Intergration of Physiology 1-5

How does the endocrine system control aspects of physiology?

Via the secretion of hormones

What are the 2 major control systems?

Endocrine and neuronal (nervous) system

What other systems does the endocrine system interact with?

Cardiovascular, digestive and immune system

What is a hormone?

Signalling molecule secreted into the blood to act on another part of the body

What hormones have slow/prolonged actions?

Steroid hormones and thyroid hormones (T3, T4)

What hormones have a rapid/short action?

Peptides and adrenal amines

What does lipophilic mean?

Fat soluble molecules that do not dissolve readily in an aqueous environment e.g blood plasma

What are the properties of a lipophilic molecule? (3)

Diffuse out of cells that synthesis them

Bound to carrier proteins in the blood

Can diffuse into target cells and act on intercellular receptors

What is an intracellular receptors?

Protein found inside a cell which ligand binds to steroids/ thyroid hormones to regulate gene hormones

What does an intracellular receptor do?

Regulate (increase/decrease) expression of hundreds of target genes

What effect does intracellular receptors have?

Effects have slow onset and prolonged duration - the change in gene expression takes time to occur

Are peptides and adrenal amines hydrophobic or hydrophilic?

Hydrophilic

What are peptides and adrenal amines stored in and how are they secreted?

Stored in vesicles and secreted by exocytosis

Why do peptides and adrenal amines need no carrier proteins?

They dissolve readily in blood plasma - soluble in watery aqueous environment

How does peptides and adrenal amines get inside their target cells?

They act on plasma membrane receptors - when they get to the target cells they have to bind to receptors expressed on the outside of the cell

What are the two effects of plasma membrane receptors?

Have rapid onset of action

Are often short lived

Membrane bound receptors are mechanism of action for?

Hydrophilic peptides and amine hormones

What is the 3 basic domain of membrane bound receptor?

Extracellular (binds hormones)

Transmembrane

Intracellular (necessary for effects in target cells - change in enzyme activity)

What are the major endocrine organs? (8)

Hypothalamus

Pituitary

Thyroid gland

Parathyroid gland

Adrenal glands - cortex and medulla

Pancreas

Testes

Ovaries

Hypothalamus

Releasing hormone - CRH, TRH, GnRH

Dopamine, somatostatin

Pituitary gland

Growth hormone, oxytocin, LH, ACTH

Thyroid gland

Thyroid hormones (T3,T4)

Calcitonin

Parathyroid glands

Parathyroid hormone

Adrenal cortex

Cortisol, aldosterone

Adrenal medulla

Epinephrine, norepinephrine

Pancreas

Insulin, glucagon

Testes

Testosteron

Ovaries

Oestrogens, progesterone

Pineal glands

Secrets melatonin - important for biological rhythms

Adipose tissue (fat) and gastrointestinal tract

Secret many hormones involved in energy balance and metabolism

Placenta

Secrets hormones involved in foetal and maternal development

Negative feed back loops

Regulates homeostasis - imposes a brake on the system

Positive feed back system

Amplifies the original signal

Requires additional control mechanism

Hypothalamo- pituitary regulation

Where is the thyroid gland located?

Adheres to the trachea, just below the larynx

What does the thryroid gland do?

Secrete T4, T3 and calcitonin

What are T3 and T4?

Iodine containing hormones acting throughout the body - important for terms of development, growth and development

What does calcitonin do?

Regulates plasma calcium

What does follicular cells do?

Secrete T4 and T3

What does the colloid do? (Lumen of the thyroid epithelial cell)

Consist of thyroglobulin (glycoprotein) this is where T3 and T4 are made

Where are c cells located?

Present in the basement membrane and between follicles

What do c cells do?

Secrete calcitonin

Why does the thyroid gland have a rich blood supply?

Lots of capillary so hormones can directly be released into the blood

Thyroid feedback pathway (4)

What two components are needed for the synthesis of T4 and T3?

Thyroglobulin and iodine

How is T3 and T4 synthesised and secreted?

Synthesised in follicular cell rough endoplasmic reticulum. Packaged into vesicles and released into linen by exocytosis

How is T4 and T3 stored as?

Colloid

Iodine trapping

Where is the adrenal gland located

Above the kidney

What are the 2 major functional regions of the adrenal cortex?

Adrenal cortex

Adrenal medulla

What does the adrenal cortex (outside) produce?

Steroid hormones

What does the adrenal medulla (inside) produce?

Small polar amine molecules

What is characterised by intracellular lipid droplets?

Adrenal cortex

What is synthesised in the adrenal cortex?

Steroid hormones

What are the three subregions of the adrenal cortex?

Zona glomerulosa

Zona fasciculata

Zona reticularis

What does the Zona glomerulosa secrete?

Mineralocorticoids

What does the Zona fasciculata secrete?

Glucocorticoid

What does Zona reticularis secrete?

Sex steroids

from what are steroid hormones synthesised from?

Cholesterol

How are steroid hormones transported from?

Transported bound to plasma proteins