Hormones

endocrine gland

a group of cells that are specialised to secrete hormones directly into the bloodstream

types of hormones

steroids, proteins, glycoproteins, polypeptides, amines or tyrosine derivatives

how can a gland be stimulated?

• change in concentration of a substance

• consequence of another hormone or a nerve impulse

how do steroid hormones stimulate target cells?

• they are lipid soluble so they pass through the lipid component of the cell membrane and bind to steroid hormones receptors to form a hormone-receptor complex

• the receptors may be present in the cytoplasm or the nucleus

• the H-R complex acts as a transcription factor which facilitates or inhibits the transcription of a specific gene

how do non-steroid hormones stimulate target cells?

• they are hydrophilic so cannot pass through the cell membrane

• instead they bind to specific receptors on the cell surface membrane of the target cell

• this triggers a cascade reaction mediated by chemicals called second messengers

characteristics of hormonal system

• communication via hormones

• transmission via blood system

• slow transmission

• hormones travel all over the body but only target organs respond

• widespread response

• slow response

• long-lasting response

• effect may be permanent and irreversible

characteristics of nervous system

• communication via nerve impulses

• transmission via neurones

• rapid transmission

• nerve impulses travel to specific parts of the body

• localised response

• rapid response

• short-lived response

• effect is temporary and reversible

glucocorticoids (where and what?)

• adrenal cortex

• e.g cortisol which helps regulate metabolism, blood pressure and cardiovascular function in response to stress

• e.g corticosterone which works with cortisol to regulate immune response and suppress inflammatory reactions

mineralocorticoids (where and what?)

• adrenal cortex

• e.g aldosterone helps control blood pressure by maintaining the balance between the salt and water concentrations in the blood and body fluids

androgens (where and what?)

• adrenal cortex

• sex hormones whose impact is relatively small compared with oestrogen and testosterone but are still important e.g after menopause

adrenaline (where and what?)

• adrenal medulla

• increases heart rate by sending blood rapidly to the muscles and brain

• increases blood glucose conc levels by glycogenolysis

noradrenaline (where and what?)

• adrenal medulla

• works with adrenaline to increase heart rate, widening of pupils, widening of air passages and the narrowing of blood vessels in non-essential organs leading to higher blood pressure

exocrine gland

a group of cells that are specialised to produce enzymes and release them via a duct into the duodenum

pancreas’ role as an exocrine gland

produces digestive enzymes e.g amylases, proteases and lipases and pancreatic juice which are secreted into ducts leading to the pancreatic duct

pancreas’ role as an endocrine gland

produces insulin and glucagon which then play a role in controlling blood glucose concentration

alpha cells of the islets of Langerhans

produce and secrete glucagon

beta cells of the islets of Langerhans

produce and secrete insulin

how do the islets of Langerhans look under a microscope?

• lightly stained

• large, spherical clusters

• endocrine pancreas

how do the pancreatic acini look under a microscope?

• darkly stained

• small , berry-like clusters

• exocrine pancreas

how can blood glucose concentration increase?

• diet - carb-rich foods and sweet foods

• natural processes of gluconeogenesis and glycogenolysis

how can blood glucose concentration decrease?

• respiration

• glycogenesis

glycogenolysis

glycogen is broken down into glucose

gluconeogenesis

glucose is formed from non-carbohydrate sources

glycogenesis

glycogen is formed from glucose

role of insulin

• insulin is produced by beta cells by the islets of Langerhans

• it then binds to its glycoprotein receptor in all cells apart from RBCs, causing a change in the tertiary structure of glucose transport protein channels

• this allows more glucose to enter the cell

• it also activates enzymes within some cells to convert glucose to glycogen and fat

specific effects of insulin

• increases rate of absorption of glucose by cells

• increases respiratory rate of cells

• increases rate of glycogenesis

• increases rate of glucose to fat conversion

• inhibits release of glucagon

role of glucagon

• glucagon is produced by the alpha cells of the islets of Langerhans

• it then binds to its glycoprotein receptor in liver and fat cells

• this initiates various effects which raise blood glucose concentration

specific effects of glucagon

• initiates glycogenolysis

• reduces amount of glucose absorbed by liver cells

• increases gluconeogenesis

insulin secretion mechanism

• at normal blood glucose concentration levels, potassium channels in the plasma membranes of beta cells are open and K+ ions diffuse out of the cell

• the inside of the cell has a potential of -70mV

• when glucose conc rises, glucose enters the cell via a glucose transporter

• the glucose is metabolised resulting in the production of ATP

• the ATP then binds to the potassium channels causing them to close

• K+ ions can’t diffuse anymore so the potential difference reduces to around -30mV and depolarisation occurs

• depolarisation causes the voltage-gated Ca2+ ion channels to open

• Ca2+ ions enter the cell and cause vehicles to release insulin via exocytosis

what is type 1 diabetes?

when a person is not able to produce insulin

what is type 2 diabetes?

when a person is not able to produce enough insulin or the person’s cells do not respond to insulin

treatment for type 1 diabetes

• insulin injections

treatment for type 2 diabetes

• diet control

• more exercise

• drugs

• insulin injections

what two systems make up the fight or flight response?

sympathetic nervous system and the adrenal-cortical system

what does the sympathetic nervous system do?

• sends out impulses to glands and smooth muscles

• activates the adrenal medulla to release adrenaline and noradrenaline into the bloodstream

• this increases heart rate

what does the adrenal-cortical system do?

• activated by the release of CRF

• pituitary gland secretes hormone ACTH

• ACTH arrives at adrenal cortex and releases approx. 30 hormones

physiological response of fight or flight

• heart rate increases

• pupils dilate

• arterioles in skin constrict

• blood glucose level increases

• smooth muscle of airways relaxes

• non-essential systems shut down

• difficulty focusing on small tasks

action of adrenaline

• adrenaline approaches its receptor on the cell surface membrane

• the adenylyl cyclase is still inactive

• adrenaline binds to the receptor

• this activates the adenylyl cyclase

• adenylyl cyclase converts ATP to cyclic AMP, which acts as a second messenger to then activate other enzymes

• these enzymes convert glycogen to glucose

what do the two centres in the medulla oblongata do?

• one increases heart rate by sending impulses via the sympathetic nervous system which are transmitted by the accelerator nerve

• one decreases heart rate by sending impulses via the parasympathetic nervous system which are transmitted by the vagus nerve

baroreceptors

pressure receptors

chemoreceptors

chemical receptors

what is the effect of increased carbon dioxide levels?

• more carbon dioxide means more carbonic acid is made

• this decreases the blood pH

• centre in medulla oblongata increases frequency of impulses to SAN

• SAN increases heart rate

• more blood is pumped which can then remove carbon dioxide faster

• carbon dioxide levels return to normal

what is the effect of increased blood pressure?

• when blood pressure increases, impulses are sent to the medulla oblongata

• the medulla oblongata sends impulses via the parasympathetic nervous system

• this decreases the heart rate, and blood pressure returns back to normal