Endocrine System – One Liners & Important Concepts 

Endocrine System Important Topics 

• Mechanisms of Hormone Actions
  • Paracrine Cell Signaling
  • Hormone Receptor Classification
  • Guanylyl Cyclase Receptor Mechanism
  • Receptor Tyrosine Kinase Mechanism
• Pituitary Hormones
  • Control of pituitary hormones
  • Somatomedins
  • Prolactin (PRL)
  • ADH Receptor and Functions
  • Disorders of ADH
  • Oxytocin
• Thyroid Hormones
  • Thyroid Hormone Synthesis
  • Peripheral Conversion
• Endocrine Pancreas
  • Insulin Receptor
  • Glucagon
• Hormonal Regulation of Calcium Balance
  • Calcium Balance
  • Vitamin D (Calcitriol)
• Adrenal Physiology
  • The adrenal gland consists of two parts
• Male Reproductive Physiology
  • Sperm Inside Epididymis
  • Leydig Cell
• Female Reproductive Physiology
  • Functions of Estrogen and Progesterone
  • Follicular Development
  • Mechanism of ovulation

Also read: Insulin Receptors: Structure, Functions and Action

Important One-liners in Endocrine System

• Steroidal Hormone Receptor Activity: At times on the plasma membrane or in the cytoplasm, certain receptors are present which are structurally like other receptors. However, the ligands of the receptors haven't been discovered yet. Such receptors are called orphan receptors. If the receptor's ligand is discovered sometime in the future, it would be called an adopted orphan receptor.
• The osteoblast cell that migrates and remains entrapped within the mineral bone is known as an osteocyte.
• Osteocyte cell functions as a mechanosensor cell of bone
• Osteoblast secretes MCSF and expresses ligand for the RANK i.e., RANK-L
• The continuous resorption and deposition on the surface of the bone in our body is known as the Bone Remodeling Unit.
• A normal person has at least 1-2 million bone remodeling units.
• Every year, approximately 5-10% of bone is remodeled.
• If the vitamin D levels are normal, it causes bone deposition.
• If the Vitamin D levels are high, it strongly stimulates the Osteoblast to produce osteoclast and eventual bone resorption.
• Osteoblast produces another factor that protects the bone from resorption, known as osteoprotegerin
• Mild hypomagnesemia acts as a stimulus for PTH secretion whereas severe hypomagnesemia acts as an inhibitor for PTH secretion.
• PCT → PTH inhibits phosphate resorption.
• DCT → PTH increases calcium reabsorption.
• There is a difference between Cushing syndrome and Cushing's disease.
• Cushing disease is caused by an ACTH-producing pituitary tumor, whereas Cushing syndrome is the set of symptoms that results when there is a surplus of cortisol in the body because of increased ACTH.
• The compartment inside the blood-testis barrier is known as the Adluminal Compartment.
• The compartment outside the blood-testis barrier is known as the Basal Compartment.
• The function of BTB is to protect the Spermatogenic/adluminal compartment from blood toxins.
• The channel responsible for sperm motility in the epididymis is Cat Sper (calcium channel of sperm) / Progressive Forward Motility.
• Sertoli cells and tight junctions form the Blood-testis barrier.
• Sertoli contains receptors for FSH and androgens (FSH and androgen aren't present on sperm).
• In humans, a single spermatogonium will give rise to 8-32 sperm cells (average = 16).
• FSH is required for early development of the spermatogonia cell whereas testosterone is particularly required for the terminal stages.
• Testosterone is responsible for development of internal genitalia, skeletal muscle, bone, Erythropoiesis, and many others.
• Dihydrotestosterone through 5a-reductase is responsible for development of external genitalia and many others.
• Ovulation in a woman who has a normal 28-day female sexual cycle occurs 14 days after the onset of menstruation.
• Ovulation takes place after 83 hours of estradiol rise. At first, estrogen will rise, then a positive feedback effect and after that LH surge is formed. This takes about 83 hours. About 24-36 hours of estradiol peak.
• Ovulation occurs 24-36 hours (Ganong's Physiology) or 34-36 (Dutta's Obstetrics) after the onset of LH surge.
• Ovulation takes place about 9 hours (Ganong's Physiology) or 10-12 hours (Dutta's Obstetrics) after the LH peak.
• Ovulation occurs about 8 hours after progesterone rises.

Also read: Nerve Muscle Physiology—Important Questions and Answers

Summary of Various Hormone Receptors

Factors Controlling Growth hormones

1. Hypoglycemia → Fasting, exercise.

2. Increase amino acids in plasma → Protein meal.

3. Stressful stimuli → Surgery, trauma

4. Sleep → NREM stimulatory, REM inhibitory

Important Questions 

Q. Which scientists were awarded the Nobel prize for the discovery of G-protein?

Ans. Alfred G. Gilman and Martin Rodbell

Also read: Physiology ​Image Based Questions for NEET PG 2025

Q. What condition results from the failure to terminate the activity of rhodopsin molecules in the retina?

Ans. Retinitis Pigmentosa

Q. A 40-year-old woman comes to her primary care clinician complaining of nervousness and an unexplained weight loss despite her impression that she is eating all the upon physical examination, her eyes were protruding, her skin was moist and warm, and her fingers had a slight tremor. Compared to a healthy individual, a biopsy of her thyroid gland wound most likely reveals which of the following:

1. Decreased numbers of reabsorption lacunae
2. Decreased evidence of endocytosis
3. A decrease in the cross-sectional area occupied by colloid
4. increased levels of NIS in the basolateral membrane of thyrocytes
5. Decreased evidence of lysosomal activity

Ans. A decrease in the cross-sectional area occupied by colloid

Q. A young woman has puffy skin and a hoarse voice. Her plasma TSH concentration is low but increases markedly when she is given TRH. She probably has

1. Hyperthyroidism due to a thyroid tumor.
2. Hypothyroidism due to a primary abnormality in the thyroid gland.
3. Hypothyroidism due to a primary abnormality in the pituitary gland.
4. Hypothyroidism due to a primary abnormality in the hypothalamus.
5. Hypothyroidism due to a primary abnormality in the hypothalamus.

Ans. Hypothyroidism due to a primary abnormality in the hypothalamus.

Also read: Important Topics in Physiology for NEET-PG 2025

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