Module 5

Lecture 1: An Introduction to the Endocrine System

Endocrine System

Regulates organ function via hormones (slow response)

→ Hormones are released into the interstitial space
where they will reach the bloodstream or lymph

Nervous System

Regulates organ function via electrochemical impulses (fast response)

Importance of ES

• Growth & development

• Electrolyte, water, & nutrient homeostasis

• Cellular metabolism & energy production

• Body defences

• Reproduction

• Cell Function

Hormones

Chemical messengers, only effects targeted cells that possess specific protein receptors

Amino Acid based hormones

• Majority of hormones
  • Made of amino acids, peptide or proteins
  • Water soluble

Steroid hormones

• Made from cholesterol

• Created in the adrenal gland, gonads and placenta

• Lipid (fat) soluble

Factors effecting target cell activation

• Blood concentration of the hormone

• Number of receptors for that hormone

• Strength (affinity) of binding

Inhibition/Antagonism

One hormone blocks the action of
another

Synergism

Two hormones exert the same effect which is
amplified when combined

Permissiveness

Needs another hormone to exert its full
effects

Control mechanism

• Sleep light

• Stress

• Night work

• Fluctuating environment stimuli

• Night work

• Changes in longitude

• Prolonged bed rest

Onset

Almost immediate to hours-days
– Some hormones are inactive when secreted & must be activated in target cells

Duration

10 sec to several hours
– Effects can disappear rapidly or persist for hours

Hormonal blood levels selectively & precisely controlled

Blood concentration at any point in time determined by:
• rate of release
• speed of clearance (inactivation/removal) – sometimes by other hormones

Lecture 2: The hypothalamus, pituitary & pineal

Hypothalamus

• Send and receive endocrine and
  neural signal

• Used for food intake, body weight, sexual behaviour

Pituary gland

→ Secretres hormones

→ Anterior and Posterior

Posterior pituary gland

→ OXT and ADH

ADH

→ Inhibits urine production / conserves water

Arterioles: vasoconstriction but only when levels are high

Kidneys: reabsorb water (AQP2) → less urine produced

OXT

→ Stimulate contractions of the uterus in labour.

→ Stimulate the flow of breastmilk after childbirth.

Anterior pituitary gland

ACT, GH, FSH, LH, TSH, Prolactin

Prolactin

Breasts → Lactation

TSH

Thyroid gland → Thyroxine

FSH AND LH

Gonads → ovaries and testes

GH

Kidney, Muscle and bones → Growth and metabolism

ACTH

Adrenal gland → Corticosteroids

Diabetes insipidus

→ ADH Deficiency

→ Intense thirst, high urine output

Causes: Pituitary tumor or externally-caused damage to hypothalamus or posterior pituitary

Syndrome of inappropriate ADH secretion (SIADH)

→ ADH Hypersecretion

→ Fluid retention, headache, disorientation due to brain edema, weight gain, & ↓ blood solute
concentration

Causes: Meningitis, neurosurgery, hypothalamic injury, cancer, after general anesthesia, or other
drugs

Lecture 3: Thyroid and Parathyroid Glands Slides

Thyroid Hormone

Metabolic

Parafollicular cell

Produces Calcitonin, a hormone involved in calcium metabolism

Follicular cell

Produces Thyroxine (T4) and Triiodothyronine (T3)

Formation of thyroid hormones

1. Iodide trapping

2. Synthesis of thyroglobulin

3. Oxidation of iodide

4. Iodination of tyrosine

5. Coupling of T1 and T2

6. Pinocytosis and digestion of colloid

7. Secretion of thyroid hormones

8. Transport in the blood

Lecture 4: Adrenal Glands

Adrenal gland

• Cortex

• Medulla

Corticosteroids

Mineralocorticoids

Glucocorticoids

Gonadocorticoids

Catecholamines

Mineralocorticoids

→ Aldosterone

→ Controls mineral ions

Glucocorticoids

→ Cortisol

→ Controls metabolism through glucose

Gonadocorticoids

→ Andogens

→ Testoterone and estrogen

Catecholamines

→ Adrenaline & Noradrenaline

Lecture 5: The pancreas

Function of pancreas

• Endocrine

• Exocrine

Endocrine

Produces hormones involved in glycemic control

Exocrine

Produces enzymes that help to digest food, particularly protein (not discussed in this module)

Cells of pancreas

Alpha (A) cells - glucagon
Beta (B) cells - insulin
Delta (D) cells - somatostatin
F cells - pancreatic polypeptide