A.1.1.2 - The endocrine system

What does the endocrine system do?

Controls body activity by releasing hormones into blood for transport to target cells

- Considerably slower than the nervous system w long lasting impacts

- Only interacts w target cells that have specific receptors

Hormones

Chemicals released by glands

- Travels through the bloodstream

Carries messages from one part of the body to the other

Two types of hormones

1. Circulating hormones

2. Local hormones

Circulating hormones

Secreted by glands and released into bloodstream

- They travel to target organs

Local hormones

- Work on neighbouring cells or the cell from which they were secreted

- DO NOT enter the bloodstream

How do hormones work?

Hormones come into contact with tissues, some with specific hormone receptors

- Allows for hormones to act as signals to trigger changes inside the cell

Major glands

- Pituitary gland

- Thyroid gland

- Adrenal gland

- Pancreas

- Testes

- Ovaries

Thyroid gland

Produces hormone thyroxine

- Regulates metabolism

- Plays role in growth and development

Detects low levels of hormones

- Releases thyroid stimulating hormone (TSH)

- Re-stimulates thyroid production

Adrenal glands

- Fight or flight

- Released during physical activity and when scared or startled

Effects:

- Increased heartrate

- Blood pumping faster

Pancreas

- Insulin

- Blood glucose regulation

Negative feedback loop

A feedback loop that causes a system to change in the opposite direction from which it is moving

- So in the event of an imbalance, the body will rebalance them using hormones

Difference between endocrine system and hormones

Hormones: chemicals secreted into blood by glands, slower spread but long lasting impacts

Nervous system: Precise and immediate, electrical signals

Hormones only interact with...

target cells that have receptors specific to the hormones.

Main hormones

- Epinephrine and norepinephrine

- Insulin and glucagon

- Antidiuretic hormone

- Oestrogen

- Progesterone

- Testosterone

Epinephrine and norepinephrine

- Stimulates by stress/exercise (fight or flight)

- Sympathetic nervous system stimulates adrenal glands to release these two hormones (work together to prep. fight/flight)

Epinephrine and norepinephrine (effects)

Increased blood pressure

Increased heart rate

increased blood glucose levels

Increase blood fatty acid levels

Increase force of heart contractions

Increased blood flow to heart, skeletal muscles and adipose tissue

Dilates airways to the lungs

Insulin and glucagon

- Insulin released when blood glucose is high (lowers blood glucose by helping cells absorb glucose from the blood)

- Glucagon released when blood glucose is low (raises GB by signalling the liver to release/breakdown stored liver glycogen to glucose)

ADH (Antidiuretic hormone)

Secreted by pituitary gland

- Regulates water retention in the kidney

- helps control water balance and prevent dehydration

ADH During dehydration

Low water means ADH response increases

- Less urine, more water retained

ADH During overhydration

High water means ADH decreases

- More urine, excess water excreted

Oestrogen

Female sex hormones secreted by ovaries

- Promotes growth and secondary sex characteristics

- Increases protein anabolism, including building strong bones

- Lowers blood cholestrol

Progesterone

Female sex hormone excreted by ovaries

- Regulates/controls the menstrual cycle and pregnancy

Testosterone

Predominant male sex hormone secreted by testes

- Needed for development of sperm

- Helps control the development of male reproductive hormones

- Promotes development and maintenance of male secondary sex characteristics

- Helps with bone formation

Hormone regulation

Ensures that the right amount of hormones are released at the right time

- Ensures homeostasis

- Done through the use of a negative feedback loop

Negative feedback loop mechanism

Change monitored by DETECTORS, while EFFECTORs are activated to induce an opposite effect

- promotes equilibrium

3 main sources of information that influences hormone secretion

1. Neural

2. Humoral

3. Hormonal

Neural information source

Stimulus comes from nervous system (e.g. epinephrine)

Humoral information source

Stimulus comes from changes in blood

Hormonal information source

Hormones act to release other hormones

Hypothalamus

Controls homeostasis and hormones

- Either direct influence of autonomic nervous system or direct secretion of hormones

- Controls the pituitary glands

- Regulates release of hormones

Pituitary glands

- Regulates hormone release

- Anterior and posterior

- In the brain but not PART of the brain

- Most important to involvement of homeostasis

- Master gland

Types of hormones

- Steroid

- Non-steroid

- Prostaglandins

Steroid hormones

- Fat soluble

- Easily able to pass through cell membranes to interact with receptors and elicit a response

- E.g. testosterone, oestrogen, progesterone

Non-steroid hormone

Non-fat soluble

- Must interact with receptors on the cell surface to trigger messenger chemicals inside cells that elicit the response

E.g. epinephrine, glucagon

Prostaglandin hormones

Produced in the membranes of most cells

- Secreted near the site of action (some can be transported a short distance before breaking down)