Lowest pH is seen in which of the gastrointestinal secretions?
Daily salivary secretion is
Inhibition of myenteric plexus results in
Which of the following is the primary site of gastrin production?
What is the primary hormone responsible for the secretion of milk?
Which of the following hormones is not stored in cells?
LH surge is associated with?
Which hormone increases with age?
The primary oocyte remains arrested in which stage until ovulation?
Which of the following statements about thyroid hormone receptors is correct?
NEET-PG 2013 - Physiology NEET-PG Practice Questions and MCQs
Question 61: Lowest pH is seen in which of the gastrointestinal secretions?
- A. Gastric juice (Correct Answer)
- B. Bile juice
- C. Saliva
- D. Pancreatic juice
Explanation: ***Gastric juice*** - Gastric juice contains **hydrochloric acid (HCl)**, secreted by parietal cells, which gives it a very **low pH (1.5-3.5)**. - This acidic environment is crucial for protein digestion by **pepsin** and for killing ingested microorganisms. *Bile juice* - Bile juice is typically **alkaline**, with a pH ranging from **7.6 to 8.6**. - Its primary role is to **emulsify fats** in the small intestine, and it does not contain significant acidic components. *Saliva* - Saliva has a relatively neutral pH, typically ranging from **6.2 to 7.6**. - It contains enzymes like **amylase** and **lipase** for initial carbohydrate and lipid digestion, but no strong acids. *Pancreatic juice* - Pancreatic juice is highly **alkaline**, with a pH usually between **8.0 and 8.3**, due to its high concentration of bicarbonate. - This alkalinity neutralizes the acidic chyme entering the duodenum from the stomach, creating an optimal environment for pancreatic enzymes.
Question 62: Daily salivary secretion is
- A. 1000-1500 ml (Correct Answer)
- B. 1500-2000 ml
- C. More than 2000 ml
- D. Less than 1000 ml
Explanation: ***1000-1500 ml*** - The average daily salivary secretion in healthy adults ranges from **1000 to 1500 ml**, with variations depending on individual factors and stimulation. - This volume is crucial for various functions, including **digestion**, oral hygiene, and speech. *1500-2000 ml* - This range is generally considered to be on the **higher side** of normal daily salivary output, exceeding the typical average. - While individual variations exist, consistent secretion at this level might suggest **hypersecretion** or ptyalism in some cases. *More than 2000 ml* - Daily salivary secretion **rarely exceeds 2000 ml** in healthy individuals. - Such high volumes could indicate a pathological condition leading to **sialorrhea** or excessive salivation. *Less than 1000 ml* - A daily salivary secretion of **less than 1000 ml** is often indicative of **hyposalivation** or dry mouth (xerostomia). - This reduced volume can lead to problems with chewing, swallowing, speaking, and an increased risk of dental caries.
Question 63: Inhibition of myenteric plexus results in
- A. Hyperacidity
- B. Diarrhea
- C. Decreased gut motility (Correct Answer)
- D. Increased secretions
Explanation: ***Decreased gut motility*** - The **myenteric plexus** (Auerbach's plexus) is primarily responsible for regulating **gastrointestinal motility**, including peristalsis and muscle contraction. - Its inhibition would therefore lead to **reduced peristaltic movements** and **decreased gut motility**. *Hyperacidity* - **Gastric acid secretion** is mainly regulated by the vagus nerve (via acetylcholine), gastrin, and histamine, not directly by the myenteric plexus. - While gut motility can indirectly affect acid exposure, a primary and direct consequence of myenteric plexus inhibition is not hyperacidity. *Diarrhea* - **Diarrhea** is typically caused by increased gut motility, increased secretion, or decreased absorption. - Inhibition of the myenteric plexus would lead to **decreased motility**, making diarrhea an unlikely outcome. *Increased secretions* - **Gastrointestinal secretions** are largely controlled by the submucosal plexus (Meissner's plexus) and hormonal factors. - While the myenteric plexus has some indirect influence, its primary role is motility, and its inhibition would not directly lead to increased secretions.
Question 64: Which of the following is the primary site of gastrin production?
- A. Gastric chief cells
- B. Pancreas
- C. Pituitary gland
- D. Gastric G cells (Correct Answer)
Explanation: ***Gastric G cells*** - **G cells**, primarily located in the **antrum of the stomach**, are the main site for **gastrin production** - Gastrin is a hormone that stimulates the secretion of **gastric acid** by the parietal cells in the oxyntic glands of the stomach - G cells are specialized endocrine cells that release gastrin in response to gastric distension, amino acids, and vagal stimulation *Pancreas* - The pancreas produces hormones such as **insulin** and **glucagon**, and digestive enzymes like **amylase** and **lipase** - While the pancreas does contain some hormone-producing cells, it is not the primary site for gastrin synthesis *Pituitary gland* - The **pituitary gland** is the master endocrine gland, regulating various **hormonal axes** like thyroid, adrenal, and reproductive functions - It does not produce gastrin; its hormones include **growth hormone**, **prolactin**, **TSH**, **ACTH**, **FSH**, and **LH** *Gastric chief cells* - Chief cells (also called zymogenic cells) are located in the **gastric glands of the fundus and body** of the stomach - They produce **pepsinogen**, the inactive precursor of the proteolytic enzyme pepsin, not gastrin
Question 65: What is the primary hormone responsible for the secretion of milk?
- A. Oxytocin
- B. Prolactin (Correct Answer)
- C. Glucocorticoids
- D. Relaxin
Explanation: ***Prolactin*** - **Prolactin** is the primary hormone synthesized and secreted by the pituitary gland that is responsible for **milk production** (lactogenesis) in the mammary glands after childbirth. - Its levels rise significantly during pregnancy and remain elevated with regular suckling, which stimulates its release and maintains milk supply. *Oxytocin* - **Oxytocin** is primarily responsible for the **milk ejection reflex** (let-down reflex), causing the contraction of myoepithelial cells around the alveoli to release milk. - It does not stimulate the production of milk itself but rather its expulsion from the breast. *Glucocorticoids* - **Glucocorticoids** (like cortisol) play a role in mammary gland development and maturation, and can have permissive effects on prolactin's action. - However, they are not the primary hormone directly responsible for stimulating milk secretion. *Relaxin* - **Relaxin** is a hormone primarily involved in relaxing ligaments in the pelvis and softening the cervix during childbirth. - It has no direct primary role in the production or secretion of breast milk.
Question 66: Which of the following hormones is not stored in cells?
- A. Thyroxin
- B. Renin
- C. Insulin
- D. Cortisol (Correct Answer)
Explanation: ***Cortisol*** - Cortisol is a **steroid hormone** that is synthesized from **cholesterol** on demand and is **not stored** in secretory vesicles or elsewhere within cells. - Being **lipophilic**, it diffuses freely across cell membranes immediately after synthesis. - Its release is regulated by the **hypothalamic-pituitary-adrenal (HPA) axis**, with synthesis and immediate secretion occurring upon stimulation. *Insulin* - Insulin is a **peptide hormone** synthesized as **proinsulin** and then cleaved into active insulin. - It is **stored in secretory granules** within pancreatic beta cells, allowing for rapid release in response to elevated blood glucose. *Thyroxine* - Thyroxine (T4) is a **thyroid hormone** that is synthesized from tyrosine and iodine. - It is **stored extracellularly** within the thyroid gland's follicles as part of a large protein called **thyroglobulin**. - Unlike cortisol (which is never stored), thyroxine has a **substantial storage pool** that can last weeks, though the storage is extracellular rather than intracellular. *Renin* - Renin is an **enzyme** produced by the **juxtaglomerular cells** of the kidney. - It is **stored in secretory granules** within these cells and released in response to decreased renal perfusion pressure or sympathetic stimulation.
Question 67: LH surge is associated with?
- A. Increased estrogen & decreased progesterone (Correct Answer)
- B. Increased estrogen & increased progesterone
- C. Decreased estrogen & increased progesterone
- D. Decreased estrogen & decreased progesterone
Explanation: ***Increased estrogen & decreased progesterone*** - The **LH surge** is triggered by a significant rise in **estrogen** levels from the dominant follicle, indicating ovarian readiness. - At the time of the LH surge, **progesterone** levels remain low; they only begin to rise significantly after ovulation, when the corpus luteum forms. *Increased estrogen & increased progesterone* - While **estrogen** levels are high, **progesterone** only significantly increases *after* ovulation, as the corpus luteum develops. - High estrogen *and* high progesterone together are typically seen in the **luteal phase**, not at the peak of the LH surge. *Decreased estrogen & increased progesterone* - A decrease in **estrogen** would suppress LH, not trigger a surge. - Increased **progesterone** would also inhibit LH release via negative feedback in the follicular phase if it were to occur pre-ovulation. *Decreased estrogen & decreased progesterone* - Both **decreased estrogen** and **decreased progesterone** would lead to low FSH/LH levels and would not promote an LH surge or ovulation. - This hormonal profile is more characteristic of the very early follicular phase or menopause.
Question 68: Which hormone increases with age?
- A. GH
- B. Prolactin
- C. Parathormone (Correct Answer)
- D. Insulin
Explanation: ***Parathormone*** - **Parathormone (PTH)** levels in the blood tend to increase with age, often due to a decline in renal function and reduced vitamin D synthesis, leading to compensatory hyperparathyroidism. - This age-related increase in PTH can contribute to **bone demineralization** and an increased risk of osteoporosis. *GH* - **Growth hormone (GH)** levels generally **decrease with age**, leading to a condition known as somatopause. - Reduced GH contributes to changes in body composition, such as increased adiposity and decreased lean muscle mass, as well as reduced bone density. *Prolactin* - **Prolactin** levels typically remain relatively stable or may slightly decrease with age in men, while in women they can fluctuate due to hormonal changes like menopause but do not show a consistent increase with age. - High prolactin levels are often associated with specific pathological conditions like **prolactinomas** rather than normal aging. *Insulin* - While **insulin resistance** often increases with age, leading to higher fasting insulin levels in some individuals, the overall picture of insulin secretion can be complex and is often influenced by factors such as diet, exercise, and genetics rather than solely age. - A *decline in pancreatic beta-cell function* with age can also lead to impaired insulin secretion in some elderly individuals, complicating the simple relationship between age and insulin levels.
Question 69: The primary oocyte remains arrested in which stage until ovulation?
- A. Diplotene stage (Correct Answer)
- B. Pachytene stage
- C. Metaphase
- D. Telophase
Explanation: ***Diplotene stage*** - The primary oocyte enters **meiosis I** during fetal development but arrests in the **prophase I substage of diplotene**. - This arrest is maintained until **puberty** and **ovulation**, when hormonal surges trigger the completion of meiosis I. *Pachytene stage* - The **pachytene stage** of prophase I is when **crossing over** (recombination) occurs between homologous chromosomes. - While an important step in meiosis, it precedes the **diplotene arrest** point. *Metaphase* - **Metaphase** is a stage where chromosomes align at the metaphase plate, either in meiosis I or meiosis II. - The primary oocyte's arrest occurs much earlier, during **prophase I**, not metaphase. *Telophase* - **Telophase** is the final stage of mitosis or meiosis where chromosomes decondense and nuclear envelopes reform. - The oocyte's initial arrest point is in **prophase I**, long before telophase.
Question 70: Which of the following statements about thyroid hormone receptors is correct?
- A. They directly bind to thyrotropin-releasing hormone (TRH)
- B. They directly bind to thyroid-stimulating hormone (TSH)
- C. They cause nuclear transcription after binding with T4
- D. They are intracellular receptors that mediate gene transcription after binding with T3 or T4, but their primary action is through T3. (Correct Answer)
Explanation: ***They are intracellular receptors that mediate gene transcription after binding with T3 or T4, but their primary action is through T3.*** - **Thyroid hormone receptors** are indeed **intracellular** and act as **ligand-activated transcription factors**, regulating gene expression. - While both **T3** and **T4** can bind, **T3 (triiodothyronine)** is the more potent and active form, binding with much higher affinity to the receptors to exert its primary metabolic effects. *They directly bind to thyrotropin-releasing hormone (TRH)* - **TRH (thyrotropin-releasing hormone)** is produced by the hypothalamus and acts on the **pituitary gland** to stimulate TSH release, not directly on thyroid hormone receptors. - Thyroid hormone receptors bind to thyroid hormones (**T3 and T4**), not to the hypothalamic releasing hormones like TRH. *They directly bind to thyroid-stimulating hormone (TSH)* - **TSH (thyroid-stimulating hormone)** is produced by the pituitary gland and primarily acts on receptors located on the **thyroid gland cells** to stimulate thyroid hormone synthesis and release. - Thyroid hormone receptors are distinct from TSH receptors and bind to the hormones themselves (**T3/T4**), not the stimulating hormone TSH. *Causes nuclear transcription after binding with T4* - While **T4 (thyroxine)** can bind to thyroid hormone receptors, it is primarily a **prohormone**. - T4 is largely converted to the more active **T3** within target cells, and **T3** is the main mediator of nuclear transcription through these receptors.