Endocrine System

Endocrine system

A system of glands that secrete hormones into the blood to target cellular receptors

• slower and longer-lasting than nervous system

Endocrine

refers to glands/ tissues that make or release hormones that travel in the bloodstream to control the actions of other cells or organs

Hormone

chemical messenger secreted into the blood/ extracellular fluid by one cell and have an effect on the functioning of other cells in other parts of the body

• does NOT include local hormones: have an effect locally not globally around body

List the main glands in the endocrine system

• hypothalamus

• pineal gland

• pituitary gland

• thyroid gland

• parathyroid gland

• thymus

• adrenal glands

• pancreas

• ovaries/ testes

Hypothalamus

secrete ‘Releasing’ hormones (TRH, CRH, GnRH)

• controls pituitary gland

• regulates hunger, thirst, temperature, circadian rhythm

Pituitary gland

Anterior pituitary hormones:

• GH (growth hormone: promotes growth of bone, muscle, adipose tissue)

• Prolactin (stimulates lactation/ maternal behaviours)

• Stimulating/ tropic hormones:

• TSH (thyroid stimulating hormone)

• FSH (follicular stimulating hormone) - spermatogenesis/ ovary follicle growth

• LH (luteinising hormone) - sex hormone

• ACTH (adrenocorticotropic hormone) - steroid hormone stimulates release of cortisol

Posterior pituitary hormones:

• oxytocin (expression of milk and uterine contraction)

• ADH (aka vasopressin) (water reabsorption in kidney, promotes vasoconstriction

why trigger vasoconstriction when blood plasma is hypertonic?

Hypertonic: conc of water in blood plasma decreased

• maintains blood pressure

Thyroid

produces:

• thyroxine (T4) and T3 (regulates metabolism, growth, heart function, etc)

• Calcitonin (regulates calcium levels)

Parathyroid

produces parathyroid hormone (PTH) (increases blood calcium levels)

Adrenal gland

produces:

• cortisol

• aldosterone

• adrenaline

• noradrenaline

All involved in stress response, metabolism, blood pressure regulation

Thymus

Produces:

• Thymosin

• Thymopoietin

• Thymulin

(Maturation of T-cells, helps establish immune competence in early life)

Pineal gland

Produces melatonin (regulates sleep-wake cycle)

Pancreas

Islets of Langerhans contain:

• alpha cells which secrete insulin (decrease blood glucose)

• beta cells which secrete glucagon (increase blood glucose)

Ovaries

Produce estrogen and progesterone (female reproductive functions, menstrual cycle)

Testes

Produce testosterone (male reproductive functions, sperm production)

Explain how lipophilic hormones interact with intracelular receptors

• dissolve into the mb, move across mb

• targets are usually intracellular receptors

Explain how lipophobic hormones interact with cell surface receptors

• unable to cross cell mb so bind to cell surface receptors which triggers intracellular cascade of response

Briefly describe the role of the hypothalamus in the endocrine system

• part of limbic system

• key in homeostasis

• central regulator of autonomic nervous system

• central regulator of endocrine system

• controls function of pituitary gland (posterior pituitary via neural connections, anterior pituitary via vascular connections) - hypothalamic-pituitary axis)

Briefly describe the role of the pituitary gland in the endocrine system

• releases ‘coordinating’ hormones

• controls hormone levels produced in other glands and tissues

Outline which hormones are produced by the anterior and posterior pituitary gland

Anterior:

• Growth hormones (of bone, muscle, adipose tissue)

• Prolactin (stimulates lactation/ maternal behaviour)

• Stimulating (tropic) hormones: Thyroid STimulating hormones (TSH), Follicular Stimulating Hormone (FSH), Luteinising Hormone (LH), Adrenocorticotropic hormone (ACTH)

Posterior:

• Oxytocin: expression of milk, uterus contraction

• Vaspressin (aka antidiuretic hormone): promotes kidney reabsorption of water, promotes vasoconstriction (increase peripheral resistance)

Describe the role of pancreatic hormones insulin and glucagon in glucose homeostasis.

• insulin: reduces blood glucose concentration

• glucagon: increases blood glucose concentration 

Action of Insulin

Secreted from β – cells when blood sugar rises

1.Stimulates glucose uptake by cells.

2.Stimulates liver to store glucose. Glycogenesis.

3.Inhibits glucagon secretion.

4.Promotes fat storage.

Action of glucagon

Secreted from α – cells when blood sugar falls

1.Stimulates glycogen breakdown. Glycogenolysis.

2.Stimulates gluconeogenesis in liver / kidney. Breakdown of lipids / proteins.

3.Stimulate fat breakdown in adipose tissue.

Describe the role of the thyroxine produced in the thyroid gland.

1. Thyroid gland produces thyroxine (T4) Note: T3 is a faster acting form of T4.

2. Highly lipid soluble (lipophilic) so enters cells.

3. Binds to cytoplasmic receptors and transported to nucleus to regulate gene activation.

• Increased metabolism.

• Burn more energy at rest.

• Enhances carbohydrate consumption.

• Increases mitochondrial function.

• Promotes growth in children.

• Increases mental activity.

Radioactive Iodine

Risk factor for cancer

Treatment option for thyroid cancer

What is T3?

T3 is more potent faster acting form of T4.

Describe the role of the parathyroid gland, parathyroid hormone.

Parathyroid glands: four glands embedded in the thyroid.

• Produce parathyroid hormone involved in blood calcium homeostasis. (break down bone)

Describe the role of calcitonin produced in the thyroid gland.

1.Thyroid produces calcitonin

2.Suppressing osteoclast activity

3.Decreases circulating Ca 2+ levels

4.Increases calcium excretion by kidneys

5.Particularly important in regulating Ca 2+  levels during development

Explain where melatonin is produced and what effect it has on the sleep cycle.

Pineal gland secretes melatonin (regulation of sleep cycles)

• sunlight detected by receptors, decreases melatonin production by pineal gland, melatonin concentration decreases

• no light = melatonin production increases = circulating melatonin concentration increases prompting sleep

Briefly outline the role of the hormones produced by the thymus.

Thymus produces:

• Thymosin

• Thymopoietin and Thymulin

Primary Function:

Facilitates the maturation of T-cells (adaptive immunity).

Helps establish immunocompetence in early life.

Activity Over Time:

Most active during childhood and adolescence.

After puberty – gradually shrinks and endocrine activity decreases.

Some residual function persists in adulthood.

Thymosin

A group of peptides that promote the development and differentiation of T-lymphocytes (T-cells).

Thymopoietin and Thymulin

Involved in T-cell maturation and immune regulation.

Describe the location and general anatomy of the adrenal glands.

Adrenal Cortex: produces steroid hormones (glucocorticois and mineralcorticoids) 

Adrenal Medulla: produces catecholamines (‘sympathetic’ hormones of adrenaline and noradrenaline)

Outline the role of androgens, cortisone and aldosterone as hormones produced by the adrenal cortex.

Cortex produces:

• zona glomerulosa: aldosterone (regulates blood pressure via the regulation of fluid and electrolyte balance)

• zona fasciculata: cortisone (stress response)

• zona reticularis: androgens - women and men (production and maintenance of sex hormones)

List the three stages of the stress response.

1. The alarm reaction: 

2. Resistance or adaptation: 

3. Exhaustion

Stage 1 of stress response: Alarm reaction

Sympathetic activation

Release of norepinephrine to activate fight or flight response

Release of epinephrine from adrenal medulla

Stage 2 of stress response: Resistance or adaptation: 

a.corticotropin-releasing hormone (CRH)

b.Stimulates anterior pituitary releasing ACTH

c.This causes adrenal cortex to release cortisol

d.Cortisol can maintain long term alert with continued triggers of stress

• increased blood glucose

• lipolysis

• glycogenolysis in liver

• suppression of immune system

• suppression of inflamatory response

Stage 3 of stress response: exhaustion

Chronic stress leads to hypertension, depression, anxiety, heart disease, diabetes

Explain the role of cortisol in maintaining the response to long term stress.

Cortisol can maintain long term alert with continued triggers of stress

•         Increased blood glucose (via pancreatic hormones)

•         Lipolysis

•         Glycogenolysis in liver

•         Suppression of immune system

•         Suppression of inflammatory response

Describe the return to rest after the stress response

Negative feedback reduces activation of HPA axis

(Time dependent)

Gradual return to former ‘rest’ state

Briefly describe how the renin angiotensin system regulates blood volume, electrolyte balance and systemic vascular resistance.

• low blood flow through glomerulus

• low perfusion triggers renin to be produced

• renin converts angioteninogen into angiotenin 1

• Angiotensin 1 converted into Angiotenin 2

• Angiotensin 2 responsible for vasoconstriction, sympathetic activation, tubular Na+ resorption and water retention

• blood perfusion to kidney increases

RAS also regulates:

• blood volume

• electrolyte balance

• systemic vascular resistance

Why trigger vasoconstriction when blood plasma is hypertonic?

Hormone secreted to maintain blood pressure