All questions of Endocrine System (BIO) for MCAT Exam

Answer:

Introduction:
Ingestion of a double-bacon cheeseburger with a milkshake can have various effects on the body, including the release of hormones that regulate digestion and metabolism. Hormones are chemical messengers produced by various glands in the body, and they play a crucial role in maintaining homeostasis.

Explanation:
The hormones that are involved in the digestion and metabolism of food include secretin, insulin, cholecystokinin, and glucagon. These hormones are released in response to specific stimuli and help regulate various processes in the body, such as the release of digestive enzymes, the uptake of glucose into cells, and the breakdown of stored glycogen.

Secretin:
Secretin is a hormone that is released from the duodenum in response to the presence of acidic chyme (partially digested food) in the small intestine. It stimulates the pancreas to release bicarbonate ions, which neutralize the acidic chyme. Therefore, after consuming a double-bacon cheeseburger with a milkshake, the acidic chyme in the small intestine would stimulate the release of secretin, causing an increase in secretin levels.

Insulin:
Insulin is a hormone that is released from the pancreas in response to high levels of glucose in the blood. It promotes the uptake of glucose into cells, where it can be used for energy or stored as glycogen. After consuming a double-bacon cheeseburger with a milkshake, the high levels of carbohydrates and sugars in the meal would lead to an increase in blood glucose levels, triggering the release of insulin to facilitate its uptake into cells.

Cholecystokinin:
Cholecystokinin (CCK) is a hormone that is released from the duodenum in response to the presence of fat and protein in the small intestine. It stimulates the gallbladder to contract and release bile, which aids in the digestion and absorption of fats. Additionally, CCK also slows down gastric emptying and promotes satiety. Therefore, after consuming a double-bacon cheeseburger with a milkshake, the presence of fat and protein in the small intestine would stimulate the release of cholecystokinin, causing an increase in CCK levels.

Glucagon:
Glucagon is a hormone that is released from the pancreas in response to low blood glucose levels. It acts to increase blood glucose levels by promoting the breakdown of glycogen into glucose in the liver. Since consuming a double-bacon cheeseburger with a milkshake would result in an increase in blood glucose levels, the release of glucagon would not be expected. Therefore, the correct answer is option D, glucagon.

Conclusion:
After consuming a double-bacon cheeseburger with a milkshake, the hormones secretin, insulin, and cholecystokinin would be expected to increase due to the presence of food and the subsequent release of digestive enzymes and regulation of blood glucose levels. However, the hormone glucagon would not be expected to increase because the meal would result in elevated blood glucose levels, triggering the release of insulin instead.

Receptor Location:
Steroid hormones are lipid-soluble molecules that can easily pass through the cell membrane. Therefore, they are more likely to have an associated receptor in the cytosol or nucleus. Once inside the cell, steroid hormones bind to their specific intracellular receptors, forming hormone-receptor complexes that then regulate gene expression.

Rapid Onset of Effect:
Unlike polypeptide hormones, steroid hormones do not demonstrate rapid onset of effect. This is because their mechanism of action involves gene regulation and protein synthesis, which takes time to produce a physiological response. As a result, the effects of steroid hormones are generally slower but more sustained compared to polypeptide hormones.

Second Messengers:
Steroid hormones do not commonly function via specific second messengers like polypeptide hormones. Instead, they directly regulate gene expression by binding to their receptors in the cytosol or nucleus. This leads to changes in protein synthesis and cellular activities over a longer period of time.

Degradation and Temporary Effects:
Steroid hormones are not rapidly degraded like polypeptide hormones. Due to their lipid-soluble nature, steroid hormones are typically bound to carrier proteins in the bloodstream, which helps protect them from immediate degradation. As a result, steroid hormones have more prolonged effects compared to polypeptide hormones and are not as quickly cleared from the body.

Thyroid hormone is a hormone produced by the thyroid gland, which is located in the neck. It plays a crucial role in regulating metabolism, growth, and development in the body. The accurate description of thyroid hormone is that it binds to receptors on the inside of the cell (option D).

Here is a detailed explanation:

Thyroid hormone production:
- The thyroid gland produces two main hormones: thyroxine (T4) and triiodothyronine (T3).
- These hormones are synthesized by the follicular cells of the thyroid gland, which take up iodine from the bloodstream and combine it with the amino acid tyrosine to produce T4 and T3.
- T4 is the inactive form of the hormone, while T3 is the active form.

Transport and conversion:
- Once synthesized, T4 and T3 are released into the bloodstream and transported to target tissues throughout the body.
- The majority of thyroid hormone in the blood is in the form of T4, while T3 is present in smaller amounts.
- T4 can be converted to T3 by enzymes in various tissues, including the liver, kidneys, and other peripheral tissues.

Thyroid hormone receptors:
- Thyroid hormone exerts its effects by binding to nuclear receptors, known as thyroid hormone receptors (TRs), inside the cells.
- TRs are found in the nucleus of target cells and act as transcription factors, regulating gene expression.
- When thyroid hormone binds to TRs, it initiates a series of molecular events that lead to changes in gene expression, ultimately affecting cellular processes such as metabolism, growth, and development.

Function of thyroid hormone:
- Thyroid hormone affects almost every cell in the body and is essential for normal growth and development, as well as maintaining metabolic homeostasis.
- It increases the basal metabolic rate, promoting the consumption of oxygen and energy production in cells.
- Thyroid hormone is also involved in the regulation of body temperature, heart rate, and digestion.

In conclusion, thyroid hormone binds to receptors on the inside of the cell, specifically nuclear receptors, to exert its effects on gene expression and cellular processes.

Paracrine Function:
Paracrine function refers to the signaling between cells in a localized area. Both growth factors and histamine act as paracrine signaling molecules, exerting their effects on nearby cells without entering the bloodstream.

Growth Factors:
- Growth factors are proteins that regulate cell growth, proliferation, differentiation, and survival.
- They play a crucial role in tissue repair, development, and maintenance.
- For example, growth factors like epidermal growth factor (EGF) stimulate cell growth and proliferation in the skin.

Histamine:
- Histamine is a compound released by immune cells in response to injury or allergens.
- It is involved in allergic reactions, inflammation, and gastric acid secretion.
- Histamine can cause vasodilation, increased vascular permeability, and smooth muscle contraction.
In conclusion, both growth factors and histamine function as paracrine signaling molecules, acting locally on neighboring cells to regulate various physiological processes.