biology module 5 hormonal communication

what are homeostatic mechanisms

they help organisms keep their internal body conditions near constant

what are the three key homeostatic mechanisms

1. thermoregulation

2. osmoregulation

3. the control of blood glucose concentration

what is the first messenger hormone

the hormone that brings the information or signal from the endocrine gland

what is the second messenger hormone

inside the cell, causes the effect

what is the mode of action for adrenaline

1. adrenaline binds to specific receptors on the membrane of liver cells

2. this causes the enzyme adenylyl cyclase to change shape and become activated

3. activated adenylyl cyclase catalyses the conversion of ATP to the second messenger molecule cyclic AMP

4. cAMP binds to protein kinase A enzymes, activating them

5. active protein kinase A enzymes initiate a series of enzyme activations that result in the breakdown of glycogen to glucose (glycogenolysis)

parts of the system in nervous system v endocrine system

N - brain, spinal cord, nerves/neurones

E - glands

type of message in nervous v endocrine system

N - electrical impulse

E - chemical hormone

method of transmission in nervous v endocrine system

N - nerves/neurone

E - bloodstream

effectors in nervous v endocrine system

N - muscles or glands

E - target cells in specific tissues

speed of transmission nervous v endocrine system

N - very fast

E - slower

length of effect nervous v endocrine system

N - short until electrical impulses stop

E - longer until hormone is broken down

where are adrenal glands located

above each kidney

what are the two main areas of adrenal glands

1. a central medulla

2. outer cortex

what does the cortex produce

steroid hormones :

aldosterone - regulates levels of salts

cortisol - primary stress hormone

what does the medulla produce

adrenaline - initiates fight or flight response in the body

where is the pancreas found

in the abdomen of mammals

what is an endocrine gland

secrete hormones directly into the blood

what is an exocrine gland

secrete a substance via a duct

is the pancreas an endocine or exocrine gland

both

what is the exocrine function of the pancreas

to produce pancreatic juice to be delivered to the small intestine where it helps in the digestion of food

what is the endocrine function of the pancreas

to produce the hormones glucagon and insulin

what are the islets of langerhans

small sections of cells throughout the organ that produce hormones via the endocrine function

which two cell types are contained in the islets of langerhans

1. alpha cells which secrete glucagon

2. beta cells which secrete insulin

how can the histology of the pancreas be studied

by staining sections of pancreatic tissue and viewing them under a microscope

what are the three ways in which glucose can enter the bloodstream

1. absorption in the guts following carbohydrate digestion

2. hydrolysis of glycogen stores

3. non carbohydrates such as lipids, lactate, and amino acids that have been converted to glucose

what happens when there is excess glucose in the blood from a carbohydrate dense meal it is removed

it is removed through increased glucose uptake and glycogenesis

what happens when there is insufficient glucose in the blood for metabolic needs

it is rapidly released from storage molecules through glycogenolysis and gluconeogenesis

what happens when there is a decrease in blood glucose concentration

1. the alpha cells respond by secreting glucagon

2. the beta cells respond by stopping the secretion of insulin

3. the decrease in blood insulin reduces the use of glucose by liver and muscle cells

4. glucagon binds to receptors in the cell surface membranes of liver cells

5. this binding causes a conformational change in the receptor protein that activates a G protein

6. this activated G protein activates the enzyme adenylyl cyclase which catalyses the conversion of ATP to the second messenger, cAMP

7. Camp binds to protein kinase A enzymes, activating them

8. active protein kinase A enzymes activate phosphorylase enzymes and catalyse glycogenolysis

what is glycogenolysis

the breakdown of glycogen to glucose

how does adrenaline also increase the concentration of blood glucose

• binds to different receptors on the surface of liver cells that activate the same enzyme cascade and leads to the same result - the breakdown of glycogen

• adrenaline also stimulates the breakdown of glycogen stores in muscle during exercise

what happens when there is an increase in blood glucose concentration

1. detected by the beta cells in the pancreas

2. glucose molecules enter the beta cells by facilitated diffusion

3. the cells respire this glucose and produce ATP

4. ATP causes the potassium channels in the beta cells to close

5. this change in the membrane potential causes the voltage gated calcium channels to open

6. the beta cells secrete insulin which stimulates the uptake of glucose by muscle cells, fat cells, and the liver

how does insulin help increase the uptake of glucose in the liver

• by stimulating glycogenesis

how is blood glucose concentration regulates by negative feedback

• receptors detect whether a specific level is too low or high

• this information is communicated through the hormonal or nervous system to effectors

• effectors react to counteract the change by bringing the level back to normal

glycogenesis

• the synthesis of glycogen from glucose molecules

• insulin triggers this process after it detects an increased blood glucose concentration

• the synthesis of glycogen removed glucose molecules from the bloodstream and decreases the blood glucose concentration to within a normal range

• glycogen acts as a compact and efficient carbohydrate storage molecule

glycogenolysis

• the breakdown of glycogen to produce glucose

• glucagon triggers this process after it detects a decreased blood glucose concentration

• it activates enzymes within the liver that breakdown glycogen molecules into glucose

• the breakdown of glycogen releases more glucose molecules to the blood stream and increases the blood glucose concentration to within the normal range

gluconeogensis

the synthesis of glucose molecules from non carbohydrate molecules

glucagon also triggers this by activating enzymes within the liver

these enzymes convert other molecules such as fatty acids and amino acids, into glucose molecules

glucose molecules are released into the blood stream which increases the blood glucose concentration to within the normal range

cause of type 1 diabetes

inability of pancreas to produce insulin

cause of type 2 diabetes

cells of the body become resistant to insulin or insufficient insulin produced by the pancreas

treatment of type 1 diabetes

monitoring blood glucose levels and injecting human insulin throughout the day

treatment of type 2 diabetes

maintain a low carb diet and regular exercise to reduce need for insulin

diabetes and blood pressure

individuals with poorly controlled diabetes often suffer from high blood pressure because the high blood glucose concentration lowers the water potential of the blood which causes more water to move from the tissues into the blood vessels by osmosis so there is a larger volume of blood within the circulatory system which causes blood pressure to increase