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Questions and Answers
Which cells in the pancreatic islets secrete glucagon?
What condition is associated with excessive secretion of growth hormone?
Which gland is primarily involved in the regulation of insulin secretion?
What is the primary hormone released by Delta cells in the pancreas?
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Which of the following conditions is associated with the adrenal gland and results in excess aldosterone?
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What is the primary function of the thyroid gland?
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Which hormone is released by the anterior pituitary gland that stimulates the thyroid gland?
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Where is the thyroid gland located in relation to the trachea?
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Which substance is essential for the synthesis of thyroid hormones?
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What type of hormones does the hypothalamus release to influence the anterior pituitary?
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What is the primary function of the endocrine system?
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Which type of hormone cannot cross the cell membrane?
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What kind of feedback mechanism can hormones use to regulate body functions?
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Which of the following is an example of a paracrine signaling mechanism?
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What is the role of receptors in hormone activity?
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Which hormone class can pass through the cell membrane?
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What type of hormone communication acts on the same cell that produced it?
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Which of the following signals primarily travels through the circulatory system?
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What type of hormones act on neighboring cells?
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Where do lipid-soluble hormones bind to exert their effects?
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Which part of the endocrine system is considered the central regulatory component?
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What is the primary function of the anterior pituitary gland?
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What is the connection between the hypothalamus and the posterior pituitary gland?
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Which artery provides blood supply to the anterior pituitary gland?
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What hormone is released by the posterior pituitary and acts on the collecting ducts of the kidney?
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Which structure lies directly superior to the anterior pituitary and could be affected by pituitary gland tumors?
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What does aldosterone primarily regulate in the body?
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What triggers the secretion of renin in the kidneys?
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Which hormone is predominantly released during the fight-or-flight response?
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What percentage of catecholamines released during stress is norepinephrine?
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Which statements are true about the function of cortisol? (Select all that apply)
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What is the primary role of the pancreas as an endocrine gland?
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What type of artery supplies the uncinate process and head of the pancreas?
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What effect does angiotensin II have on the adrenal cortex?
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Study Notes
Endocrine system
- The endocrine system is responsible for maintaining homeostasis in the body.
- Hormones are chemical messengers that enable cells to communicate and achieve homeostasis.
- Homeostasis is the maintenance of a stable internal state for optimal functioning.
Endocrine system - functions
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Short-term functions:
- Blood pressure
- pH
- Respiration
-
Long-term functions:
- Growth
- Reproduction
- Metabolism
Hormones
- Hormones are released in response to a stimulus/signal.
- The action of the hormone restores equilibrium directly or indirectly.
Hormone Activity
- Hormones only affect specific target tissues with specific receptors.
- Water-soluble hormones have receptors on the cell surface.
- Lipid-soluble hormones have intracellular receptors.
- Receptors are constantly synthesized and broken down.
- Hormone activity relies on positive and negative feedback.
Hormone types
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Ways cells communicate using hormones:
- Endocrine: transmitted by the circulatory system (distant)
- Paracrine: produced by endocrine tissue and transmitted in extracellular fluid (local)
- Autocrine: act on the same cell
- Neuroendocrine: secreted from nerve cells
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Classes of hormones:
- Polypeptides: cannot pass through cell membranes (water-soluble)
- Steroids: can cross the cell membrane (lipid-soluble)
- Modified amino acids: can cross the cell membrane
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Types of hormones:
- Circulating: circulate in blood throughout the body (e.g., insulin).
-
Local hormones: act locally
- Paracrine: act on neighboring cells.
- Autocrine: act on the same cell that secreted them (e.g., interleukin-1).
Mechanisms of Hormone action
- Lipid-soluble hormones: bind to receptors inside target cells.
-
Water-soluble hormones: bind to receptors on the plasma membrane.
- Activates a second messenger system.
- Amplifies the original small signal.
Endocrine System Organs
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Hypothalamic-pituitary axis: the central regulatory component of the endocrine system.
- Hypothalamus is sensitive to neural and hormonal stimuli.
- Hypothalamus integrates stimuli and sends signals to the pituitary.
Hypothalamus
- Located at the base of the forebrain (diencephalon).
- Structure: pituitary stalk continuous with the posterior pituitary gland.
- Functions: receives inputs from the circulation (temperature, blood sugar, hormones) and neuronal inputs (autonomic and emotional). Based on these inputs it secretes hormones that target the anterior or posterior pituitary.
- Blood supply: superior hypophyseal artery, hypophyseal portal vessels to the anterior pituitary (high hormone concentration). Drained by the cavernous sinus.
Anterior Pituitary
- Location: lies in the sella turcica. The optic chiasma lies directly superior to it (pituitary gland tumours can cause visual changes due to compression).
- Function: releases hormones after receiving a stimulus from the hypothalamus. These hormones act on other endocrine organs.
- Blood supply: superior hypophyseal artery, hypophyseal portal vessels from the hypothalamus. Drained by the cavernous sinus (hormones enter circulation).
Posterior Pituitary
- Location: posterior to the anterior pituitary.
- Structure: connected to the hypothalamus by the pituitary stalk.
- Function: releases ADH (acts on the collecting ducts of the kidney) and oxytocin.
- Blood supply: inferior hypophyseal artery. Drained by the cavernous sinus (hormones enter circulation).
- It does not synthesize the hormones it releases.
Hypothalamus - Anterior Pituitary - Posterior Pituitary link
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Hypothalamus:
- GHRH
- GHRIH
- CRH
- GnRH
- TRH
- PRF
- Dopamine
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Posterior Pituitary:
- ADH
- Oxytocin
-
Anterior Pituitary:
- GH
- TSH
- ACTH
- LH
- FSH
- PRL
Thyroid Gland
- Location: anterior to the trachea on the lower aspect of the neck.
- Structure: butterfly-shaped, two lobes 5cm long, connected by the isthmus. Attached to the trachea (when a patient swallows the thyroid gland moves upwards).
- Function: releases calcitonin (calcium homeostasis), T3, and T4 which regulate the metabolism of most cells. It stores iodine (needed to make thyroid hormones) and thyroglobin (used for thyroid hormone synthesis).
- Regulation: the anterior pituitary gland (TSH).
- Blood supply: superior and inferior thyroid arteries (thyroid ima artery supplies the isthmus in some people) and drained by the superior and middle thyroid veins into the internal jugular vein and the inferior thyroid veins into the brachiocephalic vein.
Adrenal glands
- Location: superior to the kidneys, embedded in fat.
- Structure: made up of two parts, the cortex (outer layer) and medulla (inner layer).
- Function: releases hormones that regulate metabolism, stress response, and electrolyte balance.
- Regulation: the anterior pituitary gland (ACTH).
- Blood supply: right adrenal vein drains into inferior vena cava, whereas left adrenal vein drains into left renal vein.
Adrenal Cortex
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Mineralocorticoids (e.g., Aldosterone):
- Regulate the homeostasis of potassium (K+) and sodium (Na+) ions.
- Regulation of blood pressure.
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Glucocorticoids (e.g., Cortisol):
- Most abundant and released in response to stress.
- Effects:
- Protein breakdown: increase the rate of protein breakdown in muscle fibers liberating amino acids for the synthesis of new proteins.
- Glucose formation: liver cells convert amino acids or lactic acid into glucose.
- Lipolysis: breakdown of triglycerides and release of fatty acids from adipose tissue for energy.
- Resistance to stress: provides substrates for energy production (makes the body ready to react).
- Anti-inflammatory effects: inhibits inflammatory response by suppressing the immune function (used in the treatment of inflammatory conditions).
Adrenal Medulla
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Catecholamines:
- Epinephrine/Adrenaline: 80%
- Norepinephrine/Noradrenaline: 20%
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Fight or flight response:
- Increases heart rate.
- Directs more blood to the heart, liver, and muscles.
- Dilates airways.
Pancreas
- Location: retroperitoneal gland, posterior and inferior to the stomach.
- Structure: Islets of Langerhans containing four types of cells.
- Function: endocrine (into the bloodstream), exocrine (via ducts).
- Blood supply: body and tail are supplied by branches of the splenic artery. The uncinate and head are supplied by the pancreaticoduodenal artery.
Pancreas - endocrine function
- Each pancreatic islet includes four types of hormone-secreting cells:
- Alpha or α cells: 17% of cells. Secretes glucagon which raises blood glucose.
- Beta or β cells: 70% of cells. Secretes insulin which lowers blood glucose.
- Delta or δ cells: 7% of cells. Secretes somatostatin which inhibits both glucagon and insulin release.
- F or pp cells: the remaining cells. Secretes pancreatic polypeptide which inhibits somatostatin and digestive enzymes.
Final Quiz
-
Conditions and their corresponding glands:
- Addisons disease: Adrenal insufficiency.
- Hypothyroidism: Thyroid gland, low T3 and T4.
- Cushing disease: Adrenal – raised cortisol (or too much steroid medication).
- Diabetes: Pancreas.
- Conns disease: Adrenal – too much aldosterone.
- Graves disease: Thyroid – autoimmune, raised T3 and T4.
- Acromegaly: Pituitary – too much. growth hormone.
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Description
Explore the fundamental concepts of the endocrine system, including its functions in maintaining homeostasis and the role of hormones as chemical messengers. This quiz covers both short-term and long-term functions, types of hormones, and their specific actions on target tissues.
