, IP3, Ca++ etc.) | The hormone-receptor complex interacts with the genome directly |
| Chief outcome | Regulation of cellular metabolism | Regulation of gene expression or chromosome function |
| Final result | Cumulative biochemical actions result in physiological and developmental effects | |
📐 Activity — Sort Ten Hormones by Their Route of Action
Write these ten hormones on separate slips of paper: insulin, cortisol, glucagon, testosterone, thyroxine, epinephrine, progesterone, TSH, estradiol, ANF. Now sort them into two piles — those that would use a membrane-bound receptor and those that would use an intracellular receptor.
Scenario: You sorted them by chemical class, not by which gland they came from. Two hormones from the very same gland ended up in different piles. Which gland, which two hormones, and what does this tell you about how a hormone's mechanism is determined?
Membrane-bound receptors (peptide, polypeptide, protein hormones and amino-acid derivatives): insulin, glucagon, TSH, ANF, epinephrine. These normally do not enter the target cell, but generate second messengers such as cyclic AMP, IP3 and Ca++ which in turn regulate cellular metabolism.
Intracellular receptors (steroids and iodothyronines): cortisol, testosterone, progesterone, estradiol, thyroxine. These mostly regulate gene expression or chromosome function by the interaction of the hormone-receptor complex with the genome.
The gland with hormones in both piles: the adrenal gland. Epinephrine from the adrenal medulla is an amino-acid derivative and uses a membrane-bound receptor; cortisol from the adrenal cortex is a steroid and uses an intracellular receptor. (The thyroid also splits: thyroxine is an iodothyronine acting on intracellular receptors, while thyrocalcitonin is a protein hormone.)
What this tells you: the mechanism is determined by the hormone's chemical nature, not by its gland of origin or its function. Steroids and iodothyronines can cross the cell membrane and so can reach receptors inside; peptides and proteins cannot, so they must act from the outside through second messengers.
A useful corollary: this also explains a difference in speed and duration. Changing cellular metabolism through a second messenger is quick and reversible; changing gene expression takes longer but produces lasting physiological and developmental effects — which is why steroids are the hormones of growth, development and long-term adaptation.
🎯 Interactive: Non-glandular Hormones and Hormone Action
Select an item to see its source and action.
🎯 Competency-Based Questions
Q1. A hormone reaches every tissue of the body through the blood, yet produces its effect in only a few. Explain the mechanism that makes this possible, and predict what would happen if a normally unresponsive tissue were genetically engineered to express that hormone's receptor.
The mechanism. Hormones produce their effects on target tissues by binding to specific proteins called hormone receptors, located in the target tissues only. Binding leads to the formation of a hormone-receptor complex, and this complex formation leads to certain biochemical changes in the target tissue. Moreover, each receptor is specific to one hormone only, so receptors are specific.
The selectivity therefore lies in the receiving tissue, not in the hormone or in its delivery. A tissue lacking the receptor is simply deaf to the message, no matter how much hormone bathes it.
The prediction. If a normally unresponsive tissue were made to express the receptor, it would begin to respond to that hormone: the hormone-receptor complex would form there, biochemical changes would follow, and the tissue's metabolism and physiological function would now be regulated by a hormone that previously did nothing to it.
What the thought experiment establishes: the hormone carries the signal, but the target tissue determines the response. This is the same principle you met at the chemical synapse in Chapter 18, where the post-synaptic neuron's own receptors and ion channels decide whether a neurotransmitter excites or inhibits it.
Q2. Steroid hormones act by regulating gene expression, whereas protein hormones act through second messengers. Use this difference to explain why the effects of testosterone during puberty are lasting while the effect of insulin after a meal is transient.
Testosterone — a steroid. Hormones which interact with intracellular receptors, such as steroid hormones and iodothyronines, mostly regulate gene expression or chromosome function by the interaction of the hormone-receptor complex with the genome. Changing which genes a cell expresses changes what proteins it builds, and therefore what the cell is. Androgens accordingly produce structural, developmental changes: development and maturation of the male accessory sex organs, muscular growth, growth of facial and axillary hair, low pitch of voice. Once the tissue has been rebuilt, the change persists.
Insulin — a peptide. Hormones which interact with membrane-bound receptors normally do not enter the target cell but generate second messengers (cyclic AMP, IP3, Ca++) which in turn regulate cellular metabolism. Insulin therefore alters what the existing cell machinery is doing right now — enhancing cellular glucose uptake and utilisation and stimulating glycogenesis. When the hormone leaves and the second messengers are degraded, the cell reverts to its previous behaviour.
The general rule: hormones that change gene expression produce slow, lasting, developmental effects; hormones that change metabolism through second messengers produce rapid, reversible effects. The body needs both, since glucose must be adjusted many times a day while puberty happens once.
Q3. The heart secretes a hormone that lowers blood pressure while the adrenal cortex secretes one that raises it. Name both, describe how each acts, and explain the advantage of having the heart itself as the source of one of them.
Lowering: the atrial wall of our heart secretes a peptide hormone called atrial natriuretic factor (ANF), which decreases blood pressure. When blood pressure is increased, ANF is secreted, which causes dilation of the blood vessels, and this reduces the blood pressure.
Raising: aldosterone, the main mineralocorticoid of the adrenal cortex, acts mainly at the renal tubules and stimulates reabsorption of Na+ and water, thereby helping maintain body fluid volume, osmotic pressure and blood pressure.
Why the heart is a good sensor. The atrial wall is stretched by the very quantity being regulated: when blood pressure and volume rise, the atria are distended. A hormone secreted from that wall is therefore released in direct proportion to the disturbance it must correct, and its effect — vasodilation — removes the cause of its own secretion. This is a self-limiting feedback loop with the sensor and the secretory tissue in the same place, which is faster and more reliable than routing the information through a separate gland.
A wider observation: the same design appears elsewhere in the chapter. The secretion of PTH is regulated by the circulating levels of calcium ions; insulin and glucagon respond to blood glucose. Endocrine control is generally built on the regulated variable feeding back on its own controller.
Q4. The four gastro-intestinal hormones regulate digestion between them. Trace what happens hormonally after a fatty meal, naming each hormone in the order it would act and saying what it achieves.
1. Gastrin. As food enters the stomach, gastrin acts on the gastric glands and stimulates the secretion of hydrochloric acid and pepsinogen — the acid and the protein-digesting precursor needed for gastric digestion.
2. Secretin. When the acidic contents pass into the intestine, secretin acts on the exocrine pancreas and stimulates the secretion of water and bicarbonate ions. The bicarbonate neutralises the acid, which is necessary because pancreatic enzymes cannot work in an acid medium.
3. Cholecystokinin (CCK). This acts on both pancreas and gall bladder and stimulates the secretion of pancreatic enzymes and bile juice respectively. For a fatty meal this is the crucial step: bile emulsifies the fat and pancreatic lipase digests it.
4. Gastric inhibitory peptide (GIP). This inhibits gastric secretion and motility, slowing the stomach so that the intestine is not overloaded while the fat is still being handled.
The logic of the sequence: three hormones switch digestive secretions on, each matched to where the food has reached, and the fourth switches the stomach down so that delivery matches the intestine's capacity to process. Notice also that the endocrine cells doing all this are distributed in the wall of the gastro-intestinal tract itself, not gathered into a gland — they are among the "hormone producing diffused tissues/cells" that the definition of the endocrine system includes.
Q5. A pituitary tumour destroys the cells producing LH and FSH in a young man and, separately, in a young woman. Predict the consequences in each case by tracing the chain of hormones affected.
In the young man. LH stimulates the synthesis and secretion of androgens from the testis, and FSH with androgens regulates spermatogenesis. Losing both means the Leydig cells are no longer stimulated, so the production of androgens, mainly testosterone, falls. Consequently: the development, maturation and functions of the male accessory sex organs (epididymis, vas deferens, seminal vesicles, prostate gland, urethra) are impaired; muscular growth, facial and axillary hair growth and the low pitch of voice are not maintained; spermatogenesis fails, since androgens play a major stimulatory role in it; male sexual behaviour (libido), which androgens influence through the central neural system, is reduced; and the anabolic effects on protein and carbohydrate metabolism are lost.
In the young woman. FSH stimulates the growth and development of the ovarian follicles, and LH induces ovulation of fully mature graafian follicles and maintains the corpus luteum. Losing both means follicles do not grow, so the estrogen normally synthesised and secreted mainly by the growing ovarian follicles is not produced — affecting the growth and activities of female secondary sex organs, female secondary sex characters, mammary gland development and female sexual behaviour. No ovulation occurs, so no corpus luteum forms, so progesterone is not secreted — and progesterone supports pregnancy and stimulates the formation of alveoli and milk secretion in the mammary glands. Fertility is therefore lost in both sexes.
The point of the question: a lesion high in the hierarchy produces failure of every hormone below it. This is why the hypothalamus–pituitary–peripheral gland chain, efficient as it is for coordination, concentrates risk at the top.
🧠 Assertion–Reason Questions
For each pair, decide whether both statements are true and whether the reason correctly explains the assertion.
Assertion (A): A hormone acts only on its target tissue although it circulates everywhere.
Reason (R): Hormone receptors are located in the target tissues only, and each receptor is specific to one hormone.
Both A and R are true, and R is the correct explanation of A.
Specificity resides in the receptor. Without a receptor no hormone-receptor complex can form, so no biochemical change follows in that tissue however much hormone arrives.
Assertion (A): Steroid hormones regulate gene expression.
Reason (R): Steroid hormones bind membrane-bound receptors and generate second messengers such as cyclic AMP.
A is true but R is false.
Steroid hormones interact with intracellular receptors, and mostly regulate gene expression or chromosome function by the interaction of the hormone-receptor complex with the genome. It is the hormones acting on membrane-bound receptors — protein and peptide hormones — that normally do not enter the cell and instead generate second messengers such as cyclic AMP, IP3 and Ca++.
Assertion (A): The corpus luteum secretes mainly progesterone.
Reason (R): After ovulation the ruptured ovarian follicle is converted into the corpus luteum.
Both A and R are true, and R is the correct explanation of A.
The growing follicle secretes mainly estrogen; once it has ruptured at ovulation it is transformed into the corpus luteum, whose secretion is mainly progesterone. The change of hormone follows the change of structure, and LH from the pituitary is what maintains the corpus luteum.
Frequently Asked Questions - Gonads, Non-glandular Hormones and Mechanism of Hormone Action
Which cells of the testis produce hormones and what do they produce?
The Leydig cells or interstitial cells, present in the intertubular spaces of the testis, produce a group of hormones called androgens, mainly testosterone. The testis is composed of seminiferous tubules and stromal or interstitial tissue, and it performs dual functions as a primary sex organ and as an endocrine gland.
What are the functions of androgens?
Androgens regulate the development, maturation and functions of the male accessory sex organs such as the epididymis, vas deferens, seminal vesicles, prostate gland and urethra. They stimulate muscular growth, growth of facial and axillary hair, aggressiveness and low pitch of voice, play a major stimulatory role in spermatogenesis, act on the central neural system to influence male sexual behaviour, and produce anabolic effects on protein and carbohydrate metabolism.
Which hormones does the ovary produce?
The ovary produces two groups of steroid hormones called estrogen and progesterone. Estrogen is synthesised and secreted mainly by the growing ovarian follicles, while after ovulation the ruptured follicle is converted to the corpus luteum, which secretes mainly progesterone.
What are the functions of estrogens and progesterone?
Estrogens stimulate the growth and activities of female secondary sex organs, the development of growing ovarian follicles, the appearance of female secondary sex characters such as a high pitch of voice, and mammary gland development, and they regulate female sexual behaviour. Progesterone supports pregnancy and also acts on the mammary glands, stimulating the formation of alveoli, which store milk, and milk secretion.
Which hormone is secreted by the heart and what does it do?
The atrial wall of the heart secretes a peptide hormone called atrial natriuretic factor, or ANF, which decreases blood pressure. When blood pressure is increased, ANF is secreted and causes dilation of the blood vessels, which reduces the blood pressure.
Which hormone does the kidney produce?
The juxtaglomerular cells of the kidney produce a peptide hormone called erythropoietin, which stimulates erythropoiesis, that is the formation of RBC.
What are the four hormones of the gastro-intestinal tract and their actions?
Endocrine cells in different parts of the gastro-intestinal tract secrete gastrin, secretin, cholecystokinin and gastric inhibitory peptide. Gastrin acts on the gastric glands and stimulates the secretion of hydrochloric acid and pepsinogen. Secretin acts on the exocrine pancreas and stimulates secretion of water and bicarbonate ions. CCK acts on both pancreas and gall bladder, stimulating the secretion of pancreatic enzymes and bile juice respectively. GIP inhibits gastric secretion and motility.
How do hormones produce their effects on target tissues?
Hormones produce their effects by binding to specific proteins called hormone receptors, located in the target tissues only. Receptors on the cell membrane are membrane-bound receptors and those inside the cell are intracellular receptors, mostly nuclear receptors. Binding leads to the formation of a hormone-receptor complex, which causes biochemical changes in the target tissue. Each receptor is specific to one hormone only.
What are the chemical classes of hormones?
On the basis of their chemical nature hormones are divided into peptide, polypeptide and protein hormones such as insulin, glucagon and the pituitary and hypothalamic hormones; steroids such as cortisol, testosterone, estradiol and progesterone; iodothyronines, which are the thyroid hormones; and amino-acid derivatives such as epinephrine.
What is the difference between the action of protein hormones and steroid hormones?
Hormones which interact with membrane-bound receptors normally do not enter the target cell but generate second messengers such as cyclic AMP, IP3 and Ca++, which in turn regulate cellular metabolism. Hormones which interact with intracellular receptors, such as steroid hormones and iodothyronines, mostly regulate gene expression or chromosome function by the interaction of the hormone-receptor complex with the genome. In both cases cumulative biochemical actions result in physiological and developmental effects.
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