Chapter 14 Hormonal Communication Flashcards
What is the endocrine system made up of?
Endocrine glands
= a group of cells which are specialised to secrete hormones (directly into the bloodstream)
e.g. pancreas gland and adrenal gland
Pituitary gland??
At the base of the brain makes several hormones - its close proximity to the hypothalamus ensures that the nervous and hormonal responses of the body are coordinated.
- produces GROWTH hormone
- produces ANTI-DIURETIC hormone (increases water absorption in the kidneys)
- produce GONADOTROPHINS (control the development of ovaries and testes)
Pineal gland??
- produces MELATONIN (affects the reproductive development and daily cycles)
Thyroid gland??
- produces THYROXINE (controls rate of metabolism, rate at which glucose is used up, and promotes growth)
Thymus??
- produces THYMOSIN (promotes production and maturation of white blood cells)
Adrenal gland??
- produces ADRENALINE (increases heart and breathing rate and raises blood sugar level)
Pancreas??
- produces INSULIN (converts excess glucose into glycogen in the liver and glucagon which converts glycogen back into glucose)
Testis??
- produces TESTOSTERONE (controls sperm production and secondary sexual characteristics)
Ovary??
- produces OESTROGEN (controls ovulation and secondary sexual characteristics)
- produces PROGESTERONE (prepares the uterus lining for receiving an embryo)
What is the diff between ENDOcrine glands and EXOcrine glands?
EXOcrine glands secrete chemicals through ducts into organs, or to the surface of the body.
Types of hormones?
(1) steroids
(2) proteins
(3) glycoproteins
(4) polypeptides
(5) amines
(6) tyrosine derivatives
When are hormones secreted generally?
When a gland is stimulated - which can occur as a result of…
- a change in conc.
- another hormone
- nerve impulse
Target cells??
Once secreted the hormones are transported in the blood plasma all over the body.
Hormones diffuse out of the blood and bind to specific receptors of that hormone
- found on the membranes or in the cytoplasm of cells in the target organs = target cells
Once bound to their receptors the hormones stimulate the target cells to produce a response.
What are steroid hormones?
They are LIPID SOLUBLE.
- they pass through the lipid component of the cell membrane
- they bind to steroid hormone receptors = hormone-receptor complex
(receptors either in cytoplasm or nucleus)
e.g. Oestrogen
What does the hormone-receptor complex do?
Attaches to DNA…
Acts as a transcription factor which either inhibits/facilitates the transcription of a specific gene.
What are non-steroid hormones?
They are hydrophilic so cannot pass directly through the cell membrane.
- they bind to the specific receptors at the surface membrane of the target cell
- this triggers a cascade reaction mediated by chemicals called SECOND MESSENGERS
e.g. Adrenaline
Hormonal v.s. Neuronal communication?
Hormones are to released directly onto their target cells = slower and less specific form of communication.
Hormones are not broken down as quickly as neurotransmitters, therefore have a longer lasting and widespread response.
What are the adrenal glands?
3cm- 5cm
- located at the top of each kidney and made up of 2 distinct parts surrounded by a capsule
(1) ADRENAL CORTEX
- outer region of the glands
- produces the ESSENTIAL hormones (e.g. cortisol and aldosterone)
(2) ADRENAL MEDULLA
- inner region of the glands
- produces the NON-essential (e.g. adrenaline)
What are the 3 main types of hormones produced by the adrenal cortex?
The production of hormones by the adrenal cortex is controlled by hormones released from the pituitary gland.
(1) GLUCOCORTICOIDS (release controlled by hypothalamus)
- CORTISOL (regulates metabolism - by controlling how the body converts fats, proteins, and carbs into energy) AND (regulates blood pressure and cardiovascular function in response to stress)
- CORTICOSTERONE (works with cortisol to regulate immune response and suppress inflammatory reactions)
(2) MINERALCORTICOIDS (release triggered by kidneys)
- ALDOSTERONE (which helps controls blood pressure by maintaining the balance between salt and water conc. in blood and body fluids).
(3) ANDROGENS
- small amounts of male/female sex hormones
(relatively small impact compared to those of larger amounts - oestrogen and testosterone)
- still important especially in women after menopause.
What are the hormones secreted by the adrenal medulla?
The hormones of the adrenal medulla are released when the sympathetic nervous system is stimulated (when the body is stressed).
(1) ADRENALINE
- increases the heart rate sending blood quickly to the muscles and brain
- rapidly raises blood glucose conc. levels by converting glycogen into glucose in the liver
(2) NORADRENALINE
- works with adrenaline in response to stress
- increases heart rate
- widens pupils
- widens air passages in the lungs
- narrowing of blood vessels in non-essential organs (higher blood pressure)
What are the 2 main functions of the pancreas in the body?
(1) exocrine gland
- to produce enzymes and release them via a duct into the DUODENUM
(2) endocrine gland
- to produce hormones and release them into the blood
Pancreas’ role as an EXOcrine gland? AND what three digestive hormones does it produce?
- most of the pancreas is made up of exocrine glandular tissue
(this tissue is responsible for producing digestive enzymes and an alkaline fluid - pancreatic juice) - the enzymes and pancreatic juice are secreted into ducts which eventually lead to the pancreatic duct
- they are released into the duodenum (top part of the small intestine)
(1) AMYLASE - breaks down starch into simple sugars
(2) PROTEASE - breaks down proteins into amino acids
(3) LIPASES - breaks down lipids into fatty acids and glycerol
Pancreas’ role as an ENDOcrine gland?
- the pancreas is responsible for producing insulin and glucagon (roles in blood glucose conc.)
Within the exocrine tissue, there are regions of ENDOcrine tissue = ISLETS OF LANGERHANS
- responsible for producing insulin and glucagon and secreting these directly into the blood
Histology of the pancreas? (diff between pancreatic acini and islets)
Appearance
- islets = LIGHTLY stained
- acini = DARKER staines
Shape
- islets = large, spherical clusters
- acini = small, berry-like clusters
Type of tissue
- islets = endocrine pancreas
- acini = exocrine pancreas
Function
- islets = produce and secrete hormones
- acini = produce and secrete digestive enzymes
Different types of cells in the Islets of Langerhans?
(1) a = alpha cells = produce and secrete GLUCAGON
(2) ß = beta cells = produce and secrete INSULIN
- alpha cells are larger and more numerous than beta cells within an islet.
What type of staining do you use on the pancreas?
Differential staining
ß cells = blue
a cells = pink
What is glucose?
Glucose is a small, soluble molecule that is carried in the blood plasma.
- it is normally maintained at a concentration of approx. 90mg/cm^3 of blood
When can blood glucose conc. INCREASE?
(1) Diet
- when you eat carb-rich foods (high in starch or sucrose)
- carbs are broken down into glucose
- glucose released is absorbed into the bloodstream, and blood glucose conc. rises
(2) GLYCOGENOLYSIS
- glycogen stored in the liver and muscle cells is broken down into glucose and released into the blood
(3) GLUCONEOGENESIS
- the production of glucose from non-carb sources
When can blood glucose conc. DECREASE
(1) Respiration
- some of the glucose in the blood is used up by cells to release energy.
(2) GLYCOGENESIS
- the production of glycogen (store when glucose conc. is too high)
How do the islets of Langerhans react when blood glucose conc. is too high?
Insulin is produced by the BETA cells of the islets.
Beta cells detect the rise in conc. and respond by secreting insulin directly into the bloodstream.
INSULIN??
Most body cells have insulin receptors on their cell surface membrane.
- when insulin binds to its glycoprotein receptor, it causes a change in the tertiary structure of the glucose transport protein channels.
- this causes the channels to open allowing more glucose to enter the cell
- insulin also activates enzymes within some cells to convert glucose to glycogen and fat
How does insulin lower blood glucose conc. ?
(1) increasing the rate of absorption of glucose by cells
(2) increasing the respiratory rate of cells - increases their need for glucose
(3) increasing the rate of glycogenesis - stimulates the liver
(4) increasing the rate of glucose to fat conversion
(5) inhibiting the release of glucagon from the alpha cells of the islets
Negative feedback??
When blood glucose conc. falls below a set level…
- the beta cells detect this and reduce their secretion of insulin
When blood glucose conc. rises above a set level…
- the alpha cells detect this and reduce their secretion of glucagon
GLUCAGON??
Glucagon is produced by alpha cells of the islets.
The only cells that have glucagon receptors are the liver and fat cells.
How does glucagon raise blood glucose conc. ?
(1) glycogenolysis - liver breaks down glycogen store into glucose
(2) reducing the amount of glucose absorbed by the liver cells
(3) increasing gluconeogenesis - increasing the conversion of amino acids and glycerol into glucose in the liver
Why is the system o maintaining blood glucose conc. considered to be self-regulating?
It is the level of glucose in the blood that determines the quantity of insulin and glucagon that is released.
Control of insulin secretion (mechanism)?
(1) at normal levels, POTASSIUM channels in the plasma membrane of beta cells are open and K+ ions diffuse out of the cell.
- the inside of the beta cell is at a potential of -70mV
(2) when conc. rises, glucose enters the cell by a glucose transporter
(3) the glucose is metabolised inside the mitochondria - producing ATP
(4) the ATP binds to the potassium channels and causes them to close
= ATP-sensitive potassium channels
(5) as K+ ions can no longer diffuse out of the cell, the potential reduces to -30mV and DEPOLARISATION occurs
(6) Depolarisation causes the voltage-gated CALCIUM channels to open
(7) Ca2+ (calcium ions) enter the cell and cause secretory vesicles to release the insulin they contain by EXOCYTOSIS.
