Suger 2 Flashcards
What is the purpose of the endocrine system?
Allows for integration of whole body physiology & rapid adaptive changes
Allows communication between the different cells & tissues
Long term maintenance of metabolic environment
What are the 8 main endocrine organs?
Pituitary gland Thyroid gland Breast Adrenal gland Kidneys Ovaries Uterus Testes
What are the 2 main types of hormone?
Peptide
Steroid
How are peptides synthesised?
Preprohormone made at ribosomes
Cleaved to form pro hormone by proteolytic enzymes in RER
Stored in vesicles
Where are the receptors for peptide hormones found?
Cell surface membrane of target cell
How do peptide hormones work?
Initiating other reactions in the cell’s cytoplasm
Where are steroids produced?
Adrenal cortex
Gonads
What are the steroid hormones derived from?
Cholesterol
Where are the receptors for steroid hormones found?
Intracellular
How do steroid hormones work?
Alter target cell’s gene expression & protein synthesis to change function & secretion of the cell
How are each of the main hormones found in the blood plasma?
Peptides - unbound, fast acting
Steroid - bound to proteins, slow acting
What are amines a derivative of?
Amino acid tyrosine
What are some examples of an amine?
Thyroid hormones
Adrenaline
Noradrenaline
Dopamine
What is the posterior pituitary gland made up of?
Neural tissue - axons of neutrons & their supporting glia
Connected to hypothalamus by pituitary stalk
What 2 substances does the posterior pituitary release & where are they made?
Vasopressin - supraoptic nuclei of hypothalamus
Oxytocin - paraventricular nuclei
What is the role of vasopressin/ADH?
Reabsorption of water from CD of kidneys by stimulating insertion of AQP2 aquaporin channels into the luminal membrane of the epithelial cells
What is the role of oxytocin?
Expression of milk from glands of breasts to nipples & promotes onset of labour
What is the anterior pituitary gland made up of?
Glandular epithelial tissue
What are hypophysiotrophic hormones?
Hormones that control the secretion of anterior pituitary hormones (which control the secretion of a hormone from another endocrine gland)
Sequence of 3 hormones
Where does the anterior pituitary gland recieve its blood supply from?
Portal venous system from hypothalamus
What are the 6 main hormones that are secreted from the anterior pituitary?
FSH, follicle stimulating hormone LH, lutenising hormone GH, growth hormone, somatotrophin TSH, thyroid stimulating hormone, thyrotropin Prolactin ACTH, adrenocorticotrophin hormone
What are FSH & LH stimulated to be excreted by?
GnRH, gonadotrophin releasing hormone
What do FSH & LH do?
Stimulate gonads to release sex hormones
What is GH stimulated to be excreted by?
GHRH, growth hormone releasing hormone
What does GH do?
Stimulates release of a growth-promoting peptide hormone, insulin-like growth factor 1
What is TSH stimulated to be excreted by?
TRH from hypothalamus
What does TSH do?
Stimulates thyroid to secrete thyroxine & triiodothyronine
What is prolactin stimulated to be excreted by?
Naturally inhibited by dopamine
Levels of dopamine drop, secretion increases
What does prolactin do?
Stimulates milk production
Stimulates development of mammary glands
What is ACTH stimulated to be excreted by?
CRH, corticotrophin releasing hormone
What does ACTH do?
Stimulates adrenal cortex & its secretion of cortisol
What are the 2 lobes of the thyroid gland connected by & which cartilages do they sit in front of?
Isthmus
Tracheal cartilages 2-4
What is the blood supply to the thyroid gland?
Superior & inferior thyroid arteries
Why does the thyroid gland need a rich blood supply?
Uses iodine to make hormones
What is the thyroid gland histologically made up of?
Numerous follicles
Walls - follicular cells
Lumen - contains colloid, protein rich material
What does the thyroid gland produce?
Thyroxine, T4
Triiodothyronine, T3
What hormone does the thyroid gland respond to?
TSH from the anterior pituitary
How is iodine transported into a follicular cell?
- Large negatively charged iodine ions circulating in blood co-transported from interstitial fluid into cytoplasm of follicular cells with Na+
- Too large to diffuse out (iodine trapping), so diffuse down concentration gradient to luminal surface of follicular cell
How are the thyroid hormones initially formed?
- large amount of enzyme thyroglobulin in colloid
- iodine ions rapidly oxidised by enzyme thyroid peroxidase to form free iodine radicals
- attached to tyrosine, an amino acid in the structure of the thyroglobulin enzyme
- tyrosine & 1 iodine = moniodotyrosine (MIT)
- tyrosine & 2 iodines = diiodotyrosine (DIT)
What are T4 & T3 formed from?
T4 = DIT + DIT T3 = DIT + MIT
How are the hormones transported from the colloid?
Portions of luminal membrane of follicular cells engulf the thyroglobulin structures by endocytosis
Proteolytic enzymes in lysosomes release T3 & T4
What does enzyme deiodinase do in the target cells?
Converts T4 to T3
thyroid makes more T4 then T3
What are some of the things that thyroid hormones regulate?
Breathing HR Central & peripheral NS Body weight Muscle strength Menstrual cycles Body temperature Cholesterol levels ...
Do receptors have a higher affinity for T3 or T4?
T3
What are the 3 main cell types of the islets of Langerhans?
Beta cells
Alpha cells
Delta cells
What do beta cells secrete & in response to what?
Insulin
High blood glucose levels
What do alpha cells secrete & in response to what?
Glucagon
Low blood glucose levels
What do delta cells secrete & what does it do?
Pancreatic somatostatin
Inhibitory effect on release of insulin & glucagon
What is GH release inhibited by?
Somatostatin from hypothalamus
What does glucagon do? (3)
Increases blood glucose by:
- increasing hepatic output of glucose by increasing gluconeogenesis & glycogenolysis
- reducing peripheral uptake of glucose from the bloodstream
- stimulation of peripheral release of gluconeogenic precursors (e.g. glycerol, amino acids) through stimulation of lipolysis & muscle breakdown
What are the 2 phases of insulin release?
First - rapid, from vesicles
Second - slower, release as made
What are the 8 steps of insulin release?
1) increase in amount of glucose transported into beta cells through GLUT2 glucose transporter protein when increased glucose levels in blood
2) enters glycolytic pathway & ATP moves into cell
3) extra ATP binds to K+ channels on cell surface membrane of beta cell, closing channels
4) K+ stops flowing out of cell, membrane potential altered
5) voltage-gated Ca2+ channels open
6) Ca2+ flows in
7) causes conformational changes to SNARE proteins on membranes of vesicles that contain insulin
8) vesicles can now bind with cell surface membrane & release insulin into interstitial fluid
What are incretins?
Hormones released from the gut that stimulate the release of insulin
Why is insulin greater following oral consumption of glucose compared to intravenous glucose?
Incretins stimulate the release of insulin
What does insulin do? (3)
Decreases blood glucose by:
- suppression of hepatic glucose output, decreasing gluconeogenesis & glycogenolysis
- increase glucose upstake by insulin-sensitive tissues for glycogen & protein & fatty acid synthesis
- suppression of lipolysis & breakdown of muscle
How is insulin uptaken by cells? (4 steps)
1) binds to insulin receptors on cell surface membrane (as peptide hormone)
2) intracellular signalling cascades take place
3) vesicles in cytoplasm that store GLUT4 glucose channels are mobilised to the cell surface membrane
4) increased GLUT4 results in more glucose being taken up by the cells
What are the 2 phases of the menstrual cycle?
Follicular - first 14 days
Luteal - 14 days after ovulation
What does the rise of FSH cause?
Primordial follicles in the ovaries to begin to develop
What occurs as the follicles begin to develop?
Their granulosa cells begin to secrete oestrogen
What are the effects of oestrogen during the cycle? (2)
Negative feedback effect on anterior pituitary when low levels in first 10 days
Positive feedback effect on release of LH when levels increase