L34, 35 ENDOCRINOLOGY Flashcards
L34: Endocrine system
What is the function of the endocrine system?
It regulates homeostasis by secreting hormones that influence metabolism, growth, and organ function
L34: Endocrine system
How do endocrine glands differ from exocrine glands?
Endocrine glands are ductless and release hormones directly into the bloodstream, while exocrine glands use ducts to transport secretions.
L34: Endocrine system
Where is the hypothalamus located?
At the base of the brain, just above the pituitary gland.
L34: Endocrine system
What are the main functions of the hypothalamus?
It regulates body temperature, thirst, hunger, sleep, blood pressure, and hormone secretion.
L34: Endocrine system
Where is the pituitary gland located?
It sits in the sella turcica (a cavity in the sphenoid bone) and is connected to the hypothalamus by the infundibular stalk.
L34: Endocrine system
What are the two parts of the pituitary gland?
Anterior pituitary (adenohypophysis) and posterior pituitary (neurohypophysis).
L34: Endocrine system
What is the embryological origin of the anterior pituitary?
It develops from pharyngeal tissue.
L34: Endocrine system
Name six hormones secreted by the anterior pituitary.
- ACTH (Adrenocorticotropic hormone) – Stimulates the adrenal cortex.
- TSH (Thyroid-stimulating hormone) – Stimulates the thyroid.
- LH (Luteinising hormone) – Regulates ovulation and testosterone production.
- FSH (Follicle-stimulating hormone) – Stimulates egg and sperm production.
- PRL (Prolactin) – Stimulates milk production.
- GH (Growth hormone) – Stimulates cell growth and metabolism.
L34: Endocrine system
What is the embryological origin of the posterior pituitary?
It develops from neural tissue.
L34: Endocrine system
What hormones are stored and released by the posterior pituitary?
Oxytocin – Stimulates uterine contractions and milk ejection.
Antidiuretic hormone (ADH) – Regulates water retention in the kidneys.
L34: Endocrine system
How are these hormones transported to the posterior pituitary?
Via the hypothalamohypophyseal tract (nerve axons).
L34: Endocrine system
What system connects the hypothalamus to the anterior pituitary?
The hypothalamohypophyseal portal system.
L34: Endocrine system
How does negative feedback work in hormone regulation?
High hormone levels signal the hypothalamus to reduce hormone production, preventing excess secretion.
L34: Endocrine system
Where is the thyroid gland located?
In the anterior neck, in front of the trachea, spanning C5 to T1.
L34: Endocrine system
What are the two main thyroid hormones and their functions?
- Thyroxine (T4) – Regulates metabolism.
- Triiodothyronine (T3) – Active form, increases basal metabolic rate.
L34: Endocrine system
What hormone lowers blood calcium levels, and how?
Calcitonin – It promotes calcium storage in bones.
L34: Endocrine system
How many parathyroid glands are there, and where are they located?
Four glands (two superior, two inferior) on the posterior surface of the thyroid.
L34: Endocrine system
What hormone does the parathyroid gland secrete, and what is its function?
Parathyroid hormone (PTH) – Increases blood calcium levels by stimulating bone resorption and enhancing kidney and intestinal calcium absorption.
L34: Endocrine system
Where are the adrenal glands located?
On the superior-medial aspect of the kidneys, at T11/T12 level.
L34: Endocrine system
Name the three layers of the adrenal cortex and the hormones they produce.
- Zona glomerulosa → Aldosterone (regulates water & salt balance).
- Zona fasciculata → Cortisol (regulates glucose metabolism, reduces inflammation).
- Zona reticularis → Androgens (precursors for sex hormones).
L34: Endocrine system
What does the adrenal medulla produce, and what is its function?
Adrenaline & noradrenaline → Initiate the sympathetic (fight-or-flight) response.
L34: Endocrine system
What are the two functions of the pancreas?
- Exocrine function → Secretes digestive enzymes into the duodenum.
- Endocrine function → Releases hormones into the bloodstream.
L34: Endocrine system
What are the four cell types in the Islets of Langerhans and their hormones?
- Alpha cells → Glucagon (raises blood glucose).
- Beta cells → Insulin (lowers blood glucose).
- Delta cells → Somatostatin (inhibits insulin & glucagon).
- PP cells → Pancreatic polypeptide (regulates pancreatic enzyme secretion).
L34: Endocrine system
Where are the ovaries and testes located?
Ovaries → Pelvic cavity.
Testes → Scrotum (outside the body cavity).
L34: Endocrine system
What hormones do the ovaries and testes secrete?
Ovaries → Oestrogen & progesterone (regulate the menstrual cycle & pregnancy).
Testes → Testosterone (develops male secondary sexual characteristics).
L34: Endocrine system
How does the hypothalamus communicate with the anterior and posterior pituitary?
Anterior pituitary → Hypothalamohypophyseal portal system.
Posterior pituitary → Hypothalamohypophyseal tract (nerve axons).
L34: Endocrine system
What are hormones?
Chemical messengers secreted by endocrine glands that regulate bodily functions.
L34: Endocrine system
What is the difference between endocrine and nervous system signalling?
Endocrine system → Uses hormones, slower but longer-lasting effects.
Nervous system → Uses electrical impulses, faster but short-lived responses.
L34: Endocrine system
What are the three major types of hormones?
- Peptide hormones – Made of amino acids (e.g., insulin, ADH).
- Steroid hormones – Derived from cholesterol (e.g., cortisol, oestrogen).
- Amino acid-derived hormones – Modified amino acids (e.g., adrenaline, thyroxine).
L34: Endocrine system
How do hormones travel in the body?
Through the bloodstream, binding to target cells via specific receptors.
L34: Endocrine system
What are releasing hormones from the hypothalamus?
Hormones that stimulate the anterior pituitary to release specific hormones, e.g.:
TRH (Thyrotropin-releasing hormone) → Stimulates TSH release.
CRH (Corticotropin-releasing hormone) → Stimulates ACTH release.
GnRH (Gonadotropin-releasing hormone) → Stimulates FSH & LH release.
L34: Endocrine system
What are inhibiting hormones from the hypothalamus?
Hormones that prevent the anterior pituitary from releasing specific hormones, e.g.:
Somatostatin → Inhibits GH & TSH release.
Dopamine (Prolactin-inhibiting hormone, PIH) → Inhibits prolactin release.
L34: Endocrine system
How is the anterior pituitary different from the posterior pituitary?
Anterior pituitary → Produces its own hormones, regulated by the hypothalamus.
Posterior pituitary → Stores & releases hypothalamic hormones (ADH & oxytocin).
L34: Endocrine system
What is the function of Melanocyte-Stimulating Hormone (MSH)?
Controls melanin production in the skin and may influence appetite & sexual function.
L34: Endocrine system
What mineral is required for thyroid hormone production?
Iodine – Found in iodised salt and seafood.
L34: Endocrine system
What condition results from iodine deficiency?
Goitre – An enlarged thyroid due to insufficient T3 & T4 production.
L34: Endocrine system
What is the difference between hyperthyroidism and hypothyroidism?
Hyperthyroidism → Excess thyroid hormones → Weight loss, rapid heartbeat, heat intolerance.
Hypothyroidism → Insufficient thyroid hormones → Weight gain, fatigue, cold intolerance.
L34: Endocrine system
What is the antagonist hormone to calcitonin?
Parathyroid Hormone (PTH) – Raises blood calcium by increasing bone breakdown.
L34: Endocrine system
What are the three zones of the adrenal cortex and their primary hormones?
- Zona Glomerulosa → Aldosterone (Water & sodium retention).
- Zona Fasciculata → Cortisol (Glucose metabolism, stress response).
- Zona Reticularis → Androgens (Sex hormone precursors).
L34: Endocrine system
What is Cushing’s syndrome?
Excess cortisol production → Causes weight gain, moon face, muscle weakness, high blood sugar.
L34: Endocrine system
What is Addison’s disease?
Adrenal insufficiency → Causes low cortisol & aldosterone levels, fatigue, low blood pressure.
L34: Endocrine system
How does aldosterone regulate blood pressure?
It increases sodium retention, which increases water retention, raising blood pressure.
L34: Endocrine system
What is the role of prolactin?
It stimulates milk production in breastfeeding women.
L34: Endocrine system
Which hormone is responsible for contractions during childbirth?
Oxytocin
L35: Hormone Action
What are the three superfamilies of hormones?
Peptide hormones, steroid hormones, and amino acid derivatives.
L35: Hormone Action
Give an example of each hormone superfamily.
Peptide hormone: Insulin
Steroid hormone: Cortisol
Amino acid derivative: Epinephrine/Adrenaline
L35: Hormone Action
What are the key properties of hormone receptors?
- High specificity and affinity
- Present in specific tissues
- Limited binding sites (saturable)
- Reversible binding
- Must mediate a biological response
L35: Hormone Action
What are the two types of hormone receptors?
Cell surface receptors (for hydrophilic hormones)
Intracellular receptors (for hydrophobic hormones)
L35: Hormone Action
What are the two main types of cell surface receptors?
Tyrosine Kinase Receptors
G-Protein Coupled Receptors (GPCRs)
L35: Hormone Action
How do Tyrosine Kinase Receptors function?
Transfer phosphate from ATP to tyrosine residues
Activation leads to phosphorylation and a conformational change
L35: Hormone Action
What are the two types of Tyrosine Kinase Receptor activation?
Intrinsic (e.g., Insulin Receptor)
Recruited (e.g., Growth Hormone Receptor)
L35: Hormone Action
What are the three main signalling pathways of Epidermal Growth Factor Receptor (EGFR)?
Ras pathway
Phosphatidylinositide 3-kinase (PI 3-kinase)
JAK-STAT pathway
L35: Hormone Action
How is Ras activated in signal transduction?
GDP-bound Ras is inactive
Ligand binding activates Ras via GRB and SOS proteins
GDP is exchanged for GTP, leading to downstream effects
L35: Hormone Action
What do GPCRs mediate?
Second messenger activation
L35: Hormone Action
What are three common second messengers in GPCR signalling?
Cyclic AMP (cAMP)
Inositol 1,4,5-triphosphate (IP₃)
Diacylglycerol (DAG)
L35: Hormone Action
What is the structure of a G-protein?
Composed of α, β, and γ subunits (α subunit is key for signalling)
L35: Hormone Action
Describe the GPCR signalling mechanism.
Hormone binds to receptor
Conformational change occurs
GDP on α-subunit is replaced with GTP
α-subunit dissociates and activates downstream messengers
Cellular response occurs
L35: Hormone Action
What is the role of DAG and Ca²⁺ in GPCR signalling?
DAG activates Protein Kinase C (PKC)
IP₃ releases Ca²⁺, which activates calmodulin and kinases
L35: Hormone Action
How do peptide hormone receptors function?
They use second messengers like cAMP and IP₃ to change cell function.
L35: Hormone Action
How do steroid hormones differ from peptide hormones in their mechanism?
Peptide hormones use cell surface receptors and second messengers
Steroid hormones use intracellular receptors to directly regulate gene transcription
L35: Hormone Action
How are steroid hormones transported in the blood?
Bound to plasma protein carriers; only unbound steroids diffuse into target cells.
L35: Hormone Action
What are the two types of steroid receptors?
Cytoplasmic receptors – activated steroids translocate to the nucleus
Nuclear receptors – already in the nucleus and activated upon ligand binding
L35: Hormone Action
Describe the process of steroid receptor activation.
- Steroid hormone diffuses into the cell
- Receptor-hormone complex forms
- Complex binds to DNA
- Gene transcription is altered
- mRNA is translated into proteins
L35: Hormone Action
What is the difference between Type I and Type II nuclear receptors?
Type I (homodimers): In cytoplasm, translocates to DNA upon activation (e.g., glucocorticoid receptor)
Type II (heterodimers): Always bound to DNA, activated by ligand binding (e.g., Vitamin D receptor)
What are the five regions of nuclear receptor structure?
A/B Region – Transcriptional activation
C Region – DNA-binding domain (zinc fingers)
D Region – Hinge region (allows conformational change)
E Region – Ligand-binding domain
F Region – Variable domain
L35: Hormone Action
What are the three types of Hormone Response Elements (HREs)?
Palindromic HREs (AGAACA ——- TGTTCT)
Direct Repeat HREs (AGGTCA ——- AGGTCA)
Inverted Palindrome HREs (AGAACA ——- TCTTGT)
L35: Hormone Action
What enables nuclear receptors to bind DNA?
Zinc finger domains
L35: Hormone Action
What is the role of the P-box in nuclear receptors?
Binds to DNA to enable transcription.
L35: Hormone Action
Final summary of hormone mechanisms?
Peptide hormones use surface receptors and second messengers
Steroid hormones use intracellular receptors to regulate transcription
Tyrosine Kinase Receptors and GPCRs are key surface receptors
Nuclear receptors act as transcription factors, altering gene expression
