Endocrine System

What is endocrinology? →

The study of hormones and their functions.

What do hormones regulate? →

Reproduction, growth, metabolism, water and electrolyte balance, and development.

Main endocrine glands? →

Pituitary, thyroid, parathyroid, adrenal.

Main hormone-secreting organs (non-glands)? →

Hypothalamus, pancreas, sex organs.

Endocrine hormones? →

Released into the blood to act on distant target cells.

Paracrine hormones? →

Act on nearby target cells.

Autocrine hormones? →

Act on the same cell that secreted them.

Water-soluble hormones? →

Peptide/protein hormones that dissolve in water (e.g. insulin, noradrenaline).

Lipid-soluble hormones? →

Steroid hormones derived from cholesterol (e.g. estrogen, testosterone, thyroid hormone).

How do hormones act? →

Bind to specific receptors on or in target cells.

Receptors for water-soluble hormones? →

Located on the cell surface, use second messengers.

Receptors for lipid-soluble hormones? →

Located inside the cell or nucleus, affect gene expression.

What links the endocrine and nervous systems? →

The hypothalamus.

Two lobes of the pituitary gland? →

Anterior (adenohypophysis) and Posterior (neurohypophysis).

Function of anterior pituitary? →

Synthesises and secretes hormones.

Function of posterior pituitary? →

Stores and releases hormones made by the hypothalamus.

Hormones produced by hypothalamus? →

GHRH, Somatostatin, TRH, GnRH, CRH, PRH, Dopamine.

Posterior pituitary hormones? →

Oxytocin and Antidiuretic hormone (ADH).

Oxytocin function? →

Causes uterine contractions and milk ejection during breastfeeding.

ADH function? →

Reduces urine output, conserves water, and causes vasoconstriction.

What regulates ADH? →

Osmoreceptors detect solute concentration; high solutes increase ADH release.

Main anterior pituitary cell types? →

Somatotrophs, Thyrotrophs, Gonadotrophs, Lactotrophs, Corticotrophs.

Hormones released by anterior pituitary? →

GH, TSH, LH, FSH, PRL, ACTH.

How is anterior pituitary hormone release regulated? →

Negative feedback loops via hypothalamus and target glands.

What stimulates growth hormone (GH) release? →

GHRH from hypothalamus.

What inhibits GH release? →

Somatostatin from hypothalamus.

Main effects of GH? →

Growth of bone and muscle, increased protein synthesis, increased glucose production.

GH deficiency results in? →

Dwarfism 

GH excess results in? →

Gigantism in children, acromegaly in adults.

Two main parts of adrenal gland? →

Cortex and Medulla.

Hormones from adrenal medulla? →

Adrenaline (80%) and Noradrenaline (20%).

Function of adrenal medulla hormones? →

“Fight-or-flight” response: increase heart rate, blood pressure, and metabolism.

Three zones of adrenal cortex? →

Zona glomerulosa, Zona fasciculata, Zona reticularis.

Zona glomerulosa secretes? →

Aldosterone (mineralocorticoid).

Zona fasciculata secretes? →

Cortisol (glucocorticoid).

Zona reticularis secretes? →

DHEA (androgen).

Aldosterone function? →

Increases sodium reabsorption, potassium excretion, and water retention to raise blood pressure.

Cortisol regulation pathway? →

CRH (hypothalamus) → ACTH (pituitary) → Cortisol (adrenal cortex).

Main actions of cortisol? →

Raises blood sugar, reduces immune response, manages stress.

Excess cortisol causes? →

Cushing’s syndrome.

Cortisol deficiency causes? →

Addison’s disease.

DHEA function? →

Precursor to sex hormones, promotes pubic and axillary hair growth.

Main thyroid hormones? →

T3 and T4 (thyroid hormones) and calcitonin.

Regulation of thyroid hormones? →

TRH (hypothalamus) → TSH (pituitary) → T3 & T4 (thyroid).

Main actions of thyroid hormones? →

Increase metabolism, heart rate, and heat production; support growth and brain development.

Hyperthyroidism cause? →

Graves’ disease (autoimmune).

Hypothyroidism cause? →

Iodine deficiency.

Parathyroid hormone (PTH) function? →

Raises blood calcium levels by acting on bones, kidneys, and intestines.

Calcitonin function? →

Lowers blood calcium levels (opposite of PTH).

How many parathyroid glands are there? →

Four (two on each lobe of the thyroid).

Where is the pancreas located? →

Behind the stomach, in the abdominal cavity.

Endocrine cells of the pancreas? →

Alpha cells (glucagon) and Beta cells (insulin).

Insulin function? →

Lowers blood glucose by promoting glucose uptake and storage as glycogen.

Glucagon function? →

Raises blood glucose by stimulating glycogen breakdown and glucose production.

What is diabetes mellitus? →

A condition of chronically high blood glucose due to lack or resistance of insulin.

Type 1 diabetes cause? →

Autoimmune destruction of beta cells, leading to no insulin production.

Type 2 diabetes cause? →

Insulin resistance, often linked to obesity and age.

Common diabetes symptoms? →

Increased urination, thirst, hunger, fatigue, and high blood sugar.

Diagnostic tests for diabetes? →

Blood glucose test, OGTT, HbA1c.