the endocrine system

hormones

chemical messengers which are secreted by specific glands that travel to act on specific receptors

hydrophobic hormones

ultracellular receptors, cannot be stored easily, not easily broken down

hydrophilic hormones

cell surface receptors, can be stored in cells if attached to carrier proteins, easily broken down, released on demand

3 classes of hormones

• Peptide hormones: Composed of amino acids, hydrophilic (e.g., insulin, ADH).

• Steroid hormones: Derived from cholesterol, hydrophobic (e.g., cortisol, oestrogen).

• Amine hormones: Derived from amino acids, small, potent, hydrophilic (e.g., adrenaline, thyroid hormones)

What is the primary function of the hypothalamus in the endocrine system

It links the nervous system to the endocrine system and regulates many autonomic processes e.g. thirst, appetite, temperature

What are the two parts of the pituitary gland, and what do they do

• Anterior pituitary: Produces 6 key hormones

• Posterior pituitary: Stores and releases hormones made by the hypothalamus:

  • oxytocin: involved in childbirth and milk production

  • antidiuretic hormone: regulate water balance via kidney

what are the 6 hormones being produced by the anterior pituitary

• growth hormone: stimulates body growth and metabolic function

• thyroid stimulating hormone: stimulating thyroid release

• adrenocorticotropic hormones: triggers cortisol release

• prolactin: stimulates milk production and mammary glands

• follicle stimulating hormone: promotes gamete production

• lutenising hormone: stimulates hormone production

What is the role of the pineal gland?

It regulates circadian rhythms by secreting melatonin in response to darkness

structure of thyroid gland

Butterfly shaped gland located in the neck, highly vascular and surrounded by a fibrous capsule.

What is the role of the parathyroid glands

They regulate calcium levels in the blood by secreting parathyroid hormone (PTH)

structure of adrenal glands

located on top of kidneys and made up of 2 parts: cortex, medulla

What hormones are produced by the adrenal cortex?

• Zona glomerulosa: Aldosterone

• Zona fasciculata: Cortisol

• Zona reticularis: Androgens

What hormones are produced by the adrenal medulla?

Adrenaline and noradrenaline

what hormones are produced in the hypothalamus

• releasing hormones: CRH, TRH, GnRH

• inhibiting hormones: GHTH, PIH

What are the main hormones produced by the thyroid gland?

T3, T4, and calcitonin

Which thyroid hormone is more active?

T3 is more physiologically active, while T4 is more abundant.

What stimulates the release of thyroid hormones?

Thyroid-Stimulating Hormone (TSH), triggered by Thyrotropin-Releasing Hormone (TRH) from the hypothalamus

What are the functions of T3 and T4?

• Increase basal metabolic rate

• Regulate metabolism of carbohydrates, proteins, and fats

What does calcitonin do?

Lowers blood calcium by promoting calcium storage in bones and increasing excretion in urine.

What are the symptoms of hyperthyroidism (e.g., Grave’s disease)?

Increased metabolism, feeling warm, sweating, weight loss, increased appetite, tachycardia, restlessness, diarrhoea

What are the symptoms of hypothyroidism (e.g., Hashimoto’s thyroiditis)?

Decreased metabolism, feeling cold, dry skin, weight gain, fatigue, depression, bradycardia.

how does PTH increase blood calcium levels

• Increases blood calcium by stimulating bone breakdown

• Enhances calcium absorption in the gut

• Reduces calcium excretion in the kidneys

What does aldosterone do?

• Increases sodium and water retention

• Increases blood pressure

What are the functions of cortisol?

regulates stress response and metabolism

What does adrenaline do?

• Increases heart rate

• Raises blood pressure

• Increases metabolic rate

• Enhances the fight-or-flight response

What are the endocrine functions of the pancreas?

• Alpha cells produce glucagon (raises blood glucose)

• Beta cells produce insulin (lowers blood glucose)

• Delta cells produce somatostatin (inhibits insulin and glucagon release)

how does insulin lower blood sugar?

• Increases glucose uptake by cells

• Promotes glycogen storage

• Inhibits gluconeogenesis

How does glucagon raise blood sugar?

• Stimulates glycogen breakdown (glycogenolysis)

• Promotes glucose production from non-carbohydrates (gluconeogenesis)

What is the HPA axis

Hypothalamus → CRH → Pituitary → ACTH → Adrenal Cortex → Cortisol.

How is thyroid hormone secretion regulated?

Negative feedback: Low levels of T3/T4 stimulate TRH and TSH release, high levels inhibit them.

What is Cushing's syndrome, and what causes it?

A condition caused by excess cortisol, leading to obesity, hypertension, and muscle weakness

What is addison’s disease, and what causes it?

A condition caused by low cortisol, leading to low blood pressure and fatigue