L6: Endocrine tissue Flashcards
What are the different way in which signalling molecules work?
Paracrine- Act on neighbouring cells, can travel short and intermediate distances, attract cells to an area
Autocrine- Act on themselves and other cells that are the same around them
Endocrine- Released into the blood stream and act on distant targets with the right receptor
What are the main organs that contain endocrine cells/tissue?
Pituitary gland → TSH, ACTH, FHS, LH, GH, MSH
Thyroid gland → T4 and T3, calcitonin
Parathyroid gland → PTH
Adrenal gland → corticosteroids (glucocorticoids, mineralocorticoids), androgens, oestrogen, progestin
Pancreas → endocrine portion- insulin and glucagon (beta and alpha cells respectively)
What are the different types of hormones?
Glycoproteins (peptide hormones) - made in advance
Steroid hormones - made on demand
Amino acid derived hormones - made in advance
- Catecholamines
- Thyroid hormones
What are the central organs in the endocrine system?
Hypothalamus and pituitary gland
Control all of the other major endocrine organs
What does the hypothalamus control?
Homeostasis
- Thermoregulation
- Plasma osmolality
- Heart rate, BP
- Feeding, satiety, regulation of gastrointestinal tract
- Circadian rhythms, wakefulness, sleep
- Stimuli from the autonomic nervous system
- Emotion, sexual behaviour, mood
- Lactation
What does the hypothalamus produce?
Acts on two different parts of the pituitary gland in different ways
Posterior pituitary- nerves interact with it causing the release of vasopressin (ADH) and oxytocin
Anterior pituitary- six hormones are released, travel via the hypothalamo-hypophyseal portal system to the anterior pituitary
What is a portal system?
Differs from normal circulation
Blood passes through two sets of smaller vessels before returning to the heart
Blood from one set of capillaries gathers in a portal vessel/vein which then branches into a second capillary network
What type of secretion happens at the hypothalmus/pituitary axis?
Subject to constitutive and regulated merocrine secretion
Always a small concentration of these hormones in the blood
Describe the location and anatomy of the thyroid gland?
Situation anterior to the trachea
Below the cricoid cartilage
C3/4
Butterfly shaped
- Two lobes connected by an isthmus
Products are stored extracellularly in follicles that are lined with simple cuboidal epithelial cells
Parafollicular cells - adjacent to thyroid follicles
What hormones are produced by the thyroid gland?
Produces Thyroxine (T4) and triiodothyronine (T3) in response to TSH secretion from the AP Parafollicular cells → calcitonin in response to Ca2+ levels
How is thyroid hormone release controlled?
TRH released from hypothalamus in response to low T3 and T4 levels
Acts on AP to released TSH
TSH acts on the thyroid gland causing T3 and T4 to be released
Negative feedback→ increased levels of T3 and T4 are detected by the hypothalamus which then stops releasing TRH
What are some conditions linked to the thyroid?
Hyperthyroidism, High T3 and T4 → caused by Graves Disease, toxic multinodular goitre, drugs, excessive T3/T4 therapy etc.
Hypothyroidism, Low T3 and T4→ Hashimotos Diseas, failure of thyroid gland, TSH/TRH deficiency, inadequate iodine etc…
Disregulation between T3/T4 levels and TSH release
How does Grave’s disease come about?
Hyperthyroidism
High T3 and T4
Low TSH
Problem→ Thyroid stimulating immunoglobulin (TSI)
TSI continuously stimulates thyroid hormones secreton outside of negative control
How does Hashimoto’s disease come about?
Hypothyroidism
Low T3 and T4
High TSH
Autoimmune disease results in destruction of thyroid follicles
What is the function of the parafollicular cells?
Neuroendocrine cells
Produce peptide hormone- thyrocalcitonin (cleaved to calcitonin)
Control Ca2+ levels
Inhibit osteoclast activity and the release of Ca2+ from bone
Minor function: inhibits renal Ca2+ and phosphate reabsorption in the tubular cells
Describe the structure of the parathyroid gland?
NO INPUT FROM THE HYPOTHALAMUS, ALL BASED ON CA2+ PLASMA LEVELS
4 small lobes on the posterior surface of the thyroid galnd
Composed of masses and cords supported by reticular fibres and close to capillaries
Two cell types:
1- Chief cells/ principle cells - release PTH
2- Oxyphil cells- uncertain function
What does parathyroid gland do?
Monitors plasma calcium concentration
Calcium low→ PTH released
Causes :
1. Bone resorption
2. Absorb more from GIT
Classical negative feedback loop; Calcium reaches set point, parathyroid glands stop making PTH
Negative feedback of Ca2+ levels in blood directly on parathyroid gland
What type of gland is the adrenal gland?
Mixed endocrine and neuroendocrine tissue Adrenal medulla (inner)→ composed of chromaffin cells which are modified neurones (post synaptic neurones) Adrenal cortex (outer)→ endocrine part
What is released from the adrenal medulla?
Adrenaline and noradrenaline
What is released from the adrenal cortex?
Three layers release different things
- Outer: Zona Glomerulosa, aldosterone
- Middle: Zona Fasciculata, glucocorticoids (cortisone/cortisol)
- Inner: Zona Reticularis, andorgen precursors
GFR : Salt, sugar, sex : deeper you get, sweeter it gets
What is the main function of the adrenal gland?
Stress repsonse
Define stress response?
Stress: state of real or perceived threat to homeostasis
Response: Maintenance of homeostasis in the presence of aversive stimuli (stressors), requires activation of a complex range of responses involving the endocrine, nervous, and immune systems
What are the behavioural and physiological changes that occur as a result of stress?
Behavioural
- Increased awareness
- Improved cognition
- Euphoria
- Enhanced analgesai
Physiological
- Increased cardiovascular tone
- Increased respiratory rate
- Increased intermediate metabolism
- Decreased vegetative functions
How does the adrenal gland respond to stress?
Short term response and more prolonged response
What is the short term stress repsonse?
Short term:
- Hypothalamus send nerve impulse to spinal cord
- Preganglionic sympathetic nerve fibres to adrenal medulla
- Adrenal medulla release catecholamines; adrenaline and NA
- Adrenaline and NA→
- Increase HR
- Increase BP
- Glycogen converted to glucose in liver and released into blood
- Dilation of bronchioles
- Changes in flow pattern
- Increased metabolic rate
What is the prolonged stress response?
Prolonged:
1. Hypothalamus release CRH (corticotropin releasing hormone)
2. Acts on anterior pituitary
3. AP release ACTH into blood
4. Acts on adrenal cortex→
- Mineralocorticoids
→ Retention of Na+ and H20 by the kidneys
→ Increased blood volume and blood pressure
- Glucocorticoids
→ Proteins and fat converted to glucose and metabolised for energy
→ Increased blood sugar
→ Suppression of immune system
Where is the pancreas located?
15cm long behind the stomach
Head at duodenum, body and tail towards the spleen
What is the structure of the pancreas?
Endocrine and exocrine part
Endocrine→ Islets of Langerhans
Exocrine→ Acinar glands grouped into lobules containing zymogen granules, connected through numerous intecalated ducts to pancreatic duct
What are the major cells in the Islet of Langerhans? What do they produce?
Major
Alpha→ Glucagon
Beta→ Insulin
Delta→ Somatostatin
What are the minor endocrine cells of the pancreas? What do they produce?
Minor PP cells→ pancreatic polypeptide D1 cells→ vasoactive intestinal peptide Enterochromaffin cells→ secretin, motilin and substance P E cells→ Ghrelin G cells→ Gastrin
What is the exocrine function of the pancreas?
Produce digestive enzymes
e.g. lipase, amylase, ribonucleases, deoxyribonuclease, gelatinase, elastase, trypsiogen, chymotrypsinogen
Secretes bicarbonate ions, alkaline fluid, buffers and neutralises acidic chyme
