14.1 Hormonal Communication

Question 1

What is the endocrine system, what are endocrine glands?

Answer 1

The endocrine system is made up of endocrine glands. An endocrine glad is a group of cells specialised to secrete chemicals (hormones), and are secreted directly into the bloodstream.

E.g. the pancreas (an endocrine gland) secretes insulin

Question 2

Pituitary gland

Answer 2

• Produces growth hormone which controls growth of bones and muscles
• anti-diuretic hormone which increases reabsorption of water in kidneys
• gonadotrophins which control development of ovaries and testes

Question 3

Thyroid gland

Answer 3

• produces thyroxine which controls rate of metabolism and rate that glucose is used up in respiration and promotes growth

Question 4

Adrenal gland

Answer 4

Produces adrenaline which increases heart and breathing rate and raises blood sugar level

Question 5

Pineal gland

Answer 5

• produces melatonin which affects reproductive development and daily cycles

Question 6

Thymus

Answer 6

Produces thymosin which promotes production and maturation of white blood cells

Question 7

Pancreas

Answer 7

Produces insulin which converts excess insulin into glycogen in the lives. And produces glucagon which converts glycogen back into glucose in the liver

Question 8

Testis

Answer 8

Produces testosterone which controls sperm production and secondary sexual characteristics

Question 9

Ovary

Answer 9

• produces oestrogen which controls ovulation and secondary sexual characteristics
• produces progesterone which prepares the uterus lining for receiving an embryo

Question 10

What are hormones

Answer 10

Hormones are ‘chemical messengers’ as they carry information from one part of the body to another

They can be steroids, proteins, glycoproteins, polypeptide, amines, or tyrosine derivatives

Hormone are directly secreted into the bloodstream when a gland is stimulated [this can occur as a result of a change in concentration of a particular substance e.g. blood-glucose conc or can be stimulated by electrical impulses]

Question 11

What happens once a hormone is secreted?

Answer 11

Hormones are secreted directly into the blood and are transported in the blood plasma all around the body. The hormones diffuse out of the blood and bind to specific respecters for that hormones, found on the membranes or in the cytoplasm of cells in the target organs. These are known as target cells.

Once bound to their receptors the hormone stimulate the target cells to produce a response

Question 12

Basic pathway of hormonal communication

Answer 12

Stimulus -> receptors -> hormone -> effectors -> response

Question 13

State and explain the differences between steroid and non-steroid hormones

Answer 13

• steroid hormones are lipid soluble. They pass through the lipid component of the cell membrane and bind to steroid hormone receptors to form a hormone-receptor complex.
  The receptors may be present in the cytoplasm or the nucleus depending on the hormone.
  The hormone-receptor complex acts as a transcription factor which in turn facilities or inhibits the transcription of a specific gene.
  E.g. oestrogen
• non-steroid hormones are hyrdrophilic so cannot pass directly through the cell membrane. Instead they bind to specific receptors on the cell surface membrane of the target cells. This triggers a cascade reaction medicated by chemicals called second messengers.
  E.g. adrenaline

Question 14

Compare the hormonal and nervous system

Answer 14

Hormonal system:

• communication by hormones
• transmission is by the blood stream
• transmission is usually relatively slow
• hormones travel to all parts of the body, but only target organs respond
• response is widespread
• response is slow
• response is often long lasting
• effect may be permanent and irreversible

Nervous system:

• communication by nerve impulses
• transmission by neurones
• transmission is very rapid
• nerve impulses travel to specific parts of the body
• response is localised
• response is rapid
• response is short-lived
• effect is temporary and reversible

Question 15

What is the action of a hormone (first and second messengers?)

Answer 15

A hormones is called a first messenger because it carries the chemical message the first part of the way, from the endocrine gland to the receptor on the target cells.
When a hormone binds to its receptor it activates an enzyme in the cell membrane. The enzymes catalyses the production of a molecule inside the cell called a signalling molecule - this molecule signals to other parts of the cells to change how the cell works

The signalling molecule is called a second messenger because it carries the chemicals message to the second part of the way, from the receptor to other parts of the cell.
Second messengers activate a cascade (chain of reactions) inside the cell

Question 16

Describe and explain the action of adrenaline?

Answer 16

Adrenaline is a hormone that’s secreted from your adrenal glands. It’s secreted when there’s a low concentration of glucose in your blood, when you’re stressed or when you’re exercising. Adrenaline’s gets the body ready for action by making more glucose available for muscles to respire.

Adrenaline is a first messenger; it binds to specific receptors in the cell membranes of many cells e.g. liver cells
When adrenaline binds it activates an enzymes in the membrane called adenylyl cyclase.
Activated adenylyl cyclase catalyses the production of a second messenger called cyclic AMP (cAMP) from ATP, cAMP activates a cascade , e.g cascade of enzyme reactions making more glucose available to the cell by catalysing the breakdown of glycogen into glucose

Question 17

Describe the adrenal glands

Answer 17

They are endocrine glands that are found just above your kidneys.
Each adrenal gland has an outer part called the cortex and an inner part called the medulla

Question 18

Describe and explain the role of the adrenal cortex

Answer 18

The cortex: (outer region of adrenal gland)
- the production of hormones by the adrenal cortex is controlled by hormones released from the pituitary gland
- secretes steroid hormones that are vital to life e.g. it secretes cortisol and aldosterone when youre stressed
There are three main types of hormones produced by the adrenal cortex:
- Glucocorticoids (e.g. cortisol and corticosterone) helps regulate metabolism, blood pressure, immune response. The release of these hormones is controlled by the hypothalamus
- mineralocorticoids (e.g. aldosterone - which helps control blood pressure by maintaining the balance between salt and water concentrations in the blood and body fluids). It’s release is mediated by signals triggered by kidney
- androgens. Small amounts of female and male sex hormones are released ( their impact is relatively small compared with larger amounts of hormones such as oestrogen and testosterone but are still important especially in women after menopause)

Question 19

Describe and explain the role of the adrenal medulla

Answer 19

The hormones of the adrenal medulla are released when the sympathetic nervous system is stimulated - occurs when the bod is stressed (fight or flight response)

The hormones secreted by the medulla are:

• adrenaline. This increases the heart rate sending blood quickly to the muscles and brain and it also rapidly raises blood-glucose conc
• noradrenaline. This hormone works with adrenaline in response to stress, increasing heart rate, widening pupils, widening air passages in the lungs,and narrowing blood vessels in non-essential organs (resulting in higher blood pressure)