Endocrine system

Question 1

What does the endocrine system regulate?

Answer 1

Metabolism, growth and development, reproduction, water and electrolyte balance, and behavior.

Question 2

Types of endocrine receptors:

Answer 2

Cytoplasmic or nuclear receptors for lipophilic hormones and cell surface receptors for hydrophilic proteins.

Question 3

How do second messengers in the endocrine system function?

Answer 3

Second messengers are short-lived intracellular signaling molecules that lead to rapid changes in the activity of cellular enzymes, with their concentration increasing to amplify signals.

Question 4

What happens when a hormone binds to a G-protein coupled receptor?

Answer 4

It activates adenyl cyclase to produce cAMP from ATP, which then activates cAMP-dependent protein kinase, leading to the cell’s response.

Question 5

What are the two main types of white adipose tissue ?

Answer 5

Subcutaneous adipose tissue (beneath the skin) and intra-abdominal adipose tissue (around inner organs).

Question 6

What are the primary functions of white adipose tissue ?

Answer 6

Energy storage, temperature insulation, mechanical protection, and functioning as an endocrine organ.

Question 7

Where is brown adipose tissue found in newborns and adults?

Answer 7

In newborns, BAT is found between the shoulder blades and around the adrenal glands. In adults, it is found in the cervical, supraclavicular, and paravertebral regions.

Question 8

What is the main function of brown adipose tissue ?

Answer 8

To generate heat through thermogenesis, especially important for maintaining body temperature in cold environments.

Question 9

What is the role of insulin produced by pancreatic beta cells?

Answer 9

Insulin lowers blood glucose levels by facilitating glucose uptake into tissues.

Question 10

What is the significance of glucagon produced by pancreatic alpha cells?

Answer 10

Glucagon increases blood glucose levels by promoting glucose release from the liver.

Question 11

What triggers glucose-stimulated insulin secretion (GSIS) in pancreatic beta cells?

Answer 11

A rise in blood glucose levels leads to increased intracellular calcium, triggering the exocytosis of insulin-containing granules.

Question 12

What is lipotoxicity and what causes it?

Answer 12

Lipotoxicity is damage caused to organs and tissues by excessive lipid accumulation, often due to limited lipid storage capacity in organs other than adipose tissue.

Question 13

What are the main functions of the liver?

Answer 13

Storage of glycogen, vitamins, and minerals, bile production, protein synthesis, hormone breakdown, and detoxification of harmful substances.

Question 14

What is the role of hepatocytes in the liver?

Answer 14

Hepatocytes perform synthesis, storage, and detoxification functions, and have a high capacity for regeneration.

Question 15

How do cytoplasmic and nuclear receptors in the endocrine system function with lipophilic hormones?

Answer 15

Lipophilic hormones bind to cytoplasmic or nuclear receptors, which then bind to the promoter of hormone-response elements on DNA, affecting gene expression and leading to changes in cellular activity.

Question 15

What are bile acids and their function?

Answer 15

Bile acids, produced by the liver, help in fat digestion and absorption and play a hormonal role in regulating metabolism.

Question 16

Explain how cell surface receptors induce intracellular signaling in the endocrine system.

Answer 16

Cell surface receptors, such as G-protein coupled receptors and ion channels, bind to hydrophilic hormones, which activate intracellular signaling pathways involving second messengers like cAMP, IP3, and DAG. These messengers lead to the activation of enzymes and changes in cell function.

Question 17

What is the physiological regulation of thermogenesis in brown adipose tissue?

Answer 17

A: The preoptic area of the brain senses cold and activates the hypothalamus, which increases sympathetic nervous system (SNS) activity. Norepinephrine released from sympathetic nerve terminals binds to β-adrenergic receptors on brown adipocytes, activating pathways that increase cAMP and protein kinase A (PKA), leading to the activation of UCP1 and heat production.

Question 17

What roles do white adipose tissue play as an endocrine organ?

Answer 17

WAT secretes hormones called adipokines, such as leptin and adiponectin, which are involved in regulating energy balance, metabolism, and insulin sensitivity. It also plays a role in inflammation through cytokine production.

Question 18

What is the difference between healthy and unhealthy expansion of white adipose tissue?

Answer 18

Healthy expansion involves increased adipogenesis, cell volume, and insulin sensitivity with reduced inflammation. Unhealthy expansion is characterized by decreased adipogenesis, increased cell hypertrophy, reduced insulin sensitivity, heightened low-grade inflammation, and macrophage infiltration, leading to complications like insulin resistance and type 2 diabetes.

Question 19

Describe the structure and cellular composition of white adipose tissue.

Answer 19

WAT consists primarily of adipocytes that store triglycerides and secrete hormones, preadipocytes that serve as a regenerative reservoir, immune cells that contribute to inflammation, endothelial cells, vascular smooth muscle cells, and fibroblasts that provide structural integrity and cell communication.

Question 20

How does brown adipose tissue contribute to thermogenesis and energy metabolism?

Answer 20

BAT generates heat by metabolizing lipids through the action of UCP1 in mitochondria. This process uncouples oxidative phosphorylation, allowing energy from fat oxidation to be released as heat, aiding in body temperature regulation and protection against cold.

Question 20

What is the role of insulin signaling in various tissues?

Answer 20

In muscle and adipose tissue, insulin promotes glucose uptake by translocating GLUT4 to the cell membrane. In the liver, it stimulates glycogen synthesis and inhibits gluconeogenesis. In adipose tissue, it increases lipogenesis, converting glucose into fatty acids for storage.

Question 21

Explain the roles of different cell types in the islets of Langerhans in the pancreas.

Answer 21

Beta cells produce insulin, alpha cells secrete glucagon, delta cells produce somatostatin to regulate insulin and glucagon secretion, PP cells secrete pancreatic polypeptide involved in hormone regulation, and epsilon cells produce ghrelin to regulate satiety and metabolic rate.

Question 21

Describe the process of glucose-stimulated insulin secretion (GSIS) from pancreatic beta cells.

Answer 21

When blood glucose levels rise, glucose enters beta cells through GLUT2 transporters and is metabolized to increase ATP production. This closes ATP-sensitive potassium channels, causing membrane depolarization, opening voltage-gated calcium channels, and allowing Ca2+ influx. The increased intracellular calcium triggers the exocytosis of insulin granules.

Question 22

What causes lipotoxicity and its effects on metabolic organs?

Answer 22

Lipotoxicity occurs when adipose tissue’s lipid storage capacity is exceeded, leading to lipid accumulation in other organs. This causes inflammation, oxidative stress, mitochondrial dysfunction, ER stress, and impaired autophagy, resulting in beta cell dysfunction, insulin resistance, and metabolic disorders like type 2 diabetes.

Question 23

How does the liver contribute to glucose homeostasis and overall metabolism?

Answer 23

The liver stores glycogen, produces bile for fat digestion, synthesizes proteins like albumin, breaks down hormones, and detoxifies harmful substances. It plays a crucial role in regulating blood glucose levels by responding to insulin, promoting glucose storage, and suppressing glucose production.

Question 24

What is the significance of hepatocytes in liver function and regeneration?

Answer 24

Hepatocytes are the main functional cells of the liver, responsible for synthesis, storage, and detoxification. They have a remarkable capacity for regeneration, enabling the liver to recover from significant damage or surgical removal of up to 75% of its mass.

Question 25

Describe the process and function of bile acid synthesis in the liver.

Answer 25

Bile acids are synthesized in the liver and conjugated with glycine or taurine. They aid in fat digestion by emulsifying fats and forming micelles for lipid absorption. Bile acids also regulate hepatic lipid metabolism by binding to the Farnesoid X receptor (FXR).

Question 26

How does insulin interact with the liver to maintain blood glucose levels?

Answer 26

Insulin stimulates the liver to store glucose as glycogen and suppresses gluconeogenesis, the production of glucose from non-carbohydrate sources. This interaction helps regulate blood glucose levels, ensuring they remain within a healthy range.

Question 27

How are B cells keeping blood sugar levels stable?

Answer 27

When blood sugar levels rise, glucose enters beta cells through GLUT2 transporters. Inside the cell, glucose is broken down, producing ATP. The high ATP/ADP ratio causes ATP-sensitive potassium channels to close, trapping potassium inside the cell. This closure makes the inside of the cell less negative, leading to depolarization. Depolarization opens voltage-gated calcium channels, allowing calcium to enter the cell. The influx of calcium triggers the release of insulin from storage granules into the bloodstream.

Question 28

What is lipotoxicity?

Answer 28

the damage caused to metabolic organs and tissues by excessive lipid accumulation. It occurs when the storage capacities of lipids in adipose tissue are exceeded, leading to a spillover effect where lipids accumulate in other organs, causing local cytotoxicity. The storage and metabolism of lipids predominantly take place in adipose tissue, but limited storage capacity in other organs results in lipotoxic effects.

Question 29

A mechanism of free fatty acids that leads to insulin resistance

Answer 29

FFA recruit macrophages to beta cells, which triggers an inflammatory response. The pro-inflammatory environment is facilitated by FFA binding to toll-like receptor 4 (TLR4), leading to the production of pro-inflammatory cytokines (TNFα) via the NF-κB pathway. TNFα can induce insulin resistance by blocking insulin signaling through the inhibitory serine phosphorylation of insulin receptor substrates (IRS1/2). This happens during lipotoxicity.

Question 30

How can lipotoxicity lead to death?

Answer 30

Palmitate (FFA) and diacylglycerol (DAG) induce the production of ROS. The excessive ROS generated in mitochondria lead to oxidative stress and mitochondrial dysfunction and can cause significant cellular damage, contributing to beta cell dysfunction and death.

Question 31

How can lipotoxicity trigger apoptotic pathways?

Answer 31

FFA, particularly palmitate, can induce Endoplasmic Reticulum stress by depleting (wasting) calcium levels within the ER. This stress disrupts normal protein folding and processing, leading to cellular dysfunction. The accumulation of misfolded proteins further exacerbates (worsens) cellular stress and can trigger apoptotic pathways.

Question 32

How does lipotoxicity lead to the accumulation of damaged organelles, proteins and B cell disfunction?

Answer 32

FFA like oleate and palmitate inhibit the genes involved in autophagy (=degradation and recycle cellular components). Impaired (reduced) autophagy leads to the accumulation of damaged organelles and proteins, further contributing to beta cell dysfunction.

Question 33

Functions of liver

Answer 33

The liver stores glycogen, vitamins, and minerals, serving as a reservoir to maintain energy and nutrient balance. It produces bile, which is essential for digestion and absorption of fats in the small intestine. It synthesizes various proteins, including albumin, which is crucial for maintaining blood osmotic pressure and transporting substances.
The liver breaks down hormones such as insulin, regulating their levels in the blood.It detoxifies harmful substances, such as alcohol and drugs, ensuring they do not accumulate to toxic levels in the body.