L6: Endocrine tissue

Question 1

What are the different way in which signalling molecules work?

Answer 1

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

Question 2

What are the main organs that contain endocrine cells/tissue?

Answer 2

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)

Question 3

What are the different types of hormones?

Answer 3

Glycoproteins (peptide hormones) - made in advance
Steroid hormones - made on demand
Amino acid derived hormones - made in advance
- Catecholamines
- Thyroid hormones

Question 4

What are the central organs in the endocrine system?

Answer 4

Hypothalamus and pituitary gland

Control all of the other major endocrine organs

Question 5

What does the hypothalamus control?

Answer 5

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

Question 6

What does the hypothalamus produce?

Answer 6

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

Question 7

What is a portal system?

Answer 7

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

Question 8

What type of secretion happens at the hypothalmus/pituitary axis?

Answer 8

Subject to constitutive and regulated merocrine secretion

Always a small concentration of these hormones in the blood

Question 9

Describe the location and anatomy of the thyroid gland?

Answer 9

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

Question 10

What hormones are produced by the thyroid gland?

Answer 10

Produces Thyroxine (T4) and triiodothyronine (T3) in response to TSH secretion from the AP
Parafollicular cells → calcitonin in response to Ca2+ levels

Question 11

How is thyroid hormone release controlled?

Answer 11

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

Question 12

What are some conditions linked to the thyroid?

Answer 12

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

Question 13

How does Grave’s disease come about?

Answer 13

Hyperthyroidism
High T3 and T4
Low TSH
Problem→ Thyroid stimulating immunoglobulin (TSI)
TSI continuously stimulates thyroid hormones secreton outside of negative control

Question 14

How does Hashimoto’s disease come about?

Answer 14

Hypothyroidism
Low T3 and T4
High TSH
Autoimmune disease results in destruction of thyroid follicles

Question 15

What is the function of the parafollicular cells?

Answer 15

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

Question 16

Describe the structure of the parathyroid gland?

Answer 16

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

Question 17

What does parathyroid gland do?

Answer 17

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

Question 18

What type of gland is the adrenal gland?

Answer 18

Mixed endocrine and neuroendocrine tissue 
Adrenal medulla (inner)→ composed of chromaffin cells which are modified neurones (post synaptic neurones)
Adrenal cortex (outer)→ endocrine part

Question 19

What is released from the adrenal medulla?

Answer 19

Adrenaline and noradrenaline

Question 20

What is released from the adrenal cortex?

Answer 20

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

Question 21

What is the main function of the adrenal gland?

Answer 21

Stress repsonse

Question 22

Define stress response?

Answer 22

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

Question 23

What are the behavioural and physiological changes that occur as a result of stress?

Answer 23

Behavioural

• Increased awareness
• Improved cognition
• Euphoria
• Enhanced analgesai

Physiological

• Increased cardiovascular tone
• Increased respiratory rate
• Increased intermediate metabolism
• Decreased vegetative functions

Question 24

How does the adrenal gland respond to stress?

Answer 24

Short term response and more prolonged response

Question 25

What is the short term stress repsonse?

Answer 25

Short term:

1. Hypothalamus send nerve impulse to spinal cord
2. Preganglionic sympathetic nerve fibres to adrenal medulla
3. Adrenal medulla release catecholamines; adrenaline and NA
4. 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

Question 26

What is the prolonged stress response?

Answer 26

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

Question 27

Where is the pancreas located?

Answer 27

15cm long behind the stomach

Head at duodenum, body and tail towards the spleen

Question 28

What is the structure of the pancreas?

Answer 28

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

Question 29

What are the major cells in the Islet of Langerhans? What do they produce?

Answer 29

Major
Alpha→ Glucagon
Beta→ Insulin
Delta→ Somatostatin

Question 30

What are the minor endocrine cells of the pancreas? What do they produce?

Answer 30

Minor 
PP cells→ pancreatic polypeptide 
D1 cells→ vasoactive intestinal peptide
Enterochromaffin cells→ secretin, motilin and substance P
E cells→ Ghrelin 
G cells→ Gastrin

Question 31

What is the exocrine function of the pancreas?

Answer 31

Produce digestive enzymes
e.g. lipase, amylase, ribonucleases, deoxyribonuclease, gelatinase, elastase, trypsiogen, chymotrypsinogen
Secretes bicarbonate ions, alkaline fluid, buffers and neutralises acidic chyme