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203: The endocrine system > Introduction > Flashcards

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1

Peptide hormones
- Water solubility
- Oral activity
- Receptor activity

Very water soluble

Orally active- broken down my proteases (digestive enzymes in the mouth)

Receptors are membrane bound
- Requires membrane proteins to cross membrane
- Not lipid soluble

2

Peptide hormones
- Speed of action
- Plasma half life

Rapid speed of action
- Seconds, minutes

Short plasma half life
- Protease activity

3

Steroid/thyroid hormones
- Water solubility
- Oral activity
- Receptor activity

Not water soluble, but lipid soluble

Not orally activity

Binds to intracellular receptors
- Lipid soluble, can cross plasma membrane and nuclear membrane.

4

Steroid/thyroid hormones
- Transport
- Speed of action
- Plasma half life

Transported in the blood via plasma proteins
- Not water soluble

Mostly slow acting
- Hours, days.

Slow plasma half life
- Only active when unbound

5

Hormone definition [4]

- Chemical messenger released by a ductless gland

- Transported in the blood

- Acts on specific receptors on target tissues

- One hormone can affect multiple target tissues

6

Endocrinology

Physiology of glands and hormones

7

Endocrine

Method of cell signalling
- Chemical messenger (hormone) acts on target tissue far away from signalling cell.

8

Paracrine

Method of cell signalling
- Chemical messenger acts on target tissue in close proximity to signalling cell.

9

Autocine

Method of cell signalling
- Signalling cell secretes chemical messenger that acts on itself.

10

Pituitary gland
- Location
- Anatomy
- Main function

Located at the base of the brain
- Sits in a bony case, sella turcica

Anatomy
- Connected to the hypothalamus via the infundibulum
- Portal system: hypothalamico-hypophyseal vessels---> Anterior

- Hypothalamico-hypophyseal tract---> Posterior

Function- master gland, secretes hormones to all glands.

11

Hormones of the pituitary gland

Anterior
- Prolactin
- FSH
- LH
- ACTH
- GH
- TSH

Posterior
- Oxytocin
- ADH

12

Thyroid + Parathyroid
- Anatomy
- Function

In the neck
- Below the larynx

- Controls metabolic rates
- Calcium homeostasis

13

Adrenal glands
- Anatomy
- Function

On top of the kidneys

Functions
- Stress
- Blood sodium and glucose regulation

14

Steroid hormone receptors
- Structure
- Mechanism
- Speed of action

Located in the cytoplasm or on nuclear membrane

Mechanism
1. Hormone binds to receptor to form hormone-receptor complex.

2. Complex binds to hormone-response element.

3. Hormone-response binds to DNA and affects gene transcription

Speed
- Slow acting, days of action.

15

Endocrine organs

Pituitary gland
Thymus
Thyroid and Parathyroid
Adrenal gland
Pancreas
Gonads (Testes, ovaries)

16

Tyrosine-kinase receptor - Action
- Speed
- Examples

Action: Receptor contains membrane bound enzyme
1. Hormone binds to receptor
2. Triggers phosphorylation of the receptor.
3. The receptor leads to cellular events that phosphorylates other intracellular proteins.

Speed: Very slow
- Used for growth and development

Example
- Prolactin
- Growth hormone

17

G-protein coupled receptors
- Action
- Speed
- Examples

Action:
1. Hormone binds to 7 transmembrane receptor.
2. Secondary messenger is produced (cAMP, IP3)
3. Secondary messenger causes phosphorylation or influences other intracellular activity.

cAMP= smooth muscle relaxation
IP3= smooth muscle contractrion

Speed:
- Very fast action

Example:
- Adrenaline (adrenergic receptors)
- Calcitonin
- FSH

18

Thyrotrophin releasing hormone [TRH]

Hormone released from the hypothalamus.

Triggers the release of thyroid stimulating hormone [TSH] from the anterior pituitary gland.

19

Thyroid stimulating hormone [TSH]

Released from the anterior pituitary gland.
- Thyrotophic cells

Transported in the blood to the thyroid.

Stimulates the release of thyroxine.

20

Corticotrophin releasing hormone [CRH] and adrenocorticotrophic hormone [ACTH]

CRH is released from the hypothalamus to the pituitary.
- Via hypothalamico-hypophyseal vessels.
- Triggers the release of ACTH from corticotropic cells

ACTH is released from the anterior pituitary.
- Transported in the blood to the adrenal cortex.
- Stimulates the released of cortisol.

21

Gonadotrophin releasing hormone [GnRH] and Follicle stimulating hormone [FSH]

GnRH is released from the hypothalamus to the anterior pituitary gland.
- Triggers the release of FSH from gonadotropic cells.

FSH travels to the ovaries
- Stimulates the release of oestrogen

22

Growth hormone releasing hormone [GHRH] and GH
- Secretion
- Action

GHRH is released from the hypothalamus to the anterior pituitary gland.
- Stimulates the release of GH from somatotropic cells

GH travels to the bones and stimulates linear growth.

23

Luteinising hormone [LH]
- Secretion
- Action

LH is released from the anterior pituitary gland
- From gonadotropic cells
- Stimulates the ovaries to secrete progesterone
- Triggers ovulation

24

Feedback control of hormones

Hormones can negatively inhibit the release of releasing and stimulating hormones.
- Cortisol inhibits CRH and ACTH.
- Progesterone inhibits LH.
- T3 and T4 inhibits TRH and TSH.

25

Variation of cortisol release

Diurnal variation
- Peak in the morning, after waking. 9am.
- High Cortisol inhibits ACTH release

Drop in cortisol as the day progresses
- Allows increase in ACTH
- Cortisol lowest at night/sleep, 12am.

26

Variation of oestrogen release

Monthly variation, overly roughly 28 days--> Menstruation cycle.
- Drop in oestrogen and progesterone allows disinhibition of hypothalamus to allow releasing of FSH and LH.