Lecture 25 - Endocrine System I - Organs & Disorders I

The endocrine system.

The endocrine system.

Which system exhibits slow, long-lasting results— the nervous system or the endocrine system?

(a) Hormones. (b) hormones. (c) neurotransmitters

When comparing neurotransmitters to hormones: (a) which is produced by glands, (b) which travels through the bloodstream, and (c) which generally has shorter effects?

Both serve for internal communication and both use chemical transmitters.

What commonalities exist in the overall functions of the nervous system (NS) and the endocrine system?

Yes, norepinephrine, dopamine, and ADH.

Can a single chemical function as both a neurotransmitter and a hormone? If so, give examples.

No, they might have identical effects on the same organ

Are the effects of the nervous system and hormones always opposite?

Only certain target organs or target cells respond to NT or H

Do the nervous system and hormones bind to specific target organs or cells, or can they interact with any cell?

It is made up of all the glands, tissues, and cells that secrete hormones.

What structures constitute the endocrine system?

Long distance signals (chemicals) that travel in the blood

How would you define a hormone?

Tissue that produces hormones and secretes them into the blood stream. Scattered around the body.

What characterizes an endocrine tissue or organ?

Yes, since they bind receptor molecules in the target cells.

Do hormones act as ligands?

(a) A tissue that possesses receptors to which a specific hormone acts. (b) Start dividing and/or synthesize a specific protein (gene transcription modulation).

(a) What is the definition of target cell or target tissue? (b) what is the expected outcome upon the binding of a hormone to its specific receptor?

A bodily structure responsible for producing various substances, such as hormones, digestive fluids, sweat, tears, saliva, or milk.

What is the definition of "gland"?

(A) Exocrine glands release substances into a duct or opening to the inside or outside of the body and have extracellular effects. Endocrine glands secrete hormones into the blood that have intracellular effects. (b) Endocrine glands.

(a) What is the primary distinction between exocrine and endocrine glands, and (b) which type produces hormones?

Endocrine glands are specialized organs that produce and release hormones into the bloodstream.

What are endocrine glands, and what specific substances do they release, and to where?

Both. Acinar cells release digestive enzymes into ducts and the pancreatic islets release hormones into the blood.

Is the pancreas classified as an exocrine or endocrine gland? why?

Endocrine cell clusters called pancreatic islets. They are scattered throughout the pancreas.

What are the islets of Langerhans, and where are they located?

Beta cells: insulin and amylin. Alpha cells: glucagon

Which specific pancreatic cells are responsible for the production of the hormones insulin, amylin, and glucagon?

Insulin, amylin, and glucagon

In the regulation of glucose homeostasis, which pancreatic hormones play a pivotal role?

Opposite (=antagonistic effects). Insulin has glucose lowering effects while glucagon tends to raise circulating glucose levels.

Concerning the control of glucose levels, are the functions of insulin and glucagon similar or distinct?

Increase of blood glucose leves, such as after a meal.

What initiates the release of insulin from the pancreas?

Glycogenesis is the process by which glucose is converted into glycogen for storage in the liver and muscle cells. It is stimulated by insulin.

Could you define glycogenesis and clarify whether insulin or glucagon promotes or inhibits these metabolic reactions?

Gluconeogenesis is the synthesis of glucose from non-carbohydrate sources, such as amino acids and glycerol, primarily in the liver and kidneys. it is inhibited by insulin and promoted by glucagon.

Could you define gluconeogenesis and clarify whether insulin or glucagon promotes or inhibits these metabolic reactions?

Glycogenolysis is the breakdown of glycogen into glucose, releasing it into the bloodstream to be used for energy. It is promoted by glucagon.

Could you define glycogenolysis and clarify whether insulin or glucagon promotes or inhibits these metabolic reactions?

Insulin increase glucose uptake in adipose tissue and muscle, and stimulate glycogenesis in liver while it inhibits gluconeogenesis.

What are the overall effects of insulin on adipose tissue and muscle, and which metabolic reactions does insulin influence in the liver?

Amylin is simultaneously secreted with insulin. it helps to ↓ spikes in blood glucose: Suppresses appetite, Slow gastric emptying, Inhibits glucagon release

When is amylin secreted, and what functions does it serve??

Decrease of blood glucose levels (that happens after meals). It raises circulating glucose levels by promoting both the breakdown of glycogen into glucose (glycogenolysis) & the synthesis of glucose from non-carbohydrate sources (gluconeogenesis)

What triggers the release of glucagon from the liver, and what are its primary functions?

By promoting the translocation of glucose transporters type 4 (GLUT4) from intracellular storage vesicles to the cell membrane.

How does insulin enhance glucose uptake in the muscle?

GLUT-4 or glucose transporter type 4 is responsible for transporting glucose from the bloodstream into cells, particularly muscle and adipose (fat) cells.

What is the role of GLUT4?

DM is a metabolic disease, involving inappropriately elevated blood glucose levels.

What is the definition of diabetes mellitus (DM)?

Autoimmune attack → Pancreatic β-cell destruction → deficiency of insulin secretion. Patients require insulin

Explain the development of Type I diabetes mellitus and whether insulin injection is necessary for these patients.?

Peripheral resistance to insulin action (↓ sensitivity) & Inadequate compensatory response of insulin secretion by the pancreas (progressive loss of β-cells function)

What is the etiology of Type II diabetes mellitus?

Insulin resistance: unresponsiveness of the target cells to insulin. DM II.

What is "insulin resistance", and which type of diabetes, Type I or Type II, is characterized by this state?

(a) before 30 years old. (b) after age 40.

(a) In which age group does Type I diabetes mellitus typically manifest? (b) and type II?

(a) Hypophysis. (b) 2, anterior or adenohypophyis and posterior or neurohypophysis.

(a) What is the alternate name for the pituitary gland? (b) How many lobes does the pituitary gland possess, and what are their respective names?

Hypothalamus

Which area in the diencephalon plays a crucial role in maintaining homeostasis and serves as a link between the nervous and endocrine systems through the pituitary gland?

Infundibulum

What structure connects the hypothalamus to the pituitary gland?

Through the hypothalamo-hypophyseal tract and hypophysial portal system, respectively.

How are hormones produced in the hypothalamus transported to the neurohypophysis and adenohypophysis?

They bind receptors in the anterior pituitary gland affecting pituitary hormone production and release.

What are the primary functions of hypothalamic hormones that travel through the hypophysial portal system?

Specialized network of blood vessels that connects the hypothalamus and the anterior pituitary gland.

In relation to the hypothalamus, what is the portal system?

(a) They stimulate the anterior pituitary to release hormones. (b) RH. (c) Hypothalamus.

(a) What is the purpose of releasing hormones, and (b) what is their abbreviation? (c) Where are they produced?

(a) They suppress the anterior pituitary secretion of hormones. (b) IH. (c) Hypothalamus.

What is the function of inhibiting hormones, and what is their abbreviation? Where are they produced?

those hormones which act on another endocrine gland/cells and stimulate production of other hormones. Most are produced by the anterior pituitary.

Define tropic hormones.

Corticotropin releasing hormone, Thyrotropin-RH, Gonadotropin-RH, somatostatin, Prolactin inhibiting hormone.

Provide the full names for the following hypothalamic hormones: CRH, TRH, GnRH, GHRH, SS, PIH.

adrenocorticotropic hormone, thyroid-stimlating H, Luteinizing H, follicle-stimulating H, Growth hormone, prolactin

Provide the full names for the following pituitary hormones: ACTH, TSH, LH, FSH, GH, PRL.

CRH-ACTH, TRH-TSH, GnRH-LH and FSH, GHRH-GH

Which hypothalamic hormone stimulates the release of ACTH, TSH, LH, FSH, and GH from the anterior pituitary?

Somatostatin (=growth hormone inhibiting hormone), and dopamine (=prolactin inhibiting hormone), respectively.

Which hypothalamic hormones inhibit the release of GH and PRL from the pituitary gland?

The paraventricular and supraoptic nuclei. Through the hypothalamo-hypophyseal tract.

Which hypothalamic nuclei produce the hormones oxytocin and ADH, and how are they transported to the posterior pituitary for storage?

Anterior pituitary gland: ACTH, TSH, GH, FSH, LH, and prolactin. Posterior: oxytocin and ADH.

Name the six hormones produced by the anterior pituitary gland and the two hormones produced by the posterior pituitary gland.

ACTH-adrenal cortex, TSH-Thyroid, GH- bone and muscle, FSH/LH-gonads (testes and ovaries), prolactin-breast

Identify the organ or tissue targets for ACTH, TSH, GH, FSH, LH, and prolactin.

Oxytocin-breast, ADH-kidney

Identify the organ or tissue targets for oxytocin and ADH.

Follicular cells (line the follicles). T4: tetraiodothyronine & T3: triiodothyronine (TH: Refers to both collectively)

Which cells within the thyroid gland are responsible for producing thyroid hormone (TH), and what are the two types of thyroid hormones?

Parafollicular cells (= clear or C-cells)- located at the periphery of the follicles

Which cells in the thyroid gland produce calcitonin?

Thyroglobulin (Tg)

What protein is present in the colloid of the follicles within the thyroid gland?

Circulating TH concentrations are regulated via a negative feedback system at the level of the hypothalamus and the pituitary.

How are blood levels of TH regulated?

(a) TSH. (b) TRH

(a) Which hormone stimulates the growth of the thyroid gland and the secretion of TH, and (b) what stimulates its secretion by the pituitary gland?

T3, by deiodinases, specifically D1 and D2 within the target tissues.

What is the active form of TH, and how is T4 converted into T3? Where does this conversion occur?

By deiodinase D3 (these enzymes remove iodine from the TH).

How are TH inactivated?

In the nucleus.

Where is the TH receptor located within the cell?

These loops act to oppose the stimulus, or cue, that triggers them. In this case, an increase of blood levels of TH will inhibit their own secretion by decreasing the levels of TRH and TSH.

What is a negative feedback system? How does it apply to the TH?

(a) Iodine and tyrosine. (b) from the diet (in form of iodide). (c) from thyroglobulin (Tg)

(a) What are the two main components of the TH structure? (b) From where does the iodine needed for TH synthesis come? (c) and tyrosine?

Thyroid epithelial cells or thyrocytes, forming the walls of the follicles in the thyroid gland

What are the alternative names for thyroid follicular cells, and where are they located?

Through the sodium/iodide symporter.

How does iodide from the diet enter the lumen of the thyroid follicles?

Through the oxidation of iodide (I-). Thyroperoxidase.

How is iodine (I2) formed, and which enzyme is required for this process?

Also know as colloid, it is a gel-like substance that fills the thyroid follicles

What is hydrocolloid, and where is it located within the thyroid gland?

The TSH receptor (TSHR), on the surface of thyroid follicular cells.

To which receptor does TSH bind in the thyroid gland, and where are these receptors located?

TSH stimulates TH secretion through enhancing: iodide uptake, thyroglobulin synthesis, and thyroperoxidase activity.

What are the three actions of TSH on the thyroid gland?

Thyroglobulin is a large glycoprotein synthesized by the thyroid follicular cells. It contains tyrosine residues, which serve as sites for iodination during organification. It is located inside the follicles.

What is thyroglobulin, and where is it located?

The process of organification is part of thyroid hormone synthesis and involves incorporating iodine atoms into an organic compound, specifficaly into the amino acid tyrosine within the protein thyroglobulin.

What does the "organification of iodide" implicate?

By Coupling of Iodinated Tyrosine Residues in thyroglobulin. This process results in the formation of MIT (monoiodotyrosine) and DIT (diiodotyrosine).

How are MIT and DIT formed? What do MIT and DIT stand for?

(a) The combination of one molecule of MIT with one molecule of DIT results in the formation of T3, while the combination of two molecules of DIT results in the formation of T4. (b) Tetraiodothyronine or thyroxine.

(a) How are T3 and T4 formed? (b) What is another name for T4?

Iodide oxidation, Thyroglobulin iodination, MIT and DIT coupling

What are the functions of the thyroperoxidase enzyme? (hint: 3)

(a) The hormones remains anchored to Tg in the follicles. (b) TSH

(a) Where are located TH? (b) What stimulates their secretion?

(a) Endocytosis (pinocytosis) (b) Hydrolytic enzymes located in the lysosomes of the follicular cells.

(a) How is thyroglobulin from the colloid absorbed inside the thyroid cells for TH release, (b) which enzymes facilitate the release of TH from thyroglobulin? where?

T4

What is the most abundant form of TH?

They bind to transport proteins in blood (mainly the thyroxine-binding globulin, TBG); because they are hydrophobic.

Do TH transport freely through the blood or bound to proteins? Why?

Increase the basal metabolic rate (BMR) and heat production (=calorigenic effect). Through the increase of Na+/K+ ATPase.

What is the effect of TH on metabolism and temperature, and which protein do they upregulate the expression of for this purpose?

Increase β-receptors, heart rate, stroke volume, cardiac output, and contractility. Because they exert a permissive effect on catecholamines (so increase their effects).

What are the effects of TH on the heart, and why?

Increase the oxygen consumption, respiration rate, through stimulation of respiratory centers, to increase oxygenation ensuring adequate blood and oxygen supply to meat the increased metabolic demand

What are the effects of TH on respiration, and why?

It affects fertility, ovulation, and menstruation; promote development of type II muscle fibers (fast-twitch, capable of fast and powerful contractions); needed for the maturation of brain, also affect mood; TH act synergistically with GH to stimulate bone growth

What are the effects of TH on the reproductive system, skeletal muscle, brain, and bone?

Hypothyroidism (=underactive thyroid gland) and hyperthyroidism (=overactive thyroid). (b) Hypothyroidism.

(a) What are the two main thyroid disorders? (b) If the thyroid gland is not producing enough hormone, how is this classified—hypo- or hyperthyroidism?

Autoimmune disorder that affects the thyroid gland. The immune system mistakenly attacks the thyroid tissue. The most common antibody associated with Hashimoto's is thyroid peroxidase antibody (TPO antibody). Thyroglobulin antibodies may also be present.

What is Hashimoto's disease?

Autoimmune disorder. In this case the body creates antibodies that mimic the effect of TSH and overstimulate the thyroid gland.

What is toxic goiter or Graves' disease?

Hypo-: hair loss, weight gain, muscle pain, and cold intolerance. Hyper-: heat intolerance, irritability and anxiety.

What are some symptoms of hypothyroidism and hyperthyroidism?

TSH high, T4 low - due to feedback loop mechanisms

In hypothyroidism, how are the TSH levels, and how are the T4 levels? why?

TSH low, T4 high- due to negative feedback loop mechanisms (high TH decrease the production of TRH and TSH)

In hyperthyroidism, how are the TSH levels, and how are the T4 levels? why?

(a) Parathyroid hormone. (b) Parathyroid gland. (c) regulates blood calcium levels; (d) hypocalcemia (low calcium in the blood)

(a) What does PTH stand for, and (b) where is PTH secreted? (c) What is the main role of PTH? (d) What stimulus releases PTH?

bone: increase of osteoclast activity, kidneys: increase calcium reabsorption from urine to the body, and increase vitamin D activation that will increase calcium absorption from food in the small intestine

What are the physiological responses of PTH concerning bone, kidneys, and intestines?

increase in calcium levels

What is the result in calcium levels after PTH action?