Chapter 14 - Hormonal Communication

What is a hormone

A chemical messenger which is secreted by glands into the blood stream, usually proteins/peptides

Function of thyroid gland

Produces thyroxine which controls rate of metabolism and rate that glucose is used up in respiration, also promotes growth.

Function of ovaries

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

Function of pancreas

Produces insulin which coverts excess glucose into glycogen in liver and glucagon which converts glycogen back to glucose in the liver.

Function of pineal gland

Produces melatonin which affects reproductive development and daily cycles

Function of pituitary gland

Produces growth hormone, controlling bone and muscle growth, ADH, controlling reabsorption off water in kidneys and gonadotrophins, controlling development of ovaries and testes.

Function of testes

Produce testosterone which controls sperm production and secondary sexual characteristics

Function of adrenal gland

Produces adrenaline which increases heart rate and raises blood sugar level

Function of thymus gland

Produces thymidine which promotes production and maturation of white blood cells

Describe endocrine glands

Secretions enter intercellular fluid then the blood stream. These are ductless and stay in the body, hence endo-. E.g. hormones. Examples of endocrine glands are pancreas and adrenal glands.

Describe exocrine glands

Secretions enter ducts. These exit the body, hence exo-. E.g. mucus, saliva, sweat, tears, digestive enzymes. Examples of these gland are those in the digestive system.

Describe steroid hormones

Lipid soluble so pass through phospholipid component of plasma membranes. Will bind to receptor molecule forming a hormone-receptor complex. This complex acts as a transcription factor - it facilitates/inhibits transcription of a particular gene. Receptors may be in cytoplasm or nucleus. E.g. oestrogen

Describe how a steroid hormone works

1 - Lipid-soluble steroid hormone passes through membrane

2 - Binds with receptor protein in cytoplasm forming a hormone-receptor complex

3 - Complex attaches to DNA

3 - Complex acts as a transcription factor, providing instructions for synthesis of a polypeptide

5 - Polypeptide is synthesised

Describe non-steroid hormones

Hydrophilic so cannot pass through plasma membrane so it binds to receptor molecules on the surface of the target cell. Triggers cascade reaction mediated by chemicals called second messengers. E.g. adrenaline

How does adrenaline (Non-steroid hormone) work

1 - Hormone adrenaline approaches receptor site

2 - Adrenaline fuses to receptor site and in doing so activates an enzyme inside the membrane

3 - The activated enzyme converts ATP to cyclic AMP, which acts as a second messenger that activates other enzymes that in turn convert glycogen to glucose

Why might one molecule of adrenaline have a large effect on a cell

One adrenaline molecule can cause the formation of many cAMP molecules which in turn catalyse the production of many active enzymes. Therefore, one hormone molecule results in many active enzymes within a cell.

Compare hormonal and nervous communication

Hormonal System	Nervous System
Communication is by chemicals called hormones.	Communication is by nerve impulses.
Carried in the blood.	Transmission is by nerve impulses.
Transmission is usually relatively slow.	Transmission is very rapid.
Carried to all parts of the body, but only target cells/organs respond.	Nerve impulses travel to specific parts of the body.
Widespread response.	Response is localised.
Usually a slow response.	Response is rapid.
Often a longer lasting response.	Response is often short lived.
Effects are often permanent and irreversible.	Effect is temporary and reversible.

Describe how the pancreas acts as both an exocrine and endocrine gland

Exocrine gland:

• Secretes pancreatic juice along the pancreatic duct into the duodenum

• Pancreatic juice contains:

- Lipase

- Amylase

- Protease e.g. Trypsin

- Sodium hydrogen carbonate

Endocrine gland:

• Secretes hormones directly into blood capillaries in the islets of langerhans

• Hormones are:

- Insulin

- Glucagon

Describe islet of langerhans

Group of cells located in pancreatic tissue

Made of two types of cells - alpha and beta cells

These cells detect blood glucose concentration as it passes through capillaries in islet of langerhans and respond to changes by switching on/off the secretion of insulin and glucagon

Why should normal blood glucose levels (90mg 100cm^-3) be maintained

• To provide glucose for respiration which is highly important for cells in the brain

• High glucose concentrations would decrease water potential of blood so water would leave cells by osmosis which is dangerous for cells

Reasons for increase in blood glucose

• Digestion

• Liver hydrolyses stored glycogen into glucose and releases it

• Liver converts lipids and fats into glucose and releases it

Reasons for decrease in blood glucose

• Lack of food intake

• Respiration

• Conversion of glucose into glycogen by liver and muscle cells

What is negative feedback

The mechanism that detects and reverse a change, bringing the system back to the optimum

How are alpha and beta cells involved in negative feedback when blood glucose increases and decreases

Blood glucose increase:

• Alpha cells stop secreting glucagon and beta cells secrete insulin

• Liver cells stop breaking down glycogen due to lack of glucagon and most body cells increase uptake and use of glucose due to rise in insulin

• Blood glucose stabilised

Blood glucose decrease:

• Alpha cells secrete glucagon and beta cells stop secreting insulin

• Liver cells break down glycogen into glucose due to rise in glucagon and most body cells decrease uptake and use of glucose due to fall in insulin

• Blood glucose stabilised

Describe how beta cells control insulin secretion

• Cell membranes of beta cells contain potassium and calcium ion channels

• Potassium ion channels are normally open and calcium ion channels are normally closed

• Potassium ions diffuse out of the cell, making the cell more negative, at rest the potential difference across he membrane is about -70mV

• When glucose concentration outside the cell is high, glucose molecules diffuse into the cell via a glucose transporter protein

• Glucose is phosphorylated by an enzyme, glycokinase and used in metabolism to produce ATP

• Extra ATP binds to and causes potassium ion channels to close. These are ATP sensitive channels

• Potassium ions can no longer diffuse out and this alters the potential difference across the membrane - it becomes less negative inside and the cell is depolarised

• This change in potential difference opens the voltage gated calcium ion channels

• Calcium ions enter the cells and cause the secretion of insulin by making the vesicles containing insulin move to the cell surface membrane and fuse with it, releasing insulin by exocytosis

How does the liver respond to a rise in blood glucose levels

Inserts more glucose transporter proteins into the plasma membrane so:

• More glucose enters the cell so blood glucose concentration falls

• More glucose is converted to glycogen for storage - glycogenesis

• More glucose is converted to fats

• More glucose is used in respiration by increasing the rate of respiration

How does the liver respond to a fall in blood glucose concentration

• Hydrolyses glycogen, glycogenolysis, and releases glucose into blood stream

• Removes glucose transporter proteins from membrane so less glucose is absorbed

• Uses more fatty acid in respiration

• Amino acids and fats are converted to additional glucose by gluconeogenesis

Define glucose

A monosaccharide sugar, CsH1206, occurring widely in most plant and animal tissue. It is the principal circulating sugar in the blood and the major energy source of the body.

Define glycogen

A polysaccharide, (CsH1o05)n, that is the main form of carbohydrate storage in animals and occurs primarily in the liver and muscle tissue.

Define glucagon

A hormone released by the a cells in the islets of Langerhans in the pancreas. It causes the blood glucose level to rise by converting glycogen in liver cells to glucose.

Define glycogenesis

The formation or synthesis of glycogen (genesis = creation)

Define gluconeogenesis

The synthesis of glucose from other sources, e.g. amino acids or lipids (neo = new, genesis = creation)

Define glycogenolysis

The biochemical break-down of glycogen to glucose (lysis = splitting)

Define glucokinase

An enzyme that catalyses the phosphorylation of glucose

Why does blood glucose level fall quickly after glucose ingestion in a non-diabetic person

Insulin secreted by beta cells which stimulates liver cells to take up more glucose and covert it to glycogen

Glucose used up by body cells in respiration

Why does blood glucose level also eventually fall in a diabetic person after glucose ingestion

Glucose is used up in respiration

Glucose is excreted from the body via urine

What is diabetes mellitus

A condition where blood glucose concentrations can’t be controlled effectively

Define hyperglycaemia and hypoglycaemia

Hyperglycaemia - A state in which blood glucose concentration is too high

Hypoglycaemia - A state in which blood glucose concentration is too low

Cures for diabetes

Pancreas transplant - High success rates but limited donors, lifetime of immunosuppressents, major surgery

Beta cell transplant - Lifetime of immunosuppressants, not highly successful

Stem cells - Unending source of stem cells, rejection by body, moral objections

Stem cells from somatic cell nuclear transfer - No rejection issues as embryos created from patient’s nucleus, still investigative

How does the brain activate the appropriate effector to respond to a change

• Nerve impulses are sent via the somatic nervous system to voluntary (skeletal) muscles

• Nerve impulses are sent via the autonomic nervous system to glands and involuntary (smooth) muscles

• Releases hormones via hypothalamus and pituitary gland

Draw a diagram describing how the fight or flight response is coordinated

How does each of the physiological changes prepare the body for action:

• Pupils dilate

• Heart rate/BP increases

• Blood glucose level increases

• Metabolic rate increases

• Erector pili muscles in the skin contract making hairs stand up

• Ventilation rate and depth increase

• Endorphins (painkillers) released in the brain

• Sweat production increases

• Arterioles to digestive system and skin are constricted whilst those to livers and muscles are dilated

• Pupils dilate - Take in more light hence better vision

• Heart rate/BP increases - More oxygenated blood pumped around body

• Blood glucose level increases - Respiration increases to provide energy for muscle contraction

• Metabolic rate increases - More energy/glucose provided to muscles and brain

• Erector pili muscles in the skin contract making hairs stand up - Make animal look larger/intimidating

• Ventilation rate and depth increase - Allow more oxygen to lungs

• Endorphins (painkillers) released in the brain - In case of harm

• Sweat production increases - Adrenaline activates sweat glands to prepare for intense pholical action

• Arterioles to digestive system and skin are constricted whilst those to livers and muscles are dilated - To focus resources on emergency functions

Name 3 hormones released from the adrenal cortex, what type of hormones these are and their effect

Steroid hormones:

Glucocorticoids - Regulate glucose and protein metabolism and BP, suppresses inflammatory response

Mineralcorticoids - Maintain salt concentration to control blood pressure

Androgens - Sex hormones with little effect, especially important in women after menopause

Name 2 hormones released from the adrenal medulla, what types of hormones these are and their effect

Peptide hormones:

Adrenaline - Increases heart rate and blood glucose level

Noradrenaline - Dilates pupils, vasoconstriction of blood vessels to non-essential organs

How does the cardiovascular centre in the medulla oblongata receive sensory input

• Stretch receptors in muscles

• Chemoreceptors in aorta, carotid artery and medulla oblong at a which detect CO2 levels in blood by changes in pH

• Baroreceptors (pressure receptors) in aorta and carotid arteries which detect changes in blood pressure

How does the cardiovascular centre initiate impulses

Cardiostimulatory centre initiates impulses via the sympathetic (accelerator) nerve to increase frequency of contraction

Cardioinhibitory centre initiates impulses via the parasympathetic (vagus) nerve to decrease the frequency of contraction

How do the following factors affect heart rate:

• Body movement

• Production of CO2 during exercise

• Adrenaline secretion

• High blood pressure

• Body movement - Detected by stretch receptors which send impulses to cardiovascular centre informing that extra oxygen may be required soon hence heart rate increases

• Production of CO2 during exercise - When CO2 dissolves (when it’s converted to carbonic acid by carbonic anhydrase), it reduces the pH of blood plasma and this change can be detected by chemoreceptors which send impulses to increase heart rate. Heart rate decreases when we stop exercising

• Adrenaline secretion - Presence of adrenaline due to shock is detected by cells in SAN and they increase heart rate to help prepare body for activity

• High blood pressure - Detected by baroreceptors, if it rises too high, the pressure receptors send impulses to cardiovascular centre which responds by reducing the heart rate

What happens when the heart rate is too high

An impulse is sent by the parasympathetic (vagus) nerve to the cardioinhibitory centre to decrease the frequency of contraction.

What happens when the heart rate is too low

An impulse is sent via the sympathetic (accelerator) nerve to the cardiostimulatory centre to increase the frequency of contraction