DSA Week 5: Endocrine System

Topic 1: Glands + Hormones

1. Glands:

• produce hormones in response to stimuli

• stimuli:

  • hormone signals

  • environmental signals

  • signals from nervous system

• specialised organs that produce + secrete hormones

2. Hormones:

• chemical substance secreted by glands

• in response to stimuli

• can be messengers to other glands

3. Receptors:

• proteins that bind with hormones to trigger a response

Glands in the human body:

1. Hypothalamus

   • controls growth, development, metabolism

   • regulate other glands by controlling the pituitary gland

2. Pituitary Gland:

   • “master gland”

   • anterior (produces + secretes): growth hormone, prolactin (milk), FSH (follicle stimulating hormone), LH (luteinising hormone), thyroid stimulating hormone (stimulates the thyroid gland), adrenocorticotropic hormone (stimulates adrenal gland)

   • posterior (secretes): oxytocin + ADH

3. Thyroid Gland:

   • produces thyroxine T4, Triiodothyronine T3

   • controls body’s basal metabolic rate

4. Parathyroid Gland:

   • produces parathyroid hormone

   • regulates calcium, magnesium + phosphate in the blood

5. Adrenal Gland:

   • produces cortisol + aldosterone (maintains electrolyte balance Na+/K+)

   • adrenaline + noradrenaline (fight/flight)

6. Pancreas

   • secretes insulin + glucagon

   • regulates blood sugar levels

7. Gonads

   • secretes estrogen + testosterone

   • controls growth of reproductive organs

Topic 2: Differences in Endocrine + Nervous System Signalling

Nervous: fast delivery, short lasting SHEIN

Endocrine: slow delivery, long lasting

Topic 3:

• hormone only affects “target cells” - target cells are target because of their receptors to the hormone:

  hormone can:

  • secretion

  • transport (opening/closing ion channels)

  • deactivation

  • synthetis

  • proliferation

3 TYPES OF STIMULI

1. Humoral stimuli

   • ion/nutrient levels in the blood

2. Neural stimuli

   • The hypothalamus controls the pituitary gland.

   • Hypothalamus tells the posterior pituitary to release ADH and oxytocin

   • Sympathetic nervous system controls the release of adrenaline + noradrenaline from the adrenal glands.

3. Hormonal stimuli

   1. hypothalamus secretes hormones

   2. causes the anterior pituitary gland secrete hormones

   3. causes other glands to secrete hormones

Topic 4: Factors that impact hormone activity

Topic 5: Chemical Structure of Hormones

2 Classes of hormones:

1. Amino acid based

   • includes proteins, peptides, amines

   • made from chains of amino acids

   • most hormones are amino acids

   • water soluble (blood carries it)

   • lipid insoluble (receptors must take it inside the cell)

2. Steroids (derived from cholesterol)

   • lipid soluble (must bind to a hormone carrier to be transported in the blood)

     • either a specialised hormone carrier or albumin (public transit)

   • receptors are inside the cytoplasm/nucleus

Lipid Based Hormone Signalling

• steroids are carried through the blood by a carrier

• when it reaches a target cell, it binds to a receptor

  • receptor changes shape

  • that causes chaperone to be released

  • receptor + hormone binds to a part of the DNA called “hormone response element”

  • causes activation of certain genes

  • causes protein production = reaction

• diffuses straight through the phospholipid bilayer

Amino acid Based Hormone Signalling

• Bind to receptors on the membrane that change shape and release GDP

• GDP is converted into GTP

• G protein activates when it binds to GTP

• G protein binds to and activates Adenylate Cyclase

• Adenylate Cyclase converts ATP into cAMP

• cAMP causes enzymes to create cellular response

Topic 6: Hypothalamus, Pituitary Gland + Thyroid Gland

Hypothalamus — anterior pituitary gland

1. Hormones are controlled when hypothalamic neurons secrete releasing and inhibiting hormones into the hypophyseal portal system, the blood vessels connecting the hypothalamus to the anterior pituitary.

2. Hypothalamic hormones travel through the hypophyseal portal system to the anterior pituitary where they stimulate or inhibit glandular cells to release hormones from the anterior pituitary.

3. Anterior pituitary hormones are secreted into the secondary capillary plexus, or blood vessels, for distribution throughout the body.

   

Hypothalamus — posterior pituitary gland

1. The posterior pituitary is controlled by hypothalamic neurons. Oxytocin is made primarily by the paraventricular neurons. Antidiuretic hormone (ADH) is made by the supraoptic neurons.

2. Oxytocin and ADH are transported along nerve axons through the hypothalamic hypophyseal tract to the posterior pituitary.

3. They are then stored in axon terminals in the posterior pituitary.

   
   

Hypothalamus — thyroid relationship

1. When thyroid hormone levels are low, the hypothalamus produces thyrotrophin releasing hormone or TRH.

2. TRH stimulates the anterior pituitary to produce thyroid stimulating hormone or TSH.

3. TSH signals the thyroid to increase production of its hormones.

4. When blood levels of thyroid hormones increase, they feedback to the hypothalamus and anterior pituitary gland causing a decrease in production of TRH and TSH, in a negative feedback loop, to maintain appropriate levels of thyroid hormones.