Week 1 - Endocrine Organs & Their Hormones

Question 1

What is the role of regulatory hypothalamic hormones on the pituitary gland

Answer 1

Hypothalamic-Pituitary Axis (HPA) Communication
- hypothalamus controls hormone release (from anterior pituitary gland) by secreting regulatory hormones
- hormones reach target cells of anterior pituitary via hypothalamic-pituitary portal system
- hormones are released at axon terminals then diffuse into capillary network of posterior lobe to enter posterior pituitary gland (NOT through portal system)

Regulatory hormones can be releasing or inhibiting
Hypothalamus ISN’T an endocrine
- exerts hormonal mechanism of release from pituitary gland

HPA = control centre of endocrine system + feedback control system

Hormones are released in pulsatile fashion

Question 2

Name and list the functions of the main hormones of the posterior pituitary gland

Answer 2

Gland stores + releases oxytocin and anti-diuretic hormone (ADH)

Hormones:
1. Oxytocin - essential in anxiety, maternal bonding, during pregnancy + labour
- acts on uterine muscles, mammary glands
2. Vasopressin (ADH) - reduces the removal of water + salt (Na) from body by ↑ reabsorption of water = ↓ urine output
- acts on kidney tubules

Question 3

Name and list the functions of the main hormones of the anterior pituitary gland

Answer 3

Anterior pituitary gland = most important for release of hormones

Hormones:
1. FSH and LH in women - determines menstrual cycle
2. FSH and LH in men - determines production of sperm and seminal fluid
3. Endorphins - act on opiate receptors to give pain relief
4. ACTH - adrenocorticotrophic hormone acts on adrenal cortex
5. TSH (thyroid stimulating hormone) - acts on thyroid gland

Question 4

Name and list the functions of the main hormones of the pineal gland

Answer 4

• pineal gland (pinealocytes) secretes melatonin
  - melatonin secretion is inhibited by light + permitted in darkness

Melatonin:
Regulates circadian rhythm
Influences sleepiness, wakefulness, appetite + body temp.

Question 5

Discuss how the structure of the adrenal cortex relates to steroid hormone production

Answer 5

Diff. parts of adrenal gland release diff. hormones e.g.
1. Aldosterone (mineralocorticoid - MC)
2. Cortisol (glucocorticoid - GC)
3. Androgens
4. Adrenaline (released by medulla)

Glucocorticoid and mineralocorticoid are both classed as Corticosteroids
- steroid hormones are derived from cholesterol bound to globulins
- bind to G protein-coupled receptors in plasma membrane
- this activates kinases, once inside cell GC or MC will bind to its specific receptor

Question 6

Describe the major physiological effects of cortisol (a glucocorticoid - GC)

Answer 6

1. Controls carbohydrate and protein metabolism
2. Controls metabolic effects
   - high levels GC can ↓ sensitivity of tissues to insulin
   - cortisol can ↑ gluconeogenesis (glucose synthesis) from a.acids (in liver)
   - ↑ storage of glycogen in liver + muscles
   - ↓ uptake + use of glucose in muscles / adipose tissues
3. Have anti-inflammatory effects
4. Have immunosuppressive effects
   - suppresses immune system = ↓ T cells + antibodies activation / production
   - helps with rejection in transplanted tissues / organs

Cortisol can be related due to stress, trauma, infection, surgery, disease etc.

Question 7

How does Cortisol exhibit anti-inflammatory effects

Answer 7

Supresses T cells and antibody activation

• Secreted cortisol stabilises lysosomal membranes + ↓ release of proteolytic enzymes
• ↓ permeability of capillaries = ↓ oedema
• Secreted cortisol ↓ migration of WBCs = ↓ prostaglandins, leukotrienes + other chemical mediators to inflamed area

Question 8

Describe the major physiological effects of aldosterone (a mineralocorticoid)

Answer 8

• Controls water and electrolyte balance
  - causes ↑ H20 + Na reabsorption / retention
  - ↑ secretion of K+
• Controls Na+ and K+ channels
• Contributes to homeostasis of blood pressure

Diuretics e.g. spironolactone acts as a competitive inhibitor of MC receptors

Question 9

Describe the major physiological effects of androgens

Answer 9

• Involved in maturation + development during puberty

Question 10

How does negative feedback regulate hormones

Answer 10

1. Hypothalamus releases regulating hormones e.g. CRH which acts on anterior pituitary gland
2. Anterior pituitary gland releases hormone (e.g. ACTH) which acts on a target organ (e.g. adrenal cortex) causing a hormone to be released (e.g. CORT)

Negative Feedback:
1. Final hormone released from target organ will act on anterior pituitary gland + hypothalamus (e.g. stops secretion of CRH and ACTH)
- Used to keep hormone levels in blood within range